Cell biology. Stress response and aging

Heat Shock Transcription Factor 2 Is Significantly Involved in Neurodegenerative Diseases, Inflammatory Bowel Disease, Cancer, Male Infertility, and Fetal Alcohol Spectrum Disorder: The Novel Mechanisms of Several Severe Diseases

HSF (heat shock transcription factor or heat shock factor) was discovered as a transcription factor indispensable for heat shock response. Although four classical HSFs were discovered in mammals and two major HSFs, HSF1 and HSF2, were cloned in the same year of 1991, only HSF1 was intensively studied because HSF1 can give rise to heat shock response through the induction of various HSPs' expression. On the other hand, HSF2 was not well studied for some time, which was probably due to an underestimate of HSF2 itself. Since the beginning of the 21st century, HSF2 research has progressed and many biologically significant functions of HSF2 have been revealed. For example, the roles of HSF2 in nervous system protection, inflammation, maintenance of mitosis and meiosis, and cancer cell survival and death have been gradually unveiled. However, we feel that the fact HSF2 has a relationship with various factors is not yet widely recognized; therefore, the biological significance of HSF2 has been underestimated. We strongly hope to widely communicate the significance of HSF2 to researchers and readers in broad research fields through this review. In addition, we also hope that many readers will have great interest in the molecular mechanism in which HSF2 acts as an active transcription factor and gene bookmarking mechanism of HSF2 during cell cycle progression, as is summarized in this review.

Radiation Hormesis to Improve the Quality of Adult Spodoptera litura (Fabr.)

Mass rearing of insects of high biological quality is a crucial attribute for the successful implementation of sterile insect release programs. Various ontogenetic stages of Spodoptera litura (Fabr.) were treated with a range of low doses of ionizing radiation (0.25-1.25 Gy) to assess whether these gamma doses could elicit a stimulating effect on the growth and viability of developing moths. Doses in the range of 0.75 Gy to 1.0 Gy administered to eggs positively influenced pupal weight, adult emergence, and growth index, with a faster developmental period. The enhanced longevity of adults derived from eggs treated with 0.75 Gy and 1.0 Gy, and for larvae and pupae treated with 1.0 Gy, indicated a hormetic effect on these life stages. Furthermore, the use of these hormetic doses upregulated the relative mRNA expression of genes associated with longevity (foxo, sirtuin 2 like/sirt1, atg8) and viability/antioxidative function (cat and sod), suggesting a positive hormetic effect at the transcriptional level. These results indicated the potential use of low dose irradiation (0.75-1 Gy) on preimaginal stages as hormetic doses to improve the quality of the reared moths. This might increase the efficiency of the inherited sterility technique for the management of these lepidopteran pests.

Oxysterols are potential physiological regulators of ageing

Delaying and even reversing ageing is a major public health challenge with a tremendous potential to postpone a plethora of diseases including cancer, metabolic syndromes and neurodegenerative disorders. A better understanding of ageing as well as the development of innovative anti-ageing strategies are therefore an increasingly important field of research. Several biological processes including inflammation, proteostasis, epigenetic, oxidative stress, stem cell exhaustion, senescence and stress adaptive response have been reported for their key role in ageing. In this review, we describe the relationships that have been established between cholesterol homeostasis, in particular at the level of oxysterols, and ageing. Initially considered as harmful pro-inflammatory and cytotoxic metabolites, oxysterols are currently emerging as an expanding family of fine regulators of various biological processes involved in ageing. Indeed, depending of their chemical structure and their concentration, oxysterols exhibit deleterious or beneficial effects on inflammation, oxidative stress and cell survival. In addition, stem cell differentiation, epigenetics, cellular senescence and proteostasis are also modulated by oxysterols. Altogether, these data support the fact that ageing is influenced by an oxysterol profile. Further studies are thus required to explore more deeply the impact of the "oxysterome" on ageing and therefore this cholesterol metabolic pathway constitutes a promising target for future anti-ageing interventions.

The chemoprevention of spirulina platensis and garlic against diethylnitrosamine induced liver cancer in rats via amelioration of inflammatory cytokines expression and oxidative stress

Natural antioxidant products play a vital role in the treatment and prevention of cancer disease because they have no side effects. This study aimed to compare the chemoprotective effect of Spirulina platensis (SP) and garlic against hepatocellular carcinoma (HCC) in rats. This study was being done by using 60 male Wistar rats and divided into four groups. Group (I): normal group. Group (II): HCC group induced by injection of a single dose of DEN (200 mg/kg/I.P) and after 14 days injected CCl4 (1 mg/kg/I.P) 3 times/week/six weeks. Group (III): HCC group received SP orally at a dose (500 mg/kg). Group (IV): HCC group received garlic (250 mg/kg) orally. The results revealed that the Spirulina and garlic treatment have a significant decrease in Glutamate pyruvate transaminase, Glutamate oxaloacetate transaminase, GGT, LDH, and the Malondialdehyde (MDA) activity, and furthermore, a significant increase in the total protein level, the superoxide dismutase (SOD), and Catalase (CAT) activity nearly to normal activity. Furthermore, the hepatic expression of tumor necrosis factor (TNF-α), interleukin-6 (IL-6), inducible nitric oxide synthase, transforming growth factor-beta (TGF-β1), Heat Shock Protein glycoprotein 96 (HSPgp96), and Glypican 3 (GP3) were down regulated by the Spirulina and garlic treatment in comparison with those in HCC group. All findings reported that the chemoprotective of both Spirulina and garlic that have nearly the same effect may be due to antioxidant activity and inhibition of lipid peroxidation, amelioration of pro-inflammatory cytokine, HSPgp96, and GP3.

Senescence of Normal Human Fibroblasts Relates to the Expression of Ionotropic Glutamate Receptor GluR6/Grik2

BACKGROUND/AIM

Glutamate receptor GRIK2, previously designated as GluR6, is best described in neuronal cells. However, its biological relevance in non-neuronal cells is not well understood. We have investigated the expression of this important protein in normal human fibroblasts as a function of cell proliferation.

MATERIALS AND METHODS

We introduced expression constructs of all five isoforms (A-E) of GRIK2 in normal human fibroblasts and investigated the cells for the presence and localization of GRIK2, as well as for cell proliferation and senescence over a period of 24 days.

RESULTS

The expression of GRIK2-A isoform led to immediate cessation of cell proliferation. However, the cell numbers increased by 1.5- to 9.0-fold in 24 days upon transfection with B, C, D and E isoforms, after which they entered a state of senescence. The decreased proliferation was reflected by incorporation of BrdU in only 2-8% of transfected cells even after culturing them for 16 days.

CONCLUSION

Our results are indicative of an association between GRIK2 and aging of fibroblasts.

Ionizing Radiation and Translation Control: A Link to Radiation Hormesis?

Protein synthesis, or mRNA translation, is one of the most energy-consuming functions in cells. Translation of mRNA into proteins is thus highly regulated by and integrated with upstream and downstream signaling pathways, dependent on various transacting proteins and cis-acting elements within the substrate mRNAs. Under conditions of stress, such as exposure to ionizing radiation, regulatory mechanisms reprogram protein synthesis to translate mRNAs encoding proteins that ensure proper cellular responses. Interestingly, beneficial responses to low-dose radiation exposure, known as radiation hormesis, have been described in several models, but the molecular mechanisms behind this phenomenon are largely unknown. In this review, we explore how differences in cellular responses to high- vs. low-dose ionizing radiation are realized through the modulation of molecular pathways with a particular emphasis on the regulation of mRNA translation control.

Role of hydrogen sulfide in cardiovascular ageing

Cardiovascular diseases are the main cause of morbidity and mortality in the Western society and ageing is a relevant non-modifiable risk factor. Morphological and functional alterations at endothelial level represent first events of ageing, inevitably followed by vascular dysfunction and consequent atherosclerosis that deeply influences cardiovascular health. Indeed, myocardial hypertrophy and fibrosis typically occur and contribute to compromise overall cardiac output. As regards the intracellular molecular mechanisms involved in the cardiovascular ageing, an intricate network is emerging, revealing a role for many mediators, including SIRT1/AMPK/PCG1α pathway, anti-oxidants factors (i.e. Nrf-2 and FOXOs) and pro-inflammatory cytokines. Thus, the search for pharmacological and non-pharmacological strategies that can promote a "healthy ageing", in order to slow down age-related machinery, are currently an exciting challenge for the biomedical research. Interestingly, hydrogen sulfide (H₂S) has been recently recognized as a new player capable to influence intracellular machinery involved in ageing and then it is view as a potential target for preventing cardiovascular diseases. Therefore, this review is focused on the role of H₂S in cardiovascular ageing, and on the evidence of the relationship between progressive decline in endogenous H₂S levels and the onset of various cardiovascular age-related diseases.

Polyphenols as Caloric-Restriction Mimetics and Autophagy Inducers in Aging Research

It has been thought that caloric restriction favors longevity and healthy aging where autophagy plays a vital role. However, autophagy decreases during aging and that can lead to the development of aging-associated diseases such as cancer, diabetes, neurodegeneration, etc. It was shown that autophagy can be induced by mechanical or chemical stress. In this regard, various pharmacological compounds were proposed, including natural polyphenols. Apart from the ability to induce autophagy, polyphenols, such as resveratrol, are capable of modulating the expression of pro- and anti-apoptotic factors, neutralizing free radical species, affecting mitochondrial functions, chelating redox-active transition metal ions, and preventing protein aggregation. Moreover, polyphenols have advantages compared to chemical inducers of autophagy due to their intrinsic natural bio-compatibility and safety. In this context, polyphenols can be considered as a potential therapeutic tool for healthy aging either as a part of a diet or as separate compounds (supplements). This review discusses the epigenetic aspect and the underlying molecular mechanism of polyphenols as an anti-aging remedy. In addition, the recent advances of studies on NAD-dependent deacetylase sirtuin-1 (SIRT1) regulation of autophagy, the role of senescence-associated secretory phenotype (SASP) in cells senescence and their regulation by polyphenols have been highlighted as well. Apart from that, the review also revised the latest information on how polyphenols can help to improve mitochondrial function and modulate apoptosis (programmed cell death).

The role of DNA repair genes in radiation-induced adaptive response in Drosophila melanogaster is differential and conditional

Studies in human and mammalian cell cultures have shown that induction of DNA repair mechanisms is required for the formation of stimulation effects of low doses of ionizing radiation, named "hormesis". Nevertheless, the role of cellular defense mechanisms in the formation of radiation-induced hormesis at the level of whole organism remains poorly studied. The aim of this work was to investigate the role of genes involved in different mechanisms and stages of DNA repair in radioadaptive response and radiation hormesis by lifespan parameters in Drosophila melanogaster. We studied genes that control DNA damage sensing (D-Gadd45, Hus1, mnk), nucleotide excision repair (mei-9, mus210, Mus209), base excision repair (Rrp1), DNA double-stranded break repair by homologous recombination (Brca2, spn-B, okr) and non-homologous end joining (Ku80, WRNexo), and the Mus309 gene that participates in several mechanisms of DNA repair. The obtained results demonstrate that in flies with mutations in studied genes radioadaptive response and radiation hormesis are absent or appear to a lesser extent than in wild-type Canton-S flies. Chronic exposure of γ-radiation in a low dose during pre-imaginal stages of development leads to an increase in expression of the studied DNA repair genes, which is maintained throughout the lifespan of flies. However, the activation of conditional ubiquitous overexpression of DNA repair genes does not induce resistance to an acute exposure to γ-radiation and reinforces its negative impact.

CD56bright cells respond to stimulation until very advanced age revealing increased expression of cellular protective proteins SIRT1, HSP70 and SOD2

BACKGROUND

NK cells are cytotoxic lymphocytes of innate immunity composed of: cytotoxic CD56dim and immunoregulatory CD56bright cells. The study aimed to analyze the expression of cellular protective proteins: sirtuin 1 (SIRT1), heat shock protein 70 (HSP70) and manganese superoxide dismutase (SOD2) in CD56dim and CD56bright NK cells of the young, seniors aged under 85 ('the old') and seniors aged over 85 ('the oldest'). We studied both non-stimulated NK cells and cells stimulated by IL-2, LPS or PMA with ionomycin. The expression level of proinflammatory cytokines TNF and IFN-γ was also assessed in NK cell subsets and some relationships between the studied parameters were analyzed.

RESULTS

CD56bright cells showed sensitivity to most of the applied stimulatory agents until very advanced age in regards to the expression of SIRT1 and intracellular HSP70. On the contrary, CD56dim cells, sensitive to stimulation by most of the stimulatory agents in the young and the old, in the oldest lost this sensitivity and presented rather high, constant expression of SIRT1 and HSP70, resistant to further stimulation. With reference to SOD2 expression, CD56dim cells were insensitive to stimulation in the young, but their sensitivity increased with ageing. CD56bright cells were sensitive to most of the applied agents in the young and the old but in the oldest they responded to all of the stimulatory agents used in the study. Similarly, both NK cell subsets were sensitive to stimulation until very advanced age in regards to the expression of TNF and IFN-γ.

CONCLUSIONS

CD56bright cells maintained sensitivity to stimulation until very advanced age presenting also an increased expression of SIRT1 and HSP70. CD56dim cells showed a constantly increased expression of these cellular protective proteins in the oldest, insensitive for further stimulation. The oldest, however, did not reveal an increased level of SOD2 expression, but it was significantly elevated in both NK cell subsets after stimulation.The pattern of expression of the studied cellular protective proteins in ageing process revealed the adaptation of NK cells to stress response in the oldest seniors which might accompany the immunosenescence and contribute to the long lifespan of this group of the elderly.

Deciphering the metabolic secret of longevity through the analysis of metabolic response to stress on long-lived species

Despite intensive research, no satisfactory therapeutic options have been found for aging and age-related diseases. The British scientist Leslie Orgel stated that evolution is cleverer than we are. This assumption seems correct considering that some species are naturally able to resist the age-related diseases that remain unsolved by our modern medicine. Indeed, bowhead whales can live for more than two hundred years and are suspected to possess efficient antitumor mechanisms. Naked mole-rats are exceptionally long-lived compared to similar-sized mammals and are protected from senescence and age-related diseases. Consequently, the characterization of protective molecular mechanisms in long-lived species (i.e. bowhead whale, naked mole-rat, microbat) could be of great interest for therapeutic applications in human. Cellular stress response is considered to be an anti-aging process dedicated to the prevention of damage accumulation and the maintenance of homeostasis. Interestingly, cellular stress response in plants and animals involves the production of health-promoting metabolites such as resveratrol, nicotinamide adenine dinucleotide and spermidine. Do anti-aging metabolites formed during stress exposure differ between human and extreme longevity species in terms of their nature, their quantity or their production? These questions remain unsolved and deserve to be considered. Indeed, the mimicking of anti-aging strategies selected throughout evolution in long-lived species could be of high therapeutic value for humans. This paper suggests that metabolomic studies on extreme longevity species cells exposed to mild stressors may lead to the characterization of health-promoting metabolites. If confirmed, this would provide new avenues of research for the development of innovative anti-aging strategies for humans.

SIRT4 is essential for metabolic control and meiotic structure during mouse oocyte maturation

SIRT4 modulates energy homeostasis in multiple cell types and tissues. However, its role in meiotic oocytes remains unknown. Here, we report that mouse oocytes overexpressing SIRT4 are unable to completely progress through meiosis, showing the inadequate mitochondrial redistribution, lowered ATP content, elevated reactive oxygen species (ROS) level, with the severely disrupted spindle/chromosome organization. Moreover, we find that phosphorylation of Ser293-PDHE1α mediates the effects of SIRT4 overexpression on metabolic activity and meiotic events in oocytes by performing functional rescue experiments. By chance, we discover the SIRT4 upregulation in oocytes from aged mice; and importantly, the maternal age-associated deficient phenotypes in oocytes can be partly rescued through the knockdown of SIRT4. These findings reveal the critical role for SIRT4 in the control of energy metabolism and meiotic apparatus during oocyte maturation and indicate that SIRT4 is an essential factor determining oocyte quality.

Anti-Stress and Glial Differentiation Effects of a Novel Combination of Cucurbitacin B and Withanone (CucWi-N): Experimental Evidence

Background

Natural extracts and compounds used in traditional home medicine are known for their safety and a variety of health promoting and therapeutic potentials. In contrast to the single molecule mediated targets, the combinational therapies are preferred for their multi-functional and limited toxic regimens and may be useful for disease therapeutics as well as to increase the quality of life during a variety of environmental stresses.

Purpose

We aimed to combine the active ingredients of Chinese (Helicteres angustifolia) and Indian (Withania somnifera) ginsengs to develop a natural, efficient, and welfare combinatorial mixture with high anti-stress and glial differentiation potentials.

Methods

Using cultured cells as a model system, we developed a combination of active ingredients of Chinese (Cucurbitacin B [Cuc]) and Indian (Withanone [Wi-N]) ginsengs. Eleven chemical models of environmental stresses were used. Cytotoxicity studies were performed using human skin fibroblast for anti-stress and rat glioma cells for glial differentiation effects.

Results

We demonstrate that the novel combination of Cuc and Wi-N, CucWi-N, was non-toxic to normal cells. It caused stress protection in assays using normal human fibroblasts subjected to a variety of stresses. Of note, cells showed remarkable protection against oxidative and UV stresses and marked by decrease in DNA damage and reactive oxygen species. We examined and found the glial differentiation potential of CucWi-N in rat glioblastoma cells. CucWi-N clearly induced differentiation phenotype, well-marked with upregulation of GAP43, MAP2, and GFAP, which have been shown to play a key role in glial differentiation.

Conclusion

These data demonstrate anti-stress and glial differentiation potential of CucWi-N (a novel combination of Cuc and Wi-N) that could be recruited in nutraceutical and pharmaceutical avenues and hence warrant further evaluation and mechanistic studies.

Sirtuin-4 (SIRT4), a therapeutic target with oncogenic and tumor-suppressive activity in cancer

Several members of the sirtuin (SIRT) family, a highly conserved family of NAD⁺-dependent enzymes, have been shown to play a critical role in both promoting and/or suppressing tumorigenesis. In this study, recent progress in the field concerning SIRT4 and cancer was reviewed, and the relationship between SIRT4 and tumors was investigated. Subsequently, we evaluated the role of SIRT4 with oncogenic or tumor-suppressive activity in cancer, which may provide insight in identifying the underlying mechanism of action of SIRT4 in cancer. Finally, we explored the potential of SIRT4 as a therapeutic target in cancer therapy.

NK cells of the oldest seniors represent constant and resistant to stimulation high expression of cellular protective proteins SIRT1 and HSP70

Background

Natural killer cells (NK cells) are cytotoxic lymphocytes of innate immunity that reveal some immunoregulatory properties, however, their role in the process of ageing is not completely understood. The study aimed to analyze the expression of proteins involved in cellular stress response: sirtuin 1 (SIRT1), heat shock protein 70 (HSP70) and manganese superoxide dismutase (SOD2) in human NK cells with reference to the process of ageing. Non-stimulated and stimulated with IL-2, LPS or PMA with ionomycin cells originated from peripheral blood samples of: seniors aged over 85 (‘the oldest’; n = 25; 88.5 ± 0.5 years, mean ± SEM), seniors aged under 85 (‘the old’; n = 30; 75.6 ± 0.9 years) and the young (n = 31; 20.9 ± 0.3 years). The relationships between the levels of expression of cellular protective proteins in the studied population were also analyzed. The concentrations of carbonyl groups and 8-isoprostanes, markers of oxidative stress, in both stimulated and non-stimulated cultured NK cells were measured to assess the level of the oxidative stress in the cells.

Results

The oldest seniors varied from the other age groups by significantly higher expression of SIRT1 and HSP70 both in non-stimulated and stimulated NK cells. These cells also appeared to be resistant to further stimulations with IL-2, LPS or PMA with ionomycin. Highly positive correlations between SIRT1 and intracellular HSP70 in both stimulated and non-stimulated NK cells were observed. SOD2 presented low expression in non-stimulated cells, whereas its sensitivity to stimulation increased with age of donors. High positive correlations between SOD2 and surface HSP70 were observed. We found that the markers of oxidative stress in NK cells did not change with ageing.

Conclusions

The oldest seniors revealed well developed adaptive stress response in NK cells with increased, constant levels of SIRT1 and intracellular HSP70. They presented also very high positive correlations between expression of these cellular protective proteins both in stimulated and non-stimulated cells. These phenomena may contribute to the long lifespan of this group of elderly. Interestingly, in NK cells SOD2 revealed a distinct role in cellular stress response since it showed sensitivity to stimulation increasing with age of participants. These observations provide novel data concerning the role of NK cells in the process of ageing.

Melatonin reverses H2 O2 -induced senescence in SH-SY5Y cells by enhancing autophagy via sirtuin 1 deacetylation of the RelA/p65 subunit of NF-κB

Autophagy, a degradation mechanism that plays a major role in maintaining cellular homeostasis and diminishes in aging, is considered an aging characteristic. Melatonin is an important hormone that plays a wide range of physiological functions, including the anti-aging effect, potentially via the regulation of the Sirtuin1 (SIRT1) pathway. The deacetylation ability of SIRT1 is important for controlling the function of several transcription factors, including nuclear factor kappa B (NF-ĸB). Apart from inflammation, NF-ĸB can regulate autophagy by inhibiting Beclin1, an initiator of autophagy. Although numerous studies have revealed the role of melatonin in regulating autophagy, very limited experiments have shown that melatonin can increase autophagic activity via SIRT1 in a senescent model. This study focuses on the effect of melatonin on autophagy via the deacetylation activity of SIRT1 on RelA/p65, a subunit of NF-ĸB, to determine whether melatonin can attenuate the aging condition. SH-SY5Y cells were treated with H₂ O₂ to induce the senescent state. These results demonstrated that melatonin reduced a number of beta-galactosidase (SA-βgal)-positive cells, a senescent marker. In addition, melatonin increased the protein levels of SIRT1, Beclin1, and LC3-II, a hallmark protein of autophagy, and reduced the levels of acetylated-Lys310 in the p65 subunit of NF-ĸB in SH-SY5Y cells treated with H₂ O₂ . Furthermore, in the presence of SIRT1 inhibitor, melatonin failed to increase autophagic markers. The present data indicate that melatonin enhances autophagic activity via the SIRT1 signaling pathway. Taken together, we propose that in modulating autophagy, melatonin may provide a therapeutically beneficial role in the anti-aging processes.

Gallic acid against hepatocellular carcinoma: An integrated scheme of the potential mechanisms of action from in vivo study

The global burden of hepatocellular carcinoma is increasing; actually, it is estimated as 750,000 new cases annually. This study was initiated to emphasize the possibility that gallic acid could alleviate hepatocarcinogenesis in vivo. In this study, 40 rats were enrolled and distributed as follows; group 1 was set as negative control, while all of groups 2, 3, and 4 were orally received N-nitrosodiethylamine for hepatocellular carcinoma induction. Group 2 was left untreated, whereas groups 3 and 4 were orally treated with gallic acid and doxorubicin, respectively. The current data indicated that gallic acid administration in hepatocellular carcinoma bearing rats yielded significant decline in serum levels of alpha-fetoprotein, glypican-3, and signal transducer and activator of transcription 3 along with significant enhancement in serum suppressors of cytokine signaling 3 level. Also, gallic acid-treated group displayed significant downregulation in the gene expression levels of hepatic gamma glutamyl transferase and heat shock protein gp96. Intriguingly, treatment with gallic acid remarkably ameliorated the destabilization of liver tissue architecture caused by N-nitrosodiethylamine intoxication as evidenced by histopathological investigation. In conclusion, this study demonstrates that the hepatocarcinogenic effect of N-nitrosodiethylamine can be abrogated by gallic acid supplementation owing to its affinity to regulate signal transducer and activator of transcription 3 signaling pathway through its outstanding bioactivities including antioxidant, anti-inflammatory, apoptotic, and antitumor effects.

Geroprotectors: A Unified Concept and Screening Approaches

Although the geroprotectors discovery is a new biomedicine trend and more than 200 compounds can slow aging and increase the lifespan of the model organism, there are still no geroprotectors on the market. The reasons may be partly related to the lack of a unified concept of geroprotector, accepted by the scientific community. Such concept as a system of criteria for geroprotector identification and classification can form a basis for an analytical model of anti-aging drugs, help to consolidate the efforts of various research initiatives in this area and compare their results. Here, we review the existing classification and characteristics of geroprotectors based on their effect on the survival of a group of individuals or pharmaceutics classes, according to the proposed mechanism of their geroprotective action or theories of aging. After discussing advantages and disadvantages of these approaches, we offer a new concept based on the maintenance of homeostatic capacity because aging can be considered as exponential shrinkage of homeostatic capacity leading to the onset of age-related diseases and death. Besides, we review the most promising current screening approaches to finding new geroprotectors. Establishing the classification of existing geroprotectors based on physiology and current understanding of the nature of aging is essential for putting the existing knowledge into a single system. This system could be useful to formulate standards for finding and creating new geroprotectors. Standardization, in turn, would allow easier comparison and combination of experimental data obtained by different research groups.

NAMPT inhibition synergizes with NQO1-targeting agents in inducing apoptotic cell death in non-small cell lung cancer cells

Nicotinamide phosphoribosyltransferase (NAMPT) catalyzes the first rate-limiting step in converting nicotinamide to NAD(+), essential for a number of enzymes and regulatory proteins involved in a variety of cellular processes, including deacetylation enzyme SIRT1 which modulates several tumor suppressors such as p53 and FOXO. Herein we report that NQO1 substrates Tanshione IIA (TSA) and β-lapachone (β-lap) induced a rapid depletion of NAD(+) pool but adaptively a significant upregulation of NAMPT. NAMPT inhibition by FK866 at a nontoxic dose significantly enhanced NQO1-targeting agent-induced apoptotic cell death. Compared with TSA or β-lap treatment alone, co-treatment with FK866 induced a more dramatic depletion of NAD(+), repression of SIRT1 activity, and thereby the increased accumulation of acetylated FOXO1 and the activation of apoptotic pathway. In conclusion, the results from the present study support that NAMPT inhibition can synergize with NQO1 activation to induce apoptotic cell death, thereby providing a new rationale for the development of combinative therapeutic drugs in combating non-small lung cancer.

Manganese Superoxide Dismutase Acetylation and Dysregulation, Due to Loss of SIRT3 Activity, Promote a Luminal B-Like Breast Carcinogenic-Permissive Phenotype

SIGNIFICANCE

Breast cancer is the most common nondermatologic malignancy among women in the United States, among which endocrine receptor-positive breast cancer accounts for up to 80%. Endocrine receptor-positive breast cancers can be categorized molecularly into luminal A and B subtypes, of which the latter is an aggressive form that is less responsive to endocrine therapy with inferior prognosis.

RECENT ADVANCES

Sirtuin, an aging-related gene involved in mitochondrial metabolism, is associated with life span, and more importantly, murine models lacking Sirt3 spontaneously develop tumors that resemble human luminal B breast cancer. Furthermore, these tumors exhibit aberrant manganese superoxide dismutase (MnSOD) acetylation at lysine 68 and lysine 122 and have abnormally high reactive oxygen species (ROS) levels, which have been observed in many types of breast cancer.

CRITICAL ISSUES

The mechanism of how luminal B breast cancer develops resistance to endocrine therapy remains unclear. MnSOD, a primary mitochondrial detoxification enzyme, functions by scavenging excessive ROS from the mitochondria and maintaining mitochondrial and cellular homeostasis. Sirt3, a mitochondrial fidelity protein, can regulate the activity of MnSOD through deacetylation. In this study, we discuss a possible mechanism of how loss of SIRT3-guided MnSOD acetylation results in endocrine therapy resistance of human luminal B breast cancer.

FUTURE DIRECTIONS

Acetylation of MnSOD and other mitochondrial proteins, due to loss of SIRT3, may explain the connection between ROS and development of luminal B breast cancer and how luminal B breast cancer becomes resistant to endocrine therapy. Antioxid. Redox Signal. 25, 326-336.

Adaptive homeostasis

Homeostasis is a central pillar of modern Physiology. The term homeostasis was invented by Walter Bradford Cannon in an attempt to extend and codify the principle of 'milieu intérieur,' or a constant interior bodily environment, that had previously been postulated by Claude Bernard. Clearly, 'milieu intérieur' and homeostasis have served us well for over a century. Nevertheless, research on signal transduction systems that regulate gene expression, or that cause biochemical alterations to existing enzymes, in response to external and internal stimuli, makes it clear that biological systems are continuously making short-term adaptations both to set-points, and to the range of 'normal' capacity. These transient adaptations typically occur in response to relatively mild changes in conditions, to programs of exercise training, or to sub-toxic, non-damaging levels of chemical agents; thus, the terms hormesis, heterostasis, and allostasis are not accurate descriptors. Therefore, an operational adjustment to our understanding of homeostasis suggests that the modified term, Adaptive Homeostasis, may be useful especially in studies of stress, toxicology, disease, and aging. Adaptive Homeostasis may be defined as follows: 'The transient expansion or contraction of the homeostatic range in response to exposure to sub-toxic, non-damaging, signaling molecules or events, or the removal or cessation of such molecules or events.'

Developing criteria for evaluation of geroprotectors as a key stage toward translation to the clinic

In the coming decades, a massive shift in the aging segment of the population will have major social and economic consequences around the world. One way to offset this increase is to expedite the development of geroprotectors, substances that slow aging, repair age‐associated damage and extend healthy lifespan, or healthspan. While over 200 geroprotectors are now reported in model organisms and some are in human use for specific disease indications, the path toward determining whether they affect aging in humans remains obscure. Translation to the clinic is hampered by multiple issues including absence of a common set of criteria to define, select, and classify these substances, given the complexity of the aging process and their enormous diversity in mechanism of action. Translational research efforts would benefit from the formation of a scientific consensus on the following: the definition of ‘geroprotector’, the selection criteria for geroprotectors, a comprehensive classification system, and an analytical model. Here, we review current approaches to selection and put forth our own suggested selection criteria. Standardizing selection of geroprotectors will streamline discovery and analysis of new candidates, saving time and cost involved in translation to clinic.

ROS production, intracellular HSP70 levels and their relationship in human neutrophils: effects of age

ROS production and intracellular HSP70 levels were measured in human neutrophils for three age groups: young (20-59 years), elders (60-89 years) and nonagenarians (90 years and older). Elders showed higher levels of spontaneous intracellular ROS content compared with young and nonagenarian groups, which had similar intracellular ROS levels. Zymosan-induced (non-spontaneous) extracellular ROS levels were also similar for young and nonagenarians but were lower in elders. However, spontaneous extracellular ROS production increased continuously with age. Correlation analysis revealed positive relationships between HSP70 levels and zymosan-stimulated ROS production in the elder group. This was consistent with a promoting role for HSP70 in ROS-associated neutrophils response to pathogens. No positive correlation between ROS production and intracellular HSP70 levels was found for groups of young people and nonagenarians. In contrast, significant negative correlations of some ROS and HSP70 characteriscics were found for neutrophils from young people and nonagenarians. The observed difference in ROS and HSP70 correlations in elders and nonagenarians might be associated with an increased risk of mortality in older individuals less than 90 years old.

Joining time-resolved thermometry and magnetic-induced heating in a single nanoparticle unveils intriguing thermal properties

Whereas efficient and sensitive nanoheaters and nanothermometers are demanding tools in modern bio- and nanomedicine, joining both features in a single nanoparticle still remains a real challenge, despite the recent progress achieved, most of it within the last year. Here we demonstrate a successful realization of this challenge. The heating is magnetically induced, the temperature readout is optical, and the ratiometric thermometric probes are dual-emissive Eu(3+)/Tb(3+) lanthanide complexes. The low thermometer heat capacitance (0.021·K(-1)) and heater/thermometer resistance (1 K·W(-1)), the high temperature sensitivity (5.8%·K(-1) at 296 K) and uncertainty (0.5 K), the physiological working temperature range (295-315 K), the readout reproducibility (>99.5%), and the fast time response (0.250 s) make the heater/thermometer nanoplatform proposed here unique. Cells were incubated with the nanoparticles, and fluorescence microscopy permits the mapping of the intracellular local temperature using the pixel-by-pixel ratio of the Eu(3+)/Tb(3+) intensities. Time-resolved thermometry under an ac magnetic field evidences the failure of using macroscopic thermal parameters to describe heat diffusion at the nanoscale.

SIRT3 and SIRT4 are mitochondrial tumor suppressor proteins that connect mitochondrial metabolism and carcinogenesis

It is a well-established scientific observation that mammalian cells contain fidelity proteins that appear to protect against and adapt to various forms of endogenous and exogenous cellular conditions. Loss of function or genetic mutation of these fidelity proteins has also been shown to create a cellular environment that is permissive for the development of tumors, suggesting that these proteins also function as tumor suppressors (TSs). While the first identified TSs were confined to either the nucleus and/or the cytoplasm, it seemed logical to hypothesize that the mitochondria may also contain fidelity proteins that serve as TSs. In this regard, it now appears clear that at least two mitochondrial sirtuins function as sensing, watchdog, or TS proteins in vitro, in vivo, and in human tumor samples. In addition, these new results demonstrate that the mitochondrial anti-aging or fidelity/sensing proteins, SIRT3 and SIRT4, respond to changes in cellular nutrient status to alter the enzymatic activity of specific downstream targets to maintain energy production that matches energy availability and ATP consumption. As such, it is proposed that loss of function or genetic deletion of these mitochondrial genes results in a mismatch of mitochondrial energy metabolism, culminating in a cell phenotype permissive for transformation and tumorigenesis. In addition, these findings clearly suggest that loss of proper mitochondrial metabolism, via loss of SIRT3 and SIRT4, is sufficient to promote carcinogenesis.

Dammarane triterpenes as potential SIRT1 activators from the leaves of Panax ginseng

During a search for SIRT1 activators originating in nature, three new dammarane triterpenes, 6α,20(S)-dihydroxydammar-3,12-dione-24-ene (1), 6α,20(S),24(S)-trihydroxydammar-3,12-dione-25-ene (2), and 6α,20(S),25-trihydroxydammar-3,12-dione-23-ene (3), as well as two known triterpenes, dammar-20(22),24-diene-3β,6α,12β-triol (4) and 20(S)-ginsenoside Rg3 (5), were isolated from Panax ginseng leaves. Compounds 1 and 3-5 showed potential as SIRT1 activators, as analyzed by in vitro enzyme-based SIRT1-NAD/NADH and SIRT1-p53 luciferase cell-based assays. They were also found to increase the level of NAD(+)/NADH ratio in HEK293 cells. This study presents a new class of chemical entities that may be able to be developed as SIRT1 activators for antiaging and treatment of age-associated diseases.

Regulation of MnSOD enzymatic activity by Sirt3 connects the mitochondrial acetylome signaling networks to aging and carcinogenesis

SIGNIFICANCE

It is a well-established scientific observation that mammalian cells contain fidelity or watchdog proteins that maintain the correct function of cellular organelles.

RECENT ADVANCES

Over the past several years, the Sirtuin deacetylase family protein Sirt3 has emerged as a mitochondrial fidelity protein that directs energy generation and regulates reactive oxygen species (ROS) scavenging proteins. Loss of function or genetic mutation of these fidelity proteins has been shown to create a cellular environment that is permissive for the development of cellular damage associated with processes such as aging and carcinogenesis.

CRITICAL ISSUES

Mitochondria are the primary organelles that direct oxidative metabolism for the production of ATP; however, this is also a significant source of ROS. Thus, it is reasonable to propose that mitochondria should contain proteins that would signal downstream target molecules and/or ROS scavenger enzymes to maintain mitochondrial and cellular homeostatic poise. It is also reasonable to hypothesize that the mitochondria contain fidelity proteins similar to those found in the nucleus and cytoplasm. We discuss a new role of Sirt3 in the direction of the primary superoxide scavenger protein, manganese superoxide dismutase (MnSOD), and how the acetylation or deacetylation of several specific lysines appears to direct MnSOD enzymatic dismutase activity.

FUTURE DIRECTIONS

Aberrant downstream regulation of MnSOD by Sirt3 may be a potential source of cellular damage that accumulates with aging to create a tumor-permissive phenotype. Future studies can explore the role of MnSOD in age-related illness using this new mechanism of enzymatic regulation.

Muscle heat shock protein 70 predicts insulin resistance with aging

Heat shock protein 70 (HSP70) protects cells from accumulating damaged proteins and age-related functional decline. We studied plasma and skeletal muscle (SkM) HSP70 levels in adult vervet monkeys (life span ≈ 25 years) at baseline and after 4 years (≈10 human years). Insulin, glucose, homeostasis model assessment scores, triglycerides, high-density lipoprotein and total plasma cholesterol, body weight, body mass index, and waist circumference were measured repeatedly, with change over time estimated by individual regression slopes. Low baseline SkM HSP70 was a proximal marker for developing insulin resistance and was seen in monkeys whose insulin and homeostasis model assessment increased more rapidly over time. Changes in SkM HSP70 inversely correlated with insulin and homeostasis model assessment trajectories such that a positive change in SkM level was beneficial. The strength of the relationship between changes in SkM HSP70 and insulin remained unchanged after adjustment for all covariates. Younger monkeys drove these relationships, with HSP70 alone being predictive of insulin changes with aging. Plasma and SkM HSP70 were unrelated and HSP70 release from peripheral blood mononuclear cells was positively associated with insulin concentrations in contrast to SkM. Results from aged humans confirmed this positive association of plasma HSP70 and insulin. In conclusion, higher levels of SkM HSP70 protect against insulin resistance development during healthy aging.

SIRT3 overexpression antagonizes high glucose accelerated cellular senescence in human diploid fibroblasts via the SIRT3-FOXO1 signaling pathway

Sirtuin 3 (SIRT3) is one of the seven mammalian sirtuins, which are homologs of the yeast Sir2 gene. SIRT3 is the only sirtuin reported to be associated with human life span. Many recent studies have indicated that SIRT3 levels are elevated by exercise and caloric restriction, but whether SIRT3 influences cell senescence under stressed conditions in human diploid fibroblasts has not been established. Our data showed that expression of SIRT3 is elevated in human diploid fibroblasts under low glucose (3.3 mM glucose) growth conditions and decreased under high glucose (25 mM glucose) growth conditions. We have demonstrated that SIRT3 interacts with forkhead box protein O1 (FOXO1). High glucose levels also increased aging phenotypes and FOXO1 acetylation level. We have demonstrated that overexpression of SIRT3 under high glucose conditions reduces FOXO1 acetylation, suggesting that deacetylation of FOXO1 by SIRT3 elevates the expression of the FOXO1 target genes, catalase, and manganese superoxide dismutase (MnSOD) while decreasing senescence phenotypes. We studied the effects of SIRT3 protein knockdown by shRNA under low glucose conditions. The data showed that shRNA-SIRT3 accelerated senescence phenotypes and acetylation of FOXO1; the expression level of catalase and MnSOD decreased compared with the control group. As a consequence, SIRT3 antagonized cellular senescence with the characteristic features of delayed SA-β-gal staining, senescence-associated heterochromatin foci (SAHF) formation, and p16(INK4A) expression. These results demonstrate for the first time that SIRT3 overexpression antagonizes high glucose-induced cellular senescence in human diploid fibroblasts via the SIRT3-FOXO1 signaling pathway.

Role of autophagy in aging

Constitutive autophagy is important for the control of the quality of proteins and organelles to maintain cell function. Damaged proteins and organelles accumulate in aged organs. The level of autophagic activity decreases with aging. Autophagic activity is regulated by many factors, such as the insulin receptor-signaling pathway, the TOR pathway, Sirt1, and caloric restriction. Autophagy-related genes are known to be essential for the lifespan extension of flies, nematodes, and mice. The inhibition of autophagy decreases the lifespan, and on the other hand, the induction of autophagy can prolong the lifespan. Pharmacological intervention to extend the lifespan has demonstrated a crucial role for autophagy. Heart failure is an age-related disease, as the incidence increases with age. The autophagic activity of the heart decreases during aging. Cardiac-specific autophagy-deficient mice have shown no obvious phenotype up to 10 weeks of age. However, these mice began to die after the age of 6 months, with a significant increase in the left ventricular dimensions and a decrease in the fractional shortening of the left ventricle compared with control mice. This indicates that continuous constitutive autophagy during aging has a crucial role in maintaining cardiac structure and function.

Over-expression of heat shock factor 1 phenocopies the effect of chronic inhibition of TOR by rapamycin and is sufficient to ameliorate Alzheimer's-like deficits in mice modeling the disease

Rapamycin, an inhibitor of target-of-rapamycin, extends lifespan in mice, possibly by delaying aging. We recently showed that rapamycin halts the progression of Alzheimer's (AD)-like deficits, reduces amyloid-beta (Aβ) and induces autophagy in the human amyloid precursor protein (PDAPP) mouse model. To delineate the mechanisms by which chronic rapamycin delays AD we determined proteomic signatures in brains of control- and rapamycin-treated PDAPP mice. Proteins with reported chaperone-like activity were overrepresented among proteins up-regulated in rapamycin-fed PDAPP mice and the master regulator of the heat-shock response, heat-shock factor 1, was activated. This was accompanied by the up-regulation of classical chaperones/heat shock proteins (HSPs) in brains of rapamycin-fed PDAPP mice. The abundance of most HSP mRNAs except for alpha B-crystallin, however, was unchanged, and the cap-dependent translation inhibitor 4E-BP was active, suggesting that increased expression of HSPs and proteins with chaperone activity may result from preferential translation of pre-existing mRNAs as a consequence of inhibition of cap-dependent translation. The effects of rapamycin on the reduction of Aβ, up-regulation of chaperones, and amelioration of AD-like cognitive deficits were recapitulated by transgenic over-expression of heat-shock factor 1 in PDAPP mice. These results suggest that, in addition to inducing autophagy, rapamycin preserves proteostasis by increasing chaperones. We propose that the failure of proteostasis associated with aging may be a key event enabling AD, and that chronic inhibition of target-of-rapamycin may delay AD by maintaining proteostasis in brain. Read the Editorial Highlight for this article on doi: 10.1111/jnc.12098.

TsDAF-21/Hsp90 is expressed in all examined stages of Trichinella spiralis

Trichinella is an important parasitic nematode of animals worldwide. Heat shock proteins are ubiquitous in nature and allow organisms to quickly respond to environmental stress. A portion of the Tsdaf-21 gene, a Caenorhabditis elegans daf-21 homologue encoding heat-shock protein 90 (Hsp90) was cloned from Trichinella spiralis. The partial nucleotide sequence resided near the 5'-end of the gene and encoded a polypeptide of 254 amino acid residues harboring a HATPase-c superfamily domain and Hsp90 protein domain. Phylogenetic analysis revealed that Tsdaf-21 is highly conserved and formed a monophyletic clade with other nematodes. The partial Tsdaf-21 transcript was subcloned and expressed for antibody production. Results using PCR primers specific for the Tsdaf-21 transcript, and mouse polyclonal antisera specific for the recombinant protein showed that both the RNA transcript and the corresponding protein were ubiquitously and consistently expressed in newborn larvae, muscle larvae and both male and female adult worms in the absence of any external stress or stimulation.

Exploring the electrostatic repulsion model in the role of Sirt3 in directing MnSOD acetylation status and enzymatic activity

Mitochondrial oxidative metabolism is the major site of ATP production as well as a significant source of reactive oxygen species (ROS) that can cause damage to critical biomolecules. It is well known that mitochondrial enzymes that scavenge ROS are targeted by stress responsive proteins to maintain the fidelity of mitochondrial function. Manganese superoxide dismutase (MnSOD) is a primary mitochondrial ROS scavenging enzyme, and in 1983 Irwin Fridovich proposed an elegant chemical mechanism/model whereby acetylation directs MnSOD enzymatic activity. He christened it the "electrostatic repulsion model." However, the biochemical and genetic mechanism(s) determining how acetylation directs activity and the reasons behind the evolutionarily conserved need for several layers of transcriptional and posttranslational MnSOD regulation remain unknown. In this regard, we and others have shown that MnSOD is regulated, at least in part, by the deacetylation of specific conserved lysines in a reaction catalyzed by the mitochondrial sirtuin, Sirt3. We speculate that the regulation of MnSOD activity by lysine acetylation via an electrostatic repulsion mechanism is a conserved and critical aspect of MnSOD regulation necessary to maintain mitochondrial homeostasis.

Targeting autophagy for the treatment of liver diseases

Autophagy is a lysosomal degradation pathway that can degrade bulk cytoplasm and superfluous or damaged organelles, such as mitochondria, to maintain cellular homeostasis. It is now known that dysregulation of autophagy can cause pathogenesis of numerous human diseases. Here, we discuss the critical roles that autophagy plays in the pathogenesis of liver diseases such as non-alcoholic and alcoholic fatty liver, drug-induced liver injury, protein aggregate-related liver diseases, viral hepatitis, fibrosis, aging and liver cancer. In particular, we discuss the emerging therapeutic potential by pharmacological modulation of autophagy for these liver diseases.

Aging does not reduce heat shock protein 70 in the absence of chronic insulin resistance

Heat shock protein (HSP)70 decreases with age. Often aging is associated with coincident insulin resistance and higher blood glucose levels, which also associate with lower HSP70. We aimed to understand how these factors interrelate through a series of experiments using vervet monkeys (Chlorocebus aethiops sabaeous). Monkeys (n = 284, 4-25 years) fed low-fat diets showed no association of muscle HSP70 with age (r = .04, p = .53), but levels were highly heritable. Insulin resistance was induced in vervet monkeys with high-fat diets, and muscle biopsies were taken after 0.3 or 6 years. HSP70 levels were significantly greater after 0.3 years (+72%, p < .05) but were significantly lower following 6 years of high-fat diet (-77%, p < .05). Associations with glucose also switched from being positive (r = .44, p = .03) to strikingly negative (r = -.84, p < .001) with increasing insulin resistance. In conclusion, a low-fat diet may preserve tissue HSP70 and health with aging, whereas high-fat diets, insulin resistance, and genetic factors may be more important than age for determining HSP70 levels.

Gadd45 proteins: relevance to aging, longevity and age-related pathologies

The Gadd45 proteins have been intensively studied, in view of their important role in key cellular processes. Indeed, the Gadd45 proteins stand at the crossroad of the cell fates by controlling the balance between cell (DNA) repair, eliminating (apoptosis) or preventing the expansion of potentially dangerous cells (cell cycle arrest, cellular senescence), and maintaining the stem cell pool. However, the biogerontological aspects have not thus far received sufficient attention. Here we analyzed the pathways and modes of action by which Gadd45 members are involved in aging, longevity and age-related diseases. Because of their pleiotropic action, a decreased inducibility of Gadd45 members may have far-reaching consequences including genome instability, accumulation of DNA damage, and disorders in cellular homeostasis - all of which may eventually contribute to the aging process and age-related disorders (promotion of tumorigenesis, immune disorders, insulin resistance and reduced responsiveness to stress). Most recently, the dGadd45 gene has been identified as a longevity regulator in Drosophila. Although further wide-scale research is warranted, it is becoming increasingly clear that Gadd45s are highly relevant to aging, age-related diseases (ARDs) and to the control of life span, suggesting them as potential therapeutic targets in ARDs and pro-longevity interventions.

Cellular stress responses, hormetic phytochemicals and vitagenes in aging and longevity

Modulation of endogenous cellular defense mechanisms represents an innovative approach to therapeutic intervention in diseases causing chronic tissue damage, such as in neurodegeneration. This paper introduces the emerging role of exogenous molecules in hormetic-based neuroprotection and the mitochondrial redox signaling concept of hormesis and its applications to the field of neuroprotection and longevity. Maintenance of optimal long-term health conditions is accomplished by a complex network of longevity assurance processes that are controlled by vitagenes, a group of genes involved in preserving cellular homeostasis during stressful conditions. Vitagenes encode for heat shock proteins (Hsp) Hsp32, Hsp70, the thioredoxin and the sirtuin protein systems. Dietary antioxidants, such as polyphenols and L-carnitine/acetyl-L-carnitine, have recently been demonstrated to be neuroprotective through the activation of hormetic pathways, including vitagenes. Hormesis provides the central underpinning of neuroprotective responses, providing a framework for explaining the common quantitative features of their dose response relationships, their mechanistic foundations, their relationship to the concept of biological plasticity as well as providing a key insight for improving the accuracy of the therapeutic dose of pharmaceutical agents within the highly heterogeneous human population. This paper describes in mechanistic detail how hormetic dose responses are mediated for endogenous cellular defense pathways including sirtuin, Nrfs and related pathways that integrate adaptive stress responses in the prevention of neurodegenerative diseases. This article is part of a Special Issue entitled: Antioxidants and Antioxidant Treatment in Disease.

Transformation of eEF1Bδ into heat-shock response transcription factor by alternative splicing

Protein translation factors have crucial roles in a variety of stress responses. Here, we show that eukaryotic elongation factor 1Bδ (eEF1Bδ) changes its structure and function from a translation factor into a heat-shock response transcription factor by alternative splicing. The long isoform of eEF1Bδ (eEF1BδL) is localized in the nucleus and induces heat-shock element (HSE)-containing genes in cooperation with heat-shock transcription factor 1 (HSF1). Moreover, the amino-terminal domain of eEF1BδL binds to NF-E2-related factor 2 (Nrf2) and induces stress response haem oxygenase 1 (HO1). Specific inhibition of eEF1BδL with small-interfering RNA completely inhibits Nrf2-dependent HO1 induction. In addition, eEF1BδL directly binds to HSE oligo DNA in vitro and associates with the HSE consensus in the HO1 promoter region in vivo. Thus, the transcriptional role of eEF1BδL could provide new insights into the molecular mechanism of stress responses.

The driver of malignancy in KG-1a leukemic cells, FGFR1OP2-FGFR1, encodes an HSP90 addicted oncoprotein

The KG-1a cell line is developed from a human stem cell myeloproliferative neoplasm as the result of intragenic disruption and a chromosomal translocation of the FGFR1 gene and the FGFR1OP2 gene encoding a protein of unknown function called FOP2 (FGFR1 Oncogene Partner 2). The resulting fusion protein FOP2-FGFR1 is soluble and has constitutive tyrosine kinase activity. Since the heat shock protein HSP90 and its co-chaperone CDC37 have been shown to stabilize many oncogenic proteins, we investigated the requirement for HSP90 or HSP90-CDC37 assistance to maintain the stability or activity of FOP2-FGFR1 expressed in KG-1a cells. We found that HSP90-CDC37 forms a permanent complex with FOP2-FGFR1. This results in protection against degradation of FOP2-FGFR1 and holds the oncoprotein in a permanently active conformation. Inhibition of HSP90 or depletion of CDC37 or heat shock factor 1 (HSF1) reduced the expression level of FOP2-FGFR1 and was sufficient to block the oncoprotein induced proliferation of KG-1a cells. We conclude that the driver of malignancy in KG-1a leukemic cells, FOP2-FGFR1, is an HSP90 addicted oncoprotein. This provides a rationale for the therapeutic use of HSP90 inhibitors in myeloid leukemias that contain FGFR fusion proteins.

SIRT6 promotes DNA repair under stress by activating PARP1

Sirtuin 6 (SIRT6) is a mammalian homolog of the yeast Sir2 deacetylase. Mice deficient for SIRT6 exhibit genome instability. Here, we show that in mammalian cells subjected to oxidative stress SIRT6 is recruited to the sites of DNA double-strand breaks (DSBs) and stimulates DSB repair, through both nonhomologous end joining and homologous recombination. Our results indicate that SIRT6 physically associates with poly[adenosine diphosphate (ADP)-ribose] polymerase 1 (PARP1) and mono-ADP-ribosylates PARP1 on lysine residue 521, thereby stimulating PARP1 poly-ADP-ribosylase activity and enhancing DSB repair under oxidative stress.

Acetylation of MnSOD directs enzymatic activity responding to cellular nutrient status or oxidative stress

A fundamental observation in biology is that mitochondrial function, as measured by increased reactive oxygen species (ROS), changes significantly with age, suggesting a potential mechanistic link between the cellular processes governing longevity and mitochondrial metabolism homeostasis. In addition, it is well established that altered ROS levels are observed in multiple age-related illnesses including carcinogenesis, neurodegenerative, fatty liver, insulin resistance, and cardiac disease, to name just a few. Manganese superoxide dismutase (MnSOD) is the primary mitochondrial ROS scavenging enzyme that converts superoxide to hydrogen peroxide, which is subsequently converted to water by catalase and other peroxidases. It has recently been shown that MnSOD enzymatic activity is regulated by the reversible acetylation of specific, evolutionarily conserved lysine(s) in the protein. These results, suggest for the first time, that the mitochondria contain bidirectional post-translational signaling networks, similar to that observed in the cytoplasm and nucleus, and that changes in lysine acetylation alter MnSOD enzymatic activity. In addition, these new results demonstrate that the mitochondrial anti-aging or fidelity / sensing protein, SIRT3, responds to changes in mitochondrial nutrient and/or redox status to alter the enzymatic activity of specific downstream targets, including MnSOD that adjusts and/or maintains ROS levels as well as metabolic homeostatic poise.

17β-Estradiol, aging, inflammation, and the stress response in the female heart

Heat shock proteins (HSPs) are a cardioprotective class of proteins induced by stress and regulated by the transcription factor, heat shock factor (HSF)-1. 17β-estradiol (E(2)) indirectly regulates HSP expression through rapid activation of nuclear factor-κB (NF-κB) and HSF-1 and protects against hypoxia. As males experience a loss of protective cellular responses in aging, we hypothesized that aged menopausal (old ovariectomized) rats would have an impaired HSP response, which could be prevented by immediate in vivo E(2) replacement. After measuring cardiac function in vivo, cardiac myocytes were isolated from ovariectomized adult and old rats with and without 9 weeks of E(2) replacement. Myocytes were treated with E(2) in vitro and analyzed for activation of NF-κB, HSF-1, and HSP expression. In addition, we measured inflammatory cytokine expression and susceptibility to hypoxia/reoxygenation injury. Cardiac contractility was reduced in old ovariectomized rats and could prevented by immediate E(2) replacement in vivo. Subsequent investigations in isolated cardiac myocytes found that in vitro E(2) activated NF-κB, HSF-1, and increased HSP 72 expression in adult but not old rats. In response to hypoxia/reoxygenation, myocytes from adult, but not old, rats had increased HSP 72 expression. In addition, expression of the inflammatory cytokines TNF-α and IL-1β, as well as oxidative stress, were increased in myocytes from old ovariectomized rats; only the change in cytokine expression could be attenuated by in vivo E(2) replacement. This study demonstrates that while aging in female rats led to a loss of the cardioprotective HSP response, E(2) retains its protective cellular properties.

SIRT1 contributes to telomere maintenance and augments global homologous recombination

SIRT1 is a positive regulator of telomere length and attenuates age-associated telomere shortening.

Yeast Sir2 deacetylase is a component of the silent information regulator (SIR) complex encompassing Sir2/Sir3/Sir4. Sir2 is recruited to telomeres through Rap1, and this complex spreads into subtelomeric DNA via histone deacetylation. However, potential functions at telomeres for SIRT1, the mammalian orthologue of yeast Sir2, are less clear. We studied both loss of function (SIRT1 deficient) and gain of function (SIRT1^super) mouse models. Our results indicate that SIRT1 is a positive regulator of telomere length in vivo and attenuates telomere shortening associated with aging, an effect dependent on telomerase activity. Using chromatin immunoprecipitation assays, we find that SIRT1 interacts with telomeric repeats in vivo. In addition, SIRT1 overexpression increases homologous recombination throughout the entire genome, including telomeres, centromeres, and chromosome arms. These findings link SIRT1 to telomere biology and global DNA repair and provide new mechanistic explanations for the known functions of SIRT1 in protection from DNA damage and some age-associated pathologies.

NAD(+) -dependent histone deacetylases (sirtuins) as novel therapeutic targets

Histone deacetylases (HDACs) are enzymes that cleave off acetyl groups from acetyl-lysine residues in histones and various nonhistone proteins. Four different classes of HDACs have been identified in humans so far. Although classes I, II, and IV are zinc-dependent amidohydrolases, class III HDACs depend on nicotinamide adenine dinucleotide (NAD(+)) for their catalytic activity. According to their homology to Sir2p, a yeast histone deacetylase, the class III is also termed sirtuins. Seven members have been described in humans so far. As sirtuins are involved in many physiological and pathological processes, their activity has been associated with the pathogenesis of cancer, HIV, metabolic, or neurological diseases. Herein, we present an overview over sirtuins including their biology, targets, inhibitors, and activators and their potential as new therapeutic agents.

Radiation hormesis and radioadaptive response in Drosophila melanogaster flies with different genetic backgrounds: the role of cellular stress-resistance mechanisms

The purpose of this work is to investigate the role of cellular stress-resistance mechanisms in the low-dose irradiation effects on Drosophila melanogaster lifespan. In males and females with the wild type Canton-S genotype the chronic low dose irradiation (40 cGy) induced the hormetic effect and radiation adaptive response to acute irradiation (30 Gy). The hormesis and radioadaptive responses were observed in flies with mutations in autophagy genes (atg7, atg8a) but absent in flies with mutations in FOXO, ATM, ATR, and p53 homologues. The hormetic effect was revealed in Sirt2 mutant males but not in females. On the contrary, the females but not males of JNK/+ mutant strain showed adaptive response. The obtained results demonstrate the essential role of FOXO, SIRT1, JNK, ATM, ATR, and p53 genes in hormesis and radiation adaptive response of the whole organism.

Xenohormesis: health benefits from an eon of plant stress response evolution

Xenohormesis is a biological principle that explains how environmentally stressed plants produce bioactive compounds that can confer stress resistance and survival benefits to animals that consume them. Animals can piggyback off products of plants' sophisticated stress response which has evolved as a result of their stationary lifestyle. Factors eliciting the plant stress response can judiciously be employed to maximize yield of health-promoting plant compounds. The xenohormetic plant compounds can, when ingested, improve longevity and fitness by activating the animal's cellular stress response and can be applied in drug discovery, drug production, and nutritional enhancement of diet.