AT2R deficiency mediated podocyte loss via activation of ectopic hedgehog interacting protein (Hhip) gene expression

Angiotensin II type 2 receptor (AT2R) deficiency in AT2R knockout (KO) mice has been linked to congenital abnormalities of the kidney and urinary tract; however, the mechanisms by which this occurs are poorly understood. In this study, we examined whether AT2R deficiency impaired glomerulogenesis and mediated podocyte loss/dysfunction in vivo and in vitro. Nephrin‐cyan fluorescent protein (CFP)‐transgenic (Tg) and Nephrin/AT2RKO mice were used to assess glomerulogenesis, while wild‐type and AT2RKO mice were used to evaluate maturation of podocyte morphology/function. Immortalized mouse podocytes (mPODs) were employed for in vitro studies. AT2R deficiency resulted in diminished glomerulogenesis in E15 embryos, but had no impact on actual nephron number in neonates. Pups lacking AT2R displayed features of renal dysplasia with lower glomerular tuft volume and podocyte numbers. In vivo and in vitro studies demonstrated that loss of AT2R was associated with elevated NADPH oxidase 4 levels, which in turn stimulated ectopic hedgehog interacting protein (Hhip) gene expression in podocytes. Consequently, ectopic Hhip expression activation either triggers caspase‐3 and p53‐related apoptotic processes resulting in podocyte loss, or activates TGFβ1–Smad2/3 cascades and α‐SMA expression to transform differentiated podocytes to undifferentiated podocyte‐derived fibrotic cells. We analyzed HHIP expression in the kidney disease database (Nephroseq) and then validated this using HHIP immunohistochemistry staining of human kidney biopsies (controls versus focal segmental glomerulosclerosis). In conclusion, loss of AT2R is associated with podocyte loss/dysfunction and is mediated, at least in part, via augmented ectopic Hhip expression in podocytes. Copyright © 2017 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.