Quantitative proteomics and systems analysis of cultured H9C2 cardiomyoblasts during differentiation over time supports a 'function follows form' model of differentiation

Regulation of mitochondrial calcium uniporter expression and calcium-dependent cell signaling by lncRNA Tug1 in cardiomyocytes

Cardiomyocyte calcium homeostasis is a tightly regulated process. The mitochondrial calcium uniporter (MCU) complex can buffer elevated cytosolic Ca2+ levels and consists of pore-forming proteins including MCU, and various regulatory proteins such as mitochondrial calcium uptake proteins 1 and 2 (MICU1/2). The stoichiometry of these proteins influences the sensitivity to Ca2+ and the activity of the complex. However, the factors that regulate their gene expression remain incompletely understood. Long noncoding RNAs (lncRNAs) regulate gene expression through various mechanisms, and we recently found that the lncRNA Tug1 increased the expression of Mcu and associated genes. To further explore this, we performed antisense LNA knockdown of Tug1 (Tug1 KD) in H9c2 rat cardiomyocytes. Tug1 KD increased MCU protein expression, yet pyruvate dehydrogenase dephosphorylation, which is indicative of mitochondrial Ca2+ uptake, was not enhanced. However, RNA-seq revealed that Tug1 KD increased Mcu along with differential expression of >1,000 genes including many related to Ca2+ regulation pathways in the heart. To understand the effect of this on Ca2+ signaling, we measured phosphorylation of Ca2+/calmodulin-dependent protein kinase II (CaMKII) and its downstream target cAMP Response Element-Binding protein (CREB), a transcription factor known to drive Mcu gene expression. In response to a Ca2+ stimulus, the increase in CaMKII and CREB phosphorylation was attenuated by Tug1 KD. Inhibition of CaMKII, but not CREB, partially prevented the Tug1 KD-mediated increase in Mcu. Together, these data suggest that Tug1 modulates MCU expression via a mechanism involving CaMKII and regulates cardiomyocyte Ca2+ signaling, which could have important implications for cardiac function.NEW & NOTEWORTHY Calcium is essential for signaling, excitation contraction, and energy homeostasis in the heart. Despite this, molecular regulators of these processes are not completely understood. We report that knockdown of lncRNA Tug1 alters the calcium handling transcriptome and increases mitochondrial calcium uniporter expression via a mechanism involving CaMKII. As overexpression of MCU is known to be protective against pathological cardiac remodeling, targeting Tug1 may be a potential strategy for treating cardiovascular disease.

The retinoic acid response is a minor component of the cardiac phenotype in H9c2 myoblast differentiation

The H9c2 myoblast cell line, isolated from the left ventricular tissue of rat, is currently used in vitro as a mimetic for skeletal and cardiac muscle due to its biochemical, morphological, and electrical/hormonal signaling properties. During culture, H9c2 cells acquire a myotube phenotype, where a critical component is the inclusion of retinoic acid (RA). The results from some authors on H9c2 suggested that thousands of genes respond to RA stimuli, while others report hundreds of genes responding to RA over different cell types. In this article, using a more appropriate experimental design, we first confirm the H9c2 cardiac phenotype with and without RA and report transcriptomic and physiological changes regarding calcium handling, bioenergetics, and other biological concepts. Interestingly, of the 2360 genes showing a transcriptional change, 622 genes were statistically associated with the RA response. Of these genes, only 305 were RA-specific, and the rest also showed a culture-time component. Thus, the major expression changes (from 74 to 87%) were indeed due to culture conditions over time. Unexpectedly, only a few components of the retinol pathway in KEGG responded to RA. Our results show the role of RA in the H9c2 cultures impacting the interpretation using H9c2 as an in vitro model.

Natural Guanine Derivatives Exert PARP-Inhibitory and Cytoprotective Effects in a Model of Cardiomyocyte Damage under Oxidative Stress

Inhibitors of human poly(ADP-ribose) polymerase (PARP) are considered as promising agents for treatment of cardiovascular, neurological, and other diseases accompanied by inflammation and oxidative stress. Previously, the ability of natural compounds 7-methylguanine (7mGua) and 8-hydroxy-7-methylguanine (8h7mGua) to suppress activity of the recombinant PARP protein was demonstrated. In the present work, we have investigated the possibility of PARP-inhibitory and cytoprotective action of 7mGua and 8h7mGua against the rat cardiomyoblast cultures (undifferentiated and differentiated H9c2). It was found that 7mGua and 8h7mGua rapidly penetrate into the cells and effectively suppress the H2O2-stimulated PARP activation (IC50 = 270 and 55 μM, respectively). The pronounced cytoprotective effects of 7mGua and 8h7mGua were shown in a cellular model of oxidative stress, and effectiveness of 8h7mGua exceeded the classic PARP inhibitor 3-aminobenzamide. The obtained data indicate promise for the development of PARP inhibitors based on guanine derivatives and their testing using the models of ischemia-reperfusion tissue damage.

Titanium Dioxide (E171) Induces Toxicity in H9c2 Rat Cardiomyoblasts and Ex Vivo Rat Hearts

Cardiovascular diseases are the leading cause of death worldwide. Food-grade TiO₂ (E171) is the most widely used additive in the food industry. Existing evidence shows TiO₂ nanoparticles reach systemic circulation through biological barriers, penetrate cell membranes, accumulate in cells of different organs, and cause damage; however, their effects on cardiac cells and the development of heart diseases are still unexplored. Therefore, in this work, we tested E171 toxicity in rat cardiomyoblasts and hearts. E171 internalization and impact on cell viability, proliferation, mitochondria, lysosomes, F-actin distribution, and cell morphology were evaluated in H9c2 cells. Additionally, effects of E171 were measured on cardiac function in ex vivo rat hearts. E171 was uptaken by cells and translocated into the cytoplasm. E171 particles changed cell morphology reducing proliferation and metabolic activity. Higher caspase-3 and caspase-9 expression as well as Tunel-positive cells induced by E171 exposure indicate apoptotic death. Mitochondrial and lysosome alterations resulting from mitophagy were detected after 24 and 48 h exposure, respectively. Additionally, high E171 concentrations caused rearrangements of the F-actin cytoskeleton. Finally, hearts exposed to E171 showed impaired cardiac function. These results support E171 toxicity in cardiac cells in vitro altering cardiac function in an ex vivo model, indicating that consumption of this food additive could be toxic and may lead to the development of cardiovascular disease.

The effect of all-trans retinoic acid on the mitochondrial function and survival of cardiomyoblasts exposed to local photodamage

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The Effects of Mechanical Loading Variations on the Hypertrophic, Anti-Apoptotic, and Anti-Inflammatory Responses of Differentiated Cardiomyocyte-like H9C2 Cells

Cardiomyocytes possess the ability to respond to mechanical stimuli by adapting their biological functions. This study investigated cellular and molecular events in cardiomyocyte-like H9C2 cells during differentiation as well as the signalling and gene expression responses of the differentiated cells under various mechanical stretching protocols in vitro. Immunofluorescence was used to monitor MyHC expression and structural changes during cardiomyoblast differentiation. Moreover, alterations in the expression of cardiac-specific markers, cell cycle regulatory factors, MRFs, hypertrophic, apoptotic, atrophy and inflammatory factors, as well as the activation of major intracellular signalling pathways were evaluated during differentiation and under mechanical stretching of the differentiated H9C2 cells. Compared to undifferentiated cells, advanced-differentiation cardiomyoblasts exhibited increased expression of cardiac-specific markers, MyHC, MRFs, and IGF-1 isoforms. Moreover, differentiated cells that underwent a low strain/frequency mechanical loading protocol of intermediate duration showed enhanced expression of MRFs and hypertrophic factors, along with a decreased expression of apoptotic, atrophy, and inflammatory factors compared to both high-strain/frequency loading protocols and to unloaded cells. These findings suggest that altering the strain and frequency of mechanical loading applied on differentiated H9C2 cardiomyoblasts can regulate their anabolic/survival program, with a low-strain/frequency stretching being, overall, most effective at inducing beneficial responses.

The CEP5 Peptide Promotes Abiotic Stress Tolerance, As Revealed by Quantitative Proteomics, and Attenuates the AUX/IAA Equilibrium in Arabidopsis

Peptides derived from non-functional precursors play important roles in various developmental processes, but also in (a)biotic stress signaling. Our (phospho)proteome-wide analyses of C-TERMINALLY ENCODED PEPTIDE 5 (CEP5)-mediated changes revealed an impact on abiotic stress-related processes. Drought has a dramatic impact on plant growth, development and reproduction, and the plant hormone auxin plays a role in drought responses. Our genetic, physiological, biochemical, and pharmacological results demonstrated that CEP5-mediated signaling is relevant for osmotic and drought stress tolerance in Arabidopsis, and that CEP5 specifically counteracts auxin effects. Specifically, we found that CEP5 signaling stabilizes AUX/IAA transcriptional repressors, suggesting the existence of a novel peptide-dependent control mechanism that tunes auxin signaling. These observations align with the recently described role of AUX/IAAs in stress tolerance and provide a novel role for CEP5 in osmotic and drought stress tolerance.

Down-regulation of CK2α correlates with decreased expression levels of DNA replication minichromosome maintenance protein complex (MCM) genes

Protein kinase CK2 is a serine/threonine kinase composed of two catalytic subunits (CK2α and/or CK2α’) and two regulatory subunits (CK2β). It is implicated in every stage of the cell cycle and in the regulation of various intracellular pathways associated with health and disease states. The catalytic subunits have similar biochemical activity, however, their functions may differ significantly in cells and in vivo. In this regard, homozygous deletion of CK2α leads to embryonic lethality in mid-gestation potentially due to severely impaired cell proliferation. To determine the CK2α-dependent molecular mechanisms that control cell proliferation, we established a myoblast-derived cell line with inducible silencing of CK2α and carried out a comprehensive RNA-Seq analysis of gene expression. We report evidence that CK2α depletion causes delayed cell cycle progression through the S-phase and defective response to replication stress. Differential gene expression analysis revealed that the down-regulated genes were enriched in pathways implicated in cell cycle regulation, DNA replication and DNA damage repair. Interestingly, the genes coding for the minichromosome maintenance proteins (MCMs), which constitute the core of the replication origin recognition complex, were among the most significantly down-regulated genes. These findings were validated in cells and whole mouse embryos. Taken together, our study provides new evidence for a critical role of protein kinase CK2 in controlling DNA replication initiation and the expression levels of replicative DNA helicases, which ensure maintenance of proliferative potential and genome integrity in eukaryotic cells.