A Chinese study has shown that small extracellular vesicles (sEVs) produced by microRNA (miRNA)-overexpressing mesenchymal stem cells (MSCs) improved cardiac function, reduced infarct size and promoted angiogenesis without arrhythmia in nonhuman primate (NHP) models of myocardial infarction (MI).

Led by Xinyang Hu and Jian'an Wang, professors in the Department of Cardiology at Second Affiliated Hospital, College of Medicine at Zhejiang University in Hangzhou, the study underlines the key role of sEVs containing miRNA in cardiac angiogenesis and shows that they may represent a therapeutic approach for augmenting post-MI cardiac repair.

"To our knowledge, this is the first study to demonstrate that sEVs harboring miRNA overexpression may be a novel therapeutic approach for post-MI cardiac repair in a NHP model," said study corresponding author Yinchuan Xu, a researcher in Xu's laboratory.

Enhanced angiogenesis immediately after MI has been proposed to prevent myocyte death and adverse cardiac remodeling, with therapeutic angiogenesis being considered a major cardiac repair option to prevent post-MI heart failure.

sEVs are potential major mediators of stem cell-induced angiogenesis, as they can carry multiple payloads including proteins, mRNAs and miRs, which can transfer into recipient cells and trigger downstream signaling.

Previous studies have shown that miR-126-3p from CD34+ stem cell-derived sEVs as well as miR-515-5p and miR-525-3p from cardiac progenitor cell-derived sEVs can promote cardiac angiogenesis, although the mechanisms by which sEVs mediate angiogenesis remain mostly unresolved.

The inclusion of miRNA with cardioprotective properties within sEVs to enhance angiogenic activity may therefore improve recovery of post-MI cardiac function, but this awaits thorough investigation in large animal models.

Several studies have reported using large animal models, wherein vesicles secreted by human induced pluripotent stem cell (hiPSC)-derived cardiac cells were used to evaluate their therapeutic effects, showing increased post-MI angiogenic response, decreased infarct size, and restored cardiac function.

One study has shown that delivery of exosomes secreted by hiPSC-derived cardiac cells did not increase arrhythmogenic complications, but did not investigate the miR-mediated mechanisms for sEV therapy.

In their new study reported in the March 10, 2021, edition of Science Translational Medicine, the Zhejiang University researchers assessed the safety and efficacy of miRNA-engineered sEV transplantation in animals.

This resulted in improved cardiac function, enhanced vascular density and smaller infarct size in mice treated with sEVs from hypoxia-preconditioned MSCs (HP-sEVs) than in mice treated with normoxia-preconditioned MSCs (N-sEVs).

"We observed significantly improved left ventricular ejection fraction (LVEF), enhanced vascular density and reduced infarct size in the HP-sEV-treated group than in N-sEV-treated animals," said Xu.

"These observations indicate that the benefits associated with HP-sEV transplantation may be attributed to the contents of the HP-sEVs and that the delivery of modified sEVs may represent an effective approach for cardiac repair post-MI."

Moreover, miRNA profiling revealed a higher abundance of miR-486-5p in HP-sEVs than in N-sEVs, miR-486-5p inactivation abolished the benefit of HP-sEV treatment, whereas miR-486-5p upregulation enhanced the benefit of N-sEV treatment.

"miRs are important paracrine factors within sEVs and, using unbiased miRNA profiling, we found that miR-486-5p was the most significantly altered miRNA between HP-sEV and N-sEV," Xu told BioWorld Science.

The abundance of matrix metalloproteinase 19 (MMP19) was also shown to be lower in HP-sEV- than N-sEV-treated mouse hearts, but was enriched in cardiac fibroblasts (CFs), while Mmp19 was identified as a target gene of miR-486-5p.

"RNA sequencing of cardiac tissues from HP-sEV- and N-sEV-treated animals and luciferase assays further showed that Mmp19 was one of the target genes of miR-486-5p," noted Xu.

"Together, these observations indicate that miR-486-5p/MMP19 signaling is the critical mechanism contributing to HP-sEV-mediated cardiac protection after MI."

Conditioned medium from CFs overexpressing miR-486-5p or silenced MMP19 was shown to increase angiogenic activity of endothelial cells, but medium from CFs that simultaneously overexpressed Mmp19 and miR-486-5p canceled this effect.

"We observed a significantly enhanced angiogenic activity of endothelial cells treated with conditioned medium from CFs with either miR-486-5p overexpressing or Mmp19 inhibition by an in vitro tube formation assay," said Xu.

"Together, these observations demonstrate that Mmp19 in CFs is essential for the proangiogenic effects mediated by miR-486-5p," he added.

Mmp19 silencing in CFs was then demonstrated to reduce cleavage of extracellular vascular endothelial growth factor (VEGF).

Furthermore, miR-486-5p-overexpressing N-sEV treatment was shown to promote angiogenesis and cardiac recovery, without increasing arrhythmia complications in an NHP MI model.

"Magnetic resonance imaging (MRI) revealed statistically significant improvements in the LVEF, smaller end-systolic volume (ESV) and reduced infarct size 1 month after treatment," said Xu.

"We have demonstrated that engineered sEVs containing miR-486-5p enhance angiogenic processes and improve cardiac function without increasing arrhythmia occurrence," he noted.

"Our study highlights the key role of bioengineered sEVs containing miR-486-5p in cardiac angiogenesis and may serve as a therapeutic approach for augmenting cardiac repair."

Looking ahead, he said, "we plan to investigate further the detailed molecular mechanisms of sEV delivery for cardiac repair and promote the clinical application of exosome therapy for MI treatment."