In cardiac myoblasts, cellular redox regulates FosB and Fra-1 through multiple cis-regulatory modules

Norepinephrine promotes neuronal apoptosis of hippocampal HT22 cells by up-regulating the expression of long non-coding RNA MALAT1

Stress is ever present in our modern, performance-oriented and demanding society, which causes adverse stress reactions of the body and affects health seriously. Chronic stress has been recognized as a significant risk factor leading to cognitive impairment, but the underlying mechanism is far from fully understood. Norepinephrine (NE), a pivotal stress-induced hormone, has been found to induce cell apoptosis. However, the function and the key downstream mediator of NE on the regulation of hippocampal neurons still need further exploration. In this study, we explored the role of NE in neuronal apoptosis and its association with MALAT1. Flow cytometry assay and automated western bot assay were carried out to evaluate the cell apoptosis. The data showed that the rate of apoptosis rate and the levels of apoptotic proteins (cleaved-Caspase3 and cleaved-PARP) were significantly increased in HT22 cells after a high dose of NE treatment, suggesting a facilitative role of NE on hippocampal neuronal apoptosis. Besides, a high level of NE up-regulated the expression of MALAT1 in HT22 cells. Then, a lentivirus expressing MALAT1 shRNA was constructed to investigate the role of MALAT1 in cell apoptosis and the results revealed that MALAT1 depletion decreased the cell apoptosis. Moreover, the knockdown of MALAT1 abolished the discrepancy in apoptosis between NE-treated cells and control cells. In conclusion, a high level of the stress-induced hormone NE promoted apoptosis of hippocampal neurons by elevating the expression of MALAT1. Our findings provide new experimental data supporting the epigenetic mechanisms in the regulation of stress response and may provide a potential therapeutic target for stress-related cognition dysfunction.

H2S regulates redox signaling downstream of cardiac β-adrenergic receptors in a G6PD-dependent manner

Stimulating β-adrenergic receptors (β-AR) culminates in pathological hypertrophy - a condition underlying multiple cardiovascular diseases (CVDs). The ensuing signal transduction network appears to involve mutually communicating phosphorylation-cascades and redox signaling modules, although the regulators of redox signaling processes remain largely unknown. We previously showed that H₂S-induced Glucose-6-phosphate dehydrogenase (G6PD) activity is critical for suppressing cardiac hypertrophy in response to adrenergic stimulation. Here, we extended our findings and identified novel H₂S-dependent pathways constraining β-AR-induced pathological hypertrophy. We demonstrated that H₂S regulated early redox signal transduction processes - including suppression of cue-dependent production of reactive oxygen species (ROS) and oxidation of cysteine thiols (R-SOH) on critical signaling intermediates (including AKT1/2/3 & ERK1/2). Consistently, the maintenance of intracellular levels of H₂S dampened the transcriptional signature associated with pathological hypertrophy upon β-AR-stimulation, as demonstrated by RNA-seq analysis. We further prove that H₂S remodels cell metabolism by promoting G6PD activity to enforce changes in the redox state that favor physiological cardiomyocyte growth over pathological hypertrophy. Thus, our data suggest that G6PD is an effector of H₂S-mediated suppression of pathological hypertrophy and that the accumulation of ROS in the G6PD-deficient background can drive maladaptive remodeling. Our study reveals an adaptive role for H₂S relevant to basic and translational studies. Identifying adaptive signaling mediators of the β-AR-induced hypertrophy may reveal new therapeutic targets and routes for CVD therapy optimization.

In cardiac muscle cells, both adrenergic agonists and antagonists induce reactive oxygen species from NOX2 but mutually attenuate each other's effects

In cardiac muscle cells adrenergic agonists stimulate the generation of reactive oxygen species, followed by redox signaling. We postulated that the antagonists would attenuate such reactive oxygen species generation by the agonists. H9c2 cardiac myoblasts, neonatal rat cardiac myocytes, and HEK293 cells expressing β1/β2 adrenoceptors were stimulated with several agonists and antagonists. All the agonists and antagonists independently generated reactive oxygen species; but its generation was minimum whenever an agonists was added together with an antagonist. We monitored the Ca++ signaling in the treated cells and obtained similar results. In all treatment sets, superoxide and H2O2 were generated in the mitochondria and the cytosol respectively. NOX2 inhibitor gp91ds-tat blocked reactive oxygen species generation by both the agonists and the antagonists. The level of p47phox subunit of NOX2 rapidly increased upon treatment, and it translocated to the plasma membrane, confirming NOX2 activation. Inhibitor studies showed that the activation of NOX2 involves ERK, PI3K, and tyrosine kinases. Recombinant promoter-reporter assays showed that reactive oxygen species generated by both the agonists and antagonists modulated downstream gene expression. Mice injected with the β-adrenergic agonist isoproterenol and fed with the antagonist metoprolol showed a robust induction of p47phox in the heart. We conclude that both the agonism and antagonism of adrenoceptors initiate redox signaling but when added together, they mutually counteract each other's effects. Our study thus highlights the importance of reactive oxygen species in adrenoceptor agonism and antagonism with relevance to the therapeutic use of the β blockers.

Mitoapocynin, a mitochondria targeted derivative of apocynin induces mitochondrial ROS generation and apoptosis in multiple cell types including cardiac myoblasts: a potential constraint to its therapeutic use

Mitoapocynin is a triphenylphosphonium conjugated derivative of apocynin that specifically locates to the mitochondria. It has been developed as a mitochondrially targeted therapeutic antioxidant. We attempted to attenuate the mitochondrial ROS induced in H9c2 cardiac myoblast cells treated with norepinephrine. Mitoapocynin was a poor quencher of total ROS as detected by the fluoroprobe DCFH-DA. Using mitochondrial superoxide specific probe MitoSoxRed, we found that 5-10 µM mitoapocynin itself induces superoxide over and above that is generated by the norepinephrine treatment. A supposedly control molecule to mitoapocynin, the synthetic compound PhC11TPP, having the triphenylphosphonium group and a benzene moiety with C11 aliphatic chain spacer was also found to be a robust inducer of mitochondrial ROS. Subsequent assays with several cell lines viz., NIH3T3, HEK293, Neuro2A, MCF-7 and H9c2, showed that prolonged exposure to mitoapocynin induces cell death by apoptosis that can be partially prevented by the general antioxidant N-acetyl cysteine. Analyses of mitochondrial electron transport complexes by Blue Native Polyacrylamide gel electrophoresis showed that both mitoapocynin and PhC11TPP disrupt the mitochondrial Complex I and V, and in addition, PhC11TPP also damages the Complex IV. Our data thus highlights the limitations of the therapeutic use of mitoapocynin as an antioxidant.

Catestatin reverses the hypertrophic effects of norepinephrine in H9c2 cardiac myoblasts by modulating the adrenergic signaling

Catestatin (CST) is a catecholamine release-inhibitory peptide secreted from the adrenergic neurons and the adrenal glands. It regulates the cardiovascular functions and it is associated with cardiovascular diseases. Though its mechanisms of actions are not known, there are evidences of cross-talk between the adrenergic and CST signaling. We hypothesized that CST moderates the adrenergic overdrive and studied its effects on norepinephrine-mediated hypertrophic responses in H9c2 cardiac myoblasts. CST alone regulated the expression of a number of fetal genes that are induced during hypertrophy. When cells were pre-treated CST, it blunted the modulation of those genes by norepinephrine. Norepinephrine (2 µM) treatment also increased cell size and enhanced the level of Troponin T in the sarcomere. These effects were attenuated by the treatment with CST. CST attenuated the immediate generation of ROS and the increase in glutathione peroxidase activity induced by norepinephrine treatment. Expression of fosB and AP-1 promoter-reporter constructs was used as the endpoint readout for the interaction between the CST and adrenergic signals at the gene level. It showed that CST largely attenuates the stimulatory effects of norepinephrine and other mitogenic signals through the modulation of the gene regulatory modules in a characteristic manner. Depending upon the dose, the signaling by CST appears to be disparate, and at 10-25 nM doses, it primarily moderated the signaling by the β1/2-adrenoceptors. This study, for the first time, provides insights into the modulation of adrenergic signaling in the heart by CST.

Apocynin prevents isoproterenol-induced cardiac hypertrophy in rat

Oxidative stress is implicated in the pathogenesis of a plethora of cardiovascular diseases including interstitial fibrosis, contractile dysfunction, ischemia-reperfusion injury, and cardiac remodeling. However, antioxidant therapies targeting oxidative stress in the progression of those diseases have largely been unsuccessful. The current study evaluated the effects of a NADPH oxidase inhibitor, apocynin (Apo), on the production of reactive oxygen species and the development of pathological cardiac hypertrophy under sustained β-adrenergic stimulation in male Wistar rats. As evident from the HW/BW ratio, HW/TL ratio, echocardiography, and histopathology, hypertrophic responses induced by isoproterenol (Iso; 5 mg/Kg body weight, subcutaneous) were blocked by Apo (10 mg/Kg body weight, intraperitoneal). Iso treatment increased the transcript levels of cybb and p22-phox, the two subunits of Nox. Iso treatment also caused a decrease in reduced glutathione level that was restored by Apo. Increase in mRNA levels of a number of markers of hypertrophy, viz., ANP, BNP, β-MHC, and ACTA-1 by Iso was either partially or completely prevented by Apo. Activation of key signaling kinases such as PKA, Erk, and Akt by Iso was also prevented by Apo treatment. Our study thus provided hemodynamic, biochemical, and molecular evidences supporting the therapeutic value of Apo in ameliorating adrenergic stress-induced cardiac hypertrophy.

Activation of adrenergic receptor in H9c2 cardiac myoblasts co-stimulates Nox2 and the derived ROS mediate the downstream responses

In recent years, NADPH oxidases (Noxes) have emerged as an important player in cardiovascular pathophysiology. Despite the growing evidences on the role of specific Nox isoforms, mechanisms of their activation, targets of reactive oxygen species (ROS) generated, and their downstream effects are poorly understood as yet. In this study, we treated H9c2 cardiac myoblasts with norepinephrine (NE, 2 µM), inducing ROS generation that was inhibited by Nox2-specific peptide inhibitor gp91ds-tat. Organelle-specific hydrogen peroxide-sensitive probe HyPer showed that the site of ROS generation is primarily in the cytosol, to some extent in the endoplasmic reticulum (ER) but not the mitochondria. Modulation of mRNAs of marker genes of cardiac hypertrophy i.e. induction in ANP and β-MHC, and reduction in α-MHC by NE treatment was prevented by specific inhibition of Nox2 by gp91ds-tat. Induction of ANP and β-MHC at the protein level were also attenuated by the inhibition of Nox2. Induction of c-Jun and FosB, the two members of the transcription factor family AP-1, were also blocked by the inhibition of Nox2 by gp91ds-tat. Induction of promoter-reporter constructs harboring multiple AP-1 elements and the upstream of FosB and ANP genes by NE were also blocked by the inhibition of Nox2 by gp91ds-tat and a dominant negative mutant of p22phox, a constituent of Nox2 that prevents its activation. This study for the first time establishes the significant role of Nox2 in mediating the NE-induced pathological adrenergic signaling in cardiac myoblasts.

Norepinephrine-induced apoptotic and hypertrophic responses in H9c2 cardiac myoblasts are characterized by different repertoire of reactive oxygen species generation

Despite recent advances, the role of ROS in mediating hypertrophic and apoptotic responses in cardiac myocytes elicited by norepinephrine (NE) is rather poorly understood. We demonstrate through our experiments that H9c2 cardiac myoblasts treated with 2 µM NE (hypertrophic dose) generate DCFH-DA positive ROS only for 2 h; while those treated with 100 µM NE (apoptotic dose) sustains generation for 48 h, followed by apoptosis. Though the levels of DCFH fluorescence were comparable at early time points in the two treatment sets, its quenching by DPI, catalase and MnTmPyP suggested the existence of a different repertoire of ROS. Both doses of NE also induced moderate levels of H₂O₂ but with different kinetics. Sustained but intermittent generation of highly reactive species detectable by HPF was seen in both treatment sets but no peroxynitrite was generated in either conditions. Sustained generation of hydroxyl radicals with no appreciable differences were noticed in both treatment sets. Nevertheless, despite similar profile of ROS generation between the two conditions, extensive DNA damage as evident from the increase in 8-OH-dG content, formation of γ-H2AX and PARP cleavage was seen only in cells treated with the higher dose of NE. We therefore conclude that hypertrophic and apoptotic doses of NE generate distinct but comparable repertoire of ROS/RNS leading to two very distinct downstream responses.

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H9c2 myoblasts upon treatment with 2 and 100 µM NE induces hypertrophy and apoptosis.

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Both treatments show comparable levels of DCFH fluorescence with different kinetics.

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Both treatments show comparable levels of HPF fluorescence in an oscillating manner.

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More hydroxyl radical was generated in 100 µM NE treated set.

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DNA damage and apoptosis occurs only in 100 µM NE treated sets.

Prion infections and anti-PrP antibodies trigger converging neurotoxic pathways

Prions induce lethal neurodegeneration and consist of PrP^Sc, an aggregated conformer of the cellular prion protein PrP^C. Antibody-derived ligands to the globular domain of PrP^C (collectively termed GDL) are also neurotoxic. Here we show that GDL and prion infections activate the same pathways. Firstly, both GDL and prion infection of cerebellar organotypic cultured slices (COCS) induced the production of reactive oxygen species (ROS). Accordingly, ROS scavenging, which counteracts GDL toxicity in vitro and in vivo, prolonged the lifespan of prion-infected mice and protected prion-infected COCS from neurodegeneration. Instead, neither glutamate receptor antagonists nor inhibitors of endoplasmic reticulum calcium channels abolished neurotoxicity in either model. Secondly, antibodies against the flexible tail (FT) of PrP^C reduced neurotoxicity in both GDL-exposed and prion-infected COCS, suggesting that the FT executes toxicity in both paradigms. Thirdly, the PERK pathway of the unfolded protein response was activated in both models. Finally, 80% of transcriptionally downregulated genes overlapped between prion-infected and GDL-treated COCS. We conclude that GDL mimic the interaction of PrP^Sc with PrP^C, thereby triggering the downstream events characteristic of prion infection.

Prion diseases are a group of infectious, invariably fatal neurodegenerative diseases. Progress in developing therapeutics is slow, partly because animal models of prion diseases require stringent biosafety and are very slow. We recently found that treatment of cerebellar slices with antibodies targeting the globular domain (GD ligands) of the prion protein (PrP) is neurotoxic. Here we compared this model to prion infection, and describe striking similarities. Both models involved the production of reactive oxygen species, and antioxidants could reverse the toxicity in cerebellar slices and even prolong the survival time of prion-infected mice. Antibodies targeting the flexible tail of PrP that prevent toxicity of GD ligands reduced the toxicity induced by prions. Endoplasmic reticulum stress, which is involved in prion toxicity, is also found in GD-ligand induced neurotoxicity. Finally, changes of gene expression were similar in both models. We conclude that prion infection and GD ligands use converging neurotoxic pathways. Because GD ligands induce toxicity within days rather than months and do not pose biosafety hazards, they may represent a powerful tool for furthering our understanding of prion pathogenesis and also for the discovery of antiprion drugs.

SG2NA recruits DJ-1 and Akt into the mitochondria and membrane to protect cells from oxidative damage

SG2NA is a WD-40 repeat protein with multiple protein-protein interaction domains of unknown functions. We demonstrate that it associates with the antioxidant protein DJ-1 and the survival kinase Akt. The C-terminal WD-40 repeat domain of SG2NA is required for its interaction with Akt, while DJ-1 binds it further upstream. No interaction between DJ-1 and Akt occurs in the absence of SG2NA. SG2NA, DJ-1, and Akt colocalize in mitochondria and plasma membrane. Their association is enhanced by increasing levels of reactive oxygen species up to a threshold level but falters thereafter with further increase in oxidants. Mutants of DJ-1 found in patients with familial parkinsonism are not recruited by SG2NA, suggesting its role in neuroprotection. Cells depleted of SG2NA are susceptible, while those overexpressing it are resistant to apoptosis induced by oxidative stress. Our study thus unravels a novel pathway of recruitment of Akt and DJ-1 that provides protection against oxidative stress, especially in neurons.

Cardioprotection of Shenfu preparata on cardiac myocytes through cytochrome P450 2J3

OBJECTIVE

To evaluate whether Shenfu injection (SFI) protects against cardiac myocyte injury induced by Fupian injection (FPI) in vitro.

METHODS

H9c2 cells were separately treated with FPI, Renshen injection (RSI) and SFI. Cell viability, lactate dehydrogenase (LDH) release, spontaneous beating rate of primative cardical cells, caspase-3/7 activity, cell apoptosis, and cytochrome P450 2J3 (CYP2J3) mRNA expression were analyzed.

RESULTS

The viability of H9c2 cells treated with SFI (37 and 75 mg/mL) was significantly higher than that of H9c2 cells treated with FPI (25 and 50 mg/mL) (P<0.05, P<0.01, respectively). LDH activity of H9c2 cells treated with SFI (75 mg/mL) was significantly decreased (P<0.01) compared with that of H9c2 cells treated with FPI (50 mg/mL). SFI (150 mg/mL) significantly attenuated FPI (100 mg/mL)-induced spontaneous beating rate decrease in primary myocardial cells after 4-hour treatment. Compared with FPI (12 and 25 mg/mL), SFI (18 and 37 mg/mL) treatment could effectively reverse the change of caspase-3/7 activity (P<0.01 and P<0.01, respectively). Compared with FPI (6 and 25 mg/mL), apoptotic cells decreased significantly (P<0.05, P<0.01, respectively) when H9c2 cells were incubated with SFI (9 and 37 mg/mL). The expression of CYP2J3 mRNA was down-regulated by FPI, while RSI and SFI could up-regulate the expression of CYP2J3 (P<0.01), which suggested the potential mechanism of protection of RSI against cardiac myocyte damage induced by FPI treatment.

CONCLUSION

These observations indicate that SFI has the potential to exert cardioprotective effects against FPI toxicity. The effect was possibly correlated with the activation of CYP2J3.

Cellular redox, epigenetics and diseases

Since the Central dogma of Molecular Biology was proposed about 40 years ago; our understanding of the intricacies of gene regulation has undergone tectonic shifts almost every decade. It is now widely accepted that the complexity of an organism is not directed by the sheer number of genes it carries but how they are decoded by a myriad of regulatory modules. Over the years, it has emerged that the organizations chromatins and its remodeling; splicing and polyadenylation of pre-mRNAs, stability and localization of mRNAs and modulation of their expression by non-coding and miRNAs play pivotal roles in metazoan gene expression. Nevertheless, in spite of tremendous progress in our understanding of all these mechanisms of gene regulation, the way these events are coordinated leading towards a highly defined proteome of a given cell type remains enigmatic. In that context, the structures of many metazoan genes cannot fully explain their pattern of expression in different tissues, especially during embryonic development and progression of various diseases. Further, numerous studies done during the past quarter of a century suggested that the heritable states of transcriptional activation or repression of a gene can be influenced by the covalent modifications of constituent bases and associated histones; its chromosomal context and long-range interactions between various chromosomal elements (Holliday 1987; Turner 1998; Lyon 1993). However, molecular dissection of these phenomena is largely unknown and is an exciting topic of research under the sub-discipline epigenetics (Gasser et al. 1998).

Serum response factor and cAMP response element binding protein are both required for cocaine induction of ΔFosB

The molecular mechanism underlying induction by cocaine of ΔFosB, a transcription factor important for addiction, remains unknown. Here, we demonstrate a necessary role for two transcription factors, cAMP response element binding protein (CREB) and serum response factor (SRF), in mediating this induction within the mouse nucleus accumbens (NAc), a key brain reward region. CREB and SRF are both activated in NAc by cocaine and bind to the fosB gene promoter. Using viral-mediated Cre recombinase expression in the NAc of single- or double-floxed mice, we show that deletion of both transcription factors from this brain region completely blocks cocaine induction of ΔFosB in NAc, whereas deletion of either factor alone has no effect. Furthermore, deletion of both SRF and CREB from NAc renders animals less sensitive to the rewarding effects of moderate doses of cocaine when tested in the conditioned place preference (CPP) procedure and also blocks locomotor sensitization to higher doses of cocaine. Deletion of CREB alone has the opposite effect and enhances both cocaine CPP and locomotor sensitization. In contrast to ΔFosB induction by cocaine, ΔFosB induction in NAc by chronic social stress, which we have shown previously requires activation of SRF, is unaffected by the deletion of CREB alone. These surprising findings demonstrate the involvement of distinct transcriptional mechanisms in mediating ΔFosB induction within this same brain region by cocaine versus stress. Our results also establish a complex mode of regulation of ΔFosB induction in response to cocaine, which requires the concerted activities of both SRF and CREB.