Beta-cell specific insulin resistance promotes glucose-stimulated insulin hypersecretion

Insulin receptor (Insr) protein can be found at higher levels in pancreatic b-cells than in most other cell types, but the consequences of b-cell insulin resistance remain enigmatic. Ins1cre allele was used to delete Insr specifically in b-cells of both female and male mice which were compared to Ins1cre-containing littermate controls at multiple ages and on multiple diets. RNA-seq of recombined b-cells revealed significant differences in multiple pathways previously implicated in insulin secretion and cellular fate, including rewired Ras and NFkB signaling. Male, but not female, bInsrKO mice had reduced oxygen consumption rate, while action potential and calcium oscillation frequencies were increased in Insr knockout b-cells from female, but not male mice. Female bInsrKO and bInsrHET mice exhibited elevated insulin release in perifusion experiments, during hyperglycemic clamps, and following i.p. glucose challenge. Deletion of Insr did not reduce b-cell mass up to 9 months of age, nor did it impair hyperglycemia-induced proliferation. Based on our data, we adapted a mathematical model to include b-cell insulin resistance, which predicted that b-cell Insr knockout would improve glucose tolerance depending on the degree of whole-body insulin resistance. Indeed, glucose tolerance was significantly improved in female bInsrKO and bInsrHET mice when compared to controls at 9, 21 and 39 weeks. We did not observe improved glucose tolerance in adult male mice or in high fat diet-fed mice, corroborating the prediction that global insulin resistance obscures the effects of b-cell specific insulin resistance. We further validated our in vivo findings using the Ins1-CreERT transgenic line and found improved glucose tolerance 4 weeks after tamoxifen-mediated Insr deletion. Collectively, our data show that loss of b-cell Insr alone is sufficient to drive glucose-induced hyperinsulinemia, thereby improving glucose homeostasis in otherwise insulin sensitive dietary and age contexts. Study of beta cells in mouse islets with three different genotypes for the Insr gene (WT, KO, HET) and both sexes, with between 5 and 8 replicates per genotype-sex combination.