Orexin receptor expression in human adipose tissue: effects of orexin-A and orexin-B

Orexin-A and orexin-B, via their receptors orexin-1 receptor (OX1R) and orexin-2 receptor (OX2R) have been shown to play a role in the regulation of feeding, body weight, and energy expenditure. Adipose tissue also contributes significantly to the maintenance of body weight by interacting with a complex array of bioactive peptides; however, there are no data as yet on the expression of orexin components in adipose tissue. We, therefore, analyzed the expression of OX1R and OX2R in human adipose tissue and determined functional responses to orexin-A and orexin-B. OX1R and OX2R mRNA expression was detected in subcutaneous (s.c.) and omental adipose tissue and in isolated adipocytes. Protein for OX1R and OX2R was also detected in whole adipose tissue sections and lysates. Treatment with orexin-A, and orexin-B (100 nM, 24 h) resulted in a significant increase in peroxisome proliferator-activated receptors gamma-2 mRNA expression in s.c. adipose tissue (P < 0.05). Hormone sensitive lipase mRNA was significantly reduced in omental adipose tissue with orexin-A and orexin-B treatment (P < 0.05). Glycerol release from omental adipose tissue was also significantly reduced with orexin-A treatment (P < 0.05). These findings demonstrate for the first time the presence of functional orexin receptors in human adipose tissue and suggest a role for orexins in adipose tissue metabolism and adipogenesis.