FABP4 is secreted from adipocytes by adenyl cyclase‐PKA‐ and guanylyl cyclase‐PKG‐dependent lipolytic mechanisms

Objective Fatty acid‐binding protein 4 (FABP4) is expressed in adipocytes, and elevated plasma FABP4 level is associated with obesity‐mediated metabolic phenotype. Postprandial regulation and secretory signaling of FABP4 has been investigated. Methods Time courses of FABP4 levels were examined during an oral glucose tolerance test (OGTT; n = 53) or a high‐fat test meal eating (n = 35). Effects of activators and inhibitors of adenyl cyclase (AC)‐protein kinase A (PKA) signaling and guanylyl cyclase (GC)‐protein kinase G (PKG) signaling on FABP4 secretion from mouse 3T3‐L1 adipocytes were investigated. Results FABP4 level significantly declined after the OGTT or a high‐fat meal eating, while insulin level was increased. Treatment with low and high glucose concentration or palmitate for 2 h did not affect FABP4 secretion from 3T3‐L1 adipocytes. FABP4 secretion was increased by stimulation of lipolysis using isoproterenol, a β3‐adrenoceptor agonist (CL316243), forskolin, dibutyryl‐cAMP and atrial natriuretic peptide, and the induced FABP4 secretion was suppressed by insulin or an inhibitor of PKA (H‐89), PKG (KT5823) or hormone sensitive lipase (CAY10499). Conclusions FABP4 is secreted from adipocytes in association with lipolysis regulated by AC‐PKA‐ and GC‐PKG‐mediated signal pathways. Plasma FABP4 level declines postprandially, and suppression of FABP4 secretion by insulin‐induced anti‐lipolytic signaling may be involved in this decline in FABP4 level.