The role of mitochondria in ageing and carcinogenesis

Simultaneous targeting of peripheral and brain tumors with a therapeutic nanoparticle to disrupt metabolic adaptability at both sites

Brain metastasis of advanced breast cancer often results in deleterious consequences. Metastases to the brain lead to significant challenges in treatment options, as the blood-brain barrier (BBB) prevents conventional therapy. Thus, we hypothesized that creation of a nanoparticle (NP) that distributes to both primary tumor site and across the BBB for secondary brain tumor can be extremely beneficial. Here, we report a simple targeting strategy to attack both the primary breast and secondary brain tumors utilizing a single NP platform. The nature of these mitochondrion-targeted, BBB-penetrating NPs allow for simultaneous targeting and drug delivery to the hyperpolarized mitochondrial membrane of the extracranial primary tumor site in addition to tumors at the brain. By utilizing a combination of such dual anatomical distributing NPs loaded with therapeutics, we demonstrate a proof-of-concept idea to combat the increased metabolic plasticity of brain metastases by lowering two major energy sources, oxidative phosphorylation (OXPHOS) and glycolysis. By utilizing complementary studies and genomic analyses, we demonstrate the utility of a chemotherapeutic prodrug to decrease OXPHOS and glycolysis by pairing with a NP loaded with pyruvate dehydrogenase kinase 1 inhibitor. Decreasing glycolysis aims to combat the metabolic flexibility of both primary and secondary tumors for therapeutic outcome. We also address the in vivo safety parameters by addressing peripheral neuropathy and neurobehavior outcomes. Our results also demonstrate that this combination therapeutic approach utilizes mitochondrial genome targeting strategy to overcome DNA repair-based chemoresistance mechanisms.

Nutritional approaches targeting mitochondria for the prevention of sarcopenia

A decline in function and loss of mass, a condition known as sarcopenia, is observed in the skeletal muscles with aging. Sarcopenia has a negative effect on the quality of life of elderly. Individuals with sarcopenia are at particular risk for adverse outcomes, such as reduced mobility, fall-related injuries, and type 2 diabetes mellitus. Although the pathogenesis of sarcopenia is multifaceted, mitochondrial dysfunction is regarded as a major contributor for muscle aging. Hence, the development of preventive and therapeutic strategies to improve mitochondrial function during aging is imperative for sarcopenia treatment. However, effective and specific drugs that can be used for the treatment are not yet approved. Instead studies on the relationship between food intake and muscle aging have suggested that nutritional intake or dietary control could be an alternative approach for the amelioration of muscle aging. This narrative review approaches various nutritional components and diets as a treatment for sarcopenia by modulating mitochondrial homeostasis and improving mitochondria. Age-related changes in mitochondrial function and the molecular mechanisms that help improve mitochondrial homeostasis are discussed, and the nutritional components and diet that modulate these molecular mechanisms are addressed.

Research Progress in Skin Aging, Metabolism, and Related Products

In recent years, skin aging has received increasing attention. Many factors affect skin aging, and research has shown that metabolism plays a vital role in skin aging, but there needs to be a more systematic review. This article reviews the interaction between skin metabolism and aging from the perspectives of glucose, protein, and lipid metabolism and explores relevant strategies for skin metabolism regulation. We found that skin aging affects the metabolism of three major substances, which are glucose, protein, and lipids, and the metabolism of the three major substances in the skin also affects the process of skin aging. Some drugs or compounds can regulate the metabolic disorders mentioned above to exert anti-aging effects. Currently, there are a variety of products, but most of them focus on improving skin collagen levels. Skin aging is closely related to metabolism, and they interact with each other. Regulating specific metabolic disorders in the skin is an important anti-aging strategy. Research and development have focused on improving collagen levels, while the regulation of other skin glycosylation and lipid disorders including key membrane or cytoskeleton proteins is relatively rare. Further research and development are expected.

Inverse correlation between Alzheimer's disease and cancer from the perspective of hypoxia

Sporadic Alzheimer's disease and cancer remain epidemiologically inversely related, and exploring the reverse pathogenesis is important for our understanding of both. Cognitive dysfunctions in Alzheimer's disease (AD) might result from the depletion of adaptive reserves in the brain. Energy storage in the brain is limited and is dynamically regulated by neurovascular and neurometabolic coupling. The research on neurodegenerative diseases has been dominated by the neurocentric view that neuronal defects cause the diseases. However, the proposal of the 2-hit vascular hypothesis in AD led us to focus on alterations in the vasculature, especially hypoperfusion. Chronic hypoxia is a feature shared by AD and cancer. It is interesting how contradicting chronic hypoxia's effects on both cancer and AD are. In this article, we discuss the potential links between the 2 diseases' etiology, from comparable upstream circumstances to diametrically opposed downstream effects. We suggest opposing potential mechanisms, including upregulation and downregulation of hypoxia-inducible factor-1α, the Warburg and reverse-Warburg effects, lactate-mediated intracellular acidic and alkaline conditions, and VDAC1-mediated apoptosis and antiapoptosis, and search for regulators that may be identified as the crossroads between cancer and AD.

A fruit extract of Styphnolobium japonicum (L.) counteracts oxidative stress and mediates neuroprotection in Caenorhabditis elegans

BACKGROUND

Despite its widespread uses in Chinese and European medicine, Styphnolobium japonicum (Chinese scholar tree, formerly Sophora japonicum) has not been extensively investigated for its potential to protect against neurodegenerative processes and to promote resistance to oxidative stress. In this study, we evaluated the neuroprotective activities of a hydroalcoholic extract from Chinese scholar tree fruits that could be possibly linked to its antioxidant properties using Caenorhabditis elegans as a well-established in vivo model.

METHODS

Survival rate in mutant daf-16 and skn-1 worms, stressed by the pro-oxidant juglone and treated with the extract, was tested. Localization of the transcription factors SKN-1 and DAF-16, and expression of gst-4 were measured. For evaluation of neuroprotective effects, formation of polyglutamine (polyQ40) clusters, α-synuclein aggregates, loss of amphid sensilla (ASH) neuronal function, and amyloid β (Aβ) accumulation (as markers for Huntington's, Parkinson's, and Alzheimer's) was examined.

RESULTS

The extract, which contains substantial amounts of phenolic phytochemicals, showed an increase in the survival rate of worms challenged with juglone in daf-16 mutants but not in skn-1 mutants. The transcription factor SKN-1 was activated by the extract, while DAF-16 was not affected. Upon application of the extract, a significant decline in GST-4 levels, polyQ40 cluster formation, number of lost ASH sensory neurons, α-synuclein aggregation, and paralysis resulting from Aβ accumulation was observed.

CONCLUSIONS

Styphnolobium japonicum fruit extract activated the SKN-1/Nrf2 pathway, resulting in oxidative stress resistance. It revealed promising pharmacological activities towards treatment of Huntington's, Parkinson's, and Alzheimer's diseases. Polyphenolics from Styphnolobium japonicum may be a promising route towards treatment of CNS disorders, but need to be tested in other in vivo systems.

The Extracellular Matrix Vitalizer RATM Increased Skin Elasticity by Modulating Mitochondrial Function in Aged Animal Skin

Oxidative stress-induced cellular senescence and mitochondrial dysfunction result in skin aging by increasing ECM levels-degrading proteins such as MMPs, and decreasing collagen synthesis. MMPs also destroy the basement membrane, which is involved in skin elasticity. The extracellular matrix vitalizer RATM (RA) contains various antioxidants and sodium hyaluronate, which lead to skin rejuvenation. We evaluated whether RA decreases oxidative stress and mitochondrial dysfunction, eventually increasing skin elasticity in aged animals. Oxidative stress was assessed by assaying NADPH oxidase activity, which is involved in ROS generation, and the expression of SOD, which removes ROS. NADPH oxidase activity was increased in aged skin and decreased by RA injection. SOD expression was decreased in aged skin and increased by RA injection. Damage to mitochondrial DNA and mitochondrial fusion markers was increased in aged skin and decreased by RA. The levels of mitochondrial biogenesis markers and fission markers were decreased in aged skin and increased by RA. The levels of NF-κB/AP-1 and MMP1/2/3/9 were increased in aged skin and decreased by RA. The levels of TGF-β, CTGF, and collagen I/III were decreased in aged skin and increased by RA. The expression of laminin and nidogen and basement membrane density were decreased in aged skin and increased by RA. RA increased collagen fiber accumulation and elasticity in aged skin. In conclusion, RA improves skin rejuvenation by decreasing oxidative stress and mitochondrial dysfunction in aged skin.

Mitochondrial Control Region Variants Related to Breast Cancer

Breast cancer has an important incidence in the worldwide female population. Although alterations in the mitochondrial genome probably play an important role in carcinogenesis, the actual evidence is ambiguous and inconclusive. Our purpose was to explore differences in mitochondrial sequences of cases with breast cancer compared with control samples from different origins. We identified 124 mtDNA sequences associated with breast cancer cases, of which 86 were complete and 38 were partial sequences. Of these 86 complete sequences, 52 belonged to patients with a confirmed diagnosis of breast cancer, and 34 sequences were obtained from healthy mammary tissue of the same patients used as controls. From the mtDNA analysis, two polymorphisms with significant statistical differences were found: m.310del (rs869289246) in 34.6% (27/78) of breast cancer cases and 61.7% (21/34) in the controls; and m.315dup (rs369786048) in 60.2% (47/78) of breast cancer cases and 38.2% (13/34) in the controls. In addition, the variant m.16519T>C (rs3937033) was found in 59% of the control sequences and 52% of the breast cancer sequences with a significant statistical difference. Polymorphic changes are evolutionarily related to the haplogroup H of Indo-European and Euro-Asiatic origins; however, they were found in all non-European breast cancers.

ANALYSIS OF MITOCHONDRIAL DNA CYTOCHROME-B (CYB) and ATPase-6 GENE MUTATIONS IN COVID-19 PATIENTS

BACKGROUND

Coronavirus disease of 2019 (COVID-19) is a pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Mutations of mitochondrial DNA (mtDNA) are becoming increasingly common in various diseases. This study aims to investigate mutations in the cytochrome-b (CYB) and adenosine triphosphatase-6 (ATPase-6) genes of mtDNA in COVID-19 patients. The association between mtDNA mutations and clinical outcomes is investigated.

METHODS

In the present study, mutations of the mtDNA genes CYB and ATPase-6 were investigated in COVID-19(+) (n=65) and COVID-19 (-) patients (n=65). First, we isolated DNA from the blood samples. After the PCR analyses, the mutations were defined using Sanger DNA sequencing.

RESULTS

The age, creatinine, ferritin and CRP levels of the COVID 19 (+) patients were higher than those of the COVID-19 (-) patients (p=0.0036, p=0.0383, p=0.0305, p<0.0001, respectively). We also found 16 different mutations in the CYB gene and 14 different mutations in the ATPase-6 gene. The incidences of CYB gene mutations A15326G, T15454C and C15452A were higher in COVID-19 (+) patients than COVID-19 (-) patients (p<0.0001 (OR (95% CI): 4.966 (2.215-10.89)), p=0.0226 and p=0.0226, respectively). In contrast, the incidences of A8860G and G9055A ATPase-6 gene mutations were higher in COVID-19 (+) patients than COVID-19 (-) patients (p<0.0001 (OR (95%CI): 5.333 (2.359-12.16) and p=0.0121 respectively). Yet, no significant relationship was found between mtDNA mutations and patients' age and biochemical parameters (p> 0.05).

CONCLUSIONS

The results showed that the frequency of mtDNA mutations in COVID-19 patients is quite high and it is important to investigate the association of these mutations with other genetic mechanisms in larger patient populations. This article is protected by copyright. All rights reserved.

Exposure to citrinin induces DNA damage, autophagy, and mitochondria dysfunction during first cleavage of mouse embryos

Citrinin (CTN) is a mycotoxin, which is isolated from Penicillium citrinum and widely existed in the contaminated feeds. It is reported that CTN is toxic to heart, liver, and reproductive system. Previous studies indicated that CTN induced apoptosis in oocytes and embryos. In this study, we reported the potential causes of CTN on embryo development. Our results showed that 40 μM CTN exposure significantly reduced the first cleavage of mouse embryos, showing with the low rate of 2-cell embryos. We found that CTN induced DNA damage, showing the higher positive γH2A.X signals. Autophagy was occurred since more LC3 positive autophagosomes were found in the cytoplasm. This could be confirmed by the enhanced lysosome function, since higher accumulated lysosome distribution were found and LAMP2 was also increased under CTN exposure. Besides, we showed that mitochondria distribution was disturbed, indicating that CTN could disrupt mitochondria function, which could be the possible reason for the oxidative stress and apoptosis in CTN-exposed embryos. In conclusion, our study showed that CTN exposure had adverse effects on the early embryo development during first cleavage through its effects on the induction of DNA damage, autophagy, and mitochondria dysfunction.

The Effect of Cannabidiol on UV-Induced Changes in Intracellular Signaling of 3D-Cultured Skin Keratinocytes

Human epidermal keratinocytes are constantly exposed to UV radiation. As a result, there is a significant need for safe and effective compounds to protect skin cells against this environmental damage. This study aimed to analyze the effect of phytocannabinoid-cannabinoid (CBD)-on the proteome of UVA/B irradiated keratinocytes. The keratinocytes were cultured in a three-dimensional (3D) system, designed to mimic epidermal conditions closely. The obtained results indicate that CBD protected against the harmful effects of UVA/B radiation. CBD decreased the expression of proinflammatory proteins, including TNFα/NFκB and IκBKB complex and decreased the expression of proteins involved in de novo protein biosynthesis, which are increased in UVA/B-irradiated cells. Additionally, CBD enhanced the UV-induced expression of 20S proteasome subunits. CBD also protected protein structures from 4-hydroxynonenal (HNE)-binding induced by UV radiation, which primarily affects antioxidant enzymes. CBD-through its antioxidant/anti-inflammatory activity and regulation of protein biosynthesis and degradation-protects skin cells against UVA/B-induced changes. In the future, its long-term use in epidermal cells should be investigated.

Carbon Monoxide Partially Mediates Protective Effect of Resveratrol Against UVB-Induced Oxidative Stress in Human Keratinocytes

Based on the antioxidative effect of resveratrol (RES) in mitigating reactive oxygen species (ROS) production through the induction of nuclear factor-erythroid 2-related factor-2 (Nrf2)/heme oxigenase-1 (HO-1) signaling pathway, we investigated whether the protective activity of RES against ROS-mediated cytotoxicity is mediated by intracellular carbon monoxide (CO), a product of HO-1 activity, in ultraviolet B (UVB)-irradiated human keratinocyte HaCaT cells. The cells were exposed to UVB radiation following treatment with RES and/or CO-releasing molecule-2 (CORM-2). RES and/or CORM-2 upregulated HO-1 protein expression, accompanied by a gradual reduction of UVB-induced intracellular ROS levels. CORM-2 reduced intracellular ROS in the presence of tin protoporphyrin IX, an HO-1 inhibitor, indicating that the cytoprotection observed was mediated by intracellular CO and not by HO-1 itself. Moreover, CORM-2 decreased RES-stimulated mitochondrial quantity and respiration and increased the cytosolic protein expressions of radical-scavenging superoxide dismutases, SOD1 and SOD2. Taken together, our observations suggest that RES and intracellular CO act independently, at least partly, in attenuating cellular oxidative stress by promoting antioxidant enzyme expressions and inhibiting mitochondrial respiration in UVB-exposed keratinocytes.

Circulating Cell Free Nuclear DNA, Mitochondrial DNA and Global DNA Methylation: Potential Noninvasive Biomarkers for Breast Cancer Diagnosis

Eighty seven women with benign breast lesion, 120 patients with breast cancer (BC) and one hundred controls were included in the study. Quantification of mtDNA and nDNA was done by qPCR. Global DNA methylation was measured using ELISA. Circulating cell-free nDNA and mtDNA were significantly elevated in BC and benign breast lesions patients. Global methylation was significantly low in BC patients. Combining the studied parameters in one panel, nDNA/mtDNA/hypomethylation, improved their sensitivity in detecting BC to reach 92.5%. Circulating cell-free nDNA, mtDNA and global DNA hypomethylation can be used as diagnostic and prognostic markers for BC.

Multifunctional radical quenchers as potential therapeutic agents for the treatment of mitochondrial dysfunction

Mitochondrial dysfunction is associated with a wide range of human diseases, including neurodegenerative diseases, and is believed to cause or contribute to the etiology of these diseases. These disorders are frequently associated with increased levels of reactive oxygen species. One of the design strategies for therapeutic intervention involves the development of novel small molecules containing redox cores, which can scavenge reactive oxygen radicals and selectively block oxidative damage to the mitochondria. Presently, we describe recent research dealing with multifunctional radical quenchers as antioxidants able to scavenge reactive oxygen radicals. The review encompasses ubiquinone and tocopherol analogs, as well as novel pyri(mi)dinol derivatives, and their ability to function as protective agents in cellular models of mitochondrial diseases.

Mitochondrial DNA Damage Does Not Determine C. elegans Lifespan

The mitochondrial free radical theory of aging (mFRTA) proposes that accumulation of oxidative damage to macromolecules in mitochondria is a causative mechanism for aging. Accumulation of mitochondrial DNA (mtDNA) damage may be of particular interest in this context. While there is evidence for age-dependent accumulation of mtDNA damage, there have been only a limited number of investigations into mtDNA damage as a determinant of longevity. This lack of quantitative data regarding mtDNA damage is predominantly due to a lack of reliable assays to measure mtDNA damage. Here, we report adaptation of a quantitative real-time polymerase chain reaction (qRT-PCR) assay for the detection of sequence-specific mtDNA damage in C. elegans and apply this method to investigate the role of mtDNA damage in the aging of nematodes. We compare damage levels in old and young animals and also between wild-type animals and long-lived mutant strains or strains with modifications in ROS detoxification or production rates. We confirm an age-dependent increase in mtDNA damage levels in C. elegans but found that there is no simple relationship between mtDNA damage and lifespan. MtDNA damage levels were high in some mutants with long lifespan (and vice versa). We next investigated mtDNA damage, lifespan and healthspan effects in nematode subjected to exogenously elevated damage (UV- or γ-radiation induced). We, again, observed a complex relationship between damage and lifespan in such animals. Despite causing a significant elevation in mtDNA damage, γ-radiation did not shorten the lifespan of nematodes at any of the doses tested. When mtDNA damage levels were elevated significantly using UV-radiation, nematodes did suffer from shorter lifespan at the higher end of exposure tested. However, surprisingly, we also found hormetic lifespan and healthspan benefits in nematodes treated with intermediate doses of UV-radiation, despite the fact that mtDNA damage in these animals was also significantly elevated. Our results suggest that within a wide physiological range, the level of mtDNA damage does not control lifespan in C. elegans.

Signatures of photo-aging and intrinsic aging in skin were revealed by transcriptome network analysis

There are various factors that alter physiological characteristics in skin. Elucidating the underlying mechanism of transcriptional alterations by intrinsic and extrinsic factors may lead us to understand the aging process of skin. To identify the transcriptomic changes of the aging skin, we analyzed publicly available RNA sequencing data from Genotype-Tissue Expression (GTEx) project. GTEx provided RNA sequencing data of suprapubic (n=228) and lower leg (n=349) skins, which are photo-protected and photo-damaged. Using differentially expressed gene analysis and weighted gene co-expression network analysis, we characterized transcriptomic changes due to UV exposure and aging. Genes involved in skin development such as epidermal differentiation complex component (SPRR and LCE families), vasculature development (TGFBR1, TGFBR2, TGFBR3, KDR, FGF2, and VEGFC), and matrix metalloproteinase (MMP2, MMP3, MMP8, MMP10, and MMP13) were up-regulated by UV exposure. Also, down-regulated lipid metabolism and mitochondrial biogenesis were observed in photo-damaged skin. Moreover, wound healing process was universally down-regulated in suprapubic and lower leg with aging and further down-regulation of lipid metabolism and up-regulation of vasculature development were found as photo-aging signatures. In this study, dynamic transcriptomic alterations were observed in aged skin. Hence, our findings may help to discover a potential therapeutic target for skin rejuvenation.

What is the role of mitochondrial dysfunction in skin photoaging?

Skin ageing is a complex process involving both internal and external factors, which leads to a progressive loss of cutaneous function and structure. Solar radiation is the primary environmental factor implicated in the development of skin ageing, and the term photoaging describes the distinct clinical, histological and structural features of chronically sun-exposed skin. The changes that accompany photoaging are undesirable for aesthetic reasons and can compromise the skin and make it more susceptible to a number of dermatological disorders. As a result, skin ageing is a topic that is of growing interest and concern to the general population, illustrated by the increased demand for effective interventions that can prevent or ameliorate the clinical changes associated with aged skin. In this viewpoint essay, we explore the role that mitochondria play in the process of skin photoaging. There is continuing evidence supporting the proposal that mitochondrial dysfunction and oxidative stress are important contributing factors in the development of skin photoaging. Further skin-directed mitochondrial research is warranted to fully understand the impact of mitochondrial status and function in skin health. A greater understanding of the ageing process and the regulatory mechanisms involved could lead to the development of novel preventative interventions for skin ageing.

iTRAQ-based quantitative proteomic analysis of Yamanaka factors reprogrammed breast cancer cells

Cancer cells had been developed to be reprogrammed into embryonic stem like cells by induced pluripotent stem cells (iPSCs) technology, however, the tumor differentiation/dedifferentiation mechanisms had not yet been analyzed on a genome-wide scale. Here, we inserted the four stem cell transcription factor genes OCT4, SOX2, C-MYC and KLF4 into MCF cells (MCFs), represented a female breast cancer cell type, and obtained iPSCs (Mcfips) in about 3 weeks. By using the LC MS/MS iTRAQ technology, we analyzed the proteomic changes between MCFs and Mcfips. Of identified 4,616 proteins totally, 247 and 142 differentially expressed (DE) proteins were found in Mcfips compared with human induce pluripotent stem cells (Hips) and MCFs, respectively. 35 co-up and 10 co-down regulated proteins were recognized in DE proteins. Above DE proteins were categorized with GO functional classification annotation and KEGG metabolic pathway analysis into biological processes. In the protein interaction network, we found 37 and 39 hubs interacted with more than one protein in Mcfips comparing to Hips, in addition, 25 and 9 hubs were identified in Mcfips comparing to MCFs. Importantly, the mitochondria, ribosome and tumor suppressor proteins were found to be core regulators of tumor reprogramming, which might contribute to understand the mechanisms in relation to the occurrences and progression of a tumor. Thus, our study provided a valuable data for exploring the possibility to normalize the malignant phenotype.

Biological effects and medical applications of infrared radiation

Infrared (IR) radiation is electromagnetic radiation with wavelengths between 760nm and 100,000nm. Low-level light therapy (LLLT) or photobiomodulation (PBM) therapy generally employs light at red and near-infrared wavelengths (600-100nm) to modulate biological activity. Many factors, conditions, and parameters influence the therapeutic effects of IR, including fluence, irradiance, treatment timing and repetition, pulsing, and wavelength. Increasing evidence suggests that IR can carry out photostimulation and photobiomodulation effects particularly benefiting neural stimulation, wound healing, and cancer treatment. Nerve cells respond particularly well to IR, which has been proposed for a range of neurostimulation and neuromodulation applications, and recent progress in neural stimulation and regeneration are discussed in this review. The applications of IR therapy have moved on rapidly in recent years. For example, IR therapy has been developed that does not actually require an external power source, such as IR-emitting materials, and garments that can be powered by body heat alone. Another area of interest is the possible involvement of solar IR radiation in photoaging or photorejuvenation as opposites sides of the coin, and whether sunscreens should protect against solar IR? A better understanding of new developments and biological implications of IR could help us to improve therapeutic effectiveness or develop new methods of PBM using IR wavelengths.

Overexpression of Mitochondrial GTPase MFN2 Represents a Negative Prognostic Marker in Human Gastric Cancer and Its Inhibition Exerts Anti-Cancer Effects

Background: As one of the most common malignancies in the world, little is known about the molecular mechanism underlying gastric cancer (GC) and its progression. In this study, we aimed to investigate the clinical impact of the mitochondrial GTPase mitofusin 2 (MFN2) in GC.

Methods: Immunohistochemistry was used to examine the expression levels of MFN2 in gastric tissues obtained from 141 patients with GC. The correlations between MFN2 protein level and clinicopathologic parameters, as well as the significance of MFN2 protein level for overall and disease-free survival were assessed. siRNA technology was used to study the effect of MFN2 knockdown on cell proliferation and invasion.

Results: The overexpression of MFN2 was positively associated with depth of invasion (P = 0.0430), stage (P = 0.0325) and vascular invasion (P = 0.0077). Patients with high expression levels of MFN2 had a significantly lower overall survival rate and disease-free survival rate compared with those with low expression levels (P = 0.003 and 0.001, respectively). Multivariate Cox regression analysis showed that the overexpression of MFN2 was an independent prognostic marker for inferior overall survival and disease-free survival (P = 0.015 and 0.025, respectively). In addition, studies conducted in GC cells indicated that knockdown of MFN2 suppressed cell proliferation and invasion.

Conclusions: Overexpression of MFN2 can be used as a marker to predict the outcome of patients with GC. Furthermore, targeting MFN2 might provide a new therapeutic modality for the treatment of GC.

Elevated Mitochondrial DNA Copy Number in Peripheral Blood and Tissue Predict the Opposite Outcome of Cancer: A Meta-Analysis

Previous studies have suggested that mitochondrial DNA (mtDNA) copy number was associated with cancer risk. However, no solid conclusion revealed the potential predictive value of mtDNA copy number for cancer prognosis. The present meta-analysis was performed to clarify the problem. Hence, we performed a systematic search in PubMed, EmBase, Web of Science databases independently and a total of eighteen studies comprising 3961 cases satisfied the criteria and finally enrolled. Our results didn’t show the association between them but significant heterogeneity in overall analysis (OS: HR = 0.923, 95% CI: 0.653–1.306, p = 0.652; DFS: HR = 0.997, 95% CI: 0.599–1.659, p = 0.99). However, subgroup analysis stratified by sample came to the opposite conclusion. High level mitochondrial DNA copy number in peripheral blood predicted a poor cancer prognosis (OS: HR = 1.624, 95% CI: 1.211–2.177, p = 0.001; DFS: HR = 1.582, 95% CI: 1.026–2.439, p = 0.038) while patients with high level mitochondrial DNA copy number in tumor tissue exhibited better outcomes (OS: HR = 0.604 95% CI: 0.406–0.899, p = 0.013; DFS: HR = 0.593, 95% CI: 0.411–0.857, p = 0.005). These findings were further proved in detailed analyses in blood or tissue subgroup. In conclusion, our study suggested the elevated mtDNA copy number in peripheral blood predicted a poor cancer prognosis while the better outcome was presented among patients with elevated mtDNA copy number in tumor tissue.

Mitochondrial DNA deletion percentage in sun exposed and non sun exposed skin

The percentages of mitochondrial genomes carrying the mtDNA³⁸⁹⁵ and the mtDNA⁴⁹⁷⁷ (common) deletion were quantified in sun exposed and non sun exposed skin biopsies, for five cohorts of patients varying either in sun exposure profile, age or skin cancer status. Non-melanoma skin cancer diagnoses are rising in Ireland and worldwide [12] but most risk prediction is based on subjective visual estimations of sun exposure history. A quantitative objective test for pre-neoplastic markers may result in better adherence to sun protective behaviours. Mitochondrial DNA (mtDNA) is known to be subject to the loss of a significant proportion of specific sections of genetic code due to exposure to ultraviolet light in sunlight. Although one such deletion has been deemed more sensitive, another, called the mtDNA⁴⁹⁷⁷ or common deletion, has proved to be a more useful indicator of possible risk in this study. Quantitative molecular analysis was carried out to determine the percentage of genomes carrying the deletion using non sun exposed and sun exposed skin biopsies in cohorts of patients with high or low sun exposure profiles and two high exposure groups undergoing treatment for NMSC. Results indicate that mtDNA deletions correlate to sun exposure; in groups with high sun exposure habits a significant increase in deletion number in exposed over non sun exposed skin occurred. An increase in deletion percentage was also seen in older cohorts compared to the younger group. The mtDNA³⁸⁹⁵ deletion was detected in small amounts in exposed skin of many patients, the mtDNA⁴⁹⁷⁷ common deletion, although present to some extent in non sun exposed skin, is suggested to be the more reliable and easily detected marker. In all cohorts except the younger group with relatively lower sun exposure, the mtDNA⁴⁹⁷⁷ deletion was more frequent in sun exposed skin samples compared to non-sun exposed skin.

High expression of mitochondrial intermembrane chaperone TIMM9 represents a negative prognostic marker in gastric cancer

BACKGROUND/PURPOSE

Gastric cancer (GC) is one of the most common malignant cancers worldwide. However, little is known about the molecular process underlying this disease and its progression. This study investigated correlations between the expression of a mitochondrial inner membrane protein translocase of inner mitochondrial membrane 9 homolog (TIMM9) and various clinicopathologic parameters as well as patients' survival.

METHODS

Gastric tissue samples were obtained from 140 patients with GC and expression levels of TIMM9 were analyzed through immunohistochemistry. Paired t tests were used to analyze the differences in the expression levels of TIMM9 in both tumor and nontumor tissues for each patient. Two-tailed χ² tests were performed to determine whether the differences in TIMM9 expression and clinicopathologic parameters were significant. Time-to-event endpoints for clinicopathologic parameters were plotted using the Kaplan-Meier method, and statistical significance was determined using univariate log-rank tests. Cox proportional hazard model was used for multivariate analysis to determine the independence of prognostic effects of TIMM9 expression.

RESULTS

A borderline association was found between overexpression of TIMM9 and vascular invasion (p = 0.0887). Patients with high expression levels of TIMM9 achieved a significantly lower disease-free survival rate compared with those with low expression levels (p = 0.005). Multivariate Cox regression analysis showed that overexpression of TIMM9 was an independent prognostic marker for GC (p = 0.011).

CONCLUSION

Overexpression of TIMM9 can be used as a marker to predict the outcome of patients with GC.

Oxidative stress and ageing

Oxidative stress is the resultant damage due to redox imbalances (increase in destructive free radicals [reactive oxygen species (ROS)] and reduction in antioxidant protection/pathways) and is linked to ageing in many tissues including skin. In ageing skin there are bioenergetic differences between keratinocytes and fibroblasts which provide a potential ageing biomarker. The differences in skin bioenergy are part of the mitochondrial theory of ageing which remains one of the most widely accepted ageing theories describing subsequent increasing free radical generation. Mitochondria are the major source of cellular oxidative stress and form part of the vicious cycle theory of ageing. External and internal sources of oxidative stress include UVR/IR, pollution (environment), lifestyle (exercise and diet), alcohol and smoking all of which may potentially impact on skin although many exogenous actives and endogenous antioxidant defence systems have been described to help abrogate the increased stress. This also links to differences in skin cell types in terms of the UVR action spectrum for nuclear and mitochondrial DNA damage (the latter a previously described UVR biomarker in skin). Recent work associates bioenergy production and oxidative stress with pigment production thereby providing another additional potential avenue for targeted anti-ageing intervention in skin. This new data supporting the detrimental effects of the numerous wavelengths of UVR may aid in the development of cosmetic/sunscreen design to reduce the effects of photoageing. Recently, complex II of the mitochondrial electron transport chain appears to be more important than previously thought in the generation of free radicals (suggested predominantly by non-human studies). We investigated the relationship between complex II and ageing using human skin as a model tissue. The rate of complex II activity per unit of mitochondria was determined in fibroblasts and keratinocytes cultured from skin covering a wide age range. Complex II activity significantly decreased with age in fibroblasts (P = 0·015), but not in keratinocytes. This was associated with a significant decline in transcript expression (P = 0·008 and P = 0·001) and protein levels (P = 0·0006 and P = 0·005) of the SDHA and SDHB catalytic subunits of complex II respectively. In addition there was a significant decrease in complex II activity with age (P = 0·029) that was specific to senescent skin cells, our study being the first to investigate these differences with senescence and skin age. There was no decrease in complex IV activity with increasing age, suggesting possible locality to complex II. Our study provides a future potential biomarker for monitoring the progression of skin ageing.

Role of Nrf2/HO-1 system in development, oxidative stress response and diseases: an evolutionarily conserved mechanism

The multifunctional regulator nuclear factor erythroid 2-related factor (Nrf2) is considered not only as a cytoprotective factor regulating the expression of genes coding for anti-oxidant, anti-inflammatory and detoxifying proteins, but it is also a powerful modulator of species longevity. The vertebrate Nrf2 belongs to Cap 'n' Collar (Cnc) bZIP family of transcription factors and shares a high homology with SKN-1 from Caenorhabditis elegans or CncC found in Drosophila melanogaster. The major characteristics of Nrf2 are to some extent mimicked by Nrf2-dependent genes and their proteins including heme oxygenase-1 (HO-1), which besides removing toxic heme, produces biliverdin, iron ions and carbon monoxide. HO-1 and their products exert beneficial effects through the protection against oxidative injury, regulation of apoptosis, modulation of inflammation as well as contribution to angiogenesis. On the other hand, the disturbances in the proper HO-1 level are associated with the pathogenesis of some age-dependent disorders, including neurodegeneration, cancer or macular degeneration. This review summarizes our knowledge about Nrf2 and HO-1 across different phyla suggesting their conservative role as stress-protective and anti-aging factors.

Mitochondrial damage and ageing using skin as a model organ

Ageing describes the progressive functional decline of an organism over time, leading to an increase in susceptibility to age-related diseases and eventually to death, and it is a phenomenon observed across a wide range of organisms. Despite a vast repertoire of ageing studies performed over the past century, the exact causes of ageing remain unknown. For over 50 years it has been speculated that mitochondria play a key role in the ageing process, due mainly to correlative data showing an increase in mitochondrial dysfunction, mitochondrial DNA (mtDNA) damage, and reactive oxygen species (ROS) with age. However, the exact role of the mitochondria in the ageing process remains unknown. The skin is often used to study human ageing, due to its easy accessibility, and the observation that the ageing process is able to be accelerated in this organ via environmental insults, such as ultra violet radiation (UVR). This provides a useful tool to investigate the mechanisms regulating ageing and, in particular, the role of the mitochondria. Observations from dermatological and photoageing studies can provide useful insights into chronological ageing of the skin and other organs such as the brain and liver. Moreover, a wide range of diseases are associated with ageing; therefore, understanding the cause of the ageing process as well as regulatory mechanisms involved could provide potentially advantageous therapeutic targets for the prevention or treatment of such diseases.

Alternative mitochondrial electron transfer for the treatment of neurodegenerative diseases and cancers: Methylene blue connects the dots

Brain has exceptional high requirement for energy metabolism with glucose as the exclusive energy source. Decrease of brain energy metabolism and glucose uptake has been found in patients of Alzheimer's, Parkinson's and other neurodegenerative diseases, providing a clear link between neurodegenerative disorders and energy metabolism. On the other hand, cancers, including glioblastoma, have increased glucose uptake and rely on aerobic glycolysis for energy metabolism. The switch of high efficient oxidative phosphorylation to low efficient aerobic glycolysis pathway (Warburg effect) provides macromolecule for biosynthesis and proliferation. Current research indicates that methylene blue, a century old drug, can receive electron from NADH in the presence of complex I and donates it to cytochrome c, providing an alternative electron transfer pathway. Methylene blue increases oxygen consumption, decrease glycolysis, and increases glucose uptake in vitro. Methylene blue enhances glucose uptake and regional cerebral blood flow in rats upon acute treatment. In addition, methylene blue provides protective effect in neuron and astrocyte against various insults in vitro and in rodent models of Alzheimer's, Parkinson's, and Huntington's disease. In glioblastoma cells, methylene blue reverses Warburg effect by enhancing mitochondrial oxidative phosphorylation, arrests glioma cell cycle at s-phase, and inhibits glioma cell proliferation. Accordingly, methylene blue activates AMP-activated protein kinase, inhibits downstream acetyl-coA carboxylase and cyclin-dependent kinases. In summary, there is accumulating evidence providing a proof of concept that enhancement of mitochondrial oxidative phosphorylation via alternative mitochondrial electron transfer may offer protective action against neurodegenerative diseases and inhibit cancers proliferation.

Mitochondria-targeted antioxidants

Redox homeostasis is maintained by the antioxidant defense system, which is responsible for eliminating a wide range of oxidants, including reactive oxygen species (ROS), lipid peroxides, and metals. Mitochondria-localized antioxidants are widely studied because the mitochondria, the major producers of intracellular ROS, have been linked to the cause of aging and other chronic diseases. Mitochondria-targeted antioxidants have shown great potential because they cross the mitochondrial phospholipid bilayer and eliminate ROS at the heart of the source. Growing evidence has identified mitochondria-targeted antioxidants, such as MitoQ and tiron, as potentially effective antioxidant therapies against the damage caused by enhanced ROS generation. This literature review summarizes the current knowledge on mitochondria-targeted antioxidants and their contribution to the body's antioxidant defense system. In addition to addressing the concerns surrounding current antioxidant strategies, including difficulties in targeting antioxidant treatment to sites of pathologic oxidative damage, we discuss promising therapeutic agents and new strategic approaches.

MLK3 phophorylates AMPK independently of LKB1

Emerging evidence has shown that cellular energy metabolism is regulated by the AMPK and MLK3-JNK signaling pathways, but the functional link between them remains to be determined. The present study aimed to explore the crosstalk between MLK3 and AMPK. We found that both JNK and AMPK were phosphorylated at their activation sites by TNF-α, Anisomycin, H2O2 and sorbitol. Interestingly, sorbitol stimulated phosphorylation of AMPK at T172 in LKB1-deficient cells. Following the screening of more than 100 kinases, we identified that MLK3 induced phosphorylation of AMPK at T172. Our in vitro analysis further revealed that MLK3-mediated phosphorylation of AMPK at T172 was independent of AMP, but addition of AMP caused a mobility shift of AMPK, an indication of autophosphorylation, suggesting that AMP binding and phosphorylation of T172 leads to maximal activation of AMPK. GST-pull down assays showed a direct interaction between AMPKα1 subunit and MLK3. Altogether, our results indicate that MLK3 serves as a common upstream kinase of AMPK and JNK and functions as a direct upstream kinase for AMPK independent of LKB1.

Role of the Keap1-Nrf2 pathway in cancer

The Kelch-like ECH-associated protein 1 (Keap1)-nuclear factor E2-related factor 2 (Nrf2) pathway is one of the major signaling cascades involved in cell defense and survival against endogenous and exogenous stress. While Nrf2 and its target genes provide protection against various age-related diseases including tumorigenesis, constitutively active Nrf2 in cancer cells increases the expression of cytoprotective genes and, consequently, enhances proliferation via metabolic reprogramming and inhibition of apoptosis. Herein, we review the current understanding of the regulation of Nrf2 in normal cells as well as its dual role in cancer. Furthermore, the mechanisms of Nrf2 dysregulation in cancer, consequences of unchecked Nrf2 activity, and therapies targeting the Keap1-Nrf2 system are discussed.

Common 4977 bp deletion and novel alterations in mitochondrial DNA in Vietnamese patients with breast cancer

Mitochondrial DNA (mtDNA) has been proposed to be involved in carcinogenesis and ageing. The mtDNA 4977 bp deletion is one of the most frequently observed mtDNA mutations in human tissues and may play a role in breast cancer (BC). The aim of this study was to investigate the frequency of mtDNA 4977 bp deletion in BC tissue and its association with clinical factors. We determined the presence of the 4977 bp common deletion in cancer and normal paired tissue samples from 106 Vietnamese patients with BC by sequencing PCR products. The mtDNA 4977 bp deletion was significantly more frequent in normal tissue in comparison with paired cancer tissue. Moreover, the incidence of the 4977 bp deletion in BC tissue was significantly higher in patients with estrogen receptor (ER) positive as compared with ER negative BC tissue. Preliminary results showed, in cancerous tissue, a significantly higher incidence of novel deletions in the group of patients with lymph node metastasis in comparison with the patients with no lymph node metastasis. We have found 4977 bp deletion in mtDNA to be a common event in BC and with special reference to ER positive BC. In addition, the novel deletions were shown to be related to lymph node metastasis. Our finding may provide complementary information in prediction of clinical outcome including metastasis, recurrence and survival of patients with BC.

Skin resistance to oxidative stress induced by resveratrol: from Nrf2 activation to GSH biosynthesis

Skin is particularly exposed to oxidative stress, either from environmental insults such as sunlight or pollution or as a consequence of specific impairments in antioxidant status resulting from pathologies or aging. Traditionally, antioxidant products are exogenously provided to neutralize pro-oxidant species. However, another approach based on stimulation of endogenous antioxidant defense pathways is more original. Resveratrol (RSV) was reported to display such a behavior in various tissues, but data about the mechanisms of action in skin are scarce. We show here that, in primary culture of normal human keratinocytes (NHKs) or in full-thickness reconstructed human skin, RSV activated the Nrf2 pathway at nontoxic doses, from 20 µM up to 100µM. Among the Nrf2 downstream genes, glutamylcysteinyl ligase and glutathione peroxidase-2 were induced at the mRNA and protein levels. In parallel, a significant increase in glutathione content, assessed by LC/MS analysis, was observed in both models. Nrf2 gene silencing experiments performed in NHKs confirmed that Nrf2 was involved in RSV-induced modulation of cellular antioxidant status, in part by increasing cellular glutathione content. Finally, improvement of endogenous defenses induced in RSV-pretreated reconstructed skin ensured protection against the toxic oxidative effects of cumene hydroperoxide (CHP). In fact after RSV pretreatment, in response to CHP stress, glutathione content did not decrease as in unprotected samples. Cellular alterations at the dermal-epidermal junction were clearly prevented. Together, these complementary experiments demonstrated the beneficial effects of RSV on skin, beyond its direct antioxidant properties, by upregulation of a cutaneous endogenous antioxidant pathway.

Effects of resveratrol on hydrogen peroxide-induced oxidative stress in embryonic neural stem cells

Resveratrol, a natural phenolic compound, has been shown to prevent cardiovascular diseases and cancer and exhibit neuroprotective effects. In this study, we examined the neuroprotective and antioxidant effects of resveratrol against hydrogen peroxide in embryonic neural stem cells. Hydrogen peroxide treatment alone increased catalase and glutathione peroxidase activities but did not change superoxide dismutase levels compared with hydrogen peroxide + resveratrol treatment. Nitric oxide synthase activity and concomitant nitric oxide levels increased in response to hydrogen peroxide treatment. Conversely, resveratrol treatment decreased nitric oxide synthase activity and nitric oxide levels. Resveratrol also attenuated hydrogen peroxide-induced nuclear or mitochondrial DNA damage. We propose that resveratrol may be a promising agent for protecting embryonic neural stem cells because of its potential to decrease oxidative stress by inducing higher activity of antioxidant enzymes, decreasing nitric oxide production and nitric oxide synthase activity, and alleviating both nuclear and mitochondrial DNA damage.

Damage to skin extracellular matrix induced by UV exposure

SIGNIFICANCE

Chronic exposure to environmental ultraviolet radiation (UVR) plays a key role in both photocarcinogenesis and induction of accelerated skin aging. Although the spatiotemporal consequences of UVR exposure for the composition and architecture of the dermal extracellular matrix (ECM) are well characterized, the pathogenesis of photoaging remains poorly defined. Given the compelling evidence for the role of reactive oxygen species (ROS) as mediators of photoaging, UVR-exposed human skin may be an accessible model system in which to characterize the role of oxidative damage in both internal and external tissues.

RECENT ADVANCES

Although the cell-mediated degradation of dermal components via UVR-induced expression of ECM proteases has long been identified as an integral part of the photoaging pathway, the relative importance and identity of cellular and extracellular photosensitizers (direct hit and bystanders models, respectively) in initiating this enzymatic activity is unclear. Recently, both age-related protein glycation and relative amino-acid composition have been identified as potential risk factors for photo-ionization and/or photo-sensitization. Here, we propose a selective multi-hit model of photoaging.

CRITICAL ISSUES

Bioinformatic analyses can be employed to identify candidate UVR targets/photosensitizers, but the action of UVR on protein structure and/or ROS production should be verified experimentally. Crucially, in the case of biochemically active ECM components such as fibronectin and fibrillin, the downstream effects of photo-degradation on tissue homeostasis remain to be confirmed.

FUTURE DIRECTIONS

Both topical antioxidants and inhibitors of detrimental cell signaling may be effective in abrogating the effects of specific UVR-mediated protein degradation in the dermis.

A role for human mitochondrial complex II in the production of reactive oxygen species in human skin

The mitochondrial respiratory chain is a major generator of cellular oxidative stress, thought to be an underlying cause of the carcinogenic and ageing process in many tissues including skin. Previous studies of the relative contributions of the respiratory chain (RC) complexes I, II and III towards production of reactive oxygen species (ROS) have focussed on rat tissues and certainly not on human skin which is surprising as this tissue is regularly exposed to UVA in sunlight, a potent generator of cellular oxidative stress. In a novel approach we have used an array of established specific metabolic inhibitors and DHR123 fluorescence to study the relative roles of the mitochondrial RC complexes in cellular ROS production in 2 types of human skin cells. These include additional enhancement of ROS production by exposure to physiological levels of UVA. The effects within epidermal and dermal derived skin cells are compared to other tissue cell types as well as those harbouring a compromised mitochondrial status (Rho-zero A549). The results show that the complex II inhibitor, TTFA, was the only RC inhibitor to significantly increase UVA-induced ROS production in both skin cell types (P<0.05) suggesting that the role of human skin complex II in terms of influencing ROS production is more important than previously thought particularly in comparison to liver cells. Interestingly, two-fold greater maximal activity of complex II enzyme was observed in both skin cell types compared to liver (P<0.001). The activities of RC enzymes appear to decrease with increasing age and telomere length is correlated with ageing. Our study showed that the level of maximal complex II activity was higher in the MRC5/hTERT (human lung fibroblasts transfected with telomerase) cells than the corresponding wild type cells (P=0.0012) which can be considered (in terms of telomerase activity) as models of younger and older cells respectively.

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We examined the influence of mitochondrial complex II on ROS production in human skin.

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Past studies have focussed on ROS production from mitochondrial complexes I and III.

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DHR123 fluorescence was used following individual complex inhibition and UVA exposure.

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Only complex II inhibition significantly increased ROS levels in both skin cell types.

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Complex II had a two-fold greater activity in skin cells compared to liver cells.

Mitochondrial DNA 4977 bp Deletion in Chronic Cervicitis and Cervix Cancers

Mitochondrial DNA (mtDNA) mutations have been implied in many diseases including cancer and inflammatory diseases. The aim of this study is to investigate the relationship between the 4977 bp deletion of the mtDNA and chronic cervicitis or cervix cancer in patients. The study included a group of patients with chronic cervicitis or cervix cancer, and a control group consisting of individuals without any cervical tissue disease. A total of 72 subjects in an East Turkish population were included in the study. Of these, 35 had chronic cervicitis, 21 had cervix cancer and 16 served as the control group. Isolation of mtDNA was performed from the tissues of these patients and then mtDNA deletions were studied using polymerase chain reaction (PCR). In the cancer groups, there were 9.5% heteroplasmic and homoplasmic deletions. There were no homoplasmic deletions in the cervicitis and control groups, but the frequencies of heteroplasmic deletions were 80.0 and 31.2%, respectively. Chronic inflammation leading to increased reactive oxygen species (ROS) may be the cause of the high mtDNA 4977 bp deletion frequencies in cancer and cervicitis. The older age of the cancer patient may suggest that ageing in addition to long time exposure to ROS may lead to deletions and subsequently cancer. This is the first study to investigate the relationship of the mtDNA 4977 bp deletion to chronic cervicitis and cervix cancer.

The mitochondrial genome: a biosensor for early cancer detection?

Mutations in the mitochondrial genome have been reported as biomarkers for the detection of cancer. Hallmarks of cancer development include the accumulation of genetic alterations in the mitochondrial and nuclear genomes. Damage to mitochondria affects energy metabolism, generation of reactive oxygen species, apoptosis, cell growth and other processes that contribute to the neoplastic process. Furthermore, mitochondrial DNA mutations occur frequently in cancer. Little work has been done to link a pathway between mitochondrial mutations and cancer etiology. Volumes of work have been reported on the association of mitochondrial mutations and almost all types of cancer including the use of body fluids for early detection. This review examines the measurement of mitochondrial mutations for the application of detecting human tumor tissue.

Detection and quantification of a radiation-associated mitochondrial DNA deletion by a nested real-time PCR in human peripheral lymphocytes

In this study we implemented a new assay using a nested real-time polymerase chain reaction (PCR) to detect radiation-induced common deletion (CD) in mitochondrial DNA (mtDNA) of human peripheral lymphocytes. A standard curve for real-time PCR was established by applying a plasmid DNA containing human normal mtDNA or mutated mtDNA. Human peripheral lymphocyte DNA was amplified and quantified by real-time PCR using primer sets for total damaged or mutated mtDNA, plus probes labeled with the fluorescent dyes. The first-round PCR generated multiple products were used as the template for a second-round PCR. We herein describe a nested real-time PCR assay capable of quantifying mtDNA bearing the CD in human peripheral lymphocytes following exposure (in vitro) to (137)Cs γ-rays in a dose range of 0.5 up to 5Gy. The reproducibility of this assay was evident for both unirradiated and irradiated samples by examining human blood lymphocytes from 14 donors. This technique was sensitive enough to detect deletions in mtDNA at low dose levels, as low as 0.5Gy, and higher levels of CD mtDNA were evident at higher doses (≥1Gy), however, there was no consistent dose-response relationship.

Effects of solar radiation on the skin

No one would underestimate the importance of sunlight to the evolution of life on the earth and its role in human development. However, all humans - especially individuals who are lightly pigmented or whose occupation or lifestyle exposes them to excessive amounts of sunlight - are potentially susceptible to its deleterious effects. These effects can range from acute biological responses, such as sunburn and skin tanning, to conditions resulting from chronic exposure such as photoaged skin and potentially life-threatening conditions such as skin cancer. The objective of this review is to present a concise and up-to-date perspective on the effects of UVB, UVA, visible, and infrared radiation on cutaneous biochemistry and physiology.

Changes in mitochondrial DNA alter expression of nuclear encoded genes associated with tumorigenesis

We previously reported the presence of a mtDNA mutation hotspot in UV-induced premalignant and malignant skin tumors in hairless mice. We have modeled this change (9821insA) in murine cybrid cells and demonstrated that this alteration in mtDNA associated with mtBALB haplotype can alter the biochemical characteristics of cybrids and subsequently can contribute to significant changes in their behavioral capabilities. This study shows that changes in mtDNA can produce differences in expression levels of specific nuclear-encoded genes, which are capable of triggering the phenotypes such as seen in malignant cells. From a potential list of differentially expressed genes discovered by microarray analysis, we selected MMP-9 and Col1a1 for further studies. Real-time PCR confirmed up-regulation of MMP-9 and down-regulation of Col1a1 in cybrids harboring the mtDNA associated with the skin tumors. These cybrids also showed significantly increased migration and invasion abilities compared to wild type. The non-specific MMP inhibitor, GM6001, was able to inhibit migratory and invasive abilities of the 9821insA cybrids confirming a critical role of MMPs in cellular motility. Nuclear factor-κB (NF-κB) is a key transcription factor for production of MMPs. An inhibitor of NF-κB activation, Bay 11-7082, was able to inhibit the expression of MMP-9 and ultimately decrease migration and invasion of mutant cybrids containing 9821insA. These studies confirm a role of NF-κB in the regulation of MMP-9 expression and through this regulation modulates the migratory and invasive capabilities of cybrids with mutant mtDNA. Enhanced migration and invasion abilities caused by up-regulated MMP-9 may contribute to the tumorigenic phenotypic characteristics of mutant cybrids.

Mitochondrial DNA deletion mutations in adult mouse cardiac side population cells

We investigated the presence and potential role of mitochondrial DNA (mtDNA) deletion mutations in adult cardiac stem cells. Cardiac side population (SP) cells were isolated from 12-week-old mice. Standard polymerase chain reaction (PCR) was used to screen for the presence of mtDNA deletion mutations in (a) freshly isolated SP cells and (b) SP cells cultured to passage 10. When present, the abundance of mtDNA deletion mutation was analyzed in single cell colonies. The effect of different levels of deletion mutations on SP cell growth and differentiation was determined. MtDNA deletion mutations were found in both freshly isolated and cultured cells from 12-week-old mice. While there was no significant difference in the number of single cell colonies with mtDNA deletion mutations from any of the groups mentioned above, the abundance of mtDNA deletion mutations was significantly higher in the cultured cells, as determined by quantitative PCR. Within a single clonal cell population, the detectable mtDNA deletion mutations were the same in all cells and unique when compared to deletions of other colonies. We also found that cells harboring high levels of mtDNA deletion mutations (i.e. where deleted mtDNA comprised more than 60% of total mtDNA) had slower proliferation rates and decreased differentiation capacities. Screening cultured adult stem cells for mtDNA deletion mutations as a routine assessment will benefit the biomedical application of adult stem cells.

Mitochondrial haplogroups, control region polymorphisms and malignant melanoma: a study in middle European Caucasians

Background

Because mitochondria play an essential role in energy metabolism, generation of reactive oxygen species (ROS), and apoptosis, sequence variation in the mitochondrial genome has been postulated to be a contributing factor to the etiology of multifactorial age-related diseases, including cancer. The aim of the present study was to compare the frequencies of mitochondrial DNA (mtDNA) haplogroups as well as control region (CR) polymorphisms of patients with malignant melanoma (n = 351) versus those of healthy controls (n = 1598) in Middle Europe.

Methodology and Principal Findings

Using primer extension analysis and DNA sequencing, we identified all nine major European mitochondrial haplogroups and known CR polymorphisms. The frequencies of the major mitochondrial haplogroups did not differ significantly between patients and control subjects, whereas the frequencies of the one another linked CR polymorphisms A16183C, T16189C, C16192T, C16270T and T195C were significantly higher in patients with melanoma compared to the controls. Regarding clinical characteristics of the patient cohort, none of the nine major European haplogroups was associated with either Breslow thickness or distant metastasis. The CR polymorphisms A302CC-insertion and T310C-insertion were significantly associated with mean Breslow thickness, whereas the CR polymorphism T16519C was associated with metastasis.

Conclusions and Significance

Our results suggest that mtDNA variations could be involved in melanoma etiology and pathogenesis, although the functional consequence of CR polymorphisms remains to be elucidated.

Identification of an mtDNA mutation hot spot in UV-induced mouse skin tumors producing altered cellular biochemistry

There is increasing awareness of the role of mtDNA alterations in the development of cancer, as mtDNA point mutations are found at high frequency in a variety of human tumors. To determine the biological effects of mtDNA mutations in UV-induced skin tumors, hairless mice were irradiated to produce tumors, and the tumor mtDNAs were screened for single-nucleotide changes using temperature gradient capillary electrophoresis (TGCE), followed by direct sequencing. A mutation hot spot (9821insA) in the mitochondrially encoded tRNA arginine (mt-Tr) locus (tRNA(Arg)) was discovered in approximately one-third of premalignant and malignant skin tumors. To determine the functional relevance of this particular mutation in vitro, cybrid cell lines containing different mt-Tr (tRNA(Arg)) alleles were generated. The resulting cybrid cell lines contained the same nuclear genotype and differed only in their mtDNAs. The biochemical analysis of the cybrids revealed that the mutant haplotype is associated with diminished levels of complex I protein (CI), resulting in lower levels of baseline oxygen consumption and lower cellular adenosine triphosphate (ATP) production. We hypothesize that this specific mtDNA mutation alters cellular biochemistry, supporting the development of keratinocyte neoplasia.

Mitochondrial DNA content varies with pathological characteristics of breast cancer

Changes in mitochondrial DNA (mtDNA) content in cancers have been reported with controversial results, probably due to small sample size and variable pathological conditions. In this study, mtDNA content in 302 breast tumor/surrounding normal tissue pairs were evaluated and correlated with the clinico-pathological characteristics of tumors. Overall, mtDNA content in tumor tissues is significantly lower than that in the surrounding normal tissues, P < 0.00001. MtDNA content in tumor tissues decreased with increasing tumor size. However, when the tumor is very large (>50 cm³), mtDNA content started to increase. Similarly, mtDNA content decreased from grades 0 and I to grade II tumors, but increased from grade II to grade III tumors. Tumors with somatic mtDNA alterations in coding region have significantly higher mtDNA content than tumors without somatic mtDNA alterations (P < 0.001). Tumors with somatic mtDNA alterations in the D-Loop region have significantly lower mtDNA content (P < 0.001). Patients with both low and high mtDNA content in tumor tissue have significantly higher hazard of death than patients with median levels of mtDNA content. mtDNA content in tumor tissues change with tumor size, grade, and ER/PR status; significant deviation from the median level of mtDNA content is associated with poor survival.

Mitochondrial dysfunction mediates aldosterone-induced podocyte damage: a therapeutic target of PPARγ

Aldosterone (Aldo) causes podocyte damage by an unknown mechanism. We examined the role of mitochondrial dysfunction (MtD) in Aldo-treated podocytes in vitro and in vivo. Exposure of podocytes to Aldo reduced nephrin expression dose dependently, accompanied by increased production of reactive oxygen species (ROS). The ROS generation and podocyte damage were abolished by the mitochondrial (mt) respiratory chain complex I inhibitor rotenone. Pronounced MtD, including reduced mt membrane potential, ATP levels, and mtDNA copy number were seen in Aldo-treated podocytes and in the glomeruli of Aldo-infused mice. The mineralocorticoid receptor antagonist eplerenone significantly inhibited Aldo-induced MtD. The MtD was associated with higher levels of ROS, reduction in the activity of complexes I, III, and IV, and expression of the peroxisome proliferator-activated receptor-γ (PPARγ) coactivator-1α and mt transcription factor A. Both the PPARγ agonist rosiglitazone and PPARγ overexpression protected against podocyte injury by preventing MtD and oxidative stress, as evidenced by reduced ROS production, by maintenance of mt morphology, by restoration of mtDNA copy number, by decrease in mt membrane potential loss, and by recovery of mt electron transport function. The protective effect of rosiglitazone was abrogated by the specific PPARγ small interference RNA, but not a control small interference RNA. We conclude that MtD is involved in Aldo-induced podocyte injury, and that the PPARγ agonist rosiglitazone may protect podocytes from this injury by improving mitochondrial function.