Human RBP4 adipose tissue expression is gender specific and influenced by leptin

Objective The role of retinol‐binding protein‐4 (RBP4) in human insulin resistance remains controversial, which may in part be explained by a gender‐specific secretion of RBP4 in adipose tissue (AT). The aim of the study was to determine gender‐specific depot expression of RBP4 and to identify metabolic parameters and cytokines/adipokines associated with RBP4. Research Design and Methods The study is an ex ‐ vivo prospective analysis of paired AT‐samples from 22 men and 26 women of similar age [men: 43·4 ± 13 (mean ± SD)years, women: 44·1 ± 12 years], BMI (men: 41·9 ± 18kg/m², women: 38·4 ± 11kg/m²) and homeostasis model assessment of insulin resistance taken during elective surgery and ex‐vivo culture using visceral‐AT (VAT)‐explants (n = 10). Plasma RBP4 and cytokines were measured by ELISA and mRNA expression in AT by real‐time PCR. VAT‐explants were cultured with recombinant leptin and insulin and RBP4 determined by western blot analyses. Results Overall subcutaneous AT (SCAT)‐RBP4 mRNA expression was higher than VAT‐expression [3·1 ± 0·26 signal units (SU; mean ± SE) vs 1·79 ± 0·18 SU, n = 48, P < 0·0001], but neither correlated with circulating RBP4. SCAT‐RBP4 expression was higher in women and correlated with BMI (r = ?0·5, P = 0·009) and fat mass (r = ?0·5, P = 0·002). VAT‐RBP4 correlated positively with GLUT‐4 expression and adiponectin in men only (r = 0·54, P = 0·03 and r = 0·64, P < 0·002, respectively) when correcting for age and fat mass. Multiple regression determined leptin AT‐expression as a positive predictor of AT‐RBP4 in women (SCAT: β = 0·50, P = 0·002; VAT: β = 0·58, P = 0·003) and adiponectin for VAT‐RBP4 in men (β = 0·69; P = 0·001). AT‐RBP4 mRNA expression showed no relation with insulin resistance. Leptin stimulated RBP‐4 secretion ex‐vivo, whilst insulin did not affect RBP4. Conclusion AT‐derived RBP4‐mRNA expression is gender specific and regulated by leptin. Circulating RBP4 levels appear to be independent of AT‐RBP4 secretion.