Evidence of a Role for Insulin-Like Growth Factor Binding Protein (IGFBP)-3 in Metabolic Regulation

Abstract

IGF-binding protein (IGFBP)-3 is a metabolic regulator that has been shown to inhibit insulin-stimulated glucose uptake in murine models. This finding contrasts with epidemiological evidence of decreased serum IGFBP-3 in patients with type 2 diabetes. The purpose of this study was to clarify the role of IGFBP-3 in metabolism. Four-week-old male IGFBP-3−/− and control mice were subjected to a high-fat diet (HFD) for 12 wk. IGFBP-3−/− mice were heavier before the initiation of HFD and at the end of the study period. Resting metabolic rate was significantly decreased in knockout mice; however, respiratory exchange ratio was not significantly different. Fasting blood glucose and insulin levels were significantly elevated in IGFBP-3−/− mice. However, IGFBP-3−/− mice had relatively normal glucose tolerance because the relative glucose excursion over time was not different between the groups. During hyperinsulinemic clamps, IGFBP-3−/− mice had increased basal hepatic glucose production, but after insulin stimulation, no differences in hepatic glucose production were observed. A second cohort of older IGFBP-3−/− mice on HFD displayed unexpected evidence of hepatic steatosis. In summary, glucose tolerance and clamp testing indicate that IGFBP-3−/− mice preserve insulin sensitivity despite evidence of increased basal glucose turnover and hepatic steatosis. We provide evidence that genetic deletion of IGFBP-3 modulates hepatic carbohydrate and lipid metabolism.