APOL1 Archives

$2M NIH grant for treating disease linked to APOL1

April 3, 2019

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.”

$3 million NIH grant to study APOL1 and HIV synergy

March 8, 2019

Zhe Han, Ph.D., (pictured) and Patricio E. Ray, M.D., have received a $3 million, five-year grant from the National Institutes of Health to study the mechanisms behind APOL1 and HIV nephropathies in children, using a combination of Drosophila models, cultured human podocytes and a preclinical model.

Two Children’s researchers have received a $3 million, five-year grant from the National Institutes of Health (NIH) to study the mechanisms of APOL1 and HIV nephropathies in children, using a combination of Drosophila models, cultured human podocytes and a preclinical model.

The APOL1 genetic variants G1 and G2, found almost exclusively in people of African ancestry, lead to a four-fold higher risk of end-stage kidney disease. HIV infection alone also increases the risk of kidney disease but not significantly. However, HIV-positive people who also carry the APOL1 risk alleles G1 or G2 are about 30 times more likely to develop HIV-nephropathy (HIVAN) and chronic kidney disease.

For more than 25 years, Children’s pediatric nephrology program has studied HIV/renal diseases and recently developed Drosophila APOL1-G0 and G1 transgenic lines. That pioneering research suggests that HIV-1 acts as a “second hit,” precipitating HIV-renal disease in children by infecting podocytes through a mechanism that increases expression of the APOL1-RA beyond toxic thresholds.

With this new infusion of NIH funding, labs led by Zhe Han, Ph.D., and Patricio E. Ray, M.D., will determine the phenotype of Drosophila Tg lines that express APOL1-G0/G1/G2 and four HIV genes in nephrocytes to assess how they affect structure and function. The teams also will determine whether APOL1-RA precipitates the death of nephrocytes expressing HIV genes by affecting autophagic flux.

“Our work will close a critical gap in understanding about how HIV-1 interacts with the APOL1 risk variants in renal cells to trigger chronic kidney disease, and we will develop the first APOL1/HIV transgenic fly model to explore these genetic interactions in order to screen new drugs to treat these renal diseases,” says Dr. Ray, a Children’s nephrologist.

While a large number of people from Africa have two copies of APOL1 risk alleles, they do not necessarily develop kidney disease. However, if a patient has two copies of APOL1 risk alleles and is HIV-positive, they almost certainly will develop kidney disease.

“Our work will close a critical gap in understanding about how HIV-1 interacts with the APOL1 risk variants in renal cells to trigger chronic kidney disease, and we will develop the first APOL1/HIV transgenic fly model to explore these genetic interactions in order to screen new drugs to treat these renal diseases,” says Dr. Ray, a Children’s nephrologist.

“Many teams want to solve the puzzle of how APOL1 and HIV synergize to cause kidney failure,” says Han, associate professor in Children’s Center for Genetic Medicine Research. “We are in the unique position of combining a powerful new kidney disease model system, Drosophila, with long-standing human podocyte and HIVAN studies.”

The team hypothesizes that even as an active HIV infection is held in check by powerful new medicines, preventing the virus from proliferating or infecting new cells, HIV can act as a Trojan horse by making the human cells it infects express HIV protein.

To investigate this hypothesis, the team will create a series of fly models, each expressing a major HIV protein, and will test the genetic interaction between these HIV genes with APOL1. Similar studies also will be performed using cultured human podocytes. Identified synergy will be studied further using biochemical and transcription profile analyses.

“Drosophila is a basic model system, but it has been used to make fundamental discoveries, including genetic control of how the body axes is determined and how the biological clock works – two studies that led to Nobel prizes,” Han adds. “I want to use the fly model to do something close to human disease. That is where my research passion lies.”

A growing list of factors that impact CKD severity for kids

November 20, 2018

Myriad biological and societal factors can impact the occurrence and accelerate progression of chronic kidney disease for children of African descent – including preterm birth, exposure to toxins during gestation and lower socioeconomic status – and can complicate these children’s access to effective treatments.

Myriad biological and societal factors can impact the occurrence and accelerate progression of chronic kidney disease (CKD) for children of African descent – including preterm birth, exposure to toxins during gestation and lower socioeconomic status – and can complicate these children’s access to effective treatments, according to an invited commentary published in the November 2018 edition of American Journal of Kidney Diseases.

Clinicians caring for “these vulnerable children should be mindful of these multiple competing and compounding issues as treatment options are being considered along the continuum from CKD to kidney failure to transplantation,” writes Marva Moxey-Mims, M.D., chief of the Division of Nephrology at Children’s National Health System.

The supplemental article was informed by lessons learned from The Chronic Kidney Disease in Children (CKiD) longitudinal study and conversations that occurred during the Frank M. Norfleet Forum for Advancement of Health, “African Americans and Kidney Disease in the 21^st Century.”

African American children represent 23 percent of the overall population of kids with CKD in the CKiD study. While acquired kidney diseases can get their start during childhood when the diseases betray few symptoms, the full impact of illness may not be felt until adulthood. A number of factors can uniquely affect children of African descent, heightening risk for some kids who already are predisposed to suffering more severe symptoms. These include:

Preterm birth. African American children make up 36 percent of patients in CKiD with glomerular disease, which tends to have faster progression to end-stage renal disease. These diseases impair kidney function by weakening glomeruli, which impairs the kidneys’ ability to clean blood. Patients with a high-risk apolipoprotein L1 (APOL1) genotype already are at higher risk for focal segmental glomerulosclerosis (FSGS) and CKD. Researchers hypothesize that preterm birth may represent “a second hit that facilitates the development of glomerular damage resulting from the high-risk genotype.” According to the Centers for Disease Control and Prevention, 1 in 10 U.S. infants in 2016 was born preterm, e.g., prior to 37 weeks gestation.
APOL1 genotype. Compared with children who had a low-risk genotype and FSGS, children with a high-risk genotype had higher rates of uncontrolled hypertension, left ventricular hypertrophy, elevated C-reactive protein levels and obesity.
Human immunodeficiency viral (HIV) status. About 65 percent of U.S. children with HIV-1/AIDS are African American. In a recent nested case-control study of children infected with HIV in the womb, infants with high-risk APOL1 genotypes were 3.5 times more likely to develop CKD with viral infection serving as “a likely second hit.”
Access to kidney transplant. African American adults experience a faster transition to end-stage renal disease and are less likely to receive kidney transplants. African American children with CKD from nonglomerular diseases begin renal replacement therapy 1.6 years earlier than children of other races, after adjusting for socioeconomic status. Their wait for dialysis therapy was 37.5 percent shorter. However, these African American children waited 53.7 percent longer for transplants. Although donor blood types, genetic characteristics and other biological factors each play contributing roles, “these findings may reflect sociocultural and institutional differences not captured by socioeconomic status,” Dr. Moxey-Mims writes.

To alleviate future health care disparities, she suggests that additional research explore the impact of expanding services to pregnant women to lower their chances of giving birth prematurely; early childhood interventions to help boost children’s educational outcomes, future job prospects and income levels; expanded studies about the impact of environmental toxicities on prenatal and postnatal development; and heightened surveillance of preterm infants as they grow older to spot signs of kidney disease earlier to slow or prevent disease progression.

“Clinicians can now begin to take into account genetics, socioeconomic status and the impact of the built environment, rather than blaming people and assuming that their behavior alone brought on kidney disease,” Dr. Moxey-Mims adds. “Smoking, not eating properly and not exercising can certainly make people vulnerable to disease. However, there are so many factors that go into developing a disease that patients cannot control: You don’t control to whom you’re born, where you live or available resources where you live. These research projects will be useful to help us really get to the bottom of which factors we can impact and which things can’t we prevent but can strive to mitigate.”

The article covered in this post is part of a supplement that arose from the Frank M. Norfleet Forum for Advancement of Health: African Americans and Kidney Disease in the 21st Century, held March 24, 2017, in Memphis, Tennessee. The Forum and the publication of this supplement were funded by the Frank M. Norfleet Forum for Advancement of Health, the Community Foundation of Greater Memphis and the University of Tennessee Health Science Center.

Key to genetic influence of APOL1 on chronic kidney disease

November 23, 2016

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.”

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