Tag Archive for: G1

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.”

Zhe Han

$3 million NIH grant to study APOL1 and HIV synergy

Zhe Han

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.

Patricio Ray

“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.”