A MECHANISM FOR CORTICAL BONE STEM CELL-DERIVED EXOSOMES’ THERAPEUTIC EFFECT ON POST-MYOCARDIAL INFARCTION REPERFUSION INJURY AND CARDIAC REMODELING

Abstract

Rationale: Heart failure is the one of the leading causes of death in the United States. Myocardial infarction (MI) is followed by cardiac remodeling involving extensive fibrosis and which can ultimately progress into heart failure. Previous studies have shown both that both post-MI and post-ischemia reperfusion (I/R), there is a reduction in scar size and improved cardiac function as a result of administration of cortical bone stem cell treatment. Objectives: We investigated the mechanism through which CBSC-derived exosomes altered wound healing and reduced scar formation through in vitro experimentation and in an in vivo post-I/R study in mice. The effects of CBSCs and CBSC-derived exosomes on cardiac fibroblasts was determined. The aim was to broaden our understanding of the mechanism by which CBSCs exert their anti-fibrotic effects. Methods and Results: We investigated the effects of mouse CBSCs (mCBSC), human CBSCs (hCBSC), mCBSC-derived exosomes and hCBSC-derived exosomes on murine embryonic fibroblast (MEF) migration. Treatment with both mouse and human CBSC-conditioned media (CBSC-CM) which contains exosomes caused a decrease in fibroblast migration. Exosome depletion from the CBSC-CM enhanced the reduction in fibroblast migration, implying exosome contents are involved in fibroblast migration. Treatment of fibroblasts with mCBSC-CM and mCBSC-derived exosomes showed a reduction in fibroblast-associated genes matrix metalloproteinase 9 (MMP9) and Collagen 3A1 (Col3A1), as evidenced by qPCR analysis. Next, to examine if exosomes decrease fibrotic activation, adult rat ventricular fibroblasts (ARVFs) and adult human cardiac fibroblasts (NHCFs) were treated with TGFβ to activate fibrotic signaling before treatment with mCBSC- and hCBSC-derived exosomes. mCBSC-derived exosomes cause a 40% decrease in myofibroblast activation in ARVFs compared to TGFβ activated controls. hCBSC-derived exosomes caused a 100-fold decrease in human fibroblast activation, implying an even stronger intraspecies anti-fibrotic effect. To further understand the signaling mechanisms regulating the protective decrease in fibrosis, we performed RNA sequencing on the NHCFs after hCBSC-derived exosome treatment. The group treated with both TGFβ and exosomes showed a decrease in micro RNA (miRNA) and small nucleolar RNA (snoRNA), known to be involved with ribosome stability. A 24hr I/R study on 13wk old C57B/L6NJ mice showed that injection of mCBSCs and mCBSC-derived exosomes into the ischemic region of an infarct had a protective effect against I/R injury. Conclusions: In vitro findings show that wound healing induced by CBSC-derived exosome treatment involves the reduction of myofibroblast activation. RNA-Seq analysis identified that CBSC-derived exosomes inhibit with fibroblast activation by decreasing the expression of ribosome-stabilizing snoRNA, reducing protein translation and inflammatory signaling in activated cardiac fibroblasts, culminating in a decrease of myofibroblast activation. Additionally, in vivo, we found that mCBSC-derived exosomes recapitulate the effects of CBSC treatment, indicating exosomes are partly responsible for CBSC therapeutic effects in the post-I/R heart. Both mCBSCs and mCBSC-derived exosome treatment led to lower infarct size at 24 hours post-IR.