189-OR: FGF21-Mediated Signaling Defects and Their Effects on Insulin Resistance in Insulin-Mediated Pseudoacromegaly

Abstract

Insulin-mediated pseudoacromegaly (IMPA) is a rare, severe insulin resistance syndrome linked to digenic mutations in FGFR1 and KLB. These proteins form the receptor complex for FGF21, a hepatokine that plays a critical role in adipose tissue insulin sensitivity. Patients with IMPA have normal growth hormone and IGF-1. However, they have markedly increased insulin levels, tall stature, and obesity. To assess the pathogenicity of these mutations, we isolated iPSC from the proband with IMPA. We used CRISPR gene editing to correct the FGFR1 and KLB mutations and differentiated the iPSC lines into adipocytes. Western immunoblotting demonstrated that the uncorrected (mutant) cells demonstrated decreased levels of FGFR1 and pERK1/2 in response to insulin and/or FGF21 compared to corrected (wild-type) cells. Additionally, mutant adipocytes demonstrated significantly larger lipid droplets when stained with BODIPY. To complement the iPSC work, a humanized transgenic knock-in mouse line was created using CRISPR gene editing. When exposed to a high fat diet (HFD), female mice harboring variants in FGFR1 and KLB (DM - Double Mutant) developed significant weight gain compared to wild-type (WT) littermates. The difference in body weight was attributed to a difference in body fat. Similar to the human phenotype, the DM mice experience intermittent hyperglycemia and significant hyperinsulinemia. Explants of gonadal white adipose tissue demonstrated decreased lipolysis and pAKT and pERK. Mac-2 staining of white adipose tissue demonstrated abundant adipose tissue macrophages forming crown-like structures, suggesting adipose tissue inflammation. Additionally, we measured gene expression in brown adipose tissue, and noting that Ucp1 expression in DM mice was 37% when compared to WT. These results suggest pathogenic mechanisms in which FGFR1 and KLB mutations lead to IMPA via decreased FGF21-mediated signaling in the adipose tissue. Disclosure N.Phan: None. D.M.Ornitz: None. S.I.Stone: None. Funding Eunice Kennedy Shriver National Institute of Child Health and Human Development (R21HD098872); National Institute of Diabetes and Digestive and Kidney Diseases (K08 DK124574, P30DK020579, P30DK056341); National Center for Advancing Translational Sciences