INF2 Promotes Podocyte Resilience to Ischemic and Hemodynamic Stress Through Actin Cytoskeletal Regulation

Background: Inverted formin-2 (INF2) is a member of the formin family of actin-regulating proteins known for its unique ability to accelerate both actin polymerization and depolymerization. Mutations in INF2 are linked to autosomal dominant FSGS, with evidence suggesting a gain-of-function mechanism. Podocytes express high levels of INF2. However, the specific role of INF2 in podocyte homeostasis and adaptation to stress is not well defined. This study aimed to investigate the functional role of INF2 in podocytes under both baseline and injury conditions using INF2 knockout (KO) and wild-type (WT) mouse models. Methods: We induced renal ischemia-reperfusion injury (IRI) by unilaterally clamping the right renal artery for 45 minutes on C57BL/6 WT and INF2 KO mice. To model enhanced hemodynamic stress, a subset of mice also received a continuous infusion of angiotensin II (ATII) via osmotic minipumps. Urine samples were collected on days 3, 7, and 14 post-surgery. On day 14, the mice were euthanized, and blood and kidney tissues were harvested for analysis. INF2 expression was assessed using immunofluorescence (IF) and quantitative PCR. Kidney ultrastructure was examined through electron microscopy (EM), focusing on podocyte foot process architecture. Urinary protein excretion was measured to assess glomerular injury. Results: IRI significantly increased INF2 expression in WT mice. IF analysis showed robust upregulation of INF2 in glomeruli, which was confirmed by qPCR indicating a significant increase in INF2 mRNA levels relative to baseline. Phenotypically, INF2 KO mice displayed mild proteinuria at all tested time points (days 3, 7, and 14), although this was not significantly different from WT controls. However, when exposed to subsequent ATII, INF2 KO mice exhibited significantly worsened proteinuria, a phenomenon not seen in WT mice. This suggests a synergistic effect of injury under increased vasoconstrictive stress. Furthermore, ultrastructural analysis through EM revealed greater effacement of podocyte foot processes in INF2 KO mice, indicating increased structural damage and compromised integrity of the glomerular filtration barrier. Conclusion: Our findings support a model where INF2 plays a protective, stress-adaptive role in maintaining podocyte structure and function, underscoring its importance in kidney health and disease. Funding: NIDDK Support