Trimethylamine-N-oxide affects cell type-specific pathways and networks in mouse aorta to promote atherosclerotic plaque vulnerability.

Background: Trimethylamine-N-oxide (TMAO) has been significantly linked to atherosclerosis via several mechanisms, but its direct effect on the atherosclerosis-prone vasculature remains unclear. The objective of this study was to characterize the cell type-dependent and independent effects of TMAO on key vascular cell types involved in atherosclerosis progression .

Methods: We performed single cell RNA-sequencing (scRNAseq) on aortic athero-prone regions of female mice fed control Chow, high-cholesterol (HC), or HC+TMAO diets for three months to identify which aortic cell types, differentially expressed genes, and biological pathways are affected by TMAO. We also modeled cell-cell communications and intracellular gene regulatory networks to identify gene networks perturbed by TMAO feeding. Key genes and pathways were validated using primary human smooth muscle cells exposed to TMAO. Changes in the thickness of lesional fibrous caps in response to TMAO in female mice fed HC+TMAO versus HC diets were measured using transgelin immunostaining.

Results: Our scRNAseq analysis revealed that TMAO supplementation upregulated apoptotic gene signatures and downregulated extracellular matrix (ECM) organization and collagen formation genes in a subset of atherosclerosis-specific modulated vascular smooth muscle cells (vSMCs). We also identified "degradation of the ECM" as a top pathway for SMC-derived macrophage DEGs in response to TMAO. Network analyses support that macrophage-vSMC communication mediates ECM remodeling. Using human smooth muscle cells exposed to TMAO , we confirmed the direct effect of TMAO on regulating collagen and apoptotic genes. In agreement with the changes in these pathways that affect plaque stability, we observed a significant decrease in fibrous cap thickness in mice supplemented with TMAO.

Conclusions: Our results reveal the effects of TMAO on vSMCs to promote apoptosis and decrease ECM formation, and on macrophage-mediated ECM degradation in atherosclerotic lesions to in concert enhance plaque instability.

Highlights: scRNAseq of the aortic athero-prone regions in female mice supplemented with TMAO in the diet revealed the effect of TMAO across cell types, particularly in SMC-derived macrophages and atheroprotective modulated vSMCs. TMAO increases apoptotic gene signatures and reduces ECM organization and collagen formation gene signatures in modulated vSMCs , and exposure studies support a direct effect of TMAO on these genes. Modulated vSMC-specific gene regulatory networks enriched for apoptotic genes and ECM organization genes were organized by intracellular regulators such as Ccl19 and Tnn and extracellular regulators such as Mmp9 and Spp1 from macrophages. Fibrous cap thickness, a marker of atherosclerotic plaque stability, was significantly reduced in female mice fed HC+TMAO versus HC diets for five months.