Flot2 protects against podocyte injury by maintaining the stability of synaptopodin in diabetic nephropathy

Abstract

Podocyte injury is a major determinant of diabetic nephropathy (DN). Critical structural proteins such as synaptopodin play an important role in maintaining podocyte morphology and function. Herein, we uncover a protective role of Flotillin-2 (Flot2), a lipid microdomain-associated protein, in the development of DN by maintaining the stability of synaptopodin. We found that Flot2 was downregulated in podocytes and its expression was correlated with glomerular filtration rate and proteinuria in patients with DN. Functionally, Flot2 is protective in DN as global and podocyte-specific Flot2 knockout (KO) worsened podocyte injury and aggravated the disease as demonstrated by increasing albuminuria, thickening of glomerular basement membrane, and expansion of mesangium matrix in diabetic mice. In contrast, podocyte-specific Flot2 overexpression ameliorated diabetes-induced renal dysfunction and pathology. Mechanistically, we found that Flot2 directly interacted with synaptopodin and protected synaptopodin from ubiquitin degradation via the K48-linked polyubiquitination mediated proteasome pathway. Thus, our findings demonstrate that Flot2 is protective in DN and exerts its protective role by stabilizing synaptopodin. Targeting Flot2 may be a potential therapeutic approach in DN.