Dysfunction and Pathological Origins of Lymphatic Endothelial Cells in Atherosclerosis Revealed by Single-Cell Transcriptomics

<b>Background:</b> Atherosclerosis, a leading cause of cardiovascular disease, involves complex interactions between vascular and immune cells. The role of lymphatic endothelial cells (LECs) in this process remains incompletely characterized, limiting our understanding of disease mechanisms. This study aimed to delineate the phenotypic and functional dynamics of LECs during atherosclerosis progression. <b>Methods:</b> We performed single-cell RNA sequencing on aortic cells from ApoE-/- mice on a high-fat diet at baseline, 8 weeks (early disease), and 16 weeks (late disease). Bioinformatic analyses, including clustering, differential expression, trajectory inference, and cell-cell communication analysis, were applied to characterize LEC subpopulations and their transcriptional reprogramming. <b>Results:</b> Our analysis identified two LEC subpopulations that exhibited a biphasic numerical response: expansion at the early stage followed by a decline by the late stage. Early-disease LECs displayed altered immunomodulatory capacity, with features of reduced T cell tolerance and enhanced activation via IL-7/IL-7R signaling, coupled with a downregulation of key lipid-handling genes (<i>Ldlr</i>, <i>Abca1</i>). Trajectory analysis suggested multiple cellular origins, including a conventional but delayed differentiation path from vascular endothelial cells and an atherosclerosis-specific transdifferentiation path from fibroblasts observed only in early disease. <b>Conclusions:</b> Our findings indicate that LECs undergo substantial phenotypic and functional alterations during atherosclerosis. The maladaptive differentiation and acquired dysfunction in lipid transport and immune regulation may contribute to disease progression. This study provides a foundational transcriptional atlas for understanding lymphatic involvement in vascular disease and highlights potential contexts for therapeutic modulation.