Aging augments mitochondrial susceptibility to heat stress

Heat-shock proteins, oxidative stress, and antioxidants in one-humped camels

One-humped camels (Camelus dromedarius) exhibit remarkable adaptability to harsh desert environments through various physiological adaptations. This study aimed to assess variations and reference values of Heat-shock proteins (HSPs), physiological parameters, mineral concentrations, total antioxidant capacity (TAC), and malondialdehyde (MDA) in 90 healthy female one-humped camels from Zabol's outskirts in Iran. The objective was to understand how these camels adapt to heat stress. Blood samples were collected from camels located at five geographical regions and analyzed using standard kits and methods. Reference intervals for heat-shock protein 30 (HSP30), heat-shock protein 40 (HSP40), heat-shock protein 70 (HSP70), and heat-shock protein 90 (HSP90) were determined using the reference value advisor (RVA). The study found significant differences among different regions for HSPs (P < 0.05), MDA (P = 0.021), and TAC (P = 0.042) levels, indicating variations in adaptation mechanisms. However, no notable differences were observed for other measured parameters between these regions. There were no significant differences observed in the evaluated parameters between the age categories of > 36 months and < 36 months. The positive correlation between HSPs and MDA levels (ranging from 0.754 to 0.884) suggests that the synthesis of HSPs is triggered as a response to oxidative stress caused by an imbalance between the production of reactive oxygen species (ROS) and the body's antioxidant defenses. This oxidative stress, in turn, is a consequence of thermal stress. Additionally, the study reveals a negative association between TAC and HSP levels (ranging from - 0.660 to - 0.820), emphasizing the role of antioxidants in mitigating heat stress. The findings of this research offer compelling support for the critical role that HSPs play in protecting cells from heat-induced damage. Additionally, the presence of higher levels of HSPs in regions with more severe climate conditions serves as evidence of camels' adaptation to heat stress. These findings emphasize the substantial impact of environmental factors on HSP production and further reinforce the crucial role of HSPs in bolstering the resilience of camels. Further research is needed to explore HSP expression and mechanisms to effectively manage and enhance camel resilience in extreme temperatures.

Altered accumulation of hepatic mitochondrial antioxidant proteins with age and environmental heat stress

Aging impairs overall physiological function, particularly the response to environmental stressors. Repeated heat stress elevates reactive oxygen species and macromolecular damage in the livers of aged animals, likely due to mitochondrial dysfunction. The goal of this investigation was to determine potential mechanisms for mitochondrial dysfunction after heat stress by evaluating key redox-sensitive and antioxidant proteins (Sirt-3, MnSOD, Trx-2, and Ref-1). We hypothesized that heat stress would result in greater mitochondrial abundance of these proteins, but that aging would attenuate this response. For this purpose, young (6 mo) and old (24 mo) Fisher 344 rats were exposed to heat stress on two consecutive days. During each heating trial, colonic temperature was elevated to 41°C during the first 60 min, and then clamped at this temperature for 30 min. Nonheated animals served as controls. At 2 and 24 h after the second heat stress, hepatic mitochondria were isolated from each animal, and then immunoblotted for Sirt-3, acetylated lysine residues (Ac-K), MnSOD, Trx-2, and Ref-1. Aging increased Sirt-3 and lowered Ac-K. In response to heat stress, Sirt-3, Ac-K, MnSOD, and Ref-1 increased in mitochondrial fractions in both young and old animals. At 2 h after the second heat stress, mitochondrial Trx-2 declined in old, but not in young animals. Our results suggest that some components of the response to heat stress are preserved with aging. However, the decline in Trx-2 represents a potential mechanism for age-related mitochondrial damage and dysfunction after heat stress.NEW & NOTEWORTHY Our results suggest heat stress-induced mitochondrial translocation of Sirt-3, MnSOD, and Ref-1 in young and old animals. Aged rats experienced a decline in Trx-2 after heat stress, suggesting a potential mechanism for age-related mitochondrial dysfunction.

Systems modelling predicts chronic inflammation and genomic instability prevent effective mitochondrial regulation during biological ageing

The regulation of mitochondrial turnover under conditions of stress occurs partly through the AMPK-NAD+-PGC1α-SIRT1 signalling pathway. This pathway can be affected by both genomic instability and chronic inflammation since these will result in an increased rate of NAD+ degradation through PARP1 and CD38 respectively. In this work we develop a computational model of this signalling pathway, calibrating and validating it against experimental data. The computational model is used to study mitochondrial turnover under conditions of stress and how it is affected by genomic instability, chronic inflammation and biological ageing in general. We report that the AMPK-NAD+-PGC1α-SIRT1 signalling pathway becomes less responsive with age and that this can prime for the accumulation of dysfunctional mitochondria.

Serum klotho concentrations in young and older men during prolonged exercise in temperate and hot conditions

BACKGROUND

The protein klotho protects cellular function during various physiological stressors, such as exercise, however it is unknown how the age-related decline in klotho production affects responses during exercise, especially in the heat.

OBJECTIVE

Our objective was to determine the effect of exercise in temperate and hot environmental conditions on serum klotho concentrations in young and older men.

METHODS

12 young (mean ± SD: 22 ± 3 years) and 12 older (59 ± 4 years) men performed 180 minutes of moderate-intensity treadmill walking (metabolic rate: 200 W/m2) in a temperate [wet-bulb globe temperature (WBGT) 16°C, achieved with 21.9°C, 35% relative humidity (RH)] and hot (WBGT 32°C, achieved with 41.4°C, 35% RH) environment. Serum klotho was assessed before and after exercise, as well as 60-min post-exercise recovery in the respective environments.

RESULTS

Absolute klotho concentrations were greater in young versus older men during all measured time points in the temperate (p = 0.032), but not the hot condition (p = 0.064). In the hot condition, the change in serum klotho from baseline was significantly higher after exercise in the heat (mean ± SEM: +251 ± 73 pg/mL) than the temperate (+75 ± 57 pg/mL) environment in both groups (p = 0.026). However, this elevation was not maintained during recovery.

CONCLUSION

We showed that prolonged exercise in a temperate environment does not elicit a klotho response in either group. In contrast, despite lower resting klotho levels, the older men showed a similar exercise-induced increase in serum klotho response as their younger counterparts.

Hepatic macrophage accumulation with aging: cause for concern?

Aging is associated with chronic, low-grade inflammation that adversely affects physiological function. The liver regulates systemic inflammation; it is a source of cytokine production and also scavenges bacteria from the portal circulation to prevent infection of other organs. The cells with primary roles in these functions, hepatic macrophages, become more numerous in the liver with "normal" aging (i.e., in the absence of disease). Here, we demonstrate evidence and potential mechanisms for this phenomenon, which include augmented tumor necrosis factor-α (TNF-α) and intercellular adhesion molecule-1 (ICAM-1) expression in the liver. Also, we discuss how an age-related impairment in autophagy within macrophages leads to a pro-oxidative state and ensuing production of proinflammatory cytokines, particularly interleukin 6 (IL-6). Given that the liver is a rich source of macrophages, we posit that it represents a major source of the elevated systemic IL-6 observed with aging, which is associated with physiological dysfunction. Testing a causal role for liver macrophage production of IL-6 during aging remains a challenge, yet interventions that have targeted macrophages and/or IL-6 have demonstrated promise in treating age-related diseases. These studies have demonstrated an age-related, deleterious reprogramming of macrophage function, which worsens pathology. Therefore, hepatic macrophage accrual is indeed a cause for concern, and therapies that attenuate the aged phenotype of macrophages will likely prove useful in promoting healthy aging.

The impact of red grape juice (Vitis labrusca)consumption associated with physical training on oxidative stress, inflammatory and epigenetic modulation in healthy elderly women

The imbalance of epigenetic, oxidative stress and inflammatory markers is associated with the aging physiopathology. Then, the influence of bioactive nutritional compounds and physical training on these biomarkers has been studied, although the combination of both strategies has been not investigated. Therefore, our aim was to verify the effect of the association of physical training with red grape juice (Vitis labrusca) consumption on global histone acetylation H3 and H4 levels, oxidative stress markers and interleukin 6 (IL-6) levels in peripheral blood of healthy elderly women. This double-blind randomized clinical study consisted of 29 volunteers, aged 59 years and over, divided into three groups: grape juice group (GJG, n = 9); placebo and exercise group (PLEG, n = 10) and grape juice and exercise group (GJEG, n = 10). During 1 month, GJG consumed 400 ml of grape juice per day (integral and conventional), while the PLEG and GJEG groups, besides consuming juice or placebo were submitted to a concurrent physical training protocol (two times per week, 60 min / session). The volunteers were submitted to blood collections before and after the intervention for the biomarkers analysis, e.g. IL-6, histone acetylation H3 and H4, lipid oxidative damage (TBARS), proteins (Carbonyl), non-enzymatic antioxidant defense (Sulfhydryl groups) and activity of antioxidant enzymes (superoxide dismutase and catalase). There were no statistically significant differences in the global levels of histone acetylation H3 and H4 post intervention compared to the basal period as well and between groups were found. However, PLEG and GJEG showed a remarkable reduction on IL-6 levels after intervention. We also observed an increase in Carbonyl levels, SOD activities and Sulfhydryl levels comparing before and after intervention. Considering the interaction of time and groups, a significant increase in Sulfhydryl levels only in GJG was found. The physical training protocol associated or not with grape juice consumption showed anti-inflammatory effects and an influence in the antioxidant defenses (non enzymatic and enzymatic) in elderly women. However in grape juice group, without exercise, we observed an increase in non enzymatic antioxidant defense, what could be attributed to the polyphenols content. These responses seem not to be involved with histone acetylation status.

Radical Response: Effects of Heat Stress-Induced Oxidative Stress on Lipid Metabolism in the Avian Liver

Lipid metabolism in avian species places unique demands on the liver in comparison to most mammals. The avian liver synthesizes the vast majority of fatty acids that provide energy and support cell membrane synthesis throughout the bird. Egg production intensifies demands to the liver as hepatic lipids are needed to create the yolk. The enzymatic reactions that underlie de novo lipogenesis are energetically demanding and require a precise balance of vitamins and cofactors to proceed efficiently. External stressors such as overnutrition or nutrient deficiency can disrupt this balance and compromise the liver’s ability to support metabolic needs. Heat stress is an increasingly prevalent environmental factor that impairs lipid metabolism in the avian liver. The effects of heat stress-induced oxidative stress on hepatic lipid metabolism are of particular concern in modern commercial chickens due to the threat to global poultry production. Chickens are highly vulnerable to heat stress because of their limited capacity to dissipate heat, high metabolic activity, high internal body temperature, and narrow zone of thermal tolerance. Modern lines of both broiler (meat-type) and layer (egg-type) chickens are especially sensitive to heat stress because of the high rates of mitochondrial metabolism. While this oxidative metabolism supports growth and egg production, it also yields oxidative stress that can damage mitochondria, cellular membranes and proteins, making the birds more vulnerable to other stressors in the environment. Studies to date indicate that oxidative and heat stress interact to disrupt hepatic lipid metabolism and compromise performance and well-being in both broilers and layers. The purpose of this review is to summarize the impact of heat stress-induced oxidative stress on lipid metabolism in the avian liver. Recent advances that shed light on molecular mechanisms and potential nutritional/managerial strategies to counteract the negative effects of heat stress-induced oxidative stress to the avian liver are also integrated.

Aging results in accumulation of M1 and M2 hepatic macrophages and a differential response to gadolinium chloride

Macrophages have vital roles in innate immunity by modulating the inflammatory response via their ability to alter their phenotype from pro-inflammatory (M1) to anti-inflammatory (M2). Aging increases activation of the innate immune system, and macrophage numbers increase in the aged liver. Since macrophages also produce free radical molecules, they are a potential source of age-related oxidative injury in the liver. This study evaluated macrophage phenotype in the aged liver and whether the increase in the number of macrophages with aging is associated with enhanced hepatic oxidative stress. Hepatic macrophage phenotype and oxidative stress were evaluated 2 days after a single intraperitoneal injection of saline or gadolinium chloride (GdCl₃, 10 mg/kg) in young (6 months) and aged (24 months) Fischer 344 rats. GdCl₃ has been shown to decrease the expression of macrophage-specific markers and impair macrophage phagocytosis in the liver. Saline-treated aged rats demonstrated greater numbers of both M1 (HO-1⁺/iNOS⁺) and M2 (HO-1⁺/CD163⁺) macrophages, without evidence of a phenotypic shift. GdCl₃ did not alter levels of dihydroethidium fluorescence or malondialdehyde, suggesting that macrophages are not a major contributor to steady-state levels of oxidative stress. However, GdCl₃ decreased M1 and M2 macrophage markers in both age groups, an effect that was attenuated in aged rats. In old animals, GdCl₃ decreased iNOS expression to a greater extent than HO-1 or CD163. These results suggest a novel effect of aging on macrophage biology and that GdCl₃ shifts hepatic macrophage polarization to the M2 phenotype in aged animals.

Endothelial TNF-α induction by Hsp60 secreted from THP-1 monocytes exposed to hyperglycaemic conditions

A non-resolving inflammation of the endothelium is recognised to be an important process leading to atherosclerosis. In diabetes, this process is thought to account for a significant number of cardiovascular disease-associated death and disability. However, the molecular mechanisms by which diabetes contributes to endothelial inflammation remain to be established. Whilst there is some evidence linking hyperglycaemia-induced reactive oxygen species (ROS) formation by the mitochondrial electron-transport chain to oxidative stress, cellular injury and apoptosis in the endothelium, a clear link to endothelium inflammation has not yet been established. The mitochondrial molecular stress protein Hsp60 is known to be secreted from mammalian cells and is capable of activating pro-inflammatory mediators on target cells expressing Toll-like receptors (TLRs). Hsp60 is also known to be elevated in serum of diabetes patients and has been shown to be upregulated by hyperglycaemic growth conditions in cultured human HeLa cells. This study shows that Hsp60 induced in human acute monocyte leukaemia cell line (THP-1) cells grown under hyperglycaemic conditions (25 mM glucose) was able to be secreted into growth media. Furthermore, the secretion of Hsp60 from THP-1 cells was able to be inhibited by 5,5-(N-N-dimethyl)-amiloride hydrochloride (DMA), an exosomal inhibitor. Interestingly, the conditioned media obtained from THP-1 cells grown in the presence of 25 mM glucose was able to induce the secretion of TNF-α in human vascular endothelium cell line (HUVEC). When conditioned media was immuno-depleted of Hsp60, there was a significant reduction in the release of TNF-α from the HUVEC cells. This suggests that a potential link may exist between hyperglycaemia-induced expression of Hsp60 in monocyte cells and vascular inflammation. Circulating levels of Hsp60 due to mitochondrial stress in diabetes patients could therefore be an important modulator of inflammation in endothelial cells and thus contribute to the increased incidences of atherosclerosis in diabetes mellitus.

Prolonged environment-induced hyperthermia alters autophagy in oxidative skeletal muscle in Sus scrofa

Prolonged heat stress represents a continuing threat to human health and agricultural production. Despite the broad, negative impact of prolonged hyperthermia little is known about underlying pathological mechanisms leading to negative health outcomes, which has limited the development of etiological interventions and left clinicians and producers with only cooling and rehydration strategies. The purpose of this investigation was to determine the extent to which prolonged environment-induced hyperthermia altered autophagy in oxidative skeletal muscle in a large animal model, serving the dual purpose of accurately modeling human physiology as well as agricultural production. We hypothesized that prolonged hyperthermia would induce autophagy in skeletal muscle, independent of the accompanying caloric restriction. To test this hypothesis pigs were treated as follows: thermoneutral (20 °C), heat stress (35 °C), or were held under thermoneutral conditions but pair-fed to the heat stress group for seven days. Upon euthanasia the red portion of the semitendinosus was collected. We found that prolonged hyperthermic exposure increased oxidative stress without a corresponding change in antioxidant enzyme activities. Hyperthermia prevented initiation of autophagy despite increased markers of nucleation, elongation and autophagosome formation. However, p62 relative protein abundance, which is inversely correlated with autophagic degradation, was strongly increased suggesting suppressed degradation of autophagosomes. Markers of mitophagy and mitochondrial abundance were largely similar between groups. These data indicate that faulty autophagy plays a key role in hyperthermic muscle dysfunction.

Short-term heat stress results in increased apoptotic signaling and autophagy in oxidative skeletal muscle in Sus scrofa

Prolonged environment-induced hyperthermia causes morbidities and mortality in humans and animals and appears to cause organ-specific injury and dysfunction. We have previously determined autophagic dysfunction and apoptotic signaling in oxidative skeletal muscle following prolonged hyperthermia. The aim of this investigation was to extend our knowledge regarding the early chronology of heat stress-mediated apoptotic and autophagic signaling in oxidative skeletal muscle. We hypothesized that 2, 4, and 6 h of hyperthermia would increase apoptosis and autophagy in oxidative skeletal muscle compared to thermoneutral (TN) conditions. Pigs were assigned to four groups (n = 8/group) and exposed to environmental heat stress (37 °C) for 0, 2, 4, or 6 h. Immediately following environmental exposure animals were euthanized and the red portion of the semitendinosus was collected. Markers of apoptotic signaling were increased following 2 h of heating but returned to baseline thereafter, while caspase 3 activity remained elevated 2-3 fold (p < .05) throughout the hyperthermic period. Heat stress increased (p < .05) markers of autophagic activation, and nucleation as well as autophagosome formation and degradation linearly throughout the heating intervention. In addition, 6 h of hyperthermia increased (p < .05) markers of mitophagy. These data suggest that apoptotic signaling precedes increased autophagy during acute heat stress in oxidative skeletal muscle.

Sexual dimorphism in the hepatic protein response to a moderate trans fat diet in senescence-accelerated mice

BACKGROUND

Aging is characterized by increases in inflammation and oxidative stress, conditions that are exacerbated by environmental factors such as diet. In this study, we investigated the effects of a trans-fatty acid (TFA) diet on the liver in adult (25 wk) and old (60 wk) senescence-accelerated mice (SAMP8 strain) of both sexes. Our goal was to assess the effects of the diet on protein markers of inflammation and oxidative stress in the liver.

METHODS

Male and female mice were placed on life-long diets containing similar amounts of total fat (17%), with differing amounts of TFA: 2% (moderate TFA group) or 0.2% of total energy from TFA (control diet group). At the indicated ages, livers were harvested and evaluated for markers of inflammation and oxidative stress, as well as for enzymes of fat metabolism via immunoblotting. Relative densities of protein bands were determined and compared via a three-factor ANOVA.

RESULTS

Compared to males, females demonstrated significantly lower inflammatory protein expression (ICAM-1, MCP-1, COX-2), along with lower expression of the DNA damage marker, Gadd153, and the oxidative stress marker, HO-1. Female mice demonstrated higher expression of antioxidant enzymes (SOD-1, SOD-2, and Ref-1) and lipogenic enzymes (FASN, ACLY) compared to male mice. While HO-1 was elevated in the female mice fed the TFA diet compared to controls, the diet did not affect other markers of oxidative stress or inflammation. However, the diet was associated with significant increases in FASN and ACLY in adult (25 wk) male mice.

CONCLUSIONS

Our results suggest sexually dimorphic protein expression in the liver, with female mice demonstrating lower inflammation and increased oxidative stress defenses. Additionally, considering that FASN and ACLY contribute to hepatic lipogenesis, our results suggest a potential mechanism for the dyslipidemia in adult male mice that is associated with TFA diets.

A viewpoint on considering physiological principles to study stress resistance and resilience with aging

Adaptation to stress is identified as one of the seven pillars of aging research. Our viewpoint discusses the importance of the distinction between stress resistance and resilience, highlights how integration of physiological principles is critical for further understanding in vivo stress resistance and resilience, and advocates for the use of early warning signs to prevent a tipping point in stress resistance and resilience.

To unite or divide: mitochondrial dynamics in the murine outer retina that preceded age related photoreceptor loss

Mitochondrial function declines with age and is associated with age-related disorders and cell death. In the retina this is critical as photoreceptor energy demands are the greatest in the body and aged cell loss large (~30%). But mitochondria can fuse or divide to accommodate changing demands. We explore ageing mitochondrial dynamics in young (1 month) and old (12 months) mouse retina, investigating changes in mitochondrial fission (Fis1) and fusion (Opa1) proteins, cytochrome C oxidase (COX III), which reflects mitochondrial metabolic status, and heat shock protein 60 (Hsp60) that is a mitochondrial chaperon for protein folding.Western blots showed each protein declined with age. However, within this, immunostaining revealed increases of around 50% in Fis1 and Opa1 in photoreceptor inner segments (IS). Electron microscope analysis revealed mitochondrial fragmentation with age and marked changes in morphology in IS, consistent with elevated dynamics. COX III declined by approximately 30% in IS, but Hsp60 reductions were around 80% in the outer plexiform layer.Our results are consistent with declining mitochondrial metabolism. But also with increased photoreceptor mitochondrial dynamics that differ from other retinal regions, perhaps reflecting attempts to maintain function. These changes are the platform for age related photoreceptor loss initiated after 12 months.

Heat dissipation does not suppress an immune response in laboratory mice divergently selected for basal metabolic rate (BMR)

The capacity for heat dissipation is considered to be one of the most important constraints on rates of energy expenditure in mammals. To date, the significance of this constraint has been tested exclusively under peak metabolic demands, such as during lactation. Here, we used a different set of metabolic stressors, which do not induce maximum energy expenditures and yet are likely to expose the potential constraining effect of heat dissipation. We compared the physiological responses of mice divergently selected for high (H-BMR) and low basal metabolic rate (L-BMR) to simultaneous exposure to the keyhole limpet haemocyanin (KLH) antigen and high ambient temperature (Ta). At 34°C (and at 23°C, used as a control), KLH challenge resulted in a transient increase in core body temperature (Tb) in mice of both line types (by approximately 0.4°C). Warm exposure did not produce line-type-dependent differences in Tb (which was consistently higher by ca. 0.6°C in H-BMR mice across both Ta values), nor did it result in the suppression of antibody synthesis. These findings were also supported by the lack of between-line-type differences in the mass of the thymus, spleen or lymph nodes. Warm exposure induced the downsizing of heat-generating internal organs (small intestine, liver and kidneys) and an increase in intrascapular brown adipose tissue mass. However, these changes were similar in scope in both line types. Mounting a humoral immune response in selected mice was therefore not affected by ambient temperature. Thus, a combined metabolic challenge of high Ta and an immune response did not appreciably compromise the capacity to dissipate heat, even in the H-BMR mice.

Aging impairs induction of redox factor-1 after heat stress: a potential mechanism for heat-induced liver injury

Aging is associated with reduced tolerance to physiological stressors such as hyperthermia. In animal models, heat stress is associated with increased oxidative damage in the livers of old rats. In this study, we evaluated the expression of redox factor-1 (Ref-1), a DNA repair enzyme, and thioredoxin-1 (Trx-1), an antioxidant protein. We hypothesized that these proteins would be induced by heat stress in young animals, and that aging would attenuate this response. Young (6 mo) and old (24 mo) male Fischer 344 rats were exposed to a two-heat stress protocol, and livers were harvested at several time points after the second heat stress. Ref-1 and Trx-1 were evaluated by immunoblot and immunohistochemistry. In young rats, Ref-1 was induced by ~50% immediately (0 h) after heat stress, and returned to control levels at 2 h. We observed no change in Ref-1 after hyperthermia in old rats; however, aging was associated with a 2-fold increase in Ref-1 expression. At 2 h after heat stress, Trx-1 was increased in old rats, but there was no change in young rats. In tissue sections, we observed frequent ductular reactions in the old rats that were positive for both Ref-1 and Trx-1. The impairment in the induction of Ref-1 suggests a mechanism for the increased oxidative injury observed in old rats after heat stress. Furthermore, the observation of ductular reactions positive for both Ref-1 and Trx-1 demonstrates a proliferative cellular niche that develops with aging.

Functional diversification and specialization of cytosolic 70-kDa heat shock proteins

A fundamental question in molecular evolution is how protein functional differentiation alters the ability of cells and organisms to cope with stress and survive. To answer this question we used two paralogous Hsp70s from mouse and explored whether these highly similar cytosolic molecular chaperones, which apart their temporal expression have been considered functionally interchangeable, are differentiated with respect to their lipid-binding function. We demonstrate that the two proteins bind to diverse lipids with different affinities and therefore are functionally specialized. The observed lipid-binding patterns may be related with the ability of both Hsp70s to induce cell death by binding to a particular plasma-membrane lipid, and the potential of only one of them to promote cell survival by binding to a specific lysosomal-membrane lipid. These observations reveal that two seemingly identical proteins differentially modulate cellular adaptation and survival by having acquired specialized functions via sequence divergence. Therefore, this study provides an evolutionary paradigm, where promiscuity, specificity, sub- and neo-functionalization orchestrate one of the most conserved systems in nature, the cellular stress-response.

Understanding the role of heat shock protein isoforms in male fertility, aging and apoptosis

Heat shock proteins (HSPs) play a role in the homeostasis, apoptosis regulation and the maintenance of the various other physiological processes. Aging is accompanied by a decrease in the resistance to environmental stress, while mitochondria are primary targets in the process of aging, their expression decreasing with age. Mitochondrion also plays a significant role in the process of spermatogenesis. HSPs have been shown to be involved in apoptosis with some of acting as apoptotic inhibitors and are involved in cytoprotection. In this review we discuss the roles of Hsp 27, 60, 70, and 90 in aging and male infertility and have concluded that these particular HSPs can be used as a molecular markers for mitochondrially- mediated apoptosis, aging and male infertility.

Heat stress stimulates hepcidin mRNA expression and C/EBPα protein expression in aged rodent liver

Elevations in hepatic iron content occur with aging and physiological stressors, which may promote oxidative injury to the liver. Since dysregulation of the iron regulatory hormone, hepcidin, can cause iron accumulation, our goal was to characterize the regulation of hepcidin in young (6 mo) and old (24 mo) Fischer 344 rats exposed to environmental heat stress. Liver and blood samples were taken in the control condition and after heating. Hepcidin expression did not differ between young and old rats in the control condition, despite higher levels of hepatic iron and IL-6 mRNA in the latter. Following heat stress, pSTAT3 increased in both groups, but C/EBPα and hepcidin mRNA increased only in old rats. Despite this, serum iron decreased in both age groups 2 h after heat stress, suggesting hepcidin-independent hypoferremia in the young rats. The differential regulation of hepcidin between young and old rats after hyperthermia may be due to the enhanced expression of C/EBPα protein in old rats. These data support the concept of "inflammaging" and suggest that repeated exposures to stressors may contribute to the development of anemia in older individuals.

Altered expression of iron regulatory proteins with aging is associated with transient hepatic iron accumulation after environmental heat stress

An increasing body of evidence suggests that dysregulation of iron metabolism contributes to age-related pathologies. We have previously observed increased hepatic iron with aging, and that environmental heat stress stimulates a further increase in iron and oxidative liver injury in old rats. The purpose of this study was to determine a mechanism for the increase in hepatic iron in old rats after heat stress. Young (6 mo) and old (24 mo) Fischer 344 rats were exposed to two heating bouts separated by 24 h. Livers were harvested after the second heat stress, and protein levels of the iron import protein, transferrin receptor-1 (TFR1), and the iron export protein, ferroportin (Fpn) were determined by immunoblot. In the nonheated condition, old rats had lower TFR1 expression, and higher Fpn expression. After heat stress, TFR1 declined in the old rats, and iron chelation studies demonstrated that this decline was dependent on a hyperthermia-induced increase in iron. TFR1 did not change in the young rats after heat stress. Since TFR1 is inversely regulated by iron, our results suggest that the increase in intracellular iron with aging and heat stress lower TFR1 expression. Fpn expression increased in both age groups after heat stress, but this response was delayed in old rats. This delay in the induction of an iron exporter suggests a mechanism for the increase in hepatic iron and oxidative injury after heat stress in aged organisms.

The role of heat stress on the age related protein carbonylation

Since the proteins are involved in many physiological processes in the organisms, modifications of proteins have important outcomes. Protein modifications are classified in several ways and oxidative stress related ones take a wide place. Aging is characterized by the accumulation of oxidized proteins and decreased degradation of these proteins. On the other hand protein turnover is an important regulatory mechanism for the control of protein homeostasis. Heat shock proteins are a highly conserved family of proteins in the various cells and organisms whose expressions are highly inducible during stress conditions. These proteins participate in protein assembly, trafficking, degradation and therefore play important role in protein turnover. Although the entire functions of each heat shock protein are still not completely investigated, these proteins have been implicated in the processes of protection and repair of stress-induced protein damage. This study has focused on the heat stress related carbonylated proteins, as a marker of oxidative protein modification, in young and senescent fibroblasts. The results are discussed with reference to potential involvement of induced heat shock proteins. This article is part of a Special Issue entitled: Protein Modifications.

BIOLOGICAL SIGNIFICANCE

Age-related protein modifications, especially protein carbonylation take a wide place in the literature. In this direction, to highlight the role of heat shock proteins in the oxidative modifications may bring a new aspect to the literature. On the other hand, identified carbonylated proteins in this study confirm the importance of folding process in the mitochondria which will be further analyzed in detail.

Crucial role of membrane potential in heat stress-induced overproduction of reactive oxygen species in avian skeletal muscle mitochondria

Heat stress is an environmental factor that causes oxidative stress. We found previously that acute heat stress stimulates the production of reactive oxygen species (ROS) in the skeletal muscle mitochondria of birds, and that this was accompanied by an increase of the mitochondrial membrane potential (ΔΨ) due to increased substrate oxidation by the electron transport chain. We also showed that avian uncoupling protein (avUCP) expression is decreased by the heat exposure. The present study clarifies whether ΔΨ is a major determinant of the overproduction of ROS due to acute heat stress, and if the decrease in avUCP expression is responsible for the elevation in ΔΨ. Control (24°C) and acute heat-stressed (34°C for 12 h) birds exhibited increased succinate-driven mitochondrial ROS production as indicated by an elevation of ΔΨ, with this increase being significantly higher in the heat-stressed group compared with the control group. In glutamate/malate-energized mitochondria, no difference in the ROS production between the groups was observed, though the mitochondrial ΔΨ was significantly higher in the heat-stressed groups compared with the control group. Furthermore, mitochondria energized with either succinate/glutamate or succinate/malate showed increased ROS production and ΔΨ in the heat-stressed group compared with mitochondria from the control group. These results suggest that succinate oxidation could play an important role in the heat stress-induced overproduction of mitochondrial ROS in skeletal muscle. In agreement with the notion of a decrease in avUCP expression in response to heat stress, proton leak, which was likely mediated by UCP (that part which is GDP-inhibited and arachidonic acid-sensitive), was reduced in the heat-exposed group. We suggest that the acute heat stress-induced overproduction of mitochondrial ROS may depend on ΔΨ, which may in turn result not only from increased substrate oxidation but also from a decrease in the mitochondrial avUCP content.

Plasma heat shock protein 72 as a biomarker of sarcopenia in elderly people

Sarcopenia is a geriatric syndrome in which there is a decrease of muscle mass and strength with aging. In age-related loss of muscle strength, there are numerous observations supporting the assertion that neural factors mediate muscle strength. A possible contributing cause may be that aging changes systemic extracellular heat shock protein (eHsp)72 activity. The present study was designed to assess the plasma levels of eHsp72 in elderly people and to investigate its potential interaction with components of sarcopenia. A total of 665 men and women participated in an official medical health examination and an integrated health examination, including psychological and physical fitness tests. Blood samples were assayed for levels of plasma Hsp72, serum C-reactive protein, interleukin 6, tumor necrosis factor α, and regular biomedical parameters. We found that higher Hsp72 in plasma is associated with lower muscle mass, weaker grip strength, and slower walking speed, and may be a potential biomarker of sarcopenia in elderly people. This finding was supported by other results in the present study: (1) older age and shrinking body and lower hemoglobin levels, all of which characterize sarcopenia, were related to higher eHsp72 tertiles and (2) the ORs of the highest tertile of eHsp72 for the lowest tertiles of muscle mass, grip strength, and walking speed were 2.7, 2.6, and 1.8, respectively. These ORs were independent of age, sex, and the incidence of related diseases. Our results would reveal that eHsp72 in plasma is linked to sarcopenia factors and is a potential biomarker or predictor of sarcopenia.

Cellular stress response pathways and ageing: intricate molecular relationships

Ageing is driven by the inexorable and stochastic accumulation of damage in biomolecules vital for proper cellular function. Although this process is fundamentally haphazard and uncontrollable, senescent decline and ageing is broadly influenced by genetic and extrinsic factors. Numerous gene mutations and treatments have been shown to extend the lifespan of diverse organisms ranging from the unicellular Saccharomyces cerevisiae to primates. It is becoming increasingly apparent that most such interventions ultimately interface with cellular stress response mechanisms, suggesting that longevity is intimately related to the ability of the organism to effectively cope with both intrinsic and extrinsic stress. Here, we survey the molecular mechanisms that link ageing to main stress response pathways, and mediate age-related changes in the effectiveness of the response to stress. We also discuss how each pathway contributes to modulate the ageing process. A better understanding of the dynamics and reciprocal interplay between stress responses and ageing is critical for the development of novel therapeutic strategies that exploit endogenous stress combat pathways against age-associated pathologies.

Heat shock proteins modulate keloid formation

OBJECTIVE

Heat shock proteins (HSPs) modulate the intensity of the inflammatory and synthetic response to stress in wound healing. Induction of HSPs at the site of wounds improves healing by acting as a molecular chaperone. However, the role of HSPs may augment the inflammatory response, leading to an uncontrolled synthetic process. Propensity for keloid development involves genetic predisposition, physical factors, and an aggressive inflammatory response. The aim of this study is to demonstrate the differential expressions of HSPs in keloid and normal tissues.

METHODS

Twenty-five keloid and adjacent normal tissue samples were removed from 24 patients who were between 16 and 45 years of age. Western blot, enzyme-linked immunosorbent assay, and immunofluorescence studies were performed to examine hsp27, hsp47, hsp60, hsp70, and hsp90 levels in keloid and normal tissue.

RESULTS

Our results demonstrated a significant overexpression of hsp27, hsp47, and hsp70 in keloid tissue compared to that of normal tissue. Statistical analysis using the Student t test revealed a significant difference between these 2 groups (P < .01), while the expression of hsp60 and hsp90 were not significantly different between the keloid and normal tissue samples.

CONCLUSION

The overexpression of HSPs indicates that both a proliferative (hsp70) and a matrix synthesis (hsp47, hsp27) component are present in keloid tissue. From this point of view, it is probable that HSPs play a pivotal role in keloid formation. Unveiling HSP-keloid interactions may allow us to manipulate the inflammatory and proliferative phases of wound healing with the potential to control keloid formation.

Maximal heat dissipation capacity and hyperthermia risk: neglected key factors in the ecology of endotherms

1. The role of energy in ecological processes has hitherto been considered primarily from the standpoint that energy supply is limited. That is, traditional resource-based ecological and evolutionary theories and the recent 'metabolic theory of ecology' (MTE) all assume that energetic constraints operate on the supply side of the energy balance equation. 2. For endothermic animals, we provide evidence suggesting that an upper boundary on total energy expenditure is imposed by the maximal capacity to dissipate body heat and therefore avoid the detrimental consequences of hyperthermia--the heat dissipation limit (HDL) theory. We contend that the HDL is a major constraint operating on the expenditure side of the energy balance equation, and that processes that generate heat compete and trade-off within a total boundary defined by heat dissipation capacity, rather than competing for limited energy supply. 3. The HDL theory predicts that daily energy expenditure should scale in relation to body mass (M(b)) with an exponent of about 0.63. This contrasts the prediction of the MTE of an exponent of 0.75. 4. We compiled empirical data on field metabolic rate (FMR) measured by the doubly-labelled water method, and found that they scale to M(b) with exponents of 0.647 in mammals and 0.658 in birds, not significantly different from the HDL prediction (P > 0.05) but lower than predicted by the MTE (P < 0.001). The same statistical result was obtained using phylogenetically independent contrasts analysis. Quantitative predictions of the model matched the empirical data for both mammals and birds. There was no indication of curvature in the relationship between Log(e) FMR and Log(e)M(b). 5. Together, these data provide strong support for the HDL theory and allow us to reject the MTE, at least when applied to endothermic animals. 6. The HDL theory provides a novel conceptual framework that demands a reframing of our views of the interplay between energy and the environment in endothermic animals, and provides many new interpretations of ecological and evolutionary phenomena.

Colocalization of MnSOD expression in response to oxidative stress

The loss of manganese superoxide dismutase function has been associated with increased incidence of Barrett's esophagus and esophageal adenocarcinoma. In previous studies, we have demonstrated that loss of MnSOD resulted in severe esophageal damage by both endogenous and exogenous bile. However, the alterative manner of MnSOD in esophageal epithelium is largely unknown. In this study, we investigated the expression and localization of MnSOD in response to the exposure to bile salts in an esophageal epithelial cell line. Het-1A cells were seeded at 5 x 10(5) and 10(7) and incubated with taurocholate, cholate, glycocholate, deoxycholate, and the mixture of these bile salts. Mitochondria and cytoplasma were separated, and the expression and localization of MnSOD was determined by Western blot and immunocytochemical assay. Proliferation rates were strongly inhibited in the groups with taurocholate and bile salts mixture at 4 h, with 0.367 +/- 0.042 and 0.396 +/- 0.046, respectively, compared to 0.684 +/- 0.054 in untreated groups (P < 0.05). An increased apoptotic rate compared to untreated group (3.65 +/- 0.59) were significantly increased in taurocholate group and in bile salts mixture group were 33.62 +/- 10.25 and 31.52 +/- 8.97 at 4 h, respectively (P < 0.05). The protein level of MnSOD in mitochondria was increased at 4 h, but with a decreased enzymatic activity after bile salts treatment. Cytoplasmic MnSOD was detected in the cells with bile salts treatment. Immunocytochemical staining demonstrated that esophageal epithelial cell underwent morphological alteration and MnSOD relocalization after bile salts treatment. This is the first study to demonstrate cellular cytosolic MnSOD expression and that this relocalization to the cytosol is a cause for decreased MnSOD enzymatic activity. This suggests that bile salts may contribute to the dysfunction of mitochondria, by enzymatically inhibiting of MnSOD localization and thus activation in the mitochondria.

Liver apoptosis is age dependent and is reduced by activation of peroxisome proliferator-activated receptor-gamma in hemorrhagic shock

A clinical observation in pediatric and adult intensive care units is that the incidence of multiple organ failure in pediatric trauma victims is lower than in adult patients. However, the molecular mechanisms are not yet defined. Recent experimental studies have shown that the nuclear peroxisome proliferator-activated receptor-gamma (PPARgamma) modulates the inflammatory process. In this study, we hypothesized that severity of liver injury may be age dependent and PPARgamma activation may provide beneficial effects. Hemorrhagic shock was induced in anesthetized young (3-5 mo old) and mature male Wistar rats (11-13 mo old) by withdrawing blood to a mean arterial blood pressure of 50 mmHg. After 3 h, rats were rapidly resuscitated with shed blood. Animals were euthanized 3 h after resuscitation. In mature rats, liver injury appeared more pronounced compared with young rats and was characterized by marked hepatocyte apoptosis, extravasation of erythrocytes, and accumulation of neutrophils. The ratio between the antiapoptotic protein Bcl-2 and the proapoptotic protein BAX was lower, whereas activity of caspase-3, the executioner of apoptosis, was higher in liver of mature rats compared with young rats. Plasma alanine aminotransferase levels were not different between the two age groups. This heightened liver apoptosis was associated with a significant downregulation of PPARgamma DNA binding in mature rats compared with young rats. Treatment with the PPARgamma ligand ciglitazone significantly reduced liver apoptosis in mature rats. Our data suggest that liver injury after severe hemorrhage is age dependent and PPARgamma activation is a novel hepatoprotective mechanism.