Regional specificity of ASP binding in human adipose tissue

Obesity, in particular omental (OM) adiposity, is associated with diabetes and cardiovascular disease. Thus site-specific regulation of fat storage is important to understand. Acylation-stimulating protein (ASP) is a potent stimulator of glucose transport and triglyceride synthesis in adipocytes. In the present study, we characterized receptor binding of ¹²⁵I-labeled ASP to human adipocyte plasma membranes from paired OM and subcutaneous (SC) sites in normal (N) and obese (O) male (M) and female (F) subjects (n = 24). Overall, specific binding of ¹²⁵I-ASP was in the order of SC > OM and O > N (in SC tissue, particularly in F). Receptor affinity of ¹²⁵I-ASP was higher [lower dissociation constant (K(d))] in SC than in OM (63.6 ± 16.2 vs. 160.7 ± 38.6 nM, P < 0.02), especially in F (37.0 ± 11.1 F-N and 26.3 ± 6.7 nM F-O) and lower (higher K(d)) in male OM (291.8 ± 116.8 M-N and 149.4 ± 56.4 M-O). The greater binding and higher affinity of ¹²⁵I-ASP binding to SC suggests that ASP may be an important factor in maintaining regional adipose tissue mass. Conversely, lower binding and receptor affinity in male OM adipose tissue may contribute to the fatty acid imbalance and metabolic complications associated with this syndrome, by reducing the efficiency of adipose fatty acid trapping by the ASP pathway.