Exosomes as key players in the paracrine cardioprotective effects of mesenchymal stem cells after acute myocardial infarction

Author(s)

Nathalia Corrêa de Almeida Oliveira

• Document type: Doctoral Thesis
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Faculdade de Medicina (FM/SBD)
• Defense date: 2019-10-09

Examining board members

Jose Eduardo Krieger; Mirian Aparecida Boim; Francisco Rafael Martins Laurindo; Marinilce Fagundes dos Santos

• Advisor: Jose Eduardo Krieger

Abstract

The inappropriate blood supply to the heart tissue and cardiomyocyte death are important events in cardiac deterioration post-myocardial infarction (AMI), which combined with cardiac myocytes regeneration inability, contribute to the high morbidity and mortality statistics associated with cardiovascular diseases worldwide. Post-myocardial infarction transplantation of adult adipose tissue stromal cells (ASC) results in structural and functional improvements due to decreased apoptosis in cardiomyocytes, increased vascular density and reduced/ modified a fibrotic scar. These effects are mediated by a paracrine effect exerted by ASC in the infarcted myocardium. However, the effectors of this response are yet to be elucidated. Thus, we tested the hypothesis that ASC-derived exosomes contribute to the cardioprotective effects of mesenchymal cell transplantation. To do so, we used cardiac target cells under conditions that mimic the ischemic tissue microenvironment and finally validate the results in the whole organism in the experimental rat infarction model. We found that ASC-derived exosomes influence key processes in cardiac repair, such as proliferation of hypoxia-induced neonatal cardiac myocytes (CM), proliferation, and formation of normoxic cardiac microvascular endothelial cell (CMEC) tubes. They also modulated the phenotype of hypoxia-induced cardiac fibroblasts, attenuating their proliferation and differentiation into myofibroblasts, as well as reduced synthesis of type I and III collagens expression. Additionally, ASC-derived exosomes induced the differentiation of bone marrow-derived macrophages and treatment of neonatal cardiac myocytes with the conditioned media of these differentiated macrophages promoted cell cycle progression. Finally, we validated the reparative potential of ASC exosomes in vivo to assess their potential of modulating cardiac repair in post-AMI rats and observed apoptotic inhibition in cardiac myocytes and presence of viable tissue in a thicker scar when compared to sham, suggesting that treatment with exosomes culminated in a less pronounced post-AMI cardiac remodeling. In order to determine the underlying mechanism of the exosome-associated cardioprotective response, a microarray assay of the exosome-extracted miRNAs from ASC was performed followed by an in silico enrichment approach, through which we selected the miRNA families miR-199a, miR-146b, miR-425 e miR196a as possible mediators of exosome cardioprotection to be validated in future. In synthesis, we provided evidence of a modulatory role of exosomes in the proliferation of cardiac and endothelial cells, fibroblast differentiation to myofibroblasts, and macrophage differentiation, key events taking place during cardiac repair and that recapitulate the observed outcomes in response to ASC graft post-AMI. In vivo data corroborate the in vitro findings and support the hypothesis that exosomes are cardioprotective effectors of the ASC paracrine signaling (AU)

• FAPESP's process: 17/17296-0 - Mesenchymal stem cells-derived exosomes as paracrine effectors for cardioprotection after Acute Myocardial Infarction
• Grantee: Nathalia Corrêa de Almeida Oliveira
• Support Opportunities: Scholarships in Brazil - Doctorate