Single-nucleus profiling of human coronary and internal mammary arteries

Abstract Background The internal mammary artery (LIMA) demonstrates an extraordinary resistance to atherosclerosis compared with coronary arteries (CA), even though both vessels are exposed to comparable systemic risk factors. The biological basis for this differential susceptibility remains largely unresolved. Purpose To characterize molecular and cellular features that may explain the distinct atheroresistant properties of the LIMA. Methods We generated a single-nucleus RNA-sequencing (snRNA-seq) dataset from non-atherosclerotic coronary artery (CA) tissue of heart transplant recipients with dilated (DCM) or ischemic cardiomyopathy (ICM), as well as from left internal mammary artery (LIMA) samples collected during bypass surgery. After unbiased clustering and annotation of nuclei using canonical markers, we compared cellular compositions and transcriptional states across groups. Intercellular communication was inferred from ligand-receptor co-expression patterns. Key observations were validated by tissue staining, and cultured endothelial cells (HMECs) were stimulated to probe context-dependent gene regulation. Results Across all samples, ten major cell types were identified, including smooth muscle cells (SMCs), endothelial cells (ECs), fibroblasts, immune cells, glial cells, and adipocytes. Although all cell types were represented in each group, immune and adipocyte populations were markedly reduced in LIMA relative to CA (e.g., lymphoid cells: 1.3% DCM, 2.1% ICM, 0.2% LIMA). SMCs dominated all tissues (≈64% DCM, ≈71% ICM, ≈70% LIMA), yet ligand–receptor analyses highlighted group-specific signalling. Interactions such as IGF1-IGF1R, BMP6-BMPR1A/BMPR2, and CD46-JAG1 appeared in ICM but were not detected in LIMA. SMC subclustering revealed five transcriptionally distinct SMC subsets, with one cluster enriched in CA and another prevailing in LIMA, mirroring known vessel-specific SMC diversity reported for other arterial SMCs. EC proportions did not differ significantly across groups (DCM 9%, ICM 6%, LIMA 4%). Given the reduced immune cell infiltration in LIMA, we analysed EC-immune communication in detail. CD6-ALCAM interactions were unique to ICM, consistent with elevated ALCAM levels in ICM-derived ECs. CD99-based interactions were absent in LIMA, and LIMA-ECs expressed less CD99 – confirmed by histology. In vitro, HMECs increased both ALCAM and CD99 expression upon pro-inflammatory stimulation, whereas oxidized LDL selectively induced CD99 but not ALCAM, supporting stimulus-specific regulation. Conclusion CA and LIMA differ substantially in cellular composition and intercellular signalling networks. The lack of pro-inflammatory EC-immune communication pathways in the LIMA may contribute to its well-recognized resistance to atherosclerosis. These insights uncover vessel-specific molecular programs that could guide future strategies for vascular protection and durable graft performance in CAD.