A heteroplasmic, not homoplasmic, mitochondrial DNA mutation promotes tumorigenesis via alteration in reactive oxygen species generation and apoptosis

Mitochondria in focus: From structure and function to their role in human diseases. A review

Mitochondria, double-membraned organelles within all eukaryotic cells, are essential for the proper functioning of the human organism. The frequently used phrase "powerhouses of the cell" fails to adequately capture their multifaceted roles. In addition to producing energy in the form of adenosine triphosphate through oxidative phosphorylation, mitochondria are also involved in apoptosis (programmed cell death), calcium regulation, and signaling through reactive oxygen species. Recent research suggests that they can communicate with one another and influence cellular processes. Impaired mitochondrial function on the one hand, can have widespread and profound effects on cellular and organismal health, contributing to various diseases and age-related conditions. Regular exercise on the other hand, promotes mitochondrial health by enhancing their volume, density, and functionality. Although research has made significant progress in the last few decades, mainly through the use of modern technologies, there is still a need to intensify research efforts in this field. Exploring new approaches to enhance mitochondrial health could potentially impact longevity. In this review, we focus on mitochondrial research and discoveries, examine the structure and diverse roles of mitochondria in the human body, explore their influence on energy metabolism and cellular signaling and emphasize their importance in maintaining overall health.

Mitochondrial DNA copy number alterations: Key players in the complexity of glioblastoma (Review)

Renowned as a highly invasive and lethal tumor derived from neural stem cells in the central nervous system, glioblastoma (GBM) exhibits substantial histopathological variation and genomic complexity, which drive its rapid progression and therapeutic resistance. Alterations in mitochondrial DNA (mtDNA) copy number (CN) serve a crucial role in GBM development and progression, affecting various aspects of tumor biology, including energy production, oxidative stress regulation and cellular adaptability. Fluctuations in mtDNA levels, whether elevated or diminished, can impair mitochondrial function, potentially disrupting oxidative phosphorylation and amplifying reactive oxygen species generation, thereby fueling tumor growth and influencing treatment responses. Understanding the mechanisms of mtDNA‑CN variations, and their interplay with genetic and environmental elements in the tumor microenvironment, is essential for advancing diagnostic and therapeutic strategies. Targeting mtDNA alterations could strengthen treatment efficacy, mitigate resistance and ultimately enhance the prognosis of patients with this aggressive brain tumor. The present review summarizes the existing literature on mtDNA alterations, specifically emphasizing variations in mtDNA‑CN and their association with GBM by surveying articles published between 1996 and 2024, sourced from databases such as Scopus, PubMed and Google Scholar. In addition, the review provides a brief overview of mitochondrial genome architecture, knowledge regarding the regulation of mtDNA integrity and CN, and how mitochondria significantly impact GBM tumorigenesis. This review further presents information on therapeutic approaches for restoring mtDNA‑CN that contribute to optimized mitochondrial function and improved health outcomes.

The adaptor protein Miro1 modulates horizontal transfer of mitochondria in mouse melanoma models

Recent research has shown that mtDNA-deficient cancer cells (ρ0 cells) acquire mitochondria from tumor stromal cells to restore respiration, facilitating tumor formation. We investigated the role of Miro1, an adaptor protein involved in movement of mitochondria along microtubules, in this phenomenon. Inducible Miro1 knockout (Miro1KO) mice markedly delayed tumor formation after grafting ρ0 cancer cells. Miro1KO mice with fluorescently labeled mitochondria revealed that this delay was due to hindered mitochondrial transfer from the tumor stromal cells to grafted B16 ρ0 cells, which impeded recovery of mitochondrial respiration and tumor growth. Miro1KO led to the perinuclear accumulation of mitochondria and impaired mobility of the mitochondrial network. In vitro experiments revealed decreased association of mitochondria with microtubules, compromising mitochondrial transfer via tunneling nanotubes (TNTs) in mesenchymal stromal cells. Here we show the role of Miro1 in horizontal mitochondrial transfer in mouse melanoma models in vivo and its involvement with TNTs.

The Role of mtDNA Mutations in Atherosclerosis: The Influence of Mitochondrial Dysfunction on Macrophage Polarization

Atherosclerosis is a complex inflammatory process associated with high-mortality cardiovascular diseases. Today, there is a growing body of evidence linking atherosclerosis to mutations of mitochondrial DNA (mtDNA). But the mechanism of this link is insufficiently studied. Atherosclerosis progression involves different cell types and macrophages are one of the most important. Due to their high plasticity, macrophages can demonstrate pro-inflammatory and pro-atherogenic (macrophage type M1) or anti-inflammatory and anti-atherogenic (macrophage type M2) effects. These two cell types, formed as a result of external stimuli, differ significantly in their metabolic profile, which suggests the central role of mitochondria in the implementation of the macrophage polarization route. According to this, we assume that mtDNA mutations causing mitochondrial disturbances can play the role of an internal trigger, leading to the formation of macrophage M1 or M2. This review provides a comparative analysis of the characteristics of mitochondrial function in different types of macrophages and their possible associations with mtDNA mutations linked with inflammation-based pathologies including atherosclerosis.

Somatic mtDNA mutation burden shapes metabolic plasticity in leukemogenesis

The role of somatic mitochondrial DNA (mtDNA) mutations in leukemogenesis remains poorly characterized. To determine the impact of somatic mtDNA mutations on this process, we assessed the leukemogenic potential of hematopoietic progenitor cells (HPCs) from mtDNA mutator mice (Polg D257A) with or without NMyc overexpression. We observed a higher incidence of spontaneous leukemogenesis in recipients transplanted with heterozygous Polg HPCs and a lower incidence of NMyc-driven leukemia in those with homozygous Polg HPCs compared to controls. Although mtDNA mutations in heterozygous and homozygous HPCs caused similar baseline impairments in mitochondrial function, only heterozygous HPCs responded to and supported altered metabolic demands associated with NMyc overexpression. Homozygous HPCs showed altered glucose utilization with pyruvate dehydrogenase inhibition due to increased phosphorylation, exacerbated by NMyc overexpression. The impaired growth of NMyc-expressing homozygous HPCs was partially rescued by inhibiting pyruvate dehydrogenase kinase, highlighting a relationship between mtDNA mutation burden and metabolic plasticity in leukemogenesis.

Aging through the lens of mitochondrial DNA mutations and inheritance paradoxes

Mitochondrial DNA encodes essential components of the respiratory chain complexes, serving as the foundation of mitochondrial respiratory function. Mutations in mtDNA primarily impair energy metabolism, exerting far-reaching effects on cellular physiology, particularly in the context of aging. The intrinsic vulnerability of mtDNA is increasingly recognized as a key driver in the initiation of aging and the progression of its related diseases. In the field of aging research, it is critical to unravel the intricate mechanisms underpinning mtDNA mutations in living organisms and to elucidate the pathological consequences they trigger. Interestingly, certain effects, such as oxidative stress and apoptosis, may not universally accelerate aging as traditionally perceived. These phenomena demand deeper investigation and a more nuanced reinterpretation of current findings to address persistent scientific uncertainties. By synthesizing recent insights, this review seeks to clarify how pathogenic mtDNA mutations drive cellular senescence and systemic health deterioration, while also exploring the complex dynamics of mtDNA inheritance that may propagate these mutations. Such a comprehensive understanding could ultimately inform the development of innovative therapeutic strategies to counteract mitochondrial dysfunctions associated with aging.

Pathogenic mitochondrial DNA variants are associated with response to anti-VEGF therapy in ovarian cancer PDX models

BACKGROUND

Mitochondrial DNA (mtDNA) pathogenic variants have been reported in several solid tumors including ovarian cancer (OC), the most lethal gynecologic malignancy, and raised interest as they potentially induce mitochondrial dysfunction and rewiring of cellular metabolism. Despite advances in recent years, functional characterization of mtDNA variants in cancer and their possible modulation of drug response remain largely uncharted.

METHODS

Here, we characterized mtDNA variants in OC patient derived xenografts (PDX) and investigated their impact on cancer cells at multiple levels.

RESULTS

Genetic analysis revealed that mtDNA variants predicted as pathogenic, mainly involving complex I and IV genes, were present in all but one PDX (n = 20) at different levels of heteroplasmy, including 7 PDXs with homoplasmic variants. Functional analyses demonstrated that pathogenic mtDNA variants impacted on respiratory complexes activity and subunits abundance as well as on mitochondrial morphology. Moreover, PDX cells bearing homoplasmic mtDNA variants behaved as glucose-addicted and could barely survive glucose starvation in vitro. RNA-seq analysis indicated that mtDNA mutated (heteroplasmy > 50%) PDXs were endowed with upregulated glycolysis and other pathways connected with cancer metabolism. These findings led us to investigate whether pathogenic mtDNA variants correlated with response to anti-VEGF therapy, since the latter was shown to reduce glucose availability in tumors. Strikingly, PDXs bearing homoplasmic pathogenic mtDNA variants associated with improved survival upon anti-VEGF treatment in mice, compared with mtDNA wild type or low heteroplasmy PDXs.

CONCLUSIONS

These results hint at mtDNA variants as potential biomarkers of response to antiangiogenic drugs.

Mechanisms and therapeutic targets of mitochondria in the progression of metabolic dysfunction-associated steatotic liver disease

Metabolic Dysfunction-Associated Steatotic Liver Disease (MASLD) includes liver disease processes from simple fatty liver to nonalcoholic steatohepatitis, which may progress to liver fibrosis, cirrhosis, and even hepatocellular carcinoma (HCC). As the incidence of HCC derived from viral hepatitis decreases, MASLD has emerged as a significant health threat, driven by lifestyle changes and rising obesity rates among patients. The pathogenesis of MASLD is complex, involving factors such as insulin resistance, gut microbiota imbalance, and genetic and epigenetic factors. In recent years, the role of mitochondrial dysfunction in MASLD has gained significant attention, involving β-oxidation imbalance, oxidative stress increase, mitophagy defects, and mitochondrial DNA (mtDNA) mutations. This article reviews the pathophysiological mechanisms of mitochondrial dysfunction in MASLD, diagnostic methods, and potential therapeutic strategies. By synthesizing current research findings, the review aims to highlight the critical role of mitochondrial dysfunction as a target for future diagnostic and therapeutic interventions. This focus could pave the way for innovative clinical strategies, ultimately improving treatment options and patient prognosis in MASLD.

Pathogenic mitochondrial DNA mutations inhibit melanoma metastasis

Mitochondrial DNA (mtDNA) mutations are frequent in cancer, yet their precise role in cancer progression remains debated. To functionally evaluate the impact of mtDNA variants on tumor growth and metastasis, we developed an enhanced cytoplasmic hybrid (cybrid) generation protocol and established isogenic human melanoma cybrid lines with wild-type mtDNA or pathogenic mtDNA mutations with partial or complete loss of mitochondrial oxidative function. Cybrids with homoplasmic levels of pathogenic mtDNA reliably established tumors despite dysfunctional oxidative phosphorylation. However, these mtDNA variants disrupted spontaneous metastasis from primary tumors and reduced the abundance of circulating tumor cells. Migration and invasion of tumor cells were reduced, indicating that entry into circulation is a bottleneck for metastasis amid mtDNA dysfunction. Pathogenic mtDNA did not inhibit organ colonization following intravenous injection. In heteroplasmic cybrid tumors, single-cell analyses revealed selection against pathogenic mtDNA during melanoma growth. Collectively, these findings experimentally demonstrate that functional mtDNA is favored during melanoma growth and supports metastatic entry into the blood.

Targeting mitochondria: a novel approach for treating platinum-resistant ovarian cancer

Ovarian cancer is a prevalent gynecologic malignancy with the second-highest mortality rate among gynecologic malignancies. Platinum-based chemotherapy is the first-line treatment for ovarian cancer; however, a majority of patients with ovarian cancer experience relapse and develop platinum resistance following initial treatment. Despite extensive research on the mechanisms of platinum resistance at the nuclear level, the issue of platinum resistance in ovarian cancer remains largely unresolved. It is noteworthy that mitochondrial DNA (mtDNA) exhibits higher affinity for platinum compared to nuclear DNA (nDNA). Mutations in mtDNA can modulate tumor chemosensitivity through various mechanisms, including DNA damage responses, shifts in energy metabolism, maintenance of Reactive Oxygen Species (ROS) homeostasis, and alterations in mitochondrial dynamics. Concurrently, retrograde signals produced by mtDNA mutations and their subsequent cascades establish communication with the nucleus, leading to the reorganization of the nuclear transcriptome and governing the transcription of genes and signaling pathways associated with chemoresistance. Furthermore, mitochondrial translocation among cells emerges as a crucial factor influencing the effectiveness of chemotherapy in ovarian cancer. This review aims to explore the role and mechanism of mitochondria in platinum resistance, with a specific focus on mtDNA mutations and the resulting metabolic reprogramming, ROS regulation, changes in mitochondrial dynamics, mitochondria-nucleus communication, and mitochondrial transfer.

Evidence of compensation for mitochondrial reactive oxygen species increase in Caenorhabditis briggsae cytoplasmic-nuclear hybrids

Hybrid offspring dysfunction in cytoplasmic-nuclear hybrids (cybrids) implies that one parent's mitochondrial genome is incompatible with the nuclear genome of the other parent. In Caenorhabditis briggsae , cybrids exhibit increased mitochondrial reactive oxygen species (ROS). In this study, we measured the specific activity of markers for mitochondrial abundance (citrate synthase) and antioxidant enzyme response (catalase) in four C. briggsae cybrid lines. An increase of catalase expression but not in mitochondrial abundance was found in dysfunctional cybrids. This suggests that organisms might compensate for some genetic incompatibilities by modulating gene expression of key oxidative stress enzymes such as catalase.

[Mitohormesis: a key driver of the therapy resistance in cancer cells]

A large body of literature highlights the importance of energy metabolism in the response of haematological malignancies to therapy. In this review, we are particularly interested in acute myeloid leukaemia, where mitochondrial metabolism plays a key role in response and resistance to treatment. We describe the new concept of mitohormesis in the response to therapy-induced stress and in the initiation of relapse in this disease.

Membrane-mediated modulation of mitochondrial physiology by terahertz waves

Extensive studies have demonstrated the diverse impacts of electromagnetic waves at gigahertz and terahertz (THz) frequencies on cytoplasmic membrane properties. However, there is little evidence of these impacts on intracellular membranes, particularly mitochondrial membranes crucial for mitochondrial physiology. In this study, human neuroblast-like cells were exposed to continuous 0.1 THz radiation at an average power density of 33 mW/cm2. The analysis revealed that THz exposure significantly altered the mitochondrial ultrastructure. THz waves enhanced the enzymatic activity of the mitochondrial respiratory chain but disrupted supercomplex assembly, compromising mitochondrial respiration. Molecular dynamics simulations revealed altered rates of change in the quantity of hydrogen bonds and infiltration of water molecules in lipid bilayers containing cardiolipin, indicating the specific behavior of cardiolipin, a signature phospholipid in mitochondria, under THz exposure. These findings suggest that THz radiation can significantly alter mitochondrial membrane properties, impacting mitochondrial physiology through a mechanism related to mitochondrial membrane, and provide deeper insight into the bioeffects of THz radiation.

The association between methylmalonic acid, a biomarker of mitochondrial dysfunction, and risk of prostate cancer

BACKGROUND

The aim of the study was to investigate the association between methylmalonic acid (MMA), a biomarker of mitochondrial dysfunction, and the risk of prostate cancer (PCa).

METHODS AND MATERIALS

The relevant data were collected from the National Health and Nutrition Examination Survey (NHANES). Weighted univariable and multivariable logistic regression analyses were performed to investigate the association between MMA and risk of PCa. A stratified analysis was also carried out. The dose-response relationship was elucidated by conducting a restricted cubic spline function.

RESULTS

A total of 2451 participants were included, of which 95 were PCa participants. The fully-adjusted model 2 constructed by weighted multivariable logistic regression analysis showed that the risk of PCa decreased by 53% when every MMA unit was added [OR: 0.47 (0.22-1.00), P = 0.049]. And a decrease in PCa risk was associated with a higher MMA level in MMA subgroups [OR: 0.34 (0.15-0.82), P = 0.02]. The results from a stratified analysis showed that participants in subgroups of other race, BMI (> 30 kg/m2), smoking (former and now), and hypertension (yes), an increase in every MMA unit was linked to a decrease in PCa risk. MMA and the risk of PCa were negatively correlated in a linear manner.

CONCLUSION

It was discovered in the study that an increase in MMA level is connected to a decrease in PCa risk. The serum MMA level may be helpful in assessing PCa risk.

Developing theragnostics for Alzheimer's disease: Insights from cancer treatment

The prevalence of Alzheimer's disease (AD) and its associated economic and societal burdens are on the rise, but there are no curative treatments for AD. Interestingly, this neurodegenerative disease shares several biological and pathophysiological features with cancer, including cell-cycle dysregulation, angiogenesis, mitochondrial dysfunction, protein misfolding, and DNA damage. However, the genetic factors contributing to the overlap in biological processes between cancer and AD have not been actively studied. In this review, we discuss the shared biological features of cancer and AD, the molecular targets of anticancer drugs, and therapeutic approaches. First, we outline the common biological features of cancer and AD. Second, we describe several anticancer drugs, their molecular targets, and their effects on AD pathology. Finally, we discuss how protein-protein interactions (PPIs), receptor inhibition, immunotherapy, and gene therapy can be exploited for the cure and management of both cancer and AD. Collectively, this review provides insights for the development of AD theragnostics based on cancer drugs and molecular targets.

Single-cell mtDNA dynamics in tumors is driven by coregulation of nuclear and mitochondrial genomes

The extent of cell-to-cell variation in tumor mitochondrial DNA (mtDNA) copy number and genotype, and the phenotypic and evolutionary consequences of such variation, are poorly characterized. Here we use amplification-free single-cell whole-genome sequencing (Direct Library Prep (DLP+)) to simultaneously assay mtDNA copy number and nuclear DNA (nuDNA) in 72,275 single cells derived from immortalized cell lines, patient-derived xenografts and primary human tumors. Cells typically contained thousands of mtDNA copies, but variation in mtDNA copy number was extensive and strongly associated with cell size. Pervasive whole-genome doubling events in nuDNA associated with stoichiometrically balanced adaptations in mtDNA copy number, implying that mtDNA-to-nuDNA ratio, rather than mtDNA copy number itself, mediated downstream phenotypes. Finally, multimodal analysis of DLP+ and single-cell RNA sequencing identified both somatic loss-of-function and germline noncoding variants in mtDNA linked to heteroplasmy-dependent changes in mtDNA copy number and mitochondrial transcription, revealing phenotypic adaptations to disrupted nuclear/mitochondrial balance.

Complex I activity in hypoxia: implications for oncometabolism

Certain cancer cells within solid tumors experience hypoxia, rendering them incapable of oxidative phosphorylation (OXPHOS). Despite this oxygen deficiency, these cells exhibit biochemical pathway activity that relies on NAD+. This mini-review scrutinizes the persistent, residual Complex I activity that oxidizes NADH in the absence of oxygen as the electron acceptor. The resulting NAD+ assumes a pivotal role in fueling the α-ketoglutarate dehydrogenase complex, a critical component in the oxidative decarboxylation branch of glutaminolysis - a hallmark oncometabolic pathway. The proposition is that through glutamine catabolism, high-energy phosphate intermediates are produced via substrate-level phosphorylation in the mitochondrial matrix substantiated by succinyl-CoA ligase, partially compensating for an OXPHOS deficiency. These insights provide a rationale for exploring Complex I inhibitors in cancer treatment, even when OXPHOS functionality is already compromised.

A complete workflow for single cell mtDNAseq in CHO cells, from cell culture to bioinformatic analysis

Chinese hamster ovary (CHO) cells have a long history in the biopharmaceutical industry and currently produce the vast majority of recombinant therapeutic proteins. A key step in controlling the process and product consistency is the development of a producer cell line derived from a single cell clone. However, it is recognized that genetic and phenotypic heterogeneity between individual cells in a clonal CHO population tends to arise over time. Previous bulk analysis of CHO cell populations revealed considerable variation within the mtDNA sequence (heteroplasmy), which could have implications for the performance of the cell line. By analyzing the heteroplasmy of single cells within the same population, this heterogeneity can be characterized with greater resolution. Such analysis may identify heterogeneity in the mitochondrial genome, which impacts the overall phenotypic performance of a producer cell population, and potentially reveal routes for genetic engineering. A critical first step is the development of robust experimental and computational methods to enable single cell mtDNA sequencing (termed scmtDNAseq). Here, we present a protocol from cell culture to bioinformatic analysis and provide preliminary evidence of significant mtDNA heteroplasmy across a small panel of single CHO cells.

Effect of L-4-Thiazolylalanine (Protinol™) on skin barrier strength and skin protection

OBJECTIVES

Skin barrier properties are critical for maintaining epidermal water content, protecting from environmental factors and providing the first line of defense against pathogens. In this study, we investigated the non-proteinogenic amino acid L-4-Thiazolylalanine (L4) as a potential active ingredient in skin protection and barrier strength.

METHODS

L4 on wound healing, anti-inflammatory and anti-oxidant properties were evaluated using monolayers and 3D skin equivalents. The transepithelial electrical resistance (TEER) value was used in vitro as a strong indicator of barrier strength and integrity. Clinical L4 efficacy was assessed for the evaluation of the skin barrier integrity and soothing benefits.

RESULTS

In vitro treatments of L4 show beneficial effects in wound closure mechanism, and we demonstrate that L4 anti-oxidant benefits with markedly increased HSP70 and decreased reactive oxygen species production induced by UVs exposure. Barrier strength and integrity were significantly improved by L4, confirmed clinically by an increase in 12R-lipoxygenase enzymatic activity in the stratum corneum. In addition, soothing benefits of L4 have been shown clinically with the decrease in redness after methyl nicotinate application on the inner arm and the significant reduction of the erythema and the skin desquamation on the scalp.

CONCLUSION

L4 delivered multiple skin benefits by strengthening the skin barrier, accelerating the skin repair process as well as soothing the skin and the scalp with anti-inflammaging effects. The observed efficacy validates L4 as a desirable skincare ingredient for topical treatment.

Phlorotannins: Novel Orally Administrated Bioactive Compounds That Induce Mitochondrial Dysfunction and Oxidative Stress in Cancer

Mitochondrial dysfunction is an interesting therapeutic target to help reduce cancer deaths, and the use of bioactive compounds has emerged as a novel and safe approach to solve this problem. Here, we discuss the information available related to phlorotannins, a type of polyphenol present in brown seaweeds that reportedly functions as antioxidants/pro-oxidants and anti-inflammatory and anti-tumorigenic agents. Specifically, available evidence indicates that dieckol and phloroglucinol promote mitochondrial membrane depolarization and mitochondria-dependent apoptosis. Phlorotannins also reduce pro-tumorigenic, -inflammatory, and -angiogenic signaling mechanisms involving RAS/MAPK/ERK, PI3K/Akt/mTOR, NF-κB, and VEGF. In doing so, they inhibit pathways that favor cancer development and progression. Unfortunately, these compounds are rather labile and, therefore, this review also summarizes approaches permitting the encapsulation of bioactive compounds, like phlorotannins, and their subsequent oral administration as novel and non-invasive therapeutic alternatives for cancer treatment.

IQGAP1 mediates the communication between the nucleus and the mitochondria via NDUFS4 alternative splicing

Constant communication between mitochondria and nucleus ensures cellular homeostasis and adaptation to mitochondrial stress. Anterograde regulatory pathways involving a large number of nuclear-encoded proteins control mitochondrial biogenesis and functions. Such functions are deregulated in cancer cells, resulting in proliferative advantages, aggressive disease and therapeutic resistance. Transcriptional networks controlling the nuclear-encoded mitochondrial genes are known, however alternative splicing (AS) regulation has not been implicated in this communication. Here, we show that IQGAP1, a scaffold protein regulating AS of distinct gene subsets in gastric cancer cells, participates in AS regulation that strongly affects mitochondrial respiration. Combined proteomic and RNA-seq analyses of IQGAP1KO and parental cells show that IQGAP1KO alters an AS event of the mitochondrial respiratory chain complex I (CI) subunit NDUFS4 and downregulates a subset of CI subunits. In IQGAP1KO cells, CI intermediates accumulate, resembling assembly deficiencies observed in patients with Leigh syndrome bearing NDUFS4 mutations. Mitochondrial CI activity is significantly lower in KO compared to parental cells, while exogenous expression of IQGAP1 reverses mitochondrial defects of IQGAP1KO cells. Our work sheds light to a novel facet of IQGAP1 in mitochondrial quality control that involves fine-tuning of CI activity through AS regulation in gastric cancer cells relying highly on mitochondrial respiration.

Role of mitochondrial alterations in human cancer progression and cancer immunity

Dysregulating cellular metabolism is one of the emerging cancer hallmarks. Mitochondria are essential organelles responsible for numerous physiologic processes, such as energy production, cellular metabolism, apoptosis, and calcium and redox homeostasis. Although the "Warburg effect," in which cancer cells prefer aerobic glycolysis even under normal oxygen circumstances, was proposed a century ago, how mitochondrial dysfunction contributes to cancer progression is still unclear. This review discusses recent progress in the alterations of mitochondrial DNA (mtDNA) and mitochondrial dynamics in cancer malignant progression. Moreover, we integrate the possible regulatory mechanism of mitochondrial dysfunction-mediated mitochondrial retrograde signaling pathways, including mitochondrion-derived molecules (reactive oxygen species, calcium, oncometabolites, and mtDNA) and mitochondrial stress response pathways (mitochondrial unfolded protein response and integrated stress response) in cancer progression and provide the possible therapeutic targets. Furthermore, we discuss recent findings on the role of mitochondria in the immune regulatory function of immune cells and reveal the impact of the tumor microenvironment and metabolism remodeling on cancer immunity. Targeting the mitochondria and metabolism might improve cancer immunotherapy. These findings suggest that targeting mitochondrial retrograde signaling in cancer malignancy and modulating metabolism and mitochondria in cancer immunity might be promising treatment strategies for cancer patients and provide precise and personalized medicine against cancer.

Mitochondrial DNA is a major source of driver mutations in cancer

Mitochondrial DNA (mtDNA) mutations are among the most common genetic events in all tumors and directly impact metabolic homeostasis. Despite the central role mitochondria play in energy metabolism and cellular physiology, the role of mutations in the mitochondrial genomes of tumors has been contentious. Until recently, genomic and functional studies of mtDNA variants were impeded by a lack of adequate tumor mtDNA sequencing data and available methods for mitochondrial genome engineering. These barriers and a conceptual fog surrounding the functional impact of mtDNA mutations in tumors have begun to lift, revealing a path to understanding the role of this essential metabolic genome in cancer initiation and progression. Here we discuss the history, recent developments, and challenges that remain for mitochondrial oncogenetics as the impact of a major new class of cancer-associated mutations is unveiled.

Respiratory Complex I dysfunction in cancer: from a maze of cellular adaptive responses to potential therapeutic strategies

Mitochondria act as key organelles in cellular bioenergetics and biosynthetic processes producing signals that regulate different molecular networks for proliferation and cell death. This ability is also preserved in pathologic contexts such as tumorigenesis, during which bioenergetic changes and metabolic reprogramming confer flexibility favoring cancer cell survival in a hostile microenvironment. Although different studies epitomize mitochondrial dysfunction as a protumorigenic hit, genetic ablation or pharmacological inhibition of respiratory complex I causing a severe impairment is associated with a low-proliferative phenotype. In this scenario, it must be considered that despite the initial delay in growth, cancer cells may become able to resume proliferation exploiting molecular mechanisms to overcome growth arrest. Here, we highlight the current knowledge on molecular responses activated by complex I-defective cancer cells to bypass physiological control systems and to re-adapt their fitness during microenvironment changes. Such adaptive mechanisms could reveal possible novel molecular players in synthetic lethality with complex I impairment, thus providing new synergistic strategies for mitochondrial-based anticancer therapy.

NDUFS3 knockout cancer cells and molecular docking reveal specificity and mode of action of anti-cancer respiratory complex I inhibitors

Inhibition of respiratory complex I (CI) is becoming a promising anti-cancer strategy, encouraging the design and the use of inhibitors, whose mechanism of action, efficacy and specificity remain elusive. As CI is a central player of cellular bioenergetics, a finely tuned dosing of targeting drugs is required to avoid side effects. We compared the specificity and mode of action of CI inhibitors metformin, BAY 87-2243 and EVP 4593 using cancer cell models devoid of CI. Here we show that both BAY 87-2243 and EVP 4593 were selective, while the antiproliferative effects of metformin were considerably independent from CI inhibition. Molecular docking predictions indicated that the high efficiency of BAY 87-2243 and EVP 4593 may derive from the tight network of bonds in the quinone binding pocket, although in different sites. Most of the amino acids involved in such interactions are conserved across species and only rarely found mutated in human. Our data make a case for caution when referring to metformin as a CI-targeting compound, and highlight the need for dosage optimization and careful evaluation of molecular interactions between inhibitors and the holoenzyme.

Aging-associated accumulation of mitochondrial DNA mutations in tumor origin

The majority of cancer patients are among aged population, suggesting an urgent need to advance our knowledge on complicated relationship between aging and cancer. It has been hypothesized that metabolic changes during aging could act as a driver for tumorigenesis. Given the fact that mitochondrial DNA (mtDNA) mutations are common in both tumors and aged tissues, it is interesting to contemplate possible role of age-related mtDNA mutations in tumorigenesis. MtDNA encodes genes essential for mitochondrial metabolism, and mtDNA mutates at a much higher rate than nuclear genome. Random drifting of somatic mtDNA mutations, as a result of cell division or mitochondrial turnover during aging, may lead to more and more cells harboring high-frequency pathogenic mtDNA mutations, albeit at different loci, in single-cells. Such mutations can induce metabolic reprogramming, nuclear genome instability and immune response, which might increase the likelihood of tumorigenesis. In this review, we summarize current understanding of how mtDNA mutations accumulate with aging and how these mutations could mechanistically contribute to tumor origin. We also discuss potential prevention strategies for mtDNA mutation-induced tumorigenesis, and future works needed in this direction.

The mitochondrial unfolded protein response (UPRmt): shielding against toxicity to mitochondria in cancer

Mitochondria are essential for tumor growth and progression. However, the heavy demand for mitochondrial activity in cancer leads to increased production of mitochondrial reactive oxygen species (mtROS), accumulation of mutations in mitochondrial DNA, and development of mitochondrial dysfunction. If left unchecked, excessive mtROS can damage and unfold proteins in the mitochondria to an extent that becomes lethal to the tumor. Cellular systems have evolved to combat mtROS and alleviate mitochondrial stress through a quality control mechanism called the mitochondrial unfolded protein response (UPR^mt). The UPR^mt system is composed of chaperones and proteases, which promote protein folding or eliminate mitochondrial proteins damaged by mtROS, respectively. UPR^mt is conserved and activated in cancer in response to mitochondrial stress to maintain mitochondrial integrity and support tumor growth. In this review, we discuss how mitochondria become dysfunctional in cancer and highlight the tumor-promoting functions of key components of the UPR^mt.

Mitochondrial DNA mutations in aging and cancer

Advancing age is a major risk factor for malignant transformation and the development of cancer. As such, over 50% of neoplasms occur in individuals over the age of 70. The pathologies of both ageing and cancer have been characterized by respective groups of molecular hallmarks, and while some features are divergent between the two pathologies, several are shared. Perturbed mitochondrial function is one such common hallmark, and this observation therefore suggests that mitochondrial alterations may be of significance in age‐related cancer development. There is now considerable evidence documenting the accumulation of somatic mitochondrial DNA (mtDNA) mutations in ageing human postmitotic and replicative tissues. Similarly, mutations of the mitochondrial genome have been reported in human cancers for decades. The plethora of functions in which mitochondria partake, such as oxidative phosphorylation, redox balance, apoptosis and numerous biosynthetic pathways, manifests a variety of ways in which alterations in mtDNA may contribute to tumour growth. However, the specific mechanisms by which mtDNA mutations contribute to tumour progression remain elusive and often contradictory. This review aims to consolidate current knowledge and describe future direction within the field.

Research Progress on Improving the Efficiency of CDT by Exacerbating Tumor Acidification

In recent years, chemodynamic therapy (CDT) has received extensive attention as a novel means of cancer treatment. The CDT agents can exert Fenton and Fenton-like reactions in the acidic tumor microenvironment (TME), converting hydrogen peroxide (H₂O₂) into highly toxic hydroxyl radicals (·OH). However, the pH of TME, as an essential factor in the Fenton reaction, does not catalyze the reaction effectively, hindering its efficiency, which poses a significant challenge for the future clinical application of CDT. Therefore, this paper reviews various strategies to enhance the antitumor properties of nanomaterials by modulating tumor acidity. Ultimately, the performance of CDT can be further improved by inducing strong oxidative stress to produce sufficient ·OH. In this paper, the various acidification pathways and proton pumps with potential acidification functions are mainly discussed, such as catalytic enzymes, exogenous acids, CAIX, MCT, NHE, NBCn1, etc. The problems, opportunities, and challenges of CDT in the cancer field are also discussed, thereby providing new insights for the design of nanomaterials and laying the foundation for their future clinical applications.

Mitochondrial Homeostasis–Related lncRNAs are Potential Biomarkers for Predicting Prognosis and Immune Response in Lung Adenocarcinoma

The prognosis of the most common histological subtype of lung cancer, lung adenocarcinoma (LUAD), is relatively poor. Mitochondrial homeostasis depends to a great extent on the coordination between mitophagy and mitochondrial biogenesis, the deregulation of which causes various human diseases, including cancer. There is accumulating evidence that long noncoding RNAs (lncRNAs) are critical in predicting the prognosis and immune response in carcinoma. Therefore, it is critical to discern lncRNAs related to mitochondrial homeostasis in LUAD patients. In this study, we identified mitochondrial homeostasis–related lncRNAs (MHRlncRNAs) by coexpression analysis. In order to construct a prognostic signature composed of three MHRlncRNAs, univariate and multivariate Cox regression analyses were performed. Kaplan–Meier analysis, stratification analysis, principal component analysis (PCA), receiver operating characteristic (ROC) curve, gene set enrichment analysis (GSEA), and nomogram were applied to evaluate and optimize the risk model. Subsequently, we identified the mitochondrial homeostasis–related lncRNA signature (MHLncSig) as an independent predictive factor of prognosis. Based on the LUAD subtypes regrouped by this risk model, we further investigated the underlying tumor microenvironment, tumor mutation burden, and immune landscape behind different risk groups. Likewise, individualized immunotherapeutic strategies and candidate compounds were screened to aim at different risk subtypes of LUAD patients. Finally, we validated the expression trends of lncRNAs included in the risk model using quantitative real-time polymerase chain reaction (qRT-PCR) assays. The established MHLncSig may be a promising tool for predicting the prognosis and guiding individualized treatment in LUAD.

Next-Generation Sequencing to Characterize Mitochondrial Genomic DNA Heteroplasmy

Mitochondria play a very important role in many crucial cellular functions. Each eukaryotic cell contains hundreds of mitochondria with hundreds of mitochondrial genomes. Mutant and wild-type mitochondrial DNA (mtDNA) may co-exist as heteroplasmy and cause human disease. The purpose of the protocols in this article is to simultaneously determine the mtDNA sequence and quantify the heteroplasmy level using parallel sequencing. The protocols include mitochondrial genomic DNA PCR amplification of two full-length products using two distinct sets of PCR primers. The PCR products are mixed at an equimolar ratio, and the samples are then barcoded and sequenced with high-throughput next-generation sequencing technology. This technology is highly sensitive, specific, and accurate in determining mtDNA mutations and the degree/level of heteroplasmy. © 2022 Wiley Periodicals LLC. Basic Protocol 1: PCR amplification of mitochondrial DNA Basic Protocol 2: Analysis of next-generation sequencing of mitochondrial DNA Basic Protocol 3: Mutect2 pipeline for automated sample processing and large-scale data analysis.

Head and Neck Cancer Susceptibility and Metabolism in Fanconi Anemia

Fanconi anemia (FA) is a rare inherited, generally autosomal recessive syndrome, but it displays X-linked or dominant negative inheritance for certain genes. FA is characterized by a deficiency in DNA damage repair that results in bone marrow failure, and in an increased risk for various epithelial tumors, most commonly squamous cell carcinomas of the head and neck (HNSCC) and of the esophagus, anogenital tract and skin. Individuals with FA exhibit increased human papilloma virus (HPV) prevalence. Furthermore, a subset of anogenital squamous cell carcinomas (SCCs) in FA harbor HPV sequences and FA-deficient laboratory models reveal molecular crosstalk between HPV and FA proteins. However, a definitive role for HPV in HNSCC development in the FA patient population is unproven. Cellular metabolism plays an integral role in tissue homeostasis, and metabolic deregulation is a known hallmark of cancer progression that supports uncontrolled proliferation, tumor development and metastatic dissemination. The metabolic consequences of FA deficiency in keratinocytes and associated impact on the development of SCC in the FA population is poorly understood. Herein, we review the current literature on the metabolic consequences of FA deficiency and potential effects of resulting metabolic reprogramming on FA cancer phenotypes.

Mitochondrial ROS Produced in Human Colon Carcinoma Associated with Cell Survival via Autophagy

Simple Summary

Human colon carcinoma remains one of the major causes of cancer-related death worldwide. Ubiquinol cytochrome c reductase binding protein (UQCRB) has been reported as a biomarker of colorectal cancer, but its role in tumor growth has not been clarified. CRC cells often exhibit high autophagic flux under nutrient deprivation or hypoxic condition and increased autophagy activation in cancer cells involving the recycling of cell components to facilitate survival in a tumor microenvironment. Here we show that UQCRB is overexpressed in HCT116 cells compared to CCD18co, normal colon fibroblast cells. Mechanistically, the increasing level of mitochondrial ROS (mROS) caused by UQCRB overexpression can release Ca²⁺ by the activation of the lysosomal transient receptor potential mucolipin 1 channels. This activation triggers transcription factor EB nuclear translocation and lysosome biogenesis leading to autophagy flux. Collectively, we identified that the increasing level of mROS by the overexpression of UQCRB in human colon carcinoma could link to autophagy for colorectal cancer survival. These results lead to a translational impact that a UQCRB inhibitor could be a potential anticancer agent for human colon carcinoma treatment.

Abstract

Human colon carcinomas, including HCT116 cells, often exhibit high autophagic flux under nutrient deprivation or hypoxic conditions. Mitochondrial ROS (mROS) is known as a ‘molecular switch’ for regulating the autophagic pathway, which is critical for directing cancer cell survival or death. In early tumorigenesis, autophagy plays important roles in maintaining cellular homeostasis and contributes to tumor growth. However, the relationships between mROS and the autophagic capacities of HCT116 cells are poorly understood. Ubiquinol cytochrome c reductase binding protein (UQCRB) has been reported as a biomarker of colorectal cancer, but its role in tumor growth has not been clarified. Here, we showed that UQCRB is overexpressed in HCT116 cells compared to CCD18co cells, a normal colon fibroblast cell line. Pharmacological inhibition of UQCRB reduced mROS levels, autophagic flux, and the growth of HCT116 tumors in a xenograft mouse model. We further investigated mutant UQCRB-overexpressing cell lines to identify functional links in UQCRB-mROS-autophagy. Notably, an increasing level of mROS caused by UQCRB overexpression released Ca²⁺ by the activation of lysosomal transient receptor potential mucolipin 1 (TRPML1) channels. This activation induced transcription factor EB (TFEB) nuclear translocation and lysosome biogenesis, leading to autophagy flux. Collectively, our study showed that increasing levels of mROS caused by the overexpression of UQCRB in human colon carcinoma HCT116 cells could be linked to autophagy for cell survival.

Thyroid Cancer-Associated Mitochondrial DNA Mutation G3842A Promotes Tumorigenicity via ROS-Mediated ERK1/2 Activation

Mitochondrial DNA (mtDNA) mutations have been identified in various human cancers, including thyroid cancer. However, the relationship between mtDNA and thyroid cancer remains unclear. Previous studies by others and us strongly suggested that mtDNA mutations in complex I may participate in thyroid cancer processes according to sequencing results of thyroid cancer tissue, although the associated pathogenic processes remain unknown. Here, to investigate whether mtDNA mutations contribute to thyroid cancer, we reanalyzed our sequencing results and characterized thyroid cancer-associated mutations in the mitochondrial complex. The results identified the highest mutation frequencies in nicotinamide adenine dinucleotide hydride (NADH) dehydrogenase subunit 4 gene (ND4) and cytochrome c oxidase subunit 1 gene (COI), which also harbored the highest rates of $\text{G}>\text{A}$ substitutions, with most of the mutations resulting in changes in the polarity of amino acids. We then established cybrids containing the G3842A mutation identified in papillary thyroid carcinoma, which revealed it as a mutation in NADH dehydrogenase subunit 1 gene (ND1) and is previously reported in follicular thyroid carcinoma, thereby suggesting a possibly pathogenic role in thyroid carcinoma. Additionally, we found that the G3842A mutation accelerates tumorigenicity and decreases the abundance and activity of mitochondrial complex I, the oxygen consumption rate, and adenosine triphosphate levels. By contrast, the levels of reactive oxygen species (ROS) were increased to activate extracellular signal-regulated kinase (ERK1/2) signaling, which contributed to tumorigenicity. These findings suggest for the first time that mtDNA mutations help drive tumor development and that G3842A may represent a new risk factor for thyroid cancer. Furthermore, our findings indicate that drugs targeting ROS and ERK1/2 may serve as a viable therapeutic strategy for thyroid cancer.

Metabolic tricks of cancer cells

One of the characteristics of cancer cells important for tumorigenesis is their metabolic plasticity. Indeed, in various stress conditions, cancer cells can reshape their metabolic pathways to support the increased energy request due to continuous growth and rapid proliferation. Moreover, selective pressures in the tumor microenvironment, such as hypoxia, acidosis, and competition for resources, force cancer cells to adapt by complete reorganization of their metabolism. In this review, we highlight the characteristics of cancer metabolism and discuss its clinical significance, since overcoming metabolic plasticity of cancer cells is a key objective of modern cancer therapeutics and a better understanding of metabolic reprogramming may lead to the identification of possible targets for cancer therapy.

Somatic mitochondrial DNA mutations in different grades of glioma

Aim: Mitochondrial DNA (mtDNA) alterations play an important role in the multistep processes of cancer development. Gliomas are among the most diagnosed brain cancer. The relationship between mtDNA alterations and different grades of gliomas are still elusive. This study aimed to elucidate the profile of somatic mtDNA mutations in different grades of gliomas and correlate it with clinical phenotype. Materials & methods: Forty histopathologically confirmed glioma tissue samples and their matched blood were collected and subjected for mtDNA sequencing. Results & conclusion: About 75% of the gliomas harbored at least one somatic mutation in the mtDNA gene, and 45% of these mutations were pathogenic. Mutations were scattered across the mtDNA genome, and the commonest nonsynonymous mutations were located at complex I and IV of the mitochondrial respiratory chain. These findings may have implication for future research to determine the mitochondrial energetics and its downstream metabolomics on gliomas.

Petasin potently inhibits mitochondrial complex I-based metabolism that supports tumor growth and metastasis

Mitochondrial electron transport chain complex I (ETCC1) is the essential core of cancer metabolism, yet potent ETCC1 inhibitors capable of safely suppressing tumor growth and metastasis in vivo are limited. From a plant extract screening, we identified petasin (PT) as a highly potent ETCC1 inhibitor with a chemical structure distinct from conventional inhibitors. PT had at least 1700 times higher activity than that of metformin or phenformin and induced cytotoxicity against a broad spectrum of tumor types. PT administration also induced prominent growth inhibition in multiple syngeneic and xenograft mouse models in vivo. Despite its higher potency, it showed no apparent toxicity toward nontumor cells and normal organs. Also, treatment with PT attenuated cellular motility and focal adhesion in vitro as well as lung metastasis in vivo. Metabolome and proteome analyses revealed that PT severely depleted the level of aspartate, disrupted tumor-associated metabolism of nucleotide synthesis and glycosylation, and downregulated major oncoproteins associated with proliferation and metastasis. These findings indicate the promising potential of PT as a potent ETCC1 inhibitor to target the metabolic vulnerability of tumor cells.

Mitochondrial Metabolism in Carcinogenesis and Cancer Therapy

Simple Summary

Reprogramming metabolism is a hallmark of cancer. Warburg’s effect, defined as increased aerobic glycolysis at the expense of mitochondrial respiration in cancer cells, opened new avenues of research in the field of cancer. Later findings, however, have revealed that mitochondria remain functional and that they actively contribute to metabolic plasticity of cancer cells. Understanding the mechanisms by which mitochondrial metabolism controls tumor initiation and progression is necessary to better characterize the onset of carcinogenesis. These studies may ultimately lead to the design of novel anti-cancer strategies targeting mitochondrial functions.

Abstract

Carcinogenesis is a multi-step process that refers to transformation of a normal cell into a tumoral neoplastic cell. The mechanisms that promote tumor initiation, promotion and progression are varied, complex and remain to be understood. Studies have highlighted the involvement of oncogenic mutations, genomic instability and epigenetic alterations as well as metabolic reprogramming, in different processes of oncogenesis. However, the underlying mechanisms still have to be clarified. Mitochondria are central organelles at the crossroad of various energetic metabolisms. In addition to their pivotal roles in bioenergetic metabolism, they control redox homeostasis, biosynthesis of macromolecules and apoptotic signals, all of which are linked to carcinogenesis. In the present review, we discuss how mitochondria contribute to the initiation of carcinogenesis through gene mutations and production of oncometabolites, and how they promote tumor progression through the control of metabolic reprogramming and mitochondrial dynamics. Finally, we present mitochondrial metabolism as a promising target for the development of novel therapeutic strategies.

ATM-Mediated Mitochondrial Radiation Responses of Human Fibroblasts

Ataxia telangiectasia (AT) is characterized by extreme sensitivity to ionizing radiation. The gene mutated in AT, Ataxia Telangiectasia Mutated (ATM), has serine/threonine protein kinase activity and mediates the activation of multiple signal transduction pathways involved in the processing of DNA double-strand breaks. Reactive oxygen species (ROS) created as a byproduct of the mitochondria's oxidative phosphorylation (OXPHOS) has been proposed to be the source of intracellular ROS. Mitochondria are uniquely vulnerable to ROS because they are the sites of ROS generation. ROS-induced mitochondrial mutations lead to impaired mitochondrial respiration and further increase the likelihood of ROS generation, establishing a vicious cycle of further ROS production and mitochondrial damage. AT patients and ATM-deficient mice display intrinsic mitochondrial dysfunction and exhibit constitutive elevations in ROS levels. ATM plays a critical role in maintaining cellular redox homeostasis. However, the precise mechanism of ATM-mediated mitochondrial antioxidants remains unclear. The aim of this review paper is to introduce our current research surrounding the role of ATM on maintaining cellular redox control in human fibroblasts. ATM-mediated signal transduction is important in the mitochondrial radiation response. Perturbation of mitochondrial redox control elevates ROS which are key mediators in the development of cancer by many mechanisms, including ROS-mediated genomic instability, tumor microenvironment formation, and chronic inflammation.

The implications of mitochondria in doxorubicin treatment of cancer in the context of traditional and modern medicine

Doxorubicin (DOX) is an antibiotic anthracycline extensively used in the treatment of different malignancies, such as breast cancer, lymphomas and leukemias. The cardiotoxicity induced by DOX is one of the most important pathophysiological events that limit its clinical application. Accumulating evidence highlights mitochondria as a central role in this process. Modulation of mitochondrial functions as therapeutic strategy for DOX-induced cardiotoxicity has thus attracted much attention. In particular, emerging studies investigated the potential of natural mitochondria-targeting compounds from Traditional Chinese Medicine (TCM) as adjunct or alternative treatment for DOX-induced toxicity. This review summarizes studies about the mechanisms of DOX-induced cardiotoxicity, evidencing the importance of mitochondria and presenting TCM treatment alternatives for DOX-induced cardiomyopathy.

Shared evolutionary footprints suggest mitochondrial oxidative damage underlies multiple complex I losses in fungi

Oxidative phosphorylation is among the most conserved mitochondrial pathways. However, one of the cornerstones of this pathway, the multi-protein complex NADH : ubiquinone oxidoreductase (complex I) has been lost multiple independent times in diverse eukaryotic lineages. The causes and consequences of these convergent losses remain poorly understood. Here, we used a comparative genomics approach to reconstruct evolutionary paths leading to complex I loss and infer possible evolutionary scenarios. By mining available mitochondrial and nuclear genomes, we identified eight independent events of mitochondrial complex I loss across eukaryotes, of which six occurred in fungal lineages. We focused on three recent loss events that affect closely related fungal species, and inferred genomic changes convergently associated with complex I loss. Based on these results, we predict novel complex I functional partners and relate the loss of complex I with the presence of increased mitochondrial antioxidants, higher fermentative capabilities, duplications of alternative dehydrogenases, loss of alternative oxidases and adaptation to antifungal compounds. To explain these findings, we hypothesize that a combination of previously acquired compensatory mechanisms and exposure to environmental triggers of oxidative stress (such as hypoxia and/or toxic chemicals) induced complex I loss in fungi.

Mitochondrial DNA abnormalities provide mechanistic insight and predict reactive oxygen species-stimulating drug efficacy

Background

Associations between mitochondrial genetic abnormalities (variations and copy number, i.e. mtDNAcn, change) and elevated ROS have been reported in cancer compared to normal cells. Since excessive levels of ROS can trigger apoptosis, treating cancer cells with ROS-stimulating agents may enhance their death. This study aimed to investigate the link between baseline ROS levels and mitochondrial genetic abnormalities, and how mtDNA abnormalities might be used to predict cancer cells’ response to ROS-stimulating therapy.

Methods

Intracellular and mitochondrial specific-ROS levels were measured using the DCFDA and MitoSOX probes, respectively, in four cancer and one non-cancerous cell lines. Cells were treated with ROS-stimulating agents (cisplatin and dequalinium) and the IC50s were determined using the MTS assay. Sanger sequencing and qPCR were conducted to screen the complete mitochondrial genome for variations and to relatively quantify mtDNAcn, respectively. Non-synonymous variations were subjected to 3-dimensional (3D) protein structural mapping and analysis.

Results

Our data revealed novel significant associations between the total number of variations in the mitochondrial respiratory chain (MRC) complex I and III genes, mtDNAcn, ROS levels, and ROS-associated drug response. Furthermore, functional variations in complexes I/III correlated significantly and positively with mtDNAcn, ROS levels and drug resistance, indicating they might mechanistically influence these parameters in cancer cells.

Conclusions

Our findings suggest that mtDNAcn and complexes I/III functional variations have the potential to be efficient biomarkers to predict ROS-stimulating therapy efficacy in the future.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-021-08155-2.

Mitochondrial Control of Genomic Instability in Cancer

Simple Summary

Cancer cells display among its hallmark genomic instability. This is a progressive tendency in accumulate genome alteration which contributes to the damage of genes regulating cell division and tumor suppression. Genomic instability favors the appearance of survival-promoting mutations, increasing the likelihood that those mutations will propagate into daughter cells and have a significant impact on cancer progression. Among the many factor influencing this phenomenon, mitochondrial physiology is emerging. Mitochondria are bound to genomic instability by responding to DNA alteration to trigger cell death programs and as a source for DNA damage. Mitochondrial alterations prototypical of cancer can desensitize the mitochondrial route of cell death, facilitating the survival of cell acquiring new mutations, or can stimulate mitochondrial mediated DNA damage, boosting the mutation rate and genomic instability itself.

Abstract

Mitochondria are well known to participate in multiple aspects of tumor formation and progression. They indeed can alter the susceptibility of cells to engage regulated cell death, regulate pro-survival signal transduction pathways and confer metabolic plasticity that adapts to specific tumor cell demands. Interestingly, a relatively poorly explored aspect of mitochondria in neoplastic disease is their contribution to the characteristic genomic instability that underlies the evolution of the disease. In this review, we summarize the known mechanisms by which mitochondrial alterations in cancer tolerate and support the accumulation of DNA mutations which leads to genomic instability. We describe recent studies elucidating mitochondrial responses to DNA damage as well as the direct contribution of mitochondria to favor the accumulation of DNA alterations.

Environmental toxicants, oxidative stress and health adversities: interventions of phytochemicals

OBJECTIVES

Oxidative stress is the most common factor mediating environmental chemical-induced health adversities. Recently, an exponential rise in the use of phytochemicals as an alternative therapeutics against oxidative stress-mediated diseases has been documented. Due to their free radical quenching property, plant-derived natural products have gained substantial attention as a therapeutic agent in environmental toxicology. The present review aimed to describe the therapeutic role of phytochemicals in mitigating environmental toxicant-mediated sub-cellular and organ toxicities via controlling cellular antioxidant response.

METHODS

The present review has covered the recently related studies, mainly focussing on the free radical scavenging role of phytochemicals in environmental toxicology.

KEY FINDINGS

In vitro and in vivo studies have reported that supplementation of antioxidant-rich compounds can ameliorate the toxicant-induced oxidative stress, thereby improving the health conditions. Improving the cellular antioxidant pool has been considered as a mode of action of phytochemicals. However, the other cellular targets of phytochemicals remain uncertain.

CONCLUSIONS

Knowing the therapeutic value of phytochemicals to mitigate the chemical-induced toxicity is an initial stage; mechanistic understanding needs to decipher for development as therapeutics. Moreover, examining the efficacy of phytochemicals against mixer toxicity and identifying the bioactive molecule are major challenges in the field.

Mitochondrial DNA Dynamics in Reprogramming to Pluripotency

Mammalian cells, with the exception of erythrocytes, harbor mitochondria, which are organelles that provide energy, intermediate metabolites, and additional activities to sustain cell viability, replication, and function. Mitochondria contain multiple copies of a circular genome called mitochondrial DNA (mtDNA), whose individual sequences are rarely identical (homoplasmy) because of inherited or sporadic mutations that result in multiple mtDNA genotypes (heteroplasmy). Here, we examine potential mechanisms for maintenance or shifts in heteroplasmy that occur in induced pluripotent stem cells (iPSCs) generated by cellular reprogramming, and further discuss manipulations that can alter heteroplasmy to impact stem and differentiated cell performance. This additional insight will assist in developing more robust iPSC-based models of disease and differentiated cell therapies.

Natural and Artificial Mechanisms of Mitochondrial Genome Elimination

The generally accepted theory of the genetic drift of mitochondrial alleles during mammalian ontogenesis is based on the presence of a selective bottleneck in the female germline. However, there is a variety of different theories on the pathways of genetic regulation of mitochondrial DNA (mtDNA) dynamics in oogenesis and adult somatic cells. The current review summarizes present knowledge on the natural mechanisms of mitochondrial genome elimination during mammalian development. We also discuss the variety of existing and developing methodologies for artificial manipulation of the mtDNA heteroplasmy level. Understanding of the basics of mtDNA dynamics will shed the light on the pathogenesis and potential therapies of human diseases associated with mitochondrial dysfunction.

Roles of Fibroblasts in Microenvironment Formation Associated with Radiation-Induced Cancer

In tumor tissues, activated stromal fibroblasts, termed cancer-associated fibroblasts (CAFs), exhibit similar characteristics to myofibroblasts. CAFs promote cancer cell differentiation and invasion by releasing various factors, such as growth factors, chemokines, and matrix-degrading proteases, into neighboring tumor cells. However, the roles of tumor microenvironment in case of radiation-induced carcinogenesis remain poorly understood. We recently revealed that mitochondrial oxidative stress causes tumor microenvironment formation associated with radiation-induced cancer. Repeated low-dose fractionated radiation progressively damages fibroblast mitochondria and elevates mitochondrial reactive oxygen species (ROS) levels. Excessive mitochondrial ROS activate transforming growth factor-beta (TGF-β) signaling, thereby inducing fibroblasts activation and facilitating tumor microenvironment formation. Consequently, radiation affects malignant cancer cells directly and indirectly via molecular alterations in stromal fibroblasts, such as the activation of TGF-β and angiogenic signaling. This review summarizes for the first time the roles of mitochondrial oxidative stress in microenvironment formation associated with radiation-induced cancer. This review may help us understand the risks of exposure to low-dose radiation. The cross talk between cancer cells and stromal fibroblasts contributes to the development and progression of radiation-induced cancer.

Mitochondria Autoimmunity and MNRR1 in Breast Carcinogenesis: A Review

We review here the evidence for participation of mitochondrial autoimmunity in BC inception and progression and propose a new paradigm that may challenge the prevailing thinking in oncogenesis by suggesting that mitochondrial autoimmunity is a major contributor to breast carcinogenesis and probably to the inception and progression of other solid tumors. It has been shown that MNRR1 mediated mitochondrial-nuclear function promotes BC cell growth and migration and the development of metastasis and constitutes a proof of concept supporting the participation of mitochondrial autoimmunity in breast carcinogenesis. The resemblance of the autoantibody profile in BC detected by IFA with that in the rheumatic autoimmune diseases suggested that studies on the autoantibody response to tumor associated antigens and the characterization of the mtDNA- and nDNA-encoded antigens may provide functional data on breast carcinogenesis. We also review the studies supporting the view that a panel of autoreactive nDNA-encoded mitochondrial antigens in addition to MNRR1 may be involved in breast carcinogenesis. These include GAPDH, PKM2, GSTP1, SPATA5, MFF, ncRNA PINK1-AS/DDOST as probably contributing to BC progression and metastases and the evidence suggesting that DDX21 orchestrates a complex signaling network with participation of JUND and ATF3 driving chronic inflammation and breast tumorigenesis. We suggest that the widespread autoreactivity of mtDNA- and nDNA-encoded mitochondrial proteins found in BC sera may be the reflection of autoimmunity triggered by mitochondrial and non-mitochondrial tumor associated antigens involved in multiple tumorigenic pathways. Furthermore, we suggest that mitochondrial proteins may contribute to mitochondrial dysfunction in BC even if mitochondrial respiration is found to be within normal limits. However, although the studies show that mitochondrial autoimmunity is a major factor in breast cancer inception and progression, it is not the only factor since there is a multiplex autoantibody profile targeting centrosome and stem cell antigens as well as anti-idiotypic antibodies, revealing the complex signaling network involved in breast carcinogenesis. In summary, the studies reviewed here open new, unexpected therapeutic avenues for cancer prevention and treatment of patients with cancer derived from an entirely new perspective of breast carcinogenesis.

Differential regulation of mitochondrial complex I and oxidative stress based on metastatic potential of colorectal cancer cells

Mitochondria serve a vital role in cellular homeostasis as they regulate cell proliferation and death pathways, which are attributed to mitochondrial bioenergetics, free radicals and metabolism. Alterations in mitochondrial functions have been reported in various diseases, including cancer. Colorectal cancer (CRC) is one of the most common metastatic cancer types with high mortality rates. Although mitochondrial oxidative stress has been associated with CRC, its specific mechanism and contribution to metastatic progression remain poorly understood. Therefore, the aims of the present study were to investigate the role of mitochondria in CRC cells with low and high metastatic potential and to evaluate the contribution of mitochondrial respiratory chain (RC) complexes in oncogenic signaling pathways. The present results demonstrated that cell lines with low metastatic potential were resistant to mitochondrial complex I (C-I)-mediated oxidative stress, and had C-I inhibition with impaired mitochondrial functions. These adaptations enabled cells to cope with higher oxidative stress. Conversely, cells with high metastatic potential demonstrated functional C-I with improved mitochondrial function due to coordinated upregulation of mitochondrial biogenesis and metabolic reprogramming. Pharmacological inhibition of C-I in high metastatic cells resulted in increased sensitivity to cell death and decreased metastatic signaling. The present findings identified the differential regulation of mitochondrial functions in CRC cells, based on CRC metastatic potential. Specifically, it was suggested that a functional C-I is required for high metastatic features of cancer cells, and the role of C-I could be further examined as a potential target in the development of novel therapies for diagnosing high metastatic cancer types.