Mitochondrial DNA maintenance is regulated in human hepatoma cells by glycogen synthase kinase 3β and p53 in response to tumor necrosis factor α

Mitochondrial DNA-targeted therapy: A novel approach to combat cancer

Mitochondrial DNA (mtDNA) encodes proteins and RNAs that are essential for mitochondrial function and cellular homeostasis, and participates in important processes of cellular bioenergetics and metabolism. Alterations in mtDNA are associated with various diseases, especially cancers, and are considered as biomarkers for some types of tumors. Moreover, mtDNA alterations have been found to affect the proliferation, progression and metastasis of cancer cells, as well as their interactions with the immune system and the tumor microenvironment (TME). The important role of mtDNA in cancer development makes it a significant target for cancer treatment. In recent years, many novel therapeutic methods targeting mtDNA have emerged. In this study, we first discussed how cancerogenesis is triggered by mtDNA mutations, including alterations in gene copy number, aberrant gene expression and epigenetic modifications. Then, we described in detail the mechanisms underlying the interactions between mtDNA and the extramitochondrial environment, which are crucial for understanding the efficacy and safety of mtDNA-targeted therapy. Next, we provided a comprehensive overview of the recent progress in cancer therapy strategies that target mtDNA. We classified them into two categories based on their mechanisms of action: indirect and direct targeting strategies. Indirect targeting strategies aimed to induce mtDNA damage and dysfunction by modulating pathways that are involved in mtDNA stability and integrity, while direct targeting strategies utilized molecules that can selectively bind to or cleave mtDNA to achieve the therapeutic efficacy. This study highlights the importance of mtDNA-targeted therapy in cancer treatment, and will provide insights for future research and development of targeted drugs and therapeutic strategies.

Maternal Inflammation During Pregnancy and Offspring Brain Development: The Role of Mitochondria

The association between maternal immune activation (MIA) during pregnancy and risk for offspring neuropsychiatric disorders has been increasingly recognized over the past several years. Among the mechanistic pathways that have been described through which maternal inflammation during pregnancy may affect fetal brain development, the role of mitochondria has received little attention. In this review, the role of mitochondria as a potential mediator of the association between MIA during pregnancy and offspring brain development and risk for psychiatric disorders will be proposed. As a basis for this postulation, convergent evidence is presented supporting the obligatory role of mitochondria in brain development, the role of mitochondria as mediators and initiators of inflammatory processes, and evidence of mitochondrial dysfunction in preclinical MIA exposure models and human neurodevelopmental disorders. Elucidating the role of mitochondria as a potential mediator of MIA-induced alterations in brain development and neurodevelopmental disease risk may not only provide new insight into the pathophysiology of mental health disorders that have their origins in exposure to infection/immune activation during pregnancy but also offer new therapeutic targets.

N-Acetylcysteine Reduces miR-146a and NF-κB p65 Inflammatory Signaling Following Cadmium Hepatotoxicity in Rats

We performed a thorough screening and analysis of the impact of cadmium chloride (CdCl₂) and N-acetylcysteine (NAC) on the miR146a/NF-κB p65 inflammatory pathway and mitochondrial biogenesis dysfunction in male albino rats. A total of 24 male albino rats were divided into three groups: a control group, a CdCl₂-treated group (3 mg/kg, orally), and a CdCl₂ + NAC-treated group (200 mg/kg of NAC, 1 h after CdCl₂ treatment), for 60 consecutive days. Real-time quantitative PCR was used to analyze the expression of miR146a, Irak1, Traf6, Nrf1, Nfe2l2, Pparg, Prkaa, Stat3, Tfam, Tnfa, and Il1b, whereas tumor necrosis factor-α, interleukin-1β, and cyclooxygenase-2 protein levels were assessed using ELISA, and NF-κB p65 was detected using western blotting. A significant restoration of homeostatic inflammatory processes as well as mitochondrial biogenesis was observed after NAC and CdCl₂ treatment. Decreased miR146a and NF-κB p65 were also found after treatment with NAC and CdCl₂ compared with CdCl₂ treatment alone. Collectively, our findings demonstrate that CdCl₂ caused mtDNA release because of Tfam loss, leading to NF-κB p65 activation. Co-treatment with NAC could alleviate Cd-induced genotoxicity in liver tissue. We concluded that adding NAC to CdCl₂ resulted in a decreased signaling of the NF-κB p65 signaling pathway.

Glycogen synthesis and beyond, a comprehensive review of GSK3 as a key regulator of metabolic pathways and a therapeutic target for treating metabolic diseases

Glycogen synthase kinase‐3 (GSK3) is a highly evolutionarily conserved serine/threonine protein kinase first identified as an enzyme that regulates glycogen synthase (GS) in response to insulin stimulation, which involves GSK3 regulation of glucose metabolism and energy homeostasis. Both isoforms of GSK3, GSK3α, and GSK3β, have been implicated in many biological and pathophysiological processes. The various functions of GSK3 are indicated by its widespread distribution in multiple cell types and tissues. The studies of GSK3 activity using animal models and the observed effects of GSK3‐specific inhibitors provide more insights into the roles of GSK3 in regulating energy metabolism and homeostasis. The cross‐talk between GSK3 and some important energy regulators and sensors and the regulation of GSK3 in mitochondrial activity and component function further highlight the molecular mechanisms in which GSK3 is involved to regulate the metabolic activity, beyond its classical regulatory effect on GS. In this review, we summarize the specific roles of GSK3 in energy metabolism regulation in tissues that are tightly associated with energy metabolism and the functions of GSK3 in the development of metabolic disorders. We also address the impacts of GSK3 on the regulation of mitochondrial function, activity and associated metabolic regulation. The application of GSK3 inhibitors in clinical tests will be highlighted too. Interactions between GSK3 and important energy regulators and GSK3‐mediated responses to different stresses that are related to metabolism are described to provide a brief overview of previously less‐appreciated biological functions of GSK3 in energy metabolism and associated diseases through its regulation of GS and other functions.

Stereochemical and structural effects of (2R,6R)-hydroxynorketamine on the mitochondrial metabolome in PC-12 cells

BACKGROUND

Impairment in mitochondrial biogenesis and function plays a key role in depression and anxiety, both of which being associated with changes in fatty acid and phospholipid metabolism. The antidepressant effects of (R,S)-ketamine have been linked to its conversion into (2S,6S;2R,6R)-hydroxynorketamine (HNK); however, the connection between structure and stereochemistry of ketamine and HNK in the mitochondrial homeostatic response has not yet been fully elucidated at a metabolic level.

METHODS

We used a multi-platform, non-targeted metabolomics approach to study the change in mitochondrial metabolome of PC-12 cells treated with ketamine and HNK enantiomers. The identified metabolites were grouped into pathways in order to assess global responses.

RESULTS

Treatment with (2R,6R)-HNK elicited the significant change in 49 metabolites and associated pathways implicated in fundamental mitochondrial functions such as TCA cycle, branched-chain amino acid biosynthetic pathway, glycoxylate metabolic pathway, and fatty acid β-oxidation. The affected metabolites included glycerate, citrate, leucine, N,N-dimethylglycine, 3-hexenedioic acid, and carnitine and attenuated signals associated with 9 fatty acids and elaidic acid. Important metabolites involved in the purine and pyrimidine pathways were also affected by (2R-6R)-HNK. This global metabolic profile was not as strongly impacted by treatment with (2S,6S)-HNK, (R)- and (S)-ketamine and in some instances opposite effects were observed.

CONCLUSIONS

The present data provide an overall view of the metabolic changes in mitochondrial function produced by (2R,6R)-HNK and related ketamine compounds and offer an insight into the source of the observed variance in antidepressant response elicited by the compounds.

Increased expression of mitochondrial transcription factor A and nuclear respiratory factor-1 predicts a poor clinical outcome of breast cancer

Nuclear respiratory factor-1 (Nrf1) and mitochondrial transcription factor A (TFAM) are involved in the regulation of a variety of mitochondrial functional genes, which are associated with decreased sensitivity of tumor cells to chemotherapy. However, the expression status of Nrf1 and TFAM, as well as their clinical significance in breast cancer, is unknown. In the present study, tumor tissues and corresponding adjacent normal tissues were collected from 336 patients with breast cancer, and Nrf1 and TFAM expression was analyzed by immunohistochemistry using a tissue microarray. Expression of Nrf1 and TFAM was significantly increased in breast cancer tissue compared with adjacent normal tissues. In addition, patients positive for Nrf1 or TFAM had a poorer clinical prognosis than patients who were negative, and those positive for Nrf1 and TFAM had the shortest survival time. These results suggest that Nrf1 and TFAM are potential biomarkers for the determination of individualized therapy and the prognosis of breast cancer, and molecular targeting of Nrf1 and TFAM is a promising strategy for the sensitization of breast cancer cells to chemotherapeutics.

The little big genome: the organization of mitochondrial DNA

The small (16,569 base pair) human mitochondrial genome plays a significant role in cell metabolism and homeostasis. Mitochondrial DNA (mtDNA) contributes to the generation of complexes which are essential to oxidative phosphorylation (OXPHOS). As such, mtDNA is directly integrated into mitochondrial biogenesis and signaling and regulates mitochondrial metabolism in concert with nuclear-encoded mitochondrial factors. Mitochondria are a highly dynamic, pleiomorphic network that undergoes fission and fusion events. Within this network, mtDNAs are packaged into structures called nucleoids which are actively distributed in discrete foci within the network. This sensitive organelle is frequently disrupted by insults such as oxidants and inflammatory cytokines, and undergoes genomic damage with double- and single-strand breaks that impair its function. Collectively, mtDNA is emerging as a highly sensitive indicator of cellular stress, which is directly integrated into the mitochondrial network as a contributor of a wide range of critical signaling pathways.

Commentary: Mitochondrial DNA damage and loss in diabetes

This commentary discusses damage and loss of mitochondrial DNA (mtDNA) in type 2 diabetes mellitus from both the clinical and experimental perspectives. Increasingly, an array of studies in experimental models and patients suggests that the cellular stresses of insulin resistance in type 2 diabetes damage mtDNA, leading to loss of mitochondrial genetic content. As such, mtDNA is emerging as both a valuable monitoring tool and translational preventive target for metabolic disease. Copyright © 2016 John Wiley & Sons, Ltd.

Arachidonyl-2-Chloroethylamide Alleviates Cerebral Ischemia Injury Through Glycogen Synthase Kinase-3β-Mediated Mitochondrial Biogenesis and Functional Improvement

Arachidonyl-2-chloroethylamide (ACEA), a highly selective agonist of cannabinoid receptor 1 (CB1R), has been reported to protect neurons in ischemic injury. We sought to investigate whether mitochondrial biogenesis was involved in the therapeutic effect of ACEA in cerebral ischemia. Focal cerebral ischemic injury was induced in adult male Sprague Dawley rats. Intraperitoneal injection of 1 mg/kg ACEA improved neurological behavior, reduced infarct volume, and inhibited apoptosis. The volume and numbers of mitochondria were significantly increased after ACEA administration. Expression of mitochondrial transcription factor A (Tfam), nuclear transcription factor-1 (Nrf-1), and cytochrome C oxidase subunit IV (COX IV) were also significantly up-regulated in animals administered ACEA. One thousand nanomoles of ACEA inhibited mitochondrial dysfunction in primary rat cortical neurons exposed to oxygen-glucose deprivation (OGD). Furthermore, ACEA administration increased phosphorylation of glycogen synthase kinase-3β (GSK-3β) after reperfusion. Phosphorylation of GSK-3β induced mitochondrial biogenesis and preserved mitochondrial function whereas inhibition of phosphatidylinositol 3-kinase (PI3K) dampened phosphorylation of GSK-3β and reversed induction of mitochondrial biogenesis and function following ACEA administration. In conclusion, ACEA could induce mitochondrial biogenesis and improve mitochondrial function at the beginning of cerebral ischemia, thus alleviating cerebral ischemia injury. Phosphorylation of GSK-3β might be involved in the regulation of mitochondrial biogenesis induced by ACEA.

Recombinant human augmenter of liver regeneration protects hepatocyte mitochondrial DNA in rats with obstructive jaundice

BACKGROUND

Hepatocyte mitochondrial DNA (mtDNA) damage is an important cause of mitochondrial and hepatic function impairment in obstructive jaundice (OJ). This study investigated the protective effect of recombinant human augmenter of liver regeneration (rhALR) on hepatocyte mtDNA in rats with OJ.

MATERIALS AND METHODS

Wistar rats were randomly divided into three groups as follows: sham-operation, biliary obstruction and recanalization with rhALR treatment (BDO-RBF-rhALR), and BDO-RBF-Vehicle (n = 48 per group). After biliary obstruction, rats were intraperitoneally injected with 40 μg/kg rhALR in BDO-RBF-rhALR group and same volume of normal saline in other two groups once every 12 h, until sacrifice. Mitochondrial transcription factor A (mtTFA) and nuclear respiratory factor-1 (NRF-1) expression in hepatocytes were detected by real-time reverse transcription-polymerase chain reaction and Western blot. Hepatocyte mtDNA damage was evaluated by real-time-polymerase chain reaction. Mitochondrial and hepatic functions were also assessed.

RESULTS

After biliary obstruction, hepatic function was clearly impaired, as shown by the increases in serum alanine aminotransferase, aspartate aminotransferase, and total bilirubin levels, and the decrease in albumin level. Mitochondrial respiratory control ratio, phosphorus oxygen ratio, and ATP levels (all indicators of mitochondrial function) were decreased. The relative amount of total mtDNA, mtTFA, and NRF-1 expression in rat liver tissues were decreased, whereas the relative amount of deleted mtDNA was increased. However, the damage was significantly improved in the BDO-RBF-rhALR group. After recanalization, these changes were gradually restored, but the recovery was faster in the BDO-RBF-rhALR group than in BDO-RBF-Vehicle group.

CONCLUSIONS

rhALR may protect and improve mitochondrial and hepatic functions in rats with OJ by promoting the expression of mtTFA and NRF-1 and by protecting and repairing damaged mtDNA.

Interleukin-1β causes excitotoxic neurodegeneration and multiple sclerosis disease progression by activating the apoptotic protein p53

Background

Understanding how inflammation causes neuronal damage is of paramount importance in multiple sclerosis (MS) and in other neurodegenerative diseases. Here we addressed the role of the apoptotic cascade in the synaptic abnormalities and neuronal loss caused by the proinflammatory cytokines interleukin-1β (IL-1β) and tumor necrosis factor (TNF-α) in brain tissues, and disease progression caused by inflammation in relapsing-remitting MS (RRMS) patients.

Results

The effect of IL-1β, but not of TNF-α, on glutamate-mediated excitatory postsynaptic currents was blocked by pifithrin-α (PFT), inhibitor of p53. The protein kinase C (PKC)/transient receptor potential vanilloid 1 (TRPV1) pathway was involved in IL-1β-p53 interaction at glutamatergic synapses, as pharmacological modulation of this inflammation-relevant molecular pathway affected PFT effects on the synaptic action of IL-1β. IL-1β-induced neuronal swelling was also blocked by PFT, and IL-1β increased the expression of p21, a canonical downstream target of activated p53.

Consistent with these in vitro results, the Pro/Pro genotype of p53, associated with low efficiency of transcription of p53-regulated genes, abrogated the association between IL-1β cerebrospinal fluid (CSF) levels and disability progression in RRMS patients. The interaction between p53 and CSF IL-1β was also evaluated at the optical coherence tomography (OCT), showing that IL-1β-driven neurodegenerative damage, causing alterations of macular volume and of retinal nerve fibre layer thickness, was modulated by the p53 genotype.

Conclusions

Inflammatory synaptopathy and neurodegeneration caused by IL-1β in RRMS patients involve the apoptotic cascade. Targeting IL-1β-p53 interaction might result in significant neuroprotection in MS.

A splice variant of the human ion channel TRPM2 modulates neuroblastoma tumor growth through hypoxia-inducible factor (HIF)-1/2α

The calcium-permeable ion channel TRPM2 is highly expressed in a number of cancers. In neuroblastoma, full-length TRPM2 (TRPM2-L) protected cells from moderate oxidative stress through increased levels of forkhead box transcription factor 3a (FOXO3a) and superoxide dismutase 2. Cells expressing the dominant negative short isoform (TRPM2-S) had reduced FOXO3a and superoxide dismutase 2 levels, reduced calcium influx in response to oxidative stress, and enhanced reactive oxygen species, leading to decreased cell viability. Here, in xenografts generated with SH-SY5Y neuroblastoma cells stably expressing TRPM2 isoforms, growth of tumors expressing TRPM2-S was significantly reduced compared with tumors expressing TRPM2-L. Expression of hypoxia-inducible factor (HIF)-1/2α was significantly reduced in TRPM2-S-expressing tumor cells as was expression of target proteins regulated by HIF-1/2α including those involved in glycolysis (lactate dehydrogenase A and enolase 2), oxidant stress (FOXO3a), angiogenesis (VEGF), mitophagy and mitochondrial function (BNIP3 and NDUFA4L2), and mitochondrial electron transport chain activity (cytochrome oxidase 4.1/4.2 in complex IV). The reduction in HIF-1/2α was mediated through both significantly reduced HIF-1/2α mRNA levels and increased levels of von Hippel-Lindau E3 ligase in TRPM2-S-expressing cells. Inhibition of TRPM2-L by pretreatment with clotrimazole or expression of TRPM2-S significantly increased sensitivity of cells to doxorubicin. Reduced survival of TRPM2-S-expressing cells after doxorubicin treatment was rescued by gain of HIF-1 or -2α function. These data suggest that TRPM2 activity is important for tumor growth and for cell viability and survival following doxorubicin treatment and that interference with TRPM2-L function may be a novel approach to reduce tumor growth through modulation of HIF-1/2α, mitochondrial function, and mitophagy.

Screen for mitochondrial DNA copy number maintenance genes reveals essential role for ATP synthase

The machinery of mitochondrial DNA (mtDNA) maintenance is only partially characterized and is of wide interest due to its involvement in disease. To identify novel components of this machinery, plus other cellular pathways required for mtDNA viability, we implemented a genome-wide RNAi screen in Drosophila S2 cells, assaying for loss of fluorescence of mtDNA nucleoids stained with the DNA-intercalating agent PicoGreen. In addition to previously characterized components of the mtDNA replication and transcription machineries, positives included many proteins of the cytosolic proteasome and ribosome (but not the mitoribosome), three proteins involved in vesicle transport, some other factors involved in mitochondrial biogenesis or nuclear gene expression, > 30 mainly uncharacterized proteins and most subunits of ATP synthase (but no other OXPHOS complex). ATP synthase knockdown precipitated a burst of mitochondrial ROS production, followed by copy number depletion involving increased mitochondrial turnover, not dependent on the canonical autophagy machinery. Our findings will inform future studies of the apparatus and regulation of mtDNA maintenance, and the role of mitochondrial bioenergetics and signaling in modulating mtDNA copy number.

Luminol-based chemiluminescent signals: clinical and non-clinical application and future uses

Chemiluminescence (CL) is an important method for quantification and analysis of various macromolecules. A wide range of CL agents such as luminol, hydrogen peroxide, fluorescein, dioxetanes and derivatives of oxalate, and acridinium dyes are used according to their biological specificity and utility. This review describes the application of luminol chemiluminescence (LCL) in forensic, biomedical, and clinical sciences. LCL is a very useful detection method due to its selectivity, simplicity, low cost, and high sensitivity. LCL has a dynamic range of applications, including quantification and detection of macro and micromolecules such as proteins, carbohydrates, DNA, and RNA. Luminol-based methods are used in environmental monitoring as biosensors, in the pharmaceutical industry for cellular localization and as biological tracers, and in reporter gene-based assays and several other immunoassays. Here, we also provide information about different compounds that may enhance or inhibit the LCL along with the effect of pH and concentration on LCL. This review covers most of the significant information related to the applications of luminol in different fields.

mtDNA mutations in human aging and longevity: controversies and new perspectives opened by high-throughput technologies

The last 30 years of research greatly contributed to shed light on the role of mitochondrial DNA (mtDNA) variability in aging, although contrasting results have been reported, mainly due to bias regarding the population size and stratification, and to the use of analysis methods (haplogroup classification) that resulted to be not sufficiently adequate to grasp the complexity of the phenomenon. A 5-years European study (the GEHA EU project) collected and analyzed data on mtDNA variability on an unprecedented number of long-living subjects (enriched for longevity genes) and a comparable number of controls (matched for gender and ethnicity) in Europe. This very large study allowed a reappraisal of the role of both the inherited and the somatic mtDNA variability in aging, as an association with longevity emerged only when mtDNA variants in OXPHOS complexes co-occurred. Moreover, the availability of data from both nuclear and mitochondrial genomes on a large number of subjects paves the way for an evaluation at a very large scale of the epistatic interactions at a higher level of complexity. This scenario is expected to be even more clarified in the next future with the use of next generation sequencing (NGS) techniques, which are becoming applicable to evaluate mtDNA variability and, then, new mathematical/bioinformatic analysis methods are urgently needed. Recent advances of association studies on age-related diseases and mtDNA variability will also be discussed in this review, taking into account the bias hidden by population stratification. Finally, very recent findings in terms of mtDNA heteroplasmy (i.e. the coexistence of wild type and mutated copies of mtDNA) and aging as well as mitochondrial epigenetic mechanisms will also be discussed.

Transcriptomic profiling of TK2 deficient human skeletal muscle suggests a role for the p53 signalling pathway and identifies growth and differentiation factor-15 as a potential novel biomarker for mitochondrial myopathies

Background

Mutations in the gene encoding thymidine kinase 2 (TK2) result in the myopathic form of mitochondrial DNA depletion syndrome which is a mitochondrial encephalomyopathy presenting in children. In order to unveil some of the mechanisms involved in this pathology and to identify potential biomarkers and therapeutic targets we have investigated the gene expression profile of human skeletal muscle deficient for TK2 using cDNA microarrays.

Results

We have analysed the whole transcriptome of skeletal muscle from patients with TK2 mutations and compared it to normal muscle and to muscle from patients with other mitochondrial myopathies. We have identified a set of over 700 genes which are differentially expressed in TK2 deficient muscle. Bioinformatics analysis reveals important changes in muscle metabolism, in particular, in glucose and glycogen utilisation, and activation of the starvation response which affects aminoacid and lipid metabolism. We have identified those transcriptional regulators which are likely to be responsible for the observed changes in gene expression.

Conclusion

Our data point towards the tumor suppressor p53 as the regulator at the centre of a network of genes which are responsible for a coordinated response to TK2 mutations which involves inflammation, activation of muscle cell death by apoptosis and induction of growth and differentiation factor 15 (GDF-15) in muscle and serum. We propose that GDF-15 may represent a potential novel biomarker for mitochondrial dysfunction although further studies are required.

Glycogen synthase kinase-3 (GSK3) controls deoxyglucose-induced mitochondrial biogenesis in human neuroblastoma SH-SY5Y cells

Mitochondrial biogenesis, a mitochondrial growth and division process, is crucial for adaptation to metabolic stress. The present study demonstrated that treatment with a specific inhibitor of GSK3, SB216763, attenuated induction of mitochondrial biogenesis by a glycolysis inhibitor, 2-deoxyglucose (2-DG), without affecting this biogenesis at basal condition. Additionally, overexpression of WT-GSK3β promoted whereas GSK3β-KD attenuated 2-DG-induced mitochondrial protein expression. The mitochondrial biogenesis attenuation by GSK3 inhibitor was not due to inhibition of protein degradation. Furthermore, GSK3 inhibition further reduced transcription of mitochondrial (COXII), but not nuclear (VDAC) gene by 2-DG suggesting its participation in 2-DG-induced mitochondrial transcription. Together, our results show that GSK3 regulates mitochondrial biogenesis induced by glycolysis inhibition.

GSK-3 and mitochondria in cancer cells

GSK-3 is a multifunctional kinase that is located in the cytosol, nucleus, and mitochondria of all cell types, and it is involved in the pathogenesis of a variety of diseases. In cancer, GSK-3 modulates the response of the cell death machinery to stress stimuli, including chemotherapeutics. Mitochondria are at the heart of the integration between survival and noxious signals; therefore, modulation of the mitochondrial functions carried out by GSK-3 is profoundly involved in the apoptosis escape capabilities that hallmark neoplasms. This review briefly covers the mechanistic interactions among oncogenic kinase pathways, GSK-3 activity and subsequent modulation of mitochondrial functions that shape the pro-survival phenotype of cancer cells, such as control of redox homeostasis and inhibition of the mitochondrial permeability transition pore.