Background Despite numerous studies demonstrating efficacy of cellular adoptive transfer for therapeutic myocardial regeneration, problems remain for donated cells with regard to survival, persistence, engraftment, and long-term benefits. This study redresses these concerns by enhancing the regenerative potential of adoptively transferred cardiac progenitor cells (CPCs) via genetic engineering to overexpress Pim-1, a cardioprotective kinase that enhances cell survival and proliferation. Methods and Results Intramyocardial injections of CPCs overexpressing Pim-1 were given to infarcted female mice. Animals were monitored over 4, 12, and 32-weeks to assess cardiac function and engraftment of Pim-1 CPCs using echocardiography, in vivo hemodynamics, and confocal imagery. CPCs overexpressing Pim-1 show increased proliferation and expression of markers consistent with cardiogenic lineage commitment following dexamethasone exposure in vitro. Animals that received CPCs overexpressing Pim-1 also produce greater levels of cellular engraftment, persistence, and functional improvement relative to control CPCs up to 32-weeks post-delivery. Salutary effects include reduction of infarct size, greater number of c-kit+ cells, and increased vasculature in the damaged region. Conclusions Myocardial repair is significantly enhanced by genetic engineering of CPCs using Pim-1 kinase. Ex vivo gene delivery to enhance cellular survival, proliferation, and regeneration may overcome current limitations of stem cell-based therapeutic approaches.

One of the greatest examples of integrated signal transduction is revealed by examination of effects mediated by AKT kinase in myocardial biology. Positioned at the intersection of multiple afferent and efferent signals, AKT exemplifies a molecular sensing node that coordinates dynamic responses of the cell in literally every aspect of biological responses. The balanced and nuanced nature of homeostatic signaling is particularly essential within the myocardial context, where regulation of survival, energy production, contractility, and response to pathological stress all flow through the nexus of AKT activation or repression. Equally important, the loss of regulated AKT activity is primarily the cause or consequence of pathological conditions leading to remodeling of the heart and eventual decompensation. This review presents an overview compendium of the complex world of myocardial AKT biology gleaned from more than a decade of research. Summarization of the widespread influence that AKT exerts upon myocardial responses leaves no doubt that the participation of AKT in molecular signaling will need to be reckoned with as a seemingly omnipresent regulator of myocardial molecular biological responses.

Mitochondrial morphological dynamics affect the outcome of ischemic heart damage and pathogenesis. Recently, mitochondrial fission protein dynamin-related protein 1 (Drp1) has been identified as a mediator of mitochondrial morphological changes and cell death during cardiac ischemic injury. In this study, we report a unique relationship between Pim-1 activity and Drp1 regulation of mitochondrial morphology in cardiomyocytes challenged by ischemic stress. Transgenic hearts overexpressing cardiac Pim-1 display reduction of total Drp1 protein levels, increased phosphorylation of Drp1-S637 , and inhibition of Drp1 localization to the mitochondria. Consistent with these findings, adenoviral-induced Pim-1 neonatal rat cardiomyocytes (NRCMs) retain a reticular mitochondrial phenotype after simulated ischemia (sI) and decreased Drp1 mitochondrial sequestration. Interestingly, adenovirus Pimdominant negative NRCMs show increased expression of Bcl-2 homology 3 (BH3)-only protein p53 up-regulated modulator of apoptosis (PUMA), which has been previously shown to induce Drp1 accumulation at mitochondria and increase sensitivity to apoptotic stimuli. Overexpression of the p53 up-regulated modulator of apoptosis-dominant negative adenovirus attenuates localization of Drp1 to mitochondria in adenovirus Pim-dominant negative NRCMs promotes reticular mitochondrial morphology and inhibits cell death during sI. Therefore, Pim-1 activity prevents Drp1 compartmentalization to the mitochondria and preserves reticular mitochondrial morphology in response to sI.

Background The mechanistic target of rapamycin (mTOR) comprises 2 structurally distinct multiprotein complexes, mTOR complexes 1 and 2 (mTORC1 and mTORC2). Deregulation of mTOR signaling occurs during and contributes to the severity of myocardial damage from ischemic heart disease. However, the relative roles of mTORC1 versus mTORC2 in the pathogenesis of ischemic damage are unknown. Methods and Results Combined pharmacological and molecular approaches were used to alter the balance of mTORC1 and mTORC2 signaling in cultured cardiac myocytes and in mouse hearts subjected to conditions that mimic ischemic heart disease. The importance of mTOR signaling in cardiac protection was demonstrated by pharmacological inhibition of both mTORC1 and mTORC2 with Torin1, which led to increased cardiomyocyte apoptosis and tissue damage after myocardial infarction. Predominant mTORC1 signaling mediated by suppression of mTORC2 with Rictor similarly increased cardiomyocyte apoptosis and tissue damage after myocardial infarction. In comparison, preferentially shifting toward mTORC2 signaling by inhibition of mTORC1 with PRAS40 led to decreased cardiomyocyte apoptosis and tissue damage after myocardial infarction. Conclusions These results suggest that selectively increasing mTORC2 while concurrently inhibiting mTORC1 signaling is a novel therapeutic approach for the treatment of ischemic heart disease.

Rationale Adoptive transfer of cardiac progenitor cells (CPCs) has entered clinical application despite limited mechanistic understanding of the endogenous response following myocardial infarction (MI). Extracellular matrix (ECM) undergoes dramatic changes after MI and therefore might be linked to CPC-mediated repair. Objective Demonstrate the significance of Fibronectin (Fn), a component of the ECM, for induction of the endogenous CPC response to MI. Methods and Results This report shows that presence of CPCs correlates with expression of Fn during cardiac development and after MI. In vivo, genetic conditional ablation of Fn blunts CPC response measured 7 days after MI through reduced proliferation and diminished survival. Attenuated vasculogenesis and cardiogenesis during recovery was evident at the end of a 12 week follow-up period. Impaired CPC-dependent reparative remodeling ultimately leads to continuous decline of cardiac function in Fn knockout animals. In vitro, Fn protects and induces proliferation of CPCs via β1-Integrin-FAK-Stat3-Pim1 but Akt-independent mechanism. Conclusion Fn is essential for endogenous CPC expansion and repair needed for stabilization of cardiac function after MI.

Key Words: Pim-1 Ⅲ mitochondria Ⅲ cardiomyocyte Ⅲ apoptosis C ardiovascular disease is the leading cause of death among men and women and affects approximately 33% of the US population. 1 A direct correlation between the decline in heart function and loss of cardiomyocytes via apoptosis involving the mitochondria occurs in cardiomyopathy, myocardial ischemia/reperfusion (I/R), and congestive heart failure. 2-9 Specifically, myocardial I/R injury generates calcium overload and oxidative stress, which initiate the intrinsic apoptotic pathway through activation of the mitochondrial permeability transition pore (mPTP). The ensuing chain of events result in dramatic changes to mitochondrial morphology associated with uncoupling of the electron transport chain, depolarization of the inner membrane, matrix swelling, unfolding of the cristae, and ultimately outer membrane rupture, with release of proapoptotic cytochrome c. 10 -15 Release of cytochrome c into the cytosol consequently activates apoptotic protease-activating factor, which mediates caspase cascade programmed cell death. 16 Thus, preservation of mitochondrial integrity is essential in designing molecular strategies to enhance cardiomyocyte cell survival by blunting injury attributed to cardiomyopathic insult.Cardioprotection mediated by survival kinase signal transduction acts through multiple mechanisms including preservation of mitochondrial integrity. 17 Numerous studies have documented antiapoptotic actions of the serine/threonine kinase AKT, which acts in part through protecting mitochon-

Translocation of Nur77 from the nucleus to the mitochondria in cardiomyocytes results in the loss of mitochondrial integrity and subsequent apoptosis in response to ischaemia/reperfusion injury. Our findings identify Nur77 as a novel mediator of cardiomyocyte apoptosis and warrants further investigation of mitochondrial Nur77 translocation as a mechanism to control cell death in the treatment of ischaemic heart diseases.

Pim-1 kinase exerts potent cardioprotective effects in the myocardium downstream of AKT, but the participation of Pim-1 in cardiac hypertrophy requires investigation. Cardiac-specific expression of Pim-1 (Pim-WT) or the dominant-negative mutant of Pim-1 (Pim-DN) in transgenic mice together with adenoviral-mediated overexpression of these Pim-1 constructs was used to delineate the role of Pim-1 in hypertrophy. Transgenic overexpression of Pim-1 protects mice from pressure-overload-induced hypertrophy relative to wild-type controls as evidenced by improved hemodynamic function, decreased apoptosis, increases in antihypertrophic proteins, smaller myocyte size, and inhibition of hypertrophic signaling after challenge. Similarly, Pim-1 overexpression in neonatal rat cardiomyocyte cultures inhibits hypertrophy induced by endothelin-1. On the cellular level, hearts of Pim-WT mice show enhanced incorporation of BrdU into myocytes and a hypercellular phenotype compared to wild-type controls after hypertrophic challenge. In comparison, transgenic overexpression of Pim-DN leads to dilated cardiomyopathy characterized by increased apoptosis, fibrosis, and severely depressed cardiac function. Furthermore, overexpression of Pim-DN leads to reduced contractility as evidenced by reduced Ca 2؉ transient amplitude and decreased percentage of cell shortening in isolated myocytes. These data support a pivotal role for Pim-1 in modulation of hypertrophy by impacting responses on molecular, cellular, and organ levels.