Secretion of adiponectin and regulation of apM1 gene expression in human visceral adipose tissue

Adiponectin (ApN) is thought to play a major role in the pathogenesis of th e Metabolic Syndrome. Production of ApN and regulation of its related gene (apM1) have not yet been studied in human visceral adipose tissue. ApN was mainly associated with adipocyte membranes and abundantly secreted in mediu m from isolated adipocytes. apM1 gene expression, restricted to the adipocy te fraction of adipose tissue, decreased spontaneously when adipose explant s were cultured in basal medium for 24 h while the expression of other adip ose genes barely changed (PPAR gamma, GAPDH) or increased (PAI-1). Unexpect edly, the fall of apM1 mRNA was prevented by the addition of actinomycin D, an inhibitor of transcription, or cycloheximide, an inhibitor of protein s ynthesis, and by reducing the amount of adipose tissue cultured per dish, t hereby suggesting that a newly synthesized factor released by adipose tissu e destabilizes apM1 mRNA. apM1 gene expression was also negatively regulate d by glucocorticoids and positively by insulin and IGF-1. This regulation c ould contribute to the decreased apMl/ApN levels in insulin-resistant patie nts with obesity and the Metabolic Syndrome. (C) 2001 Academic Press.