Abstract 233: CHI3L1 and Its Role in Vascular Smooth Muscle Cell Proliferation and Migration in Advanced Atherosclerosis

Abstract

Objectives: Stroke is one of the leading causes for death and disability worldwide. The underlying pathomechanism is most likely a thrombotic event caused by acute rupture or erosion of an unstable plaque in the carotid artery. Vascular smooth muscle cells (VSMCs) play an important role in both, development and rupture of atherosclerotic plaques. Thus, efforts have been devoted determining the characteristics of VSMCs in atherosclerotic plaques to develop novel diagnostic and therapeutic strategies to prevent unstable plaque rupture. Methods: Laser capture microdissections of the fibrous cap of ruptured plaques in symptomatic patients (n=20) and stable plaques in asymptomatic patients (n=20) were used to perform a GeneChip 2.0 Human Transcriptome Array. CHI3L1 could be detected as the most significantly upregulated transcript in ruptured plaques. Following, immunohistochemistry was performed to compare distribution of CHI3L1-positive cells, VSMCs and macrophages in ruptured and stable plaques. In-vitro MTT-assay, Boyden Chamber assay and TUNEL assay were performed to investigate the role of this gene in human VSMC proliferation, migration and apoptosis. Results: The MTT-assay revealed that silencing of CHI3L1 lead to a decreased proliferation of human VSMCs. Further, migration was reduced in absence of CHI3L1. Immunohistochemistry of human carotid plaques indicated that in stable plaques mainly macrophages were CHI3L1-postive, whereas in unstable plaques both macrophages and VSMCs were CHI3L1-positive. In-vitro knockdown of CHI3L1 in cultured human VSMCs significantly increased CD68 expression, suggesting a potential role in transformation of VSMCs to macrophages. CHI3L1/CD68-positive cells (putative macrophages) in unstable plaques appeared hyperproliferative (Ki-67 positive). Conclusion: In summary, CHI3L1 plays a role in VSMC-regulation in atherosclerotic plaques. Expression levels in unstable plaques are increased. Further, it seems to induce proliferation as well as migration in VSMCs. Results of CHI3L1-induced CD68 expression indicate a potential role in VSMC-macrophage transformation. <!--EndFragment-->