The discovery of >60 monogenic causes of nephrotic syndrome (NS) has revealed a central role for the actin regulators RhoA/Rac1/Cdc42 and their effectors, including the formin INF2. By whole-exome sequencing (WES), we here discovered bi-allelic variants in the formin DAAM2 in four unrelated families with steroid-resistant NS. We show that DAAM2 localizes to the cytoplasm in podocytes and in kidney sections. Further, the variants impair DAAM2-dependent actin remodeling processes: wild-type DAAM2 cDNA, but not cDNA representing missense variants found in individuals with NS, rescued reduced podocyte migration rate (PMR) and restored reduced filopodia formation in shRNA-induced DAAM2-knockdown podocytes. Filopodia restoration was also induced by the formin-activating molecule IMM-01. DAAM2 also co-localizes and co-immunoprecipitates with INF2, which is intriguing since variants in both formins cause NS. Using in vitro bulk and TIRF microscopy assays, we find that DAAM2 variants alter actin assembly activities of the formin. In a Xenopus daam2-CRISPR knockout model, we demonstrate actin dysregulation in vivo and glomerular maldevelopment that is rescued by WT-DAAM2 mRNA. We conclude that DAAM2 variants are a likely cause of monogenic human SRNS due to actin dysregulation in podocytes. Further, we provide evidence that DAAM2-associated SRNS may be amenable to treatment using actin regulating compounds.
FörderungenGSP Coordinating Center Canadian Society of Nephrology KRESCENT Program, a national kidney research training partnership of the Kidney Foundation of Canada Deutsche Forschungsgemeinschaft (DFG, German Research foundation) Paul and Daisy Soros Fellowship for New Americans Yale Predoctoral Program in Cellular and Molecular Biology Yale MSTP NIH R35 award from the National Institutes of Health National Institutes of Health Canadian Institutes of Health Research NIH Training Grant MEXT of the Japanese Government Deutsche Forschungsgemeinschaft Amgen Irish Nephrology Society Specialist Registrar Bursary International Pediatric Research Foundation Early Investigators' Exchange Program Health Research Board, Ireland NIH F32 Ruth L. Kirschstein Postdoctoral Individual National Research Service Award NIH American Society of Nephrology Lipps Research Program 2018 Polycystic Kidney Disease Foundation Jared J. Grantham Research Fellowship 2017 Post-doctoral Fellowship Grant from the Harvard Stem Cell Institute National Human Genome Research Institute