The Calcineurin-Drp1-Mediated Mitochondrial Fragmentation Is Aligned with the Differentiation of c-Kit Cardiac Progenitor Cells.

Objective: The heart contains a pool of c-kit+ progenitor cells which is believed to be able to regenerate. The differentiation of these progenitor cells is reliant on different physiological cues. Unraveling the underlying signals to direct differentiation of progenitor cells will be beneficial in controlling progenitor cell fate. In this regard, the role of the mitochondria in mediating cardiac progenitor cell fate remains unclear. Specifically, the association between changes in mitochondrial morphology with the differentiation status of c-kit+ CPCs remains elusive. In this study, we investigated the relationship between mitochondrial morphology and the differentiation status of c-kit+ progenitor cells. Methods and Results: c-kit+ CPCs were isolated from 2-month-old male wild-type FVB mice. To activate differentiation, CPCs were incubated in α-minimal essential medium containing 10 nM dexamethasone for up to 7 days. To inhibit Drp1-mediated mitochondrial fragmentation, either 10 µM or 50 µM mdivi-1 was administered once at Day 0 and again at Day 2 of differentiation. To inhibit calcineurin, either 1 µM or 5 µM ciclosporin-A (CsA) was administered once at Day 0 and again at Day 2 of differentiation. Dexamethasone-induced differentiation of c-kit+ progenitor cells is aligned with fragmentation of the mitochondria via a calcineurin-Drp1 pathway. Pharmacologically inhibiting mitochondrial fragmentation retains the undifferentiated state of the c-kit+ progenitor cells. Conclusions: The findings from this study provide an alternative view of the role of mitochondrial fusion-fission in the differentiation of cardiac progenitor cells and the potential of pharmacologically manipulating the mitochondria to direct progenitor cell fate.

Large animal models of cardiac ischemia-reperfusion injury: Where are we now?

Large animal models of cardiac ischemia-reperfusion are critical for evaluation of the efficacy of cardioprotective interventions prior to clinical translation. Nonetheless, current cardioprotective strategies/interventions formulated in preclinical cardiovascular research are often limited to small animal models, which are not transferable or reproducible in large animal models due to different factors such as: (i) complex and varied features of human ischemic cardiac disease (ICD), which are challenging to mimic in animal models, (ii) significant differences in surgical techniques applied, and (iii) differences in cardiovascular anatomy and physiology between small versus large animals. This article highlights the advantages and disadvantages of different large animal models of preclinical cardiac ischemic reperfusion injury (IRI), as well as the different methods used to induce and assess IRI, and the obstacles faced in using large animals for translational research in the settings of cardiac IR.

Ischemic Preconditioning and Postconditioning Protect the Heart by Preserving the Mitochondrial Network.

Background: Mitochondria fuse to form elongated networks which are more tolerable to stress and injury. Ischemic pre- and postconditioning (IPC and IPost, respectively) are established cardioprotective strategies in the preclinical setting. Whether IPC and IPost modulates mitochondrial morphology is unknown. We hypothesize that the protective effects of IPC and IPost may be conferred via preservation of mitochondrial network. Methods: IPC and IPost were applied to the H9c2 rat myoblast cells, isolated adult primary murine cardiomyocytes, and the Langendorff-isolated perfused rat hearts. The effects of IPC and IPost on cardiac cell death following ischemia-reperfusion injury (IRI), mitochondrial morphology, and gene expression of mitochondrial-shaping proteins were investigated. Results: IPC and IPost successfully reduced cardiac cell death and myocardial infarct size. IPC and IPost maintained the mitochondrial network in both H9c2 and isolated adult primary murine cardiomyocytes. 2D-length measurement of the 3 mitochondrial subpopulations showed that IPC and IPost significantly increased the length of interfibrillar mitochondria (IFM). Gene expression of the pro-fusion protein, Mfn1, was significantly increased by IPC, while the pro-fission protein, Drp1, was significantly reduced by IPost in the H9c2 cells. In the primary cardiomyocytes, gene expression of both Mfn1 and Mfn2 were significantly upregulated by IPC and IPost, while Drp1 was significantly downregulated by IPost. In the Langendorff-isolated perfused heart, gene expression of Drp1 was significantly downregulated by both IPC and IPost. Conclusion: IPC and IPost-mediated upregulation of pro-fusion proteins (Mfn1 and Mfn2) and downregulation of pro-fission (Drp1) promote maintenance of the interconnected mitochondrial network, ultimately conferring cardioprotection against IRI.