Mitochondrial network in the heart

Characterization of dUTPase expression in mouse postnatal development and adult neurogenesis

The enzyme dUTPase has an essential role in maintaining genomic integrity. In mouse, nuclear and mitochondrial isoforms of the enzyme have been described. Here we present the isoform-specific mRNA expression levels in different murine organs during development using RT-qPCR. In this study, we analyzed organs of 14.5-day embryos and of postnatal 2-, 4-, 10-week- and 13-month-old mice. We demonstrate organ-, sex- and developmental stage-specific differences in the mRNA expression levels of both isoforms. We found high mRNA expression level of the nuclear isoform in the embryo brain, and the expression level remained relatively high in the adult brain as well. This was surprising, since dUTPase is known to play an important role in proliferating cells, and mass production of neural cells is completed by adulthood. Thus, we investigated the pattern of the dUTPase protein expression specifically in the adult brain with immunostaining and found that dUTPase is present in the germinative zones, the subventricular and the subgranular zones, where neurogenesis occurs and in the rostral migratory stream where neuroblasts migrate to the olfactory bulb. These novel findings suggest that dUTPase may have a role in cell differentiation and indicate that accurate dTTP biosynthesis can be vital, especially in neurogenesis.

Branched Chain Amino Acids Promote ATP Production Via Translocation of Glucose Transporters

Purpose

We have previously shown that maintenance of ATP levels is a promising strategy for preventing neuronal cell death, and that branched chain amino acids (BCAAs) enhanced cellular ATP levels in cultured cells and antagonized cell death. BCAAs attenuated photoreceptor degeneration and retinal ganglion cell death in rodent models of retinal degeneration or glaucoma. This study aimed to elucidate the mechanisms through which BCAAs enhance ATP production.

Methods

Intracellular ATP concentration was measured in HeLa cells under glycolysis and citric acid cycle inhibited conditions. Next, glucose uptake was quantified in HeLa cells and in 661W retinal photoreceptor-derived cells under glycolysis inhibition, endoplasmic reticulum stress, and glucose transporters (GLUTs) inhibited conditions, by measuring the fluorescence of fluorescently labeled deoxy-glucose analog using flow cytometry. Then, the intracellular behavior of GLUT1 and GLUT3 were observed in HeLa or 661W cells transfected with enhanced green fluorescent protein-GLUTs.

Results

BCAAs recovered intracellular ATP levels during glycolysis inhibition and during citric acid cycle inhibition. BCAAs significantly increased glucose uptake and recovered decreased glucose uptake induced by endoplasmic reticulum stress or glycolysis inhibition. However, BCAAs were unable to increase intracellular ATP levels or glucose uptake when GLUTs were inhibited. Fluorescence microscopy revealed that supplementation of BCAAs enhanced the translocation of GLUTs proteins to the plasma membrane over time.

Conclusions

BCAAs increase ATP production by promoting glucose uptake through promotion of glucose transporters translocation to the plasma membrane. These results may help expand the clinical application of BCAAs in retinal neurodegenerative diseases, such as glaucoma and retinal degeneration.

Polydatin attenuates chronic alcohol consumption-induced cardiomyopathy through a SIRT6-dependent mechanism

Polydatin has attracted much attention as a potential cardioprotective agent against ischemic heart disease and diabetic cardiomyopathy. However, the effect and mechanism of polydatin supplementation on alcoholic cardiomyopathy (ACM) are still unknown. This study aimed to determine the therapeutic effect of polydatin against ACM and to explore the molecular mechanisms with a focus on SIRT6-AMP-activated protein kinase (AMPK) signaling and mitochondrial function. The ACM model was established by feeding C57/BL6 mice with an ethanol Lieber-DeCarli diet for 12 weeks. The mice received polydatin (20 mg kg^-1) or vehicle treatment. We showed that polydatin treatment not only improved cardiac function but also reduced myocardial fibrosis and dynamin-related protein 1 (Drp-1)-mediated mitochondrial fission, and enhanced PTEN-induced putative kinase 1 (PINK1)-Parkin-dependent mitophagy in alcohol-treated myocardium. Importantly, these beneficial effects were mimicked by SIRT6 overexpression but abolished by the infection of recombinant serotype 9 adeno-associated virus (AAV9) carrying SIRT6-specific small hairpin RNA. Mechanistically, alcohol consumption induced a gradual decrease in the myocardial SIRT6 level, while polydatin effectively activated SIRT6-AMPK signaling and modulated mitochondrial dynamics and mitophagy, thus reducing oxidative stress damage and preserving mitochondrial function. In summary, these data present new information regarding the therapeutic actions of polydatin, suggesting that the activation of SIRT6 signaling may represent a new approach for tackling ACM-related cardiac dysfunction.

Mitochondria damage in ambient particulate matter induced cardiotoxicity: Roles of PPAR alpha/PGC-1 alpha signaling

Particulate matter (PM) had been associated with cardiotoxicity, while the mechanism of toxicity has yet to be elucidated, with mitochondria dysfunction as a potential candidate. To investigate the potential cardiotoxic effects of ambient PM exposure and assess the damage to cardiac mitochondria, C57/B6 mice were exposed to filtered air or real ambient PM for three or six weeks. Furthermore, to reveal the role of peroxisome proliferators-activated receptor alpha (PPAR alpha) in PM exposure induced cardiotoxicity/mitochondria damage, animals were also co-treated with PPAR alpha agonist WY 14,643 or PPAR alpha antagonist GW 6471. Cardiotoxicity was assessed with echocardiography and histopathology, while mitochondria damage was evaluated with mitochondria membrane potential measurement and transmission electron microscopy. Potential impacts of PM exposure to PPAR alpha signaling were detected with co-immunoprecipitation and western blotting. The results indicated that exposure to ambient PM exposure induced cardiotoxicity in C57/B6 mice, including altered cardiac functional parameters and morphology. Cardiac mitochondria damage is detected, in the form of compromised mitochondria membrane potential and morphology. Molecular investigations revealed disruption of PPAR alpha interaction with peroxisome proliferator-activated receptor gamma coactivator-1A (PGC-1a) as well as altered expression levels of PPAR alpha downstream genes. Co-treatment with WY 14,643 alleviated the observed toxicities, while co-treatment with GW 6471 had mixed results, exaggerating most cardiotoxicity and mitochondrial damage endpoints but alleviating some cardiac functional parameters. Interestingly, WY 14,643 and GW 6471 co-treatment seemed to exhibit similar regulative effects towards PPAR alpha signaling in animals exposed to PM. In conclusion, ambient PM exposure indeed induced cardiotoxicity in C57/B6 mice, in which cardiac mitochondria damage and disrupted PPAR alpha signaling are contributors.

Protective effects of vitexin on cadmium-induced renal toxicity in rats

Cadmium (Cd) is an industrial contaminant that poses severe threats to human and animal health. Vitexin (VIT) is a polyphenolic flavonoid of characteristic pharmacological properties. We explored the curative role of vitexin on Cd-induced mitochondrial-dysfunction in rat renal tissues. Twenty-four rats were equally divided into four groups and designated as control, Cd, Cd + vitexin and vitexin treated groups. The results showed that Cd exposure increased urea and creatinine levels while decreased creatinine clearance. Cd reduced the activities of antioxidant enzymes, i.e., catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GPx) and glutathione content in the Cd exposed group. Cd exposure significantly (p < 0.05) elevated the reactive oxygen species (ROS) and Thiobarbituric acid reactive substances (TBARS) levels in rat kidney. Cd also caused a significant (p < 0.05) reduction in the mitochondrial TCA-cycle enzymes, including isocitrate dehydrogenase, succinate dehydrogenase, alpha-ketoglutarate dehydrogenase, and malate-dehydrogenase activities. Besides, mitochondrial respiratory chain enzymes, including NADH-dehydrogenase, coenzyme Q-cytochrome reductase, succinic-coenzyme Q, and cytochrome c-oxidase activities were also decreased under Cd exposure. Cd exposure also damaged the mitochondrial membrane potential (MMP). However, VIT treatment potentially reduced the detrimental effects of Cd in the kidney of rats. In conclusion, our study indicated that the VIT could attenuate the Cd-induced renal toxicity in rats.

Investigation into the difference in mitochondrial-cytosolic calcium coupling between adult cardiomyocyte and hiPSC-CM using a novel multifunctional genetic probe

Ca2+ cycling plays a critical role in regulating cardiomyocyte (CM) function under both physiological and pathological conditions. Mitochondria have been implicated in Ca2+ handling in adult cardiomyocytes (ACMs). However, little is known about their role in the regulation of Ca2+ dynamics in human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs). In the present study, we developed a multifunctional genetically encoded Ca2+ probe capable of simultaneously measuring cytosolic and mitochondrial Ca2+ in real time. Using this novel probe, we determined and compared mitochondrial Ca2+ activity and the coupling with cytosolic Ca2+ dynamics in hiPSC-CMs and ACMs. Our data showed that while ACMs displayed a highly coordinated beat-by-beat response in mitochondrial Ca2+ in sync with cytosolic Ca2+, hiPSC-CMs showed high cell-wide variability in mitochondrial Ca2+ activity that is poorly coordinated with cytosolic Ca2+. We then revealed that mitochondrial-sarcoplasmic reticulum (SR) tethering, as well as the inter-mitochondrial network connection, is underdeveloped in hiPSC-CM compared to ACM, which may underlie the observed spatiotemporal decoupling between cytosolic and mitochondrial Ca2+ dynamics. Finally, we showed that knockdown of mitofusin-2 (Mfn2), a protein tethering mitochondria and SR, led to reduced cytosolic-mitochondrial Ca2+ coupling in ACMs, albeit to a lesser degree compared to hiPSC-CMs, suggesting that Mfn2 is a potential engineering target for improving mitochondrial-cytosolic Ca2+ coupling in hiPSC-CMs. Physiological relevance: The present study will advance our understanding of the role of mitochondria in Ca2+ handling and cycling in CMs, and guide the development of hiPSC-CMs for healing injured hearts.

Extended regorafenib treatment can be linked with mitochondrial damage leading to cardiotoxicity

Regorafenib (RGF) has a great success in the treatment of colorectal cancer, gastrointestinal stromal tumours and hepatocellular carcinoma by inhibiting angiogenic, stromal and oncogenic kinases. However, RGF can induce life-threatening cardiotoxicity including hypertension and cardiac ischemia/infarction. The molecular mechanism of the adverse effects has not been elucidated. Mitochondrial dysfunction is one of the major causes of cardiac diseases since cardiac cells highly need ATP for their contractility. Therefore, we aimed to investigate molecular mechanisms of RGF-induced cardiac adverse effects using H9c2 cell model by focusing on mitochondria. Cells were treated with 0-20 μM RGF for 48 and 72 h. According to our results, RGF inhibited cell proliferation and decreased the ATP content of the cells depending on the exposure time and concentration. Loss of mitochondrial membrane potential was also observed at high dose. Mitochondrial fusion/fission genes and antioxidant SOD2 (superoxide dismutase) gene expression levels increased at high doses in both treatments. Mitochondrial DNA content decreased as exposure time and concentration increased. Also, protein expression levels of mitochondrial complex I and V have reduced and stress protein HSP70 level has increased following RGF treatment. Structural abnormalities in mitochondria was seen with transmission electron microscopy at the applied higher doses. Our findings suggest that RGF-induced cardiotoxicity may be associated with mitochondrial damage in cardiac cells.

Mitochondrial fusion promoter restores mitochondrial dynamics balance and ameliorates diabetic cardiomyopathy in an optic atrophy 1-dependent way

AIM

Imbalanced mitochondrial dynamics including suppressed mitochondrial fusion has been observed in diabetic hearts. However, it is still unknown whether mitochondrial fusion promoter is an effective protection to diabetic hearts. This study was designed to explore the efficacy of mitochondrial fusion promoter on diabetic cardiomyopathy (DCM).

METHODS

Male Sprague-Dawley rats were injected with streptozotocin (STZ, 65 mg/kg/d) intraperitoneally to induce diabetes. Seven weeks after vehicle or STZ injection, control or diabetic rats were treated with the vehicle or a mitochondrial fusion promoter-M1 (2 mg/kg/d) intraperitoneally for 6 weeks. Moreover, M1 was administrated to the primary cardiomyocytes cultured in normal glucose medium (NG, 5.5 mmol/L) or high glucose (HG, 33 mnol/L).

RESULTS

Administration of M1 significantly promoted mitochondrial fusion and attenuated the reduction in optic atrophy 1 (Opa1) expression in diabetic hearts. Importantly, M1 treatment attenuated oxidative stress, improved mitochondrial function and alleviated DCM in diabetic rats. In HG-treated cardiomyocytes, M1 treatment consistently increased the expression of Opa1, promoted mitochondrial fusion, enhanced mitochondrial respiratory capacity and reduced mitochondria-derived superoxide production, all of which were blunted by Opa1 siRNA knockdown. In addition, selective upregulation of Opa1 alone can also promote mitochondrial fusion, improve mitochondrial function and inhibit mitochondria-derived superoxide production in HG-cultured cardiomyocytes.

CONCLUSION

Our findings show for the first time that mitochondrial fusion promoter M1 effectively balances mitochondrial dynamics and protects against diabetic cardiomyopathy (DCM) via an Opa1-dependent way, suggesting that promoting mitochondrial fusion might be a potential therapeutic strategy for DCM.

Toxicity assessment of the herbicide acetochlor in the human liver carcinoma (HepG2) cell line

Acetochlor is a high-volume herbicide used on a global scale and toxicity assessments are needed to define its potential for adverse effects in wildlife and humans. This study was conducted to determine the effects of acetochlor on human liver carcinoma cells (HepG2), a cell model widely used to assess the potential for chemical hepatotoxicity. Experiments were conducted at concentrations ranging 0-800 μM acetochlor over a 12 to 48h period to quantify underlying mechanisms of toxicity. Our data indicate that acetochlor suppressed HepG2 cell proliferation in both a concentration- and time-dependent manner. Acetochlor induced reactive oxygen species (ROS) generation more than 700% with exposure to 400 μM acetochlor, and acetochlor decreased the activities and levels of anti-oxidant responses (superoxide dismutase, glutathione) following exposure to 100 μM, 200 μM and 400 μM acetochlor. Acetochlor also (1) induced HepG2 cell damage through apoptotic-signaling pathways; (2) enhanced intracellular free Ca²⁺ concentration (>400%); (3) decreased mitochondrial transmembrane potential (∼77%), and reduced ATP levels (∼65%) following exposure to 400 μM acetochlor compared to untreated cells. Notably, cell cycle progression was blocked at G0/G1 phase in HepG2 cells when treated for 24 h with 400 μM acetochlor. Taken together, acetochlor induced significant cytotoxicity toward HepG2 cells, and the underlying toxicity mechanisms appear to be related to ROS generation, mitochondrial dysfunction and disruption in the cell cycle regulation. These data contribute to toxicity assessments for acetochlor, a high-use herbicide, to quantify risk to wildlife and human health.

Mitochondrial protein 18 is a positive apoptotic regulator in cardiomyocytes under oxidative stress

Accumulation of reactive oxygen species is a common phenomenon in cardiac stress conditions, for instance, coronary artery disease, aging-related cardiovascular abnormalities, and exposure to cardiac stressors such as hydrogen peroxide (H2O2). Mitochondrial protein 18 (Mtp18) is a novel mitochondrial inner membrane protein, shown to involve in the regulation of mitochondrial dynamics. Although Mtp18 is abundant in cardiac muscles, its role in cardiac apoptosis remains elusive. The present study aimed to detect the role of Mtp18 in H2O2-induced mitochondrial fission and apoptosis in cardiomyocytes. We studied the effect of Mtp18 in cardiomyocytes by modulating its expression with lentiviral construct of Mtp18-shRNA and Mtp18 c-DNA, respectively. We then analyzed mitochondrial morphological dynamics with MitoTracker Red staining; apoptosis with terminal deoxynucleotidyl transferase-mediated dUTP nick-end-labeling (TUNEL) and cell death detection assays; and protein expression with immunoblotting. Here, we observed that Mtp18 could regulate oxidative stress- mediated mitochondrial fission and apoptosis in cardiac myocytes. Mechanistically, we found that Mtp8 induced mitochondrial fission and apoptosis by enhancing dynamin-related protein 1 (Drp1) accumulation. Conversely, knockdown of Mtp18 interfered with Drp1-associated mitochondrial fission and subsequent activation of apoptosis in both HL-1 cells and primary cardiomyocytes. However, overexpression of Mtp18 alone was not sufficient to execute apoptosis when Drp1 was minimally expressed, suggesting that Mtp18 and Drp1 are interdependent in apoptotic cascade. Together, these data highlight the role of Mtp18 in cardiac apoptosis and provide a novel therapeutic insight to minimize cardiomyocyte loss via targetting mitochondrial dynamics.

Cardioprotection by exenatide: A novel mechanism via improving mitochondrial function involving the GLP-1 receptor/cAMP/PKA pathway

Accumulating evidence suggests that glucagon-like peptide-1 (GLP-1) and its analogues exert cardioprotective effects via modulating cardiomyocyte metabolism. Mitochondria play a pivotal role in the regulation of cell metabolism. It was hypothesized that treatment with exenatide, a GLP-1 analogue, may exert cardioprotective effects by improving mitochondrial function in an in vitro model of hypoxia/reoxygenation (H/R). H9c2 cells were employed to establish an in vitro model of H/R. Exenatide was added to the cells for 30 min prior to exposure to hypoxia. The GLP-1 receptor antagonist exendin‑(9‑39), the cyclic adenosine monophosphate (cAMP) inhibitor Rp-cAMPS and the protein kinase A (PKA) inhibitor H-89 were added to the cells for 10 min prior to treatment with exenatide. The release of lactate dehydrogenase (LDH) and creatine kinase-MB (CK-MB) and cardiomyocyte apoptosis were evaluated. The characteristics of mitochondrial morphology and functions, including ATP synthesis, membrane potential (ΔΨm), mitochondrial permeability transition pore (mPTP), mitochondrial ATPase activity and oxidative stress, were determined. the mitochondrial uncoupling protein-3 (UCP-3) and nuclear respiratory factor-1 (Nrf-1) were also investigated by western blot analysis. Exenatide pretreatment significantly decreased LDH and CK-MB release and cardiomyocyte apoptosis in H9c2 cells subjected to H/R. More importantly, to the best of our knowledge, this is the first report of exenatide pretreatment decreasing mitochondrial abnormalities and reducing oxidative stress, while enhancing ATP synthesis, mitochondrial ATPase activity and ΔΨm in H9c2 cells subjected to H/R. Exenatide pretreatment also decreased mitochondrial calcium overload and inhibited the opening of mPTP in H9c2 cells subjected to H/R. Furthermore, exenatide pretreatment upregulated UCP-3 and Nrf-1 expression in H9c2 cells subjected to H/R. However, the abovementioned observed effects of exenatide were all abolished when exenatide was co-administered with exendin‑(9‑39), Rp-cAMPS and̸or H-89. Therefore, the GLP-1 analogue exenatide was found to exert cardioprotective effects in an in vitro model of H/R, and this cardioprotection may be attributed to the improvement of mitochondrial function. These effects are most likely associated with the activation of the GLP-1 receptor/cAMP/PKA signaling pathway.

Cytotoxic effects of tebufenozide in vitro bioassays

Tebufenozide is considered an environmentally friendly pesticide due to its specificity on target insects, but the effects on human are well studied. Studies on the toxicity of tebufenozide at molecular and cellular level is poorly understood. The present study reveals non-selective cytotoxic effects of tebufenozide, and the apoptotic mechanism induced by tebufenozide on HeLa and Tn5B1-4 cells. We demonstrate that the viability of HeLa and Tn5B1-4 cells is inhibited by tebufenozide in a time- and concentration-dependent manner. Intracellular biochemical assays showed that tebufenozide-induced apoptosis of two cell lines concurrent with a decrease in the mitochondrial membrane potential and an increase reactive oxygen species generation, the release of cytochrome-c into the cytosol and a marked activation of caspase-3. These results indicate that a mitochondrial-dependent intrinsic pathway contributes to tebufenozide induced apoptosis in HeLa and Tn5B1-4 cells and suggests potential threats to ecosystems and human health.

Exogenous spermine inhibits hypoxia/ischemia-induced myocardial apoptosis via regulation of mitochondrial permeability transition pore and associated pathways

Myocardial infarction (MI) is associated with a high mortality rate, which is attributed to the effects of myocyte loss that occurs as a result of ischemia-induced cell death. Very few therapies can effectively prevent or delay the effects of ischemia. Polyamines (PAs) are polycations required for cell growth and division, and their use may prevent cell loss. The aim of this study was to investigate the relationship between hypoxia/ischemia (H/I)-induced cell apoptosis and PA metabolism and to investigate the ability of spermine to limit H/I injury in cardiomyocytes by blocking the mitochondrial apoptotic pathway. Neonatal rat cardiomyocytes were placed under hypoxic conditions for 24 h after being subjected to 5 μM of spermine as a pretreatment therapy. H/I induced PA catabolism, which was indicated by a 1.3-fold up-regulation of spermidine/spermine N(1)-acetyltransferase expression. Exogenous spermine significantly reduced H/I-induced cell death rate (60 ± 2 to 36 ± 2%) and apoptosis rate (42 ± 2 to 21 ± 2%); it also attenuated lactate dehyodrogenase and creatine kinase leakage (440 ± 13 and 336 ± 16 U/L to 275 ± 15 and 235 ± 13 U/L). Furthermore, it decreases calcium overload (3.8 ± 0.2 to 2.2 ± 0.1 a.u.). Moreover, spermine pretreatment remarkably decreased cytochrome c release from the mitochondria to the cytosol, lowering the expression of cleaved caspase-3 and -9. With spermine pretreatment, there was an increase in Bcl-2 levels and phosphorylation of ERK1/2, phosphoinositide 3-kinase, Akt, and GSK-3β, preserving mitochondrial membrane potential and inducing an mitochondrial permeability transition pore opening. In conclusion, H/I decreased endogenous spermine concentrations in cardiomyocytes, which ultimately induced apoptosis. The addition of exogenous spermine effectively prevented myocyte cell death.

NFAT4-dependent miR-324-5p regulates mitochondrial morphology and cardiomyocyte cell death by targeting Mtfr1

Emerging evidence suggest that the abnormal mitochondrial fission participates in pathogenesis of cardiac diseases, including myocardial infarction and heart failure. However, the molecular components regulating mitochondrial network in heart remain largely unidentified. Here we report that NFAT4, miR-324-5p and mitochondrial fission regulator 1 (Mtfr1) function in one signaling axis that regulates mitochondrial morphology and cardiomyocyte cell death. Knocking down Mtfr1 suppresses mitochondrial fission, apoptosis and myocardial infarction. Mtfr1 is a direct target of miR-324-5p, and miR-324-5p attenuates mitochondrial fission, cardiomyocyte apoptosis and myocardial infarction by suppressing Mtfr1 translation. Finally, we show that transcription factor NFAT4 inhibits miR-324-5p expression. Knockdown of NFAT4 suppresses mitochondrial fission and protects cardiomyocyte from apoptosis and myocardial infarction. Our study defines the NFAT4/ miR-324-5p/Mtfr1 axis, which participates in the regulation of mitochondrial fission and cardiomyocyte apoptosis, and suggests potential new treatment avenues for cardiac diseases.

Ginsenoside rb1 protects neonatal rat cardiomyocytes from hypoxia/ischemia induced apoptosis and inhibits activation of the mitochondrial apoptotic pathway

Aim. To investigate the effect of Ginsenoside Rb1 (GS-Rb1) on hypoxia/ischemia (H/I) injury in cardiomyocytes in vitro and the mitochondrial apoptotic pathway mediated mechanism. Methods. Neonatal rat cardiomyocytes (NRCMs) for the H/I groups were kept in DMEM without glucose and serum, and were placed into a hypoxic jar for 24 h. GS-Rb1 at concentrations from 2.5 to 40 µM was given during hypoxic period for 24 h. NRCMs injury was determined by MTT and lactate dehydrogenase (LDH) leakage assay. Cell apoptosis, ROS accumulation, and mitochondrial membrane potential (MMP) were assessed by flow cytometry. Cytosolic translocation of mitochondrial cytochrome c and Bcl-2 family proteins were determined by Western blot. Caspase-3 and caspase-9 activities were determined by the assay kit. Results. GS-Rb1 significantly reduced cell death and LDH leakage induced by H/I. It also reduced H/I induced NRCMs apoptosis induced by H/I, in accordance with a minimal reactive oxygen species (ROS) burst. Moreover, GS-Rb1 markedly decreased the translocation of cytochrome c from the mitochondria to the cytosol, increased the Bcl-2/ Bax ratio, and preserved mitochondrial transmembrane potential (ΔΨm). Its administration also inhibited activities of caspase-9 and caspase-3. Conclusion. Administration of GS-Rb1 during H/I in vitro is involved in cardioprotection by inhibiting apoptosis, which may be due to inhibition of the mitochondrial apoptotic pathway.

Exenatide protects against hypoxia/reoxygenation-induced apoptosis by improving mitochondrial function in H9c2 cells

Glucagon-like peptide-1 (GLP-1) analogues might exert the cardioprotective effects via attenuating apoptosis. This study aimed to determine the protective effects and mechanism of exenatide, a GLP-1 analogue, on cardiomyocyte apoptosis using an in vitro model of hypoxia/reoxygenation (H/R). H9c2 cells were employed to establish an in vitro model of H/R. 200 nM exenatide pretreatment significantly reduced apoptosis measured by flow cytometry. To further study the antiapoptotic mechanism of exenatide, we used flow cytometry in combination with laser confocal microscopy to determine the interaction between exenatide and the process of mitochondria-mediated apoptosis. We found that exenatide pretreatment reduced the intracellular reactive oxygen species (ROS) levels and decreased the mitochondrial calcium overload caused by H/R. Furthermore, an increase of total superoxide dismutase (T-SOD) levels, a decrease of malondialdehyde (MDA) levels, a preservation of mitochondrial membrane potential (ΔΨm), a reduction of cytochrome-c release, a decline of cleaved caspase-3 expression, and caspase-3 activation were observed in exenatide-pretreated cultures. These results suggest that exenatide exerts a protective effect on preventing against H/R-induced apoptosis. Importantly, the protective effects of exenatide may be attributed to its role in improving mitochondrial function in H9c2 cells subjected to H/R.

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.

A pre-microRNA-149 (miR-149) genetic variation affects miR-149 maturation and its ability to regulate the Puma protein in apoptosis

MicroRNAs (miRNAs) are small, single-stranded, noncoding RNAs that function as negative regulators of gene expression. They are transcribed from endogenous DNA and form hairpin structures (termed as pre-miRNAs) that are processed to form mature miRNAs. It remains largely unknown as to the molecular consequences of the natural genetic variation in pre-miRNAs. Here, we report that an A→G polymorphism (rs71428439) is located in Homo sapiens miR-149 stem-loop region. This polymorphism results in a change in the structure of the miR-149 precursor. Our results showed that the genotype distribution of this polymorphism in myocardial infarction cases was significantly different from that in the control subjects. We examined the biological significance of this polymorphism on the production of mature miR-149, and we observed that the G-allelic miR-149 precursor displayed a lower production of mature miR-149 compared with the A-allelic one. Further investigations disclosed that miR-149 could withstand mitochondrial fission and apoptosis through targeting the pro-apoptotic factor p53-up-regulated modulator of apoptosis (Puma). Enforced expression of miR-149 promoted cell survival, whereas knockdown of miR-149 rendered cells to be sensitive to apoptotic stimulation. Intriguingly, the A to G variation led pre-miR-149 to elicit an attenuated effect on the inhibition of mitochondrial fission and apoptosis. Finally, this polymorphism exerts its influence on cardiac function in the mouse model of myocardial infarction. These data suggest that this polymorphism in the miR-149 precursor may result in important phenotypic traits of myocardial infarction. Our findings warrant further investigations on the relationship between miR-149 polymorphism and myocardial infarction.

Mitochondrial membrane permeabilization and cell death during myocardial infarction: roles of calcium and reactive oxygen species

Excess generation of reactive oxygen species (ROS) and cytosolic calcium accumulation play major roles in the initiation of programmed cell death during acute myocardial infarction. Cell death may include necrosis, apoptosis and autophagy, and combinations thereof. During ischemia, calcium handling between the sarcoplasmic reticulum and myofilament is disrupted and calcium is diverted to the mitochondria causing swelling. Reperfusion, while essential for survival, reactivates energy transduction and contractility and causes the release of ROS and additional ionic imbalance. During acute ischemia-reperfusion, the principal death pathways are programmed necrosis and apoptosis through the intrinsic pathway, initiated by the opening of the mitochondrial permeability transition pore and outer mitochondrial membrane permeabilization, respectively. Despite intense investigation, the mechanisms of action and modes of regulation of mitochondrial membrane permeabilization are incompletely understood. Extrinsic apoptosis, necroptosis and autophagy may also contribute to ischemia-reperfusion injury. In this review, the roles of dysregulated calcium and ROS and the contributions of Bcl-2 proteins, as well as mitochondrial morphology in promoting mitochondrial membrane permeability change and the ensuing cell death during myocardial infarction are discussed.

Effects of aging and exercise training on apoptosis in the heart

Aging is characterized by a progressive decline in cardiac function. A critical contributor to the age-related impairment in cardiac function is the loss of cardiac myocytes through “apoptosis”, or programmed cell death. Structural remodeling in the heart with advancing age includes (a) loss of cardiomyocytes, (b) reactive hypertrophy of the remaining cardiomyocytes, and (c) increased connective tissue and altered geometry. The loss of cardiomyocytes with aging occurs through apoptosis. Particularly, mitochondrial-mediated apoptotic pathway is the best characterized and believed critical in regulating apoptosis with aging, suggesting that mitochondria are very important sites of programmed cell death. It has been also reported that mitochondrial dysfunction, oxidative stress, and impaired stress response contribute to age-induced mechanical remodeling as well as apoptosis. In contrast, exercise training not only improves cardiac function, but also reduces the risk of heart disease. We recently found that aging increased mitochondrial-mediated apoptotic signaling and apoptosis in the left ventricle, while chronic exercise training was effective in diminishing mitochondrial-mediated apoptotic signaling pathways in the aging heart, as indicated by lower DNA fragmentation, terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL)-positive staining, and caspase-3 cleavage, when compared with left ventricles from the age-matched sedentary group. In this review, we will provide a comprehensive update regarding the effects of aging and exercise training on apoptosis in the heart.