Crosstalk between mitochondrial (dys)function and mitochondrial abundance

Circulating mitochondrial long non-coding 7S RNA in primary health care patients with depression/anxiety

BACKGROUND

The significant role of long non-coding 7S RNA in controlling mitochondrial transcription highlights its importance in mitochondrial function. Considering the suggested connection between mitochondrial dysfunction and the onset of mental disorders, this study aimed to explore the potential involvement of 7S RNA in the context of depression/anxiety.

RESULTS

A total of 181 patients in primary health care (age 20-64 years) with depression/anxiety and 59 healthy controls were included in the study. 7S RNA was measured using quantitative real-time PCR in plasma samples collected before (baseline) and after 8 weeks of treatment (mindfulness or cognitive-based behavioral therapy). Upon adjustment for age and sex, the baseline plasma levels of 7S RNA were significantly higher in patients than in healthy controls (p < 0.001). Notably, post-treatment, there was a significant reduction in 7S RNA levels (p = 0.03). These changes in 7S RNA were related to the treatment response, as indicated by HADS-D (Hospital Anxiety and Depression Scale) scores (ß = -0.04, p = 0.04), even after accounting for baseline scores and other cofounders.

CONCLUSION

The findings of this study indicate an association between plasma 7S RNA levels and depression/anxiety, as well as treatment response. While further confirmatory analyses are necessary, plasma 7S RNA holds promise as a potential predictive biomarker for both depression/anxiety and the treatment response within these disorders.

Oxidant-Dependent Sensitizing, Protective, and Mitigative Effects in X-Ray-Irradiated Pulmonary Endothelial Cells

The primary response of proliferating bovine pulmonary artery endothelial cells (BPAECs) after X-ray irradiation [≤10 gray (Gy)] is shown to be transient cell-cycle arrest. Accompanying oxidant-linked functional changes within the mitochondria are readily measured, but increased autophagy is not. Radiation-induced apoptosis is negligible in this line-important because cells undergoing apoptosis release oxygen-derived species that can overwhelm/mask the radiation-associated species and their effects that we wish to investigate. Cells irradiated and cultured at 3% oxygen exhibited delayed cell-cycle arrest (6-8 hours after 10 Gy irradiation) compared with those maintained at 20% oxygen (2-4 hours after 10 Gy irradiation). At 3% oxygen, either only during or only after irradiation, results intermediate between 20% and 3% oxygen throughout were obtained. No variability in cell-cycle distribution was observed for unirradiated cells cultured under different prevailing oxygen levels. Mitochondrially localized manganese superoxide dismutase delayed the X-ray-induced cell-cycle changes when over-expressed in BPAEC, indicating superoxide to be one of the key oxygen-derived cytotoxic species involved in the radiobiological response. Also, the peroxynitrite biomarker 3-nitrotyrosine was elevated, whereas hydrogen peroxide levels were not. Lastly, the utility of the BPAEC for screening potential countermeasures to ionizing radiation is demonstrated with some quinoline derivatives. Three of the five compounds appeared mitigative, and all were protective. It is suggested that the oxidation-reduction chemistry of these compounds probably offers a reasonable explanation for their observed ameliorative properties. Furthermore, the results suggest a promising new direction in the search for lead compounds as countermeasures to the effects of ionizing radiation. SIGNIFICANCE STATEMENT: The primary radiological response of proliferating bovine pulmonary artery endothelial cells is cell-cycle arrest, starting soon after X-ray irradiation (1-10 Gy) at 20% O2 but delayed by 4 hours at systemic (3%) O2. Oxygen/superoxide is found to be radio-sensitizing in at least two distinct time windows, during and after the irradiation, with both responses antagonized by various hydroxyquinoline derivatives. Similar responses in many other cell lines are likely to be masked by elevated oxidants associated with apoptosis.

Mitochondrial Quality Control via Mitochondrial Unfolded Protein Response (mtUPR) in Ageing and Neurodegenerative Diseases

Mitochondria play a key role in cellular functions, including energy production and oxidative stress regulation. For this reason, maintaining mitochondrial homeostasis and proteostasis (homeostasis of the proteome) is essential for cellular health. Therefore, there are different mitochondrial quality control mechanisms, such as mitochondrial biogenesis, mitochondrial dynamics, mitochondrial-derived vesicles (MDVs), mitophagy, or mitochondrial unfolded protein response (mtUPR). The last item is a stress response that occurs when stress is present within mitochondria and, especially, when the accumulation of unfolded and misfolded proteins in the mitochondrial matrix surpasses the folding capacity of the mitochondrion. In response to this, molecular chaperones and proteases as well as the mitochondrial antioxidant system are activated to restore mitochondrial proteostasis and cellular function. In disease contexts, mtUPR modulation holds therapeutic potential by mitigating mitochondrial dysfunction. In particular, in the case of neurodegenerative diseases, such as primary mitochondrial diseases, Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), Amyotrophic Lateral Sclerosis (ALS), or Friedreich's Ataxia (FA), there is a wealth of evidence demonstrating that the modulation of mtUPR helps to reduce neurodegeneration and its associated symptoms in various cellular and animal models. These findings underscore mtUPR's role as a promising therapeutic target in combating these devastating disorders.

Urolithin A alleviates neuropathic pain and activates mitophagy

Neuropathic pain (NP) occurs frequently in the general population and has a negative impact on the quality of life. There is no effective therapy available yet owing to the complex pathophysiology of NP. In our previous study, we found that urolithin A (UA), a naturally occurring microflora-derived metabolite, could relieve NP in mice by inhibiting the activation of microglia and release of inflammation factors. Here in this study, we sought to investigate whether mitophagy would be activated when UA alleviated NP in mice. We showed that the autophagy flow was blocked in the spinal dorsal horn of the chronic constriction injury (CCI) mice when the most obvious pain behavior occurs. Intraperitoneal injection of UA markedly activated the mitophagy mediated by PTEN-induced kinase 1/Parkin, promoted mitobiogenesis in both neurons and microglia, and alleviated NP in the CCI mice. In summary, our data suggest that UA alleviates NP in mice and meanwhile induces mitophagy activation, which highlights a therapeutic potential of UA in the treatment of NP.

Mitochondrial activity is the key to the protective effect of β-Lapachone, a NAD+ booster, in healthy cells against cisplatin cytotoxicity

BACKGROUND

Cisplatin (CDDP) is a first-line chemotherapeutic drug for treating various cancers. However, CDDP also damages normal cells and causes many side effects. Recently, CDDP has been demonstrated to kill cancer cells by targeting mitochondria. Protecting mitochondria might be a potential therapeutic strategy for CDDP-induced side effects. β-Lapachone (β-lap), a recognized NAD⁺ booster, has been reported to regulate mitochondrial activity. However, it remains unclear whether maintaining mitochondrial activity is the key factor in the protective effects of β-lap in CDDP-treated normal cells.

PURPOSE

In this study, the protective effects of β-lap on mitochondria against CDDP cytotoxicity in normal cells were evaluated.

STUDY DESIGN

In vitro cell models were used in this study, including 3T3 fibroblasts, human dermal fibroblasts, MCF-7 breast cancer cells, and MDA-MB-231 breast cancer cells.

METHODS

Cells were treated with CDDP and β-lap, and cell survival, NAD⁺, mitochondrial activity, autophagy, and ATP production were measured. Various inhibitors and siRNAs were used to confirm the key signal underlying the protective effects of β-lap.

RESULTS

The results demonstrated that β-lap significantly decreased CDDP cytotoxicity in normal fibroblasts. With various inhibitors and siRNAs, β-lap reduced CDDP-induced damage to normal fibroblasts by maintaining mitochondrial activity and increasing autophagy through the NQO1/NAD⁺/SIRT1 axis. Most importantly, the protective effects of β-lap in fibroblasts did not affect the therapeutic effects of CDDP in cancer cells. This study indicated that mitochondrial activity, energy production, and NQO1 levels might be crucial responses separating normal cells from cancer cells under exposure to CDDP and β-lap.

CONCLUSION

β-lap could be a good synergistic drug for reducing the side effects of CDDP without affecting the anticancer drug effect.

Remission of obesity and insulin resistance is not sufficient to restore mitochondrial homeostasis in visceral adipose tissue

Metabolic plasticity is the ability of a biological system to adapt its metabolic phenotype to different environmental stressors. We used a whole-body and tissue-specific phenotypic, functional, proteomic, metabolomic and transcriptomic approach to systematically assess metabolic plasticity in diet-induced obese mice after a combined nutritional and exercise intervention. Although most obesity and overnutrition-related pathological features were successfully reverted, we observed a high degree of metabolic dysfunction in visceral white adipose tissue, characterized by abnormal mitochondrial morphology and functionality. Despite two sequential therapeutic interventions and an apparent global healthy phenotype, obesity triggered a cascade of events in visceral adipose tissue progressing from mitochondrial metabolic and proteostatic alterations to widespread cellular stress, which compromises its biosynthetic and recycling capacity. In humans, weight loss after bariatric surgery showed a transcriptional signature in visceral adipose tissue similar to our mouse model of obesity reversion. Overall, our data indicate that obesity prompts a lasting metabolic fingerprint that leads to a progressive breakdown of metabolic plasticity in visceral adipose tissue.

Natural Products in Modulating Methamphetamine-Induced Neuronal Apoptosis

Methamphetamine (METH), an amphetamine-type psychostimulant, is highly abused worldwide. Chronic abuse of METH causes neurodegenerative changes in central dopaminergic neurons with numerous neuropsychiatric consequences. Neuronal apoptosis plays a critical role in METH-induced neurotoxicity and may provide promising pharmacological targets for preventing and treating METH addiction. In recent years, accumulating evidence has revealed that natural products may possess significant potentials to inhibit METH-evoked neuronal apoptosis. In this review, we summarized and analyzed the improvement effect of natural products on METH-induced neuronal apoptosis and their potential molecular mechanisms on modulating dopamine release, oxidative stress, mitochondrial-dependent apoptotic pathway, endoplasmic reticulum stress-mediated apoptotic pathway, and neuroinflammation. Hopefully, this review may highlight the potential value of natural products in modulating METH-caused neuronal apoptosis and provide useful information for future research and developments of novel and efficacious pharmacotherapies in this field.

DNA Methylation of PGC-1α Is Associated With Elevated mtDNA Copy Number and Altered Urinary Metabolites in Autism Spectrum Disorder

Autism spectrum disorder (ASD) is a complex disorder that is underpinned by numerous dysregulated biological pathways, including pathways that affect mitochondrial function. Epigenetic mechanisms contribute to this dysregulation and DNA methylation is an important factor in the etiology of ASD. We measured DNA methylation of peroxisome proliferator-activated receptor-gamma coactivator-1 alpha (PGC-1α), as well as five genes involved in regulating mitochondrial homeostasis to examine mitochondrial dysfunction in an ASD cohort of South African children. Using targeted Next Generation bisulfite sequencing, we found differential methylation (p < 0.05) at six key genes converging on mitochondrial biogenesis, fission and fusion in ASD, namely PGC-1α, STOML2, MFN2, FIS1, OPA1, and GABPA. PGC-1α, the transcriptional regulator of biogenesis, was significantly hypermethylated at eight CpG sites in the gene promoter, one of which contained a putative binding site for CAMP response binding element 1 (CREB1) (p = 1 × 10^–6). Mitochondrial DNA (mtDNA) copy number, a marker of mitochondrial function, was elevated (p = 0.002) in ASD compared to controls and correlated significantly with DNA methylation at the PGC-1α promoter and there was a positive correlation between methylation at PGC-1α CpG#1 and mtDNA copy number (Spearman’s r = 0.2, n = 49, p = 0.04) in ASD. Furthermore, DNA methylation at PGC-1α CpG#1 and mtDNA copy number correlated significantly (p < 0.05) with levels of urinary organic acids associated with mitochondrial dysfunction, oxidative stress, and neuroendocrinology. Our data show differential methylation in ASD at six key genes converging on PGC-1α-dependent regulation of mitochondrial biogenesis and function. We demonstrate that methylation at the PGC-1α promoter is associated with elevated mtDNA copy number and metabolomic evidence of mitochondrial dysfunction in ASD. This highlights an unexplored role for DNA methylation in regulating specific pathways involved in mitochondrial biogenesis, fission and fusion contributing to mitochondrial dysfunction in ASD.

Accurate Measurement of Cellular and Cell-Free Circulating Mitochondrial DNA Content from Human Blood Samples Using Real-Time Quantitative PCR

Changes in circulating mitochondrial DNA (mtDNA) are widely used to indicate mitochondrial dysfunction in common non-genetic diseases where mitochondrial dysfunction may play a role. However, the methodology being used is not always specific and reproducible, and most studies use whole blood rather than evaluating cellular and cell-free mtDNA separately. Cellular mtDNA is contained within the mitochondrion and encodes vital subunits of the OXPHOS machinery. Conversely, cell-free mtDNA can have harmful effects, triggering inflammatory responses and potentially contributing to pathogenic processes. In this chapter, we describe a protocol to accurately measure the amount of cellular and cell-free human mtDNA in peripheral blood. Absolute quantification is carried out using real-time quantitative PCR (qPCR) to quantify cellular mtDNA, measured as the mitochondrial genome to nuclear genome ratio (designated the Mt/N ratio) in whole blood and peripheral blood mononuclear cells (PBMCs) and the number of mtDNA copies per μL in plasma and serum. We describe how to (1) separate whole blood into PBMCs, plasma, and serum fractions, (2) prepare DNA from each of these fractions, (3) prepare dilution standards for absolute quantification, (4) carry out qPCR for either relative or absolute quantification from test samples, (5) analyze qPCR data, and (6) calculate the sample size to adequately power studies. The protocol presented here is suitable for high-throughput use and can be modified to quantify mtDNA from other body fluids, human cells, and tissues.

Xanthohumol-Induced Rat Glioma C6 Cells Death by Triggering Mitochondrial Stress

AIM: To investigate the underlying mechanisms of xanthohumol (XN) on the proliferation inhibition and death of C6 glioma cells. METHODS: To determine the effects of XN on C6 cells, cell proliferation and mortality after XN treatment were assessed by SRB assay and trypan blue assay respectively. Apoptotic rates were evaluated by flowcytometry after Annexin V-FITC/PI double staining. The influence of XN on the activity of caspase-3 was determined by Western blot (WB); and nuclear transposition of apoptosis-inducing factor (AIF) was tested by immunocytochemistry and WB. By MitoSOX^TM staining, the mitochondrial ROS were detected. Mitochondrial function was also tested by MTT assay (content of succinic dehydrogenase), flow cytometry (mitochondrial membrane potential (MMP)—JC-1 staining; mitochondrial abundance—mito-Tracker green), immunofluorescence (MMP—JC-1 staining; mitochondrial morphology—mito-Tracker green), WB (mitochondrial fusion-fission protein—OPA1, mfn2, and DRP1; mitophagy-related proteins—Pink1, Parkin, LC3B, and P62), and high-performance liquid chromatography (HPLC) (energy charge). Finally, mitochondrial protein homeostasis of C6 cells after XN treatment with and without LONP1 inhibitor bortezomib was investigated by trypan blue assay (proliferative activity and mortality) and WB (mitochondrial protease LONP1). All cell morphology images were taken by a Leica Microsystems microscope. RESULTS: XN could lead to proliferation inhibition and death of C6 cells in a time- and dose-dependent manner and induce apoptosis of C6 cells through the AIF pathway. After long incubation of XN, mitochondria of C6 cells were seriously impaired, and mitochondria had a diffuse morphology and mitochondrial ROS were increased. The content of succinic dehydrogenase per cell was significantly decreased after XN insults of 24, 48, and 72 h. The energy charge was weakened after XN insult of 24 h. Furthermore, the MMP and mitochondrial abundance were significantly decreased; the protein expression levels of OPA1, mfn2, and DRP1 were down-regulated; and the protein expression levels of Pink1, Parkin, LC3B-II/LC3B-I, and p62 were up-regulated in long XN incubation times (24, 48, and 72 h). XN incubation with bortezomib for 48 h resulted in lower proliferative activity and higher mortality of C6 cells and caused the cell to have visible vacuoles. Moreover, the protein expression levels of LONP1 was up-regulated gradually as XN treatment time increased. CONCLUSION: These data supported that XN could induce AIF pathway apoptosis of the rat glioma C6 cells by affecting the mitochondria.

Investigating the Opposing Effect of Two Different Green Tea Supplements on Oxidative Stress, Mitochondrial Function and Cell Viability in HepG2 Cells

Green tea extract (GTE) improves exercise outcomes and reduces obesity. However, case studies indicate contradictory physiology regarding liver function and toxicity. We studied the effect of two different decaffeinated GTE (dGTE) products, from a non-commercial (dGTE1) and commercial (dGTE2) supplier, on hepatocyte function using the human cell model, HepG2. dGTE1 was protective against hydrogen peroxide (H₂O₂)-induced apoptosis and cell death by attenuating oxidative stress pathways. Conversely, dGTE2 increased cellular and mitochondrial oxidative stress and apoptosis. A bioavailability study with dGTE showed the major catechin in GTE, EGCG, reached 0.263 µg·ml^-1. In vitro, at this concentration, EGCG mimicked the protective effect of dGTE1. GC/MS analysis identified steric acid and higher levels of palmitic acid in dGTE2 versus dGTE1 supplements. We demonstrate the significant biological differences between two GTE supplements which may have potential implications for manufacturers and consumers to be aware of the biological effects of supplementation.

The function of SUMOylation and its crucial roles in the development of neurological diseases

Neurological diseases are relatively complex diseases of a large system; however, the detailed mechanism of their pathogenesis has not been completely elucidated, and effective treatment methods are still lacking for some of the diseases. The SUMO (small ubiquitin-like modifier) modification is a dynamic and reversible process that is catalyzed by SUMO-specific E1, E2, and E3 ligases and reversed by a family of SENPs (SUMO/Sentrin-specific proteases). SUMOylation covalently conjugates numerous cellular proteins, and affects their cellular localization and biological activity in numerous cellular processes. A wide range of neuronal proteins have been identified as SUMO substrates, and the disruption of SUMOylation results in defects in synaptic plasticity, neuronal excitability, and neuronal stress responses. SUMOylation disorders cause many neurodegenerative diseases, such as Parkinson's disease, Alzheimer's disease, and Huntington's disease. By modulating the ion channel subunit, SUMOylation imbalance is responsible for the development of various channelopathies. The regulation of protein SUMOylation in neurons may provide a new strategy for the development of targeted therapeutic drugs for neurodegenerative diseases and channelopathies.

TBHQ-Overview of Multiple Mechanisms against Oxidative Stress for Attenuating Methamphetamine-Induced Neurotoxicity

Methamphetamine is a derivative of amphetamines, a highly addictive central stimulant with multiple systemic toxicity including the brain, heart, liver, lung, and spleen. It has adverse effects such as apoptosis and breakdown of the blood-brain barrier. Methamphetamine is a fatal and toxic chemical substance, and its lethal mechanism has been widely studied in recent years. The possible mechanism is that methamphetamine can cause cardiotoxicity and neurotoxicity mainly by inducing oxidative stress so as to generate heat, eliminate people's hunger and thirst, and maintain a state of excitement so that people can continue to exercise. According to many research, there is no doubt that methamphetamine triggers neurotoxicity by inducing reactive oxygen species (ROS) production and redox imbalance. This review summarized the mechanisms of methamphetamine-induced neurotoxicity including apoptosis and blood-brain barrier breakdown through oxidative stress and analyzed several possible antioxidative mechanisms of tert-butylhydroquinone (TBHQ) which is a kind of food additive with antioxidative effects. As a nuclear factor E2-related factor 2 (Nrf2) agonist, TBHQ may inhibit neurotoxicity caused by oxidative stress through the following three mechanisms: the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase system, the astrocytes activation, and the glutathione pathway. The mechanism about methamphetamine's toxic effects and its antioxidative therapeutic drugs would become a research hotspot in this field and has very important research significance.

Regulatory role and mechanism of the inhibition of the Mcl-1 pathway during apoptosis and polarization of H37Rv-infected macrophages

BACKGROUND

Myeloid cell leukemia-1 (Mcl-1) plays an important role in the clearance of Mycobacterium tuberculosis (MTB) infection. It has the effect of anti-apoptosis, protecting macrophages that have engulfed pathogens and preventing pathogen clearance. Meanwhile, the MAPK signaling pathway plays a significant role in regulating Mcl-1 expression during tuberculosis infection. In the case of latent infection and active infection, the apoptosis and polarization of macrophages have a great influence during MTB infection, so we discussed the effect of Mcl-1 on apoptosis and polarization. Then, further discussed its mechanism.

METHODS

An infected RAW264.7 macrophage model was established to investigate the regulatory role and mechanism of the Mcl-1 pathway inhibition during apoptosis and polarization of H37Rv infection. First, Mcl-1 protein and mRNA was identified by western blotting and Real-Time Polymerase Chain Reaction (RT-PCR). RAW264.7 macrophage apoptosis was detected by flow cytometry. RT-PCR was utilized to detect Bax, Caspase-3, Cyt-c and Bcl-2 mRNA expression. Next, Then the expression levels of inflammation factors CD86, CD206, iNOS, Fizz1, IL-6, IL-10, TNF-α, and TGF-β was detected by ELISA. SEM was used to observe macrophages phenotype. Finally, Bax, Bcl-2 and Bcl-xl the expression was detected by western blotting. Confocal microscopy was used to analyze mitochondrial membrane potential using the JC-10 kit.

RESULTS

In this study, we found that inhibiting the Mcl-1 expression signaling pathway led to infection by different virulence Mycobacterium tuberculosis, as well as changes in Mcl-1 protein and mRNA expression. Concomitantly macrophage apoptosis rate also changed, While, two phenotypic states of M1 and M2 appeared in the infected cells. We also found that the mitochondrial pathway was activated, the expression of its related genes Bax, casepase3, and Cyt-c, increased, whereas that of Bcl-2 decreased, and the mitochondrial membrane depolarization function was changed.

CONCLUSIONS

We found that Mcl-1 affected the apoptosis and polarization of macrophages infected by Mycobacterium tuberculosis, mainly M1 in the early stage and M2 in the later stage. In addition, mitochondria played a crucial role in this process.

Changes in peripheral mitochondrial DNA copy number in metformin-treated women with polycystic ovary syndrome: a longitudinal study

BACKGROUND

Patients with polycystic ovarian syndrome (PCOS) are associated with known alterations in mitochondria DNA copy number (mtDNA-CN). The aim of this study is to study the change in mtDNA-CN in patients with PCOS who were treated with metformin.

METHODS

This is a prospective cohort of patients with PCOS, who received metformin for one year. From 2009 to 2015, 88 women diagnosed with PCOS, based on the Rotterdam criteria, were enrolled. Serial measurements of mtDNA-CN, 8-hydroxydeoxyguanosine (8-OHdG), anthropometric, metabolic, endocrine, and inflammatory markers were obtained before and after 3, 6, and 12 months of treatment.

RESULTS

A significant decrease in mtDNA-CN was seen over the course of one year. Other markers, including 8-OHdG, testosterone, free androgen index, blood pressure and liver enzymes, also decreased in the same interval. On regression analysis, there was a significant association between the change in mtDNA-CN and serum total testosterone, and no association between mtDNA-CN and metabolic factors.

CONCLUSIONS

Treatment with metformin is associated with a time-dependent decrease in mtDNA-CN in patients with PCOS who are treated over the course of one year. This may signify a reduction in mitochondria dysfunction. The change in mtDNA-CN corresponds to a similar change in serum total testosterone, and suggests a possible relationship between mtDNA-CN and testosterone.

TRIAL REGISTRATION

ClinicalTrials.gov , NCT00172523 . Registered September 15, 2005.

Exposure to environmental radionuclides alters mitochondrial DNA maintenance in a wild rodent

Mitochondria are sensitive to oxidative stress, including that derived from ionizing radiation. To quantify the effects of exposure to environmental radionuclides on mitochondrial DNA (mtDNA) dynamics in wildlife, bank voles (Myodes glareolus) were collected from the chernobyl exclusion zone (CEZ), where animals are exposed to elevated levels of radionuclides, and from uncontaminated areas within the CEZ and elsewhere in Ukraine. Brains of bank voles from outside the CEZ were characterized by low mtDNA copy number and low mtDNA damage; by contrast, bank voles within the CEZ had high mtDNA copy number and high mtDNA damage, consistent with putative damaging effects of elevated radiation and a compensatory response to maintain sufficient functioning mitochondria. In animals outside the CEZ, the expression levels of PGC-1α gene and mtDNA copy number were positively correlated as expected from this gene’s prominent role in mitochondrial biogenesis; this PGC-1α-mtDNA copy number association is absent in samples from the CEZ. Our data imply that exposure to radionuclides is associated with altered mitochondrial dynamics, evident in level of mtDNA and mtDNA damage and the level of activity in mitochondrial synthesis.

Inhibition of Mitochondrial Complex I Aggravates Folic Acid-Induced Acute Kidney Injury

Background: Some researches revealed that mitochondrial dysfunction is associated with various kidney injury. However, the role of mitochondrial dysfunction in the pathogenesis of acute kidney injury (AKI) still needs evidence. Methods: We evaluated the effect of mitochondrial complex I inhibitor rotenone on folic acid (FA)-induced AKI in mice. Results: Strikingly, the mice pretreated with rotenone at a dose of 200 ppm in food showed exacerbated kidney injury as shown by higher levels of blood urea nitrogen and creatinine compared with FA alone group. Meanwhile, both renal tubular injury score and the expression of renal tubular injury marker neutrophil gelatinase-associated lipocalin were further elevated in rotenone-pretreated mice, suggesting the deteriorated renal tubular injury. Moreover, the decrements of mitochondrial DNA copy number and the expressions of mitochondrial Cytochrome c oxidase subunit 1, mitochondrial NADH dehydrogenase subunit 1, and mitochondria-specific superoxide dismutase (SOD2) in the kidneys of FA-treated mice were further reduced in rotenone-pretreated mice, indicating the aggravated mitochondrial damage. In parallel with the SOD2 reduction, the oxidative stress markers of malondialdehyde and HO-1 displayed greater increment in AKI mice with rotenone pretreatment in line with the deteriorated apoptotic response and inflammation. Conclusion: Our results suggested that the inhibition of mitochondrial complex I activity aggravated renal tubular injury, mitochondrial damage, oxidative stress, cell apoptosis, and inflammation in FA-induced AKI.

CHIR-99021 regulates mitochondrial remodelling via β-catenin signalling and miRNA expression during endodermal differentiation

Mitochondrial remodelling is a central feature of stem cell differentiation. However, little is known about the regulatory mechanisms during these processes. Previously, we found that a pharmacological inhibitor of glycogen synthase kinase-3α and -3β, CHIR-99021, initiates human adipose stem cell differentiation into human definitive endodermal progenitor cells (hEPCs), which were directed to differentiate synchronously into hepatocyte-like cells after further treatment with combinations of soluble factors. In this study, we show that CHIR-99021 promotes mitochondrial biogenesis, the expression of PGC-1α (also known as PPARGC1A), TFAM and NRF1 (also known as NFE2L1), oxidative phosphorylation capacities, and the production of reactive oxygen species in hEPCs. Blocking mitochondrial dynamics using siRNA targeting DRP1 (also known as DNM1L) impaired definitive endodermal differentiation. Downregulation of β-catenin (CTNNB1) expression weakened the effect of CHIR-99021 on the induction of mitochondrial remodelling and the expression of transcription factors for mitochondrial biogenesis. Moreover, CHIR-99021 decreased the expression of miR-19b-2-5p, miR-23a-3p, miR-23c, miR-130a-3p and miR-130a-5p in hEPCs, which target transcription factors for mitochondrial biogenesis. These data demonstrate that CHIR-99021 plays a role in mitochondrial structure and function remodelling via activation of the β-catenin signalling pathway and inhibits the expression of miRNAs during definitive endodermal differentiation.This article has an associated First Person interview with the first author of the paper.

Toxic effects and involved molecular pathways of nanoparticles on cells and subcellular organelles

Owing to the increasing application of engineered nanoparticles (NPs), besides the workplace, human beings are also exposed to NPs from nanoproducts through the skin, respiratory tract, digestive tract and vein injection. This review states pathways of cellular uptake, subcellular distribution and excretion of NPs. The uptake pathways commonly include phagocytosis, micropinocytosis, clathrin- and caveolae-mediated endocytosis, scavenger receptor-related pathway, clathrin- or caveolae-independent pathway, and direct penetration or insertion. Then the ability of NPs to decrease cell viability and metabolic activity, change cell morphology, and destroy cell membrane, cytoskeleton and cell function was presented. In addition, the lowest dose decreasing cell metabolic viability compared with the control or IC₅₀ of silver, titanium dioxide, zinc oxide, carbon black, carbon nanotubes, silica, silicon NPs and cadmium telluride quantum dots to some cell lines was gathered. Next, this review attempts to increase our understanding of NP-caused adverse effects on organelles, which have implications in mitochondrial dysfunction, endoplasmic reticulum stress and lysosomal rupture. In particular, the disturbance of mitochondrial biogenesis and mitochondrial dynamic fusion-fission, mitophagy and cytochrome c-dependent apoptosis are involved. In addition, prolonged endoplasmic reticulum stress will result in apoptosis. Rupture of the lysosomal membrane was associated with inflammation, and both induction of autophagy and blockade of autophagic flow can result in cytotoxicity. Finally, the network mechanism of the combined action of multiple organelle dysfunction, apoptosis, autophagy and oxidative stress was discussed.

Mitochondrial Proteolysis and Metabolic Control

Mitochondria are metabolic hubs that use multiple proteases to maintain proteostasis and to preserve their overall quality. A decline of mitochondrial proteolysis promotes cellular stress and may contribute to the aging process. Mitochondrial proteases have also emerged as tightly regulated enzymes required to support the remarkable mitochondrial plasticity necessary for metabolic adaptation in a number of physiological scenarios. Indeed, the mutation and dysfunction of several mitochondrial proteases can cause specific human diseases with severe metabolic phenotypes. Here, we present an overview of the proteolytic regulation of key mitochondrial functions such as respiration, lipid biosynthesis, and mitochondrial dynamics, all of which are required for metabolic control. We also pay attention to how mitochondrial proteases are acutely regulated in response to cellular stressors or changes in growth conditions, a greater understanding of which may one day uncover their therapeutic potential.

PINK1 mediates spinal cord mitophagy in neuropathic pain

Background: Mitophagy is the selective engulfment of mitochondria by autophagosomes and the subsequent mitochondrial catabolism by lysosomes. Evidence has suggested an important role for mitochondrial dynamics and mitophagic flux in the development of many different neurodegenerative diseases. Objectives: The potential role of the mechanism underlying mitochondrial dynamics and mitophagic flux as it may relate to neuropathic pain is not well understood. This is a disease that largely remains an area of mechanistic uncertainty. PINK1 is a PTEN-induced mitochondrial kinase that can be selectively activated under mitochondrial stress conditions and lead to the induction of mitophagy. Materials and methods: A neuropathic pain rat model was established via spinal nerve ligation (SNL) and nociception was assayed via the von Frey filament method. Increased expression of PINK1 and the mechanism of mitophagy was detected in GABAergic interneurons of dorsal horn neurons of mice that underwent L5 SNL in comparison to control mice counterparts (n=8, P<0.001) by Western blotting, immunohistochemistry and double immunofluorescence staining. Results: Elevated expression of PINK1 appeared to localize selectively to GABAergic interneurons, particularly within autophagic mitochondria as evidenced by co-localization studies of PINK1 with BECN1, LC3II and COX IV on immunofluorescent microscopy. Furthermore, we also detected a significant increase in autophagosomes in dorsal horn neurons of SNL mice and this was consistent with increased autophagic activity as measured by the p62 autophagic substrate. Conclusion: These results demonstrate that neuropathic pain causes aberrant mitophagic flux selectively in GABAergic interneurons and provide evidence implicating mitophagy as an important area of future molecular studies to enhance our understanding of neuropathic pain.

Inhibition of the mitochondrial complex-1 protects against carbon tetrachloride-induced acute liver injury

Mitochondrial dysfunction has been documented to play a crucial role in the pathogenesis of liver injury. In the present study, we investigated the role of rotenone, a mitochondrial complex-1 inhibitor, in carbon tetrachloride (CCl₄) -induced acute liver injury, as well as the underlying mechanisms. Before CCl₄ administration, the mice were pretreated with rotenone at a dose of 250 ppm in food for three days. Then CCl₄ was administered to the mice for 16 h by intraperitoneal injection. The liver injury, mitochondrial status, oxidative stress, and inflammation were examined. Strikingly, CCl₄ treatment markedly induced liver injury as shown by enhanced serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT) and morphological lesions (HE stating), which was significantly attenuated by rotenone treatment in line with the reduced activity of mitochondrial complex-1. Meanwhile, oxidative stress markers of malondialdehyde (MDA), 4-hydroxynonenal (HNE), and dihydroethidium (DHE) and the inflammatory markers of IL-1β, MCP-1, TNF-α, TLR-4, and IL-6 were also significantly suppressed by rotenone. More importantly, the mitochondrial abnormalities shown by the reduction of SOD2, mitochondrial transcription factor A (TFAM), mitochondrial NADH dehydrogenase subunit 1 (mtND1), and Cytb were significantly restored, indicating that rotenone protected against mitochondrial damage induced by CCl₄ in liver. Moreover, rotenone treatment alone did not significantly alter liver morphology and liver enzymes ALT and AST. CYP2E1, a metabolic enzyme of CCl₄, was also not significantly affected by rotenone. In conclusion, rotenone protected the liver from CCl₄-induced damage possibly by inhibiting the mitochondrial oxidative stress and inflammation.

Lgr5-overexpressing mesenchymal stem cells augment fracture healing through regulation of Wnt/ERK signaling pathways and mitochondrial dynamics

Fracture remains one of the most common traumatic conditions in orthopedic surgery. The use of mesenchymal stem cells (MSCs) to augment fracture repair is promising. Leucine-rich repeat-containing GPCR 5 (Lgr5), a transmembrane protein, has been identified as a novel adult stem cell marker in various organs and tissues. However, the roles of Lgr5 in MSCs are not fully understood. In this study, we investigated cellular functions of Lgr5 in MSCs and its potential implications in treating fracture. Lgr5-overexpressing MSCs (MSC^Lgr5) were established in murine SV40 promoter-driven luciferase reporter MSC line through virus transfection. Results of real-time quantitative PCR and Western blot analysis confirmed the increased expression of Lgr5 in MSC^Lgr5. MSC^Lgr5 exhibited increased osteogenic capacity, which may result from elevated expression of β-catenin and phosphorylated ERK1/2 within the nuclear region of cells. In contrast, inhibition of Lgr5 expression decreased the osteogenic differentiation ability of MSCs, accompanied with increased mitochondrial fragmentation and reduced expression of β-catenin. Local transplantation of MSC^Lgr5 at fracture sites accelerated fracture healing via enhanced osteogenesis and angiogenesis. MSC^Lgr5 stimulated the tube formation capacity of HUVECs in a Matrigel coculture system in vitro significantly. Taken together, results suggest that Lgr5 is implicated in the cellular processes of osteogenic differentiation of MSCs through regulation of Wnt and ERK signaling pathways and mitochondrial dynamics in fusion and fission. Inhibition of Lgr5 expression induced increased mitochondrial fragmentation and suppression of osteogenesis. MSC^Lgr5 exhibited enhanced therapeutic efficacy for fracture healing, which may serve as a superior cell source for bone tissue repair.-Lin, W., Xu, L., Pan, Q., Lin, S., Feng, L., Wang, B., Chen, S., Li, Y., Wang, H., Li, Y., Wang, Y., Lee, W. Y. W., Sun, D., Li, G. Lgr5-overexpressing mesenchymal stem cells augment fracture healing through regulation of Wnt/ERK signaling pathways and mitochondrial dynamics.

Drp1 Phosphorylation Is Indispensable for Steroidogenesis in Leydig Cells

The initial steps of steroidogenesis occur in the mitochondria. Dynamic changes in the mitochondria are associated with their fission and fusion. Therefore, understanding the cellular and molecular relationships between steroidogenesis and mitochondrial dynamics is important. The hypothesis of the current study is that mitochondrial fission and fusion are closely associated with steroid hormone synthesis in testicular Leydig cells. Steroid hormone production, induced by dibutyryl cAMP (dbcAMP) in Leydig cells, was accompanied by increased mitochondrial mass. Mitochondrial elongation increased during the dbcAMP-induced steroid production, whereas mitochondrial fragmentation was reduced. Among the mitochondrial-shaping proteins, the level of dynamin-associated protein 1 (Drp1) was altered in response to dbcAMP stimulation. The increase in Drp1 Ser 637 phosphorylation correlated with steroid hormone production in the MA-10 Leydig cells as well as in the primary adult rat Leydig cells. Drp1 was differentially expressed in the Leydig cells during testicular development. Finally, gonadotropin administration altered the status of Drp1 phosphorylation in the Leydig cells of immature rat testes. Overall, mitochondrial dynamics is directly linked to steroidogenesis, and Drp1 plays an important regulatory role during steroidogenesis. This study shows that Drp1 level is regulated by cAMP and that its phosphorylation via protein kinase A (PKA) activation plays a decisive role in mitochondrial shaping by offering an optimal environment for steroid hormone biosynthesis in Leydig cells. Therefore, it is suggested that PKA-mediated Drp1 Ser 637 phosphorylation is indispensable for steroidogenesis in the Leydig cells, and this phosphorylation results in mitochondrial elongation via the relative attenuation of mitochondrial fission during steroidogenesis.

Adverse Effects of Fine-Particle Exposure on Joints and Their Surrounding Cells and Microenvironment

Current understanding of the health risks and adverse effects upon exposure to fine particles is premised on the direct association of particles with target organs, particularly the lung; however, fine-particle exposure has also been found to have detrimental effects on sealed cavities distant to the portal-of-entry, such as joints. Moreover, the fundamental toxicological issues have been ascribed to the direct toxic mechanisms, in particular, oxidative stress and proinflammatory responses, without exploring the indirect mechanisms, such as compensated, adaptive, and secondary effects. In this Review, we recapitulate the current findings regarding the detrimental effects of fine-particle exposure on joints, the surrounding cells, and microenvironment, as well as their deteriorating impact on the progression of arthritis. We also elaborate the likely molecular mechanisms underlying the particle-induced detrimental influence on joints, not limited to direct toxicity, but also considering the other indirect mechanisms. Because of the similarities between fine air particles and engineered nanomaterials, we compare the toxicities of engineered nanomaterials to those of fine air particles. Arthritis and joint injuries are prevalent, particularly in the elderly population. Considering the severity of global exposure to fine particles and limited studies assessing the detrimental effects of fine-particle exposure on joints and arthritis, this Review aims to appeal to a broad interest and to promote more research efforts in this field.

Mitochondrial DNA content in blood and carbon load in airway macrophages. A panel study in elderly subjects

BACKGROUND

Mitochondria are sensitive to air pollutants due to their lack of repair capacity. Changes in mitochondrial DNA copy number (mtDNAcn) or content is a proxy of mitochondrial damage and has been associated with recent exposure to traffic-derived air pollutants, nitrogen dioxide (NO₂) and black carbon (BC). Inhaled BC can be phagocytosed by airway macrophages (AMs), and its amount in AM reflects personal exposure to traffic-related air pollution.

OBJECTIVES

The present study investigated the relation between the internal marker AM BC and ambient NO₂ concentration and examined the associations of mtDNAcn with NO₂ and AM BC.

METHODS

A panel of 20 healthy retired participants (10 couples) living in Belgium underwent repeated assessments of health and air pollution exposure at 11 time points over one year. We increased exposure contrast temporarily by moving participants for 10 days to Milan, Italy (high exposure) and to Vindeln, Sweden (low exposure). Personal exposure to NO₂ was measured during 5 consecutive days prior to each assessment time point. The amount of BC was assessed by image analysis in AMs retrieved from induced sputum collected at 7 time points. Blood mtDNAcn was determined by qPCR at each time point. Associations between AM BC and NO₂, and of mtDNAcn with NO₂ and AM BC were estimated using linear mixed effect models adjusted for covariates and potential confounders.

RESULTS

Mean concentrations of 5-day average NO₂ were higher in Milan (64 μg/m³) and lower in Vindeln (4 μg/m³) than Belgium (26 μg/m³). Each 10 μg/m³ increment in NO₂ exposure during the last 5 days was associated with 0.07 μm² (95% CI: 0.001 to 0.012) increase in median area of AM BC. A 10 μg/m³ increase in NO₂ was associated with 3.9% (95% CI: 2.2 to 5.5%) decrease in mtDNAcn. Consistently, each 1 μm² increment in median area of AM BC was associated with 24.8% (95% CI: 6.8 to 39.3%) decrease in mtDNAcn.

CONCLUSION

In this quasi-experimental setting involving moving persons to places with high and low ambient air pollution, we found changes in AM BC according to ambient air pollution levels measured during the previous 5 days. Both higher ambient NO₂ and the internal lung BC load, paralleled mitochondrial compromises as exemplified by lower mtDNA content.

Involvement of Mitochondria in Neurodegeneration in Multiple Sclerosis

Functional disruption and neuronal loss followed by progressive dysfunction of the nervous system underlies the pathogenesis of numerous disorders defined as "neurodegenerative diseases". Multiple sclerosis, a chronic inflammatory demyelinating disease of the central nervous system resulting in serious neurological dysfunctions and disability, is one of the most common neurodegenerative diseases. Recent studies suggest that disturbances in mitochondrial functioning are key factors leading to neurodegeneration. In this review, we consider data on mitochondrial dysfunctions in multiple sclerosis, which were obtained both with patients and with animal models. The contemporary data indicate that the axonal degeneration in multiple sclerosis largely results from the activation of Ca2+-dependent proteases and from misbalance of ion homeostasis caused by energy deficiency. The genetic studies analyzing association of mitochondrial DNA polymorphic variants in multiple sclerosis suggest the participation of mitochondrial genome variability in the development of this disease, although questions of the involvement of individual genomic variants are far from being resolved.

Mitochondrial quality control in AMD: does mitophagy play a pivotal role?

Age-related macular degeneration (AMD) is the predominant cause of visual loss in old people in the developed world, whose incidence is increasing. This disease is caused by the decrease in macular function, due to the degeneration of retinal pigment epithelium (RPE) cells. The aged retina is characterised by increased levels of reactive oxygen species (ROS), impaired autophagy, and DNA damage that are linked to AMD pathogenesis. Mitophagy, a mitochondria-specific type of autophagy, is an essential part of mitochondrial quality control, the collective mechanism responsible for this organelle's homeostasis. The abundance of ROS, DNA damage, and the excessive energy consumption in the ageing retina all contribute to the degeneration of RPE cells and their mitochondria. We discuss the role of mitophagy in the cell and argue that its impairment may play a role in AMD pathogenesis. Thus, mitophagy as a potential therapeutic target in AMD and other degenerative diseases is as well explored.

The Main Molecular Mechanisms Underlying Methamphetamine- Induced Neurotoxicity and Implications for Pharmacological Treatment

Methamphetamine (METH) is a popular new-type psychostimulant drug with complicated neurotoxicity. In spite of mounting evidence on METH-induced damage of neural cell, the accurate mechanism of toxic effect of the drug on central nervous system (CNS) has not yet been completely deciphered. Besides, effective treatment strategies toward METH neurotoxicity remain scarce and more efficacious drugs are to be developed. In this review, we summarize cellular and molecular bases that might contribute to METH-elicited neurotoxicity, which mainly include oxidative stress, excitotoxicity, and neuroinflammation. We also discuss some drugs that protect neural cells suffering from METH-induced neurotoxic consequences. We hope more in-depth investigations of exact details that how METH produces toxicity in CNS could be carried out in future and the development of new drugs as natural compounds and immunotherapies, including clinic trials, are expected.

Rotenone ameliorates chronic renal injury caused by acute ischemia/reperfusion

Acute kidney injury (AKI) has been widely recognized as an important risk factor leading to the occurrence and progression of chronic kidney disease (CKD). Thus, development of the strategies in retarding the transition of AKI to CKD is becoming a hot research field. Recently, accumulating evidence suggested a pathogenic role of mitochondrial dysfunction in both AKI and CKD. Therefore, in the present study, we evaluated the effect of mitochondrial complex 1 inhibition by rotenone on the chronic renal damage induced by acute ischemia-reperfusion. The mice were treated with 45 min unilateral renal ischemia and reperfusion (I/R) to induce an acute renal injury. After three days of I/R injury, rotenone at a dose of 200 ppm in food was administered to the mice. Strikingly, after three weeks treatment with rotenone, we found that the unilateral I/R-induced tubular damage, tubulointerstitial fibrosis were all attenuated by rotenone as determined by the tubular injury score, Masson staining, and the levels of collagen-I, collagen-III, fibronectin, PAI-1, and TGF-β. Meanwhile, the enhanced inflammatory markers of TNF-α, IL-1β, IL-6, and IL-18 and apoptotic markers of Bax and caspase-3 were all significantly blunted by inhibiting mitochondrial complex-1. Moreover, rotenone treatment also partially protected the mitochondria as shown by the restoration of mitochondrial SOD (SOD2), ATPB, and mitochondrial DNA copy number. These findings suggested that inhibition of mitochondrial complex-1 activity by rotenone could retard the progression of AKI to CKD probably via protecting the mitochondrial function to some extent.

Carbon black suppresses the osteogenesis of mesenchymal stem cells: the role of mitochondria

BACKGROUND

The rapid increase in carbon black poses threats to human health. We evaluated the effect of CB (Printex 90) on the osteogenesis of bone-marrow-derived mesenchymal stem cells (MSCs). Mitochondria play an important role in the osteogenesis of MSCs and are potential targets of nanomaterials, so we studied the role of mitochondria in the CB Printex 90-induced effects on osteogenesis.

RESULTS

Low doses of Printex 90 (3 ng/mL and 30 ng/mL) that did not cause deleterious effects on MSCs' viability significantly inhibited osteogenesis of MSCs. Printex 90 caused down-regulation of osteoblastic markers, reduced activity of alkaline phosphatase (ALP), and poor mineralization of osteogenically induced MSCs. Cellular ATP production was decreased, mitochondrial respiration was impaired with reduced expression of ATPase, and the mitochondrial membrane was depolarized. The quantity and quality of mitochondria are tightly controlled by mitochondrial biogenesis, mitochondrial dynamics and mitophagy. The transcriptional co-activator and transcription factors for mitochondrial biogenesis, PGC-1α, Nrf1 and TFAM, were suppressed by Printex 90 treatment, suggesting that decreased biogenesis was caused by Printex 90 treatment during osteogenesis. Mitochondrial fusion and fission were significantly inhibited by Printex 90 treatment. PINK1 accumulated in Printex 90-treated cells, and more Parkin was recruited to mitochondria, indicating that mitophagy increased to remove the damaged mitochondria.

CONCLUSIONS

This is the first report of the inhibitory effects of CB on the osteogenesis of MSCs and the involvement of mitochondria in CB Printex 90-induced suppression of MSC osteogenesis.

The Role of Mitochondria in Methamphetamine-induced inhibitory effects on osteogenesis of Mesenchymal Stem Cells

Methamphetamine (METH) abuse causes significant physical, psychological, and social concerns. Therefore, in this study, we investigated its effects on osteogenic differentiation of mesenchymal stem cells (MSCs). We found that METH dose-dependently affected MSCs viability. Upon osteogenic induction, the 3 and 30 µmol/l METH dosages without deleterious effects on MSCs viability resulted in the down-regulation of osteoblastic marker genes (Alp, Bglap, and Runx2), suppression of the protein expression of RUNX2, and decreased ALP activity and mineralization ability. Mitochondria are essential during osteogenesis of MSCs. Our analysis on mitochondrial function revealed that METH decreased ATP production, suppressed the oxygen consumption rate, and depolarized the mitochondrial membrane potential, but it had no significant effects on the protein expression of the five complexes on the respiratory chain. Additionally, METH could impair mitochondrial biogenesis, as demonstrated by decreased mtDNA and down-regulated biogenesis factors. Mitochondrial fusion regulators were also decreased at the mRNA and protein levels. However, mitochondrial fission and mitophagy were not affected. In conclusion, our study revealed that exposure to METH could result in decreased mitochondrial biogenesis and fusion as well as mitochondrial dysfunction, and thus it suppressed the osteogenesis of MSCs.

ROS-Induced DNA Damage Associates with Abundance of Mitochondrial DNA in White Blood Cells of the Untreated Schizophrenic Patients

OBJECTIVE

The aim of this study was (1) to examine the leukocyte mtDNA copy number (CN) in unmedicated (SZ (m-)) and medicated (SZ (m+)) male patients with paranoid schizophrenia (SZ) in comparison with the healthy male controls (HC) and (2) to compare the leukocyte mtDNA CN with the content of an oxidation marker 8-oxodG in lymphocytes of the SZ (m-) patients.

METHODS

We evaluated leukocyte mtDNA CN of 110 subjects with SZ in comparison with 60 male HC by the method qPCR (ratio mtDNA/nDNA (gene B2M) was detected). SZ patients were divided into two subgroups. The patients of the subgroups SZ (m+) (N = 55) were treated with standard antipsychotic medications in the hospital. The patients of the subgroup SZ (m-) (N = 55) were not treated before venous blood was sampled. To evaluate oxidative DNA damage, we quantified the levels of 8-oxodG in lymphocytes (flow cytometry) of SZ (m-) patients (N = 55) and HC (N = 30).

RESULTS

The leukocyte mtDNA CN showed no significant difference in SZ (m+) patients and HC. The mtDNA CN in the unmedicated subgroup SZ (m-) was significantly higher than that in the SZ (m+) subgroup or in HC group. The level of 8-oxodG in the subgroup SZ (m-) was significantly higher than that in HC group.

CONCLUSION

The leukocytes of the unmedicated SZ male patients with acute psychosis contain more mtDNA than the leukocytes of the male SZ patients treated with antipsychotic medications or the healthy controls. MtDNA content positively correlates with the level of 8-oxodG in the unmedicated SZ patients.

Mitophagy-driven mitochondrial rejuvenation regulates stem cell fate

Our understanding on how selective mitochondrial autophagy, or mitophagy, can sustain the archetypal properties of stem cells is incomplete. PTEN-induced putative kinase 1 (PINK1) plays a key role in the maintenance of mitochondrial morphology and function and in the selective degradation of damaged mitochondria by mitophagy. Here, using embryonic fibroblasts from PINK1 gene-knockout (KO) mice, we evaluated whether mitophagy is a causal mechanism for the control of cell-fate plasticity and maintenance of pluripotency. Loss of PINK1-dependent mitophagy was sufficient to dramatically decrease the speed and efficiency of induced pluripotent stem cell (iPSC) reprogramming. Mitophagy-deficient iPSC colonies, which were characterized by a mixture of mature and immature mitochondria, seemed unstable, with a strong tendency to spontaneously differentiate and form heterogeneous populations of cells. Although mitophagy-deficient iPSC colonies normally expressed pluripotent markers, functional monitoring of cellular bioenergetics revealed an attenuated glycolysis in mitophagy-deficient iPSC cells. Targeted metabolomics showed a notable alteration in numerous glycolysis- and TCA-related metabolites in mitophagy-deficient iPSC cells, including a significant decrease in the intracellular levels of α-ketoglutarate -a key suppressor of the differentiation path in stem cells. Mitophagy-deficient iPSC colonies exhibited a notably reduced teratoma-initiating capacity, but fully retained their pluripotency and multi-germ layer differentiation capacity in vivo. PINK1-dependent mitophagy pathway is an important mitochondrial switch that determines the efficiency and quality of somatic reprogramming. Mitophagy-driven mitochondrial rejuvenation might contribute to the ability of iPSCs to suppress differentiation by directing bioenergetic transition and metabolome remodeling traits. These findings provide new insights into how mitophagy might influence the stem cell decisions to retain pluripotency or differentiate in tissue regeneration and aging, tumor growth, and regenerative medicine.

Energetic mitochondrial failing in vitiligo and possible rescue by cardiolipin

Vitiligo is characterized by death or functional defects of epidermal melanocytes through still controversial pathogenic process. Previously, we showed that mitochondria-driven pre-senescent phenotype diminishes the capability of vitiligo melanocytes to cope with stressful stimuli. In the current study, we investigated markers of mitochondrial energy metabolism including the PGC1a axis, and then we determined the index of mitochondrial impairment using a cytomic approach. We found in cultured epidermal vitiligo melanocytes, compared to healthy ones, low ATP, increased proton leakage, and altered expression of several glycolytic enzymes (hexokinase II, pyruvic dehydrogenase kinase 1 and pyruvic kinase M2), We suggest that the low ATP production may be sufficient in steady-state conditions but it is unable to cover further needs. We also found in vitiligo melanocyrtes hyper-activation of the PGC1α axis, finalized to counteract the energy defect. Cytomic analysis, supported by MitoTracker Red pattern and ex-vivo immunohistochemistry, suggested an increased mitochondrial mass, possibly useful to ensure the essential ATP level. Finally, pharmacological cardiolipin stabilization reverted the energetic impairment, confirming the initial mitochondrial role. In conclusion, we report new insight in the pathogenetic mechanism of viitligo and indicate that the mitochondrial failure rescue by cardiolipin manipulation may be a new intriguing target in treatment development.

Mitochondrial DNA levels in Huntington disease leukocytes and dermal fibroblasts

Huntington disease (HD) is an inherited neurodegenerative disorder caused by mutations in the huntingtin gene. Involvement of mitochondrial dysfunctions in, and especially influence of the level of mitochondrial DNA (mtDNA) on, development of this disease is unclear. Here, samples of blood from 84 HD patients and 79 controls, and dermal fibroblasts from 10 HD patients and 9 controls were analysed for mtDNA levels. Although the type of mitochondrial haplogroup had no influence on the mtDNA level, and there was no correlation between mtDNA level in leukocytes in HD patients and various parameters of HD severity, some considerable differences between HD patients and controls were identified. The average mtDNA/nDNA relative copy number was significantly higher in leukocytes, but lower in fibroblasts, of symptomatic HD patients relative to the control group. Moreover, HD women displayed higher mtDNA levels in leukocytes than HD men. Because this is the largest population analysed to date, these results might contribute to explanation of discrepancies between previously published studies concerning levels of mtDNA in cells of HD patients. We suggest that the size of the investigated population and type of cells from which DNA is isolated could significantly affect results of mtDNA copy number estimation in HD. Hence, these parameters should be taken into consideration in studies on mtDNA in HD, and perhaps also in other diseases where mitochondrial dysfunction occurs.

Association of mitochondrial DNA in peripheral blood with depression, anxiety and stress- and adjustment disorders in primary health care patients

Mitochondrial dysfunction may result in a variety of diseases. The objectives here were to examine possible differences in mtDNA copy number between healthy controls and patients with depression, anxiety or stress- and adjustment disorders; the association between mtDNA copy number and disease severity at baseline; and the association between mtDNA copy number and response after an 8-week treatment (mindfulness, cognitive based therapy). A total of 179 patients in primary health care (age 20-64 years) with depression, anxiety and stress- and adjustment disorders, and 320 healthy controls (aged 19-70 years) were included in the study. Relative mtDNA copy number was measured using quantitative real-time PCR on peripheral blood samples. We found that the mean mtDNA copy number was significantly higher in patients compared to controls (84.9 vs 75.9, p<0.0001) at baseline. The difference in mtDNA copy number between patients and controls remained significant after controlling for age and sex (ß=8.13, p<0.0001; linear regression analysis). The mtDNA copy number was significantly associated with Patient Health Questionnaire (PHQ-9) scores (β=0.57, p=0.02) at baseline. After treatment, the change in mtDNA copy number was significantly associated with the treatment response, i.e., change in Hospital Anxiety and Depression Scale (HADS-D) and PHQ-9 scores (ß=1.00, p=0.03 and ß=0.65, p=0.04, respectively), after controlling for baseline scores, age, sex, BMI, smoking status, alcohol drinking and medication. Our findings show that mtDNA copy number is associated with symptoms of depression, anxiety and stress- and adjustment disorders and treatment response in these disorders.

Reductions in the mitochondrial enzyme α-ketoglutarate dehydrogenase complex in neurodegenerative disease - beneficial or detrimental?

Reductions in metabolism and excess oxidative stress are prevalent in multiple neurodegenerative diseases. The activity of the mitochondrial enzyme α-ketoglutarate dehydrogenase complex (KGDHC) appears central to these abnormalities. KGDHC is diminished in multiple neurodegenerative diseases. KGDHC can not only be rate limiting for NADH production and for substrate level phosphorylation, but is also a source of reactive oxygen species (ROS). The goal of these studies was to determine how changes in KGDHC modify baseline ROS, the ability to buffer ROS, baseline glutathionylation, calcium modulation and cell death in response to external oxidants. In vivo, reducing KGDHC with adeno virus diminished neurogenesis and increased oxidative stress. In vitro, treatments of short duration increased ROS and glutathionylation and enhanced the ability of the cells to diminish the ROS from added oxidants. However, long-term reductions lessened the ability to diminish ROS, diminished glutathionylation and exaggerated oxidant-induced changes in calcium and cell death. Increasing KGDHC enhanced the ability of the cells to diminish externally added ROS and protected against oxidant-induced changes in calcium and cell death. The results suggest that brief periods of diminished KGDHC are protective, while prolonged reductions are harmful. Furthermore, elevated KGDHC activities are protective. Thus, mitogenic therapies that increase KGDHC may be beneficial in neurodegenerative diseases. Read the Editorial Highlight for this article on Page 689.

Analysis of the mechanism of radiation-induced upregulation of mitochondrial abundance in mouse fibroblasts

Mitochondria strongly contribute to the maintenance of cellular integrity through various mechanisms, including oxidative adenosine triphosphate production and calcium homeostasis regulation. Therefore, proper regulation of the abundance, distribution and activity of mitochondria is crucial for the maintenance of cellular homeostasis. Previous studies have shown that ionizing radiation (IR) alters mitochondrial functions, suggesting that mitochondria are likely to be an important target of IR. Though IR reportedly influences cellular mitochondrial abundance, the mechanism remains largely unknown. In this study, we examined how IR influences mitochondrial abundance in mouse fibroblasts. When mouse NIH/3T3 cells were exposed to X-rays, a time-dependent increase was observed in mitochondrial DNA (mtDNA) and mitochondrial mass, indicating radiation-induced upregulation of mitochondrial abundance. Meanwhile, not only did we not observe a significant change in autophagic activity after irradiation, but in addition, IR hardly influenced the expression of two mitochondrial proteins, cytochrome c oxidase subunit IV and cytochrome c, or the mRNA expression of Polg, a component of DNA polymerase γ. We also observed that the expression of transcription factors involved in mitochondrial biogenesis was only marginally affected by IR. These data imply that radiation-induced upregulation of mitochondrial abundance is an event independent of macroautophagy and mitochondrial biogenesis. Furthermore, we found evidence that IR induced long-term cell cycle arrest and cellular senescence, indicating that these events are involved in regulating mitochondrial abundance. Considering the growing significance of mitochondria in cellular radioresponses, we believe the present study provides novel insights into understanding the effects of IR on mitochondria.

Oxidative Stress and Liver Cancer: Etiology and Therapeutic Targets

Accumulating evidence has indicated that oxidative stress (OS) is associated with the development of hepatocellular carcinoma (HCC). However, the mechanisms remain largely unknown. Normally, OS occurs when the body receives any danger signal-from either an internal or external source-and further induces DNA oxidative damage and abnormal protein expression, placing the body into a state of vulnerability to the development of various diseases such as cancer. There are many factors involved in liver carcinogenesis, including hepatitis B virus (HBV) and hepatitis C virus (HCV) infection, alcohol abuse, and nonalcoholic fatty liver disease (NAFLD). The relationship between OS and HCC has recently been attracting increasing attention. Therefore, elucidation of the impact of OS on the development of liver carcinogenesis is very important for the prevention and treatment of liver cancer. This review focuses mainly on the relationship between OS and the development of HCC from the perspective of cellular and molecular mechanisms and the etiology and therapeutic targets of HCC.

Increased mitochondrial DNA deletions and copy number in transfusion-dependent thalassemia

BACKGROUND

Iron overload is the primary cause of morbidity in transfusion-dependent thalassemia. Increase in iron causes mitochondrial dysfunction under experimental conditions, but the occurrence and significance of mitochondrial damage is not understood in patients with thalassemia.

METHODS

Mitochondrial DNA (mtDNA) to nuclear DNA copy number (Mt/N) and frequency of the common 4977-bp mitochondrial deletion (ΔmtDNA⁴⁹⁷⁷) were quantified using a quantitative PCR assay on whole blood samples from 38 subjects with thalassemia who were receiving regular transfusions.

RESULTS

Compared with healthy controls, Mt/N and ΔmtDNA⁴⁹⁷⁷ frequency were elevated in thalassemia (P = 0.038 and P < 0.001, respectively). ΔmtDNA⁴⁹⁷⁷ was increased in the presence of either liver iron concentration > 15 mg/g dry-weight or splenectomy, with the highest levels observed in subjects who had both risk factors (P = 0.003). Myocardial iron (MRI T2* < 20 ms) was present in 0%, 22%, and 46% of subjects with ΔmtDNA⁴⁹⁷⁷ frequency < 20, 20-40, and > 40/1 × 10⁷ mtDNA, respectively (P = 0.025). Subjects with Mt/N values below the group median had significantly lower Matsuda insulin sensitivity index (5.76 ± 0.53) compared with the high Mt/N group (9.11 ± 0.95, P = 0.008).

CONCLUSION

Individuals with transfusion-dependent thalassemia demonstrate age-related increase in mtDNA damage in leukocytes. These changes are markedly amplified by splenectomy and are associated with extrahepatic iron deposition. Elevated mtDNA damage in blood cells may predict the risk of iron-associated organ damage in thalassemia.

SUMO-regulated mitochondrial function in Parkinson's disease

Parkinson's disease (PD) is the second most common neurodegenerative disorder characterized by cardinal motor signs such as rigidity, bradykinesia or rest tremor that arise from a significant death of dopaminergic neurons. Non-dopaminergic degeneration also occurs and it seems to induce the deficits in olfactory, emotional, and memory functions that precede the classical motor symptoms in PD. Despite the majority of PD cases being sporadic, several genes have previously been associated with the hereditary forms of the disease. The proteins encoded by some of these genes, including α-synuclein, DJ-1, and parkin, are modified by small ubiquitin-like modifier (SUMO), a post-translational modification that regulates a variety of cellular processes. Among the several pathogenic mechanisms proposed for PD is mitochondrial dysfunction. Recent studies suggest that SUMOylation can interfere with mitochondrial dynamics, which is essential for neuronal function, and may play a pivotal role in PD pathogenesis. Here, we present an overview of recent studies on mitochondrial disturbance in PD and the potential SUMO-modified proteins and pathways involved in this process. SUMOylation, a post-translational modification, interferes with mitochondrial dynamics, and may play a pivotal role in Parkinson's disease (PD). SUMOylation maintains α-synuclein (α-syn) in a soluble form and activates DJ-1, decreasing mitochondrial oxidative stress. SUMOylation may reduce the amount of parkin available for mitochondrial recruitment and decreases mitochondrial biogenesis through suppression of peroxisomal proliferator-activated receptor-γ co-activator 1 α (PGC-1α). Mitochondrial fission can be regulated by dynamin-related protein 1 SUMO-1- or SUMO-2/3-ylation. A fine balance for the SUMOylation/deSUMOylation of these proteins is required to ensure adequate mitochondrial function in PD.

Molecular Profile of Mitochondrial Dysfunction in Kidney Transplant Biopsies Is Associated With Poor Allograft Outcome

BACKGROUND

In kidney transplantation (KT), progression of chronic histological damage with subclinical inflammation is associated with poor long-term allograft survival. The role of nonimmunological pathways in chronic allograft injury has not been fully assessed.

METHODS

We analyzed a public microarray dataset that used 1-year protocol kidney transplant biopsy specimens to investigate whether nonimmunological genes and pathways might influence long-term allograft outcome. The selected microarray dataset included 3 patient/sample groups based on their histological findings: normal histology (n = 25), interstitial fibrosis alone (IF alone, n = 24), and interstitial fibrosis with inflammation (IF+i, n = 16). The IF+i group had lower death-censored graft survival and renal function in patients with a mean follow-up of 4 years. We performed statistical analysis comparing gene expression patterns in the 3 group samples.

RESULTS

Gene cluster enrichment and group-specific expression patterns demonstrated a divergent pattern between mitochondrial and immune response genes, with downregulation of mitochondrial genes in the IF+i group. Gene ontological analysis of the downregulated mitochondrial genes identified generation of precursor metabolite and energy, and response to oxidative stress as the most significant biological processes. The transcription regulation pathway analysis of downregulated gene cluster demonstrated transcription factors involved in mitochondrial biogenesis.

CONCLUSIONS

The molecular signature of mitochondrial dysfunction reflects mitochondrial energetic insufficiency, and inadequate antioxidant response involved in mitochondria biogenesis pathways is associated with IF+i and worse long-term allograft survival. Thus, mitochondria function impairment appears to be an important nonimmune factor involved in chronic allograft injury.

Mitochondrial Alterations in Peripheral Mononuclear Blood Cells from Alzheimer's Disease and Mild Cognitive Impairment Patients

It is well recognized that mitochondrial dysfunction contributes to neurodegeneration occurring in Alzheimer's disease (AD). However, evidences of mitochondrial defects in AD peripheral cells are still inconclusive. Here, some mitochondrial-encoded and nuclear-encoded proteins, involved in maintaining the correct mitochondria machine, were investigated in terms of protein expression and enzymatic activity in peripheral blood mononuclear cells (PBMCs) isolated from AD and Mild Cognitive Impairment (MCI) patients and healthy subjects. In addition mitochondrial DNA copy number was measured by real time PCR. We found some differences and some similarities between AD and MCI patients when compared with healthy subjects. For example, cytochrome C and cytochrome B were decreased in AD, while MCI showed only a statistical reduction of cytochrome C. On the other hand, both AD and MCI blood cells exhibited highly nitrated MnSOD, index of a prooxidant environment inside the mitochondria. TFAM, a regulator of mitochondrial genome replication and transcription, was decreased in both AD and MCI patients' blood cells. Moreover also the mitochondrial DNA amount was reduced in PBMCs from both patient groups. In conclusion these data confirmed peripheral mitochondria impairment in AD and demonstrated that TFAM and mtDNA amount reduction could be two features of early events occurring in AD pathogenesis.

Fructose induces mitochondrial dysfunction and triggers apoptosis in skeletal muscle cells by provoking oxidative stress

Mitochondrial dysfunction in skeletal muscle has been implicated in the development of insulin resistance, a major characteristic of type 2 diabetes. There is evidence that oxidative stress results from the increased production of reactive oxygen species and reactive nitrogen species leads to mitochondrial dysfunction, tissue damage, insulin resistance, and other complications observed in type 2 diabetes. It has been suggested that intake of high fructose contributes to insulin resistance and other metabolic disturbances. However, there is limited information about the direct effect of fructose on the mitochondrial function of skeletal muscle, the major metabolic determinant of whole body insulin activity. Here, we assessed the effect of fructose exposure on mitochondria-mediated mechanisms in skeletal muscle cells. Exposure of L6 myotubes to high fructose stimulated the production of mitochondrial reactive oxygen species and nitric oxide (NO), and the expression of inducible NO synthase. Fructose-induced oxidative stress was associated with increased translocation of nuclear factor erythroid 2-related factor-2 to the nucleus, decreases in mitochondrial DNA content and mitochondrial dysfunctions, as evidenced by decreased activities of citrate synthase and mitochondrial dehydrogenases, loss of mitochondrial membrane potential, decreased activity of the mitochondrial respiratory complexes, and impaired mitochondrial energy metabolism. Furthermore, positive Annexin-propidium iodide staining and altered expression of Bcl-2 family members and caspases in L6 myotubes indicated that the cells progressively became apoptotic upon fructose exposure. Taken together, these findings suggest that exposure of skeletal muscle cells to fructose induced oxidative stress that decreased mitochondrial DNA content and triggered mitochondrial dysfunction, which caused apoptosis.

Murine Mesenchymal Stem Cell Commitment to Differentiation Is Regulated by Mitochondrial Dynamics

Mouse skin mesenchymal stem cells (msMSCs) are dermis CD105(+) CD90(+) CD73(+) CD29(+) CD34(-) mesodermal precursors which, after in vitro induction, undergo chondro, adipo, and osteogenesis. Extensive metabolic reconfiguration has been found to occur during differentiation, and the bioenergetic status of a cell is known to be dependent on the quality and abundance of the mitochondrial population, which may be regulated by fusion and fission. However, little is known regarding the impact of mitochondrial dynamics on the differentiation process. We addressed this knowledge gap by isolating MSCs from Swiss female mice, inducing these cells to differentiate into osteo, chondro, and adipocytes and measuring changes in mass, morphology, dynamics, and bioenergetics. Mitochondrial biogenesis was increased in adipogenesis, as evaluated through confocal microscopy, citrate synthase activity, and mtDNA content. The early steps of adipo and osteogenesis involved mitochondrial elongation, as well as increased expression of mitochondrial fusion proteins Mfn1 and 2. Chondrogenesis involved a fragmented mitochondrial phenotype, increased expression of fission proteins Drp1, Fis1, and 2, and enhanced mitophagy. These events were accompanied by profound bioenergetic alterations during the commitment period. Moreover, knockdown of Mfn2 in adipo and osteogenesis and the overexpression of a dominant negative form of Drp1 during chondrogenesis resulted in a loss of differentiation ability. Overall, we find that mitochondrial morphology and its regulating processes of fission/fusion are modulated early on during commitment, leading to alterations in the bioenergetic profile that are important for differentiation. We thus propose a central role for mitochondrial dynamics in the maintenance/commitment of mesenchymal stem cells.

AMPK activation by liquiritigenin inhibited oxidative hepatic injury and mitochondrial dysfunction induced by nutrition deprivation as mediated with induction of farnesoid X receptor

PURPOSE

Nutrition is indispensable for cell survival and proliferation. Thus, loss of nutrition caused by serum starvation in cells could induce formation of reactive oxygen species (ROS), resulting in cell death. Liquiritigenin (LQ) is an active flavonoid in licorice and plays a role in the liver as a hepatic protectant.

METHODS

This study investigated the effect of LQ, metformin [an activator of activated AMP-activated protein kinase (AMPK)] and GW4064 [a ligand of farnesoid X receptor (FXR)] on mitochondrial dysfunction and oxidative stress induced by serum deprivation as well as its molecular mechanism, as assessed by immunoblot and flow cytometer assays.

RESULTS

Serum deprivation in HepG2, H4IIE and AML12 cells successfully induced oxidative stress and apoptosis, as indicated by depletion of glutathione, formation of ROS, and altered expression of apoptosis-related proteins such as procaspase-3, poly(ADP-ribose) polymerase, and Bcl-2. However, LQ pretreatment significantly blocked these pathological changes and mitochondrial dysfunction caused by serum deprivation. Moreover, LQ activated AMPK in HepG2 cells and mice liver, as shown by phosphorylation of AMPK and ACC, and this activation was mediated by its upstream kinase (i.e., LKB1). Experiments using a chemical inhibitor of AMPK with LKB1-deficient Hela cells revealed the role of the LKB1-AMPK pathway in cellular protection conferred by LQ. LQ also induced protein and mRNA expression of both FXR as well as small heterodimer partner, which is important since treatment with FXR ligand GW4064 protected hepatocytes against cell death and mitochondrial damage induced by serum deprivation.

CONCLUSION

AMPK activators such as LQ can protect hepatocytes against oxidative hepatic injury and mitochondrial dysfunction induced by serum deprivation, and the beneficial effect might be mediated through the LKB1 pathway as well as FXR induction.

Mitochondrial miRNA (MitomiR): a new player in cardiovascular health

Cardiovascular disease is one of the major causes of human morbidity and mortality in the world. MicroRNAs (miRNAs) are small RNAs that regulate gene expression and are known to be involved in the pathogenesis of heart diseases, but the translocation phenomenon and the mode of action in mitochondria are largely unknown. Recent mitochondrial proteome analysis unveiled at least 2000 proteins, of which only 13 are made by the mitochondrial genome. There are numerous studies demonstrating the translocation of proteins into the mitochondria and also translocation of ribosomal RNA (viz., 5S rRNA) into mitochondria. Recent studies have suggested that miRNAs contain sequence elements that affect their subcellular localization, particularly nuclear localization. If there are sequence elements that direct miRNAs to the nucleus, it is also possible that similar sequence elements exist to direct miRNAs to the mitochondria. In this review we have summarized most of the miRNAs that have been shown to play an important role in mitochondrial function, either by regulating mitochondrial genes or by regulating nuclear genes that are known to influence mitochondrial function. While the focus of this review is cardiovascular diseases, we also illustrate the role of mitochondrial miRNA (MitomiR) in the initiation and progression of various diseases, including cardiovascular diseases, metabolic diseases, and cancer. Our goal here is to summarize the miRNAs that are localized to the mitochondrial fraction of cells, and how these miRNAs modulate cardiovascular health.