Repin1 maybe involved in the regulation of cell size and glucose transport in adipocytes

Replication initiator 1 (Repin1) is highly expressed in liver and adipose tissue and has been suggested as candidate gene for obesity and its related metabolic disorders in congenic and subcongenic rat strains. The cellular localization and function of Repin1 has remained elusive since its discovery in 1990. To characterize the role of Repin1 in adipocyte biology, we used siRNA knockdown technology to reduce the expression of Repin1 by electroporation of semiconfluent 3T3-L1 preadipocytes. Glucose transport, palmitate uptake as well as triglyceride content were measured. In paired samples of human visceral and subcutaneous adipose tissue, we investigated whether Repin1 mRNA expression is related to measures of fat accumulation and adipocyte size. We demonstrate that Repin1 increases during adipogenesis. RNA interference based Repin1 downregulation in mature adipocytes significantly reduces adipocyte size and causes reduced basal, but enhanced insulin stimulated glucose uptake into 3T3-L1 cells. Additionally, knockdown of Repin1 resulted in reduced palmitate uptake and significantly changed the mRNA expression of genes involved lipid droplet formation, adipogenesis, glucose and fatty acid transport. Furthermore, we found significant correlations between Repin1 mRNA expression in human paired visceral and subcutaneous adipose tissue and total body fat mass as well as adipocyte size. We have identified a potential role for Repin1 in the regulation of adipocyte size and expression of glucose transporters GLUT1 and GLUT4 in adipocytes.

Research highlights
► First notion that Repin1 regulates genes associated with lipid droplet size.
► siRNA based knockdown of Repin1 in 3T3-L1 cells causes smaller adipocyte size.
► Repin1 KO alters glucose transport into 3T3-L1 cells.
► Repin1 KO significantly changes GLUT1, GLUT4 mRNA expression in vitro.
► Human Repin1 expression (n = 196) correlates with adipocyte size, independent of BMI.