Mitochondrial Membrane Potential In Response Research Articles

Phosphate starvation signaling increases mitochondrial membrane potential through respiration-independent mechanisms.

Mitochondrial membrane potential directly powers many critical functions of mitochondria, including ATP production, mitochondrial protein import, and metabolite transport. Its loss is a cardinal feature of aging and mitochondrial diseases, and cells closely monitor membrane potential as an indicator of mitochondrial health. Given its central importance, it is logical that cells would modulate mitochondrial membrane potential in response to demand and environmental cues, but there has been little exploration of this question. We report that loss of the Sit4 protein phosphatase in yeast increases mitochondrial membrane potential, both by inducing the electron transport chain and the phosphate starvation response. Indeed, a similarly elevated mitochondrial membrane potential is also elicited simply by phosphate starvation or by abrogation of the Pho85-dependent phosphate sensing pathway. This enhanced membrane potential is primarily driven by an unexpected activity of the ADP/ATP carrier. We also demonstrate that this connection between phosphate limitation and enhancement of mitochondrial membrane potential is observed in primary and immortalized mammalian cells as well as in Drosophila. These data suggest that mitochondrial membrane potential is subject to environmental stimuli and intracellular signaling regulation and raise the possibility for therapeutic enhancement of mitochondrial function even in defective mitochondria.

Impaired mitophagy induces antimicrobial responses in macrophages infected with Mycobacterium tuberculosis

BackgroundMitophagy, mitochondrial selective autophagy, plays a pivotal role in the maintenance of cellular homeostasis in response to cellular stress. However, the role of mitophagy in macrophages during infection has not been elucidated. To determine whether mitophagy regulates intracellular pathogen survival, macrophages were infected with Mycobacterium tuberculosis (Mtb), an intracellular bacterium.ResultsWe showed that Mtb-infected macrophages induced mitophagy through BCL2/adenovirus E1B 19 kDa protein-interacting protein 3 (BNIP3) activation. In contrast, BNIP3-deficient macrophages failed to induce mitophagy, resulting in reduced mitochondrial membrane potential in response to Mtb infection. Moreover, the accumulation of damaged mitochondria due to BNIP3 deficiency generated higher levels of mitochondrial reactive oxygen species (mROS) compared to the control, suppressing the intracellular survival of Mtb. We observed that siBNIP3 suppressed intracellular Mtb in mice lungs.ConclusionWe found that BNIP3 plays a critical role in the regulation of mitophagy during Mtb infection. The inhibition of mitophagy suppresses Mtb growth in macrophages through increased mROS production. Therefore, BNIP3 might be a novel therapeutic target for tuberculosis treatment.

Intracellular Mg2+ protects mitochondria from oxidative stress in human keratinocytes

Reactive oxygen species (ROS) are harmful for the human body, and exposure to ultraviolet irradiation triggers ROS generation. Previous studies have demonstrated that ROS decrease mitochondrial membrane potential (MMP) and that Mg2+ protects mitochondria from oxidative stress. Therefore, we visualized the spatio-temporal dynamics of Mg2+ in keratinocytes (a skin component) in response to H2O2 (a type of ROS) and found that it increased cytosolic Mg2+ levels. H2O2-induced responses in both Mg2+ and ATP were larger in keratinocytes derived from adults than in keratinocytes derived from newborns, and inhibition of mitochondrial ATP synthesis enhanced the H2O2-induced Mg2+ response, indicating that a major source of Mg2+ was dissociation from ATP. Simultaneous imaging of Mg2+ and MMP revealed that larger Mg2+ responses corresponded to lower decreases in MMP in response to H2O2. Moreover, Mg2+ supplementation attenuated H2O2-induced cell death. These suggest the potential of Mg2+ as an active ingredient to protect skin from oxidative stress.

Protective effect of multifunctional peptides PIISVYWK and FSVVPSPK on oxidative stress-mediated HUVEC injury through antioxidant and anti-apoptotic action

PIISVYWK and FSVVPSPK are antioxidant peptides identified from blue mussel protein. In the present study, the cytoprotective function of the two peptides on H2O2-mediated injuries in human umbilical vein endothelial cells (HUVECs) was evaluated. The results indicated that the peptides significantly restored cell survival (p < 0.05) in response to damage caused by H2O2 exposure. HUVECs treated with H2O2 generated high levels of ROS. While the elevated intracellular levels of ROS were decreased by the treatment with peptides; the result may be attributed to the elevated heme oxygenase-1 expression through Nrf2 nuclear translocation. Investigation of another underlying mechanism revealed that the peptides inhibited the apoptotic process in HUVECs that was induced by H2O2 exposure. Highly elevated levels of apoptotic Bax expression, the release of cytochrome C into the cytoplasm, and the cleaved caspase-3 expression were observed along with the loss of mitochondrial membrane potential (MMP). The peptides downregulated the expression of Bax and the cleaved caspase-3, inhibited the release of cytochrome C, and restored MMP in response to H2O2-mediated HUVECs injuries. In addition, the peptides increased the expression of antiapoptotic Bcl-2.

High Dietary Fat Consumption Impairs Axonal Mitochondrial Function In Vivo.

Peripheral neuropathy (PN) is the most common complication of prediabetes and diabetes. PN causes severe morbidity for Type 2 diabetes (T2D) and prediabetes patients, including limb pain followed by numbness resulting from peripheral nerve damage. PN in T2D and prediabetes is associated with dyslipidemia and elevated circulating lipids; however, the molecular mechanisms underlying PN development in prediabetes and T2D are unknown. Peripheral nerve sensory neurons rely on axonal mitochondria to provide energy for nerve impulse conduction under homeostatic conditions. Models of dyslipidemia in vitro demonstrate mitochondrial dysfunction in sensory neurons exposed to elevated levels of exogenous fatty acids. Herein, we evaluated the effect of dyslipidemia on mitochondrial function and dynamics in sensory axons of the saphenous nerve of a male high-fat diet (HFD)-fed murine model of prediabetes to identify mitochondrial alterations that correlate with PN pathogenesis in vivo We found that the HFD decreased mitochondrial membrane potential (MMP) in axonal mitochondria and reduced the ability of sensory neurons to conduct at physiological frequencies. Unlike mitochondria in control axons, which dissipated their MMP in response to increased impulse frequency (from 1 to 50 Hz), HFD mitochondria dissipated less MMP in response to axonal energy demand, suggesting a lack of reserve capacity. The HFD also decreased sensory axonal Ca2+ levels and increased mitochondrial lengthening and expression of PGC1α, a master regulator of mitochondrial biogenesis. Together, these results suggest that mitochondrial dysfunction underlies an imbalance of axonal energy and Ca2+ levels and impairs impulse conduction within the saphenous nerve in prediabetic PN.SIGNIFICANCE STATEMENT Diabetes and prediabetes are leading causes of peripheral neuropathy (PN) worldwide. PN has no cure, but development in diabetes and prediabetes is associated with dyslipidemia, including elevated levels of saturated fatty acids. Saturated fatty acids impair mitochondrial dynamics and function in cultured neurons, indicating a role for mitochondrial dysfunction in PN progression; however, the effect of elevated circulating fatty acids on the peripheral nervous system in vivo is unknown. In this study, we identify early pathogenic events in sensory nerve axons of mice with high-fat diet-induced PN, including alterations in mitochondrial function, axonal conduction, and intra-axonal calcium, that provide important insight into potential PN mechanisms associated with prediabetes and dyslipidemia in vivo.

Caspase-3 Activation Correlates With the Initial Mitochondrial Membrane Depolarization in Neonatal Cerebellar Granule Neurons.

In this study we evaluated the effect of the reduction in the endoplasmic reticulum calcium concentration ([Ca2+]ER), changes in the cytoplasmic calcium concentration ([Ca2+]i), alteration of the mitochondrial membrane potential, and the ER stress in the activation of caspase-3 in neonatal cerebellar granule cells (CGN). The cells were loaded with Fura-2 to detect changes in the [Ca2+]i and with Mag-fluo-4 to measure variations in the [Ca2+]ER or with TMRE to follow modifications in the mitochondrial membrane potential in response to five different inducers of CGN cell death. These inducers were staurosporine, thapsigargin, tunicamycin, nifedipine and plasma membrane repolarization by switching culture medium from 25 mM KCl (K25) to 5 mM KCl (K5). Additionally, different markers of ER stress were determined and all these parameters were correlated with the activation of caspase-3. The different inducers of cell death in CGN resulted in three different levels of activation of caspase-3. The highest caspase-3 activity occurred in response to K5. At the same time, staurosporine, nifedipine, and tunicamycin elicited an intermediate activation of caspase-3. Importantly, thapsigargin did not activate caspase-3 at any time. Both K5 and nifedipine rapidly decreased the [Ca2+]i, but only K5 immediately reduced the [Ca2+]ER and the mitochondrial membrane potential. Staurosporine and tunicamycin increased the [Ca2+]i and they decreased both the [Ca2+]ER and mitochondrial membrane potential, but at a much lower rate than K5. Thapsigargin strongly increased the [Ca2+]i, but it took 10 min to observe any decrease in the mitochondrial membrane potential. Three cell death inducers -K5, staurosporine, and thapsigargin- elicited ER stress, but they took 30 min to have any effect. Thapsigargin, as expected, displayed the highest efficacy activating PERK. Moreover, a specific PERK inhibitor did not have any impact on cell death triggered by these cell death inducers. Our data suggest that voltage-gated Ca2+ channels, that are not dihydropyridine-sensitive, load the ER with Ca2+ and this Ca2+ flux plays a critical role in keeping the mitochondrial membrane potential polarized. A rapid decrease in the [Ca2+]ER resulted in rapid mitochondrial membrane depolarization and strong activation of caspase-3 without the intervention of the ER stress in CGN.

TGF-β1 fucosylation enhances the autophagy and mitophagy via PI3K/Akt and Ras-Raf-MEK-ERK in ovarian carcinoma

Transforming growth factor-β, a cell secretion factor of the TGF-β superfamily, is involved in the regulation of cell proliferation, differentiation, cytoskeleton formation, migration, invasion and other biological behaviors. Autophagy and mitophagy play an important role in tumor progression by regulating self-digestion, and degradation and reuse of cells and mitochondria. In this study, changes in autophagy and mitophagy processes in ovarian cancer cells under TGF-β1 treatment were detected via Western blot and immunofluorescence, as well as the role of fucosylation modification. Changes in mitochondrial membrane potential in response to TGF-β1 and fucosylation were detected via immunofluorescence. The effects of TGF-β1 and its fucosylation on autophagic flux were further determined by transient transfection of cells with Ad-mRFP-GFP-LC3 adenovirus. TGF-β1 clearly promoted autophagy and mitophagy in ovarian cancer cells. TGF-β1 fucosylation stimulated these regulatory effects on ovarian cancer cells via modulation of PI3K/Akt and Ras-Raf-MEK-ERK pathways through TAK1. Our collective data support the physiological significance of TGF-β1 and provide a novel direction for targeted therapy for ovarian cancer.

Overexpression of leukemia inhibitory factor enhances chemotherapy tolerance of endometrial cancer cells in vitro

To investigate the effect of overexpression of leukemia inhibitory factor (LIF) on cisplatin and paclitaxel resistance of endometrial cancer cells in vitro. Endometrial cancer cell lines HEC-1B and RL95-2 were infected with a recombinant lentivirus to overexpress LIF, and the changes in LIF expression was verified using RT-qPCR and ELISA. The viability of the LIF-overexpressing cells was assessed using CCK-8 assay, and the cell apoptosis and changes in mitochondrial membrane potential in response to cisplatin or paclitaxel treatment were analyzed with annexin V-FITC/PI staining and JC-1 assay, respectively. The effect of LIF overexpression on the expressions of Bcl-2 family proteins and STAT3 pathway was evaluated using Western blotting; dual-luciferase reporter gene assay was employed to detect the transcriptional activity of STAT3. The effect of STAT3 silencing on apoptosis of the LIF-overexpressing cells induced by cisplatin or paclitaxel was investigated. The cell lines infected with the recombinant lentivirus showed significantly increased mRNA and protein levels of LIF (P < 0.05) without obvious changes in the cell viability (P>0.05). LIF overexpression significantly attenuated cisplatin-or paclitaxel-induced apoptosis of the endometrial cancer cells (P < 0.05) and markedly increased mitochondrial membrane potential of the cells (P < 0.05). The expressions of Bcl-2, Bcl-xL and p-STAT3 proteins increased obviously while the expressions of Bax, Bad and STAT3 either decreased or showed no obvious changes in the LIF-overexpressing cells. Overexpressing LIF significantly enhanced the transcriptional activity of STAT3 (P < 0.05), and silencing STAT3 obviously enhanced apoptosis of the endometrial cancer cells overexpressing LIF (P < 0.05). s Overexpression of LIF can enhance cisplatin and paclitaxel resistance to endometrial cancer cells in vitro.

Emodin inhibits colon cancer by altering BCL-2 family proteins and cell survival pathways

BackgroundCurrently offered therapeutics to treat colon cancer (CoCa) are toxic when given at maximum tolerated dose to achieve optimal clinical response. Hence, less toxic therapeutic intervention is needed to treat CoCa. In this study, we investigated the effect of a natural agent, Emodin, on CoCa.MethodsCell viability (MTT) assay was used to determine the effect of Emodin on human CoCa and colon epithelial cells. Flow cytometric analysis was used to determine Emodin induced cell death. Antibody microarray and western blot analyses were used to determine Emodin induced molecular changes involved in cell death. Change in mitochondrial membrane potential in response to Emodin was determined by flow cytometric analysis. Expression and localization of Bcl-2 family proteins were assessed by western blot analysis.ResultsEmodin decreased viability of CoCa cells and induced apoptosis in a time and dose-dependent manner compared to vehicle-treated control without significantly impacting normal colon epithelial cells. Emodin activated caspases, modulated Bcl-2 family of proteins and reduced mitochondrial membrane potential to induce CoCa cell death. Further, changes in Bcl-2 family protein expression and localization correlated with loss in mitochondrial membrane potential. Signaling (MAPK/JNK, PI3K/AKT, NF-κβ and STAT) pathways associated with cell growth, differentiation, and Bcl-2 family expression or function were negatively regulated by Emodin.ConclusionsAbility of Emodin to impact molecular pathways involved in cell survival and apoptosis highlight the potential of this agent as a new and less toxic alternative for CoCa treatment.

Tubastatin A attenuates chronic angiotensin‐II‐induced autophagy

IntroductionIt has been shown that autophagy is playing one of the crucial cellular functions, which maintain the cellular homeostasis as well as cardiac hypertrophy, but the mechanism is poorly understood. Studies have shown that over activation of autophagy is not always protective but may cause autophagic cell death. Recent reports have demonstrated that STAT3 participates in the process of autophagy. Bcl2 is an anti‐apoptotic and anti‐autophagic protein that inhibits autophagy through direct interaction with the BH3 domain of pro‐autophagic protein beclin1. Here we have examined the protective role of HDAC6 inhibitor Tubastatin A (TBSA) during chronic angiotensin II‐induced autophagy in human iPSC‐derived cardiomyocytes (hiCMCs).HypothesisWe hypothesize that TBSA treatment mediated activation of STAT3‐Bcl2 is a critical regulator of angiotensin II‐induced hiCMCs autophagy and the over expression of HDAC6 in hiCMCs leads to exaggerate angiotensin II‐induced autophagy.Methods and ResultsWe have evaluated the TBSA treatment mediated effects in the contractility of hiCMCs, cell size and mitochondrial membrane potential in response to angiotensin II‐induced autophagy. Our data shows that the functional effect of hiCMCs stimulated with angiotensin II has significantly reduced the beating frequency, whereas treatment with TBSA rescued the beating frequency (Fig. A, B). Furthermore, the angiotensin II‐induced hypertrophic effect on hiCMCs is significantly reduced by TBSA treatment (Fig. C). Moreover, the immunostaining with JC1 (marker for Autophagy) shows that the mitochondrial membrane potential significantly reduced in angiotensin II‐induced hiCMCs, whereas TBSA treatment maintains the mitochondrial membrane potential (Fig D). Moreover, our electron microscopic analysis revealed a dramatic difference was observed between angiotensin II induced hiCMCs and Angiotensin II‐induced hiCMCs treated with TBSA in actin cytoskeletal protein and disorganized sarcomeres.ConclusionsWe report for the first time that the role of HDAC6 in regulation of pathological autophagy, thus can acts as a potential therapeutic target for treatment of chronic heart diseases.Support or Funding InformationAmerican Heart Association Grant‐in‐Aid Grant 16GRNT30950010This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Decanoic acid suppresses proliferation and invasiveness of human trophoblast cells by disrupting mitochondrial function

Decanoic acid (DA) is a medium-chain fatty acid used in the manufacture of various products including plastics, cosmetics, and lubricants. In addition to antiviral and antibacterial effects, DA's, reported biological activities include regulation of signaling pathways and redox homeostasis in various human cell types. The influence of DA on functional properties of human trophoblasts, including proliferation, invasion and apoptosis is currently unknown. In the present study, we evaluated the anti-proliferative and anti-invasive effects of DA on the human trophoblast cell line HTR8/SVneo. In addition, DA induced oxidative stress, as evidenced by generation of reactive oxygen species (ROS) and induction of lipid peroxidation (LPO). This oxidative stress was accompanied by activation of the mitochondria-dependent apoptotic pathway in HTR8/SVneo cells. We also observed elevated mitochondrial Ca2+, and loss of mitochondrial membrane potential in response to DA treatment. Chelation of mitochondrial Ca2+ using BAPTA-AM rescued cellular proliferation suppressed by DA. We also verified that signaling proteins including AKT, P70S6K, S6, and ERK1/2 and their targets were significantly reduced in HTR8/SVneo cells by DA treatment. Pre-treatment of cells with selective inhibitors of AKT (LY294002) and ERK1/2 (U0126) revealed that the AKT and ERK1/2 signaling pathways regulated by DA displayed cross-talk in HTR8/SVneo cells. Collectively, these results suggest that personal products containing DA will have harmful effects on human trophoblasts, and could cause implantation and placentation failure during early pregnancy.

Moderate activation of autophagy regulates the intracellular calcium ion concentration and mitochondrial membrane potential in beta-amyloid-treated PC12 cells

Alzheimer’s disease (AD) is an age-related and progressive neurodegenerative disease. Aggregated beta-amyloid (Aβ) disturbs Ca2+ homeostasis and causes mitochondrial dysfunction and finally underlies AD. Recent evidence suggests that autophagy initiation by Beclin-1 protein might be involved in the pathogenesis of AD. However, the effects of Beclin-1 dependent autophagy on intracellular calcium ion concentration ([Ca2+]i) and mitochondrial membrane potential (MMP) is unclear. The effects of Beclin-1 dependent autophagy that were activated by a gradient concentration of autophagy activator rapamycin or inhibited by autophagy inhibitor 3-methyladenine (3-MA) on cell viability and cell morphology were examined. Pretreatment with rapamycin significantly up-regulated the expression of Beclin-1 in response to Aβ1–42 application, but after pretreatment with 3-MA it was significantly down-regulated. Moderate activation of Beclin-1 dependent autophagy had an up regulation effect on cell viability and could maintain the original morphology of cells. Furthermore, rapamycin or 3-MA on [Ca2+]i and MMP in Aβ1–42 treatment of PC12 cells were evaluated. We also report that PC12 cells treated with Aβ1–42 showed an increase in [Ca2+]i but a decrease in MMP when compared to the normal control. However the application of rapamycin prior to this prevented the increase in [Ca2+]i and the decrease in MMP in response to Aβ1–42. When 3-MA was applied this exacerbated the effect of Aβ1–42 on the [Ca2+]i and the MMP. This shows that moderate activation of Beclin-1 dependent autophagy by rapamycin can modulate Ca2+ homeostasis and maintain MMP in response to Aβ1–42 induced cytotoxicity and so may have a preventive function in AD.

Evaluación del potencial de membrana mitocondrial en espermatozoides humanos capacitados

Introducción: los espermatozoides humanos durante su viaje por el tracto reproductivo sufren el proceso de capacitación espermática, evento indispensable para la fecundación y que se ha relacionado con cambios en el potencial de membrana mitocondrial. Objetivos: evaluar el efecto de la capacitación espermática sobre el potencial de membrana mitocondrial en espermatozoides humanos. Materiales y métodos: se realizó un estudio in vitro en el cual se seleccionaron los espermatozoides puros de nueve voluntarios, los cuales se sometieron a condiciones capacitantes durante seis horas. Posteriormente, se evaluó el efecto de la capacitación sobre el estado del potencial de membrana mitocondrial usando el colorante DiOC6(3) por citometría de flujo. Resultados: de las nueve muestras seminales evaluadas cinco presentaron mayor intensidad media de fluorescencia en el potencial de membrana mitocondrial poscapacitación. Todas las muestras seminales mostraron parámetros normales y no presentaron cambios en la movilidad y la viabilidad espermática durante la selección y la capacitación espermática in vitro. Conclusiones: las modificaciones en el potencial de membrana mitocondrial en respuesta al proceso de capacitación demuestra que existen diferentes poblaciones espermáticas en el eyaculado humano; entender cuál está relacionada con el proceso reproductivo exitoso permitirá aumentar la probabilidad de embarazos.

Protective effects of early hypoxic post-conditioning in cultured cortical neurons

Primary objective: Recent evidence suggests that delayed hypoxic post-conditioning is neuroprotective. The aim of the present study was to test whether early post-conditioning applied immediately after hypoxia could protect cultured neurons from hypoxia/reoxygenation (H/R)-induced injuries.Methods: Primary cortical neuronal culture depleted of microglia was exposed to H/R. Post-conditioning started immediately after hypoxia and consisted of three cycles of 15-minutes of reoxygenation and 15-minutes of hypoxia. Cell viability assay was performed using Cell Counting Kit-8 (CCK-8). Apoptosis was evaluated by Hoechst 33258 staining, FITC-Annexin V/PI double staining and Western blot assay (testing the cleaved caspase-3 expression). Reactive oxygen species (ROS), intracellular Ca2+ and mitochondrial membrane potential (MMP) were examined using confocal laser-scanning microscopy.Main results: H/R significantly reduced cell viability and increased neuronal apoptosis and necrosis. Furthermore, the expression of cleaved caspase-3, ROS production and intracellular Ca2+ were increased. MMP was attenuated. Injuries induced by H/R were substantially attenuated by early hypoxic post-conditioning. Changes in cleaved caspase-3 expression, ROS production, intracellular Ca2+ level and MMP in response to H/R were significantly decreased by the post-conditioning.Conclusions: The findings demonstrated that early hypoxic post-conditioning could protect neurons against H/R-induced injuries independent of microglial cells, possibly by inhibiting ROS over-production and intracellular Ca2+ accumulation and maintaining MMP.

Normal skin and hypertrophic scar fibroblasts differentially regulate collagen and fibronectin expression as well as mitochondrial membrane potential in response to basic fibroblast growth factor

Basic fibroblast growth factor (bFGF) regulates skin wound healing; however, the underlying mechanism remains to be defined. In the present study, we determined the effects of bFGF on the regulation of cell growth as well as collagen and fibronectin expression in fibroblasts from normal human skin and from hypertrophic scars. We then explored the involvement of mitochondria in mediating bFGF-induced effects on the fibroblasts. We isolated and cultivated normal and hypertrophic scar fibroblasts from tissue biopsies of patients who underwent plastic surgery for repairing hypertrophic scars. The fibroblasts were then treated with different concentrations of bFGF (ranging from 0.1 to 1000 ng/mL). The growth of hypertrophic scar fibroblasts became slower with selective inhibition of type I collagen production after exposure to bFGF. However, type III collagen expression was affected in both normal and hypertrophic scar fibroblasts. Moreover, fibronectin expression in the normal fibroblasts was up-regulated after bFGF treatment. bFGF (1000 ng/mL) also induced mitochondrial depolarization in hypertrophic scar fibroblasts (P < 0.01). The cellular ATP level decreased in hypertrophic scar fibroblasts (P < 0.05), while it increased in the normal fibroblasts following treatment with bFGF (P < 0.01). These data suggest that bFGF has differential effects and mechanisms on fibroblasts of the normal skin and hypertrophic scars, indicating that bFGF may play a role in the early phase of skin wound healing and post-burn scar formation.

Normal skin and hypertrophic scar fibroblasts differentially regulate collagen and fibronectin expression as well as mitochondrial membrane potential in response to basic fibroblast growth factor

Normal skin and hypertrophic scar fibroblasts differentially regulate collagen and fibronectin expression as well as mitochondrial membrane potential in response to basic fibroblast growth factor

Transient upregulation of PGC-1α diminishes cardiac ischemia tolerance via upregulation of ANT1

Prolonged cardiac overexpression of the mitochondrial biogenesis regulatory transcriptional coactivator PGC-1α disrupts cardiac contractile function and its genetic ablation limits cardiac capacity to enhance workload. In contrast, transient induction of PGC-1α alleviates neuronal cell oxidative stress and enhances skeletal myotube anti-oxidant defenses. We explored whether transient upregulation of PGC-1α in the heart protects against ischemia–reperfusion injury. The transient induction of PGC-1α in the cardiac-restricted inducible PGC-1α transgenic mouse, increased PGC-1α protein levels 5-fold. Following 25 min of ischemia and 2 h of reperfusion on a Langendorff perfusion apparatus, contractile recovery and the rate pressure product was significantly blunted in mice overexpressing PGC-1α vs. controls. Affymetrix gene array analysis showed a 3-fold PGC-1α-mediated upregulation of adenine nucleotide translocase 1 (ANT1). As ANT1 upregulation induces cardiomyocyte cell death we investigated whether the induction of ANT1 by PGC-1α contributes to this enhanced ischemia-stress susceptibility. Infection with adenovirus harboring PGC-1α into cardiac-derived H9c2 cells significantly upregulates ANT1 without changing basal cell viability. In response to anoxia-reoxygenation injury cell death is significantly increased following PGC-1α overexpression. This detrimental effect is abolished following siRNA knockdown of ANT1. Similarly, the attenuation of ANT-1 in the presence of PGC-1α overexpression preserves the mitochondrial membrane potential in response to hydrogen-peroxide stress. Interestingly, the isolated knockdown of ANT1 also protects H9c2 cells from anoxia-reoxygenation injury. Taken together these data suggest that transient induction of PGC-1α in the murine heart decreases ischemia–reperfusion contractile recovery and diminishes anoxia-reoxygenation tolerance in H9c2 cells. These adverse phenotypes appear to be mediated, in part, by PGC-1α induced upregulation of ANT1.

Assessment of mitochondrial membrane potential using an on-chip microelectrode in a microfluidic device.

The mitochondrial membrane potential is used to generate and regulate energy in living systems, driving the conversion of ADP to ATP, regulating ion homeostasis, and controlling apoptosis, all central to human health and disease. Therefore, there is a need for tools to study its regulation in a controlled environment for potential clinical and scientific applications. For this aim, an on-chip tetraphenylphosphonium (TPP(+)) selective microelectrode sensor was constructed in a microfluidic environment. The concentration of isolated mitochondria (Heb7A) used in a membrane potential measurement was 0.3 ng microL(-1), four orders of magnitude smaller than the concentration used in conventional assays (3 microg microL(-1)). In addition, the volume of the chamber (85 microL) is 2 orders of magnitude smaller than traditional experiments. As a demonstration, changes in the membrane potential are clearly measured in response to a barrage of well-known substrates and inhibitors of the electron transport chain. This general approach, which to date has not been demonstrated for study of mitochondrial function and bio-energetics in generally, can be instrumental in advancing the field of mitochondrial research and clinical applications by allowing high throughput studies of the regulation, dynamics, and statistical properties of the mitochondrial membrane potential in response to inhibitors and inducers of apoptosis in a controlled (microfluidic) chemical environment.

Increased susceptibility to oxidative damage in post-diabetic human myotubes

Obesity is an important risk factor for the development of type 2 diabetes, but not all obese individuals develop this complication. The clinical signs of type 2 diabetes can often be reversed with weight loss; however, it is unknown whether the skeletal muscle oxidative stress associated with type 2 diabetes remains after weight loss. We hypothesised that chronic exposure to high glucose and insulin would re-elicit impaired metabolism in primary myotubes from patients with a history of type 2 diabetes. Obese participants with or without type 2 diabetes completed a standardised weight loss protocol, following which all participants were euglycaemic and had similar indices of insulin sensitivity. Satellite cells were isolated from muscle biopsies and differentiated under low or high glucose and insulin conditions (HGI). Cells from participants with no history of type 2 diabetes showed robust increases in mitochondrial content, citrate synthase and cytochrome c oxidase activities when exposed to HGI. This increase in oxidative capacity was absent in cells from patients with a history of type 2 diabetes. High glucose and insulin caused increased oxidative damage in cells from the latter, despite higher superoxide dismutase expression. Cells from patients with a history of type 2 diabetes were unable to decrease mitochondrial membrane potential in response to HGI, potentially due to lower levels of uncoupling protein-3. This is the first report to note that primary myotubes from patients with a history of type 2 diabetes are unable to adapt to a hyperglycaemic-hyperinsulinaemic challenge. We have demonstrated that impaired mitochondrial biogenesis and an inability to manage oxidative stress define a muscle phenotype at risk of obesity-associated type 2 diabetes.

Functional Linkage between NOXA and Bim in Mitochondrial Apoptotic Events

NOXA is a BH3-only protein whose expression is induced by certain p53-depenent or independent apoptotic stimuli. Both NOXA and Bim are avid binders of Mcl-1, but a functional linkage between these BH3-only proteins has not yet been reported. In this study, we demonstrate that Mcl-1 binding of endogenously induced NOXA interferes with the ability of Mcl-1 to efficiently sequester endogenous Bim, as Bim is displaced from its complex with Mcl-1. Induced NOXA significantly enhances the UV sensitivity of cells, and the ensuing mitochondrial depolarization is entirely abrogated by Bim knockdown. These results demonstrate a Mcl-1-mediated cross-talk between endogenous NOXA and Bim that occurs upstream of the Bak/Bax-dependent execution of UV-induced mitochondrial depolarization. The current findings demonstrate that the mitochondrial response to an induced expression of NOXA is executed by endogenous Bim and suggest a plausible mechanism for the observed NOXA-Bim linkage.