CD8+ T Cells Drive Plaque Smooth Muscle Cell Dedifferentiation in Experimental Atherosclerosis.

Background: Atherosclerosis is driven by the infiltration of the arterial intima by diverse immune cells and smooth muscle cells (SMCs). CD8⁺ T cells promote lesion growth during atherosclerotic lesion development, but their role in advanced atherosclerosis is less clear. Here, we studied the role of CD8⁺ T cells and their effects on SMCs in established atherosclerosis.

Methods: CD8⁺ T cells were depleted in (SMC reporter) low-density lipoprotein receptor-deficient (Ldlr^-/-) mice with established atherosclerotic lesions. Atherosclerotic lesion formation was examined, and single-cell RNA sequencing of aortic SMCs and their progeny was performed. Additionally, coculture experiments with primary aortic SMCs and CD8⁺ T cells were conducted.

Results: Although we could not detect differences in atherosclerotic lesion size, an increased plaque SMC content was noted in mice after CD8⁺ T-cell depletion. Single-cell RNA sequencing of aortic lineage-traced SMCs revealed contractile SMCs and a modulated SMC cluster, expressing macrophage- and osteoblast-related genes. CD8⁺ T-cell depletion was associated with an increased contractile but decreased macrophage and osteoblast-like gene signature in this modulated aortic SMC cluster. Conversely, exposure of isolated aortic SMCs to activated CD8⁺ T cells decreased the expression of genes indicative of a contractile SMC phenotype and induced a macrophage and osteoblast-like cell state. Notably, CD8⁺ T cells triggered calcium deposits in SMCs under osteogenic conditions. Mechanistically, we identified transcription factors highly expressed in modulated SMCs, including Runx1, to be induced by CD8⁺ T cells in cultured SMCs in an IFNγ (interferon-γ)-dependent manner.

Conclusions: We here uncovered CD8⁺ T cells to control the SMC phenotype in atherosclerosis. CD8⁺ T cells promote SMC dedifferentiation and drive SMCs to adopt features of macrophage-like and osteoblast-like, procalcifying cell phenotypes. Given the critical role of SMCs in atherosclerotic plaque stability, CD8⁺ T cells could thus be explored as therapeutic target cells during lesion progression.