No abstract

Stem cell therapy represents a promising strategy in regenerative medicine. However, cells need to be carefully preserved and processed before usage. In addition, cell transplantation carries immunogenicity and/or tumourigenicity risks. Mounting lines of evidence indicate that stem cells exert their beneficial effects mainly through secretion (of regenerative factors) and membrane-based cell–cell interaction with the injured cells. Here, we fabricate a synthetic cell-mimicking microparticle (CMMP) that recapitulates stem cell functions in tissue repair. CMMPs carry similar secreted proteins and membranes as genuine cardiac stem cells do. In a mouse model of myocardial infarction, injection of CMMPs leads to the preservation of viable myocardium and augmentation of cardiac functions similar to cardiac stem cell therapy. CMMPs (derived from human cells) do not stimulate T-cell infiltration in immuno-competent mice. In conclusion, CMMPs act as ‘synthetic stem cells’ which mimic the paracrine and biointerfacing activities of natural stem cells in therapeutic cardiac regeneration.

Rationale: Cardiac stem cell-derived exosomes have been demonstrated to promote cardiac regeneration following myocardial infarction in preclinical studies. Recent studies have used intramyocardial injection in order to concentrate exosomes in the infarct. Though effective in a research setting, this method is not clinically appealing due to its invasive nature. We propose the use of a targeting peptide, cardiac homing peptide (CHP), to target intravenously-infused exosomes to the infarcted heart.Methods: Exosomes were conjugated with CHP through a DOPE-NHS linker. Ex vivo targeting was analyzed by incubating organ sections with the CHP exosomes and analyzing with fluorescence microscopy. In vitro assays were performed on neonatal rat cardiomyocytes and H9C2 cells. For the animal study, we utilized an ischemia/reperfusion rat model. Animals were treated with either saline, scramble peptide exosomes, or CHP exosomes 24 h after surgery. Echocardiography was performed 4 h after surgery and 21 d after surgery. At 21 d, animals were sacrificed, and organs were collected for analysis.Results: By conjugating the exosomes with CHP, we demonstrate increased retention of the exosomes within heart sections ex vivo and in vitro with neonatal rat cardiomyocytes. In vitro studies showed improved viability, reduced apoptosis and increased exosome uptake when using CHP-XOs. Using an animal model of ischemia/reperfusion injury, we measured the heart function, infarct size, cellular proliferation, and angiogenesis, with improved outcomes with the CHP exosomes.Conclusions: Our results demonstrate a novel method for increasing delivery of for treatment of myocardial infarction. By targeting exosomes to the infarcted heart, there was a significant improvement in outcomes with reduced fibrosis and scar size, and increased cellular proliferation and angiogenesis.

Stem cell transplantation, as used clinically, suffers from low retention and engraftment of the transplanted cells. Inspired by the ability of platelets to recruit stem cells to sites of injury on blood vessels, we hypothesized that platelets might enhance the vascular delivery of cardiac stem cells (CSCs) to sites of myocardial infarction injury. Here, we show that CSCs with platelet nanovesicles fused onto their surface membranes express platelet surface markers that are associated with platelet adhesion to injury sites. We also find that the modified CSCs selectively bind collagen-coated surfaces and endothelium-denuded rat aortas, and that in rat and porcine models of acute myocardial infarction the modified CSCs increase retention in the heart and reduce infarct size. Platelet-nanovesicle-fused CSCs thus possess the natural targeting and repairing ability of their parental cell types. This stem cell manipulation approach is fast, straightforward and safe, does not require genetic alteration of the cells, and should be generalizable to multiple cell types.