Cardiac Fibrosis Following Myocardial Ischemia is Mitigated by Mesenchymal Stem Cell Exosomes

Abstract

Objective Myocardial infarction is the leading cause of mortality worldwide. Following an ischemic event there is activation of macrophages and fibroblasts leading to scar formation. It is critical to limit the pro-fibrotic remodeling and activate the reparative, regenerative remodeling phase to limit cardiac diastolic dysfunction. We studied the effect of mesenchymal stem cell (MSC) exosomes on the extent of cardiac fibrosis in acute and chronic ischemia models. Methods Acute or chronic ischemia was induced in 8-10 week old healthy male wild-type mice by ligating the left coronary artery (LCA) for 1 hour or 7 days, respt. Mice were pretreated with MSC exosomes or saline as control. At 3 hrs (acute ischemia) or 7 days (chronic ischemia) after LCA ligation, the animals were euthanized and hearts were isolated. Hearts were sectioned into infarct and adjacent non-infarct areas and used for further studies. Results Following acute ischemia, there was activation of inflammatory signals, more in the peri-infarct than in the infarct area, in the saline treated mice. IL1b, LOX-1, PCSK9, and NFkB were overexpressed in the infarct areas. MSC exosome treatment reduced expression of IL1b, LOX-1, PCSK9, and NFkB in infarct areas of the LCA ligated mice hearts. At the same time, expression of cardiac remodeling signals (vimentin, collagens-1 and -3, fibronectin, MMP-2 and TIMP-2), was more in the infarct area. MSC exosomes treatment suppressed inflammatory signals during acute as well as chronic ischemia. Following chronic ischemia, we observed increased interstitial and peri-vascular fibrosis in saline treated mice hearts, which was suppressed by MSC exosome treatment. Proteomic analysis of the saline- and exosome-treated LCA ligated hearts revealed differentially expressed proteins and upstream regulators of cellular function. Comparison of biological processes of exosome-treated vs saline-treated LCA ligated hearts showed suppression of fibrosis and interstitial fibrosis along with fibrogenesis. There exist differential regulation of transcription factors that govern fibrotic processes. There was an intense expression of IL-1b and activation of pro-fibrotic signals in the saline-treated ischemia hearts and their suppression in MSC exosome-treated hearts. The results of proteomic studies were concordant with the limitation of fibrosis and inflammatory modulators in the exosome-treated hearts. To our knowledge, this is the first report on the early molecular events deciphering the molecular and proteomics events to explain MSC exosome-mediated suppression of scar formation in the ischemic mouse hearts. Conclusions MSC exosome treatment significantly reduced interstitial fibrosis in chronic ischemic hearts suggesting that they promote pro-regenerative cardiac ECM remodeling, in both infarct and peri-infarct areas by suppressing fibronectin secretion and by modulating collagen secretion to reduce fibrotic scar formation through altered cellular signaling pathways.