Audrey E. Mayfield

Resident cardiac stem cells and their role in stem cell therapies for myocardial repair.

Despite advances in treatment, heart failure remains one of the top killers in Canada. This recognition motivated a new research focus to harness the fundamental repair properties of the human heart. Since then, cardiac stem cells (CSCs) have emerged as a promising cell candidate to regenerate damaged hearts. The rationale of this approach is simple with ex vivo amplification of CSCs from clinical-grade biopsies, followed by delivery to areas of injury, where they engraft and regenerate the heart. In this review we will summarize recent advances and discuss future developments in CSC-mediated cardiac repair to treat the growing number of Canadians living with and dying from heart failure.

Paracrine Engineering of Human Explant‐Derived Cardiac Stem Cells to Over‐Express Stromal‐Cell Derived Factor 1α Enhances Myocardial Repair

First generation cardiac stem cell products provide indirect cardiac repair but variably produce key cardioprotective cytokines, such as stromal‐cell derived factor 1α, which opens the prospect of maximizing up‐front paracrine‐mediated repair. The mesenchymal subpopulation within explant derived human cardiac stem cells underwent lentiviral mediated gene transfer of stromal‐cell derived factor 1α. Unlike previous unsuccessful attempts to increase efficacy by boosting the paracrine signature of cardiac stem cells, cytokine profiling revealed that stromal‐cell derived factor 1α over‐expression prevented lv‐mediated “loss of cytokines” through autocrine stimulation of CXCR4+ cardiac stem cells. Stromal‐cell derived factor 1α enhanced angiogenesis and stem cell recruitment while priming cardiac stem cells to readily adopt a cardiac identity. As compared to injection with unmodified cardiac stem cells, transplant of stromal‐cell derived factor 1α enhanced cells into immunodeficient mice improved myocardial function and angiogenesis while reducing scarring. Increases in myocardial stromal‐cell derived factor 1α content paralleled reductions in myocyte apoptosis but did not influence long‐term engraftment or the fate of transplanted cells. Transplantation of stromal‐cell derived factor 1α transduced cardiac stem cells increased the generation of new myocytes, recruitment of bone marrow cells, new myocyte/vessel formation and the salvage of reversibly damaged myocardium to enhance cardiac repair after experimental infarction. Stem Cells 2016;34:1826–1835

Interleukin-6 Mediates Post-Infarct Repair by Cardiac Explant-Derived Stem Cells

Although patient-sourced cardiac explant-derived stem cells (EDCs) provide an exogenous source of new cardiomyocytes post-myocardial infarction, poor long-term engraftment indicates that the benefits seen in clinical trials are likely paracrine-mediated. Of the numerous cytokines produced by EDCs, interleukin-6 (IL-6) is the most abundant; however, its role in cardiac repair is uncertain. In this study, a custom short-hairpin oligonucleotide lentivirus was used to knockdown IL-6 in human EDCs, revealing an unexpected pro-healing role for the cytokine. Methods: EDCs were cultured from atrial appendages donated by patients undergoing clinically indicated cardiac surgery. The effects of lentiviral mediated knockdown of IL-6 was evaluated using in vitro and in vivo models of myocardial ischemia. Results: Silencing IL-6 in EDCs abrogated much of the benefits conferred by cell transplantation and revealed that IL-6 prompts cardiac fibroblasts and macrophages to reduce myocardial scarring while increasing the generation of new cardiomyocytes and recruitment of blood stem cells. Conclusions: This study suggests that IL-6 plays a pivotal role in EDC-mediated cardiac repair and may provide a means of increasing cell-mediated repair of ischemic myocardium.

Isolation of human explant derived cardiac stem cells from cryopreserved heart tissue

The value of preserving high quality bio specimens for fundamental research is significant as linking cellular and molecular changes to clinical and epidemiological data has fueled many recent advances in medicine. Unfortunately, storage of traditional biospecimens is limited to fixed samples or isolated genetic material. Here, we report the effect of cryopreservation of routine myocardial biopsies on explant derived cardiac stem cell (EDC) culture outcomes. We demonstrate that immediate cryopreservation or delayed cryopreservation after suspension within cardioplegia for 12 hours did not alter EDC yields, proliferative capacity, antigenic phenotype or paracrine signature. Cryopreservation had negligible effects on the ability of EDCs to adopt a cardiac lineage, stimulate new vessel growth, attract circulating angiogenic cells and repair injured myocardium. Finally, cryopreservation did not influence the ability of EDCs to undergo genetic reprogramming into inducible pluripotent stem cells. This study establishes a means of storing cardiac samples as a retrievable live cell source for cardiac repair or disease modeling.