Exosomes Derived from Human Umbilical Cord Mesenchymal Stem Cells Promote Fibroblast-to-Myofibroblast Differentiation in Inflammatory Environments and Benefit Cardioprotective Effects

Cardioprotective effects of exosomes derived from human umbilical cord mesenchymal stem cells (hucMSC-exosomes) postmyocardial infarction (post-MI) have been reported in our previous study. It is known that fibroblasts are pro-inflammatory phenotypes, while myofibroblasts are anti-inflammatory phenotypes. This study aimed to investigate whether hucMSC-exosomes promoted cardiac fibroblast-to-myofibroblast differentiation in inflammatory environments and protected cardiomyocytes. Rats were performed by permanent ligation of the left anterior descending coronary artery and underwent intramyocardial injection of hucMSC-exosomes or phosphate-buffered saline (PBS) in surgery. Fibroblasts were stimulated by lipopolysaccharide (LPS) to create inflammatory environments in vitro. Western blot and immunohistochemical and immunofluorescence staining for alpha-smooth muscle actin were used to demonstrate fibroblast-to-myofibroblast differentiation. Transwell migration assay and CCK-8 assay were used to evaluate migration and proliferation of fibroblasts. Reverse transcription-polymerase chain reaction, western blot, and immunohistochemical staining were used to detect expressions of inflammatory factors. To investigate cardioprotective effects, cardiomyocytes were treated with supernatant derived from fibroblasts pretreated with LPS or LPS plus hucMSC-exosomes in hypoxic environments. Cardiomyocyte apoptosis was determined using TUNEL assay and western blot. Results indicated that hucMSC-exosomes increased the density of myofibroblasts in infarct areas during inflammatory phases post-MI, promoted fibroblast-to-myofibroblast differentiation in inflammatory environments, and attenuated inflammatory responses in vitro and in vivo. Culture medium derived from fibroblasts pretreated with LPS plus hucMSC-exosomes reduced cardiomyocyte apoptosis. In vivo, apoptotic cells in acute myocardial infarction (AMI)+exosomes groups were also less than AMI+PBS groups. In conclusion, hucMSC-exosomes can promote fibroblast-to-myofibroblast differentiation in inflammatory environments, then protecting cardiomyocytes.