The double life of cardiac mesenchymal cells: Epimetabolic sensors and therapeutic assets for heart regeneration

The origin, progress, and application of cell-based cardiac regeneration therapy

Cardiovascular disease (CVD) has become a severe threat to human health, with morbidity and mortality increasing yearly and gradually becoming younger. When the disease progresses to the middle and late stages, the loss of a large number of cardiomyocytes is irreparable to the body itself, and clinical drug therapy and mechanical support therapy cannot reverse the development of the disease. To explore the source of regenerated myocardium in model animals with the ability of heart regeneration through lineage tracing and other methods, and develop a new alternative therapy for CVDs, namely cell therapy. It directly compensates for cardiomyocyte proliferation through adult stem cell differentiation or cell reprogramming, which indirectly promotes cardiomyocyte proliferation through non-cardiomyocyte paracrine, to play a role in heart repair and regeneration. This review comprehensively summarizes the origin of newly generated cardiomyocytes, the research progress of cardiac regeneration based on cell therapy, the opportunity and development of cardiac regeneration in the context of bioengineering, and the clinical application of cell therapy in ischemic diseases.

Differences in Mitochondrial Membrane Potential Identify Distinct Populations of Human Cardiac Mesenchymal Progenitor Cells

Adult human cardiac mesenchymal progenitor cells (hCmPC) are multipotent resident populations involved in cardiac homeostasis and heart repair. Even if the mechanisms have not yet been fully elucidated, the stem cell differentiation is guided by the mitochondrial metabolism; however, mitochondrial approaches to identify hCmPC with enhanced stemness and/or differentiation capability for cellular therapy are not established. Here we demonstrated that hCmPCs sorted for low and high mitochondrial membrane potential (using a lipophilic cationic dye tetramethylrhodamine methyl ester, TMRM), presented differences in energy metabolism from preferential glycolysis to oxidative rates. TMRM-high cells are highly efficient in terms of oxygen consumption rate, basal and maximal respiration, and spare respiratory capacity compared to TMRM-low cells. TMRM-high cells showed characteristics of pre-committed cells and were associated with higher in vitro differentiation capacity through endothelial, cardiac-like, and, to a lesser extent, adipogenic and chondro/osteogenic cell lineage, when compared with TMRM-low cells. Conversely, TMRM-low showed higher self-renewal potential. To conclude, we identified two hCmPC populations with different metabolic profile, stemness maturity, and differentiation potential. Our findings suggest that metabolic sorting can isolate cells with higher regenerative capacity and/or long-term survival. This metabolism-based strategy to select cells may be broadly applicable to therapies.

Empagliflozin reduces the senescence of cardiac stromal cells and improves cardiac function in a murine model of diabetes

The sodium‐glucose cotransporter 2 (SGLT2) inhibitor empagliflozin reduces heart failure in diabetes, but underlying mechanisms remain elusive. We hypothesized that empagliflozin could counteract the senescence of cardiac stromal cells (CSC), the action of which limits cardiac damage and cardiac fibrosis in diabetic‐like conditions in vitro and in vivo. CSC were isolated from murine heart biopsies (n = 5) through cardiosphere (CSp) formation and incubated for 3 or 48 hours with 5.5 mmol/L normal glucose (NG), high glucose (12‐5 and 30.5 mmol/L, HG) or a hyperosmolar control of mannitol (HM) in the presence or absence of empagliflozin 100 nmol/L. The senescent CSC status was verified by β‐gal staining and expression of the pro‐survival marker Akt (pAkt) and the pro‐inflammatory marker p38 (p‐P38). The cardiac effects of empagliflozin were also studied in vivo by echocardiography and by histology in a murine model of streptozotocin (STZ)‐induced diabetes. Compared to NG, incubations with HG and HM significantly reduced the number of CSps, increased the β‐gal‐positive CSC and P‐p38, while decreasing pAkt, all reversed by empagliflozin (P < .01). Empagliflozin also reversed cardiac dysfunction, cardiac fibrosis and cell senescence in mice with (STZ)‐induced diabetes (P < .01). Empagliflozin counteracts the pro‐senescence effect of HG and of hyperosmolar stress on CSC, and improves cardiac function via decreasing cardiac fibrosis and senescence in diabetic mice, possibly through SGLT2 off‐target effects. These effects may explain empagliflozin unexpected benefits on cardiac function in diabetic patients.

Cardiac Stem Cells in the Postnatal Heart: Lessons from Development

Heart development in mammals is followed by a postnatal decline in cell proliferation and cell renewal from stem cell populations. A better understanding of the developmental changes in cardiac microenvironments occurring during heart maturation will be informative regarding the loss of adult regenerative potential. We reevaluate the adult heart's mitotic potential and the reported adult cardiac stem cell populations, as these are two topics of ongoing debate. The heart's early capacity for cell proliferation driven by progenitors and reciprocal signalling is demonstrated throughout development. The mature heart architecture and environment may be more restrictive on niches that can host progenitor cells. The engraftment issues observed in cardiac stem cell therapy trials using exogenous stem cells may indicate a lack of supporting stem cell niches, while tissue injury adds to a hostile microenvironment for transplanted cells. Engraftment may be improved by preconditioning the cultured stem cells and modulating the microenvironment to host these cells. These prospective areas of further research would benefit from a better understanding of cardiac progenitor interactions with their microenvironment throughout development and may lead to enhanced cardiac niche support for stem cell therapy engraftment.

Isolation and Characterization of Cardiac Mesenchymal Stromal Cells from Endomyocardial Bioptic Samples of Arrhythmogenic Cardiomyopathy Patients

A normal adult heart is composed of several different cell types, among which cardiac mesenchymal stromal cells represent an abundant population. The isolation of these cells offers the possibility of studying their involvement in cardiac diseases, and, in addition, provides a useful primary cell model to investigate biological mechanisms. Here, the method for the isolation of C-MSC from arrhythmogenic cardiomyopathy patients' bioptic samples is described. The endomyocardial biopsy sampling is guided in the right ventricular areas adjacent to the scar visualized by electro-anatomical mapping. The digestion of the biopsies in collagenase and their plating on a plastic dish in culture medium to allow C-MSC growth is described. The isolated cells can be expanded in culture for several passages. To confirm their mesenchymal phenotype, the description of immuno-phenotypical characterization is provided. C-MSC are able to differentiate into several cell types like adipocytes, chondrocytes, and osteoblasts: in the context of ACM, characterized by adipocyte deposits in patients' hearts, the protocols for the adipogenic differentiation of C-MSC and the characterization of lipid droplet accumulation are described.

Stable Oxidative Cytosine Modifications Accumulate in Cardiac Mesenchymal Cells From Type2 Diabetes Patients

Rationale:

Human cardiac mesenchymal cells (CMSCs) are a therapeutically relevant primary cell population. Diabetes mellitus compromises CMSC function as consequence of metabolic alterations and incorporation of stable epigenetic changes.

Objective:

To investigate the role of α-ketoglutarate (αKG) in the epimetabolic control of DNA demethylation in CMSCs.

Methods and Results:

Quantitative global analysis, methylated and hydroxymethylated DNA sequencing, and gene-specific GC methylation detection revealed an accumulation of 5-methylcytosine, 5-hydroxymethylcytosine, and 5-formylcytosine in the genomic DNA of human CMSCs isolated from diabetic donors. Whole heart genomic DNA analysis revealed iterative oxidative cytosine modification accumulation in mice exposed to high-fat diet (HFD), injected with streptozotocin, or both in combination (streptozotocin/HFD). In this context, untargeted and targeted metabolomics indicated an intracellular reduction of αKG synthesis in diabetic CMSCs and in the whole heart of HFD mice. This observation was paralleled by a compromised TDG (thymine DNA glycosylase) and TET1 (ten–eleven translocation protein 1) association and function with TET1 relocating out of the nucleus. Molecular dynamics and mutational analyses showed that αKG binds TDG on Arg275 providing an enzymatic allosteric activation. As a consequence, the enzyme significantly increased its capacity to remove G/T nucleotide mismatches or 5-formylcytosine. Accordingly, an exogenous source of αKG restored the DNA demethylation cycle by promoting TDG function, TET1 nuclear localization, and TET/TDG association. TDG inactivation by CRISPR/Cas9 knockout or TET/TDG siRNA knockdown induced 5-formylcytosine accumulation, thus partially mimicking the diabetic epigenetic landscape in cells of nondiabetic origin. The novel compound (S)-2-[(2,6-dichlorobenzoyl)amino]succinic acid (AA6), identified as an inhibitor of αKG dehydrogenase, increased the αKG level in diabetic CMSCs and in the heart of HFD and streptozotocin mice eliciting, in HFD, DNA demethylation, glucose uptake, and insulin response.

Conclusions:

Restoring the epimetabolic control of DNA demethylation cycle promises beneficial effects on cells compromised by environmental metabolic changes.

Age-dependent increase of oxidative stress regulates microRNA-29 family preserving cardiac health

The short-lived turquoise killifish Nothobranchius furzeri (Nfu) is a valid model for aging studies. Here, we investigated its age-associated cardiac function. We observed oxidative stress accumulation and an engagement of microRNAs (miRNAs) in the aging heart. MiRNA-sequencing of 5 week (young), 12–21 week (adult) and 28–40 week (old) Nfu hearts revealed 23 up-regulated and 18 down-regulated miRNAs with age. MiR-29 family turned out as one of the most up-regulated miRNAs during aging. MiR-29 family increase induces a decrease of known targets like collagens and DNA methyl transferases (DNMTs) paralleled by 5´methyl-cytosine (5mC) level decrease. To further investigate miR-29 family role in the fish heart we generated a transgenic zebrafish model where miR-29 was knocked-down. In this model we found significant morphological and functional cardiac alterations and an impairment of oxygen dependent pathways by transcriptome analysis leading to hypoxic marker up-regulation. To get insights the possible hypoxic regulation of miR-29 family, we exposed human cardiac fibroblasts to 1% O₂ levels. In hypoxic condition we found miR-29 down-modulation responsible for the accumulation of collagens and 5mC. Overall, our data suggest that miR-29 family up-regulation might represent an endogenous mechanism aimed at ameliorating the age-dependent cardiac damage leading to hypertrophy and fibrosis.