c-Ski Inhibits Autophagy of Vascular Smooth Muscle Cells Induced by oxLDL and PDGF

Autophagy is increasingly being recognized as a critical determinant of vascular smooth muscle cell (VSMC) biology. Previously, we have demonstrated that c-Ski inhibits VSMC proliferation stimulated by transforming growth factor β (TGF-β), but it is not clear whether c-Ski has the similar protective role against other vascular injury factors and whether regulation of autophagy is involved in its protective effects on VSMC. Accordingly, in this study, rat aortic A10 VSMCs were treated with 40 µg/ml oxidized low-density lipoprotein (oxLDL) or 20 ng/ml platelet-derived growth factor (PDGF), both of which were autophagy inducers and closely related to the abnormal proliferation of VSMCs. Overexpression of c-Ski in A10 cells significantly suppressed the oxLDL- and PDGF- induced autophagy. This action of c-Ski resulted in inhibiting the cell proliferation, the decrease of contractile phenotype marker α-SMA expression while the increase of synthetic phenotype marker osteopontin expression stimulated by oxLDL or PDGF. Inversely, knockdown of c-Ski by RNAi enhanced the stimulatory effects of oxLDL or PDGF on A10 cell growth and phenotype transition. And further investigation found that inhibition of AKT phosphorylation to downregulate proliferating cell nuclear antigen (PCNA) expression, was involved in the regulation of autophagy and associated functions by c-Ski in the oxLDL- and PDGF-stimulated VSMCs. Collectively, c-Ski may play an important role in inhibiting autophagy to protect VSMCs against some harsh stress including oxLDL and PDGF.

细胞自噬（Autophagy）日益被认为是调控血管平滑肌细胞（VSMC）生物学功能的关键决定因素。此前本课题组已证实，c-Ski可抑制转化生长因子β（TGF-β）诱导的血管平滑肌细胞增殖，但尚不清楚c-Ski是否对其他血管损伤因子具有类似保护作用，以及其对血管平滑肌细胞的保护效应是否涉及自噬调控。为此，本研究采用40 μg/ml氧化低密度脂蛋白（oxLDL）或20 ng/ml血小板衍生生长因子（PDGF）处理大鼠主动脉A10血管平滑肌细胞，二者均为自噬诱导剂，且与血管平滑肌细胞异常增殖密切相关。在A10细胞中过表达c-Ski，可显著抑制oxLDL与PDGF诱导的自噬。c-Ski的这一作用可阻断细胞增殖，逆转oxLDL或PDGF刺激下收缩表型标志物α-平滑肌肌动蛋白（α-SMA）表达的下调，以及合成表型标志物骨桥蛋白（osteopontin）表达的上调。反之，通过RNA干扰（RNAi）敲低c-Ski，则会增强oxLDL或PDGF对A10细胞增殖及表型转化的促进作用。进一步研究发现，在oxLDL与PDGF刺激的血管平滑肌细胞中，c-Ski通过抑制AKT磷酸化以下调增殖细胞核抗原（PCNA）的表达，参与调控自噬及其相关功能。综上，c-Ski或可通过抑制自噬，保护血管平滑肌细胞免受oxLDL、PDGF等不良应激的损伤，发挥关键调控作用。