Reprogramming Factors Make Heart Cells Release Exosomes That Shield Neighbors From Cell Death
STEMIN and YAP5SA modRNAs trigger heart cells to release anti-apoptotic microRNA exosomes, cutting cell death in lab cultures and in infarcted mouse hearts.
Summary
After a heart attack, cardiomyocytes die by apoptosis and are replaced by scar, which can lead to heart failure. Researchers delivered modified RNAs encoding STEMIN (an engineered SRF) and YAP5SA (a constitutively active YAP1) to cardiomyocytes. The two factors opened chromatin at over 100 microRNA genes, raised anti-apoptotic microRNAs such as miR-101-3p, miR-499a-5p and let-7c-5p, and lowered caspase and TP53 expression. Exosomes from treated cells carried these microRNAs and reduced apoptosis markers in staurosporine-challenged human AC16 cells. In a small mouse infarction experiment (7 animals), a single injection lowered cleaved caspase-3 by about 28% at 48 hours. The work is preclinical, small, and cannot separate exosome effects from direct cell effects.
Detailed Summary
Cardiomyocyte apoptosis is a major driver of muscle loss after myocardial infarction and in failing or aging hearts, and even low-level caspase-3 activation can impair function. Because adult hearts regenerate poorly, strategies that both stimulate proliferation and protect surviving cells are attractive. This study asked whether two reprogramming factors previously shown to induce cardiomyocyte cell cycle re-entry, STEMIN and YAP5SA, also engage an anti-apoptotic program that spreads through exosomes.
The team delivered modRNA for STEMIN and YAP5SA (compared with wild-type SRF and YAP1) to rat and human cardiomyocytes. ATAC-seq in rat cells showed increased chromatin accessibility at roughly 105 miRNA loci (about 85% with STEMIN and 93% with YAP5SA), and 46 of these miRNAs are predicted to target caspases and TP53-family genes. RNA-seq in primary adult human cardiomyocytes showed downregulation of apoptosis-related genes (e.g., TP53, CASP3, CASP6, CASP9, BAK1, BAX) and upregulation of miR-101-3p, miR-499a-5p and let-7 family members. qPCR in AC16 cells showed CASP3 falling 67%, 84% and 98% with STEMIN, YAP5SA and the combination. Luciferase reporter assays confirmed that let-7c-5p suppresses TP53 (66%) and RB1 (50%) 3′-UTR activity; other miRNA–target effects were non-significant trends.
Exosomes from modRNA-treated AC16 cells were of expected size, carried distinct proteins and were enriched for miRNAs including let-7c-5p, miR-21-5p and miR-16-5p, about 70% of which contained known exosome-sorting motifs. In staurosporine-challenged cells, STEMIN or YAP5SA modRNAs cut cleaved caspase-3 immunofluorescence by up to 92–98%, and the individual miRNAs by 72–98%. Flow cytometry showed smaller reductions (about 16–37%). Transferring exosomes reduced cleaved caspase-3 by 46–80% in a dose-dependent manner, with TUNEL reductions significant only for YAP5SA exosomes at the higher dose. In mice with coronary ligation, one injection of STEMIN plus YAP5SA modRNA lowered cleaved caspase-3 staining about 28% at 48 hours versus control.
Taken together, the data support a model in which these factors produce a pro-survival, exosome-mediated paracrine signal alongside their pro-proliferative effects, which could be exploited for cardiac repair.
Important caveats apply: the in vivo study used only seven mice, the design cannot distinguish exosome effects from direct cell-autonomous effects, and miRNA targeting was largely predicted rather than proven. Cardiac function, proliferation's contribution to cell loss, and long-term outcomes were not measured, and several authors have commercial interests.
Key Findings
- STEMIN and YAP5SA opened chromatin at over 100 miRNA loci, with 46 miRNAs predicted to target caspases and TP53-family genes.
- In AC16 cells, combined modRNAs cut CASP3 expression 98% and TP53 94%; let-7c-5p directly suppressed TP53 and RB1 3′-UTR reporters.
- Exosomes from treated cells carried anti-apoptotic miRNAs and reduced staurosporine-induced cleaved caspase-3 by up to 80% in recipient cardiomyocytes.
- A single modRNA injection after coronary ligation in mice lowered cleaved caspase-3 staining about 28% at 48 hours (n=7).
- Flow cytometry showed more modest apoptosis reductions (16–38%) than immunofluorescence, so effect sizes depend heavily on the assay.
Methodology
Preclinical study combining ATAC-seq (rat cardiomyocytes), RNA/miRNA-seq (primary human cardiomyocytes), exosome nanoparticle tracking, proteomics and miRNA-seq, luciferase reporter assays, qPCR, immunofluorescence, TUNEL and flow cytometry in AC16 cells with staurosporine challenge. In vivo validation used mouse coronary ligation with intramyocardial modRNA injection and cleaved caspase-3 immunohistochemistry at 48 hours in 7 animals (3 control, 4 treated).
Study Limitations
The mouse experiment was very small and measured only a short-term apoptosis marker, with no cardiac function, scar or survival outcomes, and it cannot separate exosome from cell-autonomous effects. Many miRNA–target interactions are predicted or non-significant in reporter assays, no exosome-inhibition experiments were done, and assay results varied between immunofluorescence and flow cytometry. Several authors hold patent and commercial interests in the technology.
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