Grb7 ablation in mice improved glycemic control, enhanced insulin signaling and increased abdominal fat mass in females.

OBJECTIVE Growth Factor Receptor Bound Protein 7 (GRB7) is a multi-domain signaling adaptor. Members of the Grb7/10/14 family, specifically Gbrb10/14, have important roles in metabolism. We ablated the Grb7 gene in mice to examine its metabolic function. METHODS Global ablation of Grb7 in FVB/NJ mice was generated. Growth, organ weight, food intake, and glucose homeostasis were measured. Insulin signaling was examined by Western blotting. Fat and lean body mass was measured by Nuclear Magnetic Resonance, and body composition after fasting or high fat diet was assessed. Energy expenditure was measured by indirect calorimetry. Expression of adiposity and lipid metabolism genes was measured by qPCR. RESULTS Grb7-null mice were viable, fertile and without obvious phenotype. Grb7 ablation improved glycemic control and displayed sensitization to insulin signaling in the liver. Grb7-null females but not males had increased gonadal white adipose tissue mass. Following a 12-week high fat diet, Grb7-null female mice gained fat body mass and developed relative insulin resistance. With fasting, there was less decrease in fat body mass in Grb7-null female mice. Female mice with Grb7 ablation had increased baseline food intake, less energy expenditure and displayed a decrease in the expression of lipolysis and adipose browning genes in gonadal white adipose tissue by transcript and protein analysis. CONCLUSIONS Our study suggests that Grb7 is a negative regulator of glycemic control. Our results reveal a role for Grb7 in female mice in the regulation of the visceral adipose tissue mass, a powerful predictor of metabolic dysfunction in obesity.