The effect of aging on the chaperone concentrations in the hepatic, endoplasmic reticulum of male rats: the possible role of protein misfolding due to the loss of chaperones in the decline in physiological function seen with age

ER-phagy drives age-onset remodeling of endoplasmic reticulum structure-function and lifespan

The endoplasmic reticulum (ER) comprises an array of structurally distinct subdomains, each with characteristic functions. While altered ER-associated processes are linked to age-onset pathogenesis, whether shifts in ER morphology underlie these functional changes is unclear. We report that ER remodeling is a conserved feature of the aging process in models ranging from yeast to C. elegans and mammals. Focusing on C. elegans as an exemplar of metazoan aging, we find that as animals age, ER mass declines in virtually all tissues and ER morphology shifts from rough sheets to tubular ER. The accompanying large-scale shifts in proteomic composition correspond to the ER turning from protein synthesis to lipid metabolism. To drive this substantial remodeling, ER-phagy is activated early in adulthood, promoting turnover of rough ER in response to rises in luminal protein-folding burden and reduced global protein synthesis. Surprisingly, ER remodeling is a pro-active and protective response during aging, as ER-phagy impairment limits lifespan in yeast and diverse lifespan-extending paradigms promote profound remodeling of ER morphology even in young animals. Altogether our results reveal ER-phagy and ER morphological dynamics as pronounced, underappreciated mechanisms of both normal aging and enhanced longevity.

Implications of endoplasmic reticulum stress and autophagy in aging and cardiovascular diseases

The average lifespan of humans has been increasing, resulting in a rapidly rising percentage of older individuals and high morbidity of aging-associated diseases, especially cardiovascular diseases (CVDs). Diverse intracellular and extracellular factors that interrupt homeostatic functions in the endoplasmic reticulum (ER) induce ER stress. Cells employ a dynamic signaling pathway of unfolded protein response (UPR) to buffer ER stress. Recent studies have demonstrated that ER stress triggers various cellular processes associated with aging and many aging-associated diseases, including CVDs. Autophagy is a conserved process involving lysosomal degradation and recycling of cytoplasmic components, proteins, organelles, and pathogens that invade the cytoplasm. Autophagy is vital for combating the adverse influence of aging on the heart. The present report summarizes recent studies on the mechanism of ER stress and autophagy and their overlap in aging and on CVD pathogenesis in the context of aging. It also discusses possible therapeutic interventions targeting ER stress and autophagy that might delay aging and prevent or treat CVDs.

Transcriptional drift in aging cells: A global decontroller

As cells age, they undergo a remarkable global change: In transcriptional drift, hundreds of genes become overexpressed while hundreds of others become underexpressed. Using archetype modeling and Gene Ontology analysis on data from aging Caenorhabditis elegans worms, we find that the up-regulated genes code for sensory proteins upstream of stress responses and down-regulated genes are growth- and metabolism-related. We observe similar trends within human fibroblasts, suggesting that this process is conserved in higher organisms. We propose a simple mechanistic model for how such global coordination of multiprotein expression levels may be achieved by the binding of a single factor that concentrates with age in C. elegans. A key implication is that a cell's own responses are part of its aging process, so unlike wear-and-tear processes, intervention might be able to modulate these effects.

Crosstalk between protein misfolding and endoplasmic reticulum stress during ageing and their role in age-related disorders

Maintaining the proteome is crucial to retaining cell functionality and response to multiple intrinsic and extrinsic stressors. Protein misfolding increased the endoplasmic reticulum (ER) stress and activated the adaptive unfolded protein response (UPR) to restore cell homeostasis. Apoptosis occurs when ER stress is prolonged or the adaptive response fails. In healthy young cells, the ratio of protein folding machinery to quantities of misfolded proteins is balanced under normal circumstances. However, the age-related deterioration of the complex systems for handling protein misfolding is accompanied by ageing-related disruption of protein homeostasis, which results in the build-up of misfolded and aggregated proteins. This ultimately results in decreased cell viability and forms the basis of common age-related diseases called protein misfolding diseases. Proteins or protein fragments convert from their ordinarily soluble forms to insoluble fibrils or plaques in many of these disorders, which build up in various organs such as the liver, brain, or spleen. Alzheimer's, Parkinson's, type II diabetes, and cancer are diseases in this group commonly manifest in later life. Thus, protein misfolding and its prevention by chaperones and different degradation paths are becoming understood from molecular perspectives. Proteodynamics information will likely affect future interventional techniques to combat cellular stress and support healthy ageing by avoiding and treating protein conformational disorders. This review provides an overview of the diverse proteostasis machinery, protein misfolding, and ER stress involvement, which activates the UPR sensors. Here, we will discuss the crosstalk between protein misfolding and ER stress and their role in developing age-related diseases.

Transcriptional drift in aging cells: A global de-controller

As cells age, they undergo a remarkable global change: In transcriptional drift, hundreds of genes become overexpressed while hundreds of others become underexpressed. Using archetype modeling and Gene Ontology analysis on data from aging Caenorhabditis elegans worms, we find that the upregulated genes code for sensory proteins upstream of stress responses and downregulated genes are growth- and metabolism-related. We propose a simple mechanistic model for how such global coordination of multi-protein expression levels may be achieved by the binding of a single ligand that concentrates with age. A key implication is that a cell's own responses are part of its aging process, so unlike for wear-and-tear processes, intervention might be able to modulate these effects.

PDIA3 Expression Is Altered in the Limbic Brain Regions of Triple-Transgenic Mouse Model of Alzheimer's Disease

In the present study, we used a mouse model of Alzheimer's disease (AD) (3×Tg-AD mice) to longitudinally analyse the expression level of PDIA3, a protein disulfide isomerase and endoplasmic reticulum (ER) chaperone, in selected brain limbic areas strongly affected by AD-pathology (amygdala, entorhinal cortex, dorsal and ventral hippocampus). Our results suggest that, while in Non-Tg mice PDIA3 levels gradually reduce with aging in all brain regions analyzed, 3×Tg-AD mice showed an age-dependent increase in PDIA3 levels in the amygdala, entorhinal cortex, and ventral hippocampus. A significant reduction of PDIA3 was observed in 3×Tg-AD mice already at 6 months of age, as compared to age-matched Non-Tg mice. A comparative immunohistochemistry analysis performed on 3×Tg-AD mice at 6 (mild AD-like pathology) and 18 (severe AD-like pathology) months of age showed a direct correlation between the cellular level of Aβ and PDIA3 proteins in all the brain regions analysed, even if with different magnitudes. Additionally, an immunohistochemistry analysis showed the presence of PDIA3 in all post-mitotic neurons and astrocytes. Overall, altered PDIA3 levels appear to be age- and/or pathology-dependent, corroborating the ER chaperone's involvement in AD pathology, and supporting the PDIA3 protein as a potential novel therapeutic target for the treatment of AD.

Progress in biophysics and molecular biology proteostasis impairment and ALS

Amyotrophic lateral sclerosis (ALS) is a rapidly progressive and fatal neurodegenerative disease that results from the loss of both upper and lower motor neurons. It is the most common motor neuron disease and currently has no effective treatment. There is mounting evidence to suggest that disturbances in proteostasis play a significant role in ALS pathogenesis. Proteostasis is the maintenance of the proteome at the right level, conformation and location to allow a cell to perform its intended function. In this review, we present a thorough synthesis of the literature that provides evidence that genetic mutations associated with ALS cause imbalance to a proteome that is vulnerable to such pressure due to its metastable nature. We propose that the mechanism underlying motor neuron death caused by defects in mRNA metabolism and protein degradation pathways converges on proteostasis dysfunction. We propose that the proteostasis network may provide an effective target for therapeutic development in ALS.

Factors That Contribute to hIAPP Amyloidosis in Type 2 Diabetes Mellitus

Cases of Type 2 Diabetes Mellitus (T2DM) are increasing at an alarming rate due to the rise in obesity, sedentary lifestyles, glucose-rich diets and other factors. Numerous studies have increasingly illustrated the pivotal role that human islet amyloid polypeptide (hIAPP) plays in the pathology of T2DM through damage and subsequent loss of pancreatic β-cell mass. HIAPP can misfold and form amyloid fibrils which are preceded by pre-fibrillar oligomers and monomers, all of which have been linked, to a certain extent, to β-cell cytotoxicity through a range of proposed mechanisms. This review provides an up-to-date summary of recent progress in the field, highlighting factors that contribute to hIAPP misfolding and aggregation such as hIAPP protein concentration, cell stress, molecular chaperones, the immune system response and cross-seeding with other amyloidogenic proteins. Understanding the structure of hIAPP and how these factors affect amyloid formation will help us better understand how hIAPP misfolds and aggregates and, importantly, help identify potential therapeutic targets for inhibiting amyloidosis so alternate and more effective treatments for T2DM can be developed.

The Aging Liver: Redox Biology and Liver Regeneration

Significance: During aging, excessive production of reactive species in the liver leads to redox imbalance with consequent oxidative damage and impaired organ homeostasis. Nevertheless, slight amounts of reactive species may modulate several transcription factors, acting as second messengers and regulating specific signaling pathways. These redox-dependent alterations may impact the age-associated decline in liver regeneration. Recent Advances: In the last few decades, relevant findings related to redox alterations in the aging liver were investigated. Consistently, recent research broadened understanding of redox modifications and signaling related to liver regeneration. Other than reporting the effect of oxidative stress, epigenetic and post-translational modifications, as well as modulation of specific redox-sensitive cellular signaling, were described. Among them, the present review focuses on Wnt/β-catenin, the nuclear factor (erythroid-derived 2)-like 2 (NRF2), members of the Forkhead box O (FoxO) family, and the p53 tumor suppressor. Critical Issues: Even though alteration in redox homeostasis occurs both in aging and in impaired liver regeneration, the associative mechanisms are not clearly defined. Of note, antioxidants are not effective in slowing hepatic senescence, and do not clearly improve liver repopulation after hepatectomy or transplant in humans. Future Directions: Further investigations are needed to define mutual redox-dependent molecular pathways involved both in aging and in the decline of liver regeneration. Preclinical studies aimed at the characterization of these pathways would define possible therapeutic targets for human trials. Antioxid. Redox Signal. 35, 832-847.

Increased CD47 and MHC Class I Inhibitory Signals Expression in Senescent CD1 Primary Mouse Lung Fibroblasts

Cellular senescence is more than a proliferative arrest in response to various stimuli. Senescent cells (SC) participate in several physiological processes, and their adequate removal is essential to maintain tissue and organism homeostasis. However, SC accumulation in aging and age-related diseases alters the tissue microenvironment leading to deterioration. The immune system clears the SC, but the specific scenarios and mechanisms related to recognizing and eliminating them are unknown. Hence, we aimed to evaluate the existence of three regulatory signals of phagocytic function, CD47, major histocompatibility complex class I (MHC-I), and calreticulin, present in the membrane of SC. Therefore, primary fibroblasts were isolated from CD1 female mice lungs, and stress-induced premature senescence (SIPS) was induced with hydrogen peroxide. Replicative senescence (RS) was used as a second senescent model. Our results revealed a considerable increment of CD47 and MHC-I in RS and SIPS fibroblasts. At the same time, no significant changes were found in calreticulin, suggesting that those signals might be associated with evading immune system recognition and thus averting senescent cells clearance.

Exploring ER stress response in cellular aging and neuroinflammation in Alzheimer's disease

One evident hallmark of Alzheimer's disease (AD) is the irregular accumulation of proteins due to changes in proteostasis involving endoplasmic reticulum (ER) stress. To alleviate ER stress and reinstate proteostasis, cells undergo an integrated signaling cascade called the unfolded protein response (UPR) that reduces the number of misfolded proteins and inhibits abnormal protein accumulation. Aging is associated with changes in the expression of ER chaperones and folding enzymes, leading to the impairment of proteostasis, and accumulation of misfolded proteins. The disrupted initiation of UPR prevents the elimination of unfolded proteins, leading to ER stress. In AD, the accumulation of misfolded proteins caused by sustained cellular stress leads to neurodegeneration and neuronal death. Current research has revealed that ER stress can trigger an inflammatory response through diverse transducers of UPR. Although the involvement of a neuroinflammatory component in AD has been documented for decades, whether it is a contributing factor or part of the neurodegenerative events is so far unknown. Besides, a feedback loop occurs between neuroinflammation and ER stress, which is strongly associated with neurodegenerative processes in AD. In this review, we focus on the current research on ER stress and UPR in cellular aging and neuroinflammatory processes, leading to memory impairment and synapse dysfunction in AD.

Synergistic effects of brain injury and aging: common mechanisms of proteostatic dysfunction

The aftermath of TBI is associated with an acute stress response and the accumulation of insoluble protein aggregates. Even after the symptoms of TBI are resolved, insidious molecular processes continue to develop, which often ultimately result in the development of age-associated neurodegenerative disorders. The precise molecular cascades that drive unhealthy brain aging are still largely unknown. In this review, we discuss proteostatic dysfunction as a converging mechanism contributing to accelerated brain aging after TBI. We examine evidence from human tissue and in vivo animal models, spanning both the aging and injury contexts. We conclude that TBI has a sustained debilitating effect on the proteostatic machinery, which may contribute to the accelerated pathological and cognitive hallmarks of aging that are observed following injury.

Proteostasis Dysfunction in Aged Mammalian Cells. The Stressful Role of Inflammation

Aging is a biological and multifactorial process characterized by a progressive and irreversible deterioration of the physiological functions leading to a progressive increase in morbidity. In the next decades, the world population is expected to reach ten billion, and globally, elderly people over 80 are projected to triple in 2050. Consequently, it is also expected an increase in the incidence of age-related pathologies such as cancer, diabetes, or neurodegenerative disorders. Disturbance of cellular protein homeostasis (proteostasis) is a hallmark of normal aging that increases cell vulnerability and might be involved in the etiology of several age-related diseases. This review will focus on the molecular alterations occurring during normal aging in the most relevant protein quality control systems such as molecular chaperones, the UPS, and the ALS. Also, alterations in their functional cooperation will be analyzed. Finally, the role of inflammation, as a synergistic negative factor of the protein quality control systems during normal aging, will also be addressed. A better comprehension of the age-dependent modifications affecting the cellular proteostasis, as well as the knowledge of the mechanisms underlying these alterations, might be very helpful to identify relevant risk factors that could be responsible for or contribute to cell deterioration, a fundamental question still pending in biomedicine.

Protective effects of saponins from Panax japonicus on neurons of the colon myenteric plexus in aging rats through reduction of α-synuclein through endoplasmic reticulum stress

AIM

The enteric nervous system degenerates gradually with age, and α-synuclein (α-syn) is a suitable marker of enteric nervous system degeneration, which is intimately related with endoplasmic reticulum stress and unfolded protein response (UPR^ER ). Saponins from Panax japonicus (SPJ) have obvious protective effects on neurons in several degenerative disease models. Here, the study was designed to investigate whether SPJ could reverse the neuron degeneration through regulating the UPR^ER in the colon myenteric plexus of aging rats.

METHODS

Aging rats had been treated with SPJ for 6 months since they were aged 18 months. Then, the colon samples were collected and neuron morphology in the myenteric plexus was observed. Immunohistochemistry staining was used to detect the expressions of NeuN, α-syn, GRP78 and three different UPR^ER branches. Double immunofluorescence was used to determine the co-localization of α-syn and NeuN, GRP78 and NeuN.

RESULTS

Neurons degenerated in the colon myenteric plexus of aging rats, but co-localization of α-syn and NeuN increased. In addition, both the expressions of GRP78 and three UPR^ER branch signaling pathway proteins decreased in the colon myenteric plexus of aging rats. Treatment of SPJ almost alleviated the above effects in aging rats, except for ATF6.

CONCLUSIONS

SPJ could reverse the neuron loss caused by accumulation of α-syn in the myenteric plexus of colon in aging rats, which is potentially associated with increased GRP78 and most URP^ER changes. Geriatr Gerontol Int 2021; 21: 85-93.

Evaluating endoplasmic reticulum stress and unfolded protein response through the lens of ecology and evolution

Considerable progress has been made in understanding the physiological basis for variation in the life-history patterns of animals, particularly with regard to the roles of oxidative stress and hormonal regulation. However, an underappreciated and understudied area that could play a role in mediating inter- and intraspecific variation of life history is endoplasmic reticulum (ER) stress, and the resulting unfolded protein response (UPR^ER ). ER stress response and the UPR^ER maintain proteostasis in cells by reducing the intracellular load of secretory proteins and enhancing protein folding capacity or initiating apoptosis in cells that cannot recover. Proper modulation of the ER stress response and execution of the UPR^ER allow animals to respond to intracellular and extracellular stressors and adapt to constantly changing environments. ER stress responses are heritable and there is considerable individual variation in UPR^ER phenotype in animals, suggesting that ER stress and UPR^ER phenotype can be subjected to natural selection. The variation in UPR^ER phenotype presumably reflects the way animals respond to ER stress and environmental challenges. Most of what we know about ER stress and the UPR^ER in animals has either come from biomedical studies using cell culture or from experiments involving conventional laboratory or agriculturally important models that exhibit limited genetic diversity. Furthermore, these studies involve the assessment of experimentally induced qualitative changes in gene expression as opposed to the quantitative variations that occur in naturally existing populations. Almost all of these studies were conducted in controlled settings that are often quite different from the conditions animals experience in nature. Herein, we review studies that investigated ER stress and the UPR^ER in relation to key life-history traits including growth and development, reproduction, bioenergetics and physical performance, and ageing and senescence. We then ask if these studies can inform us about the role of ER stress and the UPR^ER in mediating the aforementioned life-history traits in free-living animals. We propose that there is a need to conduct experiments pertaining to ER stress and the UPR^ER in ecologically relevant settings, to characterize variation in ER stress and the UPR^ER in free-living animals, and to relate the observed variation to key life-history traits. We urge others to integrate multiple physiological systems and investigate how interactions between ER stress and oxidative stress shape life-history trade-offs in free-living animals.

Liver osteopontin is required to prevent the progression of age-related nonalcoholic fatty liver disease

Osteopontin (OPN), a senescence-associated secretory phenotype factor, is increased in patients with nonalcoholic fatty liver disease (NAFLD). Cellular senescence has been associated with age-dependent hepatosteatosis. Thus, we investigated the role of OPN in the age-related hepatosteatosis. For this, human serum samples, animal models of aging, and cell lines in which senescence was induced were used. Metabolic fluxes, lipid, and protein concentration were determined. Among individuals with a normal liver, we observed a positive correlation between serum OPN levels and increasing age. This correlation with age, however, was absent in patients with NAFLD. In wild-type (WT) mice, serum and liver OPN were increased at 10 months old (m) along with liver p53 levels and remained elevated at 20m. Markers of liver senescence increased in association with synthesis and concentration of triglycerides (TG) in 10m OPN-deficient (KO) hepatocytes when compared to WT hepatocytes. These changes in senescence and lipid metabolism in 10m OPN-KO mice liver were associated with the decrease of 78 kDa glucose-regulated protein (GRP78), induction of ER stress, and the increase in fatty acid synthase and CD36 levels. OPN deficiency in senescent cells also diminished GRP78, the accumulation of intracellular TG, and the increase in CD36 levels. In 20m mice, OPN loss led to increased liver fibrosis. Finally, we showed that OPN expression in vitro and in vivo was regulated by p53. In conclusion, OPN deficiency leads to earlier cellular senescence, ER stress, and TG accumulation during aging. The p53-OPN axis is required to inhibit the onset of age-related hepatosteatosis.

The ageing lung under stress

Healthy ageing of the lung involves structural changes but also numerous cell-intrinsic and cell-extrinsic alterations. Among them are the age-related decline in central cellular quality control mechanisms such as redox and protein homeostasis. In this review, we would like to provide a conceptual framework of how impaired stress responses in the ageing lung, as exemplified by dysfunctional redox and protein homeostasis, may contribute to onset and progression of COPD and idiopathic pulmonary fibrosis (IPF). We propose that age-related imbalanced redox and protein homeostasis acts, amongst others (e.g.cellular senescence), as a “first hit” that challenges the adaptive stress-response pathways of the cell, increases the level of oxidative stress and renders the lung susceptible to subsequent injury and disease. In both COPD and IPF, additional environmental insults such as smoking, air pollution and/or infections then serve as “second hits” which contribute to persistently elevated oxidative stress that overwhelms the already weakened adaptive defence and repair pathways in the elderly towards non-adaptive, irremediable stress thereby promoting development and progression of respiratory diseases. COPD and IPF are thus distinct horns of the same devil, “lung ageing”.

Endothelial calreticulin deletion impairs endothelial function in aged mice

Discrete calcium signals within the vascular endothelium decrease with age and contribute to impaired endothelial-dependent vasodilation. Calreticulin (Calr), a multifunctional calcium binding protein and endoplasmic reticulum (ER) chaperone, can mediate calcium signals and vascular function within the endothelial cells (ECs) of small resistance arteries. We found Calr protein expression significantly decreases with age in mesenteric arteries and examined the functional role of EC Calr in vasodilation and calcium mobilization in the context of aging. Third-order mesenteric arteries from mice with or without EC Calr knockdown were examined for calcium signals and constriction to phenylephrine (PE) or vasodilation to carbachol (CCh) after 75 wk of age. PE constriction in aged mice with or without EC Calr was unchanged. However, calcium signals and vasodilation to endothelial-dependent agonist carbachol were significantly impaired in aged EC Calr knockdown mice. Ex vivo incubation of arteries with the ER stress inhibitor tauroursodeoxycholic acid (TUDCA) significantly improved vasodilation in mice lacking EC Calr. Our data suggests diminished vascular Calr expression with age can contribute to the detrimental effects of aging on endothelial calcium regulation and vasodilation.NEW & NOTEWORTHY Calreticulin (Calr) is responsible for key physiological processes in endoplasmic reticulum, especially in aging tissue. In particular, endothelial Calr is crucial to vascular function. In this study, we deleted Calr from the endothelium and aged the mice up to 75 wk to examine changes in vascular function. We found two key differences: 1) calcium events in endothelium were severely diminished after muscarinic stimulation, which 2) corresponded with a dramatic decrease in muscarinic vasodilation. Remarkably, we were able to rescue the effect of Calr deletion on endothelial-dependent vasodilatory function using tauroursodeoxycholic acid (TUDCA), an inhibitor of endoplasmic reticulum stress that is currently in clinical trials.

Profiling the Expression of Endoplasmic Reticulum Stress Associated Heat Shock Proteins in Animal Epilepsy Models

Unfolded protein response is a signaling cascade triggered by misfolded proteins in the endoplasmic reticulum. Heat shock protein H4 (HSPH4) and A5 (HSPA5) are two chaperoning proteins present within the organelle, which target misfolded peptides during prolonged stress conditions. Epileptogenic insults and epileptic seizures are a notable source of stress on cells. To investigate whether they influence expression of these chaperones, we performed immunohistochemical stainings in brains from rats that experienced a status epilepticus (SE) as a trigger of epileptogenesis and from canine epilepsy patients. Quantification of HSPA5 and HSPH4 revealed alterations in hippocampus and parahippocampal cortex. In rats, SE induced up-regulation of HSPA5 in the piriform cortex and down-regulation of HSPA5 and HSPH4 in the hippocampus. Regionally restricted increases in expression of the two proteins has been observed in the chronic phase with spontaneous recurrent seizures. Confocal microscopy revealed a predominant expression of both proteins in neurons, no expression in microglia and circumscribed expression in astroglia. In canine patients, only up-regulation of HSPH4 expression was observed in Cornu Ammonis 1 region in animals diagnosed with structural epilepsy. This characterization of HSPA5 and HSPH4 expression provided extensive information regarding spatial and temporal alterations of the two proteins during SE-induced epileptogenesis and following epilepsy manifestations. Up-regulation of both proteins implies stress exerted on ER during these disease phases. Taken together suggest a differential impact of epileptogenesis on HSPA5 and HSPH4 expression and indicate them as a possible target for pharmacological modulation of unfolded protein response.

GRP78/BIP/HSPA5 as a Therapeutic Target in Models of Parkinson's Disease: A Mini Review

Parkinson's disease (PD) is a common neurodegenerative disorder characterized by selective loss of dopamine neurons in the substantia nigra pars compacta of the midbrain. Reports from postmortem studies in the human PD brain, and experimental PD models reveal that endoplasmic reticulum (ER) stress is implicated in the pathogenesis of PD. In times of stress, the unfolded or misfolded proteins overload the folding capacity of the ER to induce a condition generally known as ER stress. During ER stress, cells activate the unfolded protein response (UPR) to handle increasing amounts of abnormal proteins, and recent evidence has demonstrated the activation of the ER chaperone GRP78/BiP (78 kDa glucose-regulated protein/binding immunoglobulin protein), which is important for proper folding of newly synthesized and partly folded proteins to maintain protein homeostasis. Although the activation of this protein is essential for the initiation of the UPR in PD, there are inconsistent reports on its expression in various PD models. Consequently, this review article aims to summarize current knowledge on neuroprotective agents targeting the expression of GRP78/BiP in the regulation of ER stress in experimental PD models.

Endoplasmic Reticulum Unfolded Protein Response, Aging and Exercise: An Update

The endoplasmic reticulum (ER) is a dynamic and multifunctional organelle responsible for protein biosynthesis, folding, assembly and modifications. Loss of protein folding regulation, which leads to unfolded or misfolded proteins accumulation inside the ER lumen, drives ER stress (ERS) and unfolded protein response (UPR) activation. During aging, there is a decline in the ability of the cell to handle protein folding, accumulation and aggregation, and the function of UPR is compromised. There is a progressive failure of the chaperoning systems and a decline in many of its components, so that the UPR activation cannot rescue the ERS. Physical activity has been proposed as a powerful tool against aged-related diseases, which are linked to ERS. Interventional studies have demonstrated that regular exercise is able to decrease oxidative stress and inflammation and reverse mitochondrial and ER dysfunctions. Exercise-induced metabolic stress could activate the UPR since muscle contraction is directly involved in its activation, mediating exercise-induced adaptation responses. In fact, regular moderate-intensity exercise-induced ERS acts as a protective mechanism against current and future stressors. However, biological responses vary according to exercise intensity and therefore induce different degrees of ERS and UPR activation. This article reviews the effects of aging and exercise on ERS and UPR, also analyzing possible changes induced by different types of exercise in elderly subjects.

Implications of aging and the endoplasmic reticulum unfolded protein response on the molecular modality of breast cancer

The endoplasmic reticulum (ER) is an important subcellular organelle that is involved in numerous activities required to achieve and maintain functional proteins in addition to its role in the biosynthesis of lipids and as a repository of intracellular Ca²⁺. The inability of the ER to cope with protein folding beyond its capacity causes disturbances that evoke ER stress. Cells possess molecular mechanisms aimed at clearing unwanted cargo from the ER lumen as an adaptive response, but failing to do so navigates the system towards cell death. This systemic approach is called the unfolded protein response. Aging insults cells through various perturbations in homeostasis that involve curtailing ER function by mitigating the expression of its resident chaperones and enzymes. Here the unfolded protein response (UPR) cannot protect the cell due to the weakening of its protective arm, which exacerbates imbalanced homeostasis. Aging predisposed breast malignancy activates the UPR, but tumor cells maneuver the mechanistic details of the UPR, favoring tumorigenesis and thereby eliciting a treacherous condition. Tumor cells exploit UPR pathways via crosstalk involving various signaling cascades that usher tumor cells to immortality. This review aims to present a collection of data that can delineate the missing links of molecular signatures between aging and breast cancer.

PGC-1α in aging and lifelong exercise training-mediated regulation of UPR in mouse liver

Aging is associated with changes in several metabolic pathways affecting liver function including the adaptive unfolded protein response (UPR). On the other hand, exercise training has been shown to exert beneficial effects on metabolism in the liver and exercise training has been reported to affect hepatic UPR. PGC-1α is a transcriptional coactivator involved in exercise training-induced adaptations in skeletal muscle and liver. Therefore, the aim of the present study was to examine the impact of PGC-1α in aging and lifelong exercise training-induced hepatic UPR in mice. Liver was obtained from young (3months old), aged (15months old) and lifelong exercise trained aged wild-type (WT) and whole-body PGC-1α knockout (KO) mice. Hepatic BiP, IRE1α and cleaved ATF6 protein content increased, whereas PERK protein content was reduced with aging indicating both increased and decreased capacity of specific UPR pathways and increased activity of the ATF6 pathway in the liver with aging. Lifelong exercise training prevented the age-associated change in BiP and IRE1α protein, but not cleaved ATF6 protein and resulted in further decreased PERK protein. Taken together, the present study provides evidence that the capacity and activity of the three UPR pathways are differentially regulated in the liver with aging and lifelong exercise training. In addition, PGC-1α does not seem to regulate the activity of hepatic UPR in response to exercise training, but to influence the capacity of the liver to induce UPR in a pathway specific manner.

GRP78 at the Centre of the Stage in Cancer and Neuroprotection

The 78-kDa glucose-regulated protein GRP78, also known as BiP and HSP5a, is a multifunctional protein with activities far beyond its well-known role in the unfolded protein response (UPR) which is activated after endoplasmic reticulum (ER) stress in the cells. Most of these newly discovered activities depend on its position within the cell. GRP78 is located mainly in the ER, but it has also been observed in the cytoplasm, the mitochondria, the nucleus, the plasma membrane, and secreted, although it is dedicated mostly to engage endogenous cytoprotective processes. Hence, GRP78 may control either UPR and macroautophagy or may activated phosphatidylinositol 3-kinase (PI3K)/AKT pro-survival pathways. GRP78 influences how tumor cells survive, proliferate, and develop chemoresistance. In neurodegeneration, endogenous mechanisms of neuroprotection are frequently insufficient or dysregulated. Lessons from tumor biology may give us clues about how boosting endogenous neuroprotective mechanisms in age-related neurodegeneration. Herein, the functions of GRP78 are revealed at the center of the stage of apparently opposite sites of the same coin regarding cytoprotection: neurodegeneration and cancer. The goal is to give a comprehensive and critical review that may serve to guide future experiments to identify interventions that will enhance neuroprotection.

Effects of Prolonged GRP78 Haploinsufficiency on Organ Homeostasis, Behavior, Cancer and Chemotoxic Resistance in Aged Mice

GRP78, a multifunctional protein with potent cytoprotective properties, is an emerging therapeutic target to combat cancer development, progression and drug resistance. The biological consequences of prolonged reduction in expression of this essential chaperone which so far has been studied primarily in young mice, was investigated in older mice, as older individuals are likely to be important recipients of anti-GRP78 therapy. We followed cohorts of Grp78+/+ and Grp78+/- male and female mice up to 2 years of age in three different genetic backgrounds and characterized them with respect to body weight, organ integrity, behavioral and memory performance, cancer, inflammation and chemotoxic response. Our results reveal that body weight, organ development and integrity were not impaired in aged Grp78+/- mice. No significant effect on cancer incidence and inflammation was observed in aging mice. Interestingly, our studies detected some subtle differential trends between the WT and Grp78+/- mice in some test parameters dependent on gender and genetic background. Our studies provide the first evidence that GRP78 haploinsufficiency for up to 2 years of age has no major deleterious effect in rodents of different genetic background, supporting the merit of anti-GRP78 drugs in treatment of cancer and other diseases affecting the elderly.

Impact of age on plasma vaspin concentration in a group of normal Chinese people

PURPOSE

Visceral adipose tissue-derived serine protease inhibitor (vaspin) is an adipocytokine with insulin-sensitizing effects. Accumulating data implied that vaspin represents a compensatory mechanism but it is unknown how vaspin change during ageing. This study was designed to examine the correlation between plasma vaspin and age in a group of normal Chinese people.

METHODS

A total of 191 Chinese volunteers aged 19-80 years were enrolled into four groups based upon age quartiles (19-35, 36-50, 51-65 and 66-80 years). Demographic, anthropometric, metabolic covariates, vaspin and adiponectin were measured. The influence of age on plasma vaspin was analysed using SPSS 13.0.

RESULTS

Vaspin increased with ageing, with mean vaspin levels (ng/mL) of 1.01 ± 2.25, 1.67 ± 2.95, 2.05 ± 3.46 and 2.40 ± 3.06 for those between quartile ages 19-35, 36-50, 51-65 and 66-80 years. When divided into subgroups, vaspin increased with increasing age for both sexes, both insulin resistance and non-insulin resistance subjects and both obese and lean subjects. In univariate analyses, vaspin plasma level positively associated with age (r = 0.215, p = 0.003), adiponectin, insulin, homoeostasis model of assessment for insulin resistance index and waist-hip ratio in the whole population. The correlation between ageing and increasing vaspin remained significant after multivariate adjustments for factors such as sex, body mass index, waist-hip ratio, indices of glucose metabolism, white blood cell, lipid profile and adiponectin. Stepwise multiple regression analysis showed that age contributed 7.6 % on plasma vaspin level.

CONCLUSION

Vaspin level increased with ageing, independent of sex, indices of glucose metabolism, lipid profile and other markers of adiposity.

The human HSP70 family of chaperones: where do we stand?

The 70-kDa heat shock protein (HSP70) family of molecular chaperones represents one of the most ubiquitous classes of chaperones and is highly conserved in all organisms. Members of the HSP70 family control all aspects of cellular proteostasis such as nascent protein chain folding, protein import into organelles, recovering of proteins from aggregation, and assembly of multi-protein complexes. These chaperones augment organismal survival and longevity in the face of proteotoxic stress by enhancing cell viability and facilitating protein damage repair. Extracellular HSP70s have a number of cytoprotective and immunomodulatory functions, the latter either in the context of facilitating the cross-presentation of immunogenic peptides via major histocompatibility complex (MHC) antigens or in the context of acting as "chaperokines" or stimulators of innate immune responses. Studies have linked the expression of HSP70s to several types of carcinoma, with Hsp70 expression being associated with therapeutic resistance, metastasis, and poor clinical outcome. In malignantly transformed cells, HSP70s protect cells from the proteotoxic stress associated with abnormally rapid proliferation, suppress cellular senescence, and confer resistance to stress-induced apoptosis including protection against cytostatic drugs and radiation therapy. All of the cellular activities of HSP70s depend on their adenosine-5'-triphosphate (ATP)-regulated ability to interact with exposed hydrophobic surfaces of proteins. ATP hydrolysis and adenosine diphosphate (ADP)/ATP exchange are key events for substrate binding and Hsp70 release during folding of nascent polypeptides. Several proteins that bind to distinct subdomains of Hsp70 and consequently modulate the activity of the chaperone have been identified as HSP70 co-chaperones. This review focuses on the regulation, function, and relevance of the molecular Hsp70 chaperone machinery to disease and its potential as a therapeutic target.

The Progressive BSSG Rat Model of Parkinson's: Recapitulating Multiple Key Features of the Human Disease

The development of effective neuroprotective therapies for Parkinson's disease (PD) has been severely hindered by the notable lack of an appropriate animal model for preclinical screening. Indeed, most models currently available are either acute in nature or fail to recapitulate all characteristic features of the disease. Here, we present a novel progressive model of PD, with behavioural and cellular features that closely approximate those observed in patients. Chronic exposure to dietary phytosterol glucosides has been found to be neurotoxic. When fed to rats, β-sitosterol β-d-glucoside (BSSG) triggers the progressive development of parkinsonism, with clinical signs and histopathology beginning to appear following cessation of exposure to the neurotoxic insult and continuing to develop over several months. Here, we characterize the progressive nature of this model, its non-motor features, the anatomical spread of synucleinopathy, and response to levodopa administration. In Sprague Dawley rats, chronic BSSG feeding for 4 months triggered the progressive development of a parkinsonian phenotype and pathological events that evolved slowly over time, with neuronal loss beginning only after toxin exposure was terminated. At approximately 3 months following initiation of BSSG exposure, animals displayed the early emergence of an olfactory deficit, in the absence of significant dopaminergic nigral cell loss or locomotor deficits. Locomotor deficits developed gradually over time, initially appearing as locomotor asymmetry and developing into akinesia/bradykinesia, which was reversed by levodopa treatment. Late-stage cognitive impairment was observed in the form of spatial working memory deficits, as assessed by the radial arm maze. In addition to the progressive loss of TH+ cells in the substantia nigra, the appearance of proteinase K-resistant intracellular α-synuclein aggregates was also observed to develop progressively, appearing first in the olfactory bulb, then the striatum, the substantia nigra and, finally, hippocampal and cortical regions. The slowly progressive nature of this model, together with its construct, face and predictive validity, make it ideal for the screening of potential neuroprotective therapies for the treatment of PD.

Impaired unfolded protein response in the degeneration of cochlea cells in a mouse model of age-related hearing loss

Endoplasmic reticulum (ER) stress triggers the unfolded protein response (UPR) to prevent the accumulation of proteins in an aberrant conformation. The UPR can restore homeostasis by upregulating ER chaperones, such as glucose-regulated protein 78kD (GRP78), to refold the incorrectly handled protein, and by degrading the misfolded proteins via the ubiquitin-proteasome and autophagy-lysosome system. ER stress was recently demonstrated to be involved in the pathogenesis of age-related diseases. In this study, we measured the expression levels of GRP78 and ubiquitinated proteins in the cochleae of young C57BL/6 mice and aged mice to assess the capacity of the UPR. The lower expression of GRP78 and the increased number of ubiquitinated proteins observed in the cochleae of aged mice suggested that the capacity of the UPR was impaired and that the cell death pathway was activated. We found a markedly increased expression of the ER-related pro-apoptotic factor C/EBP homologous protein (CHOP) in the cochleae of aged mice, whereas the level of cleaved caspase-12 did not differ between the two groups. In addition, the cleavage of caspase-9, caspase-3 and poly [ADP-ribose] polymerase 1 was significantly increased in the aged cochleae, suggesting the activation of apoptosis in the cochleae resulting from the cross-talk between the ER and mitochondria through CHOP. These results indicated that impaired UPR in the cochleae of aged C57BL/6 mice resulting in ER stress may lead to apoptosis that is dependent on the mitochondrial pathway and that ER stress induced apoptosis may not be mediated by caspase-12.

The loss of glucose-regulated protein 78 (GRP78) during normal aging or from siRNA knockdown augments human alpha-synuclein (α-syn) toxicity to rat nigral neurons

Age-related structural changes and gradual loss of key enzymes significantly affect the ability of the endoplasmic reticulum (ER) to facilitate proper protein folding and maintain homeostasis. In this work, we present several lines of evidence supporting the hypothesis that the age-related decline in expression of the ER chaperone glucose-regulated protein 78 (GRP78) could be related to the development of Parkinson's disease. We first determined that old (24 months) rats exhibit significantly lower levels of GRP78 protein in the nigrostriatal system as compared with young (2 months) animals. Then using recombinant adeno-associate virus-mediated gene transfer, we found that GRP78 downregulation by specific small interfering RNAs (siRNAs) aggravates alpha-synuclein (α-syn) neurotoxicity in nigral dopamine (DA) neurons. Moreover, the degree of chaperone decline corresponds with the severity of neurodegeneration. Additionally, comparative analysis of nigral tissues obtained from old and young rats revealed that aging affects the capacity of nigral DA cells to upregulate endogenous GRP78 protein in response to human α-syn neurotoxicity. Finally, we demonstrated that a sustained increase of GRP78 protein over the course of 9 months protected aging nigral DA neurons in the α-syn-induced rat model of Parkinson's-like neurodegeneration. Our data indicate that the ER chaperone GRP78 may have therapeutic potential for preventing and/or slowing age-related neurodegeneration.

What determines ageing of the transplanted liver?

BACKGROUND

Liver transplantation is used to treat patients with irreversible liver failure from a variety of causes. Long-term survival has been reported, particularly in the paediatric population, with graft survival longer than 20 years now possible. The goal for paediatric liver transplantation is to increase the longevity of grafts to match the normal life expectancy of the child. This paper reviews the literature on the current understanding of ageing of the liver and biomarkers that may predict long-term survival or aid in utilization of organs.

METHODS

Scientific papers published from 1950 to 2013 were sought and extracted from the MEDLINE, PubMed and University of Melbourne databases.

RESULTS

Hepatocytes appear resistant to the ageing process, but are affected by both replicative senescence and stress-related senescence. These processes may be exacerbated by the act of transplantation. The most studied biomarkers are telomeres and SMP-30.

CONCLUSION

There are many factors that play a role in the ageing of the liver. Further studies into biomarkers of ageing and their relationship to the chronological age of the liver are required to aid in predicting long-term graft survival and utilization of organs.

Dehydroepiandrosterone, molecular chaperones and the epigenetics of primate longevity

Dehydroepiandrosterone (DHEA) and dehydroepiandrosterone-sulphate (DHEAS) are the most abundant circulating adrenal steroid hormones. The plasma level of DHEAS correlates with longevity in primates and varies during human development with a maximum in early adulthood and a marked decline during aging. DHEA promotes the expression of molecular chaperones which are housekeeping stress response proteins essential for the processes of folding, translocation, maintenance and repair of proteins, RNA and DNA, as well as for homeostasis, immune response and cancer resistance. The level of chaperone expression correlates with longevity and shows a decline during aging. DHEA-induced promotion of chaperone expression could contribute to the epigenetic evolution of primate longevity.

The amazing ubiquitin-proteasome system: structural components and implication in aging

Proteome quality control (PQC) is critical for the maintenance of cellular functionality and it is assured by the curating activity of the proteostasis network (PN). PN is constituted of several complex protein machines that under conditions of proteome instability aim to, firstly identify, and then, either rescue or degrade nonnative polypeptides. Central to the PN functionality is the ubiquitin-proteasome system (UPS) which is composed from the ubiquitin-conjugating enzymes and the proteasome; the latter is a sophisticated multi-subunit molecular machine that functions in a bimodal way as it degrades both short-lived ubiquitinated normal proteins and nonfunctional polypeptides. UPS is also involved in PQC of the nucleus, the endoplasmic reticulum and the mitochondria and it also interacts with the other main cellular degradation axis, namely the autophagy-lysosome system. UPS functionality is optimum in the young organism but it is gradually compromised during aging resulting in increasing proteotoxic stress; these effects correlate not only with aging but also with most age-related diseases. Herein, we present a synopsis of the UPS components and of their functional alterations during cellular senescence or in vivo aging. We propose that mild UPS activation in the young organism will, likely, promote antiaging effects and/or suppress age-related diseases.

ER Stress Response in Human Cellular Models of Senescence

The aging process is characterized by progressive accumulation of damaged biomolecules in the endoplasmic reticulum, as result of increased oxidative stress accompanying cellular senescence. In agreement, we hypothesized that WI-38 human cellular models of replicative senescence and stress-induced premature senescence (SIPS) induced by hydrogen peroxide (H2O2-SIPS) or copper sulfate (CuSO4-SIPS) would present endoplasmic reticulum chaperoning mechanisms impairment and unfolded protein response activation. Results show that in replicative senescence and CuSO4-SIPS, immunoglobulin binding protein, calnexin, protein disulfide isomerase, and ER oxireductin-1 levels adjust to restore proteostasis and inositol-requiring enzyme-1 (IRE1)-, activating transcription factor 6 (ATF6)-, and pancreatic ER kinase (PERK)-mediated unfolded protein response are activated. However, H2O2-SIPS does not exhibit IRE1 and ATF6 pathways activation but a PERK-mediated upregulation of CCAAT/enhancer-binding protein homologous protein, showing that CuSO4-SIPS mimics better the endoplasmic reticulum molecular events of replicative senescence than H2O2-SIPS. Moreover, unfolded protein response activation is required for both SIPS models induction, because PERK and IRE1 inhibitors decreased senescence-associated beta-galactosidase appearance. In CuSO4-SIPS, the decrease in senescence levels is associated with PERK-driven, but IRE1 independent, cell cycle arrest while in H2O2-SIPS cell proliferation is PERK independent. These results add a step further on the molecular mechanisms that regulate senescence induction; moreover, they validate CuSO4-SIPS model as a useful tool to study cellular stress responses during aging, hoping to postpone age-related health decline.

On the importance of oxidative folding in the evolution of conotoxins: cysteine codon preservation through gene duplication and adaptation

Conotoxin genes are among the most rapidly evolving genes currently known; however, despite the well-established hypervariability of the intercysteine loops, the cysteines demonstrate significant conservation, with a site-specific codon bias for each cysteine in a family of conotoxins. Herein we present a novel rationale behind the codon-level conservation of the cysteines that comprise the disulfide scaffold. We analyze cysteine codon conservation using an internal reference and phylogenetic tools; our results suggest that the established codon conservation can be explained as the result of selective pressures linked to the production efficiency and folding of conotoxins, driving the conservation of cysteine at the amino-acid level. The preservation of cysteine has resulted in maintenance of the ancestral codon in most of the daughter lineages, despite the hypervariability of adjacent residues. We propose that the selective pressures acting on the venom components of cone snails involve an interplay of biosynthetic efficiency, activity at the target receptor and the importance of that activity to effective prey immobilization. Functional redundancy in the venom can thus serve as a buffer for the energy expenditure of venom production.

Endoplasmic reticulum stress in human skeletal muscle: any contribution to sarcopenia?

Skeletal muscle is vital to life as it provides the mechanical power for locomotion, posture and breathing. Beyond these vital functions, skeletal muscle also plays an essential role in the regulation of whole body metabolism, e.g., glucose homeostasis. Although progressive loss of muscle mass with age seems unavoidable, it is critical for older people to keep the highest mass as possible. It is clear that the origin of sarcopenia is multifactorial but, in the present review, it was deliberately chosen to evaluate the likely contribution of one specific cellular stress, namely the endoplasmic reticulum (ER) stress. It is proposed that ER stress can: (1) directly impact muscle mass as one fate of prolonged and unresolved ER stress is cell death and; (2) indirectly create a state of anabolic resistance by inhibiting the mammalian target of rapamycin complex 1 (mTORC1) pathway. With age, many of the key components of the unfolded protein response, such as the chaperones and enzymes, display reduced expression and activity resulting in a dysfunctional ER, accelerating the rate of proteins discarded via the ER-associated degradation. In addition, ER stress can block the mTORC1 pathway which is essential in the response to the anabolic stimulus of nutrients and contractile activity thereby participating to the well-known anabolic resistance state in skeletal muscle during ageing. As exercise increases the expression of several chaperones, it could anticipate or restore the loss of unfolded protein response components with age and thereby reduce the level of ER stress. This hypothesis has not been tested yet but it could be a new mechanism behind the beneficial effects of exercise in the elderly not only for the preservation of muscle mass but also for the regulation of whole body metabolism.

Activation of the unfolded protein response in vascular endothelial cells of nondiabetic obese adults

CONTEXT

Activation of the unfolded protein response (UPR) is emerging as an important molecular signature of cardiometabolic diseases associated with obesity. However, despite the well-established role of the vascular endothelium in obesity-related cardiometabolic dysfunction, it is unclear whether the UPR is activated in endothelial cells of obese adults.

OBJECTIVE

The objective of the study was to determine whether markers of UPR activation are increased in endothelial cells (ECs) of nondiabetic obese adults with impaired endothelial function.

DESIGN, SETTING, AND PARTICIPANTS

Endothelial cells were obtained from antecubital veins of the nondiabetic obese adults [body mass index (BMI) ≥ 30 kg/m(2), n = 12] with impaired endothelial function and from their nonobese peers (BMI < 30 kg/m(2), n = 14).

MAIN OUTCOME VARIABLES

UPR activation via expression (quantitative immunofluorescence) of the proximal UPR sensors, inositol-requiring endoplasmic reticulum (ER)-to-nucleus signaling protein 1 (IRE1), RNA-dependent protein kinase-like ER eukaryotic initiation factor-2α kinase (PERK), and activating transcription factor 6 (ATF6), were the main outcome variables.

RESULTS

IRE1 expression was greater in obese vs nonobese individuals (0.84 ± 0.09 vs 0.47 ± 0.02 IRE1 intensity/human umbilical vein EC (HUVEC) intensity (n = 10/8, P < .01). Obese individuals also had greater EC activation of UPR stress sensors PERK and ATF6, indicated by increased expression of phosphorylated PERK [p-PERK; 0.49 ± 0.05 vs 0.36 ± 0.03, p-PERK (threonine 981) intensity/HUVEC intensity, n = 10 men, 13 women, P < .05] and nuclear localization of ATF6 (0.38 ± 0.05 vs 0.23 ± 0.02, nuclear ATF6 intensity/HUVEC intensity, n = 5 men, 9 women, P < .01), respectively. Stepwise linear regression analysis revealed that indices of body fat (BMI and waist circumference) were the strongest independent predictors of all 3 UPR mediators, explaining between 18% and 59% of the variance in endothelial cell expression of IRE1, p-PERK, and nuclear ATF6 localization.

CONCLUSION

These results provide novel evidence for UPR activation in the endothelial cells of nondiabetic obese adults with vascular endothelial dysfunction.

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.

Cellular and animal models for high-throughput screening of therapeutic agents for the treatment of the diseases of the elderly in general and Alzheimer's disease in particular(†)

It is currently thought that the dementia of Alzheimer's disease is due to the neurotoxicity of the deposits or aggregates of amyloid-β (Aβ) in the extracellular space of the cerebral cortex. This model has been widely criticized because there is a poor correlation between deposits and dementia. Others have questioned whether Aβ is truly neurotoxic. Yet, in spite of these concerns, the search for therapeutic agents has been based on the development of mouse models transfected with mutant genes associated in humans with early onset Alzheimer's disease. A major limitation of these models is that although they exhibit many of the pathological and clinical manifestation of the human disease, the bulk of individuals who develop the dementia of Alzheimer's disease have none of these mutant genes. Furthermore, nine clinical trials of drugs that were effective in transgenic mice failed to show any benefit in patients. Finally, a major unresolved issue with the Aβ model is that since Aβ is produced in everyone, why are deposits only seen in the elderly? This issue must be resolved if we are to understand the etiology of the disease and develop test systems for both diagnosis and drug discovery. Published studies from my laboratory demonstrate that in human cerebrospinal fluid immunoreactive Aβ is only present as a complex with two chaperones, ERp57 and calreticulin and is N-glycosylated. This complex formation is catalyzed by the posttranslational protein processing system of the endoplasmic reticulum (ER). Others have reported that in plaque Aβ is present only as the naked peptide. Together these results suggest that both plaque and dementia are secondary to an age related decline in the capacity of the ER to catalyze protein, posttranslational processing. Since the synaptic membrane proteins necessary for a functioning memory are also processed in the ER, these findings would suggest that the loss of cognition is due to a decline in the capacity of the neuron to produce and maintain functioning synapses. Work from my laboratory and from others further indicate that the components of the ER, posttranslational, protein processing pathway do dramatically decline with age. These data suggest that this decline may be found in all cells and could account not only for the dementia of Alzheimer's disease, but also for many of the other manifestations of the aging process. These observations also suggest that declining ER function has a role in two well-recognized phenomena associated with aging: a loss of mitochondrial function and a decrease in myelin. Finally, based on this paradigm I propose new cellular and animals models for high-throughput screening for drug discovery.

The Molecular Chaperone GRP78/BiP as a Therapeutic Target for Neurodegenerative Disorders: A Mini Review

The glucose regulated protein 78 (GRP78), also known as BiP, is the endoplasmatic reticulum (ER) homologue of HSP70, which plays a dual role in the ER by controlling protein folding, in order to prevent aggregation, and by regulating the signaling of the unfolded protein response (UPR). Most neurodegenerative disorders including Parkinson's, Alzheimer's diseases and progressive retinal degeneration are characterized by activation of the UPR and modified expression of GRP78. The expression levels and activity of GRP78 are altered with age raising the question of whether the lack of GRP78 could be a predisposing factor for many neurodegenerative disorders associated with age including PD, Alzheimer and Age-related macular degeneration. Attempts to induce or upregulate GRP78 in animal models of neurodegeneration have recently been made with the help of pharmacological BiP protein Inducer X (BIX) and GRP78 cDNA delivery via adeno-associated virus (AAV) vectors. The results of these studies validate GRP78 as a new therapeutic target for treatments of forebrain ischemia, Parkinson disease and retinal degeneration. These data, together with the results from age-related studies, highlight the importance for developing drugs to induce elevation of endogenous GRP78 in order to increase cellular survival and extend functional longevity.

GRP78/BiP is a novel downstream target of IGF-1 receptor mediated signaling

Glucose regulated protein 78/immunoglobulin binding protein (GRP78/BiP) is an endoplasmic reticulum (ER) chaperone protein and master regulator of the unfolded protein response (UPR). The response of GRP78 to overt pharmacologically induced ER stress is well established, whereas the modulation of GRP78 to physiologic changes is less characterized. In this study, we examined the regulation of GRP78 in response to reduced IGF-1 growth factor signaling, a common consequence of calorie restriction (CR). ER chaperone protein expression was quantified in cell lysates prepared from the livers of calorie restricted (CR) and ad libitum fed mice, as well as MEFs grown in normal medium or serum starved. The requirement of IGF-1 signaling on GRP78 expression was studied using MEFs with IGF-1 receptor overexpression (R+) or deletion (R-), and the regulatory mechanism was examined using mTORC1 and PI3K inhibitors, as well as R- cells with knockdown of transcription factor FOXO1 compared to shRNA control. We observed a 40% reduction in GRP78 protein expression in CR mice and in serum-starved MEF cells. R- cells had drastically reduced AKT phosphorylation and exhibited lower levels of ER chaperones, in particular 80% less GRP78. Despite an 80% reduction in GRP78 expression, R- cells were not under chronic ER stress, but were fully capable of activating the UPR. Neither forced expression of FOXO1-AAA nor knockdown of FOXO1 in R- cells affected GRP78 expression. In conclusion, we report that IGF-1 receptor signaling regulates GRP78 expression via the PI3K/AKT/mTORC1 axis independent of the canonical UPR and FOXO1.

Endoplasmic reticulum enrollment in Alzheimer's disease

Alzheimer's disease (AD) poses a huge challenge for society and health care worldwide as molecular pathogenesis of the disease is poorly understood and curative treatment does not exist. The mechanisms leading to accelerated neuronal cell death in AD are still largely unknown, but accumulation of misfolded disease-specific proteins has been identified as potentially involved. In the present review, we describe the essential role of endoplasmic reticulum (ER) in AD. Despite the function that mitochondria may play as the central major player in the apoptotic process, accumulating evidence highlights ER as a critical organelle in AD. Stress that impairs ER physiology leads to accumulation of unfolded or misfolded proteins, such as amyloid β (Aβ) peptide, the major component of amyloid plaques. In an attempt to ameliorate the accumulation of unfolded proteins, ER stress triggers a protective cellular mechanism, which includes the unfolded protein response (UPR). However, when activation of the UPR is severe or prolonged enough, the final cellular outcome is pathologic apoptotic cell death. Distinct pathways can be activated in this process, involving stress sensors such as the JNK pathway or ER chaperones such as Bip/GRP94, stress modulators such as Bcl-2 family proteins, or even stress effectors such as caspase-12. Here, we detail the involvement of the ER and associated stress pathways in AD and discuss potential therapeutic strategies targeting ER stress.

Glucose regulated protein 78 diminishes α-synuclein neurotoxicity in a rat model of Parkinson disease

Accumulation of human wild-type (wt) α-synuclein (α-syn) induces neurodegeneration in humans and in experimental rodent models of Parkinson disease (PD). It also leads to endoplasmic reticulum (ER) stress and activation of the unfolded protein response (UPR). We overexpressed glucose regulated protein 78, also known as BiP (GRP78/BiP), to test the hypothesis that this ER chaperone modulates the UPR, blocks apoptosis, and promotes the survival of nigral dopamine (DA) neurons in a rat model of PD induced by elevated level of human α-syn. We determined that α-syn activates ER stress mediators associated with pancreatic ER kinase-like ER kinase (PERK) and activating transcription factor-6 (ATF6) signaling pathways as well as proaoptotic CCAAT/-enhancer-binding protein homologous protein (CHOP) in nigral DA neurons. At the same time, overexpression of GRP78/BiP diminished α-syn neurotoxicity by down regulating ER stress mediators and the level of apoptosis, promoted survival of nigral tyrosine hydroxylase (TH) positive cells and resulted in higher levels of striatal DA, while eliminating amphetamine induced behavioral asymmetry. We also detected a complex between GRP78/BiP and α-syn that may contribute to prevention of the neurotoxicity caused by α-syn. Our data suggest that the molecular chaperone GRP78/BiP plays a neuroprotective role in α-syn-induced Parkinson-like neurodegeneration.

Pulmonary fibrosis induced by γ-herpesvirus in aged mice is associated with increased fibroblast responsiveness to transforming growth factor-β

Young (4 month) and aged (15-18 months) mice were given intranasal saline or γ--herpesvirus-68 infection. After 21 days, aged, but not young mice, showed significant increases in collagen content and fibrosis. There were no differences in viral clearance or inflammatory cells (including fibrocytes) between infected aged and young mice. Enzyme-linked immunosorbent assays showed increased transforming growth factor-β in whole lung homogenates of infected aged mice compared with young mice. When fibroblasts from aged and young mice were infected in vitro, aged, but not young, fibroblasts upregulate alpha-smooth muscle actin and collagen I protein. Infection with virus in vivo also demonstrates increased alpha-smooth muscle actin and collagen I protein and collagen I, collagen III, and fibronectin messenger RNA in aged fibroblasts. Furthermore, evaluation revealed that aged fibroblasts at baseline have increased transforming growth factor-β receptor 1 and 2 levels compared with young fibroblasts and are resistant to apoptosis. Increased responsiveness to transforming growth factor-β was verified by increased collagen III and fibronectin messenger RNA after treatment in vitro with transforming growth factor-β.

Cellular senescence and tumor suppressor gene p16

Cellular senescence is an irreversible arrest of cell growth. Biochemical and morphological changes occur during cellular senescence, including the formation of a unique cellular morphology such as flattened cytoplasm. Function of mitochondria, endoplasmic reticulum and lysosomes are affected resulting in the inhibition of lysosomal and proteosomal pathways. Cellular senescence can be triggered by a number of factors including, aging, DNA damage, oncogene activation and oxidative stress. While the molecular mechanism of senescence involves p16 and p53 tumor suppressor genes and telomere shortening, this review is focused on the mechanism of p16 control. The p16-mediated senescence acts through the retinoblastoma (Rb) pathway inhibiting the action of the cyclin dependant kinases leading to G1 cell cycle arrest. Rb is maintained in a hypophosphorylated state resulting in the inhibition of transcription factor E2F1. Regulation of p16 expression is complex and involves epigenetic control and multiple transcription factors. PRC1 (Pombe repressor complex (1) and PRC2 (Pombe repressor complex (2) proteins and histone deacetylases play an important role in the promoter hypermethylation for suppressing p16 expression. While transcription factors YY1 and Id1 suppress p16 expression, transcription factors CTCF, Sp1 and Ets family members activate p16 transcription. Senescence occurs with the inactivation of suppressor elements leading to the enhanced expression of p16.

Endoplasmic reticulum stress in wake-active neurons progresses with aging

Fragmentation of wakefulness and sleep are expected outcomes of advanced aging. We hypothesize that wake neurons develop endoplasmic reticulum dyshomeostasis with aging, in parallel with impaired wakefulness. In this series of experiments, we sought to more fully characterize age-related changes in wakefulness and then, in relevant wake neuronal populations, explore functionality and endoplasmic reticulum homeostasis. We report that old mice show greater sleep/wake transitions in the active period with markedly shortened wake periods, shortened latencies to sleep, and less wake time in the subjective day in response to a novel social encounter. Consistent with sleep/wake instability and reduced social encounter wakefulness, orexinergic and noradrenergic wake neurons in aged mice show reduced c-fos response to wakefulness and endoplasmic reticulum dyshomeostasis with increased nuclear translocation of CHOP and GADD34. We have identified an age-related unfolded protein response injury to and dysfunction of wake neurons. It is anticipated that these changes contribute to sleep/wake fragmentation and cognitive impairment in aging.

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.