Reduced mtDNA copy number increases the sensitivity of tumor cells to chemotherapeutic drugs

Overcoming the effects of fluid shear stress in ovarian cancer cell lines: Doxorubicin alone or photodynamic priming to target platinum resistance

Resistance to platinum-based chemotherapies remains a significant challenge in advanced-stage high-grade serous ovarian carcinoma, and patients with malignant ascites face the poorest outcomes. It is, therefore, important to understand the effects of ascites, including the associated fluid shear stress (FSS), on phenotypic changes and therapy response, specifically FSS-induced chemotherapy resistance and the underlying mechanisms in ovarian cancer. This study investigated the effects of FSS on response to cisplatin, a platinum-based chemotherapy, and doxorubicin, an anthracycline, both of which are commonly used to manage advanced-stage ovarian cancer. Consistent with prior research, OVCAR-3 and Caov-3 cells cultivated under FSS demonstrated significant resistance to cisplatin. Examination of the role of mitochondria revealed an increase in mitochondrial DNA copy number and intracellular ATP content in cultures grown under FSS, suggesting that changes in mitochondria number and metabolic activity may contribute to platinum resistance. Interestingly, no resistance to doxorubicin was observed under FSS, the first such observation of a lack of resistance under these conditions. Finally, this study demonstrated the potential of photodynamic priming using benzoporphyrin derivative, a clinically approved photosensitizer that localizes in part to mitochondria and endoplasmic reticula, to enhance the efficacy of cisplatin, but not doxorubicin, thereby overcoming FSS-induced platinum resistance.

PYCR3 modulates mtDNA copy number to drive proliferation and doxorubicin resistance in triple-negative breast cancer

Triple-negative breast cancer (TNBC) poses significant challenges in treatment due to its aggressive nature and limited therapeutic targets. Understanding the underlying molecular mechanisms driving TNBC progression and chemotherapy resistance is imperative for developing effective therapeutic strategies. Thus, in this study, we aimed to elucidate the role of pyrroline-5-carboxylate reductase 3 (PYCR3) in TNBC pathogenesis and therapeutic response. We observed that PYCR3 is significantly upregulated in TNBC specimens compared to normal breast tissues, correlating with a poorer prognosis in TNBC patients. Knockdown of PYCR3 not only suppresses TNBC cell proliferation but also reverses acquired resistance of TNBC cells to doxorubicin, a commonly used chemotherapeutic agent. Mechanistically, we identified the mitochondrial localization of PYCR3 in TNBC cells and demonstrated its impact on TNBC cell proliferation and sensitivity to doxorubicin through the regulation of mtDNA copy number and mitochondrial respiration. Importantly, Selective reduction of mtDNA copy number using the mtDNA replication inhibitor 2', 3'-dideoxycytidine effectively recapitulates the phenotypic effects observed in PYCR3 knockout, resulting in decreased TNBC cell proliferation and the reversal of doxorubicin resistance through apoptosis induction. Thus, our study underscores the clinical relevance of PYCR3 and highlight its potential as a therapeutic target in TNBC management. By elucidating the functional significance of PYCR3 in TNBC, our findings contribute to a deeper understanding of TNBC biology and provide a foundation for developing novel therapeutic strategies aimed at improving patient outcomes.

Regulation of metastatic potential by drug repurposing and mitochondrial targeting in colorectal cancer cells

BACKGROUND

Increased mitochondrial activities contributing to cancer cell proliferation, invasion, and metastasis have been reported in different cancers; however, studies on the therapeutic targeting of mitochondria in regulating cell proliferation and invasiveness are limited. Because mitochondria are believed to have evolved through bacterial invasion in mammalian cells, antibiotics could provide an alternative approach to target mitochondria, especially in cancers with increased mitochondrial activities. In this study, we investigated the therapeutic potential of bacteriostatic antibiotics in regulating the growth potential of colorectal cancer (CRC) cells, which differ in their metastatic potential and mitochondrial functions.

METHODS

A combination of viability, cell migration, and spheroid formation assays was used to measure the effect on metastatic potential. The effect on mitochondrial mechanisms was investigated by measuring mitochondrial DNA copy number by qPCR, biogenesis (by qPCR and immunoblotting), and functions by measuring reactive oxygen species, membrane potential, and ATP using standard methods. In addition, the effect on assembly and activities of respiratory chain (RC) complexes was determined using blue native gel electrophoresis and in-gel assays, respectively). Changes in metastatic and cell death signaling were measured by immunoblotting with specific marker proteins and compared between CRC cells.

RESULTS

Both tigecycline and tetracycline effectively reduced the viability, migration, and spheroid-forming capacity of highly metastatic CRC cells. This increased sensitivity was attributed to reduced mtDNA content, mitochondrial biogenesis, ATP content, membrane potential, and increased oxidative stress. Specifically, complex I assembly and activity were significantly inhibited by these antibiotics in high-metastatic cells. Significant down-regulation in the expression of mitochondrial-mediated survival pathways, such as phospho-AKT, cMYC, phospho-SRC, and phospho-FAK, and upregulation in cell death (apoptosis and autophagy) were observed, which contributed to the enhanced sensitivity of highly metastatic CRC cells toward these antibiotics. In addition, the combined treatment of the CRC chemotherapeutic agent oxaliplatin with tigecycline/tetracycline at physiological concentrations effectively sensitized these cells at early time points.

CONCLUSION

Altogether, our study reports that bacterial antibiotics, such as tigecycline and tetracycline, target mitochondrial functions specifically mitochondrial complex I architecture and activity and would be useful in combination with cancer chemotherapeutics for high metastatic conditions.

Mitochondrial metabolism as a dynamic regulatory hub to malignant transformation and anti-cancer drug resistance

Glycolysis is the fundamental cellular process that permits cancer cells to convert energy and grow anaerobically. Recent developments in molecular biology have made it evident that mitochondrial respiration is critical to tumor growth and treatment response. As the principal organelle of cellular energy conversion, mitochondria can rapidly alter cellular metabolic processes, thereby fueling malignancies and contributing to treatment resistance. This review emphasizes the significance of mitochondrial biogenesis, turnover, DNA copy number, and mutations in bioenergetic system regulation. Tumorigenesis requires an intricate cascade of metabolic pathways that includes rewiring of the tricarboxylic acid (TCA) cycle, electron transport chain and oxidative phosphorylation, supply of intermediate metabolites of the TCA cycle through amino acids, and the interaction between mitochondria and lipid metabolism. Cancer recurrence or resistance to therapy often results from the cooperation of several cellular defense mechanisms, most of which are connected to mitochondria. Many clinical trials are underway to assess the effectiveness of inhibiting mitochondrial respiration as a potential cancer therapeutic. We aim to summarize innovative strategies and therapeutic targets by conducting a comprehensive review of recent studies on the relationship between mitochondrial metabolism, tumor development and therapeutic resistance.

Different impact of vitamin D on mitochondrial activity and morphology in normal and malignant keratinocytes, the role of genomic pathway

Deregulation of mitochondria activity is one of the hallmarks of cancerogenesis and an important target for cancer therapy. Therefore, we compared the impact of an active form of vitamin D3 (1,25(OH)2D3) on mitochondrial morphology and bioenergetics in human squamous cell carcinoma (A431) and immortalized HaCaT keratinocytes. It was shown that mitochondria of cancerous A431 cells differ from that observed in HaCaT keratinocytes in terms of network, morphology, bioenergetics, glycolysis, and mitochondrial DNA copy number, while treatment of A431 with 1,25(OH)2D3 partially eliminates these differences. Furthermore, mitochondrial membrane potential, basal respiration, and mitochondrial reactive oxygen species production were decreased in A431 cells treated with 1,25(OH)2D3. Additionally, the expression and protein level of mitophagy marker PINK1 was significantly increased in A431 1,25(OH)2D3 treated cells, but not observed in treated HaCaT cells. Knockout of VDR (vitamin D receptor) or RXRA (binding partner retinoid X receptor) partially altered mitochondrial morphology and function as well as mitochondrial response to 1,25(OH)2D3. Transcriptomic analysis on A431 cells treated with 1,25(OH)2D3 revealed modulation of expression of several mitochondrial-related genes involved in mitochondrial depolarization, mitochondrial protein translation (i.e. LYRM9, MARS2), and fusion-fission (OPA1, FIS1, MFN1 and 2), however, none of the genes coded by mitochondrial DNA was affected. Interestingly, in silico analyses of nuclear-encoded mitochondrial genes revealed that they are rather activated by the secondary genomic response to 1,25(OH)2D3. Taken together, 1,25(OH)2D3 remodels mitochondrial architecture and bioenergetics through VDR-dependent and only partially RXRA-dependent activation of the genomic pathway, thus outlining a new perspective for anticancer properties of vitamin D3 in relation to mitochondria in squamous cell carcinoma.

Altered mitochondrial DNA copy number in cervical exfoliated cells among high‑risk HPV‑positive and HPV‑negative women

The majority of cervical cancer cases are due to human papillomavirus (HPV) infection. However, certain cases of cervical cancer are not caused by HPV. Recent studies have shown a link between altered mitochondrial DNA (mtDNA) copy number, an indicative measure of mitochondrial dysfunction, and cervical cancer in women who test positive for HPV. However, the role of the mtDNA copy number in HPV-negative cervical cancer has remained elusive. In the present study, the mtDNA copy number was determined using quantitative PCR as the ratio between mtDNA and nuclear DNA in 287 ThinPrep cervical samples, including 143 cases with cervical abnormalities and 144 control subjects with high-risk (hr)-HPV positive or HPV-negative status. In an overall analysis of cases categorized based on the cytology diagnosis into squamous cervical carcinoma/high-grade squamous intraepithelial lesions (SCC/HSIL), low-grade squamous intraepithelial lesions (LSIL) and normal controls, the mtDNA copy number was significantly higher in all cases compared to the controls and a higher mtDNA copy number was observed in SCC/HSIL compared to LSIL cases. In the stratification analyses based on hr-HPV positive and HPV-negative status, an increased mtDNA copy number was observed in the cases compared with the controls regardless of their HPV status (P<0.05). When cases with cervical abnormalities were categorized based on histological diagnosis into cervical intraepithelial neoplasia (CIN)2/CIN3 and CIN1, an overall analysis indicated an increased mtDNA copy number in CIN2/CIN3 compared to CIN1 (P=0.01). Stratification analyses of these cases based on HPV status revealed a higher mtDNA copy number in CIN2/CIN3 compared to CIN1 regardless of HPV infection (P<0.05). These results showed that an elevated mtDNA copy number in subjects with cervical abnormalities was not influenced by the HPV status and suggested the possibility of its role in the progression of cervical cancer. The increased mtDNA copy number may be an adaptive response mechanism to compensate for mtDNA oxidative stress and energy deficiency, possibly induced by HPV infection and other environmental exposures.

Methods to Evaluate Changes in Mitochondrial Structure and Function in Cancer

Mitochondria are regulators of key cellular processes, including energy production and redox homeostasis. Mitochondrial dysfunction is associated with various human diseases, including cancer. Importantly, both structural and functional changes can alter mitochondrial function. Morphologic and quantifiable changes in mitochondria can affect their function and contribute to disease. Structural mitochondrial changes include alterations in cristae morphology, mitochondrial DNA integrity and quantity, and dynamics, such as fission and fusion. Functional parameters related to mitochondrial biology include the production of reactive oxygen species, bioenergetic capacity, calcium retention, and membrane potential. Although these parameters can occur independently of one another, changes in mitochondrial structure and function are often interrelated. Thus, evaluating changes in both mitochondrial structure and function is crucial to understanding the molecular events involved in disease onset and progression. This review focuses on the relationship between alterations in mitochondrial structure and function and cancer, with a particular emphasis on gynecologic malignancies. Selecting methods with tractable parameters may be critical to identifying and targeting mitochondria-related therapeutic options. Methods to measure changes in mitochondrial structure and function, with the associated benefits and limitations, are summarized.

Cisplatin in Ovarian Cancer Treatment-Known Limitations in Therapy Force New Solutions

Cisplatin is one of the most commonly used anticancer drugs worldwide. It is mainly used in the treatment of ovarian cancer, but also used in testicular, bladder and lung cancers. The significant advantage of this drug is the multidirectional mechanism of its anticancer action, with the most important direction being damaging the DNA of cancer cells. Unfortunately, cisplatin displays a number of serious disadvantages, including toxicity to the most important organs, such as kidneys, heart, liver and inner ear. Moreover, a significant problem among patients with ovarian cancer, treated with cisplatin, is the development of numerous resistance mechanisms during therapy, including changes in the processes of cellular drug import and export, changes in the DNA damage repair mechanisms, as well as numerous changes in the processes of apoptosis and autophagy. Due to all of the mentioned problems, strategies to increase the effectiveness of cisplatin in the treatment of ovarian cancer are intensively sought. The most important strategy includes the development of less toxic cisplatin analogs. Another important direction is combination therapy, involving the simultaneous use of cisplatin with different anticancer drugs, substances derived from plants, temperature or radiotherapy. Many years of observations accompanying the presence of cisplatin in the therapy made it possible to provide a series of verifiable, statistically significant data, but also to show how, over time, with the new information and scientific discoveries, it is possible to describe and understand the therapeutic problems observed in practice, such as the acquisition of drug resistance by tumor cells or induction of changes in the tumor microenvironment. According to the authors, confronting what we knew so far with what new trends offer has a profound meaning. This paper presents information on the history of cisplatin and describes the molecular mechanisms of its action and the development of resistance by cancer cells. In addition, our goal was to highlight a number of therapeutic strategies to increase the effectiveness of cisplatin in the treatment of ovarian cancer, as well as to identify methods to eliminate problems associated with the use of cisplatin.

Associations of mitochondrial DNA copy number with incident risks of gastrointestinal cancers: A prospective case-cohort study

Epidemiological investigations implied that mitochondrial DNA copy number (mtDNAcn) variations could trigger predisposition to multiple cancers, but evidence regarding gastrointestinal cancers (GICs) was still uncertain. We conducted a case-cohort study within the prospective Dongfeng-Tongji cohort, including incident cases of colorectal cancer (CRC, n = 278), gastric cancer (GC, n = 138), and esophageal cancer (EC, n = 72) as well as a random subcohort (n = 1173), who were followed up from baseline to the end of 2018. We determined baseline blood mtDNAcn and associations of mtDNAcn with the GICs risks were estimated by using weighted Cox proportional hazards models. Significant U-shaped associations were observed between mtDNAcn and GICs risks. Compared to subjects within the second quartile (Q2) mtDNAcn subgroup, those within the 1st (Q1), 3rd (Q3), and 4th (Q4) quartile subgroups showed increased risks of CRC (hazard ratio [HR] [95% confidence interval, CI] = 2.27 [1.47-3.52], 1.65 [1.04-2.62], and 2.81 [1.85-4.28], respectively) and total GICs (HR [95%CI] = 1.84 [1.30-2.60], 1.47 [1.03-2.10], and 2.51 [1.82-3.47], respectively], and those within Q4 subgroup presented elevated GC and EC risks (HR [95% CI] = 2.16 [1.31-3.54] and 2.38 [1.13-5.02], respectively). Similar associations of mtDNAcn with CRC and total GICs risks remained in stratified analyzes by age, gender, smoking, and drinking status. This prospective case-cohort study showed U-shaped associations between mtDNAcn and GICs risks, but further research works are needed to uncover underlying biological mechanisms.

Peanut AhmTERF1 Regulates Root Growth by Modulating Mitochondrial Abundance

Mitochondria are responsible for energy generation, as well as key metabolic and signaling pathways, and thus affect the entire developmental process of plants as well as their responses to stress. In metazoans, mitochondrial transcription termination factors (mTERFs) are known to regulate mitochondrial transcription. mTERFs have also been discovered in plants, but only a few of these proteins have been explored for their biological functions. Here, we report a role in root growth for mitochondria-associated protein AhmTERF1 in peanut (Arachis hypogaea L.). Overexpressing AhmTERF1 significantly stimulated the growth of peanut hairy roots and transgenic Arabidopsis. Surprisingly, AhmTERF1 is predominantly expressed in the root meristem where it increases mitochondrial abundance. AhmTERF1 binding to mtDNA was enriched in the RRN18 and RRN26 regions, suggesting it is related to the accumulation of mitochondrial ribosomes. Peanut is one of the main oil crops and the important source of edible oil and AhmTERF1 likely affects agronomic traits related to root growth in different peanut cultivars. We propose that peanut AhmTERF1 is an important protein for root growth due to its role in regulating mitochondrial abundance.

Anticancer Properties of Plectranthus ornatus-Derived Phytochemicals Inducing Apoptosis via Mitochondrial Pathway

Since cancer treatment by radio- and chemotherapy has been linked to safety concerns, there is a need for new and alternative anticancer drugs; as such, compounds isolated from plants represent promising candidates. The current study investigates the anticancer features of halimane (11R*,13E)-11-acetoxyhalima-5,13-dien-15-oic acid (HAL) and the labdane diterpenes 1α,6β-diacetoxy-8α,13R*-epoxy-14-labden-11-one (PLEC) and forskolin-like 1:1 mixture of 1,6-di-O-acetylforskolin and 1,6-di-O-acetyl-9-deoxyforskolin (MRC) isolated from Plectranthus ornatus in MCF7 and FaDu cancer cell lines. Cytotoxicity was assessed by MTT assay, ROS production by Di-chloro-dihydro-fluorescein diacetate assay (DCFH) or Red Mitochondrial Superoxide Indicator (MitoSOX) and Mitochondrial Membrane Potential (MMP) by fluorescent probe JC-1 (5′,6,6′-tetrachloro-1,1′,3,3′-tetraethylbenzimidazolylcarbocyanine iodide). In addition, the relative amounts of mitochondrial DNA (mtDNA) were determined using quantitative Real-Time-PCR (qRT-PCR) and damage to mitochondrial DNA (mtDNA) and nuclear DNA (nDNA) by semi-long run quantitative Real-Time-PCR (SLR-qRT-PCR). Gene expression was determined using Reverse-Transcription-qPCR. Caspase-3/7 activity by fluorescence was assessed. Assessment of General In Vivo Toxicity has been determined by Brine Shrimp Lethality Bioassay. The studied HAL and PLEC were found to have a cytotoxic effect in MCF7 with IC₅₀ = 13.61 µg/mL and IC₅₀ = 17.49 µg/mL and in FaDu with IC₅₀ = 15.12 µg/mL and IC₅₀ = 32.66 µg/mL cancer cell lines. In the two tested cancer cell lines, the phytochemicals increased ROS production and mitochondrial damage in the ND1 and ND5 gene regions and reduced MMP (ΔΨm) and mitochondrial copy numbers. They also changed the expression of pro- and anti-apoptotic genes (Bax, Bcl-2, TP53, Cas-3, Cas-8, Cas-9, Apaf-1 and MCL-1). Studies demonstrated increase in caspase 3/7 activity in tested cancer cell lines. In addition, we showed no toxic effect in in vivo test for the compounds tested. The potential mechanism of action may have been associated with the induction of apoptosis in MCF7 and FaDu cancer cells via the mitochondrial pathway; however, further in vivo research is needed to understand the mechanisms of action and potential of these compounds.

Low mitochondrial DNA copy number induces chemotherapy resistance via epithelial-mesenchymal transition by DNA methylation in esophageal squamous cancer cells

Background

Esophageal squamous cell carcinoma (ESCC) is one of the most severe cancers and is characterized by chemotherapy resistance and poor prognosis associated with epithelial-mesenchymal transition (EMT). In a previous study, a low mitochondrial DNA (mtDNA) copy number was associated with poorer prognosis and induced EMT in ESCC. However, the detailed mechanism related to mtDNA copy number and EMT is unclear. The aim of this study was to clarify the mechanism by which a change in mtDNA copy number contributes to EMT and to examine treatment of chemotherapy resistance in ESCC.

Methods

The association between low mtDNA copy number and chemotherapy resistance was investigated using specimens from 88 patients who underwent surgery after neoadjuvant chemotherapy. Then, the mtDNA content of human ESCC cell lines, TE8 and TE11, was depleted by knockdown of mitochondrial transcription factor A expression. The present study focused on modulation of mitochondrial membrane potential (MMP) and DNA methylation as the mechanisms by which mtDNA copy number affects EMT. mRNA and protein expression, chemotherapy sensitivity, proliferation, MMP and DNA methylation were evaluated, and in vitro and in vivo assays were conducted to clarify these mechanisms.

Results

ESCC patients with decreased mtDNA copy number who underwent R0 resection after neoadjuvant chemotherapy had significantly worse pathological response and recurrence-free survival. Additionally, low mtDNA copy number was associated with resistance to chemotherapy in vitro and in vivo. mtDNA controlled MMP, and MMP depolarization induced EMT. Depletion of mtDNA and low MMP induced DNA methylation via a DNA methylation transcription factor (DNMT), and a DNMT inhibitor suppressed EMT and improved chemotherapy sensitivity in mtDNA-depleted ESCC cells, as shown by in vitro and in vivo assays.

Conclusion

This study showed that decreased mtDNA copy number induced EMT via modulation of MMP and DNA methylation in ESCC. Therapeutic strategies increasing mtDNA copy number and DNMT inhibitors may be effective in preventing EMT and chemosensitivity resistance.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12967-022-03594-2.

Insights regarding mitochondrial DNA copy number alterations in human cancer (Review)

Mitochondria are the critical organelles involved in various cellular functions. Mitochondrial biogenesis is activated by multiple cellular mechanisms which require a synchronous regulation between mitochondrial DNA (mtDNA) and nuclear DNA (nDNA). The mitochondrial DNA copy number (mtDNA-CN) is a proxy indicator for mitochondrial activity, and its alteration reflects mitochondrial biogenesis and function. Despite the precise mechanisms that modulate the amount and composition of mtDNA, which have not been fully elucidated, mtDNA-CN is known to influence numerous cellular pathways that are associated with cancer and as well as multiple other diseases. In addition, the utility of current technology in measuring mtDNA-CN contributes to its extensive assessment of diverse traits and tumorigenesis. The present review provides an overview of mtDNA-CN variations across human cancers and an extensive summary of the existing knowledge on the regulation and machinery of mtDNA-CN. The current information on the advanced methods used for mtDNA-CN assessment is also presented.

Integrated transcriptomic and proteomic analyses for the characterization of parathyroid oxyphil cells in uremic patients

Chief cells are the predominant cells in parathyroid glands of healthy adults; however, parathyroid oxyphil cells, whose function is unknown, increase dramatically in patients with secondary hyperparathyroidism (SHPT). Calcitriol and calcimimetics are the most powerful treatments for SHPT, while the mechanisms leading to calcitriol or calcimimetic resistance in oxyphil cell-predominant SHPT are unknown. Here we used transcriptomic and proteomic techniques to characterize oxyphil cells by comparing the differences between chief and oxyphil cell nodules of parathyroid glands in uremic patients. Compared to chief cell nodules, the most marked expression increases in oxyphil cell nodules were for mitochondrion-associated proteins. The mitochondria number and mitochondrial DNA content were also significantly increased in oxyphil cell nodules. Moreover, oxyphil cell nodules expressed parathyroid-specific factors, and exhibited lower levels of proliferation-related proteins but higher synthesis and secretion level of parathyroid hormone (PTH). The protein expression of SHPT-regulating factors, including vitamin-D receptor, calcium-sensing receptor and Klotho, were significantly downregulated in oxyphil cell nodules. Therefore, oxyphil cells characterized by enrich mitochondria in uremic patients showed higher synthesis and secretion of PTH but lower expression of SHPT regulators than chief cells, which may contribute to the pathophysiology of SHPT and the treatment resistance to calcitriol and calcimimetics.

Inhibition of PRMT6 reduces neomycin-induced inner ear hair cell injury through the restraint of FoxG1 arginine methylation

OBJECTIVE

Hair cells in the inner ear have been demonstrated to be sensitive to the ototoxicity from some beneficial pharmaceutical drugs. This study aimed to explore the role of protein arginine methyltransferase 6 (PRMT6) in the process of neomycin-induced hearing loss and the underlying mechanism.

METHODS

The neomycin-induced hearing loss mouse model and hair cell injury in vitro model were established. We took advantage of the HEI-OC1 cell line to evaluate PRMT6 expression in neomycin-induced hair cells, and the effect of PRMT6 on mitochondrial function and FoxG1 arginine methylation. Apoptotic cells were assessed and apoptotic marker cleaved caspase-3 level was detected. Reactive oxygen species (ROS) level and mitochondrial membrane potential (MMP) were subsequently measured.

RESULT

The result showed that PRMT6 was significantly upregulated in neomycin-induced HEI-OC-1 cells, and PRMT6 silencing prevented MMP loss, reduced ROS production, as well as decreased cell apoptosis under neomycin treatment. Further results showed that FoxG1 was downregulated in neomycin-induced HEI-OC-1 cells, and PRMT6 promoted the FoxG1-mediated luciferase activity, while PRMT6 silencing reversed this effect. Mechanistic experiments revealed that PRMT6 silencing reduced the arginine methylation level of FoxG1 protein. In vivo, neomycin-induced upregulation of hearing thresholds and increased cell apoptosis, whereas PRMT6 inhibitor partly reversed these effects.

CONCLUSION

Our findings suggested that inhibition of PRMT6 reduced neomycin-induced inner ear hair cell injury through the restraint of FoxG1 arginine methylation.

HEK293T Cells with TFAM Disruption by CRISPR-Cas9 as a Model for Mitochondrial Regulation

The mitochondrial transcription factor A (TFAM) is considered a key factor in mitochondrial DNA (mtDNA) copy number. Given that the regulation of active copies of mtDNA is still not fully understood, we investigated the effects of CRISPR-Cas9 gene editing of TFAM in human embryonic kidney (HEK) 293T cells on mtDNA copy number. The aim of this study was to generate a new in vitro model by CRISPR-Cas9 system by editing the TFAM locus in HEK293T cells. Among the resulting single-cell clones, seven had high mutation rates (67-96%) and showed a decrease in mtDNA copy number compared to control. Cell staining with Mitotracker Red showed a reduction in fluorescence in the edited cells compared to the non-edited cells. Our findings suggest that the mtDNA copy number is directly related to TFAM control and its disruption results in interference with mitochondrial stability and maintenance.

Effects of Pesticides on Longevity and Bioenergetics in Invertebrates-The Impact of Polyphenolic Metabolites

Environmentally hazardous substances such as pesticides are gaining increasing interest in agricultural and nutritional research. This study aims to investigate the impact of these compounds on the healthspan and mitochondrial functions in an invertebrate in vivo model and in vitro in SH-SY5Y neuroblastoma cells, and to investigate the potential of polyphenolic metabolites to compensate for potential impacts. Wild-type nematodes (Caenorhabditis elegans, N2) were treated with pesticides such as pyraclostrobin (Pyr), glyphosate (Gly), or fluopyram (Fluo). The lifespans of the nematodes under heat stress conditions (37 °C) were determined, and the chemotaxis was assayed. Energetic metabolites, including adenosine triphosphate (ATP), lactate, and pyruvate, were analyzed in lysates of nematodes and cells. Genetic expression patterns of several genes associated with lifespan determination and mitochondrial parameters were assessed via qRT-PCR. After incubation with environmentally hazardous substances, nematodes were incubated with a pre-fermented polyphenol mixture (Rechtsregulat^®Bio, RR) or protocatechuic acid (PCA) to determine heat stress resistance. Treatment with Pyr, Glyph and Fluo leads to dose-dependently decreased heat stress resistance, which was significantly improved by RR and PCA. The chemotaxes of the nematodes were not affected by pesticides. ATP levels were not significantly altered by the pesticides, except for Pyr, which increased ATP levels after 48 h leads. The gene expression of healthspan and mitochondria-associated genes were diversely affected by the pesticides, while Pyr led to an overall decrease of mRNA levels. Over time, the treatment of nematodes leads to a recovery of the nematodes on the mitochondrial level but not on stress resistance on gene expression. Fermented extracts of fruits and vegetables and phenolic metabolites such as PCA seem to have the potential to recover the vitality of C. elegans after damage caused by pesticides.

YAP1-mediated regulation of mitochondrial dynamics in IDH1 mutant gliomas

Mutation of the isocitrate dehydrogenase 1 (IDH1) gene leads to the production of oncometabolite D-2-hydroxyglutarate (2-HG) from α-ketoglutarate and is associated with better prognosis in glioma. As Yes-associated protein 1 (YAP1) is an important regulator of tumor progression, its role in glioma expressing IDH1 with an R132H mutation was investigated. Diminished nuclear levels of YAP1 in IDH1 mutant glioma tissues and cell lines were accompanied by decreased levels of mitochondrial transcription factor A (TFAM). Luciferase reporter assays and chromatin immunoprecipitation were used to investigate the functionality of the TEAD2-binding site on the TFAM promoter in mediating its YAP1-dependent expression. YAP1-dependent mitochondrial fragmentation and ROS generation were accompanied by decreased telomerase reverse transcriptase (TERT) levels and increased mitochondrial TERT localization in IDH1 R132H cells. Treatment with the Src kinase inhibitor bosutinib, which prevents extranuclear shuttling of TERT, further elevated ROS in IDH1 R132H cells and triggered apoptosis. Importantly, bosutinib treatment also increased ROS levels and induced apoptosis in IDH1 wild-type cells when YAP1 was concurrently depleted. These findings highlight the involvement of YAP1 in coupling mitochondrial dysfunction with mitochondrial shuttling of TERT to constitute an essential non-canonical function of YAP1 in the regulation of redox homeostasis. This article has an associated First Person interview with the first author of the paper.

Cashing in on ferroptosis against tumor cells: Usher in the next chapter

Ferroptosis is a new type of non-apoptotic regulated cell death (RCD) driven by unrestricted lethal lipid peroxidation, which is totally distinct from other forms of RCD in genetic and biochemical characteristics. It is generally believed that iron dependency, malfunction of the redox system, and excessive lipid peroxidation are the main hallmarks of ferroptosis. Accumulating pieces of evidence over the past few years have shown that ferroptosis is tightly related to various types of diseases, especially cancers. Ferroptosis has recently attracted great attention in the field of cancer research. A plethora of evidence shows that employing ferroptosis as a powerful weapon can remarkably enhance the efficacy of tumor cell annihilation. Better knowledge of the ferroptosis mechanisms and their interplay with cancer biology would enable us to use this fashionable tool in the best way. Herein, we will briefly present the relevant mechanisms of ferroptosis, the multifaceted relation between ferroptosis and cancer, encompassing tumor immunity, overcoming chemoresistance, and epithelial to mesenchymal transition. In the end, we will also briefly discuss the potential approaches to ferroptosis-based cancer therapy, such as using drugs and small molecules, nanoparticles, mitochondrial targeting, and photodynamic therapy.

Pomegranate Extract (POMx) Induces Mitochondrial Dysfunction and Apoptosis of Oral Cancer Cells

The anticancer effect of pomegranate polyphenolic extract POMx in oral cancer cells has rarely been explored, especially where its impact on mitochondrial functioning is concerned. Here, we attempt to evaluate the proliferation modulating function and mechanism of POMx against human oral cancer (Ca9-22, HSC-3, and OC-2) cells. POMx induced ATP depletion, subG1 accumulation, and annexin V/Western blotting-detected apoptosis in these three oral cancer cell lines but showed no toxicity to normal oral cell lines (HGF-1). POMx triggered mitochondrial membrane potential (MitoMP) disruption and mitochondrial superoxide (MitoSOX) generation associated with the differential downregulation of several antioxidant gene mRNA/protein expressions in oral cancer cells. POMx downregulated mitochondrial mass, mitochondrial DNA copy number, and mitochondrial biogenesis gene mRNA/protein expression in oral cancer cells. Moreover, POMx induced both PCR-based mitochondrial DNA damage and γH2AX-detected nuclear DNA damage in oral cancer cells. In conclusion, POMx provides antiproliferation and apoptosis of oral cancer cells through mechanisms of mitochondrial impairment.

Systematic Analysis of Survival-Associated Alternative Splicing Signatures in Thyroid Carcinoma

Alternative splicing (AS) is a key mechanism involved in regulating gene expression and is closely related to tumorigenesis. The incidence of thyroid cancer (THCA) has increased during the past decade, and the role of AS in THCA is still unclear. Here, we used TCGA and to generate AS maps in patients with THCA. Univariate analysis revealed 825 AS events related to the survival of THCA. Five prognostic models of AA, AD, AT, ES, and ME events were obtained through lasso and multivariate analyses, and the final prediction model was established by integrating all the AS events in the five prediction models. Kaplan–Meier survival analysis revealed that the overall survival rate of patients in the high-risk group was significantly shorter than that of patients in the low-risk group. The ROC results revealed that the prognostic capabilities of each model at 3, 5, and 8 years were all greater than 0.7, and the final prognostic capabilities of the models were all greater than 0.9. By reviewing other databases and utilizing qPCR, we verified the established THCA gene model. In addition, gene set enrichment analysis showed that abnormal AS events might play key roles in tumor development and progression of THCA by participating in changes in molecular structure, homeostasis of the cell environment and in cell energy. Finally, a splicing correlation network was established to reveal the potential regulatory patterns between the predicted splicing factors and AS event candidates. In summary, AS should be considered an important prognostic indicator of THCA. Our results will help to elucidate the underlying mechanism of AS in the process of THCA tumorigenesis and broaden the prognostic and clinical application of molecular targeted therapy for THCA.

Discovering Cellular Mitochondrial Heteroplasmy Heterogeneity with Single Cell RNA and ATAC Sequencing

Next-generation sequencing technologies have revolutionised the study of biological systems by enabling the examination of a broad range of tissues. Its application to single-cell genomics has generated a dynamic and evolving field with a vast amount of research highlighting heterogeneity in transcriptional, genetic and epigenomic state between cells. However, compared to these aspects of cellular heterogeneity, relatively little has been gleaned from single-cell datasets regarding cellular mitochondrial heterogeneity. Single-cell sequencing techniques can provide coverage of the mitochondrial genome which allows researchers to probe heteroplasmies at the level of the single cell, and observe interactions with cellular function. In this review, we give an overview of two popular single-cell modalities-single-cell RNA sequencing and single-cell ATAC sequencing-whose throughput and widespread usage offers researchers the chance to probe heteroplasmy combined with cell state in detailed resolution across thousands of cells. After summarising these technologies in the context of mitochondrial research, we give an overview of recent methods which have used these approaches for discovering mitochondrial heterogeneity. We conclude by highlighting current limitations of these approaches and open problems for future consideration.

FOXG1 promotes aging inner ear hair cell survival through activation of the autophagy pathway

Presbycusis is the cumulative effect of aging on hearing. Recent studies have shown that common mitochondrial gene deletions are closely related to deafness caused by degenerative changes in the auditory system, and some of these nuclear factors are proposed to participate in the regulation of mitochondrial function. However, the detailed mechanisms involved in age-related degeneration of the auditory systems have not yet been fully elucidated. In this study, we found that FOXG1 plays an important role in the auditory degeneration process through regulation of macroautophagy/autophagy. Inhibition of FOXG1 decreased the autophagy activity and led to the accumulation of reactive oxygen species and subsequent apoptosis of cochlear hair cells. Recent clinical studies have found that aspirin plays important roles in the prevention and treatment of various diseases by regulating autophagy and mitochondria function. In this study, we found that aspirin increased the expression of FOXG1, which further activated autophagy and reduced the production of reactive oxygen species and inhibited apoptosis, and thus promoted the survival of mimetic aging HCs and HC-like OC-1 cells. This study demonstrates the regulatory function of the FOXG1 transcription factor through the autophagy pathway during hair cell degeneration in presbycusis, and it provides a new molecular approach for the treatment of age-related hearing loss.

Abbreviations: AHL: age-related hearing loss; baf: bafilomycin A1; CD: common deletion; D-gal: D-galactose; GO: glucose oxidase; HC: hair cells; mtDNA: mitochondrial DNA; RAP: rapamycin; ROS: reactive oxygen species; TMRE: tetramethylrhodamine, ethyl ester

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.

Effect of mtDNA depletion from C6 glioma cells and characteristics of the generated C6ρ0 cells

Malignant tumors of the central nervous system (CNS) are among the types of cancer with the poorest prognosis and glioma is the commonest primary CNS tumor. A mitochondrial DNA (mtDNA)-depleted cell line C6ρ0 was generated from C6 glioma cells after long-term exposure to ethidium bromide and 2′,3′-dideoxycytidine in order to determine the effect of mtDNA damage on cell proliferation and pathological changes in glioma cells. Single cell clones were isolated and identified after 42 days of incubation. Repopulated cybrids were formed when the clonal C6ρ0 cells were fused with rat platelets and no difference was observed in their growth in a selective medium without uridine and pyruvate compared with the growth of the parent C6 cells. Disruption of mtDNA resulted in changes in mitochondrial morphology, decreased cell proliferation, reduced intracellular reactive oxygen species and intracellular ATP, along with decreased mtDNA and mitochondrial membrane potential in C6ρ0 cells compared with the C6 cells. Taken together, C6ρ0 cells without mtDNA were established for the first time and their characteristics were compared with parent cells. This C6ρ0 cell line could be used to explore the contribution of mitochondrial dysfunction and mtDNA mutations in the pathogenesis of glioma.

The Influence of Obesity and Associated Fatty Acids on Placental Inflammation

PURPOSE

Maternal obesity, affecting nearly 1 in 4 pregnancies, is associated with increased circulating saturated fatty acids, such as palmitate. These fatty acids are implicated in placental inflammation, which may in turn exacerbate both maternal-fetal tolerance and responses to pathogens, such as group B Streptococcus. In this review, we address the question, "How do obesity and associated fatty acids influence placental inflammation?"

METHODS

In this narrative review, we searched PubMed and Google Scholar using combinations of the key words placental inflammation or pregnancy and lipids, fatty acids, obesity, palmitate, or other closely related search terms. We also used references found within these articles that may have been absent from our original search queries. We analyzed methods and key results of these articles to compare and contrast their findings, which were occasionally at odds with each other.

FINDINGS

Although obesity can be studied as a whole, complex phenomena with in vivo mouse models and human samples from patients with obesity, in vitro modeling often relies on the treatment of cells or tissues with ≥1 fatty acids and occasionally other compounds (eg, glucose and insulin). We found that palmitate, most commonly used in vitro to recreate hallmarks of obesity, induces apoptosis, oxidative stress, mitochondrial dysfunction, autophagy defects, and inflammasome activation in many placental cell types. We compare this to in vivo models of obesity wherever possible. We found that obesity as a whole may have more complex regulation of these phenomena (apoptosis, oxidative stress, mitochondrial dysfunction, autophagy defects, and inflammasome activation) compared with in vitro models of fatty acid treatment (primarily palmitate) because of the presence of unsaturated fatty acids (ie, oleate), which may have anti-inflammatory effects.

IMPLICATIONS

The interaction of unsaturated fatty acids with saturated fatty acids may ameliorate many inflammatory effects of saturated fatty acids alone, which complicates interpretation of in vitro studies that focus on a particular fatty acid in isolation. This complication may explain why certain studies of obesity in vivo have differing outcomes from studies of specific fatty acids in vitro.

Visualizing, quantifying, and manipulating mitochondrial DNA in vivo

Mitochondrial DNA (mtDNA) encodes proteins and RNAs that support the functions of mitochondria and thereby numerous physiological processes. Mutations of mtDNA can cause mitochondrial diseases and are implicated in aging. The mtDNA within cells is organized into nucleoids within the mitochondrial matrix, but how mtDNA nucleoids are formed and regulated within cells remains incompletely resolved. Visualization of mtDNA within cells is a powerful means by which mechanistic insight can be gained. Manipulation of the amount and sequence of mtDNA within cells is important experimentally and for developing therapeutic interventions to treat mitochondrial disease. This review details recent developments and opportunities for improvements in the experimental tools and techniques that can be used to visualize, quantify, and manipulate the properties of mtDNA within cells.

Citicoline Protects Auditory Hair Cells Against Neomycin-Induced Damage

Aminoglycoside-induced hair cell (HC) loss is one of the most important causes of hearing loss. After entering the inner ear, aminoglycosides induce the production of high levels of reactive oxygen species (ROS) that subsequently activate apoptosis in HCs. Citicoline, a nucleoside derivative, plays a therapeutic role in central nervous system injury and in neurodegenerative disease models, including addictive disorders, stroke, head trauma, and cognitive impairment in the elderly, and has been widely used in the clinic as an FDA approved drug. However, its effect on auditory HCs remains unknown. Here, we used HC-like HEI-OC-1 cells and whole organ explant cultured mouse cochleae to explore the effect of citicoline on aminoglycoside-induced HC damage. Consistent with previous reports, both ROS levels and apoptosis were significantly increased in neomycin-induced cochlear HCs and HEI-OC-1 cells compared to undamaged controls. Interestingly, we found that co-treatment with citicoline significantly protected against neomycin-induced HC loss in both HEI-OC-1 cells and whole organ explant cultured cochleae. Furthermore, we demonstrated that citicoline could significantly reduce neomycin-induced mitochondrial dysfunction and inhibit neomycin-induced ROS accumulation and subsequent apoptosis. Thus, we conclude that citicoline can protect against neomycin-induced HC loss by inhibiting ROS aggregation and thus preventing apoptosis in HCs, and this suggests that citicoline might serve as a potential therapeutic drug in the clinic to protect HCs.

Reduced mitochondrial DNA copy number is associated with the haplogroup, and some clinical features of breast cancer in Mexican patients

Mitochondrial DNA (mtDNA) copy number and mitochondrial DNA haplogroups have been associated with different types of cancer, including breast cancer, because they alter cellular energy metabolism. However, whether mtDNA copy number or haplogroups are predictors of oxidative stress-related risks in human breast cancer tissue in Mexican patients remains to be determined. Using quantitative real-time PCR assays and sequencing of the mtDNA hypervariable region, analysis of mtDNA copy numbers in 82 breast cancer tissues (BCT) and matched normal adjacent tissues (NAT) was performed to determine if copy number correlated with clinical features and Amerindian haplogroups (A2, B2, B4, C1 and D1) . The results showed that the mtDNA copy number was significantly decreased in BCT compared with NAT (p = 0.010); it was significantly decreased in BCT and NAT in women > 50 years of age, compared with NAT in women < 50 years of age (p = 0.032 and p = 0.037, respectively); it was significantly decreased in NAT and BCT in the postmenopausal group and in BCT in the premenopausal group compared with NAT in the premenopausal group (p = 0.011, p = 0.010 and, p = 0.018; respectively); and it was also significantly decrease in members of the BCT group classified as having invasive ductal carcinoma I-III (IDC-I, IDC-II and IDC-III) and IDC-II for NAT compared to IDC-I of NAT (p = 0.025, p = 0.022 and p = 0.031 and p = 0.020; respectively). The mtDNA copy number for BCT from patients with haplogroup B2 was decreased compared to patients with haplogroup D1 (p = 0.01); for BCT from patients with haplogroup C1 was also decreased compare with their NAT counterpart (p = 0.006) and with BCT patients belonging to haplogroups A2 and D1 (p = 0.01 and p = 0.03; respectively). In addition, the mtDNA copy number was decrease in the sequences with three deletions relative to the rCRS at nucleotide positions A249del, A290del and A291del, or C16327T polymorphism with the same p = 0.019 for all four variants. Contrary, the copy number increased in sequences containing C16111T, G16319A or T16362C polymorphisms (p = 0.021, =0.048, and = 0.001; respectively). In conclusion, a decrease in the copy number of mtDNA in BCT compared with NAT was shown by the results, which suggests an imbalance in oxidative phosphorylation (OXPHOS) that can affect the apoptosis pathway and cancer progression. It was also observed an increase of the copy number in samples with specific polymorphisms, which may be a good sign of favourable prognosis.

Mitochondrial Metabolism in PDAC: From Better Knowledge to New Targeting Strategies

Cancer cells reprogram their metabolism to meet bioenergetics and biosynthetic demands. The first observation of metabolic reprogramming in cancer cells was made a century ago (“Warburg effect” or aerobic glycolysis), leading to the classical view that cancer metabolism relies on a glycolytic phenotype. There is now accumulating evidence that most cancers also rely on mitochondria to satisfy their metabolic needs. Indeed, the current view of cancer metabolism places mitochondria as key actors in all facets of cancer progression. Importantly, mitochondrial metabolism has become a very promising target in cancer therapy, including for refractory cancers such as Pancreatic Ductal AdenoCarcinoma (PDAC). In particular, mitochondrial oxidative phosphorylation (OXPHOS) is an important target in cancer therapy. Other therapeutic strategies include the targeting of glutamine and fatty acids metabolism, as well as the inhibition of the TriCarboxylic Acid (TCA) cycle intermediates. A better knowledge of how pancreatic cancer cells regulate mitochondrial metabolism will allow the identification of metabolic vulnerabilities and thus novel and more efficient therapeutic options for the benefit of each patient.

Effective treatment of drug-resistant lung cancer via a nanogel capable of reactivating cisplatin and enhancing early apoptosis

Cisplatin resistance is a daunting obstacle in cancer therapy and one of the major causes for treatment failure due to the inadequate drug activity and apoptosis induction. To overcome cisplatin resistance, we proposed a multifunctional nanogel (designated as Valproate-D-Nanogel) capable of reactivating cisplatin and enhancing early apoptosis. This Valproate-D-Nanogel was prepared through copolymerizing carboxymethyl chitosan with diallyl disulfide and subsequent grafting with valproate to reverse the drug-resistance in cisplatin-resistant human lung adenocarcinoma cancer. It can significantly increase the proportion of G2/M phase (up to 3.2-fold enhancement) to reactivate cisplatin via high level of G2/M arrest induced by valproate. Meanwhile, the intracellular ROS-P53 crosstalk can be upregulated by diallyl disulfide (up to 8-fold increase of ROS) and valproate (up to 18-fold increase of P53) to enhance early apoptosis. The synchronization of enhanced G2/M arrest and ROS-P53 crosstalk devotes to reverse the cisplatin resistance with a high level of resistance reversion index (50.22). As a result, improved in vivo tumor inhibition (up to 15-fold higher compared to free cisplatin) and decreased systemic toxicity was observed after treatment with Valproate-D-Nanogels. Overall, this nanogel can effectively inhibit cisplatin-resistance cancer through combined pathways and provides an effective approach for overcoming cisplatin-resistance in cancer treatment.

Thinking outside the nucleus: Mitochondrial DNA copy number in health and disease

Mitochondrial DNA copy number (mtDNA-CN) is a biomarker of mitochondrial function and levels of mtDNA-CN have been reproducibly associated with overall mortality and a number of age-related diseases, including cardiovascular disease, chronic kidney disease, and cancer. Recent advancements in techniques for estimating mtDNA-CN, in particular the use of DNA microarrays and next-generation sequencing data, have led to the comprehensive assessment of mtDNA-CN across these and other diseases and traits. The importance of mtDNA-CN measures to disease and these advancing technologies suggest the potential for mtDNA-CN to be a useful biomarker in the clinic. While the exact mechanism(s) underlying the association of mtDNA-CN with disease remain to be elucidated, we review the existing literature which supports roles for inflammatory dynamics, immune function and alterations to cell signaling as consequences of variation in mtDNA-CN. We propose that future studies should focus on characterizing longitudinal, cell-type and cross-tissue profiles of mtDNA-CN as well as improving methods for measuring mtDNA-CN which will expand the potential for its use as a clinical biomarker.

Pirfenidone Inhibits Hypoxic Pulmonary Hypertension through the NADPH/ROS/p38 Pathway in Adventitial Fibroblasts in the Pulmonary Artery

Hypoxic pulmonary hypertension (HPH) is a devastating disease characterized by progressive vasoconstriction and vascular remodeling. Pirfenidone (PFD) inhibits the progression of HPH, though the molecular mechanisms remain unknown. This study is aimed at determining the role and mechanism of PFD in HPH in human pulmonary artery adventitial fibroblasts (HPAAFs), which were cultured under normal or hypoxic conditions. NOX4 and Rac1 were inhibited or overexpressed by shRNA or pcDNA3.1, respectively. Proliferation of HPAAFs was quantified by colorimetric 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium (MTT) assays to assess cellular metabolic activity, cell counts, and ethynyldeoxyuridine (EdU) assays to detect DNA synthesis. Migration of HPAAFs was assessed by a wound healing assay. The expression levels of smooth muscle alpha-actin (a-SMA) and procollagen I (COL1A1) were assessed by RT-PCR and western blot analysis. PFD suppressed hypoxia-induced proliferation and migration of HPAAFs. Compared with the hypoxic control group, PFD reduced the expression of a-SMA and procollagen I (COL1A1). PFD reduced hypoxia-induced phosphorylation of p38 through the NOX4/reactive oxygen species (ROS) signaling pathway. Moreover, Rac1 also decreased hypoxia-induced phosphorylation of p38, without any cross-interaction with NOX4. These findings demonstrate that PFD is a novel therapeutic agent to prevent cell proliferation, migration, and fibrosis, which might be useful in inhibiting vascular remodeling in patients with HPH.

Mitochondrial DNA alterations may influence the cisplatin responsiveness of oral squamous cell carcinoma

Cisplatin is the first-line chemotherapeutic agent for the treatment of oral squamous cell carcinoma (OSCC). However, the intrinsic or acquired resistance against cisplatin remains a major obstacle to treatment efficacy in OSCC. Recently, mitochondrial DNA (mtDNA) alterations have been reported in a variety of cancers. However, the role of mtDNA alterations in OSCC has not been comprehensively studied. In this study, we evaluated the correlation between mtDNA alterations (mtDNA content, point mutations, large-scale deletions, and methylation status) and cisplatin sensitivity using two OSCC cell lines, namely SAS and H103, and stem cell-like tumour spheres derived from SAS. By microarray analysis, we found that the tumour spheres profited from aberrant lipid and glucose metabolism and became resistant to cisplatin. By qPCR analysis, we found that the cells with less mtDNA were less responsive to cisplatin (H103 and the tumour spheres). Based on the findings, we theorised that the metabolic changes in the tumour spheres probably resulted in mtDNA depletion, as the cells suppressed mitochondrial respiration and switched to an alternative mode of energy production, i.e. glycolysis. Then, to ascertain the origin of the variation in mtDNA content, we used MinION, a nanopore sequencer, to sequence the mitochondrial genomes of H103, SAS, and the tumour spheres. We found that the lower cisplatin sensitivity of H103 could have been caused by a constellation of genetic and epigenetic changes in its mitochondrial genome. Future work may look into how changes in mtDNA translate into an impact on cell function and therefore cisplatin response.

Knockdown of TFAM in Tumor Cells Retarded Autophagic Flux through Regulating p53 Acetylation and PISD Expression

Mitochondrial transcription factor A (TFAM) is required for mitochondrial DNA replication and transcription, which are essential for mitochondrial biogenesis. Previous studies reported that depleting mitochondrial functions by genetic deletion of TFAM impaired autophagic activities. However, the underlying mechanisms remain largely unknown. In the current study, we identified that knockdown of TFAM repressed the synthesis of autophagy bio-marker LC3-II in tumor cells and decreased the expression of phosphatidyl-serine decarboxylase (PISD). Besides, downregulation of PISD with siRNA reduced the level of LC3-II, indicating that depletion of TFAM retarded autophagy via inhibiting PISD expression. Furthermore, it was found that the tumor repressor p53 could stimulate the transcription and expression of PISD by binding the PISD enhancer. Additionally, the protein stability and transcriptional activity of p53 in TFAM knockdown tumor cells was attenuated, and this was associated with decreased acetylation, especially the acetylation of lysine 382 of p53. Finally, we identified that TFAM knockdown increased the NAD⁺/NADH ratio in tumor cells. This led to the upregulation of Sirtuin1 (SIRT1), a NAD-dependent protein deacetylase, to deacetylate p53 and attenuated its transcriptional activation on PISD. In summary, our study discovered a new mechanism regarding disturbed autophagy in tumor cells with mitochondrial dysfunction due to the depletion of TFAM.

Links between cancer metabolism and cisplatin resistance

Cisplatin is one of the most potent and widely used chemotherapeutic agent in the treatment of several solid tumors, despite the high toxicity and the frequent relapse of patients due to the onset of drug resistance. Resistance to chemotherapeutic agents, either intrinsic or acquired, is currently one of the major problems in oncology. Thus, understanding the biology of chemoresistance is fundamental in order to overcome this challenge and to improve the survival rate of patients. Studies over the last 30 decades have underlined how resistance is a multifactorial phenomenon not yet completely understood. Recently, tumor metabolism has gained a lot of interest in the context of chemoresistance; accumulating evidence suggests that the rearrangements of the principal metabolic pathways within cells, contributes to the sensitivity of tumor to the drug treatment. In this review, the principal metabolic alterations associated with cisplatin resistance are highlighted. Improving the knowledge of the influence of metabolism on cisplatin response is fundamental to identify new possible metabolic targets useful for combinatory treatments, in order to overcome cisplatin resistance.

ROS as a novel indicator to predict anticancer drug efficacy

Background

Mitochondria are considered a primary intracellular site of reactive oxygen species (ROS) generation. Generally, cancer cells with mitochondrial genetic abnormalities (copy number change and mutations) have escalated ROS levels compared to normal cells. Since high levels of ROS can trigger apoptosis, treating cancer cells with low doses of mitochondria-targeting / ROS-stimulating agents may offer cancer-specific therapy. This study aimed to investigate how baseline ROS levels might influence cancer cells’ response to ROS-stimulating therapy.

Methods

Four cancer and one normal cell lines were treated with a conventional drug (cisplatin) and a mitochondria-targeting agent (dequalinium chloride hydrate) separately and jointly. Cell viability was assessed and drug combination synergisms were indicated by the combination index (CI). Mitochondrial DNA copy number (mtDNAcn), ROS and mitochondrial membrane potential (MMP) were measured, and the relative expression levels of the genes and proteins involved in ROS-mediated apoptosis pathways were also investigated.

Results

Our data showed a correlation between the baseline ROS level, mtDNAcn and drug sensitivity in the tested cells. Synergistic effect of both drugs was also observed with ROS being the key contributor in cell death.

Conclusions

Our findings suggest that mitochondria-targeting therapy could be more effective compared to conventional treatments. In addition, cancer cells with low levels of ROS may be more sensitive to the treatment, while cells with high levels of ROS may be more resistant. Doubtlessly, further studies employing a wider range of cell lines and in vivo experiments are needed to validate our results. However, this study provides an insight into understanding the influence of intracellular ROS on drug sensitivity, and may lead to the development of new therapeutic strategies to improve efficacy of anticancer therapy.

Abiraterone and MDV3100 inhibits the proliferation and promotes the apoptosis of prostate cancer cells through mitophagy

BACKGROUND

Abiraterone and MDV3100 are two effective anticancer agents for prostate cancer, however, the mechanism of their downstream action remains undefined.

METHODS

A dual fluorescent biosensor plasmid was transfected in LNCaP cells to measure mitophagy. The DNA of LNCaP cells was extracted and performed with quantitative real-time PCR to detect mitochondrial DNA copy number. JC-1 staining was utilized to detect the mitochondrial membrane potential and electron microscope was performed to analyze mitochondrial morphology. Moreover, the protein levels of mitochondrial markers and apoptotic markers were detected by western blot. At last, the proliferation and apoptosis of LNCaP cells were analyzed with CCK-8 assay and flow cytometry after abiraterone or MDV3100 treatment.

RESULTS

Mitophagy was induced by abiraterone and MDV3100 in LNCaP cells. The low expression level of mitochondrial DNA copy number and mitochondrial depolarization were further identified in the abiraterone or MDV3100 treatment groups compared with the control group. Besides, severe mitochondria swelling and substantial autophagy-lysosomes were observed in abiraterone- and MDV3100-treated LNCaP cells. The expression of mitochondria-related proteins, frataxin, ACO2 and Tom20 were significantly downregulated in abiraterone and MDV3100 treated LNCaP cells, whereas the expression level of inner membrane protein of mitochondria (Tim23) was significantly upregulated in the same condition. Moreover, the proliferation of LNCaP cells were drastically inhibited, and the apoptosis of LNCaP cells was increased in abiraterone or MDV3100 treatment groups. Meanwhile, the addition of mitophagy inhibitor Mdivi-1 (mitochondrial division inhibitor 1) could conversely elevate proliferation and constrain apoptosis of LNCaP cells.

CONCLUSIONS

Our results prove that both abiraterone and MDV3100 inhibit the proliferation, promote the apoptosis of prostate cancer cells through regulating mitophagy. The promotion of mitophagy might enhance the efficacy of abiraterone and MDV3100, which could be a potential strategy to improve chemotherapy with these two reagents.

Increased mitochondrial DNA copy number protects hair cells and HEI‑OC1 cells against drug‑induced apoptosis

Several factors trigger apoptosis in cochlear hair cells. Previous studies have shown that mitochondria play key roles in apoptosis, but the role of mitochondrial deoxyribonucleic acid (mtDNA) copy number in the pathogenesis of hair cell apoptosis remains largely unknown. We used mouse cochlear hair cells and House Ear Institute-Organ of Corti 1 (HEI-OC1) cells to explore the relationship between mtDNA copy number and cell apoptosis. We found that the mtDNA copy number of hair cells was reduced relative to mitochondrial mass and hypothesized that increasing it might have a protective effect. We then increased the mtDNA copy number of the hair and HEI-OC1 cells by transfecting them with an adeno-associated virus (AAV) vector containing mitochondrial transcription factor A (TFAM). We found that the apoptosis rates decreased upon inducing apoptosis with neomycin or cisplatin (DDP). To elucidate the mechanisms, we analyzed the mitochondrial-membrane permeability and mitochondrial function of HEI-OC1 cells. Our results suggested that the increase in mtDNA copy number could protect hair cells and HEI-OC1 cells against drug-induced apoptosis by stabilizing the permeability of the mitochondrial membrane and mitochondrial function.

Mitochondrial oxidative stress-induced transcript variants of ATF3 mediate lipotoxic brain microvascular injury

Elevation of blood triglycerides, primarily triglyceride-rich lipoproteins (TGRL), is an independent risk factor for cardiovascular disease and vascular dementia (VaD). Accumulating evidence indicates that both atherosclerosis and VaD are linked to vascular inflammation. However, the role of TGRL in vascular inflammation, which increases risk for VaD, remains largely unknown and its underlying mechanisms are still unclear. We strived to determine the effects of postprandial TGRL exposure on brain microvascular endothelial cells, the potential risk factor of vascular inflammation, resulting in VaD. We showed in Aung et al., J Lipid Res., 2016 that postprandial TGRL lipolysis products (TL) activate mitochondrial reactive oxygen species (ROS) and increase the expression of the stress-responsive protein, activating transcription factor 3 (ATF3), which injures human brain microvascular endothelial cells (HBMECs) in vitro. In this study, we deployed high-throughput sequencing (HTS)-based RNA sequencing methods and mito stress and glycolytic rate assays with an Agilent Seahorse XF analyzer and profiled the differential expression of transcripts, constructed signaling pathways, and measured mitochondrial respiration, ATP production, proton leak, and glycolysis of HBMECs treated with TL. Conclusions: TL potentiate ROS by mitochondria which activate mitochondrial oxidative stress, decrease ATP production, increase mitochondrial proton leak and glycolysis rate, and mitochondria DNA damage. Additionally, CPT1A1 siRNA knockdown suppresses oxidative stress and prevents mitochondrial dysfunction and vascular inflammation in TL treated HBMECs. TL activates ATF3-MAPKinase, TNF, and NRF2 signaling pathways. Furthermore, the NRF2 signaling pathway which is upstream of the ATF3-MAPKinase signaling pathway, is also regulated by the mitochondrial oxidative stress. We are the first to report differential inflammatory characteristics of transcript variants 4 (ATF3-T4) and 5 (ATF3-T5) of the stress responsive gene ATF3 in HBMECs induced by postprandial TL. Specifically, our data indicates that ATF3-T4 predominantly regulates the TL-induced brain microvascular inflammation and TNF signaling. Both siRNAs of ATF3-T4 and ATF3-T5 suppress cells apoptosis and lipotoxic brain microvascular endothelial cells. These novel signaling pathways triggered by oxidative stress-responsive transcript variants, ATF3-T4 and ATF3-T5, in the brain microvascular inflammation induced by TGRL lipolysis products may contribute to pathophysiological processes of vascular dementia.

Transcriptional Regulation of Energy Metabolism in Cancer Cells

Cancer development, growth, and metastasis are highly regulated by several transcription regulators (TRs), namely transcription factors, oncogenes, tumor-suppressor genes, and protein kinases. Although TR roles in these events have been well characterized, their functions in regulating other important cancer cell processes, such as metabolism, have not been systematically examined. In this review, we describe, analyze, and strive to reconstruct the regulatory networks of several TRs acting in the energy metabolism pathways, glycolysis (and its main branching reactions), and oxidative phosphorylation of nonmetastatic and metastatic cancer cells. Moreover, we propose which possible gene targets might allow these TRs to facilitate the modulation of each energy metabolism pathway, depending on the tumor microenvironment.

A mechanism for increased sensitivity of acute myeloid leukemia to mitotoxic drugs

Mitochondria play a central and multifunctional role in the progression of tumorigenesis. Although many recent studies have demonstrated correlations between mitochondrial function and genetic makeup or originating tissue, it remains unclear why some cancers are more susceptible to mitocans (anticancer drugs that target mitochondrial function to mediate part or all of their effect). Moreover, fundamental questions of efficacy and mechanism of action in various tumor types stubbornly remain. Here we demonstrate that cancer type is a significant predictor of tumor response to mitocan treatment, and that acute myeloid leukemias (AML) show an increased sensitivity to these drugs. We determined that AML cells display particular defects in mitochondrial metabolism that underlie their sensitivity to mitocan treatment. Furthermore, we demonstrated that combinatorial treatment with a mitocan (CCCP) and a glycolytic inhibitor (2-deoxyglucose) has substantial synergy in AML cells, including primary cells from patients with AML. Our results show that mitocans, either alone or in combination with a glycolytic inhibitor, display anti-leukemia effects in doses much lower than needed to induce toxicity against normal blood cells, indicating that mitochondria may be an effective and selective therapeutic target.

Mitochondrial Involvement in Cisplatin Resistance

Cisplatin is one of the worldwide anticancer drugs and, despite its toxicity and frequent recurrence of resistance phenomena, it still remains the only therapeutic option for several tumors. Circumventing cisplatin resistance remains, therefore, a major goal for clinical therapy and represents a challenge for scientific research. Recent studies have brought to light the fundamental role of mitochondria in onset, progression, and metastasis of cancer, as well as its importance in the resistance to chemotherapy. The aim of this review is to give an overview of the current knowledge about the implication of mitochondria in cisplatin resistance and on the recent development in this research field. Recent studies have highlighted the role of mitochondrial DNA alterations in onset of resistance phenomena, being related both to redox balance alterations and to signal crosstalk with the nucleus, allowing a rewiring of cell metabolism. Moreover, an important role of the mitochondrial dynamics in the adaptation mechanism of cancer cells to challenging environment has been revealed. Giving bioenergetic plasticity to tumor cells, mitochondria allow cells to evade death pathways in stressful conditions, including chemotherapy. So far, even if the central role of mitochondria is recognized, little is known about the specific mechanisms implicated in the resistance. Nevertheless, mitochondria appear to be promising pharmacological targets for overcoming cisplatin resistance, but further studies are necessary.

Down-regulation of TFAM increases the sensitivity of tumour cells to radiation via p53/TIGAR signalling pathway

Mitochondrial transcription factor A (TFAM) is a key regulator of mitochondria biogenesis. Previous studies confirmed that reduced TFAM expression sensitized tumours cells to chemical therapy reagents and ionizing irradiation (IR). However, the underlying mechanisms remain largely unknown. In this study, we identified that decreased expression of TFAM impaired the proliferation of tumour cells by inducing G1/S phase arrest and reducing the expression of E2F1, phospo-Rb, PCNA and TK1. Furthermore, we proved that knockdown of TFAM enhanced the interaction between p53 and MDM2, resulting in decreased expression of p53 and the downstream target TIGAR, and thus leading to elevated level of mitochondrial superoxide and DNA double-strand break (DSB) which were exacerbated when treated the cell with ionizing radiation. Those indicated that knockdown of TFAM could aggravate radiation induced DSB levels through affecting the production of mitochondria derived reactive oxygen species. Our current work proposed a new mechanism that TFAM through p53/TIGAR signalling to regulate the sensitivity of tumour cells to ionizing radiation. This indicated that TFAM might be a potential target for increasing the sensitization of cancer cells to radiotherapy.

Numb Depletion Promotes Drp1-Mediated Mitochondrial Fission and Exacerbates Mitochondrial Fragmentation and Dysfunction in Acute Kidney Injury

AIMS

Mitochondrial fragmentation is a crucial mechanism contributing to tubular cell apoptosis during acute kidney injury (AKI). However, the mechanism of modulating mitochondrial dynamics during AKI remains unclear. Numb is a multifunction adaptor protein that is expressed in renal tubules. The aim of the present study was to evaluate the role of Numb in mitochondrial dysfunction during AKI.

RESULTS

The expression of Numb was upregulated in both ischemia-reperfusion- and cisplatin-induced AKI. Depletion of Numb from proximal tubules (PT-Nb-KO) exacerbated AKI shown as more severe renal tubular damage and higher serum creatinine than wild-type mice. Numb depletion alone significantly increased mitochondrial fragmentation without altering mitochondrial mass and function, including adenosine triphosphate production, mitochondrial membrane potential, oxygen consumption, and reactive oxygen species production. However, mitochondrial fragmentation and dysfunction were significantly aggravated after cisplatin exposure in PT-Nb-KO mice. Mechanistically, Numb depletion triggered dynamin-related protein 1 (Drp1) recruitment to mitochondria by increasing the phosphorylation of Drp1 at serine 656 residue (human Drp1 ser⁶³⁷). Inhibiting the activity of Rho-associated coiled-coil containing protein kinase (ROCK) by Y-27632 attenuated phosphorylation of Drp1 ser⁶⁵⁶ and mitochondrial fragmentation in Numb-deficient cells. Administration of mdivi-1, a pharmacological inhibitor of Drp1, restored mitochondrial morphology, attenuated cisplatin-induced tubular injury, and renal dysfunction in PT-Nb-KO mice. Innovation and Conclusion: Our data suggest that Numb depletion promotes mitochondrial fragmentation by promoting the phosphorylation of Drp1 Ser⁶³⁷ and thus exacerbates cisplatin-induced mitochondrial dysfunction and tubular cell apoptosis. These findings add a novel insight into modulating mechanism of mitochondrial dynamics during AKI.

Fetal bovine serum inhibits neomycin-induced apoptosis of hair cell-like HEI-OC-1 cells by maintaining mitochondrial function

Aging and exposure to noise or ototoxic drugs are major causes of hair cell death leading to human hearing loss, and many agents have been developed to protect hair cells from apoptosis. Fetal bovine serum (FBS) is a fundamental ingredient in the culture medium of hair cell-like House Ear Institute Organ of Corti 1 (HEI-OC-1) cells, but there have been no reports about the function of FBS in HEI-OC-1 cell apoptosis. In this study, we found that FBS deprivation alone significantly increased HEI-OC-1 cell apoptosis in the absence of neomycin exposure and that the presence of FBS significantly inhibited HEI-OC-1 cell apoptosis after neomycin exposure compared to FBS-deprived cells. Further, we found that the protective effect of FBS was dose dependent and more effective than the growth factors B27, N2, EGF, bFGF, IGF-1, and heparan sulfate. We also found that FBS deprivation significantly disrupted the expression level of mitochondrial proteins, increased pro-apoptotic gene expression, decreased the mitochondrial membrane potential, and increased reactive oxygen species accumulation in HEI-OC-1 cells after neomycin exposure. These findings indicate that FBS is involved in maintaining the level of mitochondrial proteins, maintaining the balance of oxidant gene expression, and preventing the accumulation of ROS, and thus FBS maintains normal mitochondrial function and inhibits apoptosis in HEI-OC-1 cells after neomycin exposure.

Cyclooxygenase-2-Mediated Up-Regulation of Mitochondrial Transcription Factor A Mitigates the Radio-Sensitivity of Cancer Cells

Mitochondrial transcription factor A (TFAM) regulates mitochondrial biogenesis, and it is a candidate target for sensitizing tumor during therapy. Previous studies identified that increased TFAM expression conferred tumor cells resistance to ionizing radiation. However, the mechanisms on how TFAM are regulated in irradiated tumor cells remain to be explored. In this research, we demonstrated the contribution of cyclooxygenase-2 (COX-2) to enhancing TFAM expression in irradiated tumor cells. Our results showed TFAM was concomitantly up-regulated with COX-2 in irradiated tumor cells. Inhibition of COX-2 by NS-398 blocked radiation-induced expression of TFAM, and prostaglandin E2 (PGE2) treatment stimulated TFAM expression. We next provided evidence that DRP1-mediated mitochondrial fragmentation was a reason for TFAM up-regulation in irradiated cells, by using small interfering RNA (siRNA) and selective inhibitor-targeted DRP1. Furthermore, we proved that p38-MAPK-connected COX-2, and DRP1-mediated TFAM up-regulation. Enhanced phosphorylation of p38 in irradiated tumor cells promoted DRP1 expression, mitochondrial fragmentation, and TFAM expression. NS-398 treatment inhibited radiation-induced p38 phosphorylation, while PGE2 stimulated the activation of p38. The results put forward a mechanism where COX-2 stimulates TFAM expression via p38-mediated DRP1/mitochondrial fragmentation signaling in irradiated tumor cells, which may be of value in understanding how to sensitize cancer cells during radiotherapy.