Adiponectin Inhibits TNF-α-Induced Vascular Inflammatory Response via Caveolin-Mediated Ceramidase Recruitment and Activation
Rationale: Anti-inflammatory and vascular protective actions of adiponectin (APN) are well-recognized. However, many fundamental questions remain unanswered.
Objective: The current study attempted to identify the APN receptor subtype responsible for APN's vascular protective action, and investigate the role of ceramidase activation in APN anti-inflammatory signaling.
Methods and Results: APN significantly reduced TNFα-induced ICAM-1 expression and attenuated TNFα-induced oxidative/nitrative stress in HUVECs. These anti-inflammatory actions were virtually abolished by AdipoR1-, but not AdipoR2-, knockdown (KD). Treatment with APN significantly increased neutral ceramidase (nCDase) activity (3.7-fold, P<0.01). AdipoR1-KD markedly, whereas AdipoR2-KD only slightly, reduced gAPN-induced nCDase activation. More importantly, siRNA mediated nCDase-KD markedly blocked the effect of APN upon TNFα-induced ICAM-1 expression. AMPK-KD failed to block APN-induced nCDase activation, and modestly inhibited APN anti-inflammatory effect. In contrast, in Caveolin-1 knockdown (Cav1-KD) cells, >87% of APN-induced nCDase activation was lost. Whereas APN treatment failed to inhibit TNFα-induced ICAM-1 expression, treatment with S1P or SEW (S1P receptor agonist) remained effective in Cav1-KD cells. AdipoR1 and Cav1 co-localized and co-precipitated in HUVECs. APN treatment did not affect this interaction. There is weak basal Cav1/nCDase interaction, which significantly increased following APN treatment. Knockout of AdipoR1 or Cav1 abolished the inhibitory effect of APN upon leukocyte rolling and adhesion in vivo.
Conclusions: These results demonstrate for the first time that APN inhibits TNFα-induced inflammatory response via Cav1-mediated ceramidase recruitment and activation in an AdipoR1-dependent fashion.
- Received August 16, 2013.
- Revision received January 4, 2014.
- Accepted January 6, 2014.