Chitinase 3 like 1 is a regulator of smooth muscle cell physiology and atherosclerotic lesion stability

AIMS

Atherosclerotic cerebrovascular disease underlies the majority of ischaemic strokes and is a major cause of death and disability. While plaque burden is a predictor of adverse outcomes, plaque vulnerability is increasingly recognized as a driver of lesion rupture and risk for clinical events. Defining the molecular regulators of carotid instability could inform the development of new biomarkers and/or translational targets for at-risk individuals.

METHODS AND RESULTS

Using two independent human endarterectomy biobanks, we found that the understudied glycoprotein, chitinase 3 like 1 (CHI3L1), is up-regulated in patients with carotid disease compared to healthy controls. Further, CHI3L1 levels were found to stratify individuals based on symptomatology and histopathological evidence of an unstable fibrous cap. Gain- and loss-of-function studies in cultured human carotid artery smooth muscle cells (SMCs) showed that CHI3L1 prevents a number of maladaptive changes in that cell type, including phenotype switching towards a synthetic and hyperproliferative state. Using two murine models of carotid remodelling and lesion vulnerability, we found that knockdown of Chil1 resulted in larger neointimal lesions comprised by de-differentiated SMCs that failed to invest within and stabilize the fibrous cap. Exploratory mechanistic studies identified alterations in potential downstream regulatory genes, including large tumour suppressor kinase 2 (LATS2), which mediates macrophage marker and inflammatory cytokine expression on SMCs, and may explain how CHI3L1 modulates cellular plasticity.

CONCLUSION

CHI3L1 is up-regulated in humans with carotid artery disease and appears to be a strong mediator of plaque vulnerability. Mechanistic studies suggest this change may be a context-dependent adaptive response meant to maintain vascular SMCs in a differentiated state and to prevent rupture of the fibrous cap. Part of this effect may be mediated through downstream suppression of LATS2. Future studies should determine how these changes occur at the molecular level, and whether this gene can be targeted as a novel translational therapy for subjects at risk of stroke.

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

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-->