Regulation of Retinol Binding Protein 4 Expression and Its Relation to Adipogenesis in Bovine Adipocytes

Abstract

Adipogenesis is of great importance in beef cattle. Recent findings indicate that glucose, a substrate for fatty acid biosynthesis and retinoic acid enhance adipogenesis in bovine intramuscular adipocytes. However, other recent findings indicate that Retinol-Binding Protein 4 (RBP4) interferes with glucose uptake and utilization by rodents' adipocytes. In this study we examined the regulation of RBP4 expression and its relation to adipogenesis in bovine adipocytes. Stromal vascular cells were prepared by collagenase digestion from subcutaneous and intramuscular adipose tissues of Japanese black steers. RT-PCR revealed that RBP4 mRNA was expressed in bovine adipose tissue. Northern and Western Blot analysis showed that RBP4 was highly expressed and secreted from bovine preadipocytes. However, RBP4 expression and secretion were significantly reduced by induction of the adipogenic differentiation of preadipocytes into mature adipocytes. Glucose and retinoic acid have a suppressive effect on RBP4 expression and secretion from intramuscular adipocytes. Retinoic acid significantly decreased RBP4 expression in Japanese black steer subcutaneous adipocytes. Retinoic acid itself had no effect on lipid accumulation in subcutaneous adipocytes however, retinoic acid enhanced lipid accumulation in these adipocytes after addition of acetate, a substrate for fatty acid biosynthesis in subcutaneous adipocytes. This study indicated a negative correlation between adipogenesis and RBP4 expression in bovine adipocytes and suggests possible inhibitory effect of RBP4 on adipogenesis.