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Thymoquinone Inhibits Autophagy and Induces Cathepsin-Mediated, Caspase-Independent Cell Death in Glioblastoma Cells  [PDF]
Ira O. Racoma, Walter Hans Meisen, Qi-En Wang, Balveen Kaur, Altaf A. Wani
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0072882
Abstract: Glioblastoma is the most aggressive and common type of malignant brain tumor in humans, with a median survival of 15 months. There is a great need for more therapies for the treatment of glioblastoma. Naturally occurring phytochemicals have received much scientific attention because many exhibit potent tumor killing action. Thymoquinone (TQ) is the bioactive compound of the Nigella sativa seed oil. TQ has anti-oxidant, anti-inflammatory and anti-neoplastic actions with selective cytotoxicity for human cancer cells compared to normal cells. Here, we show that TQ selectively inhibits the clonogenicity of glioblastoma cells as compared to normal human astrocytes. Also, glioblastoma cell proliferation could be impaired by chloroquine, an autophagy inhibitor, suggesting that glioblastoma cells may be dependent on the autophagic pathway for survival. Exposure to TQ caused an increase in the recruitment and accumulation of the microtubule-associated protein light chain 3-II (LC3-II). TQ also caused an accumulation of the LC3-associated protein p62, confirming the inhibition of autophagy. Furthermore, the levels of Beclin-1 protein expression were unchanged, indicating that TQ interferes with a later stage of autophagy. Finally, treatment with TQ induces lysosome membrane permeabilization, as determined by a specific loss of red acridine orange staining. Lysosome membrane permeabilization resulted in a leakage of cathepsin B into the cytosol, which mediates caspase-independent cell death that can be prevented by pre-treatment with a cathepsin B inhibitor. TQ induced apoptosis, as determined by an increase in PI and Annexin V positive cells. However, apoptosis appears to be caspase-independent due to failure of the caspase inhibitor z-VAD-FMK to prevent cell death and absence of the typical apoptosis related signature DNA fragmentation. Inhibition of autophagy is an exciting and emerging strategy in cancer therapy. In this vein, our results describe a novel mechanism of action for TQ as an autophagy inhibitor selectively targeting glioblastoma cells.
Telomere shortening may be associated with human keloids
Bruna De Felice, Robert R Wilson, Massimo Nacca
BMC Medical Genetics , 2009, DOI: 10.1186/1471-2350-10-110
Abstract: We analyzed sample tissues were obtained from 20 patients with keloid skin lesions and normal skin was obtained from 20 healthy donors. The telomeres were measured by Terminal Restriction Fragment (TRF) analysis and Real-Time PCR assay. Quantitative Real-Time RT-PCR analysis of hTERT gene expression was performed and intracellular ROS generation was measured.In this study, we determined whether telomeric shortening and the expression of human telomerase reverse transcriptase (hTERT) occurs in keloid patients. Using Terminal Restriction Fragment (TRF) analysis and Real-Time PCR assay, we detected a significant telomere shortening of 30% in keloid specimens compared to normal skin. Using quantitative Real-Time RT-PCR, telomerase activity was found absent in the keloid tissues. Moreover, an increase in ROS generation was detected in fibroblasts cell cultures from keloid specimens as more time elapsed compared to fibroblasts from normal skin.Telomere shortening has been reported in several metabolic and cardiovascular diseases. We found that telomere shortening can also be associated with human keloids. Chronic oxidative stress plays a major role in the pathophysiology of several chronic inflammatory diseases. Here we found increased ROS generation in fibroblasts from keloid fibroblasts cell cultures when compared to normal skin fibroblasts. Hence we conclude that oxidative stress might be an important modulator of telomere loss in keloid because of the absence of active telomerase that counteracts telomere shortening.Keloids (OMIM 148100) are benign skin tumors occurring during wound healing in genetically predisposed patients. The pattern of inheritance observed in 14 pedigrees with familial keloids has been consistent with an autosomal dominant mode with incomplete clinical penetrance and variable expression [1]. Keloids are characterized by the proliferation of dermal fibroblasts, overproduction of extracellular matrix components (ECM), an increased infiltration of
Genetic Anticipation Is Associated with Telomere Shortening in Hereditary Breast Cancer  [PDF]
Beatriz Martinez-Delgado equal contributor ,Kira Yanowsky equal contributor,Lucia Inglada-Perez,Samuel Domingo,Miguel Urioste,Ana Osorio,Javier Benitez
PLOS Genetics , 2011, DOI: 10.1371/journal.pgen.1002182
Abstract: There is increasing evidence suggesting that short telomeres and subsequent genomic instability contribute to malignant transformation. Telomere shortening has been described as a mechanism to explain genetic anticipation in dyskeratosis congenita and Li-Fraumeni syndrome. Since genetic anticipation has been observed in familial breast cancer, we aimed to study telomere length in familial breast cancer patients and hypothesized that genetic defects causing this disease would affect telomere maintenance resulting in shortened telomeres. Here, we first investigated age anticipation in mother-daughter pairs with breast cancer in 623 breast cancer families, classified as BRCA1, BRCA2, and BRCAX. Moreover, we analyzed telomere length in DNA from peripheral blood leukocytes by quantitative PCR in a set of 198 hereditary breast cancer patients, and compared them with 267 control samples and 71 sporadic breast cancer patients. Changes in telomere length in mother-daughter pairs from breast cancer families and controls were also evaluated to address differences through generations. We demonstrated that short telomeres characterize hereditary but not sporadic breast cancer. We have defined a group of BRCAX families with short telomeres, suggesting that telomere maintenance genes might be susceptibility genes for breast cancer. Significantly, we described that progressive telomere shortening is associated with earlier onset of breast cancer in successive generations of affected families. Our results provide evidence that telomere shortening is associated with earlier age of cancer onset in successive generations, suggesting that it might be a mechanism of genetic anticipation in hereditary breast cancer.
Artemisinin mimics calorie restriction to initiate antioxidative responses and compromise telomere shortening  [PDF]
Da-Ting Wang,Ming Wu,Si-ming Li,Qian Gao,Qing-Ping Zeng
PeerJ , 2015, DOI: 10.7287/peerj.preprints.565v1
Abstract: Calorie restriction (CR) is known to extend lifespan among organisms with the putative mechanism underlying nitric oxide (NO)-enhanced mitochondrial biogenesis. However, whether NO maintains telomere intact that is implicated in life expectancy remains unknown. We report here the artemisinin derivative artesunate in a low concentration up-regulates mitochondrial SIRT3-SOD2 expression among global activation of antioxidative networks via the NO signaling cascade AMPK→Akt→eNOS→SIRT1→PGC-1α. While the NO donor sodium nitroprusside and the NO precursor L-arginine replicate the antioxidative responses, exogenous low-dose hydrogen peroxide also leads to attenuated oxidative stress. The tumor suppressor BRCA1 and other DNA repair partners are down-regulated after scavenging of reactive oxygen species. Upon treatment, telomere shortening is damped without telomerase up-regulation, highlighting telomere maintenance rather than telomere elongation. In conclusion, artesunate can mimic CR to activate antioxidative responses and alleviate telomere attrition via NO signaling, thereby maintaining the stability and integrity of chromosomes, which are the hallmarks of longevity.
Saccharomyces cerevisiae as a Model to Study Replicative Senescence Triggered by Telomere Shortening  [PDF]
M. Teresa Teixeira
Frontiers in Oncology , 2013, DOI: 10.3389/fonc.2013.00101
Abstract: In many somatic human tissues, telomeres shorten progressively because of the DNA-end replication problem. Consequently, cells cease to proliferate and are maintained in a metabolically viable state called replicative senescence. These cells are characterized by an activation of DNA damage checkpoints stemming from eroded telomeres, which are bypassed in many cancer cells. Hence, replicative senescence has been considered one of the most potent tumor suppressor pathways. However, the mechanism through which short telomeres trigger this cellular response is far from being understood. When telomerase is removed experimentally in Saccharomyces cerevisiae, telomere shortening also results in a gradual arrest of population growth, suggesting that replicative senescence also occurs in this unicellular eukaryote. In this review, we present the key steps that have contributed to the understanding of the mechanisms underlying the establishment of replicative senescence in budding yeast. As in mammals, signals stemming from short telomeres activate the DNA damage checkpoints, suggesting that the early cellular response to the shortest telomere(s) is conserved in evolution. Yet closer analysis reveals a complex picture in which the apparent single checkpoint response may result from a variety of telomeric alterations expressed in the absence of telomerase. Accordingly, the DNA replication of eroding telomeres appears as a critical challenge for senescing budding yeast cells and the easy manipulation of S. cerevisiae is providing insights into the way short telomeres are integrated into their chromatin and nuclear environments. Finally, the loss of telomerase in budding yeast triggers a more general metabolic alteration that remains largely unexplored. Thus, telomerase-deficient S. cerevisiae cells may have more common points than anticipated with somatic cells, in which telomerase depletion is naturally programed, thus potentially inspiring investigations in mammalian cells.
TERRA Promotes Telomere Shortening through Exonuclease 1–Mediated Resection of Chromosome Ends  [PDF]
Verena Pfeiffer,Joachim Lingner
PLOS Genetics , 2012, DOI: 10.1371/journal.pgen.1002747
Abstract: The long noncoding telomeric repeat containing RNA (TERRA) is expressed at chromosome ends. TERRA upregulation upon experimental manipulation or in ICF (immunodeficiency, centromeric instability, facial anomalies) patients correlates with short telomeres. To study the mechanism of telomere length control by TERRA in Saccharomyces cerevisiae, we mapped the transcriptional start site of TERRA at telomere 1L and inserted a doxycycline regulatable promoter upstream. Induction of TERRA transcription led to telomere shortening of 1L but not of other chromosome ends. TERRA interacts with the Exo1-inhibiting Ku70/80 complex, and deletion of EXO1 but not MRE11 fully suppressed the TERRA–mediated short telomere phenotype in presence and absence of telomerase. Thus TERRA transcription facilitates the 5′-3′ nuclease activity of Exo1 at chromosome ends, providing a means to regulate the telomere shortening rate. Thereby, telomere transcription can regulate cellular lifespan through modulation of chromosome end processing activities.
Telomere Shortening Sensitizes Cancer Cells to Selected Cytotoxic Agents: In Vitro and In Vivo Studies and Putative Mechanisms  [PDF]
Orit Uziel,Einat Beery,Vladimir Dronichev,Katty Samocha,Sergei Gryaznov,Lola Weiss,Shimon Slavin,Michal Kushnir,Yardena Nordenberg,Claudette Rabinowitz,Baruch Rinkevich,Tania Zehavi,Meir Lahav
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0009132
Abstract: Telomere/telomerase system has been recently recognized as an attractive target for anticancer therapy. Telomerase inhibition results in tumor regression and increased sensitivity to various cytotoxic drugs. However, it has not been fully established yet whether the mediator of these effects is telomerase inhibition per se or telomere shortening resulting from inhibition of telomerase activity. In addition, the characteristics and mechanisms of sensitization to cytotoxic drugs caused by telomerase inhibition has not been elucidated in a systematic manner.
Telomere Shortening Impairs Regeneration of the Olfactory Epithelium in Response to Injury but Not Under Homeostatic Conditions  [PDF]
Masami Watabe-Rudolph,Yvonne Begus-Nahrmann,André Lechel,Harshvardhan Rolyan,Marc-Oliver Scheithauer,Gerhard Rettinger,Dietmar Rudolf Thal,Karl Lenhard Rudolph
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0027801
Abstract: Atrophy of the olfactory epithelium (OE) associated with impaired olfaction and dry nose represents one of the most common phenotypes of human aging. Impairment in regeneration of a functional olfactory epithelium can also occur in response to injury due to infection or nasal surgery. These complications occur more frequently in aged patients. Although age is the most unifying risk factor for atrophic changes and functional decline of the olfactory epithelium, little is known about molecular mechanisms that could influence maintenance and repair of the olfactory epithelium. Here, we analyzed the influence of telomere shortening (a basic mechanism of cellular aging) on homeostasis and regenerative reserve in response to chemical induced injury of the OE in late generation telomere knockout mice (G3 mTerc?/?) with short telomeres compared to wild type mice (mTerc+/+) with long telomeres. The study revealed no significant influence of telomere shortening on homeostatic maintenance of the OE during mouse aging. In contrast, the regenerative response to chemical induced injury of the OE was significantly impaired in G3 mTerc?/? mice compared to mTerc+/+ mice. Seven days after chemical induced damage, G3 mTerc?/? mice exhibited significantly enlarged areas of persisting atrophy compared to mTerc+/+ mice (p = 0.031). Telomere dysfunction was associated with impairments in cell proliferation in the regenerating epithelium. Deletion of the cell cycle inhibitor, Cdkn1a (p21) rescued defects in OE regeneration in telomere dysfunctional mice. Together, these data indicate that telomere shortening impairs the regenerative capacity of the OE by impairing cell cycle progression in a p21-dependent manner. These findings could be relevant for the impairment in OE function in elderly people.
The Effect of Pro-Inflammatory Conditioning and/or High Glucose on Telomere Shortening of Aging Fibroblasts  [PDF]
Klelia D. Salpea, Cecilia G. Maubaret, Annegret Kathagen, Gie Ken-Dror, Derek W. Gilroy, Steve E. Humphries
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0073756
Abstract: Cardiovascular disease and diabetes have been linked to shorter telomeres, but it is not yet clear which risk factors contribute to shorter telomeres in patients. Our aim was to examine whether pro-inflammatory conditioning, in combination or not with high glucose, result in a higher rate of telomere shortening during in vitro cellular ageing. Human fibroblasts from four donors were cultured for 90 days in: 1) medium lacking ascorbic acid only, 2) 10 mM buthionine sulphoximine (BSO) (pro-oxidant), 3) 25 mM D-glucose, 4) 1 ng/ml IL1B and 5) 25 mM D-glucose+1 ng/ml IL1B. Telomere length was measured with qPCR and intracellular reactive oxygen species (ROS) content and cell death with flow cytometry. Cultures treated with high glucose and BSO displayed a significantly lower growth rate, and cultures treated with IL1B showed a trend towards a higher growth rate, compared to the control [Glucose:0.14 PD/day, p<0.001, BSO: 0.11 PD/day, p = 0.006 and IL1B: 0.19 PD/day, p = 0.093 vs. Control:0.16 PD/day]. Telomere shortening with time was significantly accelerated in cultures treated with IL1B compared to the control [IL1B:?0.8%/day (95%CI:?1.1, ?0.5) vs. Control:?0.6%/day (95%CI:?0.8, ?0.3), p = 0.012]. The hastening of telomere shortening by IL1B was only in part attenuated after adjustment for the number of cell divisions [IL1B:?4.1%/PD (95%CI:?5.7, ?2.4) vs. Control:?2.5%/PD (95%CI:?4.4, ?0.7), p = 0.067]. The intracellular ROS content displayed 69% increase (p = 0.033) in BSO compared to the control. In aging fibroblasts, pro-inflammatory conditioning aggravates the shortening of telomeres, an effect which was only in part driven by increased cell turnover. High glucose alone did not result in greater production of ROS or telomere shortening.
γ-Tocotrienol Prevents Oxidative Stress-Induced Telomere Shortening in Human Fibroblasts Derived from Different Aged Individuals  [PDF]
Suzana Makpol,Azrina Zainal Abidin,Khalilah Sairin,Musalmah Mazlan,Gapor Md Top,Wan Zurinah Wan Ngah
Oxidative Medicine and Cellular Longevity , 2010, DOI: 10.4161/oxim.3.1.9940
Abstract: The effects of palm γ-tocotrienol (GGT) on oxidative stress-induced cellular ageing was investigated in normal human skin fibroblast cell lines derived from different age groups; young (21-year-old, YF), middle (40-year-old, MF) and old (68-year-old, OF). Fibroblast cells were treated with γ-tocotrienol for 24 hours before or after incubation with IC50 dose of H2O2 for 2 hours. Changes in cell viability, telomere length and telomerase activity were assessed using the MTS assay (Promega, USA), Southern blot analysis and telomere repeat amplification protocol respectively. Results showed that treatment with different concentrations of γ-tocotrienol increased fibroblasts viability with optimum dose of 80 μM for YF and 40 μM for both MF and OF. At higher concentrations, γ-tocotrienol treatment caused marked decrease in cell viability with IC50 value of 200 μM (YF), 300 μM (MF) and 100 μM (OF). Exposure to H2O2 decreased cell viability in dose dependent manner, shortened telomere length and reduced telomerase activity in all age groups. The IC50 of H2O2 was found to be; YF (700 μM), MF (400 μM) and OF (100 μM). Results showed that viability increased significantly (p < 0.05) when cells were treated with 80 μM and 40 μM γ-tocotrienol prior or after H2O2-induced oxidative stress in all age groups. In YF and OF, pretreatment with γ-tocotrienol prevented shortening of telomere length and reduction in telomerase activity. In MF, telomerase activity increased while no changes in telomere length was observed. However, post-treatment of γ-tocotrienol did not exert any significant effects on telomere length and telomerase activity. Thus, these data suggest that γ-tocotrienol protects against oxidative stress-induced cellular ageing by modulating the telomere length possibly via telomerase.
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