NRG-1-ICD在转录和转录后水平协同调节α-actin表达的分子机制

The actin cytoskeleton not only plays an important role in the regulation of vascular contractility and VSMC proliferation and migration, but also is involved in all the pathological changes taking place in the vascular wall. Subtle changes in α-actin expression could have profound effects on normal vascular function and likely contribute to vascular disease progression. We recently found that neuregulin-1 intracellular domain (NRG-1-ICD) regulated α-actin expression at the post-transcriptional level through inducing circActa2 formation, and circActa2 is the first functional circRNA regulating SMC differentiation control and contractile function. However, it remains unknown whether both the NRG-1-ICD and circActa2 regulate α-actin expression at the transcriptional level. Thus, in the present study, we shall investigate whether NRG-1-ICD regulates α-actin expression at the transcriptional level via interacting with KLF4/coactivators, as well as via interaction of circActa2 induced by NRG-1-ICD with RNA polymerase II or other RNA binding proteins, define the molecular mechanism underlying the synchronous regulation of α-actin expression by NRG-1-ICD at the transcriptional and post-transcriptional level. Finally, we shall explore the relationship between the alteration of NRG-1-ICD, circActa2 and miR-548f-5p expression and vascular remodeling, providing a novel mechanism for vascular homeostasis and remodeling.

由α-actin组成的细胞骨架既在血管平滑肌细胞（VSMC）收缩中发挥重要作用，又通过调制炎症和氧化应激参与血管重构，α-actin表达的微小变化即可对血管功能产生很大影响。我们发现，神经调节蛋白-1（neuregulin-1）的胞内结构域 (NRG-1-ICD) 通过诱导circActa2形成在转录后水平调节α-actin表达。circActa2是我们在VSMC中发现的第一个环状RNA，但尚不清楚NRG-1-ICD和circActa2是否也在转录水平调节α-actin表达。本项目研究NRG-1-ICD是否通过与KLF4和/或辅激活因子相互作用、以及circActa2是否通过与RNA Pol II或其他RNA结合蛋白相互作用而在转录水平调节α-actin表达，阐明NRG-1-ICD在转录和转录后对α-actin表达进行协同调节的分子机制及其与血管重构的关系，提出血管稳态调节及失衡的新机制。

血管平滑肌细胞（VSMC）位于血管壁中层，通过改变血管管径和张力而调节血压和血液分布。由α-actin组成的VSMC细胞骨架既是血管收缩的结构基础，又是VSMC增殖、迁移和收缩等生理功能和血管稳态所必需的。α-actin表达的微细变化即可对血管功能产生深远的影响，甚至引起血管疾病。因此，研究α-actin基因表达的调节机制对揭示血管病理性重构的分子基础及心血管疾病防治具有非常重要的意义。本项目研究发现：（1）KLF4、NRG-1-ICD、SRF及其辅激活因子myocardin协同调节α-actin基因表达；NRG-1-ICD介导形成的circACTA2作为一种多功能circRNA, 在α-actin基因表达和VSMC稳态维持中发挥必不可少的作用。（2）circACTA2通过与NF-κB p50亚单位相互作用抑制NLRP3炎症小体激活介导的VSMC炎症反应；同时，circACTA2抑制ILF3与CDK4 mRNA结合，调节VSMC衰老过程。（3）KLF4诱导形成的circCTDP1通过与eEF1A2相互作用在翻译水平上促进PFKFB3表达，进而驱动VSMC糖酵解及表型转换， 导致血管新生内膜形成。（4）KLF4负性调节NMHC IIA表达，KLF4表达下调解除其对NMHC IIA表达的阻抑，增加NMHC IIA表达水平，通过维持VSMC分化状态而抑制VSMC迁移及其与单核细胞黏附。（5）KLF5通过激活eIF5a表达而调节线粒体动力学和mtROS 形成，KLF5缺失通过下调eIF5a表达导致线粒体分裂。（6）KLF5通过HSP90/STUB1-Bmal1调节途径下调VSMC标志基因α-actin和SM22α表达，促进VSMC增殖、迁移及血管重构。本研究成果为防治以血管重构为特征的心血管疾病提供了新的靶点。