Research & Publications
My area of research involves podocyte biology, glomerular development and disease. Our work focuses on the role of VEGF-A and semaphorins in renal development and disease, particularly in nephrotic syndrome and diabetic nephropathy. Incomplete understanding of the molecular mechanisms that lead to both glomerular diseases has precluded identification of individuals at risk and the development of effective treatments that prevent progression to end-stage renal disease (ESRD). Focal segmental glomerulosclerosis (FSGS), a progressive form of nephrotic syndrome, is a leading cause of ESRD in children and diabetic nephropathy is the most frequent cause of ESRD in adults worldwide. My research seeks to unravel fundamental mechanisms underlying the pathogenesis of both diseases and to identify risk biomarkers and new genes involved.
Specialized Terms: Molecular and developmental biology; VEGF-A; Semaphorins; myosins; FSGS, Diabetic nephropathy; Slit-diaphragm proteins; Protein interactions; Signaling pathways;
Extensive Research Description
My lab work and research contribution to the field comprises several aspects:
- a) Role of VEGF and semaphorins in renal development. My initial independent research demonstrated that hypoxia and VEGF induce vasculogenesis and nephrogenesis during kidney organogenesis and that VEGF spatially directs the angiogenesis leading to glomerular vascularization, introducing the notion that VEGF plays critical roles in nephrovascular development. We demonstrated that sema3a is a negative regulator of vascularization, podocyte differentiation and branching morphogenesis during renal development. This work was funded by NIH-KO8 and RO1.
- b) Role of VEGF and sema3a disregulation in the pathogenesis of glomerular disease. We generated inducible VEGF gain and loss of function mouse models, and demonstrated that excess podocyte VEGF-A during renal development causes steroid resistant nephrosis, whereas in adult mice it mimics early diabetic nephropathy. Moreover, we showed that in the setting of diabetes excess podocyte VEGF leads to Kimmestiel-Wilson nodular glomerulosclerosis indistinguishable from human disease. We discovered that excess sema3a induces advanced diabetic nephropathy in mice that is abrogated by a sema3a inhibitor and by plexinA1 receptor deletion, demonstrating that excess sema3a is pathogenic in diabetic nephropathy. Consistent with this, we detected increased sema3a in human renal biopsies with advanced diabetic nephropathy. Funding by NIH-RO1 is ongoing.
- c) Podocyte signaling: Identification of direct VEGFR2-nephrin and plexinA1–nephrin interactions established mechanistic links between VEGF-A or sema3a extracellular signals and slit-diaphragm signaling at the glomerular filtration barrier, providing insight into the molecular pathogenesis of proteinuria and glomerular phenotypes resulting from disregulating these pathways. We identified the pathogenic mechanism of semaphorin3A in diabetic nephropathy using mouse models generated in the lab, and determined how semaphorin3A signals mediated by plexinA1 – MICAL1 interactions regulate podocyte shape leading to podocyte injury. Ongoing studies with T1D and T2D human samples will determine whether sema3a is a novel biomarker of progressive diabetic nephropathy. An additional area of signaling studies in my lab is the role of S-nitrosylation regulation in diabetic nephropathy and glomerular disease. We identified disregulation of nitrosylated proteins in both disease models This work is supported by NIH-RO1 and NIH-DiaComp funding.
- d) Identification and molecular characterization of new nephrotic syndrome-causing genes, in collaboration with Drs. Lifton and Bale (Genetics). We have identified a mutation in a myosin not previously reported to cause human disease, generated mutant mice carrying the mutation by gene editing, which developed FSGS, strongly suggesting this is a FSGS-causing mutation in humans. We will perform the cell biology studies to define the pathogenic mechanism of novel gene mutation identified. This work recently obtained RO1 funding.
Future directions of my research are 1) to further elucidate signaling mechanisms downstream of VEGF-A and sema3A receptors that control podocyte phenotype and glomerular function, and are regulated by nitrosylation; 2) translational studies using small molecule inhibitors targeting the sema3A pathway and testing sema3A as a biomarker for diabetic nephropathy. 3) identify novel nephrotic syndrome causing genes, by performing exome sequencing in samples from children with nephrotic syndrome refractory to treatment and FSGS from our clinic and ancillary studies to NIH funded FSGS-CT (ClinicalTrials.gov Identifier:NCT00135811).
Kidney; Congenital, Hereditary, and Neonatal Diseases and Abnormalities; Nephrology; Pediatrics; Semaphorins; Vascular Endothelial Growth Factor A; Podocytes