Lack of AMP-activated protein kinase-α1 reduces nitric oxide synthesis in thoracic aorta perivascular adipose tissue

Perivascular adipose tissue (PVAT) releases anti-contractile bioactive molecules including NO. PVAT anti-contractile activity is attenuated in mice lacking AMPKα1 (AMP-activated protein kinase-α1). As AMPK regulates endothelial NO synthase (eNOS) activity in cultured cells, NO synthesis was examined in PVAT from AMPKα1 knockout (KO) mice.

Endothelium-denuded thoracic or abdominal aortic rings were isolated from wild type (WT) and KO mice. NOS inhibition enhanced vasoconstriction in PVAT-intact thoracic aortic rings from mice of either genotype yet had no effect on abdominal rings as assessed by wire myography. Thoracic aorta PVAT exhibited increased NO production, NOS activity and levels of the brown adipose tissue marker uncoupling protein-1 (UCP1) compared to abdominal PVAT. In KO mice, NO production was significantly reduced in thoracic but not abdominal PVAT. Reduced NO production in KO thoracic PVAT was not due to altered levels or phosphorylation of eNOS but was associated with increased caveolin-1:eNOS association and caveolin-1 Tyr14 phosphorylation. A peptide that disrupts eNOS:caveolin-1 association increased NO synthesis and reduced vasoconstriction of PVAT-intact thoracic but not abdominal aortic rings. KO thoracic PVAT also exhibited reduced UCP1 levels.

Murine thoracic aorta PVAT exhibits higher NO synthesis and UCP1 levels than abdominal aortic PVAT. Downregulation of AMPK suppresses NO synthesis which may contribute to the reduced anticontractile activity and reduced brown adipose tissue phenotype of KO thoracic PVAT. The mechanism underlying the effect of AMPK downregulation likely results from increased caveolin-1:eNOS association associated with caveolin-1 Tyr14 phosphorylation.