Cardiomyogenesis of embryonic stem cells upon purinergic receptor activation by ADP and ATP

Zoxazolamine-induced stimulation of cardiomyogenesis from embryonic stem cells is mediated by Ca2+, nitric oxide and ATP release

Ca²⁺-activated potassium (K_Ca) channels of small and intermediate conductance influence proliferation, apoptosis, and cell metabolism. We analysed whether prolonged activation of K_Ca channels by zoxazolamine (ZOX) induces differentiation of mouse embryonic stem (ES) cells towards cardiomyocytes. ZOX treatment of ES cells dose-dependent increased the number and diameter of cardiac foci, the frequency of contractions as well as mRNA expression of the cardiac transcription factor Nkx-2.5, the cardiac markers cardiac troponin I (cTnI), α-myosin heavy chain (α-MHC), ventricular myosin light chain-2 (MLC2v), and the pacemaker hyperpolarization-activated, cyclic nucleotide-gated 4 channel (HCN4). ZOX induced hyperpolarization of membrane potential due to activation of IK_Ca, raised intracellular Ca²⁺ concentration ([Ca²⁺]_i) and nitric oxide (NO) in a Ca²⁺-dependent manner. The Ca²⁺ response to ZOX was inhibited by chelation of Ca²⁺ with BAPTA-AM, release of Ca²⁺ from intracellular stores by thapsigargin and the phospholipase C (PLC) antagonist U73,122. Moreover, the ZOX-induced Ca²⁺ response was blunted by the purinergic receptor antagonist pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid (PPADS) as well as the specific P2Y₁ antagonist MRS 2,179, suggesting purinergic receptor-stimulated signal transduction. Consequently, ZOX initiated ATP release from differentiating ES cells, which was inhibited by the chloride channel inhibitor NPPB and the gap junction inhibitor carbenoxolone (CBX). The stimulation of cardiomyogenesis by ZOX was blunted by the nitric oxide synthase (NOS) inhibitor l-NAME, as well as CBX and NPPB. In summary, our data suggest that ZOX enhances cardiomyogenesis of ES cells by ATP release presumably through gap junctional hemichannels, purinergic receptor activation and intracellular Ca²⁺ response, thus promoting NO generation.

Longitudinal metabolic profiling of cardiomyocytes derived from human-induced pluripotent stem cells

Human-induced pluripotent stem cells (h-iPSCs) are a unique in vitro model for cardiovascular research. To realize the potential applications of h-iPSCs-derived cardiomyocytes (CMs) for drug testing or regenerative medicine and disease modeling, characterization of the metabolic features is critical. Here, we show the transcriptional profile during stages of cardiomyogenesis of h-iPSCs-derived CMs. CM differentiation was not only characterized by the expression of mature structural components (MLC2v, MYH7) but also accompanied by a significant increase in mature metabolic gene expression and activity. Our data revealed a distinct substrate switch from glucose to fatty acids utilization for ATP production. Basal respiration and respiratory capacity in 9 days h-iPSCs-derived CMs were glycolysis-dependent with a shift towards a more oxidative metabolic phenotype at 14 and 28 day old CMs. Furthermore, mitochondrial analysis characterized the early and mature forms of mitochondria during cardiomyogenesis. These results suggest that changes in cellular metabolic phenotype are accompanied by increased O₂ consumption and ATP synthesis to fulfill the metabolic needs of mature CMs activity. To further determine functionality, the physiological response of h-iPSCs-derived CMs to β-adrenergic stimulation was tested. These data provide a unique in vitro human heart model for the understanding of CM physiology and metabolic function which may provide useful insight into metabolic diseases as well as novel therapeutic options.

P2X7 receptor in cardiovascular disease: The heart side

The P2X7 receptor is a ligand-gated purinergic receptor activated by extracellular ATP. The receptor is highly expressed in immune cells and in the brain, and, upon activation, the P2X7 receptor allows a cation flux, leading to the distinct activation of intracellular signalling pathways as the secretion of pro-inflammatory cytokines, and modulation of cell survival. Through these molecular mechanisms, P2X7 is known to play important roles in physiology and pathophysiology of a wide spectrum of diseases, including cancer, inflammatory diseases, neurological, respiratory and more recently cardiovascular diseases. Recent studies demonstrated that the P2X7 could modulate the assembly of the NLRP3 inflammasome, leading to the secretion of pro-inflammatory factors and worsen the cardiac disease phenotypes. This review discusses the critical molecular function of P2X7 in the modulation of the onset, progression and resolution of cardiovascular diseases and analyses the putative future use of P2X7-based therapies that modulate the IL-1β secretion arm and direct P2X7 antagonists.

ATP-induced Ca2+-signalling mechanisms in the regulation of mesenchymal stem cell migration

The ability of cells to migrate to the destined tissues or lesions is crucial for physiological processes from tissue morphogenesis, homeostasis and immune responses, and also for stem cell-based regenerative medicines. Cytosolic Ca²⁺ is a primary second messenger in the control and regulation of a wide range of cell functions including cell migration. Extracellular ATP, together with the cognate receptors on the cell surface, ligand-gated ion channel P2X receptors and a subset of G-protein-coupled P2Y receptors, represents common autocrine and/or paracrine Ca²⁺ signalling mechanisms. The P2X receptor ion channels mediate extracellular Ca²⁺ influx, whereas stimulation of the P2Y receptors triggers intracellular Ca²⁺ release from the endoplasmic reticulum (ER), and activation of both type of receptors thus can elevate the cytosolic Ca²⁺ concentration ([Ca²⁺]_c), albeit with different kinetics and capacity. Reduction in the ER Ca²⁺ level following the P2Y receptor activation can further induce store-operated Ca²⁺ entry as a distinct Ca²⁺ influx pathway that contributes in ATP-induced increase in the [Ca²⁺]_c. Mesenchymal stem cells (MSC) are a group of multipotent stem cells that grow from adult tissues and hold promising applications in tissue engineering and cell-based therapies treating a great and diverse number of diseases. There is increasing evidence to show constitutive or evoked ATP release from stem cells themselves or mature cells in the close vicinity. In this review, we discuss the mechanisms for ATP release and clearance, the receptors and ion channels participating in ATP-induced Ca²⁺ signalling and the roles of such signalling mechanisms in mediating ATP-induced regulation of MSC migration.

Purinergic Signaling in the Cardiovascular System

There is nervous control of the heart by ATP as a cotransmitter in sympathetic, parasympathetic, and sensory-motor nerves, as well as in intracardiac neurons. Centers in the brain control heart activities and vagal cardiovascular reflexes involve purines. Adenine nucleotides and nucleosides act on purinoceptors on cardiomyocytes, AV and SA nodes, cardiac fibroblasts, and coronary blood vessels. Vascular tone is controlled by a dual mechanism. ATP, released from perivascular sympathetic nerves, causes vasoconstriction largely via P2X1 receptors. Endothelial cells release ATP in response to changes in blood flow (via shear stress) or hypoxia, to act on P2 receptors on endothelial cells to produce nitric oxide, endothelium-derived hyperpolarizing factor, or prostaglandins to cause vasodilation. ATP is also released from sensory-motor nerves during antidromic reflex activity, to produce relaxation of some blood vessels. Purinergic signaling is involved in the physiology of erythrocytes, platelets, and leukocytes. ATP is released from erythrocytes and platelets, and purinoceptors and ectonucleotidases are expressed by these cells. P1, P2Y₁, P2Y₁₂, and P2X1 receptors are expressed on platelets, which mediate platelet aggregation and shape change. Long-term (trophic) actions of purine and pyrimidine nucleosides and nucleotides promote migration and proliferation of vascular smooth muscle and endothelial cells via P1 and P2Y receptors during angiogenesis, vessel remodeling during restenosis after angioplasty and atherosclerosis. The involvement of purinergic signaling in cardiovascular pathophysiology and its therapeutic potential are discussed, including heart failure, infarction, arrhythmias, syncope, cardiomyopathy, angina, heart transplantation and coronary bypass grafts, coronary artery disease, diabetic cardiomyopathy, hypertension, ischemia, thrombosis, diabetes mellitus, and migraine.

Coupling switch of P2Y-IP3 receptors mediates differential Ca(2+) signaling in human embryonic stem cells and derived cardiovascular progenitor cells

Purinergic signaling mediated by P2 receptors (P2Rs) plays important roles in embryonic and stem cell development. However, how it mediates Ca(2+) signals in human embryonic stem cells (hESCs) and derived cardiovascular progenitor cells (CVPCs) remains unclear. Here, we aimed to determine the role of P2Rs in mediating Ca(2+) mobilizations of these cells. hESCs were induced to differentiate into CVPCs by our recently established methods. Gene expression of P2Rs and inositol 1,4,5-trisphosphate receptors (IP3Rs) was analyzed by quantitative/RT-PCR. IP3R3 knockdown (KD) or IP3R2 knockout (KO) hESCs were established by shRNA- or TALEN-mediated gene manipulations, respectively. Confocal imaging revealed that Ca(2+) responses in CVPCs to ATP and UTP were more sensitive and stronger than those in hESCs. Consistently, the gene expression levels of most P2YRs except P2Y1 were increased in CVPCs. Suramin or PPADS blocked ATP-induced Ca(2+) transients in hESCs but only partially inhibited those in CVPCs. Moreover, the P2Y1 receptor-specific antagonist MRS2279 abolished most ATP-induced Ca(2+) signals in hESCs but not in CVPCs. P2Y1 receptor-specific agonist MRS2365 induced Ca(2+) transients only in hESCs but not in CVPCs. Furthermore, IP3R2KO but not IP3R3KD decreased the proportion of hESCs responding to MRS2365. In contrast, both IP3R2 and IP3R3 contributed to UTP-induced Ca(2+) responses while ATP-induced Ca(2+) responses were more dependent on IP3R2 in the CVPCs. In conclusion, a predominant role of P2Y1 receptors in hESCs and a transition of P2Y-IP3R coupling in derived CVPCs are responsible for the differential Ca(2+) mobilization between these cells.