Real-time PCR analysis of a 3895 bp mitochondrial DNA deletion in nonmelanoma skin cancer and its use as a quantitative marker for sunlight exposure in human skin

Topical nanoencapsulated cannabidiol cream as an innovative strategy combating UV-A-induced nuclear and mitochondrial DNA injury: A pilot randomized clinical study

BACKGROUND

UV-A radiation contributes to photoaging/photocarcinogenesis by generating inflammation and oxidative damage. Current photoprotective strategies are limited by the availability/utilization of UV-A filters, highlighting an unmet need. Cannabidiol (CBD), having anti-inflammatory/antioxidant properties via regulation of nuclear erythroid 2-related factor, heme oxygenase 1, and peroxisome proliferator-activated receptor gamma, could potentially mitigate damage from UV-A exposure.

OBJECTIVE/METHODS

This is a prospective, single-center, pilot clinical trial (NCT05279495). Nineteen participants applied nano-CBD (nCBD) or vehicle (VC) cream to randomized, blinded buttock sites twice daily for 14 days; then, the treated sites were irradiated with ≤3× UV-A minimal erythema dose. After 24 hours, punch biopsies were obtained for histology, immunohistochemistry, and real-time polymerase chain reaction.

RESULTS

At 24 hours, 21% of participants had less observed erythema on CBD-treated skin than on VC skin. Histologically, nCBD-treated skin had reduced UV-A-induced epidermal hyperplasia than VC (P = .01). Immunohistochemistry detected reduced cytoplasmic/nuclear 8-oxoguanine glycosylase 1 staining in nCBD-treated skin compared with VC (P < .01). Quantitative mtDNA polymerase chain reaction demonstrated that UV-A-induced deletion of ND4 (proxy:4977 bp deletion; P = .003) and ND1 (proxy:3895 bp deletion; P = .002) was significantly reduced by in vivo nCBD treatment compared with VC.

LIMITATIONS

Small sample size is this study's limitation.

CONCLUSION

Topically applied nCBD cream reduced UV-A-induced formation of a frequent mutagenic nuclear DNA base lesion and protected against mtDNA mutations associated with UV-A-induced skin aging. To our knowledge, this trial is the first to identify UV-protective capacity of CBD-containing topicals in humans.

Polymerase ζ is Involved in Mitochondrial DNA Maintenance Processes in Concert with APE1 Activity

Mitochondrial DNA (mtDNA) damaged by reactive oxygen species (ROS) triggers so far poorly understood processes of mtDNA maintenance that are coordinated by a complex interplay among DNA repair, DNA degradation, and DNA replication. This study was designed to identify the proteins involved in mtDNA maintenance by applying a special long-range PCR, reflecting mtDNA integrity in the minor arc. A siRNA screening of literature-based candidates was performed under conditions of enforced oxidative phosphorylation revealing the functional group of polymerases and therein polymerase ζ (POLZ) as top hits. Thus, POLZ knockdown caused mtDNA accumulation, which required the activity of the base excision repair (BER) nuclease APE1, and was followed by compensatory mtDNA replication determined by the single-cell mitochondrial in situ hybridization protocol (mTRIP). Quenching reactive oxygen species (ROS) in mitochondria unveiled an additional, ROS-independent involvement of POLZ in the formation of a typical deletion in the minor arc region. Together with data demonstrating the localization of POLZ in mitochondria, we suggest that POLZ plays a significant role in mtDNA turnover, particularly under conditions of oxidative stress.

Molecular Mechanisms of Cutaneous Squamous Cell Carcinoma

Non-melanoma skin cancers are cutaneous malignancies representing the most common form of cancer in the United States. They are comprised predominantly of basal cell carcinomas and squamous cell carcinomas (cSCC). The incidence of cSCC is increasing, resulting in substantial morbidity and ever higher treatment costs; currently in excess of one billion dollars, per annum. Here, we review research defining the molecular basis and development of cSCC that aims to provide new insights into pathogenesis and drive the development of novel, cost and morbidity saving therapies.

The Uprising of Mitochondrial DNA Biomarker in Cancer

Cancer is a heterogeneous group of diseases, the progression of which demands an accumulation of genetic mutations and epigenetic alterations of the human nuclear genome or possibly in the mitochondrial genome as well. Despite modern diagnostic and therapeutic approaches to battle cancer, there are still serious concerns about the increase in death from cancer globally. Recently, a growing number of researchers have extensively focused on the burgeoning area of biomarkers development research, especially in noninvasive early cancer detection. Intergenomic cross talk has triggered researchers to expand their studies from nuclear genome-based cancer researches, shifting into the mitochondria-mediated associations with carcinogenesis. Thus, it leads to the discoveries of established and potential mitochondrial biomarkers with high specificity and sensitivity. The research field of mitochondrial DNA (mtDNA) biomarkers has the great potential to confer vast benefits for cancer therapeutics and patients in the future. This review seeks to summarize the comprehensive insights of nuclear genome cancer biomarkers and their usage in clinical practices, the intergenomic cross talk researches that linked mitochondrial dysfunction to carcinogenesis, and the current progress of mitochondrial cancer biomarker studies and development.

Photoprotective effect of Astragalus membranaceus polysaccharide on UVA-induced damage in HaCaT cells

Background

The skin provides a predominant barrier against chemical, physical and microbial incursion. The intemperate exposure to ultraviolet A (UVA) radiation can cause excessive cellular oxidative stress, leading to skin damage, proteins damage and mitochondrial dysfunction. There is sufficient evidences supporting the proposal that mitochondria is highly implicated in skin photo-damage.

Methods

In the present study, a polysaccharide isolated from Astragalus membranaceus was further purified to be an α-glucan, which was further investigated its beneficial influence on UVA-induced photo-damage in HaCaT cells.

Results

Our results showed that the purified Astragalus membranaceus polysaccharide (AP) can protect HaCaT cells from UVA-induced photo-damage through reducing UVA-induced intracellular ROS production and mitochondrial membrane potential, thereby altering ATP content. It was found that the UVA induced damage in HaCaT cells could be effectively restored by co-treatment with AP.

Conclusions

AP exhibited promising potential for advanced application as multifunctional skin care products and drugs.

A comprehensive overview of mitochondrial DNA 4977-bp deletion in cancer studies

Mitochondria are cellular machines essential for energy production. The biogenesis of mitochondria is a highly complex and it depends on the coordination of the nuclear and mitochondrial genome. Mitochondrial DNA (mtDNA) mutations and deletions are suspected to be associated with carcinogenesis. The most described mtDNA deletion in various human cancers is called the 4977-bp common deletion (mDNA⁴⁹⁷⁷) and it has been explored since two decades. In spite of that, its implication in carcinogenesis still unknown and its predictive and prognostic impact remains controversial. This review article provides an overview of some of the cellular and molecular mechanisms underlying mDNA⁴⁹⁷⁷ formation and a detailed summary about mDNA⁴⁹⁷⁷ reported in various types of cancers. The current knowledges of mDNA⁴⁹⁷⁷ as a prognostic and predictive marker are also discussed.

Polypharmacy and sun exposure: Implications for mitochondrial DNA deletions in skin

Most somatic cells contain many copies of mitochondrial DNA (mtDNA). Because of both the high copy number and the lack of repair mechanisms available to mtDNA, damage to it largely goes unrepaired, and can accumulate over time. Large scale deletions are a recognised type of damage sustained by mtDNA as a consequence of exposure to the ultraviolet light in sunlight. A group of patients were identified as having abnormally high levels of either a 4977 base pair deletion (mtDNA⁴⁹⁷⁷) or 3895 base pair deletion (mtDNA³⁸⁹⁵), in mtDNA from sun exposed skin or skin suspected to be a non-melanoma skin cancer, but not in their non-sun exposed skin biopsies. In three of the four cases, skin cancer was ruled out due to histological testing. Additional factors from these patients' medical histories were studied, and it was noted that they shared diagnoses for multiple pathologies common to an older population, and that they were being treated with the same or related pharmaceuticals, including some that had been known to cause dermal side effects. Investigation into the biochemistry underlying the symptoms, the effects of sun exposure and side effects of the prescribed pharmaceuticals revealed a possible synergistic relationship leading to the localised high levels of mtDNA deletions.

The association between osteoporotic hip fractures and actinic lesions as a biomarker for cumulative sun exposure in older people-a retrospective case-control study in Argentina

The aim of this study was to analyze the association between the presence of actinic lesions (solar keratosis and non-melanoma skin cancer) and osteoporotic hip fractures in older patients. Both pathologies are common conditions in this age group. Since cumulative sun exposure is difficult to quantify, the presence of actinic lesions can be used to indirectly analyze the association between ultraviolet radiation and osteoporotic hip fractures. This was an observational case-control study. We reviewed the centralized medical records of patients with hip fracture (cases, n = 51) and patients with other diseases hospitalized in the same institution and period (controls, n = 59). The mean age of the patients was 80 ± 8.3 years (range 50-103 years). Differences in maternal hip fracture history were found between cases and controls (14.8 and 8 %, respectively; p = 0.047). Falls history in the past year was higher in cases than in controls (p < 0.0001). Actinic lesions were observed in 32.7 % of patients (prevalence rate 23.5 % in cases, 40.7 % in controls; p = 0.04). When considering patients with actinic lesions, controls have a higher FRAX score compared with cases. Although sun exposure is recommended for bone health, it represents a risk factor for actinic lesions. The presence of actinic lesions may indicate a lower osteoporotic hip fracture risk. A balance between adequate lifetime sun exposure and protection against its adverse effects is required for each patient, in the context of geographic location.

Energy metabolism in skin cancers: A therapeutic perspective

Skin cancers are the most common cancers worldwide. The incidence of common skin cancers, including basal cell carcinomas (BCCs), squamous cell carcinomas (SCCs) and melanomas, continues to rise by 5 to 7% per year, mainly due to ultraviolet (UV) exposure and partly because of aging. This suggests an urgent necessity to improve the level of prevention and protection for skin cancers as well as developing new prognostic and diagnostic markers of skin cancers. Moreover, despite innovative therapies especially in the fields of melanoma and carcinomas, new therapeutic options are needed to bypass resistance to targeted therapies or treatment's side effects. Since reprogramming of cellular metabolism is now considered as a hallmark of cancer, some of the recent findings on the role of energy metabolism in skin cancer initiation and progression as well as its effect on the response to targeted therapies are discussed in this review. This article is part of a Special Issue entitled Mitochondria in cancer, edited by Giuseppe Gasparre, Rodrigue Rossignol and Pierre Sonveaux.

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.

Age-Dependent Decrease of Mitochondrial Complex II Activity in Human Skin Fibroblasts

The mitochondrial theory of aging remains one of the most widely accepted aging theories and implicates mitochondrial electron transport chain dysfunction with subsequent increasing free radical generation. Recently, complex II of the electron transport chain appears to be more important than previously thought in this process, suggested predominantly by nonhuman studies. We investigated the relationship between complex II and aging 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 succinate dehydrogenase complex subunit A and subunit B 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. There was no decrease in complex IV activity with increasing age, suggesting possible locality to complex II.

Are interventions to promote sun-protective behaviors in recreational and tourist settings effective? A systematic review with meta-analysis and moderator analysis

BACKGROUND

Intermittent sun exposure and sunburn are risk factors for skin cancer that mostly occur in recreational/tourist settings. This review assesses the efficacy of skin cancer prevention interventions designed to promote sun-protective behaviors in recreational/tourist settings.

METHODS

Systematic review with meta-analyses of controlled trials with outcome measures of sun-protective behaviors and/or sunburn published until January 2011.

RESULTS

Twenty-three studies were included. We found no evidence for the efficacy of current interventions in reducing tanning or promoting protective clothing and seeking shade. Meta-analyses show a small heterogeneous effect for interventions on sun-protective behavior indices. Larger but heterogeneous effects were observed for self-reported sun exposure and sunburns. Modest methodological quality suggests risk of bias. Effective interventions were more likely to stimulate social norms supporting sun-protective behaviors and provide appearance-based information about photoaging illustrated with ultraviolet photographs.

CONCLUSION

There is weak and inconclusive evidence for the efficacy of interventions in promoting sun-protective behaviors.

Simultaneous quantification of mitochondrial DNA copy number and deletion ratio: a multiplex real-time PCR assay

Mitochondrial dysfunction is implicated in a vast array of diseases and conditions, such as Alzheimer's disease, cancer, and aging. Alterations in mitochondrial DNA (mtDNA) may provide insight into the processes that either initiate or propagate this dysfunction. Here, we describe a unique multiplex assay which simultaneously provides assessments of mtDNA copy number and the proportion of genomes with common large deletions by targeting two mitochondrial sites and one nuclear locus. This probe-based, single-tube multiplex provides high specificity while eliminating well-to-well variability that results from assaying nuclear and mitochondrial targets individually.

The simultaneous detection of mitochondrial DNA damage from sun-exposed skin of three whale species and its association with UV-induced microscopic lesions and apoptosis

Due to life history and physiological constraints, cetaceans (whales) are unable to avoid prolonged exposure to external environmental insults, such as solar ultraviolet radiation (UV). The majority of studies on the effects of UV on skin are restricted to humans and laboratory animals, but it is important to develop tools to understand the effects of UV damage on large mammals such as whales, as these animals are long-lived and widely distributed, and can reflect the effects of UV across a large geographical range. We and others have used mitochondrial DNA (mtDNA) as a reliable marker of UV-induced damage particularly in human skin. UV-induced mtDNA strand breaks or lesions accumulate throughout the lifespan of an individual, thus constituting an excellent biomarker for cumulative exposure. Based on our previous studies in human skin, we have developed for the first time in the literature a quantitative real-time PCR methodology to detect and quantify mtDNA lesions in skin from sun-blistered whales. Furthermore the methodology allows for simultaneous detection of mtDNA damage in different species. Therefore using 44 epidermal mtDNA samples collected from 15 blue whales, 10 fin whales, and 19 sperm whales from the Gulf of California, Mexico, we quantified damage across 4.3 kilobases, a large region of the ~16,400 base pair whale mitochondrial genome. The results show a range of mtDNA damage in the skin of the three different whale species. This previously unreported observation was correlated with apoptotic damage and microscopic lesions, both of which are markers of UV-induced damage. As is the case in human studies, this suggests the potential use of mtDNA as a biomarker for measuring the effect of cumulative UV exposure in whales and may provide a platform to help understand the effects of changing global environmental conditions.

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.

Pathobiology of actinic keratosis: ultraviolet-dependent keratinocyte proliferation

Actinic keratoses are proliferations of transformed neoplastic keratinocytes in the epidermis that are the result of cumulative ultraviolet (UV) radiation from sun exposure. They are commonly found on sites of sun-exposed skin such as the face, balding scalp, and back of the hand. Although UV exposure does exert certain beneficial effects on the skin, excessive exposure to UV radiation induces multiple cascades of molecular signaling events at the cellular level that produce inflammation, immunosuppression, failure of apoptosis, and aberrant differentiation. Cumulatively, these actions result in mutagenesis and, ultimately, carcinogenesis. This article provides a brief overview of the key mediators that are implicated in the pathobiology of actinic keratosis. Three evolutionary possibilities exist for these keratoses in the absence of treatment: (1) spontaneous remission, which can be common; (2) remaining stable, without further progression; or (3) transformation to invasive squamous cell carcinoma, which may metastasize. Because the effects of UV radiation on the skin are complex, it is not yet fully clear how all of the mediators of actinic keratosis progression are interrelated. Nonetheless, some represent potential therapeutic targets, because it is clear that directing therapy to the effects of UV radiation at a number of different levels could interrupt and possibly reverse the mechanisms leading to malignant transformation.

Stressed out mitochondria: the role of mitochondria in ageing and cancer focussing on strategies and opportunities in human skin

Mitochondrial DNA damage has been used as a successful and unique biomarker of tissue stress. A valuable example of this is sun damage in human skin which leads to ageing and skin cancer. The skin is constantly exposed to the harmful effects of sunlight, such as ultraviolet radiation, which causes it to age with observable characteristic features as well as clinical precancerous lesions and skin cancer. Formation of free radicals by the sun's harmful rays which contribute to oxidative stress has been linked to the induction of deletions and mutations in the mitochondrial DNA. These markers of mitochondrial DNA damage have been proposed to contribute to the mechanisms of ageing in many tissues including skin and are associated with many diseases including cancer. In this article we highlight the role of this important organelle in ageing and cancer with particular emphasis on experimental strategies in the skin.

Human mitochondrial DNA polymerase γ exhibits potential for bypass and mutagenesis at UV-induced cyclobutane thymine dimers

Cyclobutane thymine dimers (T-T) comprise the majority of DNA damage caused by short wavelength ultraviolet radiation. These lesions generally block replicative DNA polymerases and are repaired by nucleotide excision repair or bypassed by translesion polymerases in the nucleus. Mitochondria lack nucleotide excision repair, and therefore, it is important to understand how the sole mitochondrial DNA polymerase, pol γ, interacts with irreparable lesions such as T-T. We performed in vitro DNA polymerization assays to measure the kinetics of incorporation opposite the lesion and bypass of the lesion by pol γ with a dimer-containing template. Exonuclease-deficient pol γ bypassed thymine dimers with low relative efficiency; bypass was attenuated but still detectable when using exonuclease-proficient pol γ. When bypass did occur, pol γ misincorporated a guanine residue opposite the 3'-thymine of the dimer only 4-fold less efficiently than it incorporated an adenine. Surprisingly, the pol γ exonuclease-proficient enzyme excised the incorrectly incorporated guanine at similar rates irrespective of the nature of the thymines in the template. In the presence of all four dNTPs, pol γ extended the primer after incorporation of two adenines opposite the lesion with relatively higher efficiency compared with extension past either an adenine or a guanine incorporated opposite the 3'-thymine of the T-T. Our results suggest that T-T usually stalls mitochondrial DNA replication but also suggest a mechanism for the introduction of point mutations and deletions in the mitochondrial genomes of chronically UV-exposed cells.

Manganese superoxide dismutase is a mitochondrial fidelity protein that protects Polγ against UV-induced inactivation

Manganese superoxide dismutase is a nuclear encoded primary antioxidant enzyme localized exclusively in the mitochondrial matrix. Genotoxic agents, such as ultraviolet (UV) radiation, generates oxidative stress and cause mitochondrial DNA (mtDNA) damage. The mtDNA polymerase (Polγ), a major constituent of nucleoids, is responsible for the replication and repair of the mitochondrial genome. Recent studies suggest that the mitochondria contain fidelity proteins and MnSOD constitutes an integral part of the nucleoid complex. However, it is not known whether or how MnSOD participates in the mitochondrial repair processes. Using skin tissue from C57BL/6 mice exposed to UVB radiation, we demonstrate that MnSOD has a critical role in preventing mtDNA damage by protecting the function of Polγ. Quantitative-PCR analysis shows an increase in mtDNA damage after UVB exposure. Immunofluorescence and immunoblotting studies demonstrate p53 translocation to the mitochondria and interaction with Polγ after UVB exposure. The mtDNA immunoprecipitation assay with Polγ and p53 antibodies in p53(+/+) and p53(-/-) mice demonstrates an interaction between MnSOD, p53 and Polγ. The results suggest that these proteins form a complex for the repair of UVB-associated mtDNA damage. The data also demonstrate that UVB exposure injures the mtDNA D-loop in a p53-dependent manner. Using MnSOD-deficient mice we demonstrate that UVB-induced mtDNA damage is MnSOD dependent. Exposure to UVB results in nitration and inactivation of Polγ, which is prevented by addition of the MnSOD mimetic Mn(III)TE-2-PyP(5+). These results demonstrate for the first time that MnSOD is a fidelity protein that maintains the activity of Polγ by preventing UVB-induced nitration and inactivation of Polγ. The data also demonstrate that MnSOD has a role along with p53 to prevent mtDNA damage.

Molecular markers in cutaneous squamous cell carcinoma

Nonmelanoma skin carcinoma (NMSC) is the most frequent cancer in the USA with over 1.3 million new diagnoses a year; however due to an underappreciation of its associated mortality and growing incidence and its ability to be highly aggressive, the molecular mechanism is not well delineated. Whereas the molecular profiles of melanoma have been well characterized, those for cutaneous squamous cell carcinoma (cSCC) have trailed behind. This importance of the new staging paradigm is linked to the ability currently to better clinically cluster similar biologic behavior in order to risk-stratify lesions and patients. In this paper we discuss the trends in NMSC and the etiologies for the subset of NMSC with the most mortality, cutaneous SCC, as well as where the field stands in the discovery of a molecular profile. The molecular markers are highlighted to demonstrate the recent advances in cSCC.

XPC silencing in normal human keratinocytes triggers metabolic alterations that drive the formation of squamous cell carcinomas

DNA damage is a well-known initiator of tumorigenesis. Studies have shown that most cancer cells rely on aerobic glycolysis for their bioenergetics. We sought to identify a molecular link between genomic mutations and metabolic alterations in neoplastic transformation. We took advantage of the intrinsic genomic instability arising in xeroderma pigmentosum C (XPC). The XPC protein plays a key role in recognizing DNA damage in nucleotide excision repair, and patients with XPC deficiency have increased incidence of skin cancer and other malignancies. In cultured human keratinocytes, we showed that lentivirus-mediated knockdown of XPC reduced mitochondrial oxidative phosphorylation and increased glycolysis, recapitulating cancer cell metabolism. Accumulation of unrepaired DNA following XPC silencing increased DNA-dependent protein kinase activity, which subsequently activated AKT1 and NADPH oxidase-1 (NOX1), resulting in ROS production and accumulation of specific deletions in mitochondrial DNA (mtDNA) over time. Subcutaneous injection of XPC-deficient keratinocytes into immunodeficient mice led to squamous cell carcinoma formation, demonstrating the tumorigenic potential of transduced cells. Conversely, simultaneous knockdown of either NOX1 or AKT1 blocked the neoplastic transformation induced by XPC silencing. Our results demonstrate that genomic instability resulting from XPC silencing results in activation of AKT1 and subsequently NOX1 to induce ROS generation, mtDNA deletions, and neoplastic transformation in human keratinocytes.

Real-time polymerase chain reaction analysis of a 3895-bp mitochondrial DNA deletion in epithelial swabs and its use as a quantitative marker for sunlight exposure in human skin

BACKGROUND

The use of mitochondrial DNA (mtDNA) damage as a reliable and highly sensitive biomarker of ultraviolet (UV) radiation exposure in both the dermis and epidermis has now been well developed by our group and others. We have previously identified a 3895-bp mtDNA deletion which occurred more frequently and to a higher level in usually sun-exposed skin as opposed to occasionally sun-exposed skin. This work focused on older-aged individuals and, in particular, perilesional, histologically normal skin biopsies taken from patients with skin cancer.

OBJECTIVES

To develop novel, less-invasive methods of obtaining skin samples (i.e. epidermis) from volunteers covering a much wider age range and larger number of individuals (n = 239).

METHODS

The 3895-bp deletion was quantified by a specific real-time polymerase chain reaction assay in normal human epidermis samples taken from three body sites with differing sun exposure.

RESULTS

The results show a statistical increase of the level of the 3895-bp deletion with increasing sun exposure in the epidermal swabs of human skin (P < 0·001) and with increasing age of the donor in the needle biopsy samples.

CONCLUSIONS

These data suggest that the upper layers of the epidermis are an accessible and reliable site for assessing mtDNA damage caused by UV exposure.

Genistein protects against UVB-induced senescence-like characteristics in human dermal fibroblast by p66Shc down-regulation

BACKGROUND

Genistein, as an active compound of dietary antioxidants, has shown considerable promise as an effective agent against aging process. However, the effect of genistein on skin photoaging and the associated mechanism remain unclear.

OBJECTIVE

To delineate the effect of genistein on UVB-induced senescence in human dermal fibroblasts (HDFs) with emphasis on the mechanism of oxidative pathway regulated by p66Shc involved in the events.

METHODS

HDFs were induced to premature senescence by repetitive subcytotoxic doses of UVB irradiation. Cellular apoptosis and DNA cell cycle were analyzed using flow cytometry. Intracellular levels of superoxide dismutase (SOD) and malondialdehyde (MDA) were detected by ELISA. Mutation levels of two large deletions of mitochondrial DNA, 4977bp and 3895bp deletion, were determined by quantitative PCR. Western blot was applied to detect the expression and activation of p66Shc (the 66-kilodalton isoform of the growth factor adapter Shc) and FKHRL1 (a forkhead protein that is intimately linked with intracellular oxidation).

RESULTS

Strong activity of senescence-associated beta-galactosidase (SA-beta-gal), high percent of cell apoptosis as well as cell cycle arrest in G0/G1 phase, and increased intracellular oxidative stress were observed in HDFs irradiated by UVB. Genistein exerted dramatically protective effects on HDFs in a dose-dependent manner. Elevated copy numbers of large deletions in mitochondrial DNA were also inhibited by genistein. Down-regulation of total and phosphorylated p66Shc on Ser36, as well as FKHRL1 and its phosphorylation on Thr32, were observed after genistein treatment.

CONCLUSION

The results indicate that genistein protects UVB-induced senescence-like characteristics in HDFs via maintenance of antioxidant enzyme activities and modulation of mitochondrial oxidative stress through down-regulation of a p66Shc-dependent signaling pathway, which may provide potential prevention against skin aging and even photoaging.

Environmental mutagens induced transversions but not transitions in regulatory region of mitochondrial DNA

One of the long-term objectives of the research in our laboratory was to determine whether mitochondrial DNA (mtDNA) mutations were generated in cell lines exposed to a variety of known mutagens. Many of these mutagens are known to increase oxidative stress in the cell, and one potential outcome of this would be an increased incidence of point mutations in mtDNA. Recently, there has been some controversy regarding the validity of point mutations in the regulatory region of mtDNA as a predictive or causative marker for carcinogenesis. Studies were undertaken to assess whether nuclear mutagens such as arsenic (As), asbestos, and ultraviolet (UV) and gamma-radiation, induced both heteroplasmic and homoplasmic point mutations in mtDNA. A direct sequencing approach was used to reduce the occurrence of experimental errors and cross-checked all base changes with databases of known polymorphisms. Our results showed that, while base changes did occur, there was no marked difference between the number of changes in treated and untreated cells. Furthermore, in human lymphocyte samples from subjects exposed to As, most of these base changes were previously reported. Interestingly, there was an increase in the number of transversions (purine ( pyrimidine) in smokers from a human population study, but as with the findings in cell culture samples, there was no difference in the total number of base changes. Data suggest that only a change in the number of rare transversions would be indicative of an increase in point mutations in mtDNA after exposure to mutagens.

Ultraviolet radiation exposure accelerates the accumulation of the aging-dependent T414G mitochondrial DNA mutation in human skin

The accumulation of mitochondrial DNA (mtDNA) mutations has been proposed as an underlying cause of the aging process. Such mutations are thought to be generated principally through mechanisms involving oxidative stress. Skin is frequently exposed to a potent mutagen in the form of ultraviolet (UV) radiation and mtDNA deletion mutations have previously been shown to accumulate with photoaging. Here we report that the age-related T414G point mutation originally identified in skin fibroblasts from donors over 65 years also accumulates with age in skin tissue. Moreover, there is a significantly greater incidence of this mutation in skin from sun-exposed sites (chi(2)= 6.8, P < 0.01). Identification and quantification of the T414G mutation in dermal skin tissue from 108 donors ranging from 8 to 97 years demonstrated both increased occurrence with photoaging as well as an increase in the proportion of molecules affected. In addition, we have discovered frequent genetic linkage between a common photoaging-associated mtDNA deletion and the T414G mutation. This linkage indicates that mtDNA mutations such as these are unlikely to be distributed equally across the mtDNA population within the skin tissue, increasing their likelihood of exerting focal effects at the cellular level. Taken together, these data significantly contribute to our understanding of the DNA damaging effects of UV exposure and how resultant mutations may ultimately contribute towards premature aging.