PS-B01-4: ANGIOTENSIN II TYPE1 RECEPTOR INHIBITION IMPROVES VASCULAR SENESCENCE THROUGH IMPROVEMENT OF MITOCHONDRIAL QUALITY CONTROL VIA CRAF/MEK/ERK PATHWAY

Abstract

Introduction: Prevention of atherosclerotic cardiovascular disease has a problem of residual risk that is insufficient even if lipids are properly lowered by drugs such as statin. It has been reported that lectin-like oxidized low-density lipoprotein scavenger receptor-1 (LOX-1) associated with Angiotensin II Type 1 Receptor (AT1R). Mitochondria play crucial role in vascular senescence and atherosclerosis. We hypothesized receptor association with LOX-1 and AT1R might be a breakthrough to solve residual risk in terms of mitochondrial quality control. Methods: We performed in vitro and in vivo experiments using vascular smooth muscle cell (VSMC), C57BL6 (WT) and apolipoprotein E deficient (ApoE KO) mice. Results: Administration of ox-LDL to VSMC induced mitochondrial dysfunction and cellular senescence accompanied by excessive mitochondrial fission through Drp1 activation. This Drp1 activation was derived from the activation of CRAF/MEK/ERK pathway, which is a downstream of AT1R. AT1R inhibition inactivated ox-LDL-mediated Drp1 activation and retarded mitochondrial dysfunction, excessive mitochondrial fission and cellular senescence, indicating that LDL receptor LOX-1 associates with AT1R and activates CRAF/MEK/ERK/Drp1, leading to induction of mitochondrial fission and resulting in facilitating cellular senescence. AT1R inhibition also induced mitophagy assessed by electron microscopy and immunohistochemistry of LAMP2 and TOMM20. AT1R inhibition-induced mitophagy was not affected by Atg7 knockdown, whereas it was diminished by Rab9 knockdown. Immunohistochemistry showed TOMM20 dots were co-localized to LAMP2 and Rab9 but not LC3. These results suggest that AT1R signal induces mitophagy derived from Rab9-dependent alternative autophagy. Moreover, inhibition of either CRAF or MEK also decreased excessive mitochondrial fission and induced mitophagy, suggesting that AT1R signal followed by CRAF/MEK pathway modulates both mitochondrial dynamics and mitophagy. Taken together, inhibition of AT1R induces dual modification of mitochondrial dynamics and mitophagy through inactivation of CRAF/MEK/ERK axis. Finally, we confirmed that the degree of vascular senescence and the number of fragmented mitochondria were higher in ApoE KO than those of WT mice, and treatment with Candesartan to ApoE KO inhibited vascular senescence through induction of mitophagy and imbalance of mitochondrial dynamics. Conclusion: Receptor association of LOX-1 with AT1R plays a crucial role in cellular/vascular senescence induced by ox-LDL, and AT1R inhibition improves mitochondrial quality control through regulation of mitochondrial dynamics and mitophagy derived from Rab9-dependent alternative autophagy.