Persistent γH2AX: A promising molecular marker of DNA damage and aging

Ochratoxin A induced premature senescence in human renal proximal tubular cells

Ochratoxin A (OTA) has many nephrotoxic effects and is a promising compound for the study of nephrotoxicity. Human renal proximal tubular cells (HKC) are an important model for the study of renal reabsorption, renal physiology and pathology. Since the induction of OTA in renal senescence is largely unknown, whether OTA can induce renal senescence, especially at a sublethal dose, and the mechanism of OTA toxicity remain unclear. In our study, a sublethal dose of OTA led to an enhanced senescent phenotype, β-galactosidase staining and senescence associated secretory phenotype (SASP). Cell cycle arrest and cell shape alternations also confirmed senescence. In addition, telomere analysis by RT-qPCR allowed us to classify OTA-induced senescence as a premature senescence. Western blot assays showed that the p53-p21 and the p16-pRB pathways and the ezrin-associated cell spreading changes were activated during the OTA-induced senescence of HKC. In conclusion, our results demonstrate that OTA promotes the senescence of HKC through the p53-p21 and p16-pRB pathways. The understanding of the mechanisms of OTA-induced senescence is critical in determining the role of OTA in cytotoxicity and its potential carcinogenicity.

HBXIP, a binding protein of HBx, regulates maintenance of the G2/M phase checkpoint induced by DNA damage and enhances sensitivity to doxorubicin-induced cytotoxicity

To maintain the integrity of the genome, cells need to detect and repair DNA damage before they complete cell division. Hepatitis B x-interacting protein (HBXIP), a binding protein of HBx (Hepatitis B virus × protein), is aberrantly overexpressed in human cancer cells and show to promote cell proliferation and inhibit apoptosis. The present study is designed to investigate the role of HBXIP on the DNA damage response. Our results show that HBXIP acts as an important regulator of G2/M checkpoint in response to DNA damage. HBXIP knockdown increases phospho-histone H2AX expression and foci formation after treatment with ionizing radiation (IR). HBXIP regulates the ATM-Chk2 pathway following DNA damage. Depletion of HBXIP abrogates IR-induced G2/M cell cycle checkpoints, accompanying decrease the expression of phospho-Cdc25C, phospho-Cdc2 (Tyr15) and p27. We also show that downregulation of HBXIP expression sensitizes cancer cells to chemotherapy, as evidenced by an increase in apoptosis and cleavage of caspase-3 and caspase-9. Our data suggest that HBXIP can function as a mediator protein for DNA damage response signals to activate the G2/M checkpoint to maintain genome integrity and prevent cell death.

Hapten-Anti-Hapten Technique for Two-Color IHC Detection of Phosphorylated EGFR and H2AX Using Primary Antibodies Raised in the Same Host Species

Multiplex staining of cell and tissue sections with antibodies raised in the same host species is a serious challenge because of unwanted but inevitable cross-reactivity of secondary antibodies with irrelevant primary antibodies. Several techniques can be used to overcome this obstacle including direct labeling of primary antibodies with fluorescent tags and using tyramide signal amplification. Unfortunately these techniques either lack sensitivity, or require a long multistep protocol which can cause physical damage of specimens. As an alternative, we have developed a protocol based on conjugation of primary antibodies to small-size hapten molecules which can be detected with hapten-specific fluorescent secondary antibodies. This technique has been used for two-color labeling of Y845 phosphorylated Epidermal Growth Factor Receptor (EGFR) and S139 phosphorylated histone H2AX protein in A431 human epidermoid carcinoma cells. Our novel hapten-anti-hapten detection chemistry allows for generating a stronger fluorescent signal and completely avoid cross-interactions of secondary antibodies with irrelevant primary antibodies.

ATM Activation and H2AX Phosphorylation Induced by Genotoxic Agents Assessed by Flow- and Laser Scanning Cytometry

Activation of Ataxia Telangiectasia Mediated protein kinase (ATM) by its phosphorylation on serine 1981 and phosphorylation of histone H2AX on serine 139 (γH2AX) are the key events reporting DNA damage, primarily formation of DNA double strand breaks. These events are detected immunocytochemically in individual cells using phospho-specific Abs. The protocols are presented that describe the methodology of immunofluorescent labeling of cells in conjunction with specific staining of cellular DNA. Flow- and imaging-cytometry, the latter exemplified as laser scanning cytometry, is used to quantify intensity of cellular fluorescence reporting activation of ATM and induction of γH2AX with respect to cellular DNA content, which in turn reports the cell cycle phase. Different protocols are presented for analysis of cells either grown in suspension or attached to surface of culture vessels. Examples of ATM activation and H2AX phosphorylation in response to DNA damage in leukemic HL-60 cells by DNA topoisomerase I inhibitor topotecan, and in lung carcinoma A549 cells by hydrogen peroxide, are presented.

Oleanolic acid rejuvenates testicular function through attenuating germ cell DNA damage and apoptosis via deactivation of NF-κB, p53 and p38 signalling pathways

OBJECTIVES

Inflammation can cause degenerative changes of reproductive function. Oleanolic acid (OA), the effective component from Ligustrum lucidum Ait., exhibits significantly anti-inflammation and antiageing activity. However, whether OA restores testicular dysfunction via inhibition of inflammation with ageing is unclear. Here, in a natural ageing rat model, we investigated the protection effects of OA and its mechanism of action.

METHODS

Eighteen-month-old Sprague Dawley (SD) rats were randomly divided into ageing control group and two OA-treated groups (5 and 25 mg/kg). Nine-month-old SD rats were used as adult controls. All rats were received either vehicle or OA for 6 months. Then, histomorphology, weight and index of testis, protein expression and immunohistochemistry were examined.

KEY FINDINGS

Oleanolic acid significantly restored testicular morphology and improved testicular weight and index. Moreover, OA significantly inhibited phospho-NF-κB p65 and its downstream proinflammatory cytokines' expressions, including IL-1β, COX-2 and TNF-α in testis tissues. Similarly, OA remarkably inhibited IL-1β and TNF-α production. OA significantly attenuated germ cells' DNA damage and apoptosis. Such changes were accompanied by downregulation of γH2AX, p-P53 and Bax expressions, and upregulation of Bcl-2 and Bcl-2/Bax ratio. In addition, OA remarkably inhibited p38 signalling.

CONCLUSIONS

Oleanolic acid effectively rejuvenates testicular function via attenuating germ cell DNA damage and apoptosis through deactivation of NF-κB, p53 and p38 signalling pathways.

VEGF-B gene therapy inhibits doxorubicin-induced cardiotoxicity by endothelial protection

Congestive heart failure is one of the leading causes of disability in long-term survivors of cancer. The anthracycline antibiotic doxorubicin (DOX) is used to treat a variety of cancers, but its utility is limited by its cumulative cardiotoxicity. As advances in cancer treatment have decreased cancer mortality, DOX-induced cardiomyopathy has become an increasing problem. However, the current means to alleviate the cardiotoxicity of DOX are limited. We considered that vascular endothelial growth factor-B (VEGF-B), which promotes coronary arteriogenesis, physiological cardiac hypertrophy, and ischemia resistance, could be an interesting candidate for prevention of DOX-induced cardiotoxicity and congestive heart failure. To study this, we administered an adeno-associated viral vector expressing VEGF-B or control vector to normal and tumor-bearing mice 1 wk before DOX treatment, using doses mimicking the concentrations used in the clinics. VEGF-B treatment completely inhibited the DOX-induced cardiac atrophy and whole-body wasting. VEGF-B also prevented capillary rarefaction in the heart and improved endothelial function in DOX-treated mice. VEGF-B also protected cultured endothelial cells from apoptosis and restored their tube formation. VEGF-B increased left ventricular volume without compromising cardiac function, reduced the expression of genes associated with pathological remodeling, and improved cardiac mitochondrial respiration. Importantly, VEGF-B did not affect serum or tissue concentrations of DOX or augment tumor growth. By inhibiting DOX-induced endothelial damage, VEGF-B could provide a novel therapeutic possibility for the prevention of chemotherapy-associated cardiotoxicity in cancer patients.

Short-term markers of DNA damage among roofers who work with hot asphalt

BACKGROUND

Roofers are at increased risk for various malignancies and their occupational exposures to polycyclic aromatic hydrocarbons (PAHs) have been considered as important risk factors. The overall goal of this project was to investigate the usefulness of phosphorylated histone H2AX (γH2AX) as a short-term biomarker of DNA damage among roofers.

METHODS

Blood, urine, and dermal wipe samples were collected from 20 roofers who work with hot asphalt before and after 6 h of work on Monday and Thursday of the same week (4 sampling periods). Particle-bound and gas-phase PAHs were collected using personal monitors during work hours. γH2AX was quantified in peripheral lymphocytes using flow cytometry and 8-hydroxy-2-deoxyguanosine (8-OHdG) was assessed in urine using ELISA. General linear mixed models were used to evaluate associations between DNA damage and possible predictors (such as sampling period, exposure levels, work- and life-style factors). Differences in mean biomarker and DNA damage levels were tested via ANOVA contrasts.

RESULTS

Exposure measurements did not show an association with any of the urinary biomarkers or the measures of DNA damage. Naphthalene was the most abundant PAH in gas-phase, while benzo(e)pyrene was the most abundant particle-bound PAH. Post-shift levels of γH2AX and 8-OHdG were higher on both study days, when compared to pre-shift levels. Cigarette smoking was a predictor of γH2AX and urinary creatinine was a predictor of urinary 8-OHdG. Between-subject variance to total variance ratio was 35.3 % for γH2ax and 4.8 % for 8-OHdG.

CONCLUSION

γH2AX is a promising biomarker of DNA damage in occupational epidemiology studies. It has a lower within-subject variation than urinary 8-OHdG and can easily be detected in large scale groups. Future studies that explore the kinetics of H2AX phosphorylation in relation to chemical exposures may reveal the transient and persistent nature of this sensitive biomarker of early DNA damage.

Immune and inflammatory responses to DNA damage in cancer and aging

Genome instability is a hallmark of both cancer and aging processes. Beyond cell-autonomous responses, it is known that DNA damage also elicits systemic mechanisms aimed at favoring survival and damaged cells clearance. Among these mechanisms, immune activation and NF-κB-mediated inflammation play central roles in organismal control of DNA damage. We focus herein on the different experimental evidences that have allowed gaining mechanistic insight about this relationship. We also describe the functional consequences of defective immune function in cancer development and age-related alterations. Finally, we discuss different intervention strategies based on enhancing immunity or on the modulation of the inflammatory response to improve organism homeostasis in cancer and aging.

Do DNA Double-Strand Breaks Drive Aging?

DNA double-strand breaks (DSBs) are rare, but highly toxic, lesions requiring orchestrated and conserved machinery to prevent adverse consequences, such as cell death and cancer-causing genome structural mutations. DSBs trigger the DNA damage response (DDR) that directs a cell to repair the break, undergo apoptosis, or become senescent. There is increasing evidence that the various endpoints of DSB processing by different cells and tissues are part of the aging phenotype, with each stage of the DDR associated with specific aging pathologies. In this Perspective, we discuss the possibility that DSBs are major drivers of intrinsic aging, highlighting the dynamics of spontaneous DSBs in relation to aging, the distinct age-related pathologies induced by DSBs, and the segmental progeroid phenotypes in humans and mice with genetic defects in DSB repair. A model is presented as to how DSBs could drive some of the basic mechanisms underlying age-related functional decline and death.

γH2AX expression in cytological specimens as a biomarker of response to radiotherapy in solid malignancies

Many anticancer treatments, including radiotherapy, act by damaging DNA and hindering cell function and proliferation. H2AX is a histone protein directly associated with DNA that is phosphorylated to produce γH2AX that accumulates in foci in an early response to DNA double-strand breaks, the most deleterious lesion caused by anticancer therapy. This study reports a γH2AX detection assay that has the potential to be used as a biomarker of response to guide cancer treatment. γH2AX immunostaining was applied to tumour cell specimens obtained using fine needle aspiration (FNA). Liquid-based cytology and direct smear cytology methods were evaluated and immunostaining protocols established using FNA samples from five cancer patients. The assay was then applied to three patients before and after radiotherapy. Results demonstrate induction of γH2AX foci following treatment, persisting for as long as one week after therapy. Immunostaining for γH2AX has been successfully applied to FNA samples, providing an opportunity to evaluate γH2AX as a treatment response marker in cancer.