School of Cardiovascular Medicine and Sciences, King's College London British Heart Foundation Centre of Excellence, Faculty of Life Science and Medicine, King's College London, London, UK.
School of Cardiovascular Medicine and Sciences, King's College London British Heart Foundation Centre of Excellence, Faculty of Life Science and Medicine, King's College London, London, UK; Department of Heart Center, Tianjin Third Central Hospital, Tianjin, P.R. China; Tianjin Key Laboratory of Extracorporeal Life Support for Critical Diseases, Tianjin, P.R. China.
J Biol Chem. 2021 Jan-Jun;296:100541. doi: 10.1016/j.jbc.2021.100541. Epub 2021 Mar 15.
Vascular smooth muscle cells (VSMCs) contribute to the deposition of extracellular matrix proteins (ECMs), including Type IV collagen, in the vessel wall. ECMs coordinate communication among different cell types, but mechanisms underlying this communication remain unclear. Our previous studies have demonstrated that X-box binding protein 1 (XBP1) is activated and contributes to VSMC phenotypic transition in response to vascular injury. In this study, we investigated the participation of XBP1 in the communication between VSMCs and vascular progenitor cells (VPCs). Immunofluorescence and immunohistology staining revealed that Xbp1 gene was essential for type IV collagen alpha 1 (COL4A1) expression during mouse embryonic development and vessel wall ECM deposition and stem cell antigen 1-positive (Sca1)-VPC recruitment in response to vascular injury. The Western blot analysis elucidated an Xbp1 gene dose-dependent effect on COL4A1 expression and that the spliced XBP1 protein (XBP1s) increased protease-mediated COL4A1 degradation as revealed by Zymography. RT-PCR analysis revealed that XBP1s in VSMCs not only upregulated COL4A1/2 transcription but also induced the occurrence of a novel transcript variant, soluble type IV collagen alpha 1 (COL4A1s), in which the front part of exon 4 is joined with the rear part of exon 42. Chromatin-immunoprecipitation, DNA/protein pulldown and in vitro transcription demonstrated that XBP1s binds to exon 4 and exon 42, directing the transcription from exon 4 to exon 42. This leads to transcription complex bypassing the internal sequences, producing a shortened COL4A1s protein that increased Sca1-VPC migration. Taken together, these results suggest that activated VSMCs may recruit Sca1-VPCs via XBP1s-mediated COL4A1s secretion, leading to vascular injury repair or neointima formation.
血管平滑肌细胞（VSMCs）有助于细胞外基质蛋白（ECMs）的沉积，包括 IV 型胶原，在血管壁中。ECMs 协调不同类型细胞之间的通讯，但这种通讯的机制尚不清楚。我们之前的研究表明，X 盒结合蛋白 1（XBP1）被激活，并有助于 VSMC 表型转变，以响应血管损伤。在这项研究中，我们研究了 XBP1 在 VSMC 和血管祖细胞（VPC）之间通讯中的参与。免疫荧光和免疫组织化学染色显示，Xbp1 基因在小鼠胚胎发育过程中以及血管壁 ECM 沉积和血管损伤后干细胞抗原 1 阳性（Sca1）-VPC 募集过程中对 IV 型胶原α 1（COL4A1）的表达至关重要。Western blot 分析阐明了 Xbp1 基因对 COL4A1 表达的剂量依赖性影响，并且剪接的 XBP1 蛋白（XBP1s）通过凝胶电泳显示增加了蛋白酶介导的 COL4A1 降解。RT-PCR 分析显示，VSMCs 中的 XBP1s 不仅上调了 COL4A1/2 的转录，而且还诱导了一种新型转录变体，可溶性 IV 型胶原α 1（COL4A1s）的发生，其中外显子 4 的前部分与外显子 42 的后部分连接。染色质免疫沉淀、DNA/蛋白质拉下和体外转录表明，XBP1s 结合到外显子 4 和外显子 42，指导从外显子 4 到外显子 42 的转录。这导致转录复合物绕过内部序列，产生缩短的 COL4A1s 蛋白，增加 Sca1-VPC 迁移。总之，这些结果表明，激活的 VSMCs 可能通过 XBP1s 介导的 COL4A1s 分泌招募 Sca1-VPCs，导致血管损伤修复或新生内膜形成。
