Modulation of mitochondrial membrane permeability in pathogenesis, autophagy and control of metabolism

c-Src Is Responsible for Mitochondria-Mediated Arrhythmic Risk in Ischemic Cardiomyopathy

BACKGROUND

Increased mitochondrial Ca2+ uptake has been implicated in the QT prolongation and lethal arrhythmias associated with nonischemic cardiomyopathy. We attempted to define the role of mitochondria in ischemic arrhythmic risk and to identify upstream regulators.

METHODS

Myocardial infarction (MI) was induced in wild-type FVB/NJ mice by ligation of the left anterior descending coronary artery. Western blot, immunoprecipitation, ECG telemetry, and patch-clamp techniques were used.

RESULTS

After MI, c-Src (proto-oncogene tyrosine-protein kinase Src) and its active form (phosphorylated Src, p-Src) were increased. The activation of c-Src was associated with increased diastolic Ca2+ sparks, action potential duration prolongation, and arrhythmia in MI mice. c-Src upregulation and arrhythmia could be reversed by treatment of mice with the Src inhibitor PP1 but not with the inactive analogue PP3. Tyrosine phosphorylated mitochondrial Ca2+ uniporter (MCU) was upregulated in the heart tissues of MI mice and patients with ischemic cardiomyopathy. In a heterologous expression system, c-Src could bind MCU and phosphorylate MCU tyrosines. Overexpression of wild-type c-Src significantly increased the mitochondrial Ca2+ transient while overexpression of dominant-negative c-Src significantly decreased the mitochondrial Ca2+ transient. c-Src inhibition by PP1, MCU inhibition by Ru360, or MCU knockdown could reduce the action potential duration, Ca2+ sparks, and arrhythmia after MI. The human heart tissue showed that patients with ischemic cardiomyopathy had significantly increased c-Src active form associated with increased MCU tyrosine phosphorylation and ventricular arrhythmia.

CONCLUSIONS

MI leads to increased c-Src active form that results in MCU tyrosine phosphorylation, increased mitochondrial Ca2+ uptake, QT prolongation, and arrhythmia, suggesting c-Src or MCU may represent novel antiarrhythmic targets.

Mechanism and treatment of intracerebral hemorrhage focus on mitochondrial permeability transition pore

Intracerebral hemorrhage (ICH) is the second most common subtype of stroke, characterized by high mortality and a poor prognosis. Despite various treatment methods, there has been limited improvement in the prognosis of ICH over the past decades. Therefore, it is imperative to identify a feasible treatment strategy for ICH. Mitochondria are organelles present in most eukaryotic cells and serve as the primary sites for aerobic respiration and energy production. Under unfavorable cellular conditions, mitochondria can induce changes in permeability through the opening of the mitochondrial permeability transition pore (mPTP), ultimately leading to mitochondrial dysfunction and contributing to various diseases. Recent studies have demonstrated that mPTP plays a role in the pathological processes associated with several neurodegenerative diseases including Parkinson's disease, Alzheimer's disease, Huntington's disease, ischemic stroke and ischemia-reperfusion injury, among others. However, there is limited research on mPTP involvement specifically in ICH. Therefore, this study comprehensively examines the pathological processes associated with mPTP in terms of oxidative stress, apoptosis, necrosis, autophagy, ferroptosis, and other related mechanisms to elucidate the potential mechanism underlying mPTP involvement in ICH. This research aims to provide novel insights for the treatment of secondary injury after ICH.

Neutral rhodol-based dyes expressing localization in mitochondria

Neutral rhodol-based red emitters are shown to efficiently localize in mitochondria, as demonstrated by confocal microscopy and co-localization studies. A simple model is proposed to explain the localization mechanism of neutral molecules. The model takes into account the strong coupling between the molecular dipole moment and the electric field of the inner mitochondrial membrane.

Carboxylated graphene quantum dots-mediated photothermal therapy enhances drug-membrane permeability, ROS production, and the immune system recruitment on 3D glioblastoma models

Graphene quantum dots (GQDs) are biocompatible nanoparticles employed in biomedical field, thanks to their size and photophysical properties. GQDs have shown the capability to cross biological barriers, including the blood–brain barrier, which makes them promising agents for brain diseases therapy. It has been shown that surface-functionalized GQDs enhance membrane fluidity and intracellular uptake, exerting a synergistic effect with antitumor drugs at subtherapeutic doses. Here, we tested GQDs effects in combination with chemotherapeutic agents doxorubicin and temozolomide, on a complex 3D spheroid model of glioblastoma. We observed that the capability of GQDs to absorb and convert near-infrared light into heat is a key factor in membrane permeability enhancement on 3D model. This non-invasive therapeutic strategy named photothermal therapy (PTT), combined to chemotherapy at subtherapeutic doses, significantly increased the effect of antitumor drugs by reducing tumor growth and viability. Furthermore, the increase in membrane permeability due to GQDs-mediated PTT enhanced the release of reactive oxygen species with strong migration of the immune system towards irradiated cancer spheroids. Our data indicate that the increase in membrane permeability can enhance the efficacy of antitumor drugs at subtherapeutic doses against glioblastoma, reducing side effects, and directing immune response, ultimately improving quality of life for patients.

Resveratrol reverses Palmitic Acid-induced cow neutrophils apoptosis through shifting glucose metabolism into lipid metabolism via Cav-1/ CPT 1-mediated FAO enhancement

Elevated plasma nonesterified fatty acids (NEFAs) affect neutrophils function and longevity during the periparturient period in dairy cows. Previous research has shown that resveratrol (RSV) may protect cell viability from NEFA-induced damage by regulating energy metabolism. However, it is unclear whether RSV has a protective effect on palmitic acid (PA)-treated neutrophils. The aim of this study was to investigate the molecular regulatory mechanism of the protective effect of RSV on neutrophils. The results showed that treatment with high concentrations of RSV (50 μM, 100 μM) maintained neutrophils activity by inhibiting neutrophils apoptosis (P < 0.05). Further analysis showed that high concentrations of RSV enhanced fatty acid oxidation (FAO) to produce ATP by promoting the expression of CAV1, ACSL-1 and CPT1 (P < 0. 05) while inhibiting glycolysis by suppressing PFK1 activity (P < 0. 05) and reducing glucose transport-related protein (GLUT1/GLUT4) expression by inhibiting glucose uptake (P < 0.05). These results suggest that RSV protects neutrophils from PA-induced apoptosis by regulating energy metabolism. Our results revealed that RSV protects neutrophils from PA-induced apoptosis by shifting glucose metabolism to lipid metabolism. This study tenders to a meaningful understanding of the effects of RSV on neutrophils function in periparturient cows suffering from negative energy balance (NEB).

Mitochondria in the Spotlight: C. elegans as a Model Organism to Evaluate Xenobiotic-Induced Dysfunction

Mitochondria play a crucial role in cellular respiration, ATP production, and the regulation of various cellular processes. Mitochondrial dysfunctions have been directly linked to pathophysiological conditions, making them a significant target of interest in toxicological research. In recent years, there has been a growing need to understand the intricate effects of xenobiotics on human health, necessitating the use of effective scientific research tools. Caenorhabditis elegans (C. elegans), a nonpathogenic nematode, has emerged as a powerful tool for investigating toxic mechanisms and mitochondrial dysfunction. With remarkable genetic homology to mammals, C. elegans has been used in studies to elucidate the impact of contaminants and drugs on mitochondrial function. This review focuses on the effects of several toxic metals and metalloids, drugs of abuse and pesticides on mitochondria, highlighting the utility of C. elegans as a model organism to investigate mitochondrial dysfunction induced by xenobiotics. Mitochondrial structure, function, and dynamics are discussed, emphasizing their essential role in cellular viability and the regulation of processes such as autophagy, apoptosis, and calcium homeostasis. Additionally, specific toxins and toxicants, such as arsenic, cadmium, and manganese are examined in the context of their impact on mitochondrial function and the utility of C. elegans in elucidating the underlying mechanisms. Furthermore, we demonstrate the utilization of C. elegans as an experimental model providing a promising platform for investigating the intricate relationships between xenobiotics and mitochondrial dysfunction. This knowledge could contribute to the development of strategies to mitigate the adverse effects of contaminants and drugs of abuse, ultimately enhancing our understanding of these complex processes and promoting human health.

Identity, structure, and function of the mitochondrial permeability transition pore: controversies, consensus, recent advances, and future directions

The mitochondrial permeability transition (mPT) describes a Ca2+-dependent and cyclophilin D (CypD)-facilitated increase of inner mitochondrial membrane permeability that allows diffusion of molecules up to 1.5 kDa in size. It is mediated by a non-selective channel, the mitochondrial permeability transition pore (mPTP). Sustained mPTP opening causes mitochondrial swelling, which ruptures the outer mitochondrial membrane leading to subsequent apoptotic and necrotic cell death, and is implicated in a range of pathologies. However, transient mPTP opening at various sub-conductance states may contribute several physiological roles such as alterations in mitochondrial bioenergetics and rapid Ca2+ efflux. Since its discovery decades ago, intensive efforts have been made to identify the exact pore-forming structure of the mPT. Both the adenine nucleotide translocase (ANT) and, more recently, the mitochondrial F1FO (F)-ATP synthase dimers, monomers or c-subunit ring alone have been implicated. Here we share the insights of several key investigators with different perspectives who have pioneered mPT research. We critically assess proposed models for the molecular identity of the mPTP and the mechanisms underlying its opposing roles in the life and death of cells. We provide in-depth insights into current controversies, seeking to achieve a degree of consensus that will stimulate future innovative research into the nature and role of the mPTP.

Human PNPase causes RNA stabilization and accumulation of R-loops in the Escherichia coli model system

Polyribonucleotide phosphorylase (PNPase) is a phosphorolytic RNA exonuclease highly conserved throughout evolution. In Escherichia coli, PNPase controls complex phenotypic traits like biofilm formation and growth at low temperature. In human cells, PNPase is located in mitochondria, where it is implicated in the RNA import from the cytoplasm, the mitochondrial RNA degradation and the processing of R-loops, namely stable RNA-DNA hybrids displacing a DNA strand. In this work, we show that the human PNPase (hPNPase) expressed in E. coli causes oxidative stress, SOS response activation and R-loops accumulation. Hundreds of E. coli RNAs are stabilized in presence of hPNPase, whereas only few transcripts are destabilized. Moreover, phenotypic traits typical of E. coli strains lacking PNPase are strengthened in presence of the human enzyme. We discuss the hypothesis that hPNPase expressed in E. coli may bind, but not degrade, the RNA, in agreement with previous in vitro data showing that phosphate concentrations in the range of those found in the bacterial cytoplasm and, more relevant, in the mitochondria, inhibit its activity.

The Journey of Mitochondrial Protein Import and the Roadmap to Follow

Mitochondria are double membrane-bound organelles that play critical functions in cells including metabolism, energy production, regulation of intrinsic apoptosis, and maintenance of calcium homeostasis. Mitochondria are fascinatingly equipped with their own genome and machinery for transcribing and translating 13 essential proteins of the oxidative phosphorylation system (OXPHOS). The rest of the proteins (99%) that function in mitochondria in the various pathways described above are nuclear-transcribed and synthesized as precursors in the cytosol. These proteins are imported into the mitochondria by the unique mitochondrial protein import system that consists of seven machineries. Proper functioning of the mitochondrial protein import system is crucial for optimal mitochondrial deliverables, as well as mitochondrial and cellular homeostasis. Impaired mitochondrial protein import leads to proteotoxic stress in both mitochondria and cytosol, inducing mitochondrial unfolded protein response (UPR^mt). Altered UPR^mt is associated with the development of various disease conditions including neurodegenerative and cardiovascular diseases, as well as cancer. This review sheds light on the molecular mechanisms underlying the import of nuclear-encoded mitochondrial proteins, the consequences of defective mitochondrial protein import, and the pathological conditions that arise due to altered UPR^mt.

Analysis of mitochondrial function in lymphocytes obtained from COVID-19 patients

OBJECTIVES

There is a significant decline in the lymphocyte subset counts in the peripheral blood of COVID-19 patients. However, the mitochondrial function of lymphocytes obtained from COVID-19 patients has rarely been studied.

METHODS

A case-control study was conducted in 115 COVID-19 patients and 50 healthy controls from December 2022 to February 2023. The extent of lymphocytic mitochondrial damage in these patients using mitochondrial fluorescence staining and flow cytometry. Clinical symptoms were evaluated using the SOFA and APACHE II scores.

RESULTS

The mitochondrial function of lymphocytes was severely impaired in the peripheral blood of COVID-19 patients, compared to healthy controls, and was characterized by an increased single-cell mitochondrial mass (SCMM) and increased percentage of low mitochondrial membrane potential. The increase in the SCMM of T cells was more notable in patients with severe COVID-19 and was positively correlated with the SOFA and APACHE II scores. When the SCMM-CD8 cutoff value was 38.775, the AUC for distinguishing between severe and mild COVID-19 was 0.740, and the sensitivity, specificity, and Youden index were 65.8%, 82.1%, and 0.478, respectively.

CONCLUSION

SCMM-CD8 could act as a diagnostic biomarker of COVID-19 progression. However, this needs to be verified in other multi-center studies with a larger sample size.

Mitochondrial Autophagy in Ischemic Aged Livers

Mitochondrial autophagy (mitophagy) is a central catabolic event for mitochondrial quality control. Defective or insufficient mitophagy, thus, can result in mitochondrial dysfunction, and ultimately cell death. There is a strong causal relationship between ischemia/reperfusion (I/R) injury and mitochondrial dysfunction following liver resection and transplantation. Compared to young patients, elderly patients poorly tolerate I/R injury. Accumulation of abnormal mitochondria after I/R is more prominent in aged livers than in young counterparts. This review highlights how altered autophagy is mechanistically involved in age-dependent hypersensitivity to reperfusion injury.

The Potential Role of Voltage-Dependent Anion Channel in the Treatment of Parkinson’s Disease

Parkinson’s disease (PD) is a neurodegenerative disease second only to Alzheimer’s disease in terms of prevalence. Previous studies have indicated that the occurrence and progression of PD are associated with mitochondrial dysfunction. Mitochondrial dysfunction is one of the most important causes for apoptosis of dopaminergic neurons. Therefore, maintaining the stability of mitochondrial functioning is a potential strategy in the treatment of PD. Voltage-dependent anion channel (VDAC) is the main component in the outer mitochondrial membrane, and it participates in a variety of biological processes. In this review, we focus on the potential roles of VDACs in the treatment of PD. We found that VDACs are involved in PD by regulating apoptosis, autophagy, and ferroptosis. VDAC1 oligomerization, VDACs ubiquitination, regulation of mitochondrial permeability transition pore (mPTP) by VDACs, and interaction between VDACs and α-synuclein (α-syn) are all promising methods for the treatment of PD. We proposed that inhibition of VDAC1 oligomerization and promotion of VDAC1 ubiquitination as an effective approach for the treatment of PD. Previous studies have proven that the expression of VDAC1 has a significant change in PD models. The expression levels of VDAC1 are decreased in the substantia nigra (SN) of patients suffering from PD compared with the control group consisting of normal individuals by using bioinformatics tools. VDAC2 is involved in PD mainly through the regulation of apoptosis. VDAC3 may have a similar function to VDAC1. It can be concluded that the functional roles of VDACs contribute to the therapeutic strategy of PD.

Recent Advances in Glycyrrhetinic Acid-Functionalized Biomaterials for Liver Cancer-Targeting Therapy

Liver cancer is one of the most common causes of cancer mortality worldwide. Chemotherapy and radiotherapy are the conventional therapies generally employed in patients with liver tumors. The major issue associated with the administration of chemotherapeutics is their high toxicity and lack of selectivity, leading to systemic toxicity that can be detrimental to the patient's quality of life. An important approach to the development of original liver-targeted therapeutic products takes advantage of the employment of biologically active ligands able to bind specific receptors on the cytoplasmatic membranes of liver cells. In this perspective, glycyrrhetinic acid (GA), a pentacyclic triterpenoid present in roots and rhizomes of licorice, has been used as a ligand for targeting the liver due to the expression of GA receptors on the sinusoidal surface of mammalian hepatocytes, so it may be employed to modify drug delivery systems (DDSs) and obtain better liver or hepatocyte drug uptake and efficacy. In the current review, we focus on the most recent and interesting research advances in the development of GA-based hybrid compounds and DDSs developed for potential employment as efficacious therapeutic options for the treatment of hepatic cancer.

Mitochondrial Damage of Lymphocytes in Patients with Acute Relapse of Schizophrenia: A Correlational Study with Efficacy and Clinical Symptoms

OBJECTIVE

Accumulating evidence has demonstrated that schizophrenia is associated with mitochondrial and immune abnormalities. In this pilot case-control study, we investigated the level of mitochondrial impairment in lymphocytes in patients with acute relapse of schizophrenia and explored the correlation between the level of mitochondrial damage and symptoms or treatment response.

METHODS

Lymphocytic mitochondrial damage was detected using mitochondrial fluorescence staining and flow cytometry in 37 patients (at admission and discharge) and 24 controls. Clinical symptoms were assessed using the Positive and Negative Syndrome Scale (PANSS) and Clinical Global Impression Scale (CGI-S).

RESULTS

The levels of mitochondrial damage in CD3+ T, CD4+ T, and CD8+ T lymphocytes of the patients with schizophrenia at admission were significantly higher than those of the controls (p<0.05) and did not return to normal at discharge (p>0.05). The mitochondrial damage of T cells significantly improved at discharge for responsive patients only, as compared with that at admission (P<0.05). However, no significant difference was found in mitochondrial damage in CD19+ B cells between patients and healthy controls, or between admission and discharge (p>0.05). Furthermore, the reduction in mitochondrial damage of CD3, CD4, and CD8 lymphocytes was positively correlated with the reduction of the score of the PANSS positive scale at discharge (p<0.05), while no significant correlation was found between the level of mitochondrial damage in lymphocytes and the scores of PANSS and CGI-S.

CONCLUSION

Acute relapse of schizophrenia might be associated with higher levels of mitochondrial damage in peripheral blood T lymphocytes. The degree of recovery of mitochondrial impairment in the T cells may be used as a predictor of treatment response in schizophrenia. As this is a pilot study, the conclusion still needs further verification in large-scale studies.

Estrogen Regulates Glucose Metabolism in Cattle Neutrophils Through Autophagy

Hypoglycemia resulting from a negative energy balance (NEB) in periparturient cattle is the major reason for a reduced glycogen content in polymorphonuclear neutrophils (PMNs). The lack of glycogen induces PMNs dysfunction and is responsible for the high incidence of perinatal diseases. The perinatal period is accompanied by dramatic changes in sex hormones levels of which estrogen (17β-estradiol, E2) has been shown to be closely associated with PMNs function. However, the precise regulatory mechanism of E2 on glucose metabolism in cattle PMNs has not been elucidated. Cattle PMNs were cultured in RPMI 1640 with 2.5 (LG), 5.5 (NG) and 25 (HG) mM glucose and E2 at 20 (EL), 200 (EM) and 450 (EH) pg/mL. We found that E2 maintained PMNs viability in different glucose conditions, and promoted glycogen synthesis by inhibiting PFK1, G6PDH and GSK-3β activity in LG while enhancing PFK1 and G6PDH activity and inhibiting GSK-3β activity in HG. E2 increased the ATP content in LG but decreased it in HG. This indicated that the E2-induced increase/decrease of ATP content may be independent of glycolysis and the pentose phosphate pathway (PPP). Further analysis showed that E2 promoted the activity of hexokinase (HK) and GLUT1, GLUT4 and SGLT1 expression in LG, while inhibiting GLUT1, GLUT4 and SGLT1 expression in HG. Finally, we found that E2 increased LC3, ATG5 and Beclin1 expression, inhibited p62 expression, promoting AMPK-dependent autophagy in LG, but with the opposite effect in HG. Moreover, E2 increased the Bcl-2/Bax ratio and decreased the apoptosis rate of PMNs in LG but had the opposite effect in HG. These results showed that E2 could promote AMPK-dependent autophagy and inhibit apoptosis in response to glucose-deficient environments. This study elucidated the detailed mechanism by which E2 promotes glycogen storage through enhancing glucose uptake and retarding glycolysis and the PPP in LG. Autophagy is essential for providing ATP to maintain the survival and immune potential of PMNs. These results provided significant evidence for further understanding the effects of E2 on PMNs immune potential during the hypoglycemia accompanying perinatal NEB in cattle.

Targeted antioxidant delivery modulates mitochondrial functions, ameliorates oxidative stress and preserve sperm quality during cryopreservation

Mitochondria are vital organelles with a multifaceted role in cellular bioenergetics, biosynthesis, signaling and calcium homeostasis. During oxidative phosphorylation, sperm mitochondria generate reactive oxygen species (ROS) at physiological levels mediating signaling pathways essential for sperm fertilizing competence. Moreover, sperm subpopulation with active mitochondria is positively associated with sperm motility, chromatin and plasma membrane integrity, and normal morphology. However, the osmotic and thermal stress, and intracellular ice crystal formation generate excess ROS to cause mitochondrial dysfunction, potentiating cryoprotectant-induced calcium overload in the mitochondrial matrix. It further stimulates the opening of mitochondrial permeability transition pores (mPTP) to release pro-apoptotic factors from mitochondria and initiate apoptotic cascade, with a decrease in Mitochondrial Membrane Potential (MMP) and altered sperm functions. To improve the male reproductive potential, it is essential to address challenges in semen cryopreservation, precisely the deleterious effects of oxidative stress on sperm quality. During semen cryopreservation, the supplementation of extended semen with conventional antioxidants is extensively reported. However, the outcomes of supplementation to improve semen quality are inconclusive across different species, which is chiefly attributed to the unknown bioavailability of antioxidants at the primary site of ROS generation, i.e., mitochondria. Increasing evidence suggests that the targeted delivery of antioxidants to sperm mitochondria is superior in mitigating oxidative stress and improving semen freezability than conventional antioxidants. Therefore, the present review comprehensively describes mitochondrial-targeted antioxidants, their mechanism of action and effects of supplementation on improving semen cryopreservation efficiency in different species. Moreover, it also discusses the significance of active mitochondria in determining sperm fertilizing competence, cryopreservation-induced oxidative stress and mitochondrial dysfunction, and its implications on sperm fertility. The potential of mitochondrial-targeted antioxidants to modulate mitochondrial functions and improve semen quality has been reviewed extensively.

Effects of Siberian fir terpenes extract Abisil on antioxidant activity, autophagy, transcriptome and proteome of human fibroblasts

Background: Abisil is an extract of Siberian fir terpenes with antimicrobial and wound healing activities. Previous studies revealed that Abisil has geroprotective, anti-tumorigenic, and anti-angiogenic effects. Abisil decreased the expression of cyclin D1, E1, A2, and increased the phosphorylation rate of AMPK.

Objective: In the present study, we analyzed the effect of Abisil on autophagy, the mitochondrial potential of embryonic human lung fibroblasts. We evaluated its antioxidant activity and analyzed the transcriptomic and proteomic effects of Abisil treatment.

Results: Abisil treatment resulted in activation of autophagy, reversal of rotenone-induced elevation of reactive oxygen species (ROS) levels and several-fold decrease of mitochondrial potential. Lower doses of Abisil (25 μg/ml) showed a better oxidative effect than high doses (50 or 125 μg/ml). Estimation of metabolic changes after treatment with 50 μg/ml has not shown any changes in oxygen consumption rate, but extracellular acidification rate decreased significantly. Abisil treatment (5 and 50 μg/ml) of MRC5-SV40 cells induced a strong transcriptomic shift spanning several thousand genes (predominantly, expression decrease). Among down-regulated genes, we noticed an over-representation of genes involved in cell cycle progression, oxidative phosphorylation, and fatty acid biosynthesis. Additionally, we observed predominant downregulation of genes encoding for kinases. Proteome profiling also revealed that the content of hundreds of proteins is altered after Abisil treatment (mainly, decreased). These proteins were involved in cell cycle regulation, intracellular transport, RNA processing, translation, mitochondrial organization.

Conclusions: Abisil demonstrated antioxidant and autophagy stimulating activity. Treatment with Abisil results in the predominant downregulation of genes involved in the cell cycle and oxidative phosphorylation.

Mitochondrial DNA in innate immune responses against infectious diseases

Mitochondrial DNA (mtDNA) can initiate an innate immune response when mislocalized in a compartment other than the mitochondrial matrix. mtDNA plays significant roles in regulating mitochondrial dynamics as well as mitochondrial unfolded protein response (UPR). The mislocalized extra-mtDNA can elicit innate immune response via cGAS-STING (cyclic GMP-AMP synthase-stimulator of interferon genes) pathway, inducing the expression of the interferon-stimulated genes (ISGs). Also, cytosolic damaged mtDNA is cleared up by various pathways which are responsible for participating in the activation of inflammatory responses. Four pathways of extra-mitochondrial mtDNA clearance are highlighted in this review - the inflammasome activation mechanism, neutrophil extracellular traps formation, recognition by Toll-like receptor 9 and transfer of mtDNA between cells packaged into extracellular vesicles. Anomalies in these pathways are associated with various diseases. We posit our review in the present pandemic situation and discuss how mtDNA elicits innate immune responses against different viruses and bacteria. This review gives a comprehensive picture of the role of extra-mitochondrial mtDNA in infectious diseases and speculates that research towards its understanding would help establish its therapeutic potential.

Trauma-Hemorrhage Stimulates Immune Defense, Mitochondrial Dysfunction, Autophagy, and Apoptosis in Pig Liver at 72 h

ABSTRACT

Hepatic dysfunction frequently occurs after trauma-hemorrhage, resulting in severe pathophysiological responses that include leukocyte shifting and self-mediated mechanisms of cells, such as autophagy and apoptosis. This in vivo study aimed to characterize mitochondrial morphology, leukocyte reaction, and the processes of autophagy and apoptosis after polytrauma hemorrhage (TH) in a long-term, large animal model.Liver tissue was taken from a porcine TH model (hemorrhagic shock, blunt chest trauma, tibia fracture, and liver laceration) with an intensive care unit follow-up of 72 h. The ultrastructural changes of the liver tissue after TH were evaluated by transmission electron microscopy. The leukocyte phenotypes and autophagy and apoptosis pathways were elucidated by immunohistofluorescence, Western blot, and terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL).In addition to post-traumatic changes in the mitochondrial morphology, the biomarkers of anti-inflammatory macrophages (CD163) and reparative monocytes (CD11R3 and CD16) were upregulated, while the inducible nitric oxide synthase was downregulated after TH. Furthermore, the autophagy-related protein expressions of LC3 and Beclin-1 were upregulated, whereas the protein expression of P62 was downregulated after TH. Costaining showed that the macrophages were LC3 (or Beclin-1) positive and that CD163 was copositive and upregulated. Apoptosis biomarkers (cleaved-caspase-3/caspase-3 and Bcl-2) increased after TH, which is in line with TUNEL results.In conclusion, the observed findings indicate that mitochondrial dysfunction might be one trigger of hepatic autophagy and apoptosis after TH. These processes occur together with the activation of anti-inflammatory leukocytes in liver tissue. Further studies are needed to elucidate the potential therapeutic effects of inhibiting mitochondrial swelling during autophagy or apoptosis.

Mitochondrial function in immune cells in health and disease

One of the main functions of mitochondria is production of ATP for cellular energy needs, however, it becomes more recognized that mitochondria are involved in differentiation and activation processes of immune cells. Upon activation, immune cells have a high need for energy. Immune cells have different strategies to generate this energy. In pro-inflammatory cells, such as activated monocytes and activated T and B cells, the energy is generated by increasing glycolysis, while in regulatory cells, such as regulatory T cells or M2 macrophages, energy is generated by increasing mitochondrial function and beta-oxidation. Except for being important for energy supply during activation, mitochondria also induce immune responses. During an infection, they release mitochondrial danger associated molecules (DAMPs) that resemble structures of bacterial derived pathogen associated molecular patterns (PAMPs). Such mitochondrial DAMPS are for instance mitochondrial DNA with hypomethylated CpG motifs or a specific lipid that is only present in prokaryotic bacteria and mitochondria, i.e. cardiolipin. Via release of such DAMPs, mitochondria guide the immune response towards an inflammatory response against pathogens. This is an important mechanism in early detection of an infection and in stimulating and sustaining immune responses to fight infections. However, mitochondrial DAMPs may also have a negative impact. If mitochondrial DAMPs are released by damaged cells, without the presence of an infection, such as after a trauma, mitochondrial DAMPs may induce an undesired inflammatory response, resulting in tissue damage and organ dysfunction. Thus, immune cells have developed mechanisms to prevent such undesired immune activation by mitochondrial components. In the present narrative review, we will describe the current view of mitochondria in regulation of immune responses. We will also discuss the current knowledge on disturbed mitochondrial function in immune cells in various immunological diseases.

Physical exercise and liver "fitness": Role of mitochondrial function and epigenetics-related mechanisms in non-alcoholic fatty liver disease

BACKGROUND

Modern lifestyles, especially high-caloric intake and physical inactivity, contribute to the increased prevalence of non-alcoholic fatty liver disease (NAFLD), which becomes a significant health problem worldwide. Lifestyle changes, however, affect not only parental generation, but also their offspring, reinforcing the need for efficient preventive approaches to deal with this disease. This transgenerational influence of phenotypes dependent on parents (particularly maternal) behaviours may open additional research avenues. Despite persistent attempts to design an effective pharmacological therapy against NAFLD, physical activity, as a non-pharmacological approach, emerges as an exciting strategy.

SCOPE OF REVIEW

Here we briefly review the effect of physical exercise on liver mitochondria adaptations in NAFLD, highlighting the importance of mitochondrial metabolism and transgenerational and epigenetic mechanisms in liver diseases.

MAJOR CONCLUSIONS

A deeper look into cellular mechanisms sheds a light on possible effects of physical activity in the prevention and treatment of NAFLD through modulation of function and structure of particular organelles, namely mitochondria. Additionally, despite of increasing evidence regarding the contribution of epigenetic mechanisms in the pathogenesis of different diseases, the role of microRNAs, DNA methylation, and histone modification in NAFLD pathogenesis still needs to be elucidated.

VDAC2 interacts with PFKP to regulate glucose metabolism and phenotypic reprogramming of glioma stem cells

Plastic phenotype convention between glioma stem cells (GSCs) and non-stem tumor cells (NSTCs) significantly fuels glioblastoma heterogeneity that causes therapeutic failure. Recent progressions indicate that glucose metabolic reprogramming could drive cell fates. However, the metabolic pattern of GSCs and NSTCs and its association with tumor cell phenotypes remain largely unknown. Here we found that GSCs were more glycolytic than NSTCs, and voltage-dependent anion channel 2 (VDAC2), a mitochondrial membrane protein, was critical for metabolic switching between GSCs and NSTCs to affect their phenotypes. VDAC2 was highly expressed in NSTCs relative to GSCs and coupled a glycolytic rate-limiting enzyme platelet-type of phosphofructokinase (PFKP) on mitochondrion to inhibit PFKP-mediated glycolysis required for GSC maintenance. Disruption of VDAC2 induced dedifferentiation of NSTCs to acquire GSC features, including the enhanced self-renewal, preferential expression of GSC markers, and increased tumorigenicity. Inversely, enforced expression ofVDAC2 impaired the self-renewal and highly tumorigenic properties of GSCs. PFK inhibitor clotrimazole compromised the effect of VDAC2 disruption on glycolytic reprogramming and GSC phenotypic transition. Clinically, VDAC2 expression inversely correlated with glioma grades (Immunohistochemical staining scores of VDAC2 were 4.7 ± 2.8, 3.2 ± 1.9, and 1.9 ± 1.9 for grade II, grade III, and IV, respectively, p < 0.05 for all) and the patients with high expression of VDAC2 had longer overall survival than those with low expression of VDAC2 (p = 0.0008). In conclusion, we demonstrate that VDAC2 is a new glycolytic regulator controlling the phenotype transition between glioma stem cells and non-stem cells and may serves as a new prognostic indicator and a potential therapeutic target for glioma patients.

Indirubin and NAD+ prevent mitochondrial ischaemia/reperfusion damage in fatty livers

BACKGROUND

Fatty livers are considerably more susceptible to acute stressors, such as ischaemia/reperfusion (I/R). As the incidence of I/R is high due to surgical events and some pathologies, there is an urgent need to find strategies against I/R injury (I/RI) in fatty livers. We postulate that an acute pretreatment with indirubin-3'-oxime (Ind) or NAD+ prevents mitochondrial dysfunction associated with warm I/RI in fatty livers.

MATERIALS AND METHODS

Zucker fatty rats were subjected to warm ischaemia and 12 hours of reperfusion. Ind or NAD+ was administered in the hepatic artery 30 minutes before ischaemia. Hepatic mitochondrial isolation was performed, and functional assays as well as molecular analysis were performed.

RESULTS

Pretreatment decreased markers of liver injury while preserving mitochondrial cytochrome c content, which is related to the prevention of calcium-induced mitochondrial permeability transition (mPT), the decline in mitochondrial respiratory state 3 and ATP content. The generation of reactive oxygen species (ROS) was also diminished. Inhibition of GSK-3ß by Ind resulted in the prevention of cyclophilin-D (CypD) phosphorylation, unabling it to bind to the adenine nucleotide translocator (ANT), thus, preventing mPT induction. Furthermore, deacetylation of CypD at Lys residue by sirtuin 3 (SIRT3) caused its dissociation from ANT, contributing to an increase in mPT threshold in NAD+ -pretreated animals.

CONCLUSIONS

Pretreatment with Ind or NAD+ protects fatty livers by maintaining mitochondrial calcium homoeostasis, thus, preserving mitochondrial function and energetic balance. As such, CypD might be a new protective target against I/RI in fatty livers.

Expanding the phenotype of SLC25A42-associated mitochondrial encephalomyopathy

SLC25A42 gene encodes an inner mitochondrial membrane protein that imports Coenzyme A into the mitochondrial matrix. A mutation in this gene was recently reported in a subject born to consanguineous parents who presented with mitochondrial myopathy with muscle weakness and lactic acidosis. In this report, we present 12 additional individuals with the same founder mutation who presented with variable manifestations ranging from asymptomatic lactic acidosis to a severe phenotype characterized by developmental regression and epilepsy. Our report confirms the link between SLC25A42 and mitochondrial disease in humans, and suggests that pathogenic variants in SLC25A42 should be interpreted with the understanding that the associated phenotype may be highly variable.

Mito-xenophagic killing of bacteria is coordinated by a metabolic switch in dendritic cells

Chlamydiae are bacterial pathogens that grow in vacuolar inclusions. Dendritic cells (DCs) disintegrate these compartments, thereby eliminating the microbes, through auto/xenophagy, which also promotes chlamydial antigen presentation via MHC I. Here, we show that TNF-α controls this pathway by driving cytosolic phospholipase (cPLA)2-mediated arachidonic acid (AA) production. AA then impairs mitochondrial function, which disturbs the development and integrity of these energy-dependent parasitic inclusions, while a simultaneous metabolic switch towards aerobic glycolysis promotes DC survival. Tubulin deacetylase/autophagy regulator HDAC6 associates with disintegrated inclusions, thereby further disrupting their subcellular localisation and stability. Bacterial remnants are decorated with defective mitochondria, mito-aggresomal structures, and components of the ubiquitin/autophagy machinery before they are degraded via mito-xenophagy. The mechanism depends on cytoprotective HSP25/27, the E3 ubiquitin ligase Parkin and HDAC6 and promotes chlamydial antigen generation for presentation on MHC I. We propose that this novel mito-xenophagic pathway linking innate and adaptive immunity is critical for effective DC-mediated anti-bacterial resistance.

A New Chemical Compound, NecroX-7, Acts as a Necrosis Modulator by Inhibiting High-Mobility Group Box 1 Protein Release During Massive Ischemia-Reperfusion Injury

BACKGROUND

Necrotic cell death is common in a wide variety of pathologic conditions, including ischemia-reperfusion (IR) injury. The aim of this study was to develop an IR injury-induced hepatic necrosis model in dogs by means of selective left hepatic inflow occlusion and to test the efficacy of a new chemical compound, NecroX-7, against the IR injury-induced hepatic damage.

METHODS

A group of male Beagle dogs received intravenous infusions of either vehicle or different doses of NecroX-7 (1.5, 4.5, or 13 mg/kg) for a 20-minute period before a 90-minute left hepatic inflow occlusion followed by reperfusion.

RESULTS

The gross morphology in the NecroX-7-treated groups after occlusion appeared to be less congested and less swollen than that in vehicle-treated control group. Circulating alanine transaminase and aspartate transaminase levels in the control group were elevated during the course of IR, and were effectively blocked in the 4.5 and 13 mg/kg NecroX-7-treated groups. The serum levels of high-mobility group box 1 protein showed a peak at 8 hours after occlusion in control group, and this elevation was significantly blunted by 4.5 mg/kg NecroX-7 treatment. Histologic analysis showed a marked ischemia or IR injury-induced hepatocytic degenerations, sinusoidal and portal vein congestions, and inflammatory cell infiltrations in the control group, whereas the treatment groups showed significantly diminished histopathology in a dose-dependent manner.

CONCLUSIONS

These results demonstrated that NecroX-7 attenuated the hepatocyte lethality caused by hepatic IR injury in a large animal setting. We conclude that NecroX-7 may provide a wide variety of therapeutic options for IR injury in human patients.

Autophagy in ethanol-exposed liver disease

Ethanol metabolism in hepatocytes causes the generation of reactive oxygen species, endoplasmic reticulum stress and alterations in mitochondrial energy and REDOX metabolism. In ethanol-exposed liver disease, autophagy not only acts as a cleanser to remove damaged organelles and cytosolic components, but also selectively clears specific targets such as lipid droplets and damaged mitochondria. Moreover, ethanol appears to play a role in protecting hepatocytes from apoptosis at certain concentrations. This article describes the evidence, function and potential mechanism of autophagy in ethanol-exposed liver disease and the controversy surrounding the effects of ethanol on autophagy.

Antifungal drug itraconazole targets VDAC1 to modulate the AMPK/mTOR signaling axis in endothelial cells

Itraconazole, a clinically used antifungal drug, was found to possess potent antiangiogenic and anticancer activity that is unique among the azole antifungals. Previous mechanistic studies have shown that itraconazole inhibits the mechanistic target of rapamycin (mTOR) signaling pathway, which is known to be a critical regulator of endothelial cell function and angiogenesis. However, the molecular target of itraconazole that mediates this activity has remained unknown. Here we identify the major target of itraconazole in endothelial cells as the mitochondrial protein voltage-dependent anion channel 1 (VDAC1), which regulates mitochondrial metabolism by controlling the passage of ions and small metabolites through the outer mitochondrial membrane. VDAC1 knockdown profoundly inhibits mTOR activity and cell proliferation in human umbilical vein cells (HUVEC), uncovering a previously unknown connection between VDAC1 and mTOR. Inhibition of VDAC1 by itraconazole disrupts mitochondrial metabolism, leading to an increase in the cellular AMP:ATP ratio and activation of the AMP-activated protein kinase (AMPK), an upstream regulator of mTOR. VDAC1-knockout cells are resistant to AMPK activation and mTOR inhibition by itraconazole, demonstrating that VDAC1 is the mediator of this activity. In addition, another known VDAC-targeting compound, erastin, also activates AMPK and inhibits mTOR and proliferation in HUVEC. VDAC1 thus represents a novel upstream regulator of mTOR signaling in endothelial cells and a promising target for the development of angiogenesis inhibitors.

Overexpression of Catalase Diminishes Oxidative Cysteine Modifications of Cardiac Proteins

Reactive protein cysteine thiolates are instrumental in redox regulation. Oxidants, such as hydrogen peroxide (H₂O₂), react with thiolates to form oxidative post-translational modifications, enabling physiological redox signaling. Cardiac disease and aging are associated with oxidative stress which can impair redox signaling by altering essential cysteine thiolates. We previously found that cardiac-specific overexpression of catalase (Cat), an enzyme that detoxifies excess H₂O₂, protected from oxidative stress and delayed cardiac aging in mice. Using redox proteomics and systems biology, we sought to identify the cysteines that could play a key role in cardiac disease and aging. With a ‘Tandem Mass Tag’ (TMT) labeling strategy and mass spectrometry, we investigated differential reversible cysteine oxidation in the cardiac proteome of wild type and Cat transgenic (Tg) mice. Reversible cysteine oxidation was measured as thiol occupancy, the ratio of total available versus reversibly oxidized cysteine thiols. Catalase overexpression globally decreased thiol occupancy by ≥1.3 fold in 82 proteins, including numerous mitochondrial and contractile proteins. Systems biology analysis assigned the majority of proteins with differentially modified thiols in Cat Tg mice to pathways of aging and cardiac disease, including cellular stress response, proteostasis, and apoptosis. In addition, Cat Tg mice exhibited diminished protein glutathione adducts and decreased H₂O₂ production from mitochondrial complex I and II, suggesting improved function of cardiac mitochondria. In conclusion, our data suggest that catalase may alleviate cardiac disease and aging by moderating global protein cysteine thiol oxidation.

The Saccharomyces cerevisiae mitochondrial unselective channel behaves as a physiological uncoupling system regulated by Ca2+, Mg2+, phosphate and ATP

It is proposed that the Saccharomyces cerevisiae the Mitochondrial Unselective Channel ((Sc)MUC) is tightly regulated constituting a physiological uncoupling system that prevents overproduction of reactive oxygen species (ROS). Mg(2+), Ca(2+) or phosphate (Pi) close (Sc)MUC, while ATP or a high rate of oxygen consumption open it. We assessed (Sc)MUC activity by measuring in isolated mitochondria the respiratory control, transmembrane potential (ΔΨ), swelling and production of ROS. At increasing [Pi], less [Ca(2+)] and/or [Mg(2+)] were needed to close (Sc)MUC or increase ATP synthesis. The Ca(2+)-mediated closure of (Sc)MUC was prevented by high [ATP] while the Mg(2+) or Pi effect was not. When Ca(2+) and Mg(2+) were alternatively added or chelated, (Sc)MUC opened and closed reversibly. Different effects of Ca(2+) vs Mg(2+) effects were probably due to mitochondrial Mg(2+) uptake. Our results suggest that (Sc)MUC activity is dynamically controlled by both the ATP/Pi ratio and divalent cation fluctuations. It is proposed that the reversible opening/closing of (Sc)MUC leads to physiological uncoupling and a consequent decrease in ROS production.

The Mitochondrial Permeability Transition Pore: Channel Formation by F-ATP Synthase, Integration in Signal Transduction, and Role in Pathophysiology

The mitochondrial permeability transition (PT) is a permeability increase of the inner mitochondrial membrane mediated by a channel, the permeability transition pore (PTP). After a brief historical introduction, we cover the key regulatory features of the PTP and provide a critical assessment of putative protein components that have been tested by genetic analysis. The discovery that under conditions of oxidative stress the F-ATP synthases of mammals, yeast, and Drosophila can be turned into Ca(2+)-dependent channels, whose electrophysiological properties match those of the corresponding PTPs, opens new perspectives to the field. We discuss structural and functional features of F-ATP synthases that may provide clues to its transition from an energy-conserving into an energy-dissipating device as well as recent advances on signal transduction to the PTP and on its role in cellular pathophysiology.

Maternal stress predicts altered biogenesis and the profile of mitochondrial proteins in the frontal cortex and hippocampus of adult offspring rats

Currently, much attention is focused on the influence of mitochondrial disturbances at the onset of depression. The goal of this study was to investigate the impact of prenatal stress (an animal model of depression) on the mitochondrial biogenesis proteins and mitoproteome profile in the frontal cortex and hippocampus of adult 3-month-old male rats following a prenatal stress procedure. Our results show that rats that were exposed to prenatal stress stimuli displayed depression-like behaviors based on the sucrose preference and elevated plus maze tests. It has been found that the level of the PGC-1α protein was reduced in the frontal cortex and hippocampus of the adult offspring after the prenatal stress procedure. Moreover, in the frontal cortex, the level of the pro-apoptotic protein Bax was up-regulated. Two-dimensional electrophoresis coupled with mass spectrometry showed the statistically significant down-regulation of the mitochondrial ribosomal protein L12 (Mrpl12) and mitochondrial NADH dehydrogenase [ubiquinone] flavoprotein 2 (NDUFV2) as well as the up-regulation of the Tubulin Polymerization Promoting Proteins (Tppp/p25) in the frontal cortex. In contrast, in the hippocampus, the mitochondrial pyruvate dehydrogenase E1 component subunit beta, the voltage-dependent anion-selective channel protein 2 (VDAC2), and the GTP-binding nuclear protein RAN (RAN) were down-regulated and the expression of phosphatidylethanolamine-binding protein 1 (PEBP-1) was enhanced. These findings provide new evidence that stress during pregnancy may lead not only to behavioral deficits, but also to disturbances in the brain mitoproteome profile in adult rat offspring.

Identification of active elementary flux modes in mitochondria using selectively permeabilized CHO cells

Metabolic compartmentation is a key feature of mammalian cells. Mitochondria are the powerhouse of eukaryotic cells, responsible for respiration and the TCA cycle. We accessed the mitochondrial metabolism of the economically important Chinese hamster ovary (CHO) cells using selective permeabilization. We tested key substrates without and with addition of ADP. Based on quantified uptake and production rates, we could determine the contribution of different elementary flux modes to the metabolism of a substrate or substrate combination. ADP stimulated the uptake of most metabolites, directly by serving as substrate for the respiratory chain, thus removing the inhibitory effect of NADH, or as allosteric effector. Addition of ADP favored substrate metabolization to CO2 and did not enhance the production of other metabolites. The controlling effect of ADP was more pronounced when we supplied metabolites to the first part of the TCA cycle: pyruvate, citrate, α-ketoglutarate and glutamine. In the second part of the TCA cycle, the rates were primarily controlled by the concentrations of C4-dicarboxylates. Without ADP addition, the activity of the pyruvate carboxylase-malate dehydrogenase-malic enzyme cycle consumed the ATP produced by oxidative phosphorylation, preventing its accumulation and maintaining metabolic steady state conditions. Aspartate was taken up only in combination with pyruvate, whose uptake also increased, a fact explained by complex regulatory effects. Isocitrate dehydrogenase and α-ketoglutarate dehydrogenase were identified as the key regulators of the TCA cycle, confirming existent knowledge from other cells. We have shown that selectively permeabilized cells combined with elementary mode analysis allow in-depth studying of the mitochondrial metabolism and regulation.

Tissue distribution of olive flounder VDAC2 and its expression in fish cell lines

Voltage-dependent anion channel (VDAC) is located in the mitochondrial outer membrane, which plays a crucial role in regulating cell life and death. In this study, the tissue distribution of olive flounder Paralichthys olivaceus VDAC2 (PoVDAC2) was detected by quantitative real-time PCR and Western blot analysis. The qRT-PCR results showed that the expression level of PoVDAC2 was abundant in heart, muscle and gill tissues. Western blot analysis revealed a protein of 32 kDa detected in all six tissues. Furthermore, a recombinant eukaryotic expression plasmid pEGFP-N3-PoVDAC2 was successfully constructed and transiently expressed the fusion protein in fish cell lines. Subcellular localization indicated that PoVDAC2-GFP was distributed in a punctate mitochondria-like pattern throughout the cytoplasm in flounder embryonic cells (FEC). The distribution of native VDAC2 in untransfected fish cells was also investigated by immunofluorescence microscopy. The punctate VDAC2 fluorescence signals of both FEC and EPC cells were identically observed in the cytoplasm but not in the nucleus. These results laid a foundation for investigating the functional relevance of VDAC response to pathogens in flounder.

Improvement of liver injury and survival by JNK2 and iNOS deficiency in liver transplants from cardiac death mice

BACKGROUND & AIMS

Inclusion of liver grafts from cardiac death donors (CDD) would increase the availability of donor livers but is hampered by a higher risk of primary non-function. Here, we seek to determine mechanisms that contribute to primary non-function of liver grafts from CDD with the goal to develop strategies for improved function and outcome, focusing on c-Jun-N-terminal kinase (JNK) activation and mitochondrial depolarization, two known mediators of graft failure.

METHODS

Livers explanted from wild-type, inducible nitric oxide synthase knockout (iNOS(-/-)), JNK1(-/-) or JNK2(-/-) mice after 45-min aorta clamping were implanted into wild-type recipients. Mitochondrial depolarization was detected by intravital confocal microscopy in living recipients.

RESULTS

After transplantation of wild-type CDD livers, graft iNOS expression and 3-nitrotyrosine adducts increased, but hepatic endothelial NOS expression was unchanged. Graft injury and dysfunction were substantially higher in CDD grafts than in non-CDD grafts. iNOS deficiency and inhibition attenuated injury and improved function and survival of CDD grafts. JNK1/2 and apoptosis signal-regulating kinase-1 activation increased markedly in wild-type CDD grafts, which was blunted by iNOS deficiency. JNK inhibition and JNK2 deficiency, but not JNK1 deficiency, decreased injury and improved function and survival of CDD grafts. Mitochondrial depolarization and binding of phospho-JNK2 to Sab, a mitochondrial protein linked to the mitochondrial permeability transition, were higher in CDD than in non-CDD grafts. iNOS deficiency, JNK inhibition and JNK2 deficiency all decreased mitochondrial depolarization and blunted ATP depletion in CDD grafts. JNK inhibition and deficiency did not decrease 3-nitrotyrosine adducts in CDD grafts.

CONCLUSION

The iNOS-JNK2-Sab pathway promotes CDD graft failure via increased mitochondrial depolarization, and is an attractive target to improve liver function and survival in CDD liver transplantation recipients.

Downregulation of connexin 32 attenuates hypoxia/reoxygenation injury in liver cells

Gap junction intercellular communication is involved in ischemia-reperfusion (IR) injury of organs. Connexins are proteins that are critical to the function of gap junctions. To clarify the role of gap junctions in IR injury in liver cells, the function of gap junctions was modulated in an in vitro hypoxia/reoxygenation (H/R) model. BRL-3A rat liver cells, endogenously expressing connexins Cx32 and Cx43, were used to model the process of hepatic IR injury. Suppression of gap junction activity was achieved genetically, using Cx32-specific small interfering RNA (siRNA), or chemically, with pharmacological inhibitors, oleamide, and 18-α-GA. BRL-3A cells subjected to H/R exhibited reduced cell survival and pathologies indicative of IR injury. Cx32-specific siRNA, oleamide, and 18-α-GA, respectively, decreased gap junction permeability, as assessed by the parachute assay. Pretreatment with Cx32-specific siRNA increased cell survival. Pretreatment with oleamide or 18-α-GA did not improve cell survival. Modulating gap junction by Cx32 gene silencing protected BRL-3A liver cells from H/R.

Metabolic control of the epigenome in systemic Lupus erythematosus

Epigenetic mechanisms are proposed to underlie aberrant gene expression in systemic lupus erythematosus (SLE) that results in dysregulation of the immune system and loss of tolerance. Modifications of DNA and histones require substrates derived from diet and intermediary metabolism. DNA and histone methyltransferases depend on S-adenosylmethionine (SAM) as a methyl donor. SAM is generated from adenosine triphosphate (ATP) and methionine by methionine adenosyltransferase (MAT), a redox-sensitive enzyme in the SAM cycle. The availability of B vitamins and methionine regulate SAM generation. The DNA of SLE patients is hypomethylated, indicating dysfunction in the SAM cycle and methyltransferase activity. Acetyl-CoA, which is necessary for histone acetylation, is generated from citrate produced in mitochondria. Mitochondria are also responsible for de novo synthesis of flavin adenine dinucleotide (FAD) for histone demethylation. Mitochondrial oxidative phosphorylation is the dominant source of ATP. The depletion of ATP in lupus T cells may affect MAT activity as well as adenosine monophosphate (AMP) activated protein kinase (AMPK), which phosphorylates histones and inhibits mechanistic target of rapamycin (mTOR). In turn, mTOR can modify epigenetic pathways including methylation, demethylation, and histone phosphorylation and mediates enhanced T-cell activation in SLE. Beyond their role in metabolism, mitochondria are the main source of reactive oxygen intermediates (ROI), which activate mTOR and regulate the activity of histone and DNA modifying enzymes. In this review we will focus on the sources of metabolites required for epigenetic regulation and how the flux of the underlying metabolic pathways affects gene expression.

F1FO ATPase vesicle preparation and technique for performing patch clamp recordings of submitochondrial vesicle membranes

Mitochondria are involved in many important cellular functions including metabolism, survival(1), development and, calcium signaling(2). Two of the most important mitochondrial functions are related to the efficient production of ATP, the energy currency of the cell, by oxidative phosphorylation, and the mediation of signals for programmed cell death(3). The enzyme primarily responsible for the production of ATP is the F1FO-ATP synthase, also called ATP synthase(4-5). In recent years, the role of mitochondria in apoptotic and necrotic cell death has received considerable attention. In apoptotic cell death, BCL-2 family proteins such as Bax enter the mitochondrial outer membrane, oligomerize and permeabilize the outer membrane, releasing pro-apoptotic factors into the cytosol(6). In classic necrotic cell death, such as that produced by ischemia or excitotoxicity in neurons, a large, poorly regulated increase in matrix calcium contributes to the opening of an inner membrane pore, the mitochondrial permeability transition pore or mPTP. This depolarizes the inner membrane and causes osmotic shifts, contributing to outer membrane rupture, release of pro-apoptotic factors, and metabolic dysfunction. Many proteins including Bcl-xL(7) interact with F1FO ATP synthase, modulating its function. Bcl-xL interacts directly with the beta subunit of F1FO ATP synthase, and this interaction decreases a leak conductance within the F1FOATPasecomplex, increasing the net transport of H+ by F1FO during F1FO ATPase activity(8) and thereby increasing mitochondrial efficiency. To study the activity and modulation of the ATP synthase, we isolated from rodent brain submitochondrial vesicles (SMVs) containing F1FO ATPase. The SMVs retain the structural and functional integrity of the F1FO ATPase as shown in Alavian et al. Here, we describe a method that we have used successfully for the isolation of SMVs from rat brain and we delineate the patch clamp technique to analyze channel activity (ion leak conductance) of the SMVs.

Integration of cellular bioenergetics with mitochondrial quality control and autophagy

Bioenergetic dysfunction is emerging as a cornerstone for establishing a framework for understanding the pathophysiology of cardiovascular disease, diabetes,cancer and neurodegeneration. Recent advances in cellular bioenergetics have shown that many cells maintain a substantial bioenergetic reserve capacity, which is a prospective index of ‘ healthy ’ mitochondrial populations.The bioenergetics of the cell are likely regulated by energy requirements and substrate availability. Additionally,the overall quality of the mitochondrial population and the relative abundance of mitochondria in cells and tissues also impinge on overall bioenergetic capacity and resistance to stress. Because mitochondria are susceptible to damage mediated by reactive oxygen/nitrogen and lipid species, maintaining a ‘ healthy ’ population of mitochondria through quality control mechanisms appears to be essential for cell survival under conditions of pathological stress. Accumulating evidence suggest that mitophagy is particularly important for preventing amplification of initial oxidative insults, which otherwise would further impair the respiratory chain or promote mutations in mitochondrial DNA (mtDNA). The processes underlying the regulation of mitophagy depend on several factors, including the integrity of mtDNA, electron transport chain activity, and the interaction and regulation of the autophagic machinery. The integration and interpretation of cellular bioenergetics in the context of mitochondrial quality control and genetics is the theme of this review.

Hepatic insulin signaling changes: possible mechanism in prenatal hypoxia-increased susceptibility of fatty liver in adulthood

Nonalcoholic fatty liver disease (NAFLD) is strongly linked to insulin resistance. Prenatal hypoxia (PH) is a risk factor in programming of insulin resistance, glucose intolerance, and metabolic dysfunctions in later life, although the mechanisms are unclear. In this study, the role of metabolic and histological changes as well as the hepatic insulin signaling mechanisms were determined in increasing susceptibility of NAFLD in the fetus and offspring exposed to PH. Pregnant rats exposed to hypoxia (O(2) 10%) during pregnancy demonstrated decreased fetal body and liver weight as well as liver to body weight ratio, whereas these changes were not observed in the offspring. However, male liver to body weight ratio increased after PH stress. Microscopic analysis demonstrated that exposure to PH resulted in distorted architecture of the hepatic parenchyma cells with reduced cellularity in the fetus and offspring. Blood glucose and insulin levels were lower with enhanced insulin sensitivity and increased expression of hepatic insulin-signaling elements in the fetus. Furthermore, insulin resistance, impaired glucose homeostasis, and altered expression of insulin-signaling elements occurred in the offspring. Postnatal hypoxia increased hepatic lipid droplets and triglyceride in liver, whereas expressions of insulin-signaling elements were less in the offspring exposed to PH except glucose transporters 2. The results indicated that PH contributed to hepatocyte heteroplasia and metabolic changes that enhanced vulnerability for NAFLD in the offspring, probably via affecting insulin signaling pathway, including glucose transporters 2.

Ultrastructural modifications in the mitochondria of hypoxia-adapted Drosophila melanogaster

Chronic hypoxia (CH) occurs under certain physiological or pathological conditions, including in people who reside at high altitude or suffer chronic cardiovascular or pulmonary diseases. As mitochondria are the predominant oxygen-consuming organelles to generate ATP through oxidative phosphorylation in cells, their responses, through structural or molecular modifications, to limited oxygen supply play an important role in the overall functional adaptation to hypoxia. Here, we report the adaptive mitochondrial ultrastructural modifications and the functional impacts in a recently generated hypoxia-adapted Drosophila melanogaster strain that survives severe, otherwise lethal, hypoxic conditions. Using electron tomography, we discovered increased mitochondrial volume density and cristae abundance, yet also cristae fragmentation and a unique honeycomb-like structure in the mitochondria of hypoxia-adapted flies. The homeostatic levels of adenylate and energy charge were similar between hypoxia-adapted and naïve control flies and the hypoxia-adapted flies remained active under severe hypoxia as quantified by negative geotaxis behavior. The equilibrium ATP level was lower in hypoxia-adapted flies than those of the naïve controls tested under severe hypoxia that inhibited the motion of control flies. Our results suggest that the structural rearrangement in the mitochondria of hypoxia-adapted flies may be an important adaptive mechanism that plays a critical role in preserving adenylate homeostasis and metabolism as well as muscle function under chronic hypoxic conditions.

The formation and functional consequences of heterogeneous mitochondrial distributions in skeletal muscle

Diffusion plays a prominent role in governing both rates of aerobic metabolic fluxes and mitochondrial organization in muscle fibers. However, there is no mechanism to explain how the non-homogeneous mitochondrial distributions that are prevalent in skeletal muscle arise. We propose that spatially variable degradation with dependence on O(2) concentration, and spatially uniform signals for biogenesis, can account for observed distributions of mitochondria in a diversity of skeletal muscle. We used light and transmission electron microscopy and stereology to examine fiber size, capillarity and mitochondrial distribution in fish red and white muscle, fish white muscle that undergoes extreme hypertrophic growth, and four fiber types in mouse muscle. The observed distributions were compared with those generated using a coupled reaction-diffusion/cellular automata (CA) mathematical model of mitochondrial function. Reaction-diffusion analysis of metabolites such as oxygen, ATP, ADP and PCr involved in energy metabolism and mitochondrial function were considered. Coupled to the reaction-diffusion approach was a CA approach governing mitochondrial life cycles in response to the metabolic state of the fiber. The model results were consistent with the experimental observations and showed higher mitochondrial densities near the capillaries because of the sometimes steep gradients in oxygen. The present study found that selective removal of mitochondria in the presence of low prevailing local oxygen concentrations is likely the primary factor dictating the spatial heterogeneity of mitochondria in a diversity of fibers. The model results also suggest decreased diffusional constraints corresponding to the heterogeneous mitochondrial distribution assessed using the effectiveness factor, defined as the ratio of the reaction rate in the system with finite rates of diffusion to that in the absence of any diffusion limitation. Thus, the non-uniform distribution benefits the muscle fiber by increasing the energy status and increasing sustainable metabolic rates.

Infusion of a glucose solution reduces autophagy in the liver after LPS-induced systemic inflammation

Autophagy is a natural process by which a cell maintains homeostasis, usually taking place unnoticed by adjacent cells. Glucose is involved in a negative feedback loop in autophagy. Autophagy is characterized by the induction and secretion of HMGB1, yet the nature of the inflammatory response during and the effect of glucose administration on autophagy are not well understood. Systemic inflammation was induced in experimental animals by LPS injection (7.5 mg/kg) followed by a continuous infusion of either 1%, 5%, or 25% glucose. Autophagy was visualized by immunohistochemistry 12 h after LPS injection. Likewise, protein levels of microtubule-associated protein light chain 3 (LC3)-II, autophagy-related protein 7 (Atg7), and high-mobility group box 1 (HMGB1) were assayed by western blot analysis. We found that autophagy increased in liver tissue in response to LPS-induced systemic inflammation. However, protein levels decreased in rats receiving LPS and a 5% glucose solution. Our results suggest that LPS-induced systemic inflammation increases autophagy in liver cells, potentially involving the upregulation of LC3-II, Atg7, and HMGB1. We also show that a 5% glucose infusion reduces autophagy. We propose that maintaining serum glucose levels with an adequate glucose dose improves systemic inflammation by reducing autophagy.

Mitochondrial morphology and dynamics in hepatocytes from normal and ethanol-fed rats

Mitochondrial structure and function are central to cell physiology and are mutually interdependent. Mitochondria represent a primary target of the alcohol-induced tissue injury, particularly in the liver, where the metabolic effects of ethanol are predominant. However, the effect of ethanol on hepatic mitochondrial morphology and dynamics remain to be established. In the present work, we employed the organelle-targeted photoactivatable fluorescent protein technology and electron microscopy to study hepatic mitochondrial structure and dynamics. Hepatocytes in perfused liver as well as in primary cultures showed mostly discrete globular or short tubular mitochondria. The mitochondria showed few fusion events and little movement activity. By contrast, human hepatoma (HepG2)-derived VL-17A cells, expressing the major hepatic ethanol metabolizing enzymes, alcohol dehydrogenase and cytochrome P450 2E1, have elongated and interconnected mitochondria showing matrix continuity and many fusion events. Hepatocytes isolated from chronically ethanol-fed rats showed some increase in mitochondrial volume and exhibited a substantial suppression of mitochondrial dynamics. In VL-17A cells, prolonged ethanol exposure also caused decreased mitochondrial continuity and dynamics. Collectively, these results indicate that mitochondria in normal hepatocytes show relatively slow dynamics, which is very sensitive to suppression by ethanol exposure.

Effects of dexpramipexole on brain mitochondrial conductances and cellular bioenergetic efficiency

Cellular stress or injury can result in mitochondrial dysfunction, which has been linked to many chronic neurological disorders including amyotrophic lateral sclerosis (ALS) and Parkinson's disease (PD). Stressed and dysfunctional mitochondria exhibit an increase in large conductance mitochondrial membrane currents and a decrease in bioenergetic efficiency. Inefficient energy production puts cells, and particularly neurons, at risk of death when energy demands exceed cellular energy production. Here we show that the candidate ALS drug dexpramipexole (DEX; KNS-760704; ((6R)-4,5,6,7-tetrahydro-N6-propyl-2,6-benzothiazole-diamine) and cyclosporine A (CSA) inhibited increases in ion conductance in whole rat brain-derived mitochondria induced by calcium or treatment with a proteasome inhibitor, although only CSA inhibited calcium-induced permeability transition in liver-derived mitochondria. In several cell lines, including cortical neurons in culture, DEX significantly decreased oxygen consumption while maintaining or increasing production of adenosine triphosphate (ATP). DEX also normalized the metabolic profile of injured cells and was protective against the cytotoxic effects of proteasome inhibition. These data indicate that DEX increases the efficiency of oxidative phosphorylation, possibly by inhibition of a CSA-sensitive mitochondrial conductance.

NAD(+) administration decreases ischemic brain damage partially by blocking autophagy in a mouse model of brain ischemia

Nicotinamide adenine dinuleotide (NAD(+)) plays critical roles in multiple biological functions. Previous studies have indicated that NAD(+) treatment decreases oxidative stress-induced death of primary neurons and astrocytes. Intranasal administration of NAD(+) also reduces brain damage in a rat model of transient focal brain ischemia. However, the mechanisms underlying this protective effect remain unknown. In this study, we used a mouse model of brain ischemia to test our hypothesis that NAD(+) decreases ischemic brain damage partially by preventing autophagy. Adult male mice were subjected to transient middle cerebral artery occlusion (tMCAO) for 90min, and NAD(+) was administered intraperitoneally (i.p.) immediately after reperfusion started. We found that administration with 50mg/kg NAD(+) led to significant decreases in infarct size, edema formation, and neurological deficits at 48h after ischemia. NAD(+) administration also significantly decreased brain ischemia-induced autophagy in the cortex and hippocampus. We further found that prevention of autophagy by 3-methyladenine (3-MA), a selective autophagy inhibitor, significantly reduced ischemic brain damage, suggesting an important role of autophagy in the ischemic brain injury in our animal model. Collectively, our findings have suggested that NAD(+) administration decreases ischemic brain damage at least partially by blocking autophagy. This is the first suggested mechanism regarding the protective effects of NAD(+) in cerebral ischemia, which further highlights the promise of NAD(+) for treating brain ischemia.