Hydrogen Peroxide-Induced DNA Damage and Repair through the Differentiation of Human Adipose-Derived Mesenchymal Stem Cells

Why the ROS matters: One-electron oxidants focus DNA damage and repair on G-quadruplexes for gene regulation

Hydrogen peroxide is a precursor to reactive oxygen species (ROS) in cells because of its high reactivity with iron(II) carbonate complexes formed in the labile iron pool due to a high concentration of intracellular bicarbonate (25-100 mM). This chemistry leads to the formation of carbonate radical anion rather than hydroxyl radical, and unlike the latter ROS, CO3•- is a milder one-electron oxidant with high specificity for guanine oxidation in DNA and RNA. In addition to metabolism, another major source of DNA oxidation is inflammation which generates peroxynitrite, another precursor to CO3•- via reaction with dissolved CO2. The identity of the ROS is important because not all radicals react with DNA in the same way. Whereas hydroxyl radical forms adducts at all four bases and reacts with multiple positions on ribose leading to base loss and strand breaks, carbonate radical anion is focused on guanosine oxidation to yield 8-oxo-7,8-dihydroguanosine in nucleic acids and the nucleotide pool, a modification that can function epigenetically in the context of a G-quadruplex. DNA sequences of multiple adjacent guanines, as found in G-quadruplex-forming sequences of gene promoters, are particularly susceptible to oxidative damage, and the focusing of CO3•- chemistry on these sites can lead to a transcriptional response during base excision repair. In this pathway, AP-endonuclease 1 plays a key role in accelerating G-quadruplex folding as well as recruiting activating transcription factors to impact gene expression.

Identification and in vitro genotoxicity assessment of forced degradation products of glimepiride and glyburide using HEK cell-based COMET assay

This study focuses on characterizing the forced degradation products of antidiabetic drugs glimepiride (GMD) and glyburide (GBD), with previously unexplored genotoxicity. Drugs underwent stress induced by acid, base, and hydrogen peroxide. For GMD, impurities were profiled and isolated using Hypersil Gold C8 (250 × 10 mm, 5 μ) through semi-preparative HPLC with a fraction collector. For GBD, impurity profiling was performed using semi-preparative HPLC (Hypersil GOLD C18, 250 × 10 mm, 5 μ), and reverse-phase flash chromatography (FP ECOFLEX C18 4 g column) for isolation. Although five GMD and three GBD impurities were detected, only three GMD and two GBD impurities were separated and assessed for purity using analytical RP-HPLC with the purity percentages ranging from 96.6% to 99.9%. LC-Orbitrap MS was used to identify these three GMD impurities (m/z: 408.122, 338.340, 381.160) and two GBD impurities (m/z: 369.065, 325.283). ProTox-II in silico predictions classified all impurities as class 4 and 5, with no positive genotoxicity indications. In vitro comet assays, using HEK cells, indicated that for GMD, impurity 2 and impurity 5 were less genotoxic, whereas impurity 4 exhibited genotoxicity. For GBD, both impurities 1 and 3 were found to be genotoxic, with impurity 3 showing a higher level of genotoxicity than impurity 1.

Exploring the antimicrobial and antioxidant potential of bacterial cellulose-cerium oxide nanoparticles hydrogel: Design, characterization and biomedical properties

Bacterial cellulose (BC) is a promising natural polymer prized for its biocompatibility, microporosity, transparency, conformability, elasticity, and ability to maintain a moist wound environment while absorbing exudates. These attributes make BC an attractive material in biomedical applications, particularly in skin tissue repair. However, its lack of inherent antimicrobial activity limits its effectiveness. In this study, BC was enhanced by incorporating cerium (IV)-oxide (CeO2) nanoparticles, resulting in a series of bacterial cellulose-CeO2 (BC-CeO2) composite materials. Characterization via FESEM, XRD, and FTIR confirmed the successful synthesis of the composites. Notably, BC-CeO2-1 exhibited no cytotoxic or genotoxic effects on peripheral blood lymphocytes, and it additionally protected cells from genotoxic and cytotoxic effects in H2O2-treated cultures. Redox parameters in blood plasma samples displayed concentration and time-dependent trends in PAB and LPP assays. The incorporation of CeO2 nanoparticles also bolstered antimicrobial activity, expanding the potential biomedical applications of these composites.

Microwave-assisted synthesis of silver nanoparticles as a colorimetric sensor for hydrogen peroxide

To consider silver nanoparticles (AgNPs) as a colorimetric sensor for H2O2 we require investigation of the effects of the homogeneity of the nanoparticle size and morphology on the sensor parameters. Uniformly-sized Ag nanoparticles with diameters of ∼18.8 ± 2.8 nm were produced using microwave irradiation (AgNP1) but non-uniform particles with diameters of ∼71.2 ± 19.4 nm (AgNP2) were formed without microwave irradiation. Microwave synthesis produced AgNP1 with superiority in terms of repeatability, selectivity and sensor stability for up to eight months of storage over AgNP2. AgNP1 exhibited higher sensitivity and detection limits in the working range of 0.01-40000 μM as compared to AgNP2. The application of the AgNP sensor to milk samples provided recovery values of 99.09-100.56% for AgNP1 and 98.18-101.90% for AgNP2. Microwave irradiation resulted in strong and uniform PVP-Ag interactions for isotropic growth into small nanoparticles. Size and morphology uniformity determined the characteristics of the AgNP sensor that can be applied for H2O2 detection in a wide range of concentrations and real-time evaluation, with the potential for industrial applications.

Polyphenol Mediated Suppression of Hepatocellular Carcinoma (HepG2) Cell Proliferation by Clerodendrum infortunatum L. Root

OBJECTIVE

Clerodendrum infortunatum L. has long been used in traditional medicine in Sri Lanka for tumours, cancer, and certain skin diseases. The present study aimed to assess the anticancer properties of the aqueous extract of C. infortunatum L. root (AECIR) through the activation of the apoptotic pathway on hepatocellular carcinoma (HepG2) and thus give it a scientific validation. Further, the contribution of polyphenols in antioxidant activity and cell cytotoxicity was investigated.

METHODS

Powdered plant material was boiled with water (100°C) to obtained AECIR.  The DPPH assay was used to determine the antioxidant potential. The activity of AECIR on HepG2 and normal rat fibroblast (CC1) cell growth was determined using MTT assay. The morphological changes related to apoptotic pathway was examined by Ethidium Bromide/Acridine Orange (EB/AO), Rhodamine 123 (Rh123) and DNA fragmentation assay.

RESULTS

The AECIR demonstrated antioxidant potential with an EC50 of 350.2 ± 1.5 ug/mL for DPPH assay. The HO•, H2O2 and •NO free radical scavenging activity was observed with EC50 of 19.7 ± 2.3, 11.7 ± 0.1 and 273.1 ± 0.9 ug/mL, respectively. The antiproliferative effect of AECIR on HepG2 cells was observed in a time and dose dependent manner with an EC50 of 239.1 ± 1.3 μg/mL while CC1 cells showed a nontoxic effect with an EC50 1062.7 ± 3.4 μg/mL after 24hrs treatment. A significant decrease in antioxidant activity (p<0.001) and 90% HepG2 cell viability was observed with polyphenol removed AECIR compared to the polyphenol present AECIR. The EB/AO uptake, depletion of mitochondrial transmembrane potential, and DNA fragmentation assay results revealed that the apoptosis was induced by AECIR.

CONCLUSION

The obtained result of the present study demonstrates that the antioxidant potential and antiproliferative activity of AECIR is attributed to the presence of polyphenols. Furthermore, the findings provide the scientific base for anti-cancer potential of AECIR.

Oleoylethanolamide protects mesenchymal stem/stromal cells (MSCs) from oxidative stress and reduces adipogenic related genes expression in adipose-derived MSCs undergoing adipocyte differentiation

BACKGROUND

Human mesenchymal stem/stromal cells (hMSCs) are known for their pronounced therapeutic potential; however, they are still applied in limited clinical cases for several reasons. ROS-mediated oxidative stress is among the chief causes of post-transplantation apoptosis and death of hMSCs. It has been reported that a strategy to protect hMSCs against ROS is to pretreat them with antioxidants. Oleoylethanolamide (OEA) is a monounsaturated fatty acid derived from oleic acid and it has many protective properties, including anti-obesity, anti-inflammatory, and antioxidant effects. OEA is also used as a weight loss supplement; due to its high affinity for the PPAR-α receptor, OEA increases the fat metabolism rate.

METHODS AND RESULTS

This study hence assessed the effects of OEA pretreatment on the in vitro survival rate and resistance of hMSCs under oxidative stress as well as the cellular and molecular events in the biology of stem/stromal cells affected by oxidative stress and free radicals. Considering the role of MSCs in adipogenesis and obesity, the expression of the main genes involved in adipogenesis was also addressed in this study. Results revealed that OEA increases the in vitro proliferation of MSCs and inhibits cell apoptosis by reducing the induction of oxidative stress. The results also indicated that OEA exerts its antioxidant properties by both activating the Nrf2/NQO-1/HO-1 signaling pathway and directly combating free radicals. Moreover, OEA can reduce adipogenesis through reducing the expression of PPARγ, leptin and CEBPA genes in hMSCs undergoing adipocyte differentiation.

CONCLUSIONS

Thus, OEA protects hMSCs from oxidative stress and reduces adipogenic related genes expression and can be regarded as a therapeutic agent for this purpose.

Deciphering the Cell-Specific Effect of Osteoblast-Macrophage Crosstalk in Periodontitis

In periodontitis, the bone remodeling process is disrupted by the prevalent involvement of bacteria-induced proinflammatory macrophage cells and their interaction with osteoblast cells residing within the infected bone tissue. The complex interaction between the cells needs to be deciphered to understand the dominant player in tipping the balance from osteogenesis to osteoclastogenesis. Yet, only a few studies have examined the crosstalk interaction between osteoblasts and macrophages using biomimetic three-dimensional (3D) tissue-like matrices. In this study, we created a cell-laden 3D tissue analog to study indirect crosstalk between these two cell types and their direct synergistic effect when cultured on a 3D scaffold. The cell-specific role of osteoclast differentiation was investigated through osteoblast- and proinflammatory macrophage-specific feedback studies. The results suggested that when macrophages were exposed to osteoblasts-derived conditioned media from the mineralized matrix, the M1 macrophages tended to maintain their proinflammatory phenotype. Further, when osteoblasts were exposed to secretions from proinflammatory macrophages, they demonstrated elevated receptor activator of nuclear factor-κB ligand (RANKL) expression and decreased alkaline phosphate (ALP) activities compared to osteoblasts exposed to only osteogenic media. In addition, the upregulation of tumor necrosis factor-alpha (TNF-α) and c-Fos in proinflammatory macrophages within the 3D matrix indirectly increased the RANKL expression and reduced the ALP activity of osteoblasts, promoting osteoclastogenesis. The contact coculturing with osteoblast and proinflammatory macrophages within the 3D matrix demonstrated that the proinflammatory markers (TNF-α and interleukin-1β) expressions were upregulated. In contrast, anti-inflammatory markers (c-c motif chemokine ligand 18 [CCL18]) were downregulated, and osteoclastogenic markers (TNF receptor associated factor 6 [TRAF6] and acid phosphatase 5, tartrate resistant [ACP5]) were unchanged. The data suggested that the osteoblasts curbed the osteoclastogenic differentiation of macrophages while macrophages still preserved their proinflammatory lineages. The osteoblast within the 3D coculture demonstrated increased ALP activity and did not express RANKL significantly different than the osteoblast cultured within a 3D collagen matrix without macrophages. Contact coculturing has an anabolic effect on bone tissue in a bacteria-derived inflammatory environment.

Sodium Nitroprusside Stimulation of Elastic Matrix Regeneration by Aneurysmal Smooth Muscle Cells

The chronic overexpression of matrix metalloproteases leading to consequent degradation and loss of the elastic matrix with the reduction in tissue elasticity is central to the pathophysiology of proteolytic disorders, such as abdominal aortic aneurysms (AAAs), which are localized rupture-prone aortic expansions. Effecting tissue repair to alleviate this condition is contingent on restoring elastic matrix homeostasis in the aortic wall. This is naturally irreversible due to the poor elastogenicity of adult and diseased vascular cells, and the impaired ability to assemble mature elastic fibers, more so in the context of phenotypic changes to medial smooth muscle cells (SMCs) owing to the loss of nitric oxide (NO) signaling in the AAA wall tissue. In this study, we report the benefits of the exposure of primary human aneurysmal SMCs (aHASMCs) to NO donor drug, sodium nitroprusside (SNP), in improving extracellular matrix homeostasis, particularly aspects of elastic fiber assembly, and inhibition of proteolytic degradation. SNP treatment (100 nM) upregulated elastic matrix regeneration at both gene (p < 0.05) and protein levels (p < 0.01) without affecting cell proliferation, improved gene, and protein expression of crosslinking enzyme, lysyl oxidase (p < 0.05), inhibited the expression of MMP2 (matrix metalloprotease 2) significantly (p < 0.05) and promoted contractile SMC phenotypes in aHASMC culture. In addition, SNP also attenuated the expression of mitogen-activated protein kinases, a significant player in AAA formation and progression. Our results indicate the promise of SNP for therapeutic augmentation of elastic matrix regeneration, with prospects for wall repair in AAAs. Impact Statement Chronic and naturally irreversible enzymatic degradation and loss of elastic fibers are centric to proteolytic disorders such as abdominal aortic aneurysms (AAAs). This is linked to poor elastogenicity of adult and diseased vascular cells, compromising their ability to assemble mature elastic fibers. Toward addressing this, we demonstrate the phenotype-modulatory properties of a nitric oxide donor drug, sodium nitroprusside on aneurysmal smooth muscle cells, and its dose-specific proelastogenic and antiproteolytic properties for restoring elastic matrix homeostasis. Combined with the development of vehicles for site-localized, controlled drug delivery, this can potentially lead to a new nonsurgical approach for AAA wall repair in the future.

α-synucleinopathy exerts sex-dimorphic effects on the multipurpose DNA repair/redox protein APE1 in mice and humans

Lewy body disorders are characterized by oxidative damage to DNA and inclusions rich in aggregated forms of α-synuclein. Among other roles, apurinic/apyrimidinic endonuclease 1 (APE1) repairs oxidative DNA damage, and APE1 polymorphisms have been linked to cases of Lewy body disorders. However, the link between APE1 and α-synuclein is unexplored. We report that knockdown or inhibition of APE1 amplified inclusion formation in primary hippocampal cultures challenged with preformed α-synuclein fibrils. Fibril infusions into the mouse olfactory bulb/anterior olfactory nucleus (OB/AON) elicited a modest decrease in APE1 expression in the brains of male mice but an increase in females. Similarly, men with Lewy body disorders displayed lower APE1 expression in the OB and amygdala compared to women. Preformed fibril infusions of the mouse OB/AON induced more robust base excision repair of DNA lesions in females than males. No fibril-mediated loss of APE1 expression was observed in male mice when the antioxidant N-acetylcysteine was added to their diet. These findings reveal a potential sex-biased link between α-synucleinopathy and APE1 in mice and humans. Further studies are warranted to determine how this multifunctional protein modifies α-synuclein inclusions and, conversely, how α-synucleinopathy and biological sex interact to modify APE1.

Development of an ATP-independent bioluminescent probe for detection of extracellular hydrogen peroxide

This work reports a new ATP-independent bioluminescent probe (bor-DTZ) for detecting hydrogen peroxide that is compatible with the Nanoluciferase enzyme. The probe is designed with an arylboronate ester protecting group appended to a diphenylterazine core via a self-immolative phenolate linker. Reaction with hydrogen peroxide reveals diphenylterazine, which can then react with Nanoluciferase to produce a detectable bioluminescent signal. Bor-DTZ shows a dose-dependent response to hydrogen peroxide and selectivity over other biologically relevant reactive oxygen species and can be applied to detect either intra- or extracellular species. We further demonstrate the ability of this platform to monitor fluxes in extracellular hydrogen peroxide in a breast cancer cell line in response to the anticancer treatment, cisplatin.

Rare germline alterations of myeloperoxidase predispose to myeloid neoplasms

Myeloperoxidase (MPO) gene alterations with variable clinical penetrance have been found in hereditary MPO deficiency, but their leukemia association in patients and carriers has not been established. Germline MPO alterations were found to be significantly enriched in myeloid neoplasms: 28 pathogenic/likely pathogenic variants were identified in 100 patients. The most common alterations were c.2031-2 A > C, R569W, M519fs* and Y173C accounting for about half of the cases. While functional experiments showed that the marrow stem cell pool of Mpo^-/- mice was not increased, using competitive repopulation demonstrated that Mpo^-/- grafts gained growth advantage over MPO wild type cells. This finding also correlated with increased clonogenic potential after serial replating in the setting of H₂O₂-induced oxidative stress. Furthermore, we demonstrated that H₂O₂-induced DNA damage and activation of error-prone DNA repair may result in secondary genetic damage potentially predisposing to leukemia leukemic evolution. In conclusion, our study for the first time demonstrates that germline MPO variants may constitute risk alleles for MN evolution.

Cockayne syndrome without UV-sensitivity in Vietnamese siblings with novel ERCC8 variants

Cockayne syndrome (CS) is a rare progeroid disorder characterized by growth failure, microcephaly, photosensitivity, and premature aging, mainly arising from biallelic ERCC8 (CS-A) or ERCC6 (CS-B) variants. In this study we describe siblings suffering from classical Cockayne syndrome but without photosensitivity, which delayed a clinical diagnosis for 16 years. By whole-exome sequencing we identified the two novel compound heterozygous ERCC8 variants c.370_371del (p.L124Efs*15) and c.484G>C (p.G162R). The causality of the ERCC8 variants, of which one results in a frameshift and the other affects the WD3 domain, was tested and confirmed by a rescue experiment investigating DNA repair in H₂O₂ treated patient fibroblasts. Structural modeling of the p.G162R variant indicates effects on protein-protein interaction. This case shows the importance to test for ERCC6 and ERCC8 variants even if patients do not present with a complete CS phenotype.

SREBP1c-PARP1 axis tunes anti-senescence activity of adipocytes and ameliorates metabolic imbalance in obesity

Emerging evidence indicates that the accretion of senescent cells is linked to metabolic disorders. However, the underlying mechanisms and metabolic consequences of cellular senescence in obesity remain obscure. In this study, we found that obese adipocytes are senescence-susceptible cells accompanied with genome instability. Additionally, we discovered that SREBP1c may play a key role in genome stability and senescence in adipocytes by modulating DNA-damage responses. Unexpectedly, SREBP1c interacted with PARP1 and potentiated PARP1 activity during DNA repair, independent of its canonical lipogenic function. The genetic depletion of SREBP1c accelerated adipocyte senescence, leading to immune cell recruitment into obese adipose tissue. These deleterious effects provoked unhealthy adipose tissue remodeling and insulin resistance in obesity. In contrast, the elimination of senescent adipocytes alleviated adipose tissue inflammation and improved insulin resistance. These findings revealed distinctive roles of SREBP1c-PARP1 axis in the regulation of adipocyte senescence and will help decipher the metabolic significance of senescence in obesity.

Puerarin alleviates the ototoxicity of gentamicin by inhibiting the mitochondria‑dependent apoptosis pathway

Gentamicin (GM) is a commonly used antibiotic, and ototoxicity is one of its side effects. Puerarin (PU) is an isoflavone in kudzu roots that exerts a number of pharmacological effects, including antioxidative and free radical scavenging effects. The present study investigated whether PU could protect against GM-induced ototoxicity in C57BL/6J mice and House Ear Institute-Organ of Corti 1 (HEI-OC1) cells. C57BL/6J mice and HEI-OC1 cells were used to establish models of GM-induced ototoxicity in this study. Auditory brainstem responses were measured to assess hearing thresholds, and microscopy was used to observe the morphology of cochlear hair cells after fluorescent staining. Cell viability was examined with Cell Counting Kit-8 assays. To evaluate cell apoptosis and reactive oxygen species (ROS) production, TUNEL assays, reverse transcription-quantitative PCR, DCFH-DA staining, JC-1 staining and western blotting were performed. PU protected against GM-induced hearing damage in C57BL/6J mice. PU ameliorated the morphological changes of mouse cochlear hair cells and reduced the apoptosis rate of HEI-OC1 cells after GM-mediated damage. GM-induced ototoxicity may be closely related to the upregulation of p53 expression and the activation of endogenous mitochondrial apoptosis pathways, and PU could protect cochlear hair cells from GM-mediated damage by reducing the production of ROS and inhibiting the mitochondria-dependent apoptosis pathway.

Sustained Activation of TNFα-Induced DNA Damage Response in Newly Differentiated Adipocytes

The response to DNA damage is the mechanism that allows the interaction between stress signals, inflammatory secretions, DNA repair, and maintenance of cell and tissue homeostasis. Adipocyte dysfunction is the cellular trigger for various disease states such as insulin resistance, diabetes, and obesity, among many others. Previously, our group demonstrated that adipogenesis per se, from mesenchymal/stromal stem cells derived from human adipose tissue (hASCs), involves an accumulation of DNA damage and a gradual loss of the repair capacity of oxidative DNA damage. Therefore, our objective was to identify whether healthy adipocytes differentiated for the first time from hASCs, when receiving inflammatory signals induced with TNFα, were able to persistently activate the DNA Damage Response and thus trigger adipocyte dysfunction. We found that TNFα at similar levels circulating in obese humans induce a sustained response to DNA damage response as part of the Senescence-Associated Secretory Phenotype. This mechanism shows the impact of inflammatory environment early affect adipocyte function, independently of aging.

Kinetics of γH2AX and phospho-histone H3 following pulse treatment of TK6 cells provides insights into clastogenic activity

The desire for in vitro genotoxicity assays to provide higher information content, especially regarding chemicals' predominant genotoxic mode of action, has led to the development of a novel multiplexed assay available under the trade name MultiFlow®. We report here on an experimental design variation that provides further insight into clastogens' genotoxic activity. First, the standard MultiFlow DNA Damage Assay-p53, γ H2AX, phospho-histone H3 was used with human TK6 lymphoblastoid cells that were exposed for 24 continuous hours to each of 50 reference clastogens. This initial analysis correctly identified 48/50 compounds as clastogenic. These 48 compounds were then evaluated using a short-term, 'pulse' treatment protocol whereby cells were exposed to test chemical for 4 h, a centrifugation/washout step was performed, and cells were allowed to recover for 20 h. MultiFlow analyses were accomplished at 4 and 24 h. The γ H2AX and phospho-histone H3 biomarkers were found to exhibit distinct differences in terms of their persistence across chemical classes. Unsupervised hierarchical clustering analysis identified three groups. Examination of the compounds within these groups showed one cluster primarily consisting of alkylators that directly target DNA. The other two groups were dominated by non-DNA alkylators and included anti-metabolites, oxidative stress inducers and chemicals that inhibit DNA-processing enzymes. These results are encouraging, as they suggest that a simple follow-up test for in vitro clastogens provides mechanistic insights into their genotoxic activity. This type of information will contribute to improve decision-making and help guide further testing.

DNA damage and repair in differentiation of stem cells and cells of connective cell lineages: A trigger or a complication?

The review summarizes literature data on the role of DNA breaks and DNA repair in the differentiation of pluripotent stem cells (PSC) and connective cell lineages. PSC, including embryonic stem cells (ESC) and induced pluripotent stem cells (iPSC), are rapidly dividing cells with highly active DNA damage response (DDR) mechanisms to ensure the stability and integrity of the DNA. In PSCs, the most common DDR mechanism is error-free homologous recombination (HR) that is primarily active during the S phase of the cell cycle, whereas in quiescent, slow-dividing or non-dividing tissue progenitors and terminally differentiated cells, errorprone non-homologous end joining (NHEJ) mechanism of the double-strand break (DSB) repair is dominating. Thus, it seems that reprogramming and differentiation induce DNA strand breaks in stem cells which itself may trigger the differentiation process. Somatic cell reprogramming to iPSCs is preceded by a transient increase of the DSBs induced presumably by the caspase-dependent DNase or reactive oxygen species. In general, pluripotent stem cells possess stronger DNA repair systems compared to differentiated cells. Nonetheless, during a prolonged cell culture propagation, DNA breaks can accumulate due to the DNA polymerase stalling. Consequently, the DNA damage might trigger the differentiation of stem cells or replicative senescence of somatic cells. The differentiation process per se is often accompanied by a decrease in the DNA repair capacity. Thus, the differentiation might be triggered by DNA breaks, alternatively, the breaks can be a consequence of the decay in the DNA repair capacity of differentiated cells.

Cholinergic drugs bind at the minor groove and reverse induced oxidative stress of calf thymus DNA: a new perspective towards an unexplored therapeutic efficacy

Four FDA approved cholinesterase inhibitors reverse the hydrogen peroxide induced oxidative damage of ct-DNA.

HSATII RNA is induced via a noncanonical ATM-regulated DNA damage response pathway and promotes tumor cell proliferation and movement

Pericentromeric human satellite II (HSATII) repeats are normally silent but can be actively transcribed in tumor cells, where increased HSATII copy number is associated with a poor prognosis in colon cancer, and in human cytomegalovirus (HCMV)-infected fibroblasts, where the RNA facilitates viral replication. Here, we report that HCMV infection or treatment of ARPE-19 diploid epithelial cells with DNA-damaging agents, etoposide or zeocin, induces HSATII RNA expression, and a kinase-independent function of ATM is required for the induction. Additionally, various breast cancer cell lines growing in adherent, two-dimensional cell culture express HSATII RNA at different levels, and levels are markedly increased when cells are infected with HCMV or treated with zeocin. High levels of HSATII RNA expression correlate with enhanced migration of breast cancer cells, and knockdown of HSATII RNA reduces cell migration and the rate of cell proliferation. Our investigation links high expression of HSATII RNA to the DNA damage response, centered on a noncanonical function of ATM, and demonstrates a role for the satellite RNA in tumor cell proliferation and movement.

Nicotine Prevents Oxidative Stress-Induced Hippocampal Neuronal Injury Through α7-nAChR/Erk1/2 Signaling Pathway

Oxidative stress-induced neuronal damage has been implicated to play a dominant role in neurodegenerative disorders, such as Alzheimer’s disease (AD). Nicotine, a principal additive compound for tobacco users, is thought as a candidate to attenuate amyloid-β-mediated neurotoxicity and NMDA-induced excitotoxicity. Previous studies demonstrated that nicotine exerted this neuroprotective action on oxidative stress. However, the mechanisms underlying how nicotine contributes on oxidative injury in immortalized hippocampal HT-22 cells remain largely unknown. Therefore, in this study we investigated that the potential effects of nicotine on hydrogen peroxide (H₂O₂)-induced oxidative injury and underlying mechanisms in HT-22 cells. We found that pretreatment with nicotine at low concentrations markedly recovered the cell cycle that was arrested at the G2/M phase in the presence of H₂O₂ through reduced intracellular ROS generation. Moreover, nicotine attenuated H₂O₂-induced mitochondrial dysfunctions. Mechanistically, the application of nicotine significantly upregulated the levels of phosphorylated Erk1/2. The neuroprotective effects of nicotine, in turn, were abolished by PD0325901, a selective Erk1/2 inhibitor. Further obtained investigation showed that nicotine exerted its neuroprotective effects via specifically activating α7 nicotinic acetylcholine receptors (α7-nAChRs). A selective inhibitor of α7-nAChRs, methyllycaconitine citrate (MLA), not only completely prevented nicotine-mediated antioxidation but also abolished expression of p-Erk1/2. Taken together, our findings suggest that nicotine suppresses H₂O₂-induced HT-22 cell injury through activating the α7-nAChR/Erk1/2 signaling pathway, which indicates that nicotine may be a novel strategy for the treatment of neurodegenerative disorders.

Reactive Oxygen Species Induced p53 Activation: DNA Damage, Redox Signaling, or Both?

Significance: The p53 tumor suppressor has been dubbed the "guardian of genome" because of its various roles in the response to DNA damage such as DNA damage repair, cell cycle arrest, senescence, and apoptosis, all of which are in place to prevent mutations from being passed on down the lineage. Recent Advances: Reactive oxygen species (ROS), for instance hydrogen peroxide derived from mitochondrial respiration, have long been regarded mainly as a major source of cellular damage to DNA and other macromolecules. Critical Issues: More recently, ROS have been shown to also play important physiological roles as second messengers in so-called redox signaling. It is, therefore, not clear whether the observed activation of p53 by ROS is mediated through the DNA damage response, redox signaling, or both. In this review, we will discuss the similarities and differences between p53 activation in response to DNA damage and redox signaling in terms of upstream signaling and downstream transcriptional program activation. Future Directions: Understanding whether and how DNA damage and redox signaling-dependent p53 activation can be dissected could be useful to develop anti-cancer therapeutic p53-reactivation strategies that do not depend on the induction of DNA damage and the resulting additional mutational load.

RNA helicase p68 inhibits the transcription and post-transcription of Pkd1 in ADPKD

Background: Autosomal dominant polycystic kidney disease (ADPKD) is caused by mutations of the PKD1 and PKD2 genes. Dysregulation of the expression of PKD genes, the abnormal activation of PKD associated signaling pathways, and the expression and maturation of miRNAs regulates cyst progression. However, the upstream factors regulating these abnormal processes in ADPKD remain elusive.

Methods: To investigate the roles of an RNA helicase, p68, in ADPKD, we performed Western blot and qRT-PCR analysis, immunostaining and ChIP assay in cystic renal epithelium cells and tissues.

Results: We found that p68 was upregulated in cystic renal epithelial cells and tissues. p68 represses Pkd1 gene expression via transcriptional and posttranscriptional mechanisms in renal epithelial cells, in that 1) p68 binds to the promoter of the Pkd1 gene together with p53 to repress transcription; and 2) p68 promotes the expression and maturation of miR-17, miR-200c and miR-182 and via these miRNAs, post-transcriptionally regulates the expression of Pkd1 mRNA. Drosha is involved in this process by forming a complex with p68. p68 also regulates the phosphorylation and activation of PKD proliferation associated signaling and the expression of fibrotic markers in Pkd1 mutant renal epithelial cells. Silence of p68 delays cyst formation in collecting duct cell mediated 3D cultures. In addition, the expression of p68 is induced by H₂O₂-dependent oxidative stress and DNA damage which causes downregulation of Pkd1 transcription in cystic renal epithelial cells and tissues.

Conclusions: p68 plays a critical role in negatively regulating the expression of the PKD1 gene along with positively regulating the expression and maturation of miRNAs and activation of PKD associated signaling pathways to cause renal cyst progression and fibrosis in ADPKD.

Genoprotective activities of plant natural substances in cancer and chemopreventive strategies in the context of 3P medicine

Severe durable changes may occur to the DNA structure caused by exogenous and endogenous risk factors initiating the process of carcinogenesis. By evidence, a large portion of malignancies have been demonstrated as being preventable. Moreover, the targeted prevention of cancer onset is possible, due to unique properties of plant bioactive compounds. Although genoprotective effects of phytochemicals have been well documented, there is an evident lack of articles which would systematically present the spectrum of anticancer effects by phytochemicals, plant extracts, and plant-derived diet applicable to stratified patient groups at the level of targeted primary (cancer development) and secondary (cancer progression and metastatic disease) prevention. Consequently, clinical implementation of knowledge accumulated in the area is still highly restricted. To stimulate coherent co-development of the dedicated plant bioactive compound investigation on one hand and comprehensive cancer preventive strategies on the other hand, the current paper highlights and deeply analyses relevant evidence available in the area. Key molecular mechanisms are presented to detail genoprotective and anticancer activities of plants and phytochemicals. Clinical implementation is discussed. Based on the presented evidence, advanced chemopreventive strategies in the context of 3P medicine are considered.

Base excision repair but not DNA double-strand break repair is impaired in aged human adipose-derived stem cells

The decline in DNA repair capacity contributes to the age-associated decrease in genome integrity in somatic cells of different species. However, due to the lack of clinical samples and appropriate tools for studying DNA repair, whether and how age-associated changes in DNA repair result in a loss of genome integrity of human adult stem cells remains incompletely characterized. Here, we isolated 20 eyelid adipose-derived stem cell (ADSC) lines from healthy individuals (young: 10 donors with ages ranging 17-25 years; old: 10 donors with ages ranging 50-59 years). Using these cell lines, we systematically compared the efficiency of base excision repair (BER) and two DNA double-strand break (DSB) repair pathways-nonhomologous end joining (NHEJ) and homologous recombination (HR)-between the young and old groups. Surprisingly, we found that the efficiency of BER but not NHEJ or HR is impaired in aged human ADSCs, which is in contrast to previous findings that DSB repair declines with age in human fibroblasts. We also demonstrated that BER efficiency is negatively associated with tail moment, which reflects a loss of genome integrity in human ADSCs. Mechanistic studies indicated that at the protein level XRCC1, but not other BER factors, exhibited age-associated decline. Overexpression of XRCC1 reversed the decline of BER efficiency and genome integrity, indicating that XRCC1 is a potential therapeutic target for stabilizing genomes in aged ADSCs.