Abstract 296: Decreased Hepatic Avpr1a Gene Expression and Elevated Serum Bile Acid in Mouse Model of Metabolic Syndrome

Abstract

The KK/HIJ mouse has been demonstrated to have polygenic obesity and insulin resistance and serve as a model of metabolic syndrome. From microarray studies in this mouse strain, we observed hepatic gene expression of arginine vasopressin receptor 1A (Avpr1a) as the most differentially elevated gene in the liver following 3-week of voluntary wheel running activity. Subsequent studies validated that hepatic Avpr1a gene expression is significantly upregulated following voluntary activity and also highly suppressed (4 to 8-fold) in 2 independent models of insulin resistance (including obesity and lipoatrophic models). Although Avpr1a is highly abundant in the liver, its physiologic role is not well described. One proposed role for hepatic Avpr1a is mediation of vasopressin-induced bile acid secretion. To further evaluate the relationship between hepatic Avpr1a and bile acid homeostasis, we determined the age-related change in these variables in female KK mice. To investigate, adipose tissue, liver and serum were collected from female KK mice from before sexual maturity (PRE: 4.5 weeks old, n=9) and after sexual maturation (POST: 6 to 30 weeks old, n=12). Consistent with previous studies using this obesity-prone strain, we observed a robust increase in adiposity with age despite a standard rodent chow diet. RT-PCR studies of hepatic gene expression revealed a 53% lower Avpr1a in POST compared to PRE mice (p<0.00001). In parallel with the drop in hepatic Avpr1a gene expression was an increase in serum bile acids (PRE: 26.56± 9.98μmol/L; POST: 39.40± 9.63μmol/L; p<0.01). A negative correlation was evident between hepatic Avpr1a gene expression and serum bile acid level (R= -0.51). The change in Avpr1a and bile acids was pronounced at the age of onset of estrous cycling. In conclusion, female KK mice have a significant increase in fat mass with age in parallel with an elevation of serum bile acids and downregulation of hepatic Avpr1a gene expression. We propose that suppression of hepatic Avpr1a increases hydrophobic bile acids in the liver and serum and promotes hepatic inflammation, contributing to symptoms of the metabolic syndrome.