Joint effect of insulin signaling genes on insulin secretion and glucose homeostasis.

CONTEXT: Reduced insulin signaling in insulin secreting β-cells causes defective insulin secretion and hyperglycemia in mice.

OBJECTIVE

We investigated whether functional polymorphisms affecting insulin signaling (ie, ENPP1 K121Q, rs1044498; IRS1 G972R, rs1801278; and TRIB3 Q84R, rs2295490) exert a joint effect on insulin secretion and abnormal glucose homeostasis (AGH).

DESIGN

Insulin secretion was evaluated by 1) the disposition index (DI) from an oral glucose tolerance test (OGTT) in 829 individuals; 2) insulin secretion stimulation index (SI) in islets from nondiabetic donors after glucose (n = 92) or glibenclamide (n = 89) stimulation. AGH (including impaired fasting glucose and/or impaired glucose tolerance or type 2 diabetes; T2D) was evaluated in case-control studies from the GENetics of Type 2 Diabetes in Italy and the United States (GENIUS T2D) Consortium (n = 6607).

RESULTS

Genotype risk score, obtained by totaling individual weighted risk allele effects, was associated with the following: 1) DI (P = .005); 2) glucose and glibenclamide SI (P = .046 and P = .009); or 3) AGH (odds ratio 1.08, 95% confidence interval 1.03-1.13; P = .001). We observed an inverse relationship between genetic effect and age at AGH onset, as indicated by a linear correlation between AGH-genotype risk score odds ratios and age-at-diagnosis cutoffs (R(2) = 0.80, P < .001).

CONCLUSIONS

Functional polymorphisms affecting insulin signaling exert a joint effect on both in vivo and in vitro insulin secretion as well as on early-onset AGH. Our data provide further evidence that abnormal insulin signaling reduces β-cell function and impairs glucose homeostasis.