2555-P: Double Knockout of INHBC and INHBE Protect against Diet-Induced Obesity and Insulin Resistance in Mice

Introduction and Objective: ACVR1C and INHBE pLOFs and missense variants are associated with protection from type 2 diabetes. Ablation of Acvr1c or Inhbe in rodents drives body weight and fat loss, as well as fatty liver and insulin resistance, contradictory to the human genetic evidence. INHBC, encoding Activin C, has structural similarities to Activin E in the type I and II receptor binding domains, suggesting potential biological redundancies. The aim is to assess whether knocking out Inhbc in addition to Inhbe protects against the development of insulin resistance and fatty liver on high fat diet. Methods: Human primary adipocytes (ZenBio) were treated with ligands (R&D systems) or antagonist antibodies. Inhbc and Inhbe double knockout (DKO) mice were generated in-house and phenotyped along with wildtype (WT) controls. Activin competition assays were performed in engineered reporter cells that express ACVR1B. Results: DKO mice gained 19% (±9% SD) body weight compared to 51% (±9% SD) in WT after 7 weeks of HFD, had improved insulin sensitivity, and liver weights were reduced by 21% (±8% SEM) compared to WT. Activin AB, AC and AE heterodimers were immunoprecipitated with an activin A antibody from obese mouse serum. The role of activin AC on activin A signaling was assessed in a competition assay, and results show activin AC blocks activin A signaling via Alk4. Conclusion: Activin AC, C and E are Alk7-specific inducers of pSmad3 in primary human adipocytes. DKO mice are protected from HFD-induced obesity and insulin resistance which was not observed with Inhbe or Acvr1c single KO mice. Inhbc KO is required to prevent ectopic liver lipid storage, which is surprising because single Inhbc KO is not associated with body weight or liver phenotypes. Activin AC and AE heterodimers were detected in mouse serum and may serve as antagonists to activin A signaling with Alk4. This data highlights the need to investigate the role of Activin E and C, as well as potential heterodimers, on adipose and liver metabolism. Disclosure D. Li: Employee; Current; Regeneron Pharmaceuticals Inc. Stock/Shareholder; Current; Regeneron Pharmaceuticals Inc. J. Mastaitis: Employee; Current; Regeneron Pharmaceuticals Inc. S.H. Min: Employee; Current; Regeneron Pharmaceuticals Inc. E. Goebel: Employee; Current; Regeneron Pharmaceuticals Inc. Y. Liu: Employee; Current; Regeneron Pharmaceuticals Inc. A. Ho: None. J. Altarejos: Employee; Current; Regeneron Pharmaceuticals Inc. Stock/Shareholder; Current; Regeneron Pharmaceuticals Inc.