Tag Archive for: nephrocytes

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 the 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.

Zhe Han lab 2018

$2 million NIH grant to study nephrotic syndrome

Zhe Han lab 2018

A Children’s researcher has received a $2 million grant from the National Institutes of Health (NIH) to study nephrotic syndrome in Drosophila, a basic model system that has revealed groundbreaking insights into human health. The award for Zhe Han, Ph.D., an associate professor in Children’s Center for Genetic Medicine Research, is believed to be the first ever NIH Research Project grant (R01)  to investigate glomerular kidney disease using Drosophila. Nephrotic syndrome is mostly caused by damage of glomeruli, so it is equivalent to glomerular kidney disease.

“Children’s National leads the world in using Drosophila to model human kidney diseases,” Han says.

In order to qualify for the five-year funding renewal, Han’s lab needed to successfully accomplish the aims of its first five years of NIH funding.  During the first phase of funding, Han established that nephrocytes in Drosophila serve the same functions as glomeruli in humans, and his lab created a series of fly models that are relevant for human glomerular disease.

“Some 85 percent of the genes known to be involved in nephrotic syndrome are conserved from the fly to humans. They play similar roles in the nephrocyte as they play in the podocytes in human kidneys,” he adds.

Pediatric nephrotic syndrome is a constellation of symptoms that indicate when children’s kidneys are damaged, especially the glomeruli, units within the kidney that filter blood. Babies as young as 1 year old can suffer proteinuria, which is characterized by too much protein being released from the blood into the urine.

“It’s a serious disease and can be triggered by environmental factors, taking certain prescription medicines or inflammation, among other factors.  Right now, that type of nephrotic syndrome is mainly treated by steroids, and the steroid treatment works in many cases,” he says.

However, steroid-resistant nephrotic syndrome occurs primarily due to genetic mutations that affect the kidney’s filtration system: These filters are either broken or the protein reabsorption mechanism is disrupted.

“When genetics is to blame, we cannot turn to steroids. Right now there is no treatment. And many of these children are too young to be considered for a kidney transplant,” he adds. “We have to understand exactly which genetic mutation caused the disease in order to develop a targeted treatment.”

With the new funding, Han will examine a large array of genetic mutations that cause nephrotic syndrome. He’s focusing his efforts on genes involved in the cytoskeleton, a network of filaments and tubules in the cytoplasm of living cells that help them to maintain shape and carry out important functions.

“Right now, we don’t really understand the cytoskeleton of podocytes – highly specialized cells that wrap around the capillaries of the glomerulus – because podocytes are difficult to access. To change a gene requires time and considerable effort in other experimental models. However, changing genes in Drosophila is very easy, quick and inexpensive. We can examine hundreds of genes involving the cytoskeleton and see how changing those genes affect kidney cell function,” he says.

Han’s lab already found that Coenzyme Q10, one of the best-selling nutrient supplements to support heart health also could be beneficial for kidney health. For the cytoskeleton, he has a different targeted medicine in mind to determine whether Rho inhibitors also could be beneficial for kidney health for patients with certain genetic mutations affecting their podocyte cytoskeleton.

“One particular aim of our research is to use the same strategy as we employed for the Coq2 gene to generate a personalized fly model for patients with cytoskeleton gene mutations and test potential target drugs, such as Rho inhibitors.” Han added. “As far as I understand, this is where the future of medicine is headed.”

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.