Unraveling the Molecular Landscape of Myocardial Fibrosis in Myocardial Infarction using Single-Cell Multi-Omics

Introduction: Myocardial infarction (MI), arising from thrombosis or vascular occlusion, stands as the predominant cause of morbidity and mortality among all cardiovascular diseases. Following MI, the swift formation of myocardial fibrosis within the infarct zone is a pivotal mechanism for preventing cardiac rupture. Conversely, the development of myocardial fibrosis in the border zone is associated with harmful effects, including cardiac arrhythmias and chronic remodeling. Despite its significance, our understanding of fibrosis formation in the border zone remains limited. The objective of this study is to investigate the differences in fibroblasts (Fbs) between the infarct zone and border zone in a myocardial infarction mouse model by single-cell multi-omics.

Methods and results: Using a single-cell multi-omics strategy including spatial transcriptome analysis (SPT), single-nucleus RNA sequencing (snRNA-seq), and single-nucleus assay for transposase-accessible chromatin sequencing (snATAC-seq) on heart samples collected at different time points (3 days, 7 days, and 14 days) post-LAD ligation, as well as sham group. Our study showed significant differences in gene expression between the border zone and infarct zone after MI. We provided elucidation of upregulated genes in the border zone, including cell-specific markers for cardiomyocytes (Xirp2, Sorbs2, Des, Flnc, Nrap, Synpol2, Enah) and Fbs (Mfap5). Utilizing the distribution pattern of Mfap5, we identified a subpopulation of Fb_Mfap5 located in the border zone. GO enrichment analysis highlighted that Fb_Mfap5 were enriched in terms associated with the extracellular matrix containing collagen, mitochondrial matrix, and Golgi membrane. Col1a1 is considered a marker for the infarct zone, leading to the definition of a subpopulation of Fb_Col1a1 as infarct zone Fbs. GO enrichment for this subpopulation primarily involved terms related to contractile fiber, cell leading edge, and cell-matrix junction. Next, we applied CellChat bioinformatics analysis tool to understand the cell to cell communication. Comparing with sham control group, CellChat analysis indicated significant differences in the communication network architecture and signal strength between Fbs and cardiomyocytes at different time points (3 days, 7 days) in MI group. Three days after MI, The number of overall communications in Fb_Mfap5 exceeded those in Fb_Col1a1. By the 7th day after MI, Fb_Mfap5 maintained a stable overall signals number, while Fb_Col1a1 exhibited a further decrease compared to the 3^rd day. Additionally, distinctive signaling transmission patterns between the two subpopulations were observed. Specifically, on the 3rd day, outgoing Fibronectin (FN1) signals were observed from Fb_Col1a1, while incoming FN1 signals were directed towards both Fb_Mfap5 and Fb_Col1a1. Post the 7th day, Fb_Col1a1continued to transmit outgoing FN1 signals; however, it shifted to Fb_Mfap5 receiving incoming FN1 signals.

Conclusion: Taken together, these findings provide a more in-depth understanding of the complex dynamic changes in gene expression and communication networks between border zone and infarct zone cells after MI. This offers a perspective on pinpointing potential therapeutic targets that specifically hinder the development of fibrosis in the border zone, thereby averting cardiac arrhythmias and chronic remodeling.