Adiponectin-induced eNOS activation and Nitric Oxide Production are Mediated by APPL1 in Endothelial Cells

Adiponectin protects the vascular system partly through stimulation of endothelial nitric oxide (NO) production and endothelium-dependent vasodilation. The present study investigated the role of the two recently identified adiponectin receptors (AdipoR1 and AdipoR2) and their downstream effectors in mediating the endothelium actions of adiponectin. In human umbilical vein endothelial cells (HUVECs), adiponectin-induced phosphorylation of eNOS at Ser and NO production were abrogated when expression of adipoR1 and adipoR2 was simultaneously suppressed. The proteomic analysis demonstrated that the cytoplasmic tails of both adipoR1 and adipoR2 interacted with APPL1, an adaptor protein that contains pleckstrin homology domain, phosphotyrosine-binding domain and a leucine zipper motif. Suppression of APPL1 expression by RNAi significantly attenuated adiponectin-induced phosphorylation of AMP-activated protein kinase (AMPK) at Thr and eNOS at Ser, and the complex formation between eNOS and heat shock protein (HSP) 90, resulting in a marked reduction of NO production. Adenovirusmediated overexpression of a constitutively active version of AMPK reversed these changes. In db/db diabetic mice, both APPL1 expression and adiponectin-induced vasodilation were significantly decreased compared with those in their lean littermates. Taken together, these results suggest that APPL1 acts as a common downstream effector of adipoR1 and adipoR2 mediating adiponectin-evoked endothelial NO production and endothelium-dependent vasodilation.