Animal Models of Haploinsufficiency Revealed the Isoform-Specific Role of GSK-3 in HFD-Induced Obesity and Glucose Intolerance.

ABSTRACT

Glycogen synthase kinase 3 (GSK-3), a serine-threonine kinase with two isoforms (α and ß) is implicated in the pathogenesis of Type 2 diabetes mellitus (T2D). Recently, we reported the isoform-specific role of GSK-3 in T2D using homozygous GSK-3α/ß Knock-Out mice. While the homozygous inhibition models are idealistic in a preclinical setting, they do not mimic the inhibition seen with pharmacological agents. Hence, in this study, we sought to investigate the dose-response effect of GSK-3α/ß inhibition in the pathogenesis of obesity-induced T2D. Specifically, to gain insight into the dose-response effect of GSK-3 isoforms in T2D, we generated tamoxifen-inducible global GSK-3α/ß heterozygous mice. GSK-3α/ß heterozygous and control mice were fed a high-fat diet (HFD) for sixteen weeks. At baseline, the body weight and glucose tolerance of GSK-3α heterozygous and controls were comparable. In contrast, at baseline, a modest but significantly higher body weight (higher lean mass) was seen in GSK-3ß heterozygous compared to controls. Post-HFD, GSK-3α heterozygous and controls displayed a comparable phenotype. However, GSK-3ß heterozygous were significantly protected against obesity-induced glucose intolerance. Interestingly, the improved glucose tolerance in GSK-3ß heterozygous animals was dampened with chronic HFD-feeding, likely due to significantly higher fat mass and lower lean mass in the GSK-3ß animals. These findings suggest that GSK-3ß is the dominant isoform in glucose metabolism. However, to avail of the metabolic benefits of GSK-3ß inhibition, it is critical to maintain a healthy weight.