α7 Nicotinic Acetylcholine Receptor Relieves Angiotensin II-Induced Senescence in Vascular Smooth Muscle Cells by Raising Nicotinamide Adenine Dinucleotide-Dependent SIRT1 Activity

Abstract

Objective: α7 nicotinic acetylcholine receptor (α7nAChR) is a subtype of nAChR and has been reported to be involved in hypertension end-organ damage. In this study, we tested the role of α7nAChR in angiotensin II (Ang II)-induced senescence of vascular smooth muscle cells (VSMCs).

Approach and results: Expression of α7nAChR was not influenced by Ang II. Ang II induced remarkable senescent phenotypes in rodent and human VSMCs, including increased senescence-associated β-galactosidase activity, phosphorylation of H2A.X(Ser139), phosphorylation of Chk1(Ser317), reduced replication, and downregulation of proliferating cell nuclear antigen. Activation of α7nAChR with a selective agonist PNU-282987 blocked Ang II-induced senescence in cultured VSMCs. Moreover, PNU-282987 treatment attenuated the Ang II infusion-induced VSMC senescence in wild-type but not in α7nAChR(-/-) mice. PNU-282987 reduced the Ang II-enhanced reactive oxygen species, lipid peroxidation, and the expression of NADPH oxidase 1, NADPH oxidase 4, and p22(phox) in cultured VSMCs isolated from wild-type but not in α7nAChR(-/-) mice. Furthermore, PNU-282987 diminished Ang II-induced prosenescence signaling pathways, including p53, acetyl-p53, p21, and p16(INK4a). Finally, although α7nAChR activation by PNU-282987 did not affect the Ang II-induced downregulation of sirtuin 1 (SIRT1), it significantly increased intracellular NAD(+) levels, and thereby enhanced SIRT1 activity in an AMP-dependent protein kinase-independent manner. Depletion of SIRT1 by knockdown or SIRT1 inhibitor EX527 abrogated the antisenescence effect of α7nAChR against Ang II.

Conclusions: Our results demonstrate that activation of α7nAChR alleviates Ang II-induced VSMC senescence through promoting NAD(+)-SIRT1 pathway, suggesting that α7nAChR may be a potential therapeutic target for the treatment of Ang II-associated vascular aging disorders.

Keywords: angiotensin II; hypertension; lipid peroxidation; mice; reactive oxygen species.