Transcriptome analysis revealed a two-step transformation of vascular smooth muscle cells to macrophage-like cells

It is known that vascular smooth muscle cells (VSMCs) represent a major part of the atherosclerotic plaque. In addition to forming fibrous cap cells that stabilize the atherosclerotic plaque, VSMCs trans-differentiate into macrophage-like cells that exacerbate the necrotic core. Here, we aim to address the question of how VSMCs are selected to perform distinct functions under a similar environmental stress, and how much cellular reprogramming happens during VSMC-to-macrophage-like transformation.Single-cell RNA-Sequencing (scRNA-Seq) analysis, in vitro transcriptional and metabolic studies, and pathological sample examinations were performed to decipher the cellular reprogramming during VSMC-to-macrophage-like cell transformation.By analyzing scRNA-Seq data of the atherosclerotic plaque, VSMC-derived macrophage-like cells were found to undergo a series promotion of lysosome-related and inflammation-related genes. In vitro transcriptional studies further confirmed that suppression of NOTCH signaling is the prerequisite for VSMCs to undergo sufficient genetic and metabolic reprogramming to a macrophage-like state and perform macrophage-like functions, while high-lipid treatment alone only promote VSMCs into a pro-inflammatory state without gain of lysosome-related functions. Mechanistic studies showed that NOTCH inhibition shifted VSMCs into a de-differentiated state by suppressing the developmental program, including key factor Myocd, leading to complete transformation into macrophage-like cells.NOTCH, a signaling mediated by consistent cell contacts, prevents the complete transformation of VSMCs into macrophage-like cells under high lipid stress. We hope our study could offer some insights into the retarded VSMC-to-macrophage-like transformation observed in previous in vitro studies and clarify the cellular reprogramming underlying the VSMC-to-macrophage-like cell transformation.