Hypertrophy of human embryonic stem cell-derived cardiomyocytes supported by positive feedback between Ca2+ and diacylglycerol signals

Evaluation of Ouabain's Tissue Distribution in C57/Black Mice Following Intraperitoneal Injection, Using Chromatography and Mass Spectrometry

Cardiotonic steroids (CTSs), such as digoxin, are used for heart failure treatment. However, digoxin permeates the brain-blood barrier (BBB), affecting central nervous system (CNS) functions. Finding a CTS that does not pass through the BBB would increase CTSs' applicability in the clinic and decrease the risk of side effects on the CNS. This study aimed to investigate the tissue distribution of the CTS ouabain following intraperitoneal injection and whether ouabain passes through the BBB. After intraperitoneal injection (1.25 mg/kg), ouabain concentrations were measured at 5 min, 15 min, 30 min, 1 h, 3 h, 6 h, and 24 h using HPLC-MS in brain, heart, liver, and kidney tissues and blood plasma in C57/black mice. Ouabain was undetectable in the brain tissue. Plasma: Cmax = 882.88 ± 21.82 ng/g; Tmax = 0.08 ± 0.01 h; T1/2 = 0.15 ± 0.02 h; MRT = 0.26 ± 0.01. Cardiac tissue: Cmax = 145.24 ± 44.03 ng/g (undetectable at 60 min); Tmax = 0.08 ± 0.02 h; T1/2 = 0.23 ± 0.09 h; MRT = 0.38 ± 0.14 h. Kidney tissue: Cmax = 1072.3 ± 260.8 ng/g; Tmax = 0.35 ± 0.19 h; T1/2 = 1.32 ± 0.76 h; MRT = 1.41 ± 0.71 h. Liver tissue: Cmax = 2558.0 ± 382.4 ng/g; Tmax = 0.35 ± 0.13 h; T1/2 = 1.24 ± 0.7 h; MRT = 0.98 ± 0.33 h. Unlike digoxin, ouabain does not cross the BBB and is eliminated quicker from all the analyzed tissues, giving it a potential advantage over digoxin in systemic administration. However, the inability of ouabain to pass though the BBB necessitates intracerebral administration when used to investigate its effects on the CNS.

Influence of acidic metabolic environment on differentiation of stem cell-derived cardiomyocytes

Stem cell-based myocardial regeneration is a frontier topic in the treatment of myocardial infarction. Manipulating the metabolic microenvironment of stem cells can influence their differentiation into cardiomyocytes, which have promising clinical applications. pH is an important indicator of the metabolic environment during cardiomyocyte development. And lactate, as one of the main acidic metabolites, is a major regulator of the acidic metabolic environment during early cardiomyocyte development. Here, we summarize the progress of research into the influence of pH value and lactate on cardiomyocyte survival and differentiation, as well as related mechanisms.

Constitutive Plasma Membrane Turnover in T-REx293 cells via Ordered Membrane Domain Endocytosis under Mitochondrial Control

Clathrin/dynamin-independent endocytosis of ordered plasma membrane domains (ordered membrane domain endocytosis, OMDE) can become massive in response to cytoplasmic Ca elevations, G protein activation by non-hydrolyzable GTP analogs, and enhanced oxidative metabolism. In patch-clamped murine bone marrow macrophages (BMMs), cytoplasmic succinate and pyruvate, but not β-hydroxybutyrate, induce OMDE of 75% of the plasma membrane within 2 min. The responses require palmitoylation of membrane proteins, being decreased by 70% in BMMs lacking the acyltransferase, DHHC5, by treatment with carnitine to shift long-chain acyl groups from cytoplasmic to mitochondrial acyl-CoAs, by bromopalmitate/albumin complexes to block DHHCs, and by the mitochondria-specific cyclosporin, NIM811, to block permeability transition pores that may release mitochondrial coenzyme A into the cytoplasm. Using T-REx293 cells, OMDE amounts to 40% with succinate, pyruvate, or GTPγS, and it is inhibited by actin cytoskeleton disruption. Pyruvate-induced OMDE is blocked by the hydrophobic antioxidant, edaravone, which prevents permeability transition pore openings. Using fluorescent 3kD dextrans to monitor endocytosis, OMDE appears to be constitutively active in T-REx293 cells but not in BMMs. After 1 h without substrates or bicarbonate, pyruvate and hydroxybutyrate inhibit constitutive OMDE, as expected for a shift of CoA from long-chain acyl-CoAs to other CoA metabolites. In the presence of bicarbonate, pyruvate strongly enhances OMDE, which is then blocked by β-hydroxybutyrate, bromopalmitate/albumin complexes, cyclosporines, or edaravone. After pyruvate responses, T-REx293 cells grow normally with no evidence for apoptosis. Fatty acid-free albumin (15 μM) inhibits basal OMDE in T-REx293 cells, as do cyclosporines, carnitine, and RhoA blockade. Surprisingly, OMDE in the absence of substrates and bicarbonate is not inhibited by siRNA knockdown of the acyltransferases, DHHC5 or DHHC2, which are required for activated OMDE in patch clamp experiments. We verify biochemically that small CoA metabolites decrease long-chain acyl-CoAs. We verify also that palmitoylations of many PM-associated proteins decrease and increase when OMDE is inhibited and stimulated, respectively, by different metabolites. STED microscopy reveals that vesicles formed during constitutive OMDE in T-REX293 cells have 90 to 130 nm diameters. In summary, OMDE is likely a major G-protein-dependent endocytic mechanism that can be constitutively active in some cell types, albeit not BMMs. OMDE depends on different DHHC acyltransferases in different circumstances and can be limited by local supplies of fatty acids, CoA, and long-chain acyl-CoAs.

The Multifunctional TRPC6 Protein: Significance in the Field of Cardiovascular Studies

Cardiovascular disease is the leading cause of death, medical complications, and healthcare costs. Although recent advances have been in treating cardiovascular disorders linked with a reduced ejection fraction, acutely decompensate cardiac failure remains a significant medical problem. The transient receptor potential cation channel (TRPC6) family responds to neurohormonal and mechanical stress, playing critical roles in cardiovascular diseases. Therefore, TRP C6 channels have great promise as therapeutic targets. Numerous studies have investigated the roles of TRP C6 channels in pain neurons, highlighting their significance in cardiovascular research. The TRPC6 protein exhibits a broad distribution in various organs and tissues, including the brain, nerves, heart, blood vessels, lungs, kidneys, gastrointestinal tract, and other bodily structures. Its activation can be triggered by alterations in osmotic pressure, mechanical stimulation, and diacylglycerol. Consequently, TRPC6 plays a significant role in the pathophysiological mechanisms underlying diverse diseases within living organisms. A recent study has indicated a strong correlation between the disorder known as TRPC6 and the development of cardiovascular diseases. Consequently, investigations into the association between TRPC6 and cardiovascular diseases have gained significant attention in the scientific community. This review explores the most recent developments in the recognition and characterization of TRPC6. Additionally, it considers the field's prospects while examining how TRPC6 might be altered and its clinical applications.

Longitudinal diffusion barriers imposed by myofilaments and mitochondria in murine cardiac myocytes

Using optical and electrical methods, we document that diffusion in the cytoplasm of BL6 murine cardiomyocytes becomes restricted >20-fold as molecular weight increases from 30 to 2,000, roughly as expected for pores with porin channel dimensions. Bodipy-FL ATP diffuses >40-fold slower than in free water at 25°C. From several fluorophores analyzed, bound fluorophore fractions range from 0.1 for a 2 kD FITC-labeled polyethylene glycol to 0.93 for sulforhodamine. Unbound fluorophores diffuse at 0.5-8 × 10-7 cm2/s (5-80 μm2/s). Analysis of Na/K pump and veratridine-modified Na channel currents suggests that Na diffusion is nearly unrestricted at 35°C (time constant for equilibration with the pipette tip, ∼20 s). Using multiple strategies, we estimate that at 35°C, ATP diffuses four to eight times slower than in free water. To address whether restrictions are caused more by protein or membrane networks, we verified first that a protein gel, 10 g% gelatin, restricts diffusion with strong dependence on molecular weight. Solute diffusion in membrane-extracted cardiac myofilaments, confined laterally by suction into large-diameter pipette tips, is less restricted than in intact myocytes. Notably, myofilaments extracted similarly from skeletal (diaphragm) myocytes are less restrictive. Solute diffusion in myocytes with sarcolemma permeabilized by β-escin (80 µM) is similar to diffusion in intact myocytes. Restrictions are strain-dependent, being twofold greater in BL6 myocytes than in CD1/J6/129svJ myocytes. Furthermore, longitudinal diffusion is 2.5-fold more restricted in CD1/J6/129svJ myocytes lacking the mitochondrial porin, VDAC1, than in WT CD1/J6/129svJ myocytes. Thus, mitochondria networks restrict long-range diffusion while presumably optimizing nucleotide transfer between myofilaments and mitochondria. We project that diffusion restrictions imposed by both myofilaments and the outer mitochondrial membrane are important determinants of total free cytoplasmic AMP and ADP (∼10 μM). However, the capacity of diffusion to deliver ATP to myofilaments remains ∼100-fold greater than ATP consumption.

Ferroptosis in calcium oxalate kidney stone formation and the possible regulatory mechanism of ANKRD1

The objective of this study was to explore the role of ferroptosis in the formation of calcium oxalate (CaOx) kidney stones and the regulatory mechanism of the ankyrin repeat domain 1 (ANKRD1) gene. The study found that the Nrf2/HO-1 and p53/SLC7A11 signaling pathways were activated in the kidney stone model group, and the expression of the ferroptosis marker proteins SLC7A11 and GPX4 was significantly reduced, while the expression of ACSL4 was significantly increased. The expression of the iron transport-related proteins CP and TF increased significantly, and Fe²⁺ accumulated in the cell. The expression of HMGB1 increased significantly. In addition, the level of intracellular oxidative stress was increased. The gene with the most significant difference caused by CaOx crystals in HK-2 cells was ANKRD1. Silencing or overexpression of ANKRD1 by lentiviral infection technology regulated the expression of the p53/SLC7A11 signaling pathway, which regulated the ferroptosis induced by CaOx crystals. In conclusion, CaOx crystals can mediate ferroptosis through the Nrf2/HO-1 and p53/SLC7A11 pathways, thereby weakening the resistance of HK-2 cells to oxidative stress and other unfavorable factors, enhancing cell damage, and increasing crystal adhesion and CaOx crystal deposition in the kidney. ANKRD1 participates in the formation and development of CaOx kidney stones by activating ferroptosis mediated by the p53/SLC7A11 pathway.

The generation of a lactate-rich environment stimulates cell cycle progression and modulates gene expression on neonatal and hiPSC-derived cardiomyocytes

In situ tissue engineering strategies are a promising approach to activate the endogenous regenerative potential of the cardiac tissue helping the heart to heal itself after an injury. However, the current use of complex reprogramming vectors for the activation of reparative pathways challenges the easy translation of these therapies into the clinic. Here, we evaluated the response of mouse neonatal and human induced pluripotent stem cell-derived cardiomyocytes to the presence of exogenous lactate, thus mimicking the metabolic environment of the fetal heart. An increase in cardiomyocyte cell cycle activity was observed in the presence of lactate, as determined through Ki67 and Aurora-B kinase. Gene expression and RNA-sequencing data revealed that cardiomyocytes incubated with lactate showed upregulation of BMP10, LIN28 or TCIM in tandem with downregulation of GRIK1 or DGKK among others. Lactate also demonstrated a capability to modulate the production of inflammatory cytokines on cardiac fibroblasts, reducing the production of Fas, Fraktalkine or IL-12p40, while stimulating IL-13 and SDF1a. In addition, the generation of a lactate-rich environment improved ex vivo neonatal heart culture, by affecting the contractile activity and sarcomeric structures and inhibiting epicardial cell spreading. Our results also suggested a common link between the effect of lactate and the activation of hypoxia signaling pathways. These findings support a novel use of lactate in cardiac tissue engineering, modulating the metabolic environment of the heart and thus paving the way to the development of lactate-releasing platforms for in situ cardiac regeneration.

Multi-Omics Characterization of a Human Stem Cell-Based Model of Cardiac Hypertrophy

Cardiac hypertrophy is an important and independent risk factor for the development of cardiac myopathy that may lead to heart failure. The mechanisms underlying the development of cardiac hypertrophy are yet not well understood. To increase the knowledge about mechanisms and regulatory pathways involved in the progression of cardiac hypertrophy, we have developed a human induced pluripotent stem cell (hiPSC)-based in vitro model of cardiac hypertrophy and performed extensive characterization using a multi-omics approach. In a series of experiments, hiPSC-derived cardiomyocytes were stimulated with Endothelin-1 for 8, 24, 48, and 72 h, and their transcriptome and secreted proteome were analyzed. The transcriptomic data show many enriched canonical pathways related to cardiac hypertrophy already at the earliest time point, e.g., cardiac hypertrophy signaling. An integrated transcriptome–secretome analysis enabled the identification of multimodal biomarkers that may prove highly relevant for monitoring early cardiac hypertrophy progression. Taken together, the results from this study demonstrate that our in vitro model displays a hypertrophic response on both transcriptomic- and secreted-proteomic levels. The results also shed novel insights into the underlying mechanisms of cardiac hypertrophy, and novel putative early cardiac hypertrophy biomarkers have been identified that warrant further investigation to assess their potential clinical relevance.

Measuring hypertrophy in neonatal rat primary cardiomyocytes and human iPSC-derived cardiomyocytes

In the heart, left ventricular hypertrophy is initially an adaptive mechanism that increases wall thickness to preserve normal cardiac output and function in the face of coronary artery disease or hypertension. Cardiac hypertrophy develops in response to pressure and volume overload but can also be seen in inherited cardiomyopathies. As the wall thickens, it becomes stiffer impairing the distribution of oxygenated blood to the rest of the body. With complex cellular signalling and transcriptional networks involved in the establishment of the hypertrophic state, several model systems have been developed to better understand the molecular drivers of disease. Immortalized cardiomyocyte cell lines, primary rodent and larger animal models have all helped understand the pathological mechanisms underlying cardiac hypertrophy. Induced pluripotent stem cell-derived cardiomyocytes are also used and have the additional benefit of providing access to human samples with direct disease relevance as when generated from patients suffering from hypertrophic cardiomyopathies. Here, we briefly review in vitro and in vivo model systems that have been used to model hypertrophy and provide detailed methods to isolate primary neonatal rat cardiomyocytes as well as to generate cardiomyocytes from human iPSCs. We also describe how to model hypertrophy in a "dish" using gene expression analysis and immunofluorescence combined with automated high-content imaging.

The role of hormones and neurons in cardiomyocyte maturation

The heart undergoes profound morphological and functional changes as it continues to mature postnatally. However, this phase of cardiac development remains understudied. More recently, cardiac maturation research has attracted a lot of interest due to the need for more mature stem cell-derived cardiomyocytes for disease modeling, drug screening and heart regeneration. Additionally, neonatal heart injury models have been utilized to study heart regeneration, and factors regulating postnatal heart development have been associated with adult cardiac disease. Critical components of cardiac maturation are systemic and local biochemical cues. Specifically, cardiac innervation and the concentration of various metabolic hormones appear to increase perinatally and they have striking effects on cardiomyocytes. Here, we first report some of the key parameters of mature cardiomyocytes and then discuss the specific effects of neurons and hormonal cues on cardiomyocyte maturation. We focus primarily on the structural, electrophysiologic, metabolic, hypertrophic and hyperplastic effects of each factor. This review highlights the significance of underappreciated regulators of cardiac maturation and underscores the need for further research in this exciting field.

Cardiac hypertrophy in a dish: a human stem cell based model

Cardiac hypertrophy is an important and independent risk factor for the development of heart failure. To better understand the mechanisms and regulatory pathways involved in cardiac hypertrophy, there is a need for improved in vitro models. In this study, we investigated how hypertrophic stimulation affected human induced pluripotent stem cell (iPSC)-derived cardiomyocytes (CMs). The cells were stimulated with endothelin-1 (ET-1) for 8, 24, 48, 72, or 96 h. Parameters including cell size, ANP-, proBNP-, and lactate concentration were analyzed. Moreover, transcriptional profiling using RNA-sequencing was performed to identify differentially expressed genes following ET-1 stimulation. The results show that the CMs increase in size by approximately 13% when exposed to ET-1 in parallel to increases in ANP and proBNP protein and mRNA levels. Furthermore, the lactate concentration in the media was increased indicating that the CMs consume more glucose, a hallmark of cardiac hypertrophy. Using RNA-seq, a hypertrophic gene expression pattern was also observed in the stimulated CMs. Taken together, these results show that hiPSC-derived CMs stimulated with ET-1 display a hypertrophic response. The results from this study also provide new molecular insights about the underlying mechanisms of cardiac hypertrophy and may help accelerate the development of new drugs against this condition.