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Zhe Han

$2M NIH grant for treating disease linked to APOL1

Zhe Han

Children’s researcher Zhe Han, Ph.D., has received a $2 million award from the National Institutes of Health (NIH) to study new approaches to treat kidney disease linked to inheriting Apolipoprotein L1 (APOL1) risk alleles. These risk alleles are particularly common among persons of recent African descent, and African Americans are disproportionately affected by the increased risk in kidney disease associated with these risk alleles.

Han, an associate professor in Children’s Center for Genetic Medicine Research, has established a leading research program that uses the fruit fly Drosophila as a model system to study how genetic mutations lead to disease.

Drosophila is a very basic model, but studies in the fly have led to major breakthroughs in understanding fundamental biological processes that underlie health and disease in humans,” Han says. “Since coming to Children’s National five years ago, I have focused a significant part of my research studying particular fly cells called nephrocytes that carry out many of the important roles of human kidney glomeruli, units within the kidney where blood is cleaned. Working together with clinician colleagues here, we have demonstrated that these Drosophila cells can be used to very efficiently study different types of renal disease caused by genetic mutations.”

The APOL1 risk alleles are genetic variants, termed G1 and G2, found almost exclusively in people of African ancestry and can lead to a four-fold higher risk of end-stage kidney disease, the last of five stages of chronic kidney disease. Exactly how inheriting these risk alleles increases the risk of kidney disease remains an unanswered question and the focus of considerable research activity. Han’s laboratory has developed a Drosophila model of APOL1-linked renal disease by producing the G1 and G2 forms of APOL1 specifically in nephrocytes. This led to defects in fly renal cells that strikingly overlap with disease-associated changes in experimental model and human kidney cells expressing APOL1 risk alleles.

The new NIH award will fund large-scale screening and functional testing to identify new treatment targets and new drugs to treat kidney disease linked to APOL1. Using a genetic screening approach, Han’s lab will identify nephrocyte “modifier” genes that interact with APOL1 proteins and counter the toxic effects of risk-associated G1 and G2 variants.

The team also will identify nephrocyte genes that are turned on or off in the presence of APOL1 risk alleles, and confirm that such “downstream” APOL1-regulated genes are similarly affected in experimental model and human kidney cells. The potential of the newly identified “modifier” and “downstream” genes to serve as targets of novel therapeutic interventions will be experimentally tested in fly nephrocytes in vivo and in cultured mammalian kidney cells.

Finally, the Drosophila model will be used as a drug screening platform for in vivo evaluation of positive “hits” from a cell-based APOL1 drug screening study in order to identify compounds that are most effective with the fewest side effects.

“These types of studies can be most efficiently performed in Drosophila,” Han adds.  “They take advantage of the speed and low cost of the fly model system and the amazing array of well-established, sophisticated genetic tools available for the fly. Using this model to elucidate human disease mechanisms and to identify new effective therapies has truly become my research passion.”

DNA strands on teal background

NUP160 genetic mutation linked to steroid-resistant nephrotic syndrome

DNA strands on teal background

Mutations in the NUP160 gene, which encodes one protein component of the nuclear pore complex nucleoporin 160 kD, are implicated in steroid-resistant nephrotic syndrome, an international team reports March 25, 2019, in Journal of the American Society of Nephrology. Mutations in this gene have not been associated with steroid-resistant nephrotic syndrome previously.

“Our findings indicate that NUP160 should be included in the gene panel used to diagnose steroid-resistant nephrotic syndrome to identify additional patients with homozygous or compound-heterozygous NUP160 mutations,” says Zhe Han, Ph.D., an associate professor in the Center for Genetic Medicine Research at Children’s National and the study’s senior author.

The kidneys filter blood and ferry waste out of the body via urine. Nephrotic syndrome is a kidney disease caused by disruption of the glomerular filtration barrier, permitting a significant amount of protein to leak into the urine. While some types of nephrotic syndrome can be treated with steroids, the form of the disease that is triggered by genetic mutations does not respond to steroids.

The patient covered in the JASN article had experienced persistently high levels of protein in the urine (proteinuria) from the time she was 7. By age 10, she was admitted to a Shanghai hospital and underwent her first renal biopsy, which showed some kidney damage. Three years later, she had a second renal biopsy showing more pronounced kidney disease. Treatment with the steroid prednisone; cyclophosphamide, a chemotherapy drug; and tripterygium wilfordii glycoside, a traditional therapy, all failed. By age 15, the girl’s condition had worsened and she had end stage renal disease, the last of five stages of chronic kidney disease.

An older brother and older sister had steroid-resistant nephrotic syndrome as well and both died from end stage kidney disease before reaching 17. When she was 16, the girl was able to receive a kidney transplant that saved her life.

Han learned about the family while presenting research findings in China. An attendee of his session said that he suspected an unknown mutation might be responsible for steroid-resistant nephrotic syndrome in this family, and he invited Han to work in collaboration to solve the genetic mystery.

By conducting whole exome sequencing of surviving family members, the research team found that the mother and father each carry one mutated copy of NUP160 and one good copy. Their children inherited one mutated copy from either parent, the variant E803K from the father and the variant R1173X, which causes truncated proteins, from the mother. The woman (now 29) did not have any mutations in genes known to be associated with steroid-resistant nephrotic syndrome.

Some 50 different genes that serve vital roles – including encoding components of the slit diaphragm, actin cytoskeleton proteins and nucleoporins, building blocks of the nuclear pore complex – can trigger steroid-resistant nephrotic syndrome when mutated.

With dozens of possible suspects, they narrowed the list to six variant genes by analyzing minor allele frequency, mutation type, clinical characteristics and other factors.

The NUP160 gene is highly conserved from flies to humans. To prove that NUP160 was the true culprit, Dr. Han’s group silenced the Nup160 gene in nephrocytes, the filtration kidney cells in flies. Nephrocytes share molecular, cellular, structural and functional similarities with human podocytes. Without Nup160, nephrocytes had reduced nuclear volume, nuclear pore complex components were dispersed and nuclear lamin localization was irregular. Adult flies with silenced Nup160 lacked nephrocytes entirely and lived dramatically shorter lifespans.

Significantly, the dramatic structural and functional defects caused by silencing of fly Nup160 gene in nephrocytes could be completely rescued by expressing the wild-type human NUP160 gene, but not by expressing the human NUP160 gene carrying the E803K or R1173X mutation identified from the girl’s  family.

“This study identified new genetic mutations that could lead to steroid-resistant nephrotic syndrome,” Han notes. “In addition, it demonstrates a highly efficient Drosophila-based disease variant functional study system. We call it the ‘Gene Replacement’ system since it replaces a fly gene with a human gene. By comparing the function of the wild-type human gene versus mutant alleles from patients, we could determine exactly how a specific mutation affects the function of a human gene in the context of relevant tissues or cell types. Because of the low cost and high efficiency of the Drosophila system, we can quickly provide much-needed functional data for novel disease-causing genetic variants using this approach.”

In addition to Han, Children’s co-authors include Co-Lead Author Feng Zhao, Co-Lead Author Jun-yi Zhu, Adam Richman, Yulong Fu and Wen Huang, all of the Center for Genetic Medicine Research; Nan Chen and Xiaoxia Pan, Shanghai Jiaotong University School of Medicine; and Cuili Yi, Xiaohua Ding, Si Wang, Ping Wang, Xiaojing Nie, Jun Huang, Yonghui Yang and Zihua Yu, all of Fuzhou Dongfang Hospital.

Financial support for research described in this post was provided by the Nature Science Foundation of Fujian Province of China, under grant 2015J01407; National Nature Science Foundation of China, under grant 81270766; Key Project of Social Development of Fujian Province of China, under grant 2013Y0072; and the National Institutes of Health, under grants DK098410 and HL134940.

Lisa M. Guay-Woodford, M.D

Serving patients with polycystic kidney disease

Lisa M. Guay-Woodford, M.D

Lisa M. Guay-Woodford, M.D., is internationally recognized for her examination of the mechanisms that make certain inherited renal disorders particularly lethal, a research focus inspired by her patients.

When Children’s National pediatric nephrologist Lisa Guay-Woodford, M.D., was an intern at Boston Children’s Hospital, a baby with autosomal recessive polycystic kidney disease (ARPKD) was admitted to one of the hospital’s neonatal intensive care units (NICU). This disease, which causes cysts to form in the kidney and liver, kills about one-fifth of babies within the newborn period due to related problems that affect lung development.

But this baby seemed like a survivor, Dr. Guay-Woodford remembers. The child passed the newborn period and graduated from the NICU, although she went home with severe blood pressure issues. Along with a team of colleagues, Dr. Guay-Woodford helped to manage this patient’s care, juggling normal infant concerns with her ARPKD.

As far as Dr. Guay-Woodford knew at the time, this baby was beating the odds against her, growing and thriving. But one day near the end of her internship period, Dr. Guay-Woodford was called to the emergency department. Her patient was in a hypertensive crisis that ultimately killed her.

“It was absolutely devastating to all of us. This was supposed to be a good news kind of story, that she survived the newborn period and had gone home and was growing and developing,” Dr. Guay-Woodford says. “I realized then that a big part of the tragedy of this disease is how little we knew about it.”

Dr. Guay-Woodford vowed to change that. Since then, she’s devoted her career to studying ARPKD and other inherited kidney diseases.

After finishing her residency and fellowship in Boston, Dr. Guay-Woodford was recruited to the University of Alabama, where she began caring for a cadre of 40 patients with inherited renal disorders. Fueled by the research questions that arose while working with these patients, she and her colleagues searched for PKD-related genes in the cpk mouse model, an animal that mimics many of the features of human ARPKD.

Dr. Guay-Woodford and her team cloned several of the key genes that caused recessive PKD in this mouse and other mouse models and eventually went on to identify the first major genetic modifier of PKD in these animals – a gene that wasn’t directly responsible for the disease but could sway its course. In time, her collaborative group became one of two that co-indentified the major gene responsible for human ARPKD. In 2005, Dr. Guay-Woodford led a team of investigators at the University of Alabama-Birmingham to establish one of just four PKD translational core centers funded by a National Institutes of Health P30 grant.

After moving to Children’s National in 2012, Dr. Guay-Woodford still co-directs this PKD translational core center while also caring for patients at her inherited renal disorders clinic. She and her colleagues here and beyond continue to work with mouse models of this disease, trying to ferret out the vast network of genes that interact in ARPKD and their specific roles.

“You can use a variety of strategies to compare these patients’ gene portfolios with those of healthy patients and pick out the disease genes. But at the end of the day, to me, that’s just the opening chapter,” she says. “To really make a story, you’ve got to understand what is it that gene does, what protein it makes, and how that protein works together with others involved in this disease.”

She and her team also are currently working with a pharmaceutical company to develop the first clinical trial to test a treatment for ARPKD. This effort has relied heavily on a clinical database that Dr. Guay-Woodford and colleagues worldwide maintain to track patients with this and related conditions. Through the extensive collection of clinical information in this database – including a variety of data on patients’ gestation and birth, growth, and kidney structure and function – the team has identified a core cohort of patients whose disease is rapidly progressing, a characteristic that makes them prime candidates to test this potential new treatment.

“Everything I do in the clinic informs the work I do in the lab, and everything I do in the lab is to help the patients I see in the clinic. It’s this constant dance back and forth between our human patients and animal models,” she says. “One day, this dance will help lessen the burden of this disease for these kids and their families.”

Enhancing pediatric nephrology clinical trial development

Fewer than 50 percent of pharmaceuticals approved by federal authorities are explicitly approved for use in kids, and even fewer devices are labeled for pediatric use.

When children develop kidney disease, it can play out in dramatically different ways. They can experience relatively mild disorders that respond to existing treatments and only impact their lives for the short term. Children also can develop chronic kidney disease that defies current treatments and can imperil or end their lives.

Fewer than 50 percent of pharmaceuticals approved by federal authorities are explicitly approved for use in kids, and even fewer devices are labeled for pediatric use. Congress has offered incentives to manufacturers who study their treatments in children, but the laws do not require drug makers to demonstrate statistical significance or for the clinical trial to improve or extend children’s lives.

To overcome such daunting obstacles, the American Society of Pediatric Nephrology established a Therapeutics Development Committee to forge more effective public-private partnerships and to outline strategies to design and carry out pediatric nephrology clinical trials more expeditiously and effectively.

“We have seen how other pediatric subspecialties, such as cancer and arthritis, have leveraged similar consortia to address mutual concerns and to facilitate development of new therapeutics specific to those diseases,” says Marva Moxey-Mims, M.D., chief of the Division of Nephrology at Children’s National Health System and a founding committee member. “As a group, we aim to collectively identify and remedy the most pressing needs in pediatric nephrology. As just one example, the committee could help to increase the number of sites that host research studies, could expand the pool of potential study volunteers and could lower the chances of duplicating efforts.”

A paper summarizing their efforts thus far, “Enhancing clinical trial development for pediatric kidney diseases,” written by Dr. Moxey-Mims and 15 co-authors, was published online Aug. 30 by Pediatric Research. The journal’s editors will feature the review article in the “Editor’s Focus” of an upcoming print edition of the publication.

The committee is comprised of academic pediatric nephrologists, patient advocates, private pharmaceutical company representatives and public employees at the Food and Drug Administration and the National Institutes of Health. But it is likely to grow in size and in stakeholder diversity.

Already, committee members have learned that they achieve better results by working together. Early communication can avoid flaws in designing clinical trials, such as overestimating the volume of clinical samples that can feasibly be collected from a small child, or that could misinterpret the type of data needed to secure federal approval.

While public and private investigators took similar approaches to clinical trial design, academic investigators were more conceptual as they summarized their study design Road Map. Industry representatives, by contrast, included more granular detail about study organization and milestones along the path toward regulatory approval.

According to the study authors, both groups understand the critical role that patients and families can play in early research study design, such as accelerating patient recruitment, bolstering the credibility of research and helping to translate research results into actual clinical practice.

“We are pleased to have created a forum that allows participants to share valuable viewpoints and concerns and to understand how regulations and laws could be changed to facilitate development of effective medicines for children with kidney disease,” says Dr. Moxey-Mims. “We hope the relationships and trust forged through these conversations help to speed the development and approval of the next generation of therapies for pediatric renal disease.”

A close-up of Dr. Marva Moxey Mims at Children's National.

Children’s National welcomes Marva Moxey-Mims, M.D., renowned nephrologist, as incoming Division Chief

A close-up of Dr. Marva Moxey Mims at Children's National.

Marva Moxey-Mims, M.D., a leading expert in chronic kidney disease and glomerular disease who has conceptualized and overseen multicenter clinical studies aimed at improving chronic kidney disease treatment, has been named Chief of Pediatric Nephrology at Children’s National Health System.

Dr. Moxey-Mims comes to Children’s National from the National Institute of Diabetes and Digestive and Kidney Diseases at the National Institutes of Health where she served as Deputy Director for clinical science and oversaw a research portfolio that included clinical trials for kidney disease and genitourinary dysfunction in adults and children. As Pediatric Nephrology Division Chief, Dr. Moxey-Mims plans to add new staff and restructure a division already ranked among the nation’s leaders by U.S. News & World Report in order to carve out dedicated time for research and improve care for children with kidney disease.

”Children’s National is honored to welcome Dr. Moxey-Mims as the new leader for our talented nephrology team,” says Robin Steinhorn, M.D., senior vice president of the Center for Hospital-Based Specialties. “She brings unparalleled expertise in this field, is a member of a number of influential national committees and has authored more than 90 scientific publications, including peer-reviewed articles and book chapters. Under her guidance, Pediatric Nephrology at Children’s is well-positioned to continue to lead the nation in clinical care and research.”

“I want to inspire the division,” Dr. Moxey-Mims says. “I want the faculty to be happy in their work here and to look forward to coming to work every day. I want them to have enough time to pursue their academic interests, so clinicians not only continue to provide excellent patient care but also can conduct research. All of the staff has potential projects in mind; it’s just a matter of finding the time to do them.”

From a pragmatic standpoint, Children’s pediatric nephrologists will start with what is feasible: Continuing and expanding current cross-disciplinary research projects.

“There are some research projects that will be important to pursue, but we just don’t have the building blocks in place right now to move in that specific direction,” Dr. Moxey-Mims says. “However, continuing ongoing collaborations with our colleagues in neonatologyoncologyhematology and urology are reasonable places to start. I agree with the cliché that success breeds success. If we have an established collaboration and can build on it, that is how we start expanding our research enterprise.”

To that end, the division is in the early stage of joining an existing consortium that is studying four types of glomerular disease, conditions caused by varying mechanisms that often lead to kidney failure. “Information that is gathered will inform care going forward,” she says. “Part of what is being done in these studies is obtaining a better understanding of how disease progresses in different groups of children and adults and quantifying the impact of varying treatment approaches. It’s very exciting for Children’s National to be a new player in this.”

Dr. Moxey-Mims received her undergraduate degree from McGill University in Montreal and her medical degree from Howard University in Washington, D.C. She completed her pediatric residency and clinical pediatric nephrology training at Children’s National and from 1994 to 1999 worked at Children’s National as a staff nephrologist.

“Returning to Children’s has been a wonderful homecoming,” Dr. Moxey-Mims says. “I wanted to return to the hospital setting and have direct exposure to patients. I missed that. In this new role, I can participate in patient care, as well as foster an environment that spurs even more research. It’s really the best of both worlds.”

cancer-patient-Sully-Shields

New approach improves pediatric kidney cancer outcomes

cancer-patient-Sully-Shields

Wilms tumor, also known as nephroblastoma, is the most common pediatric kidney cancer, typically seen in children ages three to four. Compared to patients with unilateral Wilms tumors, children with bilateral Wilms tumors (BWT) have poorer event-free survival (EFS) and are at higher risk for later effects such as renal failure. The treatment of BWT is challenging because it involves surgical removal of the cancer, while preserving as much healthy kidney tissue as possible to avoid the need for an organ transplant.

A new Children’s Oncology Group (COG) study published in the September issue of the Annals of Surgery demonstrated an exciting new approach to treating children diagnosed with BWT that significantly improved EFS and overall survival (OS) rates after four years when compared to historical rates. Jeffrey Dome, M.D., Ph.D., Vice President of the Center for Cancer and Blood Disorders at Children’s National Health System, was co-senior author of this first-ever, multi-institutional prospective study of children with BWT.

Historically, patients with BWT have had poor outcomes, especially if they have tumors with unfavorable histology. In this study, Dr. Dome and 18 other clinical researchers followed a new treatment approach consisting of three chemotherapy drugs before surgery rather than the standard two drug regimen, surgical removal of cancerous tissue within 12 weeks of diagnosis, and postoperative chemotherapy that was adjusted based on histology.

The study found that preoperative chemotherapy expedited surgical treatment, with 84 percent of patients having surgery within 12 weeks of diagnosis. The new treatment approach also vastly improved EFS and OS rates for patients participating in the study. The four-year EFS rate was 82.1 percent, compared to 56 percent on the predecessor National Wilms Tumor Study-5 (NWTS-5) study. The four-year OS rate was 94.9 percent, compared to 80.8 percent on NWTS-5.

“I am very encouraged by these results, which I believe will serve as a benchmark for future studies and lead to additional treatment improvements, giving more children the chance to overcome this diagnosis while sparing kidney tissue,” says Dr. Dome.

A total of 189 patients at children’s hospitals, universities and cancer centers in the United States and Canada participated in this study. These patients will continue to be followed for 10 years to track kidney failure rates. This study was funded by grants from the National Institutes of Health to the Children’s Oncology Group.

Patricio Ray

Toward a better definition for AKI in newborns

Patricio Ray

The National Institute of Diabetes and Digestive and Kidney Diseases convened a meeting of expert neonatologists and pediatric nephrologists, including Dr. Patricio Ray, to review state-of-the-art knowledge about acute kidney injury in neonates and to evaluate the best method to assess these patients’ kidney function.

Each year, thousands of infants in the United States end up in neonatal intensive care units (NICUs) with acute kidney injury (AKI), a condition in which the kidneys falter in performing the critical role of filtering waste products and excess fluid from the blood to produce urine. Being able to identify neonates during the early stages of AKI is critical to doctors and clinician-scientists who treat and study this condition, explains Patricio Ray, M.D., a nephrologist at Children’s National Health System.

Without an accurate definition and early identification of newborns with AKI, it is difficult for doctors to limit the use of antibiotics or other medications that can be harmful to the kidneys. Neonates who have AKI should not receive large volumes of fluids, a treatment that can cause severe complications when the kidneys do not properly function.

Until recently, there was no standard definition for AKI, leaving doctors and researchers to develop their own guidelines. Lacking set criteria led to confusion, Dr. Ray says. For example, different studies estimating the percentage of infants in NICUs with AKI ranged from 8 percent to 40 percent, depending on which definition was used. In 2012, a group known as the Kidney Disease Improved Global Outcome (KDIGO) issued practice guidelines for AKI that provide a standard for doctors and researchers to follow. They focus largely on measuring the relative levels of serum creatinine, a protein produced by muscles that is filtered by the kidneys, and the amount of urine output, which typically declines in adults and older children with failing kidneys.

The problem with these guidelines, Dr. Ray explains, is they are not sensitive enough to identify newborns experiencing the early stages of AKI during the first week of life. Newborns can have high serum creatinine levels during the first week of life due to residual levels transferred from mothers through the placenta. Also, because their kidneys are immature, failure often can mean higher – not diminished – urine production.

In 2013, the National Institute of Diabetes and Digestive and Kidney Diseases, part of the National Institutes of Health, convened a meeting of leading neonatologists and pediatric nephrologists – including Dr. Ray – to review state-of-the-art knowledge about AKI in neonates and to evaluate the best manner to assess kidney function in these patients. They published a summary of their discussion online June 12, 2017 in Pediatric Research.

Among other findings, the group concluded that the current definition of AKI lacks the sensitivity needed to identify the early stages of AKI in neonates’ first week of life. They also said that more research was needed to fill this gap.

That’s where Dr. Ray’s current research comes in. Working with fellow Children’s Nephrologist Charu Gupta, M.D., and Children’s Neonatologist An Massaro, M.D., the three clinician-scientists reviewed the medical records of 106 infants born at term with a condition known as hypoxic ischemic encephalopathy (HIE), in which the brain doesn’t receive enough oxygen. Not only does this often lead to brain injury, but it also greatly increases the risk of AKI.

Because these babies had been followed closely in the NICU to assess the possibility of AKI, their serum creatinine had been checked frequently. The researchers found that about 69 percent of the infants with HIE followed at Children’s National never developed signs of kidney failure during their first week of life. These babies’ serum creatinine concentrations dropped by 50 percent or more by the time they were 1 week old, about the same as reported previously in healthy neonates. Another 12 percent of the infants with HIE developed AKI according to the definition established by the KDIGO group in 2012. These infants:

  • Required more days of mechanical ventilation and medications to increase their blood pressure
  • Had higher levels of antibiotics in their bloodstreams
  • Retained more fluid
  • Had lower urinary levels of a molecule that their kidneys should have been cleared and
  • Had to stay in the hospital longer

A third group of the infants with HIE, about 19 percent, did not meet the standard criteria for AKI. However, these babies had a rate of decline of serum creatinine that was significantly slower than the normal newborns and the infants with HIE who had excellent outcomes. Rather, their outcomes matched those of infants with established AKI.

Dr. Ray notes that by following the rate of serum creatinine decline during the first week of life physicians could identify neonates with impaired kidney function. This approach provides a more sensitive method to identify the early stages of AKI in neonates. “By looking at how fast babies were clearing their serum creatinine compared with the day they were born, we could predict how well their kidneys were working,” he says. Dr. Ray and colleagues published these findings July 2016 in Pediatric Nephrology.

He adds that further studies will be necessary to confirm the utility of this new approach to assess the renal function of term newborns with other diseases and preterm neonates. Eventually, he hopes this new approach will become uniform clinical practice.

Coenzyme Q10

Supplement might help kidney disease

Coenzyme Q10

A research team was able to “rescue” phenotypes caused by silencing the fly CoQ2 gene by providing nephrocytes with a normal human CoQ2 gene, as well as by providing flies with Q10, a popular supplement.

A new study led by Children’s National research scientists shows that coenzyme Q10 (CoQ10), a popular over-the-counter supplement sold for pennies a dose, could alleviate genetic problems that affect kidney function. The work, done in genetically modified fruit flies — a common model for human genetic diseases since people and fruit flies share a majority of genes — could give hope to human patients with problems in the same genetic pathway.

The new study, published April 20 by Journal of the American Society of Nephrology, focuses on genes the fly uses to create CoQ10.

“Transgenic Drosophila that carry mutations in this critical pathway are a clinically relevant model to shed light on the genetic mutations that underlie severe kidney disease in humans, and they could be instrumental for testing novel therapies for rare diseases, such as focal segmental glomerulosclerosis (FSGS), that currently lack treatment options,” says Zhe Han, Ph.D., principal investigator and associate professor in the Center for Cancer & Immunology Research at Children’s National and senior study author.

Nephrotic syndrome (NS) is a cluster of symptoms that signal kidney damage, including excess protein in the urine, low protein levels in blood, swelling and elevated cholesterol. The version of NS that is resistant to steroids is a major cause of end stage renal disease. Of the more than 40 genes that cause genetic kidney disease, the research team concentrated on mutations in genes involved in the biosynthesis of CoQ10, an important antioxidant that protects the cell against damage from reactive oxygen.

Drosophila pericardial nephrocytes perform renal cell functions including filtering of hemolymph (the fly’s version of blood), recycling of low molecular weight proteins and sequestration of filtered toxins. Nephrocytes closely resemble, in structure and function, the podocytes of the human kidney.  The research team tailor-made a Drosophila model to perform the first systematic in vivo study to assess the roles of CoQ10 pathway genes in renal cell health and kidney function.

One by one, they silenced the function of all CoQ genes in nephrocytes. If any individual gene’s function was silenced, fruit flies died prematurely. But silencing three specific genes in the pathway associated with NS in humans – Coq2, Coq6 and Coq8 – resulted in abnormal localization of slit diaphragm structures, the most important of the kidney’s three filtration layers; collapse of membrane channel networks surrounding the cell; and increased numbers of abnormal mitochondria with deformed inner membrane structure.

Journal of the American Society of Nephrology September 2017 cover

The flies also experienced a nearly three-fold increase in levels of reactive oxygen, which the study authors say is a sufficient degree of oxidative stress to cause cellular injury and to impair function – especially to the mitochondrial inner membrane. Cells rely on properly functioning mitochondria, the cell’s powerhouse, to convert energy from food into a useful form. Impaired mitochondrial structure is linked to pathogenic kidney disease.

The research team was able to “rescue” phenotypes caused by silencing the fly CoQ2 gene by providing nephrocytes with a normal human CoQ2 gene, as well as by providing flies with Q10, a readily available dietary supplement. Conversely, a mutant human CoQ2 gene from an patient with FSGS failed to rescue, providing evidence in support of that particular CoQ2 gene mutation causing the FSGS. The finding also indicated that the patient could benefit from Q10 supplementation.

“This represents a benchmark for precision medicine,” Han adds. “Our gene-replacement approach silenced the fly homolog in the tissue of interest – here, the kidney cells – and provided a human gene to supply the silenced function. When we use a human gene carrying a mutation from a patient for this assay, we can discover precisely how a specific mutation – in many cases only a single amino acid change – might lead to severe disease. We can then use this personalized fly model, carrying a patient-derived mutation, to perform drug testing and screening to find and test potential treatments. This is how I envision using the fruit fly to facilitate precision medicine.”

Related resources:
News release: Drosophila effectively models human genes responsible for genetic kidney diseases
Video: Using the Drosophila model to learn more about disease in humans

fruit fly

Studying fruit flies to better understand human kidneys

fruit fly

In his latest study, Zhe Han and co-authors zeroed in on Rab genes to determine their role in fruit fly renal function.

It’s a given that fruit flies and humans are different. Beyond the obvious are a litany of less-apparent distinctions. For example, fruit flies have hemolymph instead of blood. Arranged around a single cardiac chamber, compared with humans’ four-chamber hearts, are a group of cells called nephrocytes that serve the same function as human kidneys, filtering toxins and waste from hemolymph.

But despite the dissimilarities between these two organisms, fly nephrocytes and human kidney cells are similar enough to allow the fruit fly, a common lab model that shares about 60 percent of its DNA with people, to provide insights on kidney disease in people. In a new study in fruit flies led by Zhe Han, Ph.D., principal investigator and associate professor in the Center for Cancer and Immunology Research at Children’s National Health System, researchers identified several new genes thought to be critical for renal function in humans. The findings could lend insight to the inner workings of this organ down to the molecular level and eventually help further the understanding or treatment of kidney disorders.

Han explains that recent research by his group tied 80 fruit fly genes to renal function. Many of these newly identified genes were Rab GTPases, a family of genes that make proteins whose job is to move substances around in cells through membrane-enclosed pouches called vesicles. For example, Rab proteins might put some substances on the path to destruction by moving them into lysosomes, vesicles with enzymes that break down all kinds of biomolecules. Rab proteins might help other substances be reused by steering them into recycling endosomes, vesicles that shuttle biomolecules that are still useful to where they will be used next.

In their latest study, published online Feb. 8, 2017 in Cell & Tissue Research, Han and co-authors zeroed in on these Rab genes to determine their role in fruit fly renal function. The researchers accomplished this by using genetic alterations to shut down each gene selectively in fruit fly nephrocytes. They then evaluated these transgenic flies on a number of different characteristics, including ability to effectively filter proteins from the blood, whether toxins placed in their food accumulated in their nephrocytes, how they developed and how they survived.

Their findings readily identified five Rab genes that seemed more important for these functions than the others: Rabs 1, 5, 7, 11 and 35, which all have analogous genes in humans.

Peering into the nephrocytes of flies in which these three Rabs had been silenced, the researchers made critical discoveries. Turning off Rab 7 appeared to block the path toward biomolecules in the cell entering lysosomes. Rather than biomolecules being destroyed, they instead were shuttled to the recycling route. Turning off Rab 11 had the reverse effect; recycling endosomes were drastically reduced, while lysosomes dramatically increased. Turning off Rab 5 had the most striking effect: All vesicles going in or out were blocked – like a cellular traffic jam – filling the cell with biomolecules that had no place to go, Han says.

Han, who has long tracked renal-related mutations in humans, says that no patients with kidney disease have turned up so far with Rab mutations. These genes are critical for functions throughout the body, he explains, so any embryos with these mutations are unlikely to survive. However, he adds, a host of other renal-related genes work in parallel or are controlled by different Rabs. So understanding the role of Rabs in renal function provides some insight into how these genes operate as well as what might happen when the function of these genes goes awry.

Han plans to study how Rabs 5, 7 and 11 fit into networks of renal genes as well as the role of the other Rabs that could play novel roles in the nephrocyte cell trafficking.

“These findings in fly Rabs provide the framework to study the major causes of kidney disease in human patients,” he adds.

Zhe Han

Fruit flies can model human genetic kidney disease

Zhe Han

Zhe Han, Ph.D., has found that a majority of human genes known to be associated with nephrotic syndrome play conserved roles in renal function, from fruit flies to humans.

Drosophila melanogaster, the common fruit fly, has played a key role in genetic research for decades. Even though D. melanogaster and humans look vastly different, researchers estimate that about 75 percent of human disease-causing genes have a functional homolog in the fly.

A Children’s National Health System research team reported in a recent issue of Human Molecular Genetics that the majority of genes associated with nephrotic syndrome (NS) in humans also play pivotal roles in Drosophila renal function, a conservation of function across species that validates transgenic flies as ideal pre-clinical models to improve understanding of human disease.

NS is a cluster of symptoms that signal kidney damage, including excess protein in urine, low protein levels in blood, elevated cholesterol and swelling. Research teams have identified mutations in more than 40 genes that cause genetic kidney disease, but knowledge gaps remain in understanding the precise roles that specific genes play in kidney cell biology and renal disease. To address those research gaps, Zhe Han, Ph.D., a principal investigator and associate professor in the Center for Cancer & Immunology Research at Children’s National, and colleagues systematically studied NS-associated genes in the Drosophila model, including seven genes whose renal function had never been analyzed in a pre-clinical model.

“Eighty-five percent of these genes are required for nephrocyte function, suggesting that a majority of human genes known to be associated with NS play conserved roles in renal function from flies to humans,” says Han, the paper’s senior author. “To hone in on functional conservation, we focused on Cindr, the fly’s version of the human NS gene, CD2AP,” Han adds. “Silencing Cindr in nephrocytes led to dramatic impairments in nephrocyte function, shortened their life span, collapsed nephrocyte lacunar channels – the fly’s nutrient circulatory system – and effaced nephrocyte slit diaphragms, which diminished filtration function.”

And, to confirm that the phenotypes they were studying truly caused human disease, they reversed the damage by expressing a wild-type human CD2AP gene. A mutant allele derived from a patient with CD2AP-associated NS did not rescue the phenotypes.

Thus, the Drosophila nephrocyte can be used to explain the clinically relevant molecular mechanisms underlying the pathogenesis of most monogenic forms of NS, the research team concludes. “This is a landmark paper for using the fly to study genetic kidney diseases,” Han adds. “For the first time, we realized that the functions of essential kidney genes could be so similar from the flies to humans.”

A logical next step will be to generate personalized in vivo models of genetic renal diseases bearing patient-specific mutations, Han says. These in vivo models can be used for drug screens to identify treatments for kidney diseases that currently lack therapeutic options, such as most of the 40 genes studies in this paper as well as the APOL1 gene that is associated with the higher risk of kidney diseases among millions of African Americans.

Lisa M. Guay-Woodford, M.D

Lisa Guay-Woodford: minimizing kidney disease effects

Lisa M. Guay-Woodford, M.D

Lisa M. Guay-Woodford, M.D., is internationally recognized for her examination of the mechanisms that make certain inherited renal disorders particularly lethal, a research focus inspired by her patients.

The artist chose tempera paint for her oeuvre. The flower’s petals are the color of Snow White’s buddy, the Bluebird of Happiness. Each petal is accentuated in stop light red, and the blossom’s leaves stretch up toward the sun. With its bold strokes and exuberant colors, the painting exudes life itself.

It’s the first thing Lisa M. Guay-Woodford, M.D., sees when she enters her office. It’s the last thing she sees as she leaves.

Dr. Guay-Woodford, a pediatric nephrologist, is internationally recognized for her research into the mechanisms that make certain inherited renal disorders, such as autosomal recessive polycystic kidney disease (ARPKD), particularly lethal. She also studies disparate health disorders that have a common link: Disruption to the cilia, slim hair-like structures that protrude from almost every cell in the human body and that play pivotal roles in human genetic disease.

Sarah, the artist who painted the bright blue flower more than 20 years ago when she was 8, was one of Dr. Guay-Woodford’s patients. And she’s part of the reason why Dr. Guay-Woodford has spent much of her career focused on the broader domain of disorders tied to just a single defective gene, such as ARPKD.

“It dates back to when I was a house officer and took care of kids with this disorder,” Dr. Guay-Woodford says. “Maybe 30 percent die in the newborn period. Others survive, but they have a whole range of complications.”

Two of her favorite patients died from ARPKD-related reasons in the same year. One died from uncontrolled high blood pressure. The other, Sarah, died from complications from a combined kidney and liver transplant.

“The picture she drew hangs in my office,” she says. “She was a wonderful kid who was really full of life, and what she chose really mirrored who she was as a person. We put up lots of those sorts of those things in my office. It’s a daily reminder of why we do the things we do and the end goal.”

ARPKD is characterized by the growth of cysts in the liver, the kidney – which can lead to kidney failure – and complications within other structures, such as blood vessels in the heart and brain, according to the National Institutes of Health. About 1 in 20,000 live births is complicated by the genetic disorder. The age at which symptoms arise varies.

“Given the way it plays out, starting in utero, this is not a disease we are likely to cure,” she says. “But there are children who have very minimal complications. The near-term goal is to use targeted therapies to convert the children destined to have a more severe disease course to one that is less complicated so that no child suffers the full effects of the disease.”

That’s why it is essential to attain detailed knowledge about the defective gene responsible for ARPKD. To that end, Dr. Guay-Woodford participated in an international collaboration – one of three separate groups that 14 years ago identified PKHD1 as the defective gene that underlies ARPKD.

“The progress has been slow, partly because the gene and its protein products are very complex,” she says. “The good news is the gene has been identified. The daunting news is the identification did not leap us forward. It is just sort of an important step in what is going to be a fits-and-starts kind of journey.”

The field is trying to emulate the clinical successes that have occurred for patients with cystic fibrosis, which now can be treated by a drug that targets the defective gene, attacking disease at a fundamental level. Patient outcomes also have improved due to codifying care.

When she was a resident in the 1980s, children with cystic fibrosis died in their teens. “Now, they’re living well into their 40s because of careful efforts by really astute clinicians to deliver a standardized approach to care, an approach now enhanced by a terrific new drug. We measure quality care in terms of patient outcomes. That has allowed us to really understand how to effectively use antibiotics, physical therapy and how to think about nutrition – which makes a hugely important contribution that previously had been underappreciated.”

Standardizing clinical approaches dramatically improved and extended patients’ lives. “For renal cystic disease, we are beginning to do that better and better,” she adds.

There’s no targeted medicine yet for ARPKD. But thanks to an international conference that Dr. Guay-Woodford convened in Washington in 2013, such consensus expert recommendations have been published to guide diagnosis, surveillance and management of pediatric patients with ARPKD.

“There is an awful lot we can do in the way we systematically look at the clinical disease in these patients and improve our management. And, if you can overlay on top of that specific insights about why one person goes one way in disease progression versus another way, I think we can boost the baseline by developing good standards of care,” she says.

“Science does march on. There are a number of related research studies that are expanding our understanding of ARPKD. Within the next decade, we probably will be able to capitalize on not just the work in ARPKD but work in related diseases to learn the entry points for targeting therapies. That way, we can build a portfolio of markers of disease progression and test how effective these potential therapies are in slowing the course of the disease.”

Zhe Han, PhD

Key to genetic influence of APOL1 on chronic kidney disease

Zhe Han

Drosophila melanogaster nephrocytes share structural and functional similarities with human renal cells, making the fruit fly an ideal pre-clinical model for studying how the APOL1 gene contributes to renal disease in humans.

Using the Drosophila melanogaster pre-clinical model, a Children’s National Health System research team identified a key mechanism by which the APOL1 gene contributes to chronic kidney disease in people of African descent. The model exploits the structural and functional similarities between the fruit fly’s nephrocytes and renal cells in humans to give scientists an unprecedented ability to study gene-to-cell interactions, identify other proteins that interact with APOL1 in renal disease, and target novel therapies, according to a paper published November 18 in the Journal of the American Society of Nephrology.

“This is one of the hottest research topics in the kidney field. We are the first group to generate this result in fruit flies,” says Zhe Han, Ph.D., a senior Drosophila specialist and associate professor in the Center for Cancer & Immunology Research at Children’s National. Han, senior author of the paper, presented the study results this month during Kidney Week 2016, the American Society of Nephrology’s annual gathering in Chicago that was expected to draw more than 13,000 kidney professionals from around the world.

The advantages of Drosophila for biomedical research include its rapid generation time and an unparalleled wealth of sophisticated genetic tools to probe deeply into fundamental biological processes underlying human diseases. People of African descent frequently inherit a mutant version of the APOL1 gene that affords protection from African sleeping sickness, but is associated with a 17- to 30-fold greater chance of developing certain types of kidney disease. That risk is even higher for individuals infected with the human immunodeficiency virus (HIV). Drosophila renal cells, called nephrocytes, accurately mimic pathological features of human kidney cells during APOL1-associated renal disease.

“Nephrocytes share striking structural and functional similarities with mammalian podocytes and renal proximal tubule cells, and therefore provide us a simple model system for kidney diseases,” says Han, who has studied the fruit fly for 20 years and established the fly nephrocyte as a glomerular kidney disease model in 2013 with two research papers in the Journal of the American Society of Nephrology.

In this most recent study, Han’s team cloned a mutated APOL1 gene from podocyte cells cultured from a patient with HIV-associated nephropathy. They created transgenic flies making human APOL1 in nephrocytes and observed that initially the transgene caused increased cellular functional activity. As flies aged, however, APOL1 led to reduced cellular function, increased cell size, abnormal vesicle acidification, and accelerated cell death.

“The main functions of nephrocytes are to filter proteins and remove toxins from the fly’s blood, to reabsorb protein components, and to sequester harmful toxins. It was surprising to see that these cells first became more active and temporarily functioned at higher levels,” says Han. “The cells got bigger and stronger but, ultimately, could not sustain that enhancement. After swelling to almost twice their normal size, the cells died. Hypertrophy is the way that the human heart responds to stress overload. We think kidney cells may use the same coping mechanism.”

The Children’s research team is a multidisciplinary group with members from the Center for Cancer & Immunology Research, the Center for Genetic Medicine Research, and the Division of Nephrology. The team also characterized fly phenotypes associated with APOL1 expression that will facilitate the design and execution of powerful Drosophila genetic screening approaches to identify proteins that interact with APOL1 and contribute to disease mechanisms. Such proteins represent potential therapeutic targets. Currently, transplantation is the only option for patients with kidney disease linked to APOL1.

“This is only the beginning,” Han says. “Now, we have an ideal pre-clinical model. We plan to start testing off-the-shelf therapeutic compounds, for example different kinase inhibitors, to determine whether they block any of the steps leading to renal cell disease.”

‘Trojan horse’ macrophage TNF-alpha opens door for HIV-1 to enter kidney epithelial cells, causing nephropathy

macrophage

Like a Trojan horse, the macrophage sits atop the epithelial cell with HIV hidden inside, opening a doorway into the kidney cell for high levels of HIV-1 to enter.

When nephrologist Patricio Ray, M.D., began investigating human immunodeficiency virus (HIV) as a renal fellow, children infected with the virus had a life expectancy of no more than seven years, and kids of African descent curiously were developing a type of HIV-related kidney disease.

HIV-associated nephropathy (HIVAN) is a progressive kidney disease seen in people who are both HIV-positive and of African ancestry. Kids who carry a modified protein that protects them against sleeping sickness are 80 times more likely to develop this type of kidney disease. Due to the kidney damage, they can have abnormal amounts of protein in their urine, focal segmental glomerulosclerosis, and microcystic tubular dilation, which can lead to enlarged kidneys and chronic kidney failure.

“No one understood how HIV could affect kidney cells that lack the receptors expressed in T cells and white cells,” recalls Dr. Ray, Robert Parrott Professor of Pediatrics at Children’s National Health System. Virologists said kidney epithelial cells that lacked CD4, a major receptor where HIV attaches, could not be infected with the virus. Nephrologists, meanwhile, were seeing that HIV infection was damaging these cells.

It’s taken two decades to unravel the medical mystery, aided by urine samples he coaxed kids to donate by offering them the latest music from New Kids on the Block in exchange for each urine bottle. Many of the kids died years ago, but their immortalized cells were essential in determining, through a process of elimination, which renal cell types were capable of being infected by HIV-1.

The paper represents the capstone of Dr. Ray’s career.

“This is how difficult it is to get an important contribution in science,” he says. “It’s 20 years of work involving the excellent contributions of many people, but that’s why research is called research. In the end, it’s all a learning process. But, it’s amazing how the puzzle pieces begin to fit. When the puzzle fits, it’s good.”

Dr. Ray, in collaboration with lead author Jinliang Li, Ph.D., and four additional Children’s National co-authors, published a paper November 3 in the Journal of the American Society of Nephrology that establishes a new role for transmembrane TNF-alpha, that of a facilitator that makes it easier for the HIV virus to enter certain cell types and replicate there.  Like a Trojan horse, the macrophage sits atop the epithelial cell with HIV hidden inside, opening a doorway into the kidney cell for high levels of HIV-1 to enter.

As a starting point, the research team cultured podocytes from the urine of kids with HIVAN. Through a number of steps, they isolated the unique contributions of the HIV envelope, heparan sulfate proteoglycans as attachment receptors – the glue that binds HIV to podocytes – and the essential role played by TNF-a, a 212-amino acid long type 2 transmembrane protein, in regulating at least two processes, including viral entry and fusion. They used a fluorescent marker to tag HIV-1 viruses, so it lit up bright green. Thus primed with transmembrane TNF-a, the podocytes were susceptible to HIV-1 infection when exposed to high viral loads.

Additional research is needed, such as in vitro work to help understand how HIV traffics within the cell, Dr. Ray says. Those insights could winnow the list of existing therapies that could block key steps, such as attachment to the viral envelope, which could help all people of African descent carrying the genetic mutation, including underserved kids in sub-Saharan Africa.

Another open research question is that certain cells located in the placenta and cervix express TNF-a, and may be more likely to be infected by HIV. Blocking that process could help prevent pregnant HIV-positive mothers from transmitting illness to their offspring.