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. The relationship between Pim1 and TGFβ has not been explored. This study delineates the mechanism of telomere length regulation by the interplay between Pim1 and components of TGFβ signalling pathways in proliferating A549 cells and post-mitotic cardiomyocytes. Methods and results Telomere length was maintained by lentiviral-mediated overexpression of PIM1 and inhibition of TGFβ signalling in A549 cells. Telomere length maintenance was further demonstrated in isolated cardiomyocytes from mice with cardiac-specific overexpression of PIM1 and by pharmacological inhibition of TGFβ signalling. Mechanistically, Pim1 inhibited phosphorylation of Smad2, preventing its translocation into the nucleus and repressing expression of TGFβ pathway genes. Conclusion Pim1 maintains telomere lengths in cardiomyocytes by inhibiting phosphorylation of the TGFβ pathway downstream effectors Smad2 and Smad3, which prevents repression of telomerase reverse transcriptase. Findings from this study demonstrate a novel mechanism of telomere length maintenance and provide a potential target for preserving cardiac function.

Enhancing cardiomyocyte survival is crucial to blunt deterioration of myocardial structure and function following pathological damage. PIM1 (Proviral Insertion site in Murine leukemia virus (PIM) kinase 1) is a cardioprotective serine threonine kinase that promotes cardiomyocyte survival and antagonizes senescence through multiple concurrent molecular signaling cascades. In hematopoietic stem cells, PIM1 interacts with the receptor tyrosine kinase c-Kit upstream of the ERK (Extracellular signal-Regulated Kinase) and Akt signaling pathways involved in cell proliferation and survival. The relationship between PIM1 and c-Kit activity has not been explored in the myocardial context. This study delineates the interaction between PIM1 and c-Kit leading to enhanced protection of cardiomyocytes from stress. Elevated c-Kit expression is induced in isolated cardiomyocytes from mice with cardiac-specific overexpression of PIM1. Co-immunoprecipitation and proximity ligation assay reveal protein–protein interaction between PIM1 and c-Kit. Following treatment with Stem Cell Factor, PIM1-overexpressing cardiomyocytes display elevated ERK activity consistent with c-Kit receptor activation. Functionally, elevated c-Kit expression confers enhanced protection against oxidative stress in vitro. This study identifies the mechanistic relationship between PIM1 and c-Kit in cardiomyocytes, demonstrating another facet of cardioprotection regulated by PIM1 kinase.

Vaping of flavored liquids has been touted as safe alternative to traditional cigarette smoking with decreased health risks. The popularity of vaping has dramatically increased over the last decade, particularly among teenagers who incorporate vaping into their daily life as a social activity. Despite widespread and increasing adoption of vaping among young adults, there is little information on long-term consequences of vaping and potential health risks. This study demonstrates vaping-induced pulmonary injury using commercial JUUL pens with flavored vape juice using an inhalation exposure murine model. Profound pathological changes to upper airway, lung tissue architecture, and cellular structure are evident within 9 wk of exposure. Marked histologic changes include increased parenchyma tissue density, cellular infiltrates proximal to airway passages, alveolar rarefaction, increased collagen deposition, and bronchial thickening with elastin fiber disruption. Transcriptional reprogramming includes significant changes to gene families coding for xenobiotic response, glycerolipid metabolic processes, and oxidative stress. Cardiac systemic output is moderately but significantly impaired with pulmonary side ventricular chamber enlargement. This vaping-induced pulmonary injury model demonstrates mechanistic underpinnings of vaping-related pathologic injury.

Vaping of flavored liquids has been touted as safe alternative to traditional cigarette smoking with decreased health risks. The popularity of vaping has dramatically increased over the last decade, particularly among teenagers who incorporate vaping into their daily life as a social activity. Despite widespread and increasing adoption of vaping among young adults there is little information on long term consequences of vaping and potential health risks. This study demonstrates Vaping-Induced Pulmonary Injury (VAPI) using commercial JUUL pens with flavored vape juice using an inhalation exposure murine model. Profound pathological changes to upper airway, lung tissue architecture, and cellular structure are evident within 9 weeks of exposure. Marked histologic changes include increased parenchyma tissue density, cellular infiltrates proximal to airway passages, alveolar rarefaction, increased collagen deposition, and bronchial thickening with elastin fiber disruption. Transcriptional reprogramming includes significant changes to gene families coding for xenobiotic response, glycerolipid metabolic processes, and oxidative stress. Cardiac contractile performance for systemic output is moderately but significantly impaired, and the shows severe pulmonary side structural remodeling with chamber enlargement. This VAPI model with pulmonary circuit failure demonstrates mechanistic underpinnings of vaping-related pathologic injury.

Introduction: De novo cardiomyogenesis versus polyploidy in myocardial homeostasis, aging, and response to injury is a controversial research area of intense investigation. Our lab recently created the Fluorescent Ubiquitin Cell Cycle Indicator transgenic (FUCCI-Tg) mouse model to study cardiomyocyte (CM) cell cycle progression. Therefore, the FUCCI-Tg model was used to track CM cell cycle correlated to ploidy state in response to myocardial infarction (MI). Hypothesis: Adult FUCCI-Tg cardiomyocytes progress into S/G2/M phase of cell cycle by 10 days after infarction resulting in binucleation rather than de novo cardiomyogenesis. Methods and Results: CMs isolated from FUCCI-Tg were analyzed 3 and 10 days following MI using confocal microscopy and flow cytometry. At 3 days post-MI, the ratio of mono- to binucleated CMs remained unchanged from non-injury CMs. At day 10 post-MI, frequency of mononuclear CMs significantly decreased compared to normal or 3-day post-MI CMs. Coincident with nucleation state, myocytes were only found to enter S/G2/M phase at day 10 post-MI. These results were verified by visualization of FUCCI in isolated CMs using Amnis ImageStream flow cytometry. Ploidy state and CM size was assessed in the infarction / border (left ventricle (LV)) and remote zone (right ventricle (RV)) at day 10 post-MI and compared to the normal and sham LV and RV. Binucleation significantly increased in the LV after MI compared to normal LV, whereas RV CM binucleation and size significantly increased in both sham and MI at 10 days after MI compared to normal RV. Conclusion: Adult murine CMs enter cell cycle in response to MI but primarily undergo endomitosis / endoreplication rather than complete cell cycle reflecting increases in nucleation and/or myocyte size rather than de novo cardiomyogenesis. Future studies will assess CM ploidy in mouse strains purported to possess enhanced cardiomyogenesis following MI injury and the biological significance of ploidy for mediating myocardial repair.

Introduction: Declining cellular functional capacity resulting from stress or aging 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 aging 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. Hypothesis: Lin28A redistribution is indicative of stress response in CIC associated with aging and senescence. Methods and Results: Localization of Lin28A was assessed by multiple experimental analyses and treatment conditions and correlated to oxidative stress, senescence, and ploidy in adult murine CICs. Surface Lin28A expression is present on 5% of fresh CICs and maintained through passage 2, increasing to 21% in hyperoxic conditions but lowered to 14% in physiologic normoxia. Surface Lin28A is coincident with elevated Beta-galactosidase (Beta-gal) expression in CICs expanded in hyperoxia, and also increases with polyploidization and binucleation of CICs regardless of oxygen culture. Transcriptional profiling of CICs using single cell RNASeq reveals upregulation of pathways associated with oxidative stress in CICs exhibiting surface Lin28A. Induction of surface Lin28A by oxidative stress is blunted by treatment of cells with the antioxidant Trolox in a dose-dependent manner, with 300uM Trolox exposure maintaining characteristics of freshly isolated CICs possessing low expression of surface Lin28A and Beta-gal with predominantly diploid content. Conclusion: Surface Lin28A is a marker of environmental oxidative stress in CICs and antioxidant treatment antagonizes this phenotype. The biological significance of Lin28 surface expression and consequences for myocardial responses may provide important insights regarding mitigation of cardiac stress and aging.

Introduction: Fibroblasts are critical contributors to myocardial development, tissue homeostasis and remodeling. Cardiac fibroblast population heterogeneity and plasticity present a challenge for categorization of biological and functional properties. Distinct molecular markers and associated signaling pathways provide valuable insight for cardiac fibroblast biology and interventional strategies to influence injury response and remodeling. Receptor tyrosine kinase c-Kit mediates cell survival, proliferation, migration, and is activated by pathological injury. However, the biological significance of c-Kit within cardiac fibroblast population has not been addressed. Approach: An inducible c-Kit reporter mouse detects promoter activation with Green Fluorescent Protein (GFP) expression in cardiac interstitial cells (CICs). Coincidence of GFP and c-Kit with the DDR2 fibroblast marker was confirmed at protein level using flow cytometry and immunohistochemistry. Subsequently, cardiac fibroblasts expressing DDR2 with or without c-Kit were isolated and characterized in vitro . Results: A subset of DDR2 + cardiac fibroblasts also express c-Kit with coincidence in ~8% of total CICs. Pathological injury induces coincidence as well as expression of c-Kit and DDR2. Cultured cardiac DDR2+ fibroblasts that are c-Kit+ exhibit youthful morphological and functional phenotypes compared to c-Kit- cells including 1) significantly smaller size, 2) higher cellular motility, 3) enhanced proliferation, 4) less multinucleation, 5) decreased senescence-associated β-galactosidase staining, and 6) down-regulation of p53 senescence marker. Mechanistically, c-Kit expression correlates with signaling implicated in proliferation and cell migration including phospho-ERK and pro-Caspase 3. Conclusion: The phenotype of c-kit+ on DDR2+ cardiac fibroblasts correlates with multiple characteristics of ‘youthful’ cells. To our knowledge, this represents the first evaluation of c-Kit biology within DDR2+ cardiac fibroblast population and provides a fundamental basis for future studies to influence myocardial biology, cardiac remodeling, and response to pathological injury.

Aims Declining cellular functional capacity resulting from stress or aging 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 aging 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. Surface Lin28A redistribution is indicative of stress response in CIC associated with aging and senescence. Methods and Results Localization of Lin28A was assessed by multiple experimental analyses and treatment conditions and correlated to oxidative stress, senescence, and ploidy in adult murine CICs. Surface Lin28A expression is present on 5% of fresh CICs and maintained through passage 2, increasing to 21% in hyperoxic conditions but lowered to 14% in physiologic normoxia. Surface Lin28A is coincident with elevated senescence marker p16 and beta-galactosidase (β-gal) expression in CICs expanded in hyperoxia, and also increases with polyploidization and binucleation of CICs regardless of oxygen culture. Transcriptional profiling of CICs using single cell RNASeq reveals upregulation of pathways associated with oxidative stress in CICs exhibiting surface Lin28A. Induction of surface Lin28A by oxidative stress is blunted by treatment of cells with the antioxidant Trolox in a dose-dependent manner, with 300uM Trolox exposure maintaining characteristics of freshly isolated CICs possessing low expression of surface Lin28A and β-gal with predominantly diploid content. Conclusion Surface Lin28A is a marker of environmental oxidative stress in CICs and antioxidant treatment antagonizes this phenotype. The biological significance of Lin28 surface expression and consequences for myocardial responses may provide important insights regarding mitigation of cardiac stress and aging. Translational Perspective Cellular phenotypic changes occurring in response to oxidative stress provides critical insights into biological processes of pathological injury and aging. Surface Lin28A is novel surface marker of oxidative stress conditions that cause DNA damage and cellular senescence. Accumulation of surface Lin28A was inhibited by antioxidant treatment with lowered indices of cellular stress and senescence, revealing the potential of surface Lin28A as a diagnostic stress marker. Furthermore, therapeutic strategies targeted toward surface Lin28 expression set the stage for next generation senolytics to remove stressed or senescent cells and promote recovery from tissue injury or aging.