Cardiosphere-derived cells (CDCs) have been shown to regenerate infarcted myocardium in patients after myocardial infarction (MI). However, whether the cells of the newly formed myocardium originate from the proliferation of adult cardiomyocytes or from the differentiation of endogenous stem cells remains unknown. Using genetic fate mapping to mark resident myocytes in combination with long-term BrdU pulsing, we investigated the origins of postnatal cardiomyogenesis in the normal, infarcted and cell-treated adult mammalian heart. In the normal mouse heart, cardiomyocyte turnover occurs predominantly through proliferation of resident cardiomyocytes at a rate of ∼1.3–4%/year. After MI, new cardiomyocytes arise from both progenitors as well as pre-existing cardiomyocytes. Transplantation of CDCs upregulates host cardiomyocyte cycling and recruitment of endogenous progenitors, while boosting heart function and increasing viable myocardium. The observed phenomena cannot be explained by cardiomyocyte polyploidization, bi/multinucleation, cell fusion or DNA repair. Thus, CDCs induce myocardial regeneration by differentially upregulating two mechanisms of endogenous cell proliferation.

BACKGROUND Cardiosphere-derived cells (CDCs) mediate therapeutic regeneration in patients after myocardial infarction and are undergoing further clinical testing for cardiomyopathy. The beneficial effects of CDCs are mediated by the secretion of exosomes and possibly other extracellular membrane vesicles (EMV). OBJECTIVES We investigated the effect of cardiosphere-derived EMVs (CSp-EMV) on fibroblasts in vitro and tested whether priming with CSp-EMV could confer salutary properties on fibroblasts in vivo. METHODS CSp-EMVs were isolated from serum-free media conditioned for 3 days by cardiospheres. Dermal fibroblasts were primed with CSp-EMV for 24 h followed by exosomal micro-ribonucleic acid (miRNA) profiling. In vivo, we injected CSp-EMV-primed or -unprimed dermal fibroblasts (or CSp-EMV) in a chronic rat model of myocardial infarction and defined the functional and structural consequences. RESULTS CSp-EMV amplified their own biological signals: exposure of “inert” fibroblasts to CSp-EMV rendered the fibroblasts therapeutic. Intramyocardially-injected CSp-EMV-primed (but not unprimed) fibroblasts increased global pump function and vessel density while reducing scar mass. CSp-EMV priming caused fibroblasts to secrete much higher levels of stromal-cell derived factor 1 and vascular endothelial growth factor, and dramatically changed the microRNA profile of fibroblast-secreted EMVs in vitro. The priming was followed by significant angiogenic and cardioprotective effects. CONCLUSIONS CSp-EMVs alter fibroblast phenotype and secretome in a salutary positive-feedback loop. The phenotypic conversion of inert cells to therapeutically-active cells reveals a novel mechanism for amplification of exosome bioactivity.

SummaryGenetic deficiency of dystrophin leads to disability and premature death in Duchenne muscular dystrophy (DMD), affecting the heart as well as skeletal muscle. Here, we report that clinical-stage cardiac progenitor cells, known as cardiosphere-derived cells (CDCs), improve cardiac and skeletal myopathy in the mdx mouse model of DMD. Injection of CDCs into the hearts of mdx mice augments cardiac function, ambulatory capacity, and survival. Exosomes secreted by human CDCs reproduce the benefits of CDCs in mdx mice and in human induced pluripotent stem cell-derived Duchenne cardiomyocytes. Surprisingly, CDCs and their exosomes also transiently restored partial expression of full-length dystrophin in mdx mice. The findings further motivate the testing of CDCs in Duchenne patients, while identifying exosomes as next-generation therapeutic candidates.

Chronic TIN is associated with impaired Nrf2 activity which contributes to the pathogenesis of oxidative stress and inflammation and amplifies their damaging effects on the kidney.