Abstract
Adiponectin is a fat tissue-derived adipokine with beneficial effects against diabetes, cardiovascular diseases, and cancer. Accordingly, adiponectin-mimetic molecules possess significant pharmacological potential. Oligomeric states of adiponectin appear to determine its biological activity. We identified a highly conserved, 13-residue segment (ADP-1) from adiponectin's collagen domain, which comprises GXXG motifs and has one asparagine and two histidine residues that assist in oligomeric protein assembly. We therefore hypothesized that ADP-1 promotes oligomeric assembly and thereby mediates potential metabolic effects. We observed here that ADP-1 is stable in human serum and oligomerizes in aqueous environments. We also found that ADP-1 activates AMP-activated protein kinase (AMPK) in an adaptor protein, phosphotyrosine interacting with PH domain and leucine zipper 1 (APPL1)-dependent pathway and stimulates glucose uptake in rat skeletal muscle cells (L6 myotubes). ADP-1-induced glucose transport coincided with ADP-1-induced biosynthesis of glucose transporter 4 and its translocation to the plasma membrane. ADP-1 induced an interaction between APPL1 and the small GTPase Rab5, resulting in AMPK phosphorylation, in turn leading to phosphorylation of p38 mitogen-activated protein kinase (MAPK), acetyl-CoA carboxylase, and peroxisome proliferator-activated receptor α. Similar to adiponectin, ADP-1 increased the expression of the adiponectin receptor 1 (AdipoR1) gene. Of note, ADP-1 decreased blood glucose levels and enhanced insulin production in pancreatic β cells in db/db mice. Further, ADP-1 beneficially affected lipid metabolism by enhancing lipid globule formation in mouse 3T3-L1 adipocytes. To our knowledge, this is the first report on identification of a short peptide from adiponectin with positive effects on glucose or fatty acid metabolism.