Surface Lin28A expression consistent with cellular stress parallels indicators of senescence.

Aims: Declining cellular functional capacity resulting from stress or ageing is a primary contributor to impairment of myocardial performance. Molecular pathway regulation of biological processes in cardiac interstitial cells (CICs) is pivotal in stress and ageing responses. Altered localization of the RNA-binding protein Lin28A has been reported in response to environmental stress, but the role of Lin28A in response to stress in CICs has not been explored.

Transcriptional features of biological age maintained in human cultured cardiac interstitial cells.

Ex vivo expansion of cells is necessary in regenerative medicine to generate large populations for therapeutic use. Adaptation to culture conditions prompt an increase in transcriptome diversity and decreased population heterogeneity in cKit+ cardiac interstitial cells (cCICs). The "transcriptional memory" influenced by cellular origin remained unexplored and is likely to differ between neonatal versus senescent input cells undergoing culture expansion.

Enhancing myocardial repair with CardioClusters.

Cellular therapy to treat heart failure is an ongoing focus of intense research, but progress toward structural and functional recovery remains modest. Engineered augmentation of established cellular effectors overcomes impediments to enhance reparative activity. Such 'next generation' implementation includes delivery of combinatorial cell populations exerting synergistic effects.

Pim1 maintains telomere length in mouse cardiomyocytes by inhibiting TGFβ signalling.

Aims: Telomere attrition in cardiomyocytes is associated with decreased contractility, cellular senescence, and up-regulation of proapoptotic transcription factors. Pim1 is a cardioprotective kinase that antagonizes the aging phenotype of cardiomyocytes and delays cellular senescence by maintaining telomere length, but the mechanism remains unknown. Another pathway responsible for regulating telomere length is the transforming growth factor beta (TGFβ) signalling pathway where inhibiting TGFβ signalling maintains telomere length.

Adaptation within embryonic and neonatal heart environment reveals alternative fates for adult c-kit cardiac interstitial cells.

Cardiac interstitial cells (CICs) perform essential roles in myocardial biology through preservation of homeostasis as well as response to injury or stress. Studies of murine CIC biology reveal remarkable plasticity in terms of transcriptional reprogramming and ploidy state with important implications for function. Despite over a decade of characterization and in vivo utilization of adult c-Kit CIC (cCIC), adaptability and functional responses upon delivery to adult mammalian hearts remain poorly understood.

Cardiac interstitial tetraploid cells can escape replicative senescence in rodents but not large mammals.

Cardiomyocyte ploidy has been described but remains obscure in cardiac interstitial cells. Ploidy of c-kit+ cardiac interstitial cells was assessed using confocal, karyotypic, and flow cytometric technique. Notable differences were found between rodent (rat, mouse) c-kit+ cardiac interstitial cells possessing mononuclear tetraploid (4n) content, compared to large mammals (human, swine) with mononuclear diploid (2n) content.

Hypoxia Prevents Mitochondrial Dysfunction and Senescence in Human c-Kit Cardiac Progenitor Cells.

Senescence-associated dysfunction deleteriously affects biological activities of human c-Kit cardiac progenitor cells (hCPCs), particularly under conditions of in vitro culture. In comparison, preservation of self-renewal and decreases in mitochondrial reactive oxygen species (ROS) are characteristics of murine CPCs in vivo that reside within hypoxic niches. Recapitulating hypoxic niche oxygen tension conditions of ∼1% O in vitro for expansion of hCPCs rather than typical normoxic cell culture conditions (21% O ) could provide significant improvement of functional and biological activities of hCPCs.

Cardiomyocyte cell cycle dynamics and proliferation revealed through cardiac-specific transgenesis of fluorescent ubiquitinated cell cycle indicator (FUCCI).

Rationale: Understanding and manipulating the cardiomyocyte cell cycle has been the focus of decades of research, however the ultimate goal of activating mitotic activity in adult mammalian cardiomyocytes remains elusive and controversial. The relentless pursuit of controlling cardiomyocyte mitosis has been complicated and obfuscated by a multitude of indices used as evidence of cardiomyocyte cell cycle activity that lack clear identification of cardiomyocyte "proliferation" versus cell cycle progression, endoreplication, endomitosis, and even DNA damage. Unambiguous appreciation of the complexity of cardiomyocyte replication that avoids oversimplification and misinterpretation is desperately needed.

Cardiac c-Kit Biology Revealed by Inducible Transgenesis.

Rationale: Biological significance of c-Kit as a cardiac stem cell marker and role(s) of c-Kit+ cells in myocardial development or response to pathological injury remain unresolved because of varied and discrepant findings. Alternative experimental models are required to contextualize and reconcile discordant published observations of cardiac c-Kit myocardial biology and provide meaningful insights regarding clinical relevance of c-Kit signaling for translational cell therapy.

Objective: The main objectives of this study are as follows: demonstrating c-Kit myocardial biology through combined studies of both human and murine cardiac cells; advancing understanding of c-Kit myocardial biology through creation and characterization of a novel, inducible transgenic c-Kit reporter mouse model that overcomes limitations inherent to knock-in reporter models; and providing perspective to reconcile disparate viewpoints on c-Kit biology in the myocardium.

Empowering human cardiac progenitor cells by P2Y nucleotide receptor overexpression.

Key Points: Autologous cardiac progenitor cell (CPC) therapy is a promising approach for treatment of heart failure (HF). There is an unmet need to identify inherent deficits in aged/diseased human CPCs (hCPCs) derived from HF patients in the attempts to augment their regenerative capacity prior to use in the clinical setting. Here we report significant functional correlations between phenotypic properties of hCPCs isolated from cardiac biopsies of HF patients, clinical parameters of patients and expression of the P2Y purinergic receptor (P2Y R), a crucial detector for extracellular UDP-sugars released during injury/stress.

P2Y Nucleotide Receptor Prompts Human Cardiac Progenitor Cell Activation by Modulating Hippo Signaling.

Rationale: Autologous stem cell therapy using human c-Kit cardiac progenitor cells (hCPCs) is a promising therapeutic approach for treatment of heart failure (HF). However, hCPCs derived from aged patients with HF with genetic predispositions and comorbidities of chronic diseases exhibit poor proliferative and migratory capabilities, which impair overall reparative potential for injured myocardium. Therefore, empowering functionally compromised hCPCs with proregenerative molecules ex vivo is crucial for improving the therapeutic outcome in patients with HF.

Concurrent Isolation of 3 Distinct Cardiac Stem Cell Populations From a Single Human Heart Biopsy.

Rationale: The relative actions and synergism between distinct myocardial-derived stem cell populations remain obscure. Ongoing debates on optimal cell population(s) for treatment of heart failure prompted implementation of a protocol for isolation of multiple stem cell populations from a single myocardial tissue sample to develop new insights for achieving myocardial regeneration.

Objective: Establish a robust cardiac stem cell isolation and culture protocol to consistently generate 3 distinct stem cell populations from a single human heart biopsy.

Functional Effect of Pim1 Depends upon Intracellular Localization in Human Cardiac Progenitor Cells.

Human cardiac progenitor cells (hCPC) improve heart function after autologous transfer in heart failure patients. Regenerative potential of hCPCs is severely limited with age, requiring genetic modification to enhance therapeutic potential. A legacy of work from our laboratory with Pim1 kinase reveals effects on proliferation, survival, metabolism, and rejuvenation of hCPCs in vitro and in vivo.

Rejuvenation of human cardiac progenitor cells with Pim-1 kinase.

Rationale: Myocardial function is enhanced by adoptive transfer of human cardiac progenitor cells (hCPCs) into a pathologically challenged heart. However, advanced age, comorbidities, and myocardial injury in patients with heart failure constrain the proliferation, survival, and regenerative capacity of hCPCs. Rejuvenation of senescent hCPCs will improve the outcome of regenerative therapy for a substantial patient population possessing functionally impaired stem cells.