Two Stem Cell Populations Including VSELs and CSCs Detected in the Pericardium of Adult Mouse Heart

Do PGCCs in Solid Tumors Appear Due to Treatment-related Stress or Clonal Expansion of CSCs that Survive Oncotherapy?

Dedifferentiation of epithelial cells during epithelial-mesenchymal transition (EMT) results in circulating tumor cells (CTCs) that are mobilized singly or in clusters in association with blood cells and results in metastasis. However, lineage tracing studies have failed to delineate any role of EMT during metastasis. Research is also focused on polyploid giant cancer cells (PGCCs) in solid tumors which appear in response to oncotherapy-related stress for their role in metastasis. But how to explain PGCCs role in metastatic tumors in treatment-naïve patients? Studies done using mouse models and clinical samples suggest that cancer initiates due to dysfunctions of tissue-resident, pluripotent very small embryonic-like stem cells (VSELs). VSELs are the most primitive and pluripotent stem cells that exist at top of cellular hierarchy in multiple tissues. They are normally quiescent and undergo asymmetrical cell divisions to give rise to two cells of different sizes and fates including smaller cells to self-renew and bigger tissue-specific progenitors. Progenitors undergo symmetrical cell divisions and clonal expansion (rapid proliferation, endoduplication with incomplete cytokinesis) to form giant cells that further breakdown and differentiate into tissue-specific cell types. Oncotherapy destroys actively dividing cells, but CSCs survive. We hypothesize that excessive self-renewal and clonal expansion of cancer stem cells (CSCs, dysfunctional VSELs) result in multinucleated giant cells (PGCCs) that accumulate as further differentiation into tissue-specific cell types is blocked in cancerous conditions. PGCCS are being reported by multiple groups whereas CSCs remain elusive due to small size and low abundance and actually contribute to both cancer initiation and metastasis.

Small extracellular vesicles enhance the survival of Sca-1+ cardiac stem cells against ROS-induced ischemic-reoxygenation injury in vitro

BACKGROUND

Ischemic reperfusion (IR) generates reactive oxygen species (ROS) that inevitably result in myocardial cell death and heart failure. The regenerative power of cardiac progenitor/stem pools (CSCs), especially the Sca1+ population, in response to IR injury remains unclear.

METHODS

Our work sought to investigate whether small extracellular vesicles (sEVs) isolated from bone marrow-mesenchymal stem cells (BMMSCs) could rescue CSCs, specifically Sca-1+/CSCs, from IR by increasing their proliferative capacity and limiting their apoptosis in vitro. The Sca-1+/CSCs-IR model was induced by the oxygen-glucose deprivation/reoxygenation method (OGD/R). The effects of treatment with BMMSCs-derived sEVs on oxidative stress, cell proliferation, apoptosis, and cell cycle were assessed. To further test the mechanistic action, we assessed the PTEN/pAkt/HIF-1α pathway.

RESULTS

Compared to hypoxic untreated CSCs, BMMSCs-derived sEVs-treated cells had shifted from their quiescent to proliferative phase (p > 0.05) and showed decreased apoptosis (p < 0.001). sEVs-treated CSCs were predominately in the S phase (11.8 ± 0.9%) (p < 0.01). We identified an abundance of miRNA-21-5P in BMMSCs. HIF-1α expression was highest in CSCs treated with sEVs (p < 0.05). Moreover, miRNA-21-5p-rich sEVs shifted the redox state, reducing oxidative stress and promoting balance (p > 0.05).

CONCLUSION

Conditioning Sca-1+/CSCs, an essential population in the postnatal heart, with sEVs rich in miRNA-21 robustly enhanced the proliferation, and synthesis phase of the cell cycle, and stabilized HIF-1α while alleviating oxidative stress and apoptosis. Such sEVs rich in miRNA-21-5p can be further used as a preconditioning tool to enhance endogenous Sca-1+/CSCs regeneration in response to IR injury.

Murine and Human-Purified very Small Embryonic-like Stem Cells (VSELs) Express Purinergic Receptors and Migrate to Extracellular ATP Gradient

Purinergic signaling is an ancient primordial signaling system regulating tissue development and specification of various types of stem cells. Thus, functional purinergic receptors are present in several types of cells in the body, including multiple populations of stem cells. However, one stem cell type that has not been evaluated for expression of purinergic receptors is very small embryonic stem cells (VSELs) isolated from postnatal tissues. Herein, we report that human umbilical cord blood (UCB) and murine bone marrow (BM) purified VSELs express mRNA for P1 and P2 purinergic receptors and CD39 and CD73 ectonucleotidases converting extracellular ATP (eATP) into its signaling metabolite extracellular adenosine (eAdo), that antagonizes eATP effects. More importantly, we demonstrate that human and murine VSELs respond by chemotaxis to eATP, and eAdo inhibits this migration. These responses to eATP are mediated by activation of Nlrp3 inflammasome, and exposure of VSELs to its specific inhibitor MCC950 abolished the chemotactic response to ATP. We conclude that purinergic signaling plays an essential, underappreciated role in the biology of these cells and their potential role in response to tissue/organ injuries.

Cardiac Differentiation of Mesenchymal Stem Cells: Impact of Biological and Chemical Inducers

Cardiovascular disorders (CVDs) are the leading cause of global death, widely occurs due to irreparable loss of the functional cardiomyocytes. Stem cell-based therapeutic approaches, particularly the use of Mesenchymal Stem Cells (MSCs) is an emerging strategy to regenerate myocardium and thereby improving the cardiac function after myocardial infarction (MI). Most of the current approaches often employ the use of various biological and chemical factors as cues to trigger and modulate the differentiation of MSCs into the cardiac lineage. However, the recent advanced methods of using specific epigenetic modifiers and exosomes to manipulate the epigenome and molecular pathways of MSCs to modify the cardiac gene expression yield better profiled cardiomyocyte like cells in vitro. Hitherto, the role of cardiac specific inducers triggering cardiac differentiation at the cellular and molecular level is not well understood. Therefore, the current review highlights the impact and recent trends in employing biological and chemical inducers on cardiac differentiation of MSCs. Thereby, deciphering the interactions between the cellular microenvironment and the cardiac inducers will help us to understand cardiomyogenesis of MSCs. Additionally, the review also provides an insight on skeptical roles of the cell free biological factors and extracellular scaffold assisted mode for manipulation of native and transplanted stem cells towards translational cardiac research.