After myocardial infarction (MI), the subsequent loss of cardiomyocytes leads to complex remodelling processes and fibrotic scar formation. The epicardium undergoes epicardial to mesenchymal transition (EMT) after MI, expands near the injured area and affects ECM deposition, neovascularization and immune responses. Transcription factor Sox9 is a critical embryonic developmental factor, which plays a regulatory role in EMT, cardiac fibrosis and inflammation. Following MI, Sox9 is upregulated in the epicardium, but its impact on EMT and myocardial scar development are not well understood. Although the initial infarct size can be reduced by immediate interventions to reopen the occluded coronary vessel after MI, current therapies do not target ECM deposition, scar expansion and inflammation. Whether epicardial Sox9 is suitable as therapeutic target to modulate scar remodelling after MI is currently unknown.
To investigate the role of Sox9 after MI we generated tamoxifen-inducible epicardial-specific Sox9 knockout mice (Sox9-EpiCre). Littermate Sox9fl/fl mice were used as controls. MI was induced via ultrasound-guided coagulation of the left anterior descending artery (LAD) and confirmed by absence of distal blood flow, akinesia and ECG changes. Sham mice were subjected to the same procedure without occlusion of the LAD. Echocardiography and histological analyses were conducted at multiple time points after MI and sham surgery. RNA bulk and single cell sequencing were performed from scar tissue of infarcted knockout and control mice at early and late timepoints after MI. As therapeutic approach, C57Bl/6N mice were treated with intra-pericardial adeno-associated virus 9 (AAV9) shRNA to inhibit epicardial Sox9 expression following MI.
Echocardiography showed sex-specific differences in scar and ventricular remodelling. In particular, male mice benefited more from the epicardial Sox9 knockout, as evident from the improvement of several functional cardiac parameters, e.g. global longitudinal strain and ejection fraction. Scar size and remote fibrosis were reduced due to epicardial Sox9 deletion mainly in male mice. Bulk RNA sequencing experiments from scar tissue showed significantly different transcriptomes between male and female mice as well as significant alterations following epicardial Sox9 deletion. Single cell transcriptomics revealed strong changes in several cell population in male mice, including immune cells, fibroblast and epicardial cells. Improved cardiac functions and ventricular remodelling were also observed in male mice receiving AAV9-shSox9 treatment.
In conclusion, our findings reveal that epicardial Sox9 plays an important role in post-infarction remodelling. Epicardial-specific deletion of Sox9 leads to improved cardiac function, reduced scar formation, and attenuated fibrosis predominantly in male mice. Ongoing analyses aim to elucidate the molecular mechanisms underlying epicardial Sox9-mediated regulation, with a focus on its influence on cell-specific signalling pathways, extracellular matrix formation and immune cell interaction.
