SM22蛋白蓄积在血管平滑肌细胞衰老中的作用和机制

It is known that transgenlin (namely SM22), as a marker of vascular smooth muscle cell (VSMC) differentiation, plays key role in regulation of stress fibre formation and vascular contraction. The expression of SM22 is controlled by myocardin which is a coactivator of serum response factor (SRF). The recent studies show that expression of SM22 is upregulated in senescence cells, which increases in p21 and results in cell cycle arrest. However, the mechanism of SM22 induction of senescence is unclear. We hypothesized that accumulation of SM22 promoted VSMC senescence, which was associated with vascular hypertrophy and hypertension. The goals of this project are, 1) to find the direct evidences for involvement of SM22 in VSMC senescence and vascular ageing; 2) to investigate the mechanism of SM22 turnover during cell senescence, and relationship between it and senescence response in VSMCs; 3) to elucidate the fashion and significances of cytoskeleton dynamics induced by SM22 excess, which plays roles and signaling during cell senescence; 4) to determine the effects of SM22-mediated actin cytoskeleton reorganization on the activation of p53-p21 pathways. Our findings will provide novel insight for understanding the molecular mechanisms governing vascular aging development as well as predicting the new molecular therapeutic target for vascular hypertrophy and hypertension.

平滑肌分化标志物SM22蛋白具有调节应力纤维形成和血管平滑肌收缩性的生理功能；在衰老的细胞，SM22表达上调，SM22已被公认是新的细胞衰老标志物。我们前期发现，过表达SM22可阻断平滑肌细胞生长信号转导、上调p21、抑制细胞周期进程。我们假设，SM22蓄积诱发细胞衰老和血管老化。本项目将分别从SM22代谢更新、actin细胞骨架组构和信号途径等方面探讨SM22蓄积与平滑肌细胞衰老的因果关系；考查衰老刺激下，SM22基因表达与泛素化降解之间动态平衡变化和调节机制，及其对细胞衰老应答的影响；SM22蓄积对actin细胞骨架组构的影响及在细胞衰老中的意义；明确SM22蓄积抑制生长应答、激活衰老相关途径SIRT1-p53和p53-p21轴的分子机制、以及对内皮功能的影响；利用SM22敲除小鼠于颈总动脉过表达SM22,体内验证SM22蓄积促血管老化效应；探寻靶向SM22的抗血管老化防治策略。

本研究以Ang II为诱导因素，通过建立VSMC衰老模型和高血压动物模型，试图从体内外证实SM22α在VSMC衰老和血管老化进程中的作用，并探讨其作用机制，以期为揭示衰老相关心血管疾病的发生机制提供研究证据。我们发现，在Ang II诱导的VSMC衰老过程中，SM22α的表达与细胞衰老进程具有平行关系；敲低SM22α表达可降低衰老标志物的表达水平和活性；而过表达SM22α则可促进Ang II诱导的SA-β-gal活性增高以及p53和p21表达增加。SM22α对Ang II诱导的VSMC衰老具有促进作用。Sm22α-/-小鼠血压升高幅度较野生型小鼠明显降低，并且其主动脉组织中p53和p21蛋白表达水平和SA-β-gal活性也低于野生型小鼠。进一步提示SM22α表达增加与VSMC衰老具有因果关系。敲低SM22α可提高p53泛素化降解活性，而过表达SM22α则降低p53泛素化。机制研究显示，SM22α表达下调可促进Mdm-2与p53的结合以及p53泛素化降解；反之，上调SM22α表达则抑制Mdm-2与p53的结合，这种抑制与稳定细胞骨架有关。而且，SM22α对p53泛素化降解的调节是通过Akt-Mdm-2信号通路介导的，过量的SM22α具有稳定p53的作用。此外，还证实SM22α可降低Ras与RasGAP的相互作用进而抑制Ras激活，降低Arp2/3复合物的形成和actin的成核活性，伪足形成障碍，细胞迁移活性降低。黄芩苷可通过上调SM22α表达进而抑制PDGF-BB诱导的迁移。SM22α该作用的主要意义在于，通过抑制细胞迁移而使细胞生长空间受限，最终可能诱导合成型细胞生长停滞、发生衰老。第三个发现是， circ-Sirt1可阻止PDGF-BB诱导的c-Myc核转位和细胞增殖活性（PCNA减少）。circ-Sirt1-SIRT1-SM22α分子网络可能是抑制VSMC炎性衰老的新机制。