Cells depleted of mitochondrial DNA (rho0) yield insight into physiological mechanisms

Mitochondrial mechanotransduction through MIEF1 coordinates the nuclear response to forces

Tissue-scale architecture and mechanical properties instruct cell behaviour under physiological and diseased conditions, but our understanding of the underlying mechanisms remains fragmentary. Here we show that extracellular matrix stiffness, spatial confinements and applied forces, including stretching of mouse skin, regulate mitochondrial dynamics. Actomyosin tension promotes the phosphorylation of mitochondrial elongation factor 1 (MIEF1), limiting the recruitment of dynamin-related protein 1 (DRP1) at mitochondria, as well as peri-mitochondrial F-actin formation and mitochondrial fission. Strikingly, mitochondrial fission is also a general mechanotransduction mechanism. Indeed, we found that DRP1- and MIEF1/2-dependent fission is required and sufficient to regulate three transcription factors of broad relevance-YAP/TAZ, SREBP1/2 and NRF2-to control cell proliferation, lipogenesis, antioxidant metabolism, chemotherapy resistance and adipocyte differentiation in response to mechanical cues. This extends to the mouse liver, where DRP1 regulates hepatocyte proliferation and identity-hallmark YAP-dependent phenotypes. We propose that mitochondria fulfil a unifying signalling function by which the mechanical tissue microenvironment coordinates complementary cell functions.

mtDNA amplifies beryllium sulfate-induced inflammatory responses via the cGAS-STING pathway in 16HBE cells

Beryllium sulfate (BeSO4) can cause inflammation through the mechanism, which has not been elucidated. Mitochondrial DNA (mtDNA) is a key contributor of inflammation. With mitochondrial damage, released mtDNA can bind to specific receptors (e.g., cGAS) and then activate related pathway to promote inflammatory responses. To investigate the mechanism of mtDNA in BeSO4-induced inflammatory response in 16HBE cells, we established the BeSO4-induced 16HBE cell inflammation model and the ethidium bromide (EB)-induced ρ016HBE cell model to detect the mtDNA content, oxidative stress-related markers, mitochondrial membrane potential, the expression of the cGAS-STING pathway, and inflammation-related factors. Our results showed that BeSO4 caused oxidative stress, decline of mitochondrial membrane potential, and the release of mtDNA into the cytoplasm of 16HBE cells. In addition, BeSO4 induced inflammation in 16HBE cells by activating the cGAS-STING pathway. Furthermore, mtDNA deletion inhibited the expression of cGAS-STING pathway, IL-10, TNF-α, and IFN-β. This study revealed a novel mechanism of BeSO4-induced inflammation in 16HBE cells, which contributes to the understanding of the molecular mechanism of beryllium and its compounds-induced toxicity.

Mitochondrial metabolism and the continuing search for ultimate regulators of developmental rate

The rate of embryonic development is a species-specific trait that depends on the properties of the intracellular environment, namely, the rate at which gene products flow through the central dogma of molecular biology. Although any given step in the production and degradation of gene products could theoretically be co-opted by evolution to modulate developmental speed, species are observed to accelerate or slow down all steps simultaneously. This suggests the rate of these molecular processes is jointly regulated by an upstream, ultimate factor. Mitochondrial metabolism was recently proposed to act as an ultimate regulator by controlling the pace of protein synthesis upstream of developmental tempo. Alternative candidates for ultimate regulators include species-specific gene expression levels of factors involved in the central dogma, as well as species-specific cell size. Overall, much work remains to be done before we can confidently identify the ultimate causes of species-specific developmental rates.

Regulation of nuclear transcription by mitochondrial RNA in endothelial cells

Chromatin-associated RNAs (caRNAs) form a relatively poorly recognized layer of the epigenome. The caRNAs reported to date are transcribed from the nuclear genome. Here, leveraging a recently developed assay for detection of caRNAs and their genomic association, we report that mitochondrial RNAs (mtRNAs) are attached to the nuclear genome and constitute a subset of caRNA, thus termed mt-caRNA. In four human cell types analyzed, mt-caRNAs preferentially attach to promoter regions. In human endothelial cells (ECs), the level of mt-caRNA-promoter attachment changes in response to environmental stress that mimics diabetes. Suppression of a non-coding mt-caRNA in ECs attenuates stress-induced nascent RNA transcription from the nuclear genome, including that of critical genes regulating cell adhesion, and abolishes stress-induced monocyte adhesion, a hallmark of dysfunctional ECs. Finally, we report increased nuclear localization of multiple mtRNAs in the ECs of human diabetic donors, suggesting many mtRNA translocate to the nucleus in a cell stress and disease-dependent manner. These data nominate mt-caRNAs as messenger molecules responsible for mitochondrial-nuclear communication and connect the immediate product of mitochondrial transcription with the transcriptional regulation of the nuclear genome.

Lactate activates the mitochondrial electron transport chain independently of its metabolism

Lactate has long been considered a cellular waste product. However, we found that as extracellular lactate accumulates, it also enters the mitochondrial matrix and stimulates mitochondrial electron transport chain (ETC) activity. The resulting increase in mitochondrial ATP synthesis suppresses glycolysis and increases the utilization of pyruvate and/or alternative respiratory substrates. The ability of lactate to increase oxidative phosphorylation does not depend on its metabolism. Both L- and D-lactate are effective at enhancing ETC activity and suppressing glycolysis. Furthermore, the selective induction of mitochondrial oxidative phosphorylation by unmetabolized D-lactate reversibly suppressed aerobic glycolysis in both cancer cell lines and proliferating primary cells in an ATP-dependent manner and enabled cell growth on respiratory-dependent bioenergetic substrates. In primary T cells, D-lactate enhanced cell proliferation and effector function. Together, these findings demonstrate that lactate is a critical regulator of the ability of mitochondrial oxidative phosphorylation to suppress glucose fermentation.

Targeting mitochondrial transcription factor A sensitizes pancreatic cancer cell to gemcitabine

BACKGROUND

The survival of pancreatic cancer cells, particularly cancer stem cells which are responsible for tumor relapse, depends on mitochondrial function. Mitochondrial transcription factor A (TFAM) is critical for the regulation of mitochondrial DNA and thus mitochondrial function. However, the possible involvement of TFAM in pancreatic cancer is unknown.

METHODS

Human samples were obtained from pancreatic cancers and their adjacent tissues; human pancreatic cell lines were cultured in RPMI1640 medium. TFAM expressions in pancreatic tissues and cultured cells were determined using immunohistochemistry, ELISA, and reverse transcription polymerase chain reaction (RT-PCR). The effect of TFAM on cell growth, migration, colony formation and apoptosis were evaluated. Mitochondrial biogenesis in pancreatic cancer and normal cells were examined.

RESULTS

The majority of pancreatic cancer tissues exhibited higher TFAM expression compared to the adjacent counterparts. Consistently, TFAM mRNA and protein levels were higher in pancreatic cancer cell lines than in immortalized normal pancreatic epithelial cells. There was no difference on TFAM level between gemcitabine-sensitive and resistant pancreatic cancer cells. Functional analysis demonstrated that TFAM overexpression activated pancreatic normal and tumor cells whereas TFAM inhibition effectively inhibited the growth of pancreatic cancer cells. TFAM inhibition enhanced gemcitabine's cytotoxicity and suppressed growth, anchorage-independent colony formation and survival of gemcitabine-resistant pancreatic cancer cells. Mechanistic studies showed that TFAM inhibition resulted in remarkable mitochondrial dysfunction and energy crisis followed by oxidative stress. The basal mitochondrial biogenesis level correlated well with TFAM level in pancreatic cancer cells.

CONCLUSIONS

TFAM played essential roles in pancreatic cancer via regulating mitochondrial functions which highlighted the therapeutic value of inhibiting TFAM to overcome gemcitabine resistance.

Lactate activates the mitochondrial electron transport chain independent of its metabolism

Lactate has long been considered a cellular waste product. However, we found that as extracellular lactate accumulates, it also enters the mitochondrial matrix and stimulates mitochondrial electron transport chain (ETC) activity. The resulting increase in mitochondrial ATP synthesis suppresses glycolysis and increases the utilization of pyruvate and/or alternative respiratory substrates. The ability of lactate to increase oxidative phosphorylation does not depend on its metabolism. Both L- and D-lactate are effective at enhancing ETC activity and suppressing glycolysis. Furthermore, the selective induction of mitochondrial oxidative phosphorylation by unmetabolized D-lactate reversibly suppressed aerobic glycolysis in both cancer cell lines and proliferating primary cells in an ATP-dependent manner and enabled cell growth on respiratory-dependent bioenergetic substrates. In primary T cells, D-lactate enhanced cell proliferation and effector function. Together, these findings demonstrate that lactate is a critical regulator of the ability of mitochondrial oxidative phosphorylation to suppress glucose fermentation.

Targeting Mitochondrial DNA Transcription by POLRMT Inhibition or Depletion as a Potential Strategy for Cancer Treatment

Transcription of the mitochondrial genome is essential for the maintenance of oxidative phosphorylation (OXPHOS) and other functions directly related to this unique genome. Considerable evidence suggests that mitochondrial transcription is dysregulated in cancer and cancer metastasis and contributes significantly to cancer cell metabolism. Recently, inhibitors of the mitochondrial DNA-dependent RNA polymerase (POLRMT) were identified as potentially attractive new anti-cancer compounds. These molecules (IMT1, IMT1B) inactivate cancer cell metabolism through reduced transcription of mitochondrially-encoded OXPHOS subunits such as ND1-5 (Complex I) and COI-IV (Complex IV). Studies from our lab have discovered small molecule regulators of the mitochondrial matrix caseinolytic protease (ClpP) as probable inhibitors of mitochondrial transcription. These compounds activate ClpP proteolysis and lead to the rapid depletion of POLRMT and other matrix proteins, resulting in inhibition of mitochondrial transcription and growth arrest. Herein we present a comparison of POLRMT inhibition and ClpP activation, both conceptually and experimentally, and evaluate the results of these treatments on mitochondrial transcription, inhibition of OXPHOS, and ultimately cancer cell growth. We discuss the potential for targeting mitochondrial transcription as a cancer cell vulnerability.

Lauric Acid Overcomes Hypoxia-Induced Gemcitabine Chemoresistance in Pancreatic Ductal Adenocarcinoma

Although gemcitabine (GEM) is widely used in chemotherapy for pancreatic ductal adenocarcinoma (PDA), drug resistance restricts its clinical effectiveness. To examine the mechanism of GEM resistance, we established two GEM-resistant cell lines from human PDA cells by continuous treatment with GEM and CoCl₂-induced chemical hypoxia. One resistant cell line possessed reduced energy production and decreased mitochondrial reactive oxygen species levels, while the other resistant cell line possessed increased stemness. In both cell lines, ethidium bromide-stained mitochondrial DNA levels decreased, suggesting mitochondrial DNA damage. Inhibition of hypoxia-inducible factor-1α in both cell lines did not restore the GEM sensitivity. In contrast, treatment of both cell types with lauric acid (LAA), a medium-chain fatty acid, restored GEM sensitivity. These results suggest that decreased energy production, decreased mitochondrial reactive oxygen species levels, and increased stemness associated with mitochondrial damage caused by GEM lead to GEM resistance, and that hypoxia may promote this process. Furthermore, forced activation of oxidative phosphorylation by LAA could be a tool to overcome GEM resistance. Clinical verification of the effectiveness of LAA in GEM resistance is necessary in the future.

Targeting ATP Synthase by Bedaquiline as a Therapeutic Strategy to Sensitize Ovarian Cancer to Cisplatin

Cisplatin is a common chemotherapeutic drug for treating ovarian cancer, but its clinical efficacy is hampered by intrinsic and acquired resistance. Previous studies had shown inhibiting oxidative phosphorylation overcomes cisplatin resistance in ovarian cancer. Studies reveal that bedaquiline, a clinically available antimicrobial drug, inhibits cancer via targeting mitochondria. This study systematically assessed the efficacy of bedaquiline in ovarian cancer and its underlying mechanism. Using a panel of ovarian cancer cell lines and normal ovary cells, we demonstrated bedaquiline is selective for anti-ovarian cancer activities. Furthermore, the sensitivity varied among different ovarian cancer cell lines regardless of their sensitivity to cisplatin. Bedaquiline inhibited growth, survival and migration, through decreasing levels of ATP synthase subunit, complex V activity, mitochondrial respiration and ATP. We further found that ovarian cancer displayed increased levels of ATP, oxygen consumption rate (OCR), complex V activity and ATP synthase subunits compared to normal counterpart. Combination index analysis showed that bedaquiline and cisplatin is synergistic. Bedaquiline remarkably enhanced the efficacy of cisplatin in inhibiting ovarian cancer growth in mice. Our study provides evidence to repurpose bedaquiline for ovarian cancer treatment and suggests that ATP synthase is a selective target to overcome cisplatin resistance in ovarian cancer.

The Role of Mitochondrial Enzymes, Succinate-Coupled Signaling Pathways and Mitochondrial Ultrastructure in the Formation of Urgent Adaptation to Acute Hypoxia in the Myocardium

The effect of a single one-hour exposure to three modes of hypobaric hypoxia (HBH) differed in the content of O₂ in inhaled air (FiO₂-14%, 10%, 8%) in the development of mitochondrial-dependent adaptive processes in the myocardium was studied in vivo. The following parameters have been examined: (a) an urgent reaction of catalytic subunits of mitochondrial enzymes (NDUFV2, SDHA, Cyt b, COX2, ATP5A) in the myocardium as an indicator of the state of the respiratory chain electron transport function; (b) an urgent activation of signaling pathways dependent on GPR91, HIF-1α and VEGF, allowing us to assess their role in the formation of urgent mechanisms of adaptation to hypoxia in the myocardium; (c) changes in the ultrastructure of three subpopulations of myocardial mitochondria under these conditions. The studies were conducted on two rat phenotypes: rats with low resistance (LR) and high resistance (HR) to hypoxia. The adaptive and compensatory role of the mitochondrial complex II (MC II) in maintaining the electron transport and energy function of the myocardium in a wide range of reduced O₂ concentrations in the initial period of hypoxic exposure has been established. The features of urgent reciprocal regulatory interaction of NAD- and FAD-dependent oxidation pathways in myocardial mitochondria under these conditions have been revealed. The data indicating the participation of GPR91, HIF-1a and VEGF in this process have been obtained. The ultrastructure of the mitochondrial subpopulations in the myocardium of LR and HR rats differed in normoxic conditions and reacted differently to hypoxia of varying severity. The parameters studied together are highly informative indicators of the quality of cardiac activity and metabolic biomarkers of urgent adaptation in various hypoxic conditions.

The F1Fo-ATPase inhibitor protein IF1 in pathophysiology

The endogenous inhibitor of ATP synthase is a protein of about 10 kDa, known as IF1 which binds to the catalytic domain of the enzyme during ATP hydrolysis. The main role of IF1 consists of limiting ATP dissipation under condition of severe oxygen deprivation or in the presence of dysfunctions of mitochondrial respiratory complexes, causing a collapse in mitochondrial membrane potential and therefore ATP hydrolysis. New roles of IF1 are emerging in the fields of cancer and neurodegeneration. Its high expression levels in tumor tissues have been associated with different roles favouring tumor formation, progression and evasion. Since discordant mechanisms of action have been proposed for IF1 in tumors, it is of the utmost importance to clarify them in the prospective of defining novel approaches for cancer therapy. Other IF1 functions, including its involvement in mitophagy, may be protective for neurodegenerative and aging-related diseases. In the present review we aim to clarify and discuss the emerging mechanisms in which IF1 is involved, providing a critical view of the discordant findings in the literature.

The Multifaceted ATPase Inhibitory Factor 1 (IF1) in Energy Metabolism Reprogramming and Mitochondrial Dysfunction: A New Player in Age-Associated Disorders?

Significance: The mitochondrial oxidative phosphorylation (OXPHOS) system, comprising the electron transport chain and ATP synthase, generates membrane potential, drives ATP synthesis, governs energy metabolism, and maintains redox balance. OXPHOS dysfunction is associated with a plethora of diseases ranging from rare inherited disorders to common conditions, including diabetes, cancer, neurodegenerative diseases, as well as aging. There has been great interest in studying regulators of OXPHOS. Among these, ATPase inhibitory factor 1 (IF1) is an endogenous inhibitor of ATP synthase that has long been thought to avoid the consumption of cellular ATP when ATP synthase acts as an ATP hydrolysis enzyme. Recent Advances: Recent data indicate that IF1 inhibits ATP synthesis and is involved in a multitude of mitochondrial-related functions, such as mitochondrial quality control, energy metabolism, redox balance, and cell fate. IF1 also inhibits the ATPase activity of cell-surface ATP synthase, and it is used as a cardiovascular disease biomarker. Critical Issues: Although recent data have led to a paradigm shift regarding IF1 functions, these have been poorly studied in entire organisms and in different organs. The understanding of the cellular biology of IF1 is, therefore, still limited. The aim of this review was to provide an overview of the current understanding of the role of IF1 in mitochondrial functions, health, and diseases. Future Directions: Further investigations of IF1 functions at the cell, organ, and whole-organism levels and in different pathophysiological conditions will help decipher the controversies surrounding its involvement in mitochondrial function and could unveil therapeutic strategies in human pathology. Antioxid. Redox Signal. 37, 370-393.

Mitochondrial genome engineering coming-of-age

The mitochondrial genome has been difficult to manipulate because it is shielded by the organelle double membranes, preventing efficient nucleic acid entry. Moreover, mitochondrial DNA (mtDNA) recombination is not a robust system in most species. This limitation has forced investigators to rely on naturally occurring alterations to study both mitochondrial function and pathobiology. Because most pathogenic mtDNA mutations are heteroplasmic, the development of specific nucleases has allowed us to selectively eliminate mutant species. Several 'protein only' gene-editing platforms have been successfully used for this purpose. More recently, a DNA double-strand cytidine deaminase has been identified and adapted to edit mtDNA. This enzyme was also used as a component to adapt a DNA single-strand deoxyadenosine deaminase to mtDNA editing. These are major advances in our ability to precisely alter the mtDNA in animal cells.

Monensin inhibits anaplastic thyroid cancer via disrupting mitochondrial respiration and AMPK/mTOR signaling

OBJECTIVE

The clinical management of anaplastic thyroid cancer (ATC) remains challenging and novel treatment methods are needed. Monensin is a carboxyl polyether ionophore that potently inhibits the growth of various cancer types. Our current work investigates whether monensin has selective anti-ATC activity and systematically explores its underlying mechanisms.

METHODS

Proliferation and apoptosis assays were performed using a panel of thyroid cancer cell lines. Mitochondrial biogenesis profiles, ATP levels, oxidative stress, AMPK and mTOR were examined in these cells after monensin treatment.

RESULTS

Monensin is effective to inhibit proliferation and induce apoptosis in a number of thyroid cancer cell lines. The results are consistent across cell lines of varying cellular origins and genetic mutations. Compared to other thyroid cancer cell types, ATC cell lines are the most sensitive to monensin. Of note, monensin used at our experimental concentration affects less of normal cells. Mechanistic studies reveal that monensin acts on ATC cells through disrupting mitochondrial function, inducing oxidative stress and damage, and AMPK activation-induced mTOR inhibition. We further show mitochondrial respiration is a critical target for monensin in ATC cells.

CONCLUSIONS

Our pre-clinical findings demonstrate the selective anti-ATC activities of monensin. This is supported by increasing evidence monensin can to be repurposed as a potential anti-cancer drug.

Assessing Mitochondrial DNA Release into the Cytosol and Subsequent Activation of Innate Immune-related Pathways in Mammalian Cells

Mitochondria have emerged as key drivers of mammalian innate immune responses, functioning as signaling hubs to trigger inflammation and orchestrating metabolic switches required for phagocyte activation. Mitochondria also contain damage-associated molecular patterns (DAMPs), molecules that share similarity with pathogen-associated molecular patterns (PAMPs) and can engage innate immune sensors to drive inflammation. The aberrant release of mitochondrial DAMPs during cellular stress and injury is an increasingly recognized trigger of inflammatory responses in human diseases. Mitochondrial DNA (mtDNA) is a particularly potent DAMP that engages multiple innate immune sensors, although mounting evidence suggests that cytosolic mtDNA is primarily detected via the cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING) pathway. cGAS and STING are widely expressed in mammalian cells and serve as key regulators of type I interferon and cytokine expression in both infectious and inflammatory diseases. Despite growing roles for the mtDNA-cGAS-STING axis in human disease, assays to quantify mtDNA release into the cytosol and approaches to link mtDNA to cGAS-STING signaling are not standardized, which increases the possibility for experimental artifacts and misinterpretation of data. Here, we present a series of protocols for assaying the release of mtDNA into the cytosol and subsequent activation of innate immune signaling in mammalian cells. We highlight genetic and pharmacological approaches to induce and inhibit mtDNA release from mitochondria. We also describe immunofluorescence microscopy and cellular fractionation assays to visualize morphological changes in mtDNA and quantify mtDNA accumulation in the cytosol. Finally, we include protocols to examine mtDNA-dependent cGAS-STING activation by RT-qPCR and western blotting. These methods can be performed with standard laboratory equipment and are highly adaptable to a wide range of mammalian cell types. They will permit researchers working across the spectrum of biological and biomedical sciences to accurately and reproducibly measure cytosolic mtDNA release and resulting innate immune responses. © 2022 Wiley Periodicals LLC. Basic Protocol 1: siRNA-mediated knockdown of TFAM to induce mtDNA instability, cytosolic release, and activation of the cGAS-STING pathway Alternate Protocol: Pharmacological induction of mtDNA release and cGAS-STING activation using ABT-737 and Q-VD-OPH Basic Protocol 2: Isolation and quantitation of DNA from cytosolic, mitochondrial, and nuclear fractions Basic Protocol 3: Pharmacological inhibition of mtDNA replication and release.

Doxycycline sensitizes renal cell carcinoma to chemotherapy by preferentially inhibiting mitochondrial translation

Objectives

The anti-cancer activity of doxycycline has been reported in many cancers but not renal cell carcinoma (RCC). This study aimed to determine the efficacy of doxycycline alone and in combination with paclitaxel and analyze the underlying mechanism in RCC.

Methods

Proliferation, colony formation and apoptosis assays were performed in RCC cell lines after drug treatments. An RCC xenograft mouse model was generated, and tumor growth was monitored. Mechanistic studies focused on mitochondrial translation and functions.

Results

Doxycycline at clinically achievable concentrations inhibited proliferation and colony formation and induced apoptosis in RCC cell lines. In normal kidney cells, doxycycline at the same concentrations either had no effect or was less effective. The combination index value demonstrated that doxycycline and paclitaxel were synergistic in vitro. Consistently, this combination therapy was significantly more effective than the monotherapy in RCC xenograft mice without causing significant toxicity. Mechanistic studies revealed that doxycycline acts on RCC cells via preferentially inhibiting mitochondrial DNA translation, thereby disrupting multiple mitochondrial complexes and impairing mitochondrial respiration.

Conclusions

Doxycycline is a useful addition to the treatment strategy for RCC. Our work also highlights the therapeutic value of mitochondrial translation inhibition in sensitizing RCC to chemotherapy.

Pre-clinical evidence that salinomycin is active against retinoblastoma via inducing mitochondrial dysfunction, oxidative damage and AMPK activation

The poor outcomes in retinoblastoma necessitate new treatments. Salinomycin is an attractive candidate, and has demonstrated selective anti-cancer properties in different cancer types. This work addressed the efficacy of salinomycin in retinoblastoma models and probe the associated mechanisms. Cellular functional assays were conducted to determine the effects salinomycin in vitro. Xenograft retinoblastoma mouse model was established to investigate the efficacy of salinomycin in vivo. Biochemical assays were conducted to analyze the mechanism of salinomycin's action focusing on mitochondrial functions, energy reduction-related signaling pathways. Salinomycin has positive effects towards retinoblastoma cells regardless of heterogeneity through suppressing growth and inducing apoptosis. Salinomycin also specifically inhibits cells displaying stemness and highly invasive phenotypes. Using retinoblastoma xenograft mouse model, we show that salinomycin at non-toxic dose effectively inhibits growth and induces apoptosis. Mechanistic studies show that salinomycin inhibits mitochondrial respiration via specifically suppressing complex I and II activities, reduces mitochondrial membrane potential and decreases energy reduction, followed by induction of oxidative stress and damage, AMPK activation and mTOR inhibition. Our study highlights that adding salinomycin to the existing treatment armamentarium for retinoblastoma is beneficial.

CD4+ T-cell differentiation and function: Unifying glycolysis, fatty acid oxidation, polyamines NAD mitochondria

The progression through different steps of T-cell development, activation, and effector function is tightly bound to specific cellular metabolic processes. Previous studies established that T-effector cells have a metabolic bias toward aerobic glycolysis, whereas naive and regulatory T cells mainly rely on oxidative phosphorylation. More recently, the field of immunometabolism has drifted away from the notion that mitochondrial metabolism holds little importance in T-cell activation and function. Of note, T cells possess metabolic promiscuity, which allows them to adapt their nutritional requirements according to the tissue environment. Altogether, the integration of these metabolic pathways culminates in the generation of not only energy but also intermediates, which can regulate epigenetic programs, leading to changes in T-cell fate. In this review, we discuss the recent literature on how glycolysis, amino acid catabolism, and fatty acid oxidation work together with the tricarboxylic acid cycle in the mitochondrion. We also emphasize the importance of the electron transport chain for T-cell immunity. We also discuss novel findings highlighting the role of key enzymes, accessory pathways, and posttranslational protein modifications that distinctively regulate T-cell function and might represent prominent candidates for therapeutic purposes.

A flow-cytometry-based protocol for detection of mitochondrial ROS production under hypoxia

Hypoxia is known to stimulate mitochondrial reactive oxygen species (mROS) in cells. Here, we present a detailed protocol to detect mROS using MitoSOX staining in live cells under normoxia and hypoxia. Flow cytometry allows sensitive and reliable quantification of mROS by FlowJo software. We optimized several aspects of the procedure including hypoxic treatment, working concentrations of the staining buffer, and quantitative analyses. Here, we use HepG2 cells, but the protocol can be applied to other cell lines. For complete details on the use and execution of this protocol, please refer to Yang et al. (2020).

Elevated levels of mitochondrial CoQ10 induce ROS-mediated apoptosis in pancreatic cancer

Reactive oxygen species (ROS) are implicated in triggering cell signalling events and pathways to promote and maintain tumorigenicity. Chemotherapy and radiation can induce ROS to elicit cell death allows for targeting ROS pathways for effective anti-cancer therapeutics. Coenzyme Q10 is a critical cofactor in the electron transport chain with complex biological functions that extend beyond mitochondrial respiration. This study demonstrates that delivery of oxidized Coenzyme Q10 (ubidecarenone) to increase mitochondrial Q-pool is associated with an increase in ROS generation, effectuating anti-cancer effects in a pancreatic cancer model. Consequent activation of cell death was observed in vitro in pancreatic cancer cells, and both human patient-derived organoids and tumour xenografts. The study is a first to demonstrate the effectiveness of oxidized ubidecarenone in targeting mitochondrial function resulting in an anti-cancer effect. Furthermore, these findings support the clinical development of proprietary formulation, BPM31510, for treatment of cancers with high ROS burden with potential sensitivity to ubidecarenone.

Autophagy restricts mitochondrial DNA damage-induced release of ENDOG (endonuclease G) to regulate genome stability

Genotoxic insult causes nuclear and mitochondrial DNA damages with macroautophagy/autophagy induction. The role of mitochondrial DNA (mtDNA) damage in the requirement of autophagy for nuclear DNA (nDNA) stability is unclear. Using site-specific DNA damage approaches, we show that specific nDNA damage alone does not require autophagy for repair unless in the presence of mtDNA damage. We provide evidence that after IR exposure-induced mtDNA and nDNA damages, autophagy suppression causes non-apoptotic mitochondrial permeability, by which mitochondrial ENDOG (endonuclease G) is released and translocated to nuclei to sustain nDNA damage in a TET (tet methylcytosine dioxygenase)-dependent manner. Furthermore, blocking lysosome function is sufficient to increase the amount of mtDNA leakage to the cytosol, accompanied by ENDOG-free mitochondrial puncta formation with concurrent ENDOG nuclear accumulation. We proposed that autophagy eliminates the mitochondria specified by mtDNA damage-driven mitochondrial permeability to prevent ENDOG-mediated genome instability. Finally, we showed that HBx, a hepatitis B viral protein capable of suppressing autophagy, also causes mitochondrial permeability-dependent ENDOG mis-localization in nuclei and is linked to hepatitis B virus (HBV)-mediated hepatocellular carcinoma development.Abbreviations: 3-MA: 3-methyladenine; 5-hmC: 5-hydroxymethylcytosine; ACTB: actin beta; ATG5: autophagy related 5; ATM: ATM serine/threonine kinase; DFFB/CAD: DNA fragmentation factor subunit beta; cmtDNA: cytosolic mitochondrial DNA; ConA: concanamycin A; CQ: chloroquine; CsA: cyclosporin A; Dox: doxycycline; DSB: double-strand break; ENDOG: endonuclease G; GFP: green fluorescent protein; Gy: gray; H2AX: H2A.X variant histone; HBV: hepatitis B virus; HBx: hepatitis B virus X protein; HCC: hepatocellular carcinoma; I-PpoI: intron-encoded endonuclease; IR: ionizing radiation; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MOMP: mitochondrial outer membrane permeability; mPTP: mitochondrial permeability transition pore; mtDNA: mitochondrial DNA; nDNA: nuclear DNA; 4-OHT: 4-hydroxytamoxifen; rDNA: ribosomal DNA; ROS: reactive oxygen species; SQSTM1/p62: sequestosome 1; TET: tet methylcytosine dioxygenase; TFAM: transcription factor A, mitochondrial; TOMM20: translocase of outer mitochondrial membrane 20; VDAC: voltage dependent anion channel.

Pathological and Pharmacological Roles of Mitochondrial Reactive Oxygen Species in Malignant Neoplasms: Therapies Involving Chemical Compounds, Natural Products, and Photosensitizers

Oxidative stress plays an important role in cellular processes. Consequently, oxidative stress also affects etiology, progression, and response to therapeutics in various pathological conditions including malignant tumors. Oxidative stress and associated outcomes are often brought about by excessive generation of reactive oxygen species (ROS). Accumulation of ROS occurs due to dysregulation of homeostasis in an otherwise strictly controlled physiological condition. In fact, intracellular ROS levels are closely associated with the pathological status and outcome of numerous diseases. Notably, mitochondria are recognized as the critical regulator and primary source of ROS. Damage to mitochondria increases mitochondrial ROS (mROS) production, which leads to an increased level of total intracellular ROS. However, intracellular ROS level may not always reflect mROS levels, as ROS is not only produced by mitochondria but also by other organelles such as endoplasmic reticulum and peroxisomes. Thus, an evaluation of mROS would help us to recognize the biological and pathological characteristics and predictive markers of malignant tumors and develop efficient treatment strategies. In this review, we describe the pathological significance of mROS in malignant neoplasms. In particular, we show the association of mROS-related signaling in the molecular mechanisms of chemically synthesized and natural chemotherapeutic agents and photodynamic therapy.

The role of SIRT3-mediated mitochondrial homeostasis in osteoarthritis

Osteoarthritis is the most common degenerative joint disease and causes major pain and disability in adults. It has been reported that mitochondrial dysfunction in chondrocytes is associated with osteoarthritis. Sirtuins are a family of nicotinamide adenine dinucleotide-dependent histone deacetylases that have the ability to deacetylate protein targets and play an important role in the regulation of cell physiological and pathological processes. Among sirtuin family members, sirtuin 3, which is mainly located in mitochondria, can exert its deacetylation activity to regulate mitochondrial function, regeneration, and dynamics; these processes are presently recognized to maintain redox homeostasis to prevent oxidative stress in cell metabolism. In this review, we provide present opinions on the effect of mitochondrial dysfunction in osteoarthritis. Furthermore, the potential protective mechanism of SIRT3-mediated mitochondrial homeostasis in the progression of osteoarthritis is discussed.

High-content fluorescence imaging with the metabolic flux assay reveals insights into mitochondrial properties and functions

Metabolic flux technology with the Seahorse bioanalyzer has emerged as a standard technique in cellular metabolism studies, allowing for simultaneous kinetic measurements of respiration and glycolysis. Methods to extend the utility and versatility of the metabolic flux assay would undoubtedly have immediate and wide-reaching impacts. Herein, we describe a platform that couples the metabolic flux assay with high-content fluorescence imaging to simultaneously provide means for normalization of respiration data with cell number; analyze cell cycle distribution; and quantify mitochondrial content, fragmentation state, membrane potential, and mitochondrial reactive oxygen species. Integration of fluorescent dyes directly into the metabolic flux assay generates a more complete data set of mitochondrial features in a single assay. Moreover, application of this integrated strategy revealed insights into mitochondrial function following PGC1a and PRC1 inhibition in pancreatic cancer and demonstrated how the Rho-GTPases impact mitochondrial dynamics in breast cancer.

Mitochondrial fragmentation, elevated mitochondrial superoxide and respiratory supercomplexes disassembly is connected with the tamoxifen-resistant phenotype of breast cancer cells

Tamoxifen resistance remains a clinical obstacle in the treatment of hormone sensitive breast cancer. It has been reported that tamoxifen is able to target respiratory complex I within mitochondria. Therefore, we established two tamoxifen-resistant cell lines, MCF7 Tam5R and T47D Tam5R resistant to 5 μM tamoxifen and investigated whether tamoxifen-resistant cells exhibit mitochondrial changes which could help them survive the treatment. The function of mitochondria in this experimental model was evaluated in detail by studying i) the composition and activity of mitochondrial respiratory complexes; ii) respiration and glycolytic status; iii) mitochondrial distribution, dynamics and reactive oxygen species production. We show that Tam5R cells exhibit a significant decrease in mitochondrial respiration, low abundance of assembled mitochondrial respiratory supercomplexes, a more fragmented mitochondrial network connected with DRP1 Ser637 phosphorylation, higher glycolysis and sensitivity to 2-deoxyglucose. Tam5R cells also produce significantly higher levels of mitochondrial superoxide but at the same time increase their antioxidant defense (CAT, SOD2) through upregulation of SIRT3 and show phosphorylation of AMPK at Ser 485/491. Importantly, MCF7 ρ0 cells lacking functional mitochondria exhibit a markedly higher resistance to tamoxifen, supporting the role of mitochondria in tamoxifen resistance. We propose that reduced mitochondrial function and higher level of reactive oxygen species within mitochondria in concert with metabolic adaptations contribute to the phenotype of tamoxifen resistance.

Mitochondrial dysfunction increases pro-inflammatory cytokine production and impairs repair and corticosteroid responsiveness in lung epithelium

COPD is characterized by chronic lung inflammation and irreversible lung tissue damage. Inhaled noxious gases, including cigarette smoke, are the major risk factor for COPD. Inhaled smoke first encounters the epithelial lining of the lungs, causing oxidative stress and mitochondrial dysfunction. We investigated whether a mitochondrial defect may contribute to increased lung epithelial pro-inflammatory responses, impaired epithelial repair and reduced corticosteroid sensitivity as observed in COPD. We used wild-type alveolar epithelial cells A549 and mitochondrial DNA-depleted A549 cells (A549 Rho-0) and studied pro-inflammatory responses using (multiplex) ELISA as well as epithelial barrier function and repair (real-time impedance measurements), in the presence and absence of the inhaled corticosteroid budesonide. We observed that A549 Rho-0 cells secrete higher levels of pro-inflammatory cytokines than wild-type A549 cells and display impaired repair upon wounding. Budesonide strongly suppressed the production of neutrophil attractant CXCL8, and promoted epithelial integrity in A549 wild-type cells, while A549 Rho-0 cells displayed reduced corticosteroid sensitivity compared to wild-type cells. The reduced corticosteroid responsiveness may be mediated by glycolytic reprogramming, specifically glycolysis-associated PI3K signaling, as PI3K inhibitor LY294002 restored the sensitivity of CXCL8 secretion to corticosteroids in A549 Rho-0 cells. In conclusion, mitochondrial defects may lead to increased lung epithelial pro-inflammatory responses, reduced epithelial repair and reduced corticosteroid responsiveness in lung epithelium, thus potentially contributing to the pathogenesis of COPD.

Mitochondrial DNA in liver inflammation and oxidative stress

The function of liver is highly dependent on mitochondria producing ATP for biosynthetic and detoxifying properties. Accumulating evidence indicates that most hepatic disorders are characterized by profound mitochondrial dysfunction. Mitochondrial dysfunction not only exhibits mitochondrial DNA (mtDNA) damage and depletion, but also releases mtDNA. mtDNA is a closed circular molecule encoding 13 of the polypeptides of the oxidative phosphorylation system. Extensive mtDNA lesions could exacerbate mitochondrial oxidative stress and subsequently cause damage to hepatocytes. When mtDNA leaves the confines of mitochondria to the cytosolic and extracellular environment, it can act as damage-associated molecular patterns (DAMPs) to trigger the inflammatory response through the Toll-like receptor 9, inflammasomes, and stimulator of interferon genes (STING) pathways and further exacerbate hepatocellular damage and even remote organs injury. In addition, mtDNA also plays a vital role in hepatitis B virus (HBV)-related liver injury and hepatocellular carcinoma (HCC). In this review, we describe mtDNA alterations during liver injury, focusing on the mechanisms of mtDNA-mediated liver inflammation and oxidative stress injury.

Circulating mitochondria DNA, a non-invasive cancer diagnostic biomarker candidate

The mitochondria are defined by their unique structure and cellular functions which includes energy production, metabolic regulation, apoptosis, calcium homeostasis, cell proliferation, cell motility and transport as well as free radical generation. Recent advances geared towards enhancing the diagnostic and prognostic value of cancer patients have targeted the circulating mitochondria genome due to its specific and unique characteristics. Circulating mitochondria DNA is known to possess short length, relatively simple molecular structure and a high copy number. These coupled with its ability to serve as a liquid biopsy makes it an easily accessible non-invasive biomarker for diagnostics and prognostics of various forms of solid tumors. In this article, we review recent findings on circulating mitochondria DNA content in cancer. In addition, we provide an insight into the potential of circulating mitochondria DNA to act as a non-invasive diagnostic biomarker and its linearity with clinical and sociodemographic characteristics.

Inhibition of mitochondrial respiration overcomes hepatocellular carcinoma chemoresistance

The clinical management of advanced hepatocellular carcinoma (HCC) is challenging due to its resistance to chemotherapy. In our work, we demonstrate that an antiparasitic drug atovaquone at clinically relevant concentrations is active against chemoresistant HCC. We show that atovaquone inhibits proliferation and induces apoptosis in not only HCC parental cells but also cells exposed to long time culture of chemotherapeutic agents. Consistently, the combination of atovaquone with cisplatin or doxorubicin achieved remarkably greater efficacy than single drug alone. Mechanistically, atovaquone overcomes HCC chemoresistance via supressing mitochondrial respiration and inducing oxidative stress. Atovaquone but not cisplatin or doxorubicin is ineffective in mitochondrial respiration-deficient ρ0, confirming mitochondria as a specific upstream target of atovaquone. Interestingly, we show that prolonged exposure of HCC cells to chemotherapeutic agents induces higher level of mitochondrial respiration, suggesting that tumors which develop chemoresistance after chemotherapy might be more dependent on mitochondrial respiration than primary tumors and explaining the sensitivity of chemoresistant HCC cells to atovaquone. We further show that atovaquone at tolerable does significantly inhibits chemoresistant HCC growth in mice throughout the duration of treatment. In line with in vitro data, we observe the increased oxidative stress in atovaquone-treated tumors. Our findings highlight the dependency of chemoresistant HCC on mitochondrial respiration and demonstrate that atovaquone is a potential drug to overcome HCC chemoresistance.

Tigecycline as a dual inhibitor of retinoblastoma and angiogenesis via inducing mitochondrial dysfunctions and oxidative damage

Retinoblastoma is the most common intraocular malignancy in children with poor prognosis. The progression of retinoblastoma is dependent on a robust angiogenic response. Targeting both retinoblastoma cells and angiogenesis may therefore provide an alternative therapeutic strategy in retinoblastoma. Here, we demonstrated the inhibitory effects of tigecycline, a FDA-approved antibiotic, in retinoblastoma and angiogenesis in vitro and in vivo. We showed that tigecycline significantly inhibited growth and induced caspase-dependent apoptosis of multiple retinoblastoma cell lines. Tigecycline also effectively inhibited angiogenesis through suppressing capillary network formation, migration, proliferation and survival of human retinal microvascular endothelial cell (HREC). Mechanistically, tigecycline acts on both retinoblastoma cells and HREC via inhibiting mitochondrial protein translation, resulting in mitochondrial dysfunction, energy crisis, and oxidative damage. Importantly, we demonstrated the in vivo efficacy of tigecycline in inhibiting retinoblastoma and angiogenesis, and inducing oxidative stress on xenograft mouse model. In addition, ATP levels and growth rates were largely affected in retinoblastoma ρ0 cells that lacked mitochondrial respiration. Our work provides systematic pre-clinical evidence for repurposing tigecycline from its traditional use for retinoblastoma treatment. Our work demonstrates the essential roles of mitochondrial metabolism in both retinoblastoma and its angiogenesis.

Inflammation-induced DNA methylation of DNA polymerase gamma alters the metabolic profile of colon tumors

Background

Inflammation, metabolism, and epigenetic modulation are highly interconnected processes that can be altered during tumorigenesis. However, because of the complexity of these interactions, direct cause and effect during tumorigenesis have been difficult to prove. Previously, using a murine model of inflammation-induced colon tumorigenesis, we determined that the promoter of the catalytic subunit of DNA polymerase gamma (Polg) is DNA hypermethylated and silenced in inflammation-induced tumors, but not in non-inflammation-induced (mock) tumors, suggesting that inflammation can induce silencing of Polg through promoting DNA methylation during tumorigenesis. Polg is the only mitochondrial DNA polymerase and mutations in Polg cause mitochondrial diseases in humans. Because of the role of mitochondria in metabolism, we hypothesized that silencing of Polg in inflammation-induced tumors would result in these tumors having altered metabolism in comparison to mock tumors.

Methods

Inflammation-induced and mock colon tumors and colon epithelium from a mouse model of inflammation-induced colon tumorigenesis were assayed for alterations in Polg expression, mitochondria, and metabolism. Organoids derived from these tissues were used to study the direct effect of loss of Polg on mitochondria and metabolism.

Results

We demonstrate that inflammation-induced tumors with reduced Polg expression have decreased mitochondrial DNA content and numbers of mitochondria compared to normal epithelium or mock tumors. Tumoroids derived from mock and inflammation-induced tumors retained key characteristics of the original tumors. Inflammation-induced tumoroids had increased glucose uptake and lactate secretion relative to mock tumoroids. shRNA-mediated knockdown of Polg in mock tumoroids reduced mtDNA content, increased glucose uptake and lactate secretion, and made the tumoroids more resistant to oxidative stress.

Conclusions

These results suggest that inflammation-induced DNA methylation and silencing of Polg plays an important role in the tumorigenesis process by resulting in reduced mitochondria levels and altered metabolism. An enhanced understanding of how metabolism is altered in and drives inflammation-induced tumorigenesis will provide potential therapeutic targets.

Electronic supplementary material

The online version of this article (10.1186/s40170-018-0182-7) contains supplementary material, which is available to authorized users.

Mannan oligosaccharide requires functional ETC and TLR for biological radiation protection to normal cells

BACKGROUND

Low LET Ionizing radiation is known to alter intracellular redox balance by inducing free radical generation, which may cause oxidative modification of various cellular biomolecules. The extent of biomolecule-modifications/ damages and changes in vital processes (viz. cellular homeostasis, inter-/intra-cellular signaling, mitochondrial physiology/dynamics antioxidant defence systems) are crucial which in turn determine fate of cells.

RESULTS

In the present study, we expended TLR expressing (normal/ transformed) and TLR null cells; and we have shown that mannan pretreatment in TLR expressing normal cells offers survival advantage against lethal doses of ionizing radiation. On the contrary, mannan pretreatment does not offer any protection against radiation to TLR null cells, NKE ρ° cells and transformed cells. In normal cells, abrupt decrease in mitochondrial membrane potential and endogenous ROS levels occurs following treatment with mannan. We intend to irradiate mannan-pretreated cells at a specific stage of perturbed mitochondrial functioning and ROS levels to comprehend if mannan pretreatment offers any survival advantage against radiation exposure to cells. Interestingly, pre-irradiation treatment of cells with mannan activates NFκB, p38 and JNK, alters mitochondrial physiology, increases expression of Cu/ZnSOD and MnSOD, minimizes oxidation of mitochondrial phospholipids and offers survival advantage in comparison to irradiated group, in TLR expressing normal cells.

CONCLUSION

The study demonstrates that TLR and mitochondrial ETC functions are inevitable in radio-protective efficacy exhibited by mannan.

Mitochondrial DNA copy number is associated with risk of head and neck squamous cell carcinoma in Chinese population

Mitochondria show the special role in cellular bioenergy and many essential physiological activities. Previous researches have suggested that variations of mitochondrial DNA copy number contribute to development of different types of carcinomas. However, the relationship of mtDNA copy number in peripheral blood leukocytes (PBLs) with the risk of head and neck squamous cell carcinoma (HNSCC) is still inconclusive. We investigated the association of mtDNA with HNSCC risk through a case-control study including 570 HNSCC cases and 597 cancer-free controls. mtDNA copy number in PBLs was measured by real-time qPCR. Logistic regression was performed to estimate the association between the mtDNA copy number in PBLs and HNSCC risk. A U-shaped relation between the mtDNA copy number and HNSCC risk was found. Compared with those in the second quartile group, the adjusted odds ratios (ORs) and 95% confidence interval (CI) for those in the first and the forth quartile groups were 1.95 (1.37-2.76) and 2.16 (1.53-3.04), respectively. Using restricted cubic spline analysis, we confirmed such a significant U-shaped relation. Furthermore, the U-shaped association remained significant in different subgroups stratified by age, gender, tobacco smoking, and alcohol consumption. Both extremely low and high mtDNA copy numbers had significant associations with the increased HNSCC risk.

Targeting mitochondrial respiration as a therapeutic strategy for cervical cancer

Targeting mitochondrial respiration has been documented as an effective therapeutic strategy in cancer. However, the impact of mitochondrial respiration inhibition on cervical cancer cells are not well elucidated. Using a panel of cervical cancer cell lines, we show that an existing drug atovaquone is active against the cervical cancer cells with high profiling of mitochondrial biogenesis. Atovaquone inhibited proliferation and induced apoptosis with varying efficacy among cervical cancer cell lines regardless of HPV infection, cellular origin and their sensitivity to paclitaxel. We further demonstrated that atovaquone acts on cervical cancer cells via inhibiting mitochondrial respiration. In particular, atovaquone specifically inhibited mitochondrial complex III but not I, II or IV activity, leading to respiration inhibition and energy crisis. Importantly, we found that the different sensitivity of cervical cancer cell lines to atovaquone were due to their differential level of mitochondrial biogenesis and dependency to mitochondrial respiration. In addition, we demonstrated that the in vitro observations were translatable to in vivo cervical cancer xenograft mouse model. Our findings suggest that the mitochondrial biogenesis varies among patients with cervical cancer. Our work also suggests that atovaquone is a useful addition to cervical cancer treatment, particularly to those with high dependency on mitochondrial respiration.

Pre-diagnostic leukocyte mitochondrial DNA copy number and risk of lung cancer

We prospectively investigated the relationship between mtCN and the risk of lung cancer in 463 case-control pairs from two prospective cohort studies, the Nurses’ Health Study (NHS) and the Health Professionals Follow-Up Study (HPFS). The adjusted least-squares means of log-transformed mtCN (log_mtCN) by smoking status were estimated by generalized linear models. Multivariable conditional logistic regression model adjusting for confounders was used to obtain the odds ratios (ORs) and 95% confidence intervals (CIs) for the association between log_mtCN and lung cancer risk. The adjusted least-squares mean of log_mtCN in heavy smokers was significantly lower than that in never smokers (P = 0.05). Compared to the high log_mtCN group, the risk of lung cancer was 1.29 (95% CI = 0.89–1.87) for the median group, and 1.11 (95% CI = 0.75–1.64) for the low group. Among current smokers, compared to participants with high levels of log_mtCN, those with median levels had a significantly higher risk of lung cancer (OR = 2.09; 95% CI = 1.12–3.90), but not those with low levels (OR = 1.37; 95% CI = 0.75–2.48). Further studies are warranted to confirm these findings.

Alternative Polyadenylation of PRELID1 Regulates Mitochondrial ROS Signaling and Cancer Outcomes

Disruption of posttranscriptional gene regulation is a critical step in oncogenesis that can be difficult to observe using traditional molecular techniques. To overcome this limitation, a modified polyadenylation site sequencing (PAS-seq) protocol was used to generate a genome-wide map of alternative polyadenylation (APA) events in human primary breast tumor specimens and matched normal tissue. This approach identified an APA event in the PRELID1 mRNA that enhances its steady-state level and translational efficiency, and is a strong breast cancer subtype-dependent predictor of patient clinical outcomes. Furthermore, it has been demonstrated that PRELID1 regulates stress response and mitochondrial reactive oxygen species (ROS) production in a cell type-specific manner. Modulation of PRELID1 expression, including its posttranscriptional control, appears to be a common stress response across different cancer types. These data reveal that PRELID1 mRNA processing is an important regulator of cell type-specific responses to stress used by multiple cancers and is associated with patient outcomes.Implications: This study suggests that the regulation of PRELID1 expression, by APA and other mechanisms, plays a role in mitochondrial ROS signaling and represents a novel prognostic factor and therapeutic target in cancer. Mol Cancer Res; 15(12); 1741-51. ©2017 AACR.

Distinct radiation responses after in vitro mtDNA depletion are potentially related to oxidative stress

Several clinically used drugs are mitotoxic causing mitochondrial DNA (mtDNA) variations, and thereby influence cancer treatment response. We hypothesized that radiation responsiveness will be enhanced in cellular models with decreased mtDNA content, attributed to altered reactive oxygen species (ROS) production and antioxidant capacity. For this purpose BEAS-2B, A549, and 143B cell lines were depleted from their mtDNA (ρ⁰). Overall survival after irradiation was increased (p<0.001) for BEAS-2B ρ⁰ cells, while decreased for both tumor ρ⁰ lines (p<0.05). In agreement, increased residual DNA damage was observed after mtDNA depletion for A549 and 143B cells. Intrinsic radiosensitivity (surviving fraction at 2Gy) was not influenced. We investigated whether ROS levels, oxidative stress and/or antioxidant responses were responsible for altered radiation responses. Baseline ROS formation was similar between BEAS-2B parental and ρ⁰ cells, while reduced in A549 and 143B ρ⁰ cells, compared to their parental counterparts. After irradiation, ROS levels significantly increased for all parental cell lines, while levels for ρ⁰ cells remained unchanged. In order to investigate the presence of oxidative stress upon irradiation reduced glutathione: oxidized glutathione (GSH:GSSG) ratios were determined. Irradiation reduced GSH:GSSG ratios for BEAS-2B parental and 143B ρ⁰, while for A549 this ratio remained equal. Additionally, changes in antioxidant responses were observed. Our results indicate that mtDNA depletion results in varying radiation responses potentially involving variations in cellular ROS and antioxidant defence mechanisms. We therefore suggest when mitotoxic drugs are combined with radiation, in particular at high dose per fraction, the effect of these drugs on mtDNA copy number should be explored.

Polymorphisms in POLG were associated with the prognosis and mtDNA content in hepatocellular carcinoma patients

BACKGROUND

POLG is a gene that codes for the catalytic subunit of the mitochondrial DNA polymerase, which is involved in the replication of mitochondrial DNA. Genetic variants in mitochondrial DNA polymerase-γ (POLG) have been associated with several malignancies. However, as an important metabolic tissue, association between genetic polymorphisms of POLG and the prognosis and mitochondrial DNA (mtDNA) content in hepatocellular carcinoma (HCC) remains unknown. Here we investigated the association between in POLG with the prognosis and mitochondrial DNA (mtDNA) content in hepatocellular carcinoma (HCC).

METHODS

Three nucleotide polymorphisms (SNPs) of rs1061316, rs2247233 and rs758130 in POLG were examined in 416 patients from two cohorts undergoing transcatheter arterial chemoembolization treatment. Leukocyte mtDNA content from 216 patients in cohort 2 was measured using a real-time PCR-based method. The association of SNPs with prognosis and of mtDNA content of patients was analyzed.

RESULTS

The rs758130 in POLG gene was significantly associated with the prognosis of patients in a dose-dependent manner. Moreover, GG genotype in rs1061316 showed significantly high mtDNA content, an indicator of better prognosis.

CONCLUSIONS

Our study for the first time demonstrates that rs1061316 and rs758130 in POLG is associated with the prognosis and leukocyte mtDNA content in HCC patients.

Mitochondrial DNA copy number in peripheral blood leukocytes and the aggressiveness of localized prostate cancer

We investigated whether low mitochondrial DNA copy number (mtDNAcn) in peripheral blood leukocytes at diagnosis was associated with an increased risk of the aggressive form of the tumor and disease progression among localized prostate cancer (PCa) patients. We recruited 1,751 non-Hispanic white men with previously untreated PCa from The University of Texas MD Anderson Cancer Center. mtDNAcn was categorized into three groups according to tertiles. We used multivariate logistic regression to estimate the odds ratios (ORs) and 95 percent confidence intervals (95% CIs) for the association of mtDNAcn with the risk of having aggressive PCa at diagnosis. We used Cox proportional hazards model to estimate hazard ratios (HRs) and 95% CIs for disease progression. We observed an inverse association between aggressiveness of PCa and mtDNAcn (P < 0.001). In multivariate analysis, compared to patients in the highest tertile of mtDNAcn, those in the second and lowest tertiles had significantly increased risks of presenting with the high-risk form of PCa, as defined by the D'Amico criteria, with ORs of 1.33 (95% CI, 0.89–1.98; P = 0.17) and 1.53 (95% CI, 1.02–2.30; P = 0.04), respectively. Furthermore, PCa patients in the lowest and second tertiles combined relative to those in the highest tertile had a 56% increased risk of disease progression (HR, 1.56; 95% CI, 0.96–2.54; P = 0.07). In summary, our results suggested that low mtDNAcn in peripheral blood leukocytes was associated with aggressive PCa at diagnosis and might further predict poor progression-free survival among localized PCa patients.

Pyrvinium selectively targets blast phase-chronic myeloid leukemia through inhibition of mitochondrial respiration

The use of BCR-ABL1 tyrosine kinase inhibitors (TKI) has led to excellent clinical responses in patients with chronic phase chronic myeloid leukemia (CML). However these inhibitors have been less effective as single agents in the terminal blast phase (BP). We show that pyrvinium, a FDA-approved anthelminthic drug, selectively targets BP-CML CD34⁺ progenitor cells. Pyrvinium is effective in inducing apoptosis, inhibiting colony formation and self-renewal capacity of CD34⁺ cells from TKI-resistant BP-CML patients, while cord blood CD34⁺ are largely unaffected. The effects of pyrvinium are further enhanced upon combination with dasatinib, a second generation BCR-ABL1 TKI. In a CML xenograft model pyrvinium significantly inhibits tumor growth as a single agent, with complete inhibition in combination with dasatinib. While pyrvinium has been shown to inhibit the Wnt/β-catenin signalling pathway via activation of casein kinase 1α, we find its activity in CML is not dependent on this pathway. Instead, we show that pyrvinium localizes to mitochondria and induces apoptosis by inhibiting mitochondrial respiration. Our study suggests that pyrvinium is a useful addition to the treatment armamentarium for BP-CML and that targeting mitochondrial respiration may be a potential therapeutic strategy in aggressive leukemia.

Fly Models of Human Diseases: Drosophila as a Model for Understanding Human Mitochondrial Mutations and Disease

Mitochondrial diseases are a prevalent, heterogeneous class of diseases caused by defects in oxidative phosphorylation, whose severity depends upon particular genetic mutations. These diseases can be difficult to diagnose, and current therapeutics have limited efficacy, primarily treating only symptoms. Because mitochondria play a pivotal role in numerous cellular functions, especially ATP production, their diminished activity has dramatic physiological consequences. While this in and of itself makes treating mitochondrial disease complex, these organelles contain their own DNA, mtDNA, whose products are required for ATP production, in addition to the hundreds of nucleus-encoded proteins. Drosophila offers a tractable whole-animal model to understand the mechanisms underlying loss of mitochondrial function, the subsequent cellular and tissue damage that results, and how these organelles are inherited. Human and Drosophila mtDNAs encode the same set of products, and the homologous nucleus-encoded genes required for mitochondrial function are conserved. In addition, Drosophila contain sufficiently complex organ systems to effectively recapitulate many basic symptoms of mitochondrial diseases, yet are relatively easy and fast to genetically manipulate. There are several Drosophila models for specific mitochondrial diseases, which have been recently reviewed (Foriel, Willems, Smeitink, Schenck, & Beyrath, 2015). In this review, we highlight the conservation between human and Drosophila mtDNA, the present and future techniques for creating mtDNA mutations for further study, and how Drosophila has contributed to our current understanding of mitochondrial inheritance.

Mitochondrial DNA depletion causes decreased ROS production and resistance to apoptosis

Mitochondrial DNA (mtDNA) depletion occurs frequently in many diseases including cancer. The present study was designed in order to examine the hypothesis that mtDNA‑depleted cells are resistant to apoptosis and to explore the possible mechanisms responsible for this effect. Parental human osteosarcoma 143B cells and mtDNA‑deficient (Rho˚ or ρ˚) 206 cells (derived from 143B cells) were exposed to different doses of solar-simulated ultraviolet (UV) radiation. The effects of solar irradiation on cell morphology were observed under both light and fluorescence microscopes. Furthermore, apoptosis, mitochondrial membrane potential (MMP) disruption and reactive oxygen species (ROS) production were detected and measured by flow cytometry. In both cell lines, apoptosis and ROS production were clearly increased, whereas MMP was slightly decreased. However, apoptosis and ROS production were reduced in the Rho˚206 cells compared with the 143B cells. We also performed western blot analysis and demonstrated the increased release of cytosolic Cyt c from mitochondria in the 143B cells compared with that in the Rho˚206 cells. Thus, we concluded that Rho˚206 cells exhibit more resistance to solar‑simulated UV radiation‑induced apoptosis at certain doses than 143B cells and this is possibly due to decreased ROS production.

A novel thiophene-3-carboxamide analog of annonaceous acetogenin exhibits antitumor activity via inhibition of mitochondrial complex I

Previously we synthesized JCI‐20679, a novel thiophene‐3‐carboxamide analog of annonaceous acetogenins which have shown potent antitumor activity, with no serious side effects, in mouse xenograft models. In this study, we investigated the antitumor mechanism of JCI‐20679. The growth inhibition profile (termed “fingerprint”) of this agent across a panel of 39 human cancer cell lines (termed “JFCR39”) was measured; this fingerprint was analyzed by the COMPARE algorithm utilizing the entire drug sensitivity database for the JFCR39 panel. The JCI‐20679‐specific fingerprint exhibited a high similarity to those of two antidiabetic biguanides and a natural rotenoid deguelin which were already known to be mitochondrial complex I inhibitors. In addition, the fingerprint exhibited by JCI‐20679 was not similar to that displayed by any typical anticancer drugs within the database, suggesting that it has a unique mode of action. In vitro experiments using bovine heart‐derived mitochondria showed direct inhibition of mitochondrial complex I by JCI‐20679 and associated derivatives. This inhibition of enzymatic activity positively correlated with tumor cell growth inhibition. Furthermore, a fluorescently labeled derivative of JCI‐20679 localized to the mitochondria of live cancer cells in vitro. These results suggest that JCI‐20679 can inhibit cancer cell growth by inhibiting mitochondrial complex I. Our results show that JCI‐20679 is a novel anticancer drug lead with a unique mode of action.