Differentiation of H9c2 cardiomyoblasts: The role of adenylate cyclase system

Positron Emission Tomography (PET) with 18F-FGA for Diagnosis of Myocardial Infarction in a Coronary Artery Ligation Model

Location and extent of necrosis are valuable information in the management of myocardial infarction (MI). Methods. We investigated 2-deoxy-2-18F-fluoro glucaric acid (FGA), a novel infarct-avid agent, for positron emission tomography (PET) of MI. We synthesized FGA from commercially available 18F-fluoro-2-deoxy-2-D-glucose (FDG). MI was induced in mice by permanently occluding the left anterior descending coronary artery. Biodistribution of FGA was assessed 1 h after FGA injection (11 MBq). PET/CT was conducted 1 h, 6 h, 1 d, 3 d, and 4 d after MI. Subcellular compartment of FGA accumulation in necrosis was studied by tracing the uptake of biotin-labeled glucaric acid with streptavidin-HRP in H2O2-treated H9c2 cardiomyoblasts. Streptavidin-reactive protein bands were identified by LC-MS/MS. Results. We obtained a quantitative yield of FGA from FDG within 7 min ( $\text{radiochemical}\text{purity}>99\%$ ). Cardiac uptake of FGA was significantly higher in MI mice than that in control mice. Imaging after 1 h of FGA injection delineated MI for 3 days after MI induction, with negligible background signal from surrounding tissues. Myocardial injury was verified by tetrazolium staining and plasma troponin (47.63 pg/mL control versus 311.77 pg/mL MI). In necrotic H9c2 myoblasts, biotinylated glucaric acid accumulated in nuclear fraction. LC-MS/MS primarily identified fibronectin in necrotic cells as a putative high fidelity target of glucaric acid. Conclusion. FGA/PET detects infarct early after onset of MI and FGA accumulation in infarct persists for 3 days. Its retention in necrotic cells appears to be a result of interaction with fibronectin that is known to accumulate in injured cardiac tissue.

A Small Peptide Targeting the Ligand-Induced Androgen Receptor/Filamin a Interaction Inhibits the Invasive Phenotype of Prostate Cancer Cells

Prostate cancer (PC) is one of the most widespread malignancies among males worldwide. The androgen receptor (AR) plays a major role in prostate cancer development and progression and is the main target of PC therapy. Nonetheless, its action is not yet fully elucidated. We report here that the AR associates with Filamin A (FlnA) promoting migration and invasiveness of various PC-derived cells after androgen challenging. Inhibition of the AR/FlnA complex assembly by a very low concentration of Rh-2025u, an AR-derived peptide specifically interfering with this association, impairs such phenotype in monolayer cells and in 3D models. This study, together with our recent data in cancer-associated fibroblasts (CAFs), indicates that targeting the AR/FlnA complex could improve the clinical management of invasive PC, as the limited number of new drugs reaching the market suggests that we must re-examine the way invasive PC is currently treated. In this context, the synthesis of new biologically active molecules, such as the Rh-2025u peptide, which has been shown to efficiently interfere in the complex assembly in CAFs and PC cells, should overcome the limits of current available therapies, mostly based on hormone antagonists.

Therapeutic potential of TRPM8 antagonists in prostate cancer

Transient receptor potential melastatin-8 (TRPM8) represents an emerging target in prostate cancer, although its mechanism of action remains unclear. Here, we have characterized and investigated the effects of TRPM8 modulators in prostate cancer aggressiveness disclosing the molecular mechanism underlying their biological activity. Patch-clamp and calcium fluorometric assays were used to characterize the synthesized compounds. Androgen-stimulated prostate cancer-derived cells were challenged with the compounds and the DNA synthesis was investigated in a preliminary screening. The most effective compounds were then employed to inhibit the pro-metastatic behavior of in various PC-derived cells, at different degree of malignancy. The effect of the compounds was then assayed in prostate cancer cell-derived 3D model and the molecular targets of selected compounds were lastly identified using transcriptional and non-transcriptional reporter assays. TRPM8 antagonists inhibit the androgen-dependent prostate cancer cell proliferation, migration and invasiveness. They are highly effective in reverting the androgen-induced increase in prostate cancer cell spheroid size. The compounds also revert the proliferation of castrate-resistant prostate cancer cells, provided they express the androgen receptor. In contrast, no effects were recorded in prostate cancer cells devoid of the receptor. Selected antagonists interfere in non-genomic androgen action and abolish the androgen-induced androgen receptor/TRPM8 complex assembly as well as the increase in intracellular calcium levels in prostate cancer cells. Our results shed light in the processes controlling prostate cancer progression and make the transient receptor potential melastatin-8 as a ‘druggable’ target in the androgen receptor-expressing prostate cancers.

Targeting the Nerve Growth Factor Signaling Impairs the Proliferative and Migratory Phenotype of Triple-Negative Breast Cancer Cells

Triple-negative breast cancer is a heterogeneous disease that still lacks specific therapeutic approaches. The identification of new biomarkers, predictive of the disease's aggressiveness and pharmacological response, is a challenge for a more tailored approach in the clinical management of patients. Nerve growth factor, initially identified as a key factor for neuronal survival and differentiation, turned out to be a multifaceted molecule with pleiotropic effects in quite divergent cell types, including cancer cells. Many solid tumors exhibit derangements of the nerve growth factor and its receptors, including the tropomyosin receptor kinase A. This receptor is expressed in triple-negative breast cancer, although its role in the pathogenesis and aggressiveness of this disease is still under investigation. We now report that triple-negative breast cancer-derived MDA-MB-231 and MDA-MB-453 cells express appreciable levels of tropomyosin receptor kinase A and release a biologically active nerve growth factor. Activation of tropomyosin receptor kinase by nerve growth factor treatment positively affects the migration, invasion, and proliferation of triple-negative breast cancer cells. An increase in the size of triple-negative breast cancer cell spheroids is also detected. This latter effect might occur through the nerve growth factor-induced release of matrix metalloproteinase 9, which contributes to the reorganization of the extracellular matrix and cell invasiveness. The tropomyosin receptor kinase A inhibitor GW441756 reverses all these responses. Co-immunoprecipitation experiments in both cell lines show that nerve growth factor triggers the assembly of the TrkA/β1-integrin/FAK/Src complex, thereby activating several downstream effectors. GW441756 prevents the complex assembly induced by nerve growth factor as well as the activation of its dependent signaling. Pharmacological inhibition of the tyrosine kinases Src and FAK (focal adhesion kinase), together with the silencing of β1-integrin, shows that the tyrosine kinases impinge on both proliferation and motility, while β1-integrin is needed for motility induced by nerve growth factor in triple-negative breast cancer cells. The present data support the key role of the nerve growth factor/tropomyosin receptor kinase A pathway in triple-negative breast cancer and offer new hints in the diagnostic and therapeutic management of patients.

The androgen receptor/filamin A complex as a target in prostate cancer microenvironment

Prostate cancer represents the major cause of cancer-related death in men and patients frequently develop drug-resistance and metastatic disease. Most studies focus on hormone-resistance mechanisms related to androgen receptor mutations or to the acquired property of prostate cancer cells to over-activate signaling pathways. Tumor microenvironment plays a critical role in prostate cancer progression. However, the mechanism involving androgen/androgen receptor signaling in cancer associated fibroblasts and consequences for prostate cancer progression still remains elusive. We now report that prostate cancer associated fibroblasts express a transcriptional-incompetent androgen receptor. Upon androgen challenging, the receptor co-localizes with the scaffold protein filamin A in the extra-nuclear compartment of fibroblasts, thus mediating their migration and invasiveness. Cancer-associated fibroblasts move towards epithelial prostate cancer cells in 2D and 3D cultures, thereby inducing an increase of the prostate cancer organoid size. Androgen enhances both these effects through androgen receptor/filamin A complex assembly in cancer-associated fibroblasts. An androgen receptor-derived stapled peptide, which disrupts the androgen receptor/filamin A complex assembly, abolishes the androgen-dependent migration and invasiveness of cancer associated fibroblasts. Notably, the peptide impairs the androgen-induced invasiveness of CAFs in 2D models and reduces the overall tumor area in androgen-treated 3D co-culture. The androgen receptor in association with β1 integrin and membrane type-matrix metalloproteinase 1 activates a protease cascade triggering extracellular matrix remodeling. The peptide also impairs the androgen activation of this cascade. This study offers a potential new marker, the androgen receptor/filamin A complex, and a new therapeutic approach targeting intracellular pathways activated by the androgen/androgen receptor axis in prostate cancer-associated fibroblasts. Such a strategy, alone or in combination with conventional therapies, may allow a more efficient treatment of prostate cancer.

Optimizing mechanical stretching protocols for hypertrophic and anti-apoptotic responses in cardiomyocyte-like H9C2 cells

Cardiomyocytes possess the ability to respond to mechanical stimuli by reprogramming their gene expression. This study investigated the effects of different loading protocols on signaling and expression responses of myogenic, anabolic, inflammatory, atrophy and pro-apoptotic genes in cardiomyocyte-like H9C2 cells. Differentiated H9C2 cells underwent various stretching protocols by altering their elongation, frequency and duration, utilizing an in vitro cell tension system. The loading-induced expression changes of MyoD, Myogenin, MRF4, IGF-1 isoforms, Atrogin-1, Foxo1, Fuca and IL-6 were measured by Real Time-PCR. The stretching-induced activation of Akt and Erk 1/2 was also evaluated by Western blot analysis. Low strain (2.7% elongation), low frequency (0.25 Hz) and intermediate duration (12 h) stretching protocol was overall the most effective in inducing beneficial responses, i.e., protein synthesis along with the suppression of apoptosis, inflammation and atrophy, in the differentiated cardiomyocytes. These findings demonstrated that varying the characteristics of mechanical loading applied on H9C2 cells in vitro can regulate their anabolic/survival program.

Drug-induced cardiomyopathy: Characterization of a rat model by [18F]FDG/PET and [99mTc]MIBI/SPECT

BACKGROUND

Drug-induced cardiomyopathy is a significant medical problem. Clinical diagnosis of myocardial injury is based on initial electrocardiogram, levels of circulating biomarkers, and perfusion imaging with single photon emission computed tomography (SPECT). Positron emission tomography (PET) is an alternative imaging modality that provides better resolution and sensitivity than SPECT, improves diagnostic accuracy, and allows therapeutic monitoring. The objective of this study was to assess the detection of drug-induced cardiomyopathy by PET using 2-deoxy-2-[18F]fluoro-D-glucose (FDG) and compare it with the conventional SPECT technique with [99mTc]-Sestamibi (MIBI).

METHODS

Cardiomyopathy was induced in Sprague Dawley rats using high-dose isoproterenol. Nuclear [18F]FDG/PET and [99mTc]MIBI/SPECT were performed before and after isoproterenol administration. [18F]FDG (0.1 mCi, 200-400 µL) and [99mTc]MIBI (2 mCi, 200-600 µL) were administered via the tail vein and imaging was performed 1 hour postinjection. Isoproterenol-induced injury was confirmed by the plasma level of cardiac troponin and triphenyltetrazolium chloride (TTC) staining.

RESULTS

Isoproterenol administration resulted in an increase in circulating cardiac troponin I and showed histologic damage in the myocardium. Visually, preisoproterenol and postisoproterenol images showed alterations in cardiac accumulation of [18F]FDG, but not of [99mTc]MIBI. Image analysis revealed that myocardial uptake of [18F]FDG reduced by 60% after isoproterenol treatment, whereas that of [99mTc]MIBI decreased by 45%.

CONCLUSION

We conclude that [18F]FDG is a more sensitive radiotracer than [99mTc]MIBI for imaging of drug-induced cardiomyopathy. We theorize that isoproterenol-induced cardiomyopathy impacts cellular metabolism more than perfusion, which results in more substantial changes in [18F]FDG uptake than in [99mTc]MIBI accumulation in cardiac tissue.

Nerve Growth Factor Induces Proliferation and Aggressiveness In Prostate Cancer Cells

Resistance to hormone therapy and disease progression is the major challenge in clinical management of prostate cancer (PC). Drugs currently used in PC therapy initially show a potent antitumor effects, but PC gradually develops resistance, relapses and spreads. Most patients who fail primary therapy and have recurrences eventually develop castration-resistant prostate cancer (CRPC), which is almost incurable. The nerve growth factor (NGF) acts on a variety of non-neuronal cells by activating the NGF tyrosine-kinase receptor, tropomyosin receptor kinase A (TrkA). NGF signaling is deregulated in PC. In androgen-dependent PC cells, TrkA mediates the proliferative action of NGF through its crosstalk with the androgen receptor (AR). Epithelial PC cells, however, acquire the ability to express NGF and TrkA, as the disease progresses, indicating a role for NGF/TrkA axis in PC progression and androgen-resistance. We here report that once activated by NGF, TrkA mediates proliferation, invasiveness and epithelial-mesenchymal transition (EMT) in various CRPC cells. NGF promotes organoid growth in 3D models of CRPC cells, and specific inhibition of TrkA impairs all these responses. Thus TrkA represents a new biomarker to target in CRPC.

Estrogens Modulate Somatostatin Receptors Expression and Synergize With the Somatostatin Analog Pasireotide in Prostate Cells

Prostate cancer (PC) is one of the most frequently diagnosed cancers and a leading cause of cancer-related deaths in Western society. Current PC therapies prevalently target the functions of androgen receptor (AR) and may only be effective within short time periods, beyond which the majority of PC patients progress to castration-resistant PC (CRPC) and metastatic disease. The role of estradiol/estradiol receptor (ER) axis in prostate transformation and PC progression is well established. Further, considerable efforts have been made to investigate the mechanism by which somatostatin (SST) and somatostatin receptors (SSTRs) influence PC growth and progression. A number of therapeutic strategies, such as the combination of SST analogs with other drugs, show, indeed, strong promise. However, the effect of the combined treatment of SST analogs and estradiol on proliferation, epithelial mesenchyme transition (EMT) and migration of normal- and cancer-derived prostate cells has not been investigated so far. We now report that estradiol plays anti-proliferative and pro-apoptotic effect in non-transformed EPN prostate cells, which express both ERα and ERβ. A weak apoptotic effect is observed in transformed CPEC cells that only express low levels of ERβ. Estradiol increases, mainly through ERα activation, the expression of SSTRs in EPN, but not CPEC cells. As such, the hormone enhances the anti-proliferative effect of the SST analog, pasireotide in EPN, but not CPEC cells. Estradiol does not induce EMT and the motility of EPN cells, while it promotes EMT and migration of CPEC cells. Addition of pasireotide does not significantly modify these responses. Altogether, our results suggest that pasireotide may be used, alone or in combination with other drugs, to limit the growth of prostate proliferative diseases, provided that both ER isoforms (α and β) are present. Further investigations are needed to better define the cross talk between estrogens and SSTRs as well as its role in PC.

Three-dimensional spherical gelatin bubble-based scaffold improves the myotube formation of H9c2 myoblasts

Microenvironmental factors including physical and chemical cues can regulate stem cells as well as terminally differentiated cells to modulate their biological function and differentiation. However, one of the physical cues, the substrate's dimensionality, has not been studied extensively. In this study, the flow-focusing method with a microfluidic device was used to generate gelatin bubbles to fabricate highly ordered three-dimensional (3D) scaffolds. Rat H9c2 myoblasts were seeded into the 3D gelatin bubble-based scaffolds and compared to those grown on 2D gelatin-coating substrates to demonstrate the influences of spatial cues on cell behaviors. Relative to cells on the 2D substrates, the H9c2 myoblasts were featured by a good survival and normal mitochondrial activity but slower cell proliferation within the 3D scaffolds. The cortical actin filaments of H9c2 cells were localized close to the cell membrane when cultured on the 2D substrates, while the F-actins distributed uniformly and occupied most of the cell cytoplasm within the 3D scaffolds. H9c2 myoblasts fused as multinuclear myotubes within the 3D scaffolds without any induction but cells cultured on the 2D substrates had a relatively lower fusion index even differentiation medium was provided. Although there was no difference in actin α 1 and myosin heavy chain 1, H9c2 cells had a higher myogenin messenger RNA level in the 3D scaffolds than those of on the 2D substrates. This study reveals that the dimensionality influences differentiation and fusion of myoblasts.

New Three-Dimensional Poly(decanediol-co-tricarballylate) Elastomeric Fibrous Mesh Fabricated by Photoreactive Electrospinning for Cardiac Tissue Engineering Applications

Reactive electrospinning is capable of efficiently producing in situ crosslinked scaffolds resembling the natural extracellular matrix with tunable characteristics. In this study, we aimed to synthesize, characterize, and investigate the in vitro cytocompatibility of electrospun fibers of acrylated poly(1,10-decanediol-co-tricarballylate) copolymer prepared utilizing the photoreactive electrospinning process with ultraviolet radiation for crosslinking, to be used for cardiac tissue engineering applications. Chemical, thermal, and morphological characterization confirmed the successful synthesis of the polymer used for production of the electrospun fibrous scaffolds with more than 70% porosity. Mechanical testing confirmed the elastomeric nature of the fibers required to withstand cardiac contraction and relaxation. The cell viability assay showed no significant cytotoxicity of the fibers on cultured cardiomyoblasts and the cell-scaffolds interaction study showed a significant increase in cell attachment and growth on the electrospun fibers compared to the reference. This data suggests that the newly synthesized fibrous scaffold constitutes a promising candidate for cardiac tissue engineering applications.

Heart-on-a-Chip: An Investigation of the Influence of Static and Perfusion Conditions on Cardiac (H9C2) Cell Proliferation, Morphology, and Alignment

Lab-on-a-chip systems are increasingly used as tools for cultures and investigation of cardiac cells. In this article, we present how the geometry of microsystems and microenvironmental conditions (static and perfusion) influence the proliferation, morphology, and alignment of cardiac cells (rat cardiomyoblasts-H9C2). Additionally, studies of cell growth after incubation with verapamil hydrochloride were performed. For this purpose, poly(dimethylsiloxane) (PDMS)/glass microfluidic systems with three different geometries of microchambers (a circular chamber, a longitudinal channel, and three parallel microchannels separated by two rows of micropillars) were prepared. It was found that static conditions did not enhance the growth of H9C2 cells in the microsystems. On the contrary, perfusion conditions had an influence on division, morphology, and the arrangement of the cells. The highest number of cells, their parallel orientation, and their elongated morphology were obtained in the longitudinal microchannel. It showed that this kind of microsystem can be used to understand processes in heart tissue in detail and to test newly developed compounds applied in the treatment of cardiac diseases.

Biomimetic Cardiac Tissue Model Enables the Adaption of Human Induced Pluripotent Stem Cell Cardiomyocytes to Physiological Hemodynamic Loads

Induced pluripotent stem cell derived cardiomyocytes (iPSC-CMs) provide a human source of cardiomyocytes for use in cardiovascular research and regenerative medicine. However, attempts to use these cells in vivo have resulted in drastic cell death caused by mechanical, metabolic, and/or exogenous factors. To explore this issue, we designed a Biomimetic Cardiac Tissue Model (BCTM) where various parameters associated with heart function including heart rate, peak-systolic pressure, end-diastolic pressure and volume, end-systolic pressure and volume, and ratio of systole to diastole can all be precisely manipulated to apply hemodynamic loading to culture cells. Using the BCTM, two causes of low survivability in current cardiac stem cell therapies, mechanical and metabolic, were explored. iPSC-CMs were subject to physiologically relevant mechanical loading (50 mmHg systolic, 10% biaxial stretch) in either a low- or high-serum environment and mechanical loads were applied either immediately or gradually. Results confirm that iPSC-CMs subject to mechanical loading in low-serum conditions experienced widespread cell death. The rate of application of stress also played an important role in adaptability to mechanical loading. Under high-serum conditions, iPSC-CMs subject to gradual imposition of stress were comparable to iPSC-CMs maintained in static culture when evaluated in terms of cell viability, sarcomeric structure, action potentials and conduction velocities. In contrast, iPSC-CMs that were immediately exposed to mechanical loading had significantly lower cell viability, destruction of sarcomeres, smaller action potentials, and lower conduction velocities. We report that iPSC-CMs survival under physiologically relevant hemodynamic stress requires gradual imposition of mechanical loads in a nutrient-rich environment.

Gene Expression Profiling of H9c2 Myoblast Differentiation towards a Cardiac-Like Phenotype

H9c2 myoblasts are a cell model used as an alternative for cardiomyocytes. H9c2 cells have the ability to differentiate towards a cardiac phenotype when the media serum is reduced in the presence of all-trans-retinoic acid (RA), creating multinucleated cells with low proliferative capacity. In the present study, we performed for the first time a transcriptional analysis of the H9c2 cell line in two differentiation states, i.e. embryonic cells and differentiated cardiac-like cells. The results show that RA-induced H9c2 differentiation increased the expression of genes encoding for cardiac sarcomeric proteins such as troponin T, or calcium transporters and associated machinery, including SERCA2, ryanodine receptor and phospholamban as well as genes associated with mitochondrial energy production including respiratory chain complexes subunits, mitochondrial creatine kinase, carnitine palmitoyltransferase I and uncoupling proteins. Undifferentiated myoblasts showed increased gene expression of pro-survival proteins such as Bcl-2 as well as cell cycle-regulating proteins. The results indicate that the differentiation of H9c2 cells lead to an increase of transcripts and protein levels involved in calcium handling, glycolytic and mitochondrial metabolism, confirming that H9c2 cell differentiation induced by RA towards a more cardiac-like phenotype involves remodeled mitochondrial function. PI3K, PDK1 and p-CREB also appear to be involved on H9c2 differentiation. Furthermore, complex analysis of differently expressed transcripts revealed significant up-regulation of gene expression related to cardiac muscle contraction, dilated cardiomyopathy and other pathways specific for the cardiac tissue. Metabolic and gene expression remodeling impacts cell responses to different stimuli and determine how these cells are used for biochemical assays.

Myogenic stem cell-laden hydrogel scaffold in wound healing of the disrupted external anal sphincter

OBJECTIVE

To evaluate the effect of myogenic stem cell-laden hydrogel scaffold on contractile function and histomorphology of the external anal sphincter (EAS) after transection without repair.

METHODS

Eighty female rats underwent anal sphincter transection without repair. After 2 weeks, animals were injected at the transection site with: nothing (non-repaired control, NRC group); a polyethylene glycol-based hydrogel matrix scaffold combined with phosphate-buffered saline (PBS/hydrogel group); a hydrogel matrix scaffold combined with myogenic stem cells (stem cell/hydrogel group): or type I collagen (collagen) group. 4 (n = 40) or 12 (n = 40) weeks later, the anal sphincter complexes were dissected out and analyzed for contractile function, disruption, and striated muscle volume. Time-matched unoperated controls (UOC) were utilized for each of the two time points (n = 20).

RESULTS

After 4 weeks, maximal electrical field-stimulated (EFS) contractions were significantly decreased in all four non-repaired treatment groups compared with UOC. However, EFS-stimulated contractions, tetanic force generation, and twitch tension were improved in non-repaired EAS injected with stem cell/hydrogel group relative to the NRC, PBS/hydrogel, or collagen groups. NRC and sphincters injected with PBS/hydrogel deteriorated further by 12 weeks, while those receiving stem cell/hydrogel maintained improved contractile function at varying frequencies and voltages. Striated muscle volume increased from 4 to 12 weeks for PBS/hydrogel and stem cell/hydrogel animals. At 12 weeks, stem cell/hydrogel animals had greater sphincter striated muscle volumes compared with all other treatment groups.

CONCLUSION

In this animal model, sustained improvement of contractile responses in non-repaired EAS treated with biogel scaffold and myogenic stem cells suggests that a biologically compatible matrix may facilitate stem cell survival, differentiation, or function leading to recovery of contractile function even after persistent disruption.

H9c2 and HL-1 cells demonstrate distinct features of energy metabolism, mitochondrial function and sensitivity to hypoxia-reoxygenation

Dysfunction of cardiac energy metabolism plays a critical role in many cardiac diseases, including heart failure, myocardial infarction and ischemia-reperfusion injury and organ transplantation. The characteristics of these diseases can be elucidated in vivo, though animal-free in vitro experiments, with primary adult or neonatal cardiomyocytes, the rat ventricular H9c2 cell line or the mouse atrial HL-1 cells, providing intriguing experimental alternatives. Currently, it is not clear how H9c2 and HL-1 cells mimic the responses of primary cardiomyocytes to hypoxia and oxidative stress. In the present study, we show that H9c2 cells are more similar to primary cardiomyocytes than HL-1 cells with regard to energy metabolism patterns, such as cellular ATP levels, bioenergetics, metabolism, function and morphology of mitochondria. In contrast to HL-1, H9c2 cells possess beta-tubulin II, a mitochondrial isoform of tubulin that plays an important role in mitochondrial function and regulation. We demonstrate that H9c2 cells are significantly more sensitive to hypoxia-reoxygenation injury in terms of loss of cell viability and mitochondrial respiration, whereas HL-1 cells were more resistant to hypoxia as evidenced by their relative stability. In comparison to HL-1 cells, H9c2 cells exhibit a higher phosphorylation (activation) state of AMP-activated protein kinase, but lower peroxisome proliferator-activated receptor gamma coactivator 1-alpha levels, suggesting that each cell type is characterized by distinct regulation of mitochondrial biogenesis. Our results provide evidence that H9c2 cardiomyoblasts are more energetically similar to primary cardiomyocytes than are atrial HL-1 cells. H9c2 cells can be successfully used as an in vitro model to simulate cardiac ischemia-reperfusion injury.

Overexpression of ryanodine receptor type 1 enhances mitochondrial fragmentation and Ca2+-induced ATP production in cardiac H9c2 myoblasts

Ca(+) influx to mitochondria is an important trigger for both mitochondrial dynamics and ATP generation in various cell types, including cardiac cells. Mitochondrial Ca(2+) influx is mainly mediated by the mitochondrial Ca(2+) uniporter (MCU). Growing evidence also indicates that mitochondrial Ca(2+) influx mechanisms are regulated not solely by MCU but also by multiple channels/transporters. We have previously reported that skeletal muscle-type ryanodine receptor (RyR) type 1 (RyR1), which expressed at the mitochondrial inner membrane, serves as an additional Ca(2+) uptake pathway in cardiomyocytes. However, it is still unclear which mitochondrial Ca(2+) influx mechanism is the dominant regulator of mitochondrial morphology/dynamics and energetics in cardiomyocytes. To investigate the role of mitochondrial RyR1 in the regulation of mitochondrial morphology/function in cardiac cells, RyR1 was transiently or stably overexpressed in cardiac H9c2 myoblasts. We found that overexpressed RyR1 was partially localized in mitochondria as observed using both immunoblots of mitochondrial fractionation and confocal microscopy, whereas RyR2, the main RyR isoform in the cardiac sarcoplasmic reticulum, did not show any expression at mitochondria. Interestingly, overexpression of RyR1 but not MCU or RyR2 resulted in mitochondrial fragmentation. These fragmented mitochondria showed bigger and sustained mitochondrial Ca(2+) transients compared with basal tubular mitochondria. In addition, RyR1-overexpressing cells had a higher mitochondrial ATP concentration under basal conditions and showed more ATP production in response to cytosolic Ca(2+) elevation compared with nontransfected cells as observed by a matrix-targeted ATP biosensor. These results indicate that RyR1 possesses a mitochondrial targeting/retention signal and modulates mitochondrial morphology and Ca(2+)-induced ATP production in cardiac H9c2 myoblasts.

Mitochondrial disruption occurs downstream from β-adrenergic overactivation by isoproterenol in differentiated, but not undifferentiated H9c2 cardiomyoblasts: differential activation of stress and survival pathways

β-Adrenergic receptor stimulation plays an important role in cardiomyocyte stress responses, which may result in apoptosis and cardiovascular degeneration. We previously demonstrated that toxicity of the β-adrenergic agonist isoproterenol on H9c2 cardiomyoblasts depends on the stage of cell differentiation. We now investigate β-adrenergic receptor downstream signaling pathways and stress responses that explain the impact of muscle cell differentiation on hyper-β-adrenergic stimulation-induced cytotoxicity. When incubated with isoproterenol, differentiated H9c2 muscle cells have increased cytosolic calcium, cyclic-adenosine monophosphate content and oxidative stress, as well as mitochondrial depolarization, increased superoxide anion, loss of subunits from the mitochondrial respiratory chain, decreased Bcl-xL content, increased p53 and phosphorylated-p66Shc as well as activated caspase-3. Undifferentiated H9c2 cells incubated with isoproterenol showed increased Bcl-xL protein and increased superoxide dismutase 2 which may act as protective mechanisms. We conclude that the differentiation of H9c2 is associated with differential regulation of stress responses, which impact the toxicity of several agents, namely those acting through β-adrenergic receptors and resulting in mitochondrial disruption in differentiated cells only.

Effects of vitamin D3 and paricalcitol on immature cardiomyocytes: a novel role for vitamin D analogs in the prevention of cardiovascular diseases

Cardiovascular diseases are more prevalent in patients with chronic kidney disease than in the general population and they are considered the leading cause of death in patients with end-stage renal disease. The discovery that vitamin D₃ plays a considerable role in cardiovascular protection has led, in recent years, to an increase in the administration of therapies based on the use of this molecule; nevertheless, several studies warned that an excess of vitamin D₃ may increase the risk of hypercalcemia and vascular calcifications. In this study we evaluated the effects of vitamin D₃, and of its selective analog paricalcitol, on immature cardiomyocytes. Results show that vitamin D₃ induces cAMP-mediated cell proliferation and significant intracellular calcification. Paricalcitol, however, induces cell differentiation, morphological modifications in cell shape and size, and no intracellular calcification. Furthermore, vitamin D₃ and paricalcitol differently affect cardiomyoblasts responses to acetylcholine treatment. In conclusion, our results demonstrate that the effects of vitamin D₃ and paricalcitol on cardiomyoblasts are different and, if these in vitro observations could be extrapolated in vivo, they suggest that paricalcitol has the potential for cardiovascular protection without the risk of inducing intracellular calcification.

Function and expression of ATIP and its variants in cardiomyoblast cell line H9c2

HYPOTHESIS

Cardiac hypertrophy in myocytes is in part regulated by changes in expression of a novel Ang II type 2 receptor (AT2-receptor) interacting protein identified as ATIP.

INTRODUCTION

The role of the AT2-receptor in cardiac hypertrophy is controversial, with some reports indicating that AT2-receptor activation has detrimental effects on disease progression, whereas others indicate that it has a beneficial role.

MATERIALS AND METHODS

In an effort to unravel this paradox, we examined the expression and function of ATIP in cell-based models of cardiac hypertrophy using QPCR, immunohistochemistry, cell proliferation, morphological and transfection techniques in H9c2 cardio-myoblast and myotubules.

RESULTS

These studies indicate that in cultured cardio-myoblast and myotubules, Ang II mediates cellular hypertrophy and proliferation solely via the AT1-receptor, the ATIP variants are abundantly expressed and that ATIP3 may play an anti-proliferative/hypertrophic role in these cells in the absence of AT2-receptor expression or activation.

CONCLUSIONS

Previously ATIP has been shown to inhibit growth factor signalling in cancerous cells via an interaction with the AT2-receptor. This is the first report to identify that ATIP may have a similar role in other disease states characterised by excessive growth and indicates that for ATIP3, at least, an interaction with the AT2-receptor may not be necessary.

PKC-δ signalling pathway is involved in H9c2 cells differentiation

H9c2 are rat heart embryonic myoblasts, with skeletal muscle properties, which terminally differentiate by fusing and forming multinucleated myotubes. Here we investigated the possible involvement of Protein Kinases C (PKCs) in H9c2 cell differentiation and explored the interplay of these enzymes both with reactive oxygen species (ROS), upstream physiological mediators of cell differentiation, and with nitric oxide (NO), downstream target of PKC activation, known for being involved in apoptosis induction in differentiated myoblasts. Cells were induced to differentiate (6 days) under low serum culture conditions and assayed for the expression of cell cycle (cyclin A) and differentiation markers (morphology and myogenin). Both ROS and in vivo production of NO were found increased after 6 days of differentiation, when the activation of PKC-δ isoform was 14-fold increased compared with the undifferentiated control cells. The parallel analysis of apoptotic features demonstrated a small increase in Annexin-V+ cells and a concomitant increase in PARP cleavage and Bax expression. Interestingly, a reduced percentage of differentiated cells was obtained both in the presence of Rottlerin, a highly selective PKC-δ pharmacologic inhibitor, and, moreover, with the use of PKC-δ siRNA technology, further supporting the involvement of PKC-δ in switching on the events related to skeletal muscle myoblast differentiation.

Leptin potentiates antiproliferative action of cAMP elevation via protein kinase A down-regulation in breast cancer cells

Previously, we have shown that leptin potentiates the antiproliferative action of cAMP elevating agents in breast cancer cells and that the protein kinase A (PKA) inhibitor KT-5720 prevented the antiproliferative effects induced by the leptin plus cAMP elevation. The present experiments were designed to gain a better understanding about the PKA role in the antitumor interaction between leptin and cAMP elevating agents and on the underlying signaling pathways. Here we show that exposure of MDA-MB-231 breast cancer cells to leptin resulted in a strong phosphorylation of both ERK1/2 and STAT3. Interestingly, intracellular cAMP elevation upon forskolin pretreatment completely abrogated both ERK1/2 and STAT3 phosphorylation in response to leptin and was accompanied by a consistent CREB phosphorylation. Notably, leptin plus forskolin cotreatments resulted in a strong decrease of both PKA regulatory RIα and catalytic subunits protein levels. Importantly, pretreatment with the PKA inhibitor KT-5720 blocked the forskolin-induced CREB phosphorylation and prevented both the inhibition by forskolin of leptin-induced ERK1/2 and STAT3 phosphorylation and the PKA subunits down-regulation induced by the combination of leptin and forskolin. Altogether, our results indicate that leptin-dependent signaling pathways are influenced by cAMP elevation and identify PKA as relevantly involved in the pharmacological antitumor interaction between leptin and cAMP elevating drugs in MDA-MB-231 cells. We propose a molecular model by which PKA confers its effects. Potential therapeutic applications by our data will be discussed.

Effect of myogenic stem cells on contractile properties of the repaired and unrepaired transected external anal sphincter in an animal model

OBJECTIVE

To estimate the effect of myogenic stem cells on contractile function of the external anal sphincter after transection with or without repair in an animal model.

METHODS

One hundred twenty virginal female rats were randomly assigned to repair (n=60) or no repair (n=60) after anal sphincter transection. Animals were further divided into two groups: 40-microliter injection at the transection site with either phosphate-buffered solution (control) or myogenic stem cells (3.2x10 cells). Animals were killed at 7, 21, or 90 days, and the anal sphincter complex dissected and analyzed for contractile function.

RESULTS

Contractile function of the external anal sphincter was severely impaired 7 days after sphincter transection with or without repair. Twitch tension, maximal tetanic contraction, and maximal contractile force in response to electrical field stimulation improved significantly with time after sphincter repair. Injection of myogenic stem cells in the anal sphincter at the time of repair resulted in superior contractile function at both 7 days and 90 days compared with controls. Interestingly, contractile function of the nonrepaired external anal sphincter did not improve with time with or without myogenic stem cells. Indicators of denervation (fatigue and twitch or tetany ratios) did not change among groups.

CONCLUSION

In this animal model, injection of myogenic stem cells at the time of external anal sphincter repair resulted in enhanced contractile function at 90 days compared with repair alone. Without repair, function of the external anal sphincter was not improved by stem cell therapy at any time point. These results suggest that addition of myogenic stem cells improves both acute and long-term function of the external anal sphincter after mechanical injury.

Differential translocation of nuclear factor-kappaB in a cardiac muscle cell line under gravitational changes

Microgravity (micro-g) environments have been shown to elicit dysregulation of specific genes in a wide assay of cell types. It is known that the activation of transcription factors and molecular signaling pathways influence various physiological outcomes associated with stress and adaptive responses. Nuclear factor-kappa B (NF-kappaB) is one of the most prevailing oxidation-sensitive transcription factors. It is hypothesized that simulated microgravity would activate NF-kappaB and its downstream transcriptional networks, thus suggesting a role for NF-kappaB in microgravity induced muscle atrophy. To investigate the activation of NF-kappaB in a rat cardiac cell line (H9c2) under micro-g, rotating wall vessel bioreactors were used to simulate micro-g conditions. Western blotting revealed that mean nuclear translocation of NF-kappaB p65 subunit was 69% for micro-g and 46% for unit-g dynamic control as compared with a 30 min TNF-alpha positive control (p<0.05, n=3). The results from western blots were confirmed by enzyme-linked immunosorbent assay, which showed 66% for micro-g and 45% for dynamic control as compared with positive control (p<0.05, n=3). These results show significant differential translocation of NF-kappaB p65 under simulated micro-g. These results may be expanded upon to explain physiological changes such as muscle atrophy and further identify the regulatory pathways and effector molecules activated under exposure to micro-g.

Change in TNF-alpha receptor expression is a relevant event in doxorubicin-induced H9c2 cardiomyocyte cell death

Doxorubicin (Doxo) is a widely used anticancer drug given for the treatment of leukemias, lymphomas, and solid tumors. Despite its potent antitumor effects, the cardiotoxicity of this drug limits its clinical use. The biochemical mechanisms of Doxo-induced cardiotoxicity remain unclear. Doxo has been shown to induce apoptosis in cardiomyocytes that seems to be responsible, at least in part, for Doxo cardiotoxicity. In this study, we investigated tumor necrosis factor-alpha (TNF-alpha) receptor-mediated signaling to better understand the causes of Doxo-induced cardiotoxicity. Here, we report that Doxo is a potent inducer of apoptosis in both H9c2 cardiomyocytes and U2OS osteosarcoma tumor cells, with significant differences in terms of kinetics and caspase activation between the two cell lines. Interestingly, Doxo-induced apoptosis is accompanied by relevant changes in TNF-alpha receptor levels in H9c2 cardiomyocytes but not in U2OS cells. Moreover, treatment with exogenous TNF-alpha strongly potentiates the apoptotic effect of Doxo in H9c2 cardiomyocytes but not in U2OS cells. Our findings show that the function of TNF receptors I and II is affected by Doxo to ultimately modulate apoptosis and cell survival in H9c2 cardiomyocytes, reinforcing the recent evidence of the relevant role of TNF-alpha receptor-mediated signaling in cardiotoxicity induced by anthracyclines.

Effect of resveratrol on proliferation and differentiation of embryonic cardiomyoblasts

Resveratrol (trans-3,5,4'-trihydroxystilbene), a polyphenolic compound found largely in the skins of red grapes, has been used as a nutritional supplement or an investigational new drug for prevention of cardiovascular diseases. Previous reports showed that resveratrol had a protective effect against oxidative agent-induced cell injury. Our studies indicate that resveratrol plays a role in the differentiation of cardiomyoblasts. The cardiomyoblast cell line, H9c2, was exposed to 30-120 microM resveratrol for up to 5 days. Resveratrol inhibits cardiomyoblast proliferation without causing cells injury. Moreover, resveratrol treatment modulated the differentiation of morphological characteristics including elongation and cell fusion in cardiomyoblasts. Proliferation and differentiation of H9c2 cells were further revealed by measurement of the mRNA expression of a cell cycle marker (CDK2), a differentiation marker (myogenin), and a contractile apparatus protein (MLC-2). Gene expression analysis revealed that resveratrol promoted entry into cell cycle arrest but extended the myogenic differentiation progress. These results have implications for the role of resveratrol in modulating cell cycle control and differentiation in cardiomyoblasts.

Adenylate cyclase/cAMP pathway downmodulation counteracts apoptosis induced by IFN-alpha in human epidermoid cancer cells

We have reported previously that interferon-alpha (IFN-alpha) induces apoptosis that is counteracted by an epidermal growth factor (EGF) --> Ras --> extracellular signal-regulated kinase (ERK)-dependent survival response in human epidermoid cancer KB cells. We have studied the effects of the cytokine on the cAMP-dependent pathway in these cells. A decrease in the intracellular cAMP levels was recorded in KB cells treated with IFN-alpha, whereas forskolin induced an increase in the production of cAMP that was reduced in the presence of IFN-alpha, suggesting a reduction in the activity of adenylate cyclase (AC) induced by IFN-alpha. These effects were paralleled by significant change in the expression of some AC catalytic subunit(s) and by reduction in the activity of protein kinase A (PKA). 8-Br-cAMP completely antagonized the reduction of PKA activity induced by IFN-alpha, whereas PKA inhibitor KT5720 enhanced the reduction of the enzyme activity induced by IFN-alpha. We have found that IFN-alpha induced a decrease in cAMP response element binding protein (CREB) phosphorylation without changes in its total expression. The concomitant treatment with IFN-alpha and 8-Br-cAMP potentiated and KT5720 counteracted apoptosis induced by IFN-alpha alone. In conclusion, these data suggest that the decrease in AC/cAMP pathway activity is a survival response to the apoptosis induced by IFN-alpha. Therefore, this pathway could represent a target to enhance the antitumor activity of IFN-alpha.

Apoptosis repressor with caspase recruitment domain (ARC) inhibits myogenic differentiation

Apoptosis repressor with caspase recruitment domain (ARC), an anti-apoptotic protein, is highly expressed in differentiated heart and skeletal muscle. Apoptosis and differentiation share numerous common pathways; therefore, we examined the impact of ARC on H9c2-myoblast differentiation. We demonstrate that ARC expression levels increase and stabilize upon differentiation. ARC-overexpression in pre-differentiated H9c2-cells suppresses differentiation; indicated by increased myotube formation, nuclear fusion and expression of the differentiation markers myogenin and troponin-T. ARC-overexpression inhibited myoblast differentiation associated caspase-3 activation, suggesting ARC inhibits myogenic differentiation through caspase inhibition. In summary, we show a novel role for ARC in the regulation of muscle differentiation.

Inorganic phosphate inhibits growth of human osteosarcoma U2OS cells via adenylate cyclase/cAMP pathway

In order to elucidate how phosphate regulates cellular functions, we investigated the effects of inorganic phosphate (Pi) on adenylate cyclase (AC)/cyclic AMP (cAMP) axis. Here we describe that Pi treatment of human osteosarcoma U2OS cells results in a decrease of both intracellular cAMP levels and AC activity, and in a cell growth inhibition. The phosphate-triggered effects observed in U2OS cells are not a widespread phenomenon regarding all cell lines, since other cell lines screened respond differently to parallel Pi treatments. In U2OS cell line, the AC activity/cAMP downregulation is accompanied by significant variations in the levels of some membrane proteins belonging to the AC system. Remarkably, the above effects are blunted by pharmacological inhibition of sodium-dependent phosphate transport. Moreover, 8-Br-cAMP and other cAMP-elevating agents, such as IBMX and forskolin, interestingly, prevent the cell growth inhibition in response to phosphate. Our results enforce the increasing evidences of phosphate as a signaling molecule, identifying in U2OS cell line the AC/cAMP axis, as a novel-signaling pathway modulated by phosphate to ultimately affect cell growth.