The role of interleukin-10 in mitigating endoplasmic reticulum stress in aged mice through exercise.

Although unfolded protein response (UPR) is essential for cellular protection, its prolonged activation may induce apoptosis, compromising cellular longevity. The aging process increases the endoplasmic reticulum (ER) stress in skeletal muscle. However, whether combined exercise can prevent age-induced ER stress in skeletal muscle remains unknown. Evidence suggests that ER stress may increase inflammation by counteracting the positive effects of interleukin-10 (IL-10), whereas its administration in cells inhibits ER stress and apoptosis. This study verified the effects of aging and combined exercise on physical performance, ER stress markers, and inflammation in the quadriceps of mice. Moreover, we verified the effects of IL-10 on ER stress markers. C57BL/6 mice were distributed into young (Y, 6 mo old), old sedentary (OS, sedentary, 24 mo old), and old trained group (OT, submitted to short-term combined exercise, 24 mo old). To clarify the role of IL-10 in UPR pathways, knockout mice lacking IL-10 were used. The OS mice presented worse physical performance and higher ER stress-related proteins, such as C/EBP homologous protein (CHOP) and phospho-eukaryotic translation initiation factor 2 alpha (p-eIF2α/eIF2α). The exercise protocol increased muscle strength and IL-10 protein levels in OT while inducing the downregulation of CHOP protein levels compared with OS. Furthermore, mice lacking IL-10 increased BiP, CHOP, and p-eIF2α/eIF2α protein levels, indicating this cytokine can regulate the ER stress response in skeletal muscle. Bioinformatics analysis showed that endurance and resistance training downregulated DNA damage inducible transcript 3 (DDIT3) and XBP1 gene expression in the vastus lateralis of older people, reinforcing our findings. Thus, combined exercise is a potential therapeutic intervention for promoting adjustments in ER stress markers in aged skeletal muscle.NEW & NOTEWORTHY Aging elevates endoplasmic reticulum (ER) stress in skeletal muscle, potentially heightening inflammation by opposing interleukin-10 (IL-10) effects. This study found that short-term combined exercise boosted strength and IL-10 protein levels while reducing CHOP protein levels in older mice. In addition, IL-10-deficient mice exhibited increased ER stress markers, highlighting IL-10's role in regulating ER stress in skeletal muscle. Consequently, combined exercise emerges as a therapeutic intervention to elevate IL-10 and adjust ER stress markers in aging.

Electroacupuncture attenuates neuropathic pain via suppressing BIP-IRE-1α-mediated endoplasmic reticulum stress in the anterior cingulate cortex.

Studies have suggested that endoplasmic reticulum stress (ERS) is involved in neurological dysfunction and that electroacupuncture (EA) attenuates neuropathic pain (NP) via undefined pathways. However, the role of ERS in the anterior cingulate cortex (ACC) in NP and the effect of EA on ERS in the ACC have not yet been investigated. In this study, an NP model was established by chronic constriction injury (CCI) of the left sciatic nerve in rats, and mechanical and cold tests were used to evaluate behavioral hyperalgesia. The protein expression and distribution were evaluated using western blotting and immunofluorescence. The results showed that glucose-regulated protein 78 (BIP) and inositol-requiring enzyme 1α (IRE-1α) were co-localized in neurons in the ACC. After CCI, BIP, IRE-1α, and phosphorylation of IRE-1α were upregulated in the ACC. Intra-ACC administration of 4-PBA and Kira-6 attenuated pain hypersensitivity and downregulated phosphorylation of IRE-1α, while intraperitoneal injection of 4-PBA attenuated hyperalgesia and inhibited the activation of P38 and JNK in ACC. In contrast, ERS activation by intraperitoneal injection of tunicamycin induced behavioral hyperalgesia in naive rats. Furthermore, EA attenuated pain hypersensitivity and inhibited the CCI-induced overexpression of BIP and pIRE-1α. Taken together, these results demonstrate that EA attenuates NP by suppressing BIP- and IRE-1α-mediated ERS in the ACC. Our study presents novel evidence that ERS in the ACC is implicated in the development of NP and provides insights into the molecular mechanisms involved in the analgesic effect of EA.

Manipulation of unfolded protein response by zoonotic vaccinia virus strains Guarani P1 and Passatempo.

The replicative success of vaccinia virus (VACV) depends on its ability to subvert host functions. Poxviruses multiplication and maturation are closely associated with the endoplasmic reticulum (ER) and its membranes. This organelle responds to disturbances caused by the accumulation of misfolded proteins, leading to processing of these proteins or even programmed cell death through the unfolded protein response (UPR). Several studies show that different viruses can activate UPR pathway components and negatively modulate others. Here, we investigate the effects of infections by zoonotic VACV strains from Brazil, Guarani P1 virus (GP1V) and Passatempo virus (PSTV), in the activation of UPR pathway sensors. We observed translocation of ATF6 to the nucleus as well as transcriptional increase after GP1V, PSTV, and reference strain Western Reserve (WR) infection. XBP1 processing appears to be negatively modulated after VACV infection; however, inhibition of the inositol-requiring enzyme 1 (IRE1) kinase domain led to a reduction in plaque sizes for these viruses. The absence of PKR-like endoplasmic reticulum kinase (PERK) has an impact on the plaque phenotype of GP1V, PSTV viruses, as well as for the prototypical strain WR. These results indicate that the VACV manipulates the three arms of the UPR path differently to ensure replicative success.

High-intensity interval training (treadmill) effects in myokines and endoplasmic reticulum stress of calf muscles in obese mice / Efectos del entrenamiento interválico de alta intensidad (trotadora) en miocinas y estrés del retículo endoplasmático de los músculos surales en ratones obesos

SUMMARY: Obesity is commonly associated with chronic tissue inflammation and skeletal muscle dysfunction. The study aimed to investigate the effects of High-Intensity Interval training (HIIT) on myokines and endoplasmic reticulum (ER) stress of diet- induced obese (DIO) mice. Three-month-old C57BL/6 male mice were fed a control (C) diet (n=20) or a high-fat (HF) diet (n=20) for 16 weeks. Then, half of the groups underwent HIIT (treadmill running) for an additional four weeks. HIIT increased calf muscles' contribution to BW (+24 %) and reduced weight gain in HF/HIIT than in HF (-120 %). Intramuscular fat accumulation was observed in HF and HF/ HIIT. Peak velocity was higher in HF/HIIT compared to HF (+26 %). Plasma insulin did not change, but glycemia was lower in HF/HIIT than in HF (-30 %). Fndc5 (+418 %) and Irisin (+72 %) were higher in HF/HIIT than in HF. Muscle Fgf21 was higher in HF/HIIT compared to HF (+30 %). In addition, NfKb (-53 %) and Tnfa (-63 %) were lower in HF/HIIT than in HF. However, Il1b (-86 %), Il6 (- 48 %), Il7 (-76 %), and Il15 (-21 %) were lower in HF/HIIT than in HF. Finally, HIIT reduced ER stress in HF/HIIT compared to HF: Atf4, -61 %; Chop, -61 %; Gadd45, -95 %. In conclusion, HIIT leads to weight loss and avoids muscle depletion. HIIT improves blood glucose, Irisin-Fndc5, and peak velocity. In addition, HIIT mitigates muscle inflammation and ER stress.

La obesidad es asociada comúnmente con inflamación tisular crónica y disfunción del músculo esquelético. El estudio tuvo como objetivo investigar los efectos del entrenamiento de intervalos de alta intensidad (HIIT) en las mioquinas y el estrés del retículo endoplásmico (ER) de ratones obesos inducidos por dieta (DIO). Se alimentó a ratones macho C57BL/6 de tres meses de edad con una dieta control (C) (n=20) o una dieta rica en grasas (HF) (n=20) durante 16 semanas. Luego, la mitad de los grupos se sometieron a HIIT (carrera en una trotadora) durante cuatro semanas más. HIIT aumentó la contribución de los músculos de la pantorrilla al BW (+24 %) y redujo el aumento de peso en HF/HIIT en HF (-120 %). Se observó acumulación de grasa intramuscular en HF y HF/HIIT. La velocidad máxima fue mayor en HF/HIIT en comparación con HF (+26 %). La insulina plasmática no cambió, pero la glucemia fue menor en HF/HIIT que en HF (-30 %). Fndc5 (+418 %) e Irisin (+72 %) fueron mayores en HF/HIIT que en HF. El Fgf21 muscular fue mayor en HF/ HIIT en comparación con HF (+30 %). Además, NfKb (-53 %) y Tnfa (-63 %) fueron menores en HF/HIIT que en HF. Sin embar- go, Il1b (-86 %), Il6 (-48 %), Il7 (-76 %) e Il15 (-21 %) fueron más bajos en HF/HIIT que en HF. Finalmente, HIIT redujo el estrés de RE en HF/HIIT en comparación con HF: Atf4, -61 %; Picar, - 61 %; Gadd45, -95 %. En conclusión, HIIT conduce a la pérdida de peso y evita el agotamiento muscular. HIIT mejora la glucosa en sangre, Irisin-Fndc5 y la velocidad máxima. Además, HIIT mitiga la inflamación muscular y el estrés ER.

Antioxidants affect endoplasmic reticulum stress-related diseases.

The endoplasmic reticulum (ER) is a complex multifunctional organelle that maintains cell homeostasis. Intrinsic and extrinsic factors alter ER functions, including the rate of protein folding that triggers the accumulation of misfolded proteins and alters homeostasis, thus generating stress in the ER, which activates the unfolded protein response (UPR) pathway to promote cell survival and restore their homeostasis; however, if the damage is not corrected, it could also trigger cell death. In addition, ER stress and oxidative stress are closely related because excessive production of reactive oxygen species (ROS), a well-known inducer of ER stress, promotes the accumulation of misfolded proteins; at the same time, the ER stress enhances ROS production, generating a pathological cycle. Furthermore, it has been described that the dysregulation of the UPR contributes to the progression of various diseases, so the use of compounds capable of regulating ER stress, such as antioxidants, has been used in several experimental models of diseases to alleviate the damage induced by the maladaptive signaling of the UPR, the mechanism of action of antioxidants generally is dose-dependent, and it is specific in each tissue and pathology, could decrease or enhance specific proteins of the UPR to have beneficial or detrimental effects.

Potential role of endoplasmic reticulum stress in the pathophysiology of polycystic ovary syndrome.

Polycystic ovary syndrome (PCOS) is an endocrine disorder that affects million women worldwide, presenting a complex pathophysiology that has not been fully elucidated yet. Recently, it has been suggested that PCOS triggers the endoplasmic reticulum (ER) stress, thus being associated with unfolded protein response (UPR) activation. Indeed, the UPR response has been associated with several pathological conditions, including in the reproductive system. Several studies demonstrated that ovarian UPR markers are upregulated in PCOS, being associated with worst ovarian outcomes, and this was ameliorated by ER stress inhibition. In this review, we aim to summarize the main findings from previous studies covering this topic, in an attempt to clarify the potential role of ER stress and the UPR response in the pathophysiology of PCOS.

Autoantibodies in the pathogenesis of idiopathic inflammatory myopathies: Does the endoplasmic reticulum stress response have a role?

Idiopathic inflammatory myopathies (IIMs) are a group of rare, acquired autoimmune diseases characterized by profound muscle weakness and immune cell invasion into non-necrotic muscle. They are related to the presence of antibodies known as myositis-specific antibodies and myositis-associated antibodies, which are associated with various IIM phenotypes and the clinical prognosis. The possibility of the participation of other pathological mechanisms involved in the inflammatory response in IIM has been proposed. Such mechanisms include the overexpression of major histocompatibility complex class I in myofibers, which correlates with the activation of stress responses of the endoplasmic reticulum (ER). Taking into account the importance of the ER for the maintenance of homeostasis of the musculoskeletal system in the regulation of proteins, there is probably a relationship between immunological and non-immunological processes and autoimmunity, and an example of this might be IIM. We propose that ER stress and its relief mechanisms could be related to inflammatory mechanisms triggering a humoral response in IIM, suggesting that ER stress might be related to the triggering of IIMs and their auto-antibodies' production.

Ca2+ signalling system initiated by endoplasmic reticulum stress stimulates PERK activation.

The accumulation of unfolded proteins within the Endoplasmic Reticulum (ER) activates a signal transduction pathway termed the unfolded protein response (UPR), which attempts to restore ER homoeostasis. If this cannot be done, UPR signalling ultimately induces apoptosis. Ca2+ depletion in the ER is a potent inducer of ER stress. Despite the ubiquity of Ca2+ as an intracellular messenger, the precise mechanism(s) by which Ca2+ release affects the UPR remains unknown. Tethering a genetically encoded Ca2+ indicator (GCamP6) to the ER membrane revealed novel Ca2+ signalling events initiated by Ca2+ microdomains in human astrocytes under ER stress, induced by tunicamycin (Tm), an N-glycosylation inhibitor, as well as in a cell model deficient in all three inositol triphosphate receptor isoforms. Pharmacological and molecular studies indicate that these local events are mediated by translocons and that the Ca2+ microdomains impact (PKR)-like-ER kinase (PERK), an UPR sensor, activation. These findings reveal the existence of a Ca2+ signal mechanism by which stressor-mediated Ca2+ release regulates ER stress.

[Activation of endoplasmic reticulum stress sensors by metabolic disease-associated diets and COVID-19]. / Activación de sensores del estrés del retículo endoplásmico por dietas asociadas a enfermedades metabólicas y COVID-19.

The endoplasmic reticulum is an abundant, dynamic and energy-sensing organelle. Its abundant membranes, rough and smooth, are distributed in different proportions depending on the cell lineage and requirement. Its function is to carry out protein and lipid synthesis, and it is the main intracellular Ca2+ store. Caloric overload and glycolipotoxicity generated by hypercaloric diets cause alteration of the endoplasmic reticulum, activating the Unfolded Protein Response (UPR) as a reaction to cellular stress related to the endoplasmic reticulum and whose objective is to restore the homeostasis of the organelle by decreasing oxidative stress, protein synthesis and Ca2+ leakage. However, during chronic stress, the UPR induces reactive oxygen species formation, inflammation and apoptosis, exacerbating the state of the endoplasmic reticulum and propagating a deleterious effect on the other organelles. This is why endoplasmic reticulum stress has been considered an inducer of the onset and development of metabolic diseases, including the aggravation of COVID-19. So far, few strategies exist to reestablish endoplasmic reticulum homeostasis, which are targeted to sensors that trigger UPR. Therefore, the identification of new mechanisms and novel therapies related to mitigating the impact of endoplasmic reticulum stress and associated complications is urgently warranted.

El retículo endoplásmico es un organelo abundante, dinámico y sensor de energía. Sus abundantes membranas, rugosa y lisa, se encuentran distribuidas en diferentes proporciones dependiendo del linaje y requerimiento celular. Su función es llevar a cabo la síntesis de proteínas y lípidos, y es el almacén principal de Ca2+ intracelular. La sobrecarga calórica y la glucolipotoxicidad generada por dietas hipercalóricas provoca la alteración del retículo endoplásmico, activando la respuesta a proteínas mal plegadas (UPR, Unfolded Protein Response, por sus siglas en inglés) como reacción al estrés celular relacionado con el retículo endoplásmico y cuyo objetivo es restablecer la homeostasis del organelo al disminuir el estrés oxidante, la síntesis de proteínas y la fuga de Ca2+. Sin embargo, durante un estrés crónico, la UPR induce formación de especies reactivas de oxígeno, inflamación y apoptosis, exacerbando el estado del retículo endoplásmico y propagando un efecto nocivo para los demás organelos. Es por ello que el estrés del retículo endoplásmico se ha considerado un inductor del inicio y desarrollo de enfermedades metabólicas, incluido el agravamiento de COVID-19. Hasta el momento, existen pocas estrategias para reestablecer la homeostasis del retículo endoplásmico, las cuales son dirigidas a los sensores que desencadenan la UPR. Por tanto, se justifica con urgencia la identificación de nuevos mecanismos y terapias novedosas relacionadas con mitigar el impacto del estrés del retículo endoplásmico y las complicaciones asociadas.

Role of sulforaphane in endoplasmic reticulum homeostasis through regulation of the antioxidant response.

Nowadays, the nutraceutical agent sulforaphane (SFN) shows great versatility in turning on different cellular responses. Mainly, this isothiocyanate acts as a master regulator of cellular homeostasis due to its antioxidant response and cytoplasmic, mitochondrial, and endoplasmic reticulum (ER) protein modulation. Even more, SFN acts as an effective strategy to counteract oxidative stress, apoptosis, and ER stress, among others as seen in different injury models. Particularly, ER stress is buffered by the unfolded protein response (UPR) activation, which is the first instance in orchestrating the recovery of ER function. Interestingly, different studies highlight a close interrelationship between ER stress and oxidative stress, two events driven by the accumulation of reactive oxygen species (ROS). This response inevitably perpetuates itself and acts as a vicious cycle that triggers the development of different pathologies, such as cardiovascular diseases, neurodegenerative diseases, and others. Accordingly, it is vital to target ER stress and oxidative stress to increase the effectiveness of clinical therapies used to treat these diseases. Therefore, our study is focused on the role of SFN in preserving cellular homeostasis balance by regulating the ER stress response through the Nrf2-modulated antioxidant pathway.

Activación de sensores del estrés del retículo endoplásmico por dietas asociadas a enfermedades metabólicas y COVID-19 / Activation of endoplasmic reticulum stress sensors by metabolic disease-associated diets and COVID-19

El retículo endoplásmico es un organelo abundante, dinámico y sensor de energía. Sus abundantes membranas, rugosa y lisa, se encuentran distribuidas en diferentes proporciones dependiendo del linaje y requerimiento celular. Su función es llevar a cabo la síntesis de proteínas y lípidos, y es el almacén principal de Ca2+ intracelular. La sobrecarga calórica y la glucolipotoxicidad generada por dietas hipercalóricas provoca la alteración del retículo endoplásmico, activando la respuesta a proteínas mal plegadas (UPR, Unfolded Protein Response, por sus siglas en inglés) como reacción al estrés celular relacionado con el retículo endoplásmico y cuyo objetivo es restablecer la homeostasis del organelo al disminuir el estrés oxidante, la síntesis de proteínas y la fuga de Ca2+. Sin embargo, durante un estrés crónico, la UPR induce formación de especies reactivas de oxígeno, inflamación y apoptosis, exacerbando el estado del retículo endoplásmico y propagando un efecto nocivo para los demás organelos. Es por ello que el estrés del retículo endoplásmico se ha considerado un inductor del inicio y desarrollo de enfermedades metabólicas, incluido el agravamiento de COVID-19. Hasta el momento, existen pocas estrategias para reestablecer la homeostasis del retículo endoplásmico, las cuales son dirigidas a los sensores que desencadenan la UPR. Por tanto, se justifica con urgencia la identificación de nuevos mecanismos y terapias novedosas relacionadas con mitigar el impacto del estrés del retículo endoplásmico y las complicaciones asociadas.

The endoplasmic reticulum is an abundant, dynamic and energy-sensing organelle. Its abundant membranes, rough and smooth, are distributed in different proportions depending on the cell lineage and requirement. Its function is to carry out protein and lipid synthesis, and it is the main intracellular Ca2+ store. Caloric overload and glycolipotoxicity generated by hypercaloric diets cause alteration of the endoplasmic reticulum, activating the Unfolded Protein Response (UPR) as a reaction to cellular stress related to the endoplasmic reticulum and whose objective is to restore the homeostasis of the organelle by decreasing oxidative stress, protein synthesis and Ca2+ leakage. However, during chronic stress, the UPR induces reactive oxygen species formation, inflammation and apoptosis, exacerbating the state of the endoplasmic reticulum and propagating a deleterious effect on the other organelles. This is why endoplasmic reticulum stress has been considered an inducer of the onset and development of metabolic diseases, including the aggravation of COVID-19. So far, few strategies exist to reestablish endoplasmic reticulum homeostasis, which are targeted to sensors that trigger UPR. Therefore, the identif ication of new mechanisms and novel therapies related to mitigating the impact of endoplasmic reticulum stress and associated complications is urgently warranted.

Proteostasis and resilience: on the interphase between individual's and intracellular stress.

A long proportion of the population is resilient to the negative consequences of stress. Glucocorticoids resulting from endocrine responses to stress are essential adaptive mediators, but also drive alterations to brain function, negatively impacting neuronal connectivity, synaptic plasticity, and memory-related processes. Recent evidence has indicated that organelle function and cellular stress responses are relevant determinant of vulnerability and resistance to environmental stress. At the molecular level, a fundamental mechanism of cellular stress adaptation is the maintenance of proteostasis, which also have key roles in sustaining basal neuronal function. Here, we discuss recent evidence suggesting that proteostasis unbalance at the level of the endoplasmic reticulum, the main site for protein folding in the cell, represents a possible mechanistic link between individuals and cellular stress.

Muscle endoplasmic reticulum stress in exercise.

The endoplasmic reticulum (ER) is an organelle responsible for the post-translational folding and modification of proteins. Under stress conditions, such as physical exercise, there is accumulation of misfolded proteins. The increased load of proteins in the ER results in ER stress, which activates the unfolded protein response (UPR). UPR is comprised of three parallel pathways, responsible for ensuring the quality of secreted proteins. Scientific studies show that resistance or endurance acute physical exercise can induce ER stress and activate the UPR pathways. On the other hand, regular moderate-intensity exercise can attenuate the responses of genes and proteins related to ER stress. However, these positive adaptations do not occur when exercise intensity and volume increase without adequate rest periods, which is observed in overtraining. The current review discusses the frontier-of-knowledge findings on the effects of different acute and chronic physical exercise protocols on skeletal muscle ER stress and its metabolic consequences.

Assays to Study IRE1 Activation and Signaling.

The endoplasmic reticulum (ER) stress sensor IRE1 is a a major player of the unfolded protein response (UPR), the main pathway driving adaptation processes to restore proteostasis.  In addition, overactivation of IRE1 signaling contributes to a variety of pathologies including diabetes, neurodegenerative diseases, and cancer. Under ER stress, IRE1 auto-transphosphorylates and oligomerizes, triggering the activation of its endoribonuclease domain located in the cytosolic region. Active IRE1 catalyzes the splicing of the mRNA encoding for the XBP1 transcription factor, in addition to degrade several RNAs through a process known as regulated IRE1-dependent decay of mRNA (RIDD). Besides its role as an UPR transducer, several posttranslational modifications and protein-protein interactions can regulate IRE1 activity and modulate its signaling in the absence of stress. Thus, investigating the function of IRE1 in physiology and disease requires the use of complementary approaches. Here, we provide detailed protocols to perform four different assays to study IRE1 activation and signaling: (i) Phos-tag gels to evaluate the phosphorylation status of IRE1, (ii) microscopy using TREX-IRE1-GFP cells to measure IRE1 oligomerization, (iii) conventional RT-PCR to assess XBP1 mRNA processing, and (iv) quantitative PCR to determine the levels of canonical UPR target genes and the degradation of several mRNAs that are target of RIDD. We propose to use these experimental strategies as "gold standards" to study IRE1 signaling.

The endoplasmic reticulum stress sensor IRE1α modulates macrophage metabolic function during Brucella abortus infection.

Endoplasmic reticulum (ER) stress plays a major role in several inflammatory disorders. ER stress induces the unfolded protein response (UPR), a conserved response broadly associated with innate immunity and cell metabolic function in various scenarios. Brucella abortus, an intracellular pathogen, triggers the UPR via Stimulator of interferon genes (STING), an important regulator of macrophage metabolism during B. abortus infection. However, whether ER stress pathways underlie macrophage metabolic function during B. abortus infection remains to be elucidated. Here, we showed that the UPR sensor inositol-requiring enzyme 1α (IRE1α) is as an important component regulating macrophage immunometabolic function. In B. abortus infection, IRE1α supports the macrophage inflammatory profile, favoring M1-like macrophages. IRE1α drives the macrophage metabolic reprogramming in infected macrophages, contributing to the reduced oxidative phosphorylation and increased glycolysis. This metabolic reprogramming is probably associated with the IRE1α-dependent expression and stabilization of hypoxia-inducible factor-1 alpha (HIF-1α), an important molecule involved in cell metabolism that sustains the inflammatory profile in B. abortus-infected macrophages. Accordingly, we demonstrated that IRE1α favors the generation of mitochondrial reactive oxygen species (mROS) which has been described as an HIF-1α stabilizing factor. Furthermore, in infected macrophages, IRE1α drives the production of nitric oxide and the release of IL-1ß. Collectively, these data unravel a key mechanism linking the UPR and the immunometabolic regulation of macrophages in Brucella infection and highlight IRE1α as a central pathway regulating macrophage metabolic function during infectious diseases.

Proteostasis deregulation as a driver of C9ORF72 pathogenesis.

Amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) are two related neurodegenerative disorders that display overlapping features. The hexanucleotide repeat expansion GGGGCC (G4 C2 ) in C9ORF72 gene has been causally linked to both ALS and FTD emergence, thus opening a novel potential therapeutic target for disease intervention. The main driver of C9ORF72 pathology is the disruption of distinct cellular processes involved in the function of the proteostasis network. Here we discuss main findings relating to the induction of neurodegeneration by C9ORF72 mutation and proteostasis deregulation, highlighting the role of the endoplasmic reticulum stress, nuclear transport, and autophagy in the disease process. We further discuss possible points of intervention to target proteostasis mediators to treat C9ORF72-linked ALS/FTD.

HSPB1 Is Essential for Inducing Resistance to Proteotoxic Stress in Beta-Cells.

During type 1 diabetes mellitus (T1DM) development, beta-cells undergo intense endoplasmic reticulum (ER) stress that could result in apoptosis through the failure of adaptation to the unfolded protein response (UPR). Islet transplantation is considered an attractive alternative among beta-cell replacement therapies for T1DM. To avoid the loss of beta-cells that will jeopardize the transplant's outcome, several strategies are being studied. We have previously shown that prolactin induces protection against proinflammatory cytokines and redox imbalance-induced beta-cell death by increasing heat-shock protein B1 (HSPB1) levels. Since the role of HSPB1 in beta cells has not been deeply studied, we investigated the mechanisms involved in unbalanced protein homeostasis caused by intense ER stress and overload of the proteasomal protein degradation pathway. We tested whether HSPB1-mediated cytoprotective effects involved UPR modulation and improvement of protein degradation via the ubiquitin-proteasome system. We demonstrated that increased levels of HSPB1 attenuated levels of pro-apoptotic proteins such as CHOP and BIM, as well as increased protein ubiquitination and the speed of proteasomal protein degradation. Our data showed that HSPB1 induced resistance to proteotoxic stress and, thus, enhanced cell survival via an increase in beta-cell proteolytic capacity. These results could contribute to generate strategies aimed at the optimization of beta-cell replacement therapies.

HSPB1 influences mitochondrial respiration in ER-stressed beta cells.

Beta-cell death and dysfunction are involved in the development of type 1 and 2 diabetes. ER-stress impairs beta-cells function resulting in pro-apoptotic stimuli that promote cell death. Hence, the identification of protective mechanisms in response to ER-stress could lead to novel therapeutic targets and insight in the pathology of these diseases. Here, we report the identification of proteins involved in dysregulated pathways upon thapsigargin treatment of MIN6 cells. Utilizing quantitative proteomics we identified upregulation of proteins involved in protein folding, unfolded protein response, redox homeostasis, proteasome processes associated with endoplasmic reticulum and downregulation of TCA cycle, cellular respiration, lipid metabolism and ribosome assembly processes associated to mitochondria and eukaryotic initiation translation factor components. Subsequently, pro-inflammatory cytokine treatment was performed to mimic pathological changes observed in beta-cells during diabetes. Cytokines induced ER stress and impaired mitochondrial function in beta-cells corroborating the results obtained with the proteomic approach. HSPB1 levels are increased by prolactin on pancreatic beta-cells and this protein is a key factor for cytoprotection although its role has not been fully elucidated. Here we show that while up-regulation of HSPB1 was able to restore the mitochondrial dysfunction induced by beta-cells' exposure to inflammatory cytokines, silencing of this chaperone abrogated the beneficial effects promoted by PRL. Taken together, our results outline the importance of HSPB1 to mitigate beta-cell dysfunction. Further studies are needed to elucidate its role in diabetes.

Glucose-regulated protein (GRP78) is an important cell surface receptor for viral invasion, cancers, and neurological disorders.

The 78 kDa glucose-regulated protein (GRP78) is an endoplasmic reticulum (ER)-resident molecular chaperone. GRP78 is a member of the 70 kDa heat shock family of proteins involved in correcting and clearing misfolded proteins in the ER. In response to cellular stress, GRP78 escapes from the ER and moves to the plasma membrane where it (a) functions as a receptor for many ligands, and (b) behaves as an autoantigen for autoantibodies that contribute to human disease and cancer. Cell surface GRP78 (csGRP78) associates with the major histocompatibility complex class I (MHC-I), and is the port of entry for several viruses, including the predictive binding of the novel SARS-CoV-2. Furthermore, csGRP78 is found in association with partners as diverse as the teratocarcinoma-derived growth factor 1 (Cripto), the melanocortin-4 receptor (MC4R) and the DnaJ-like protein MTJ-1. CsGRP78 also serves as a receptor for a large variety of ligands including activated α2 -macroglobulin (α2 M*), plasminogen kringle 5 (K5), microplasminogen, the voltage-dependent anion channel (VDAC), tissue factor (TF), and the prostate apoptosis response-4 protein (Par-4). In this review, we discuss the mechanisms involved in the translocation of GRP78 from the ER to the cell surface, and the role of secreted GRP78 and its autoantibodies in cancer and neurological disorders.

Idiopathic inflammatory myopathy human derived cells retain their ability to increase mitochondrial function.

Idiopathic Inflammatory Myopathies (IIMs) have been studied within the framework of autoimmune diseases where skeletal muscle appears to have a passive role in the illness. However, persiting weakness even after resolving inflammation raises questions about the role that skeletal muscle plays by itself in these diseases. "Non-immune mediated" hypotheses have arisen to consider inner skeletal muscle cell processes as trigger factors in the clinical manifestations of IIMs. Alterations in oxidative phosphorylation, ATP production, calcium handling, autophagy, endoplasmic reticulum stress, among others, have been proposed as alternative cellular pathophysiological mechanisms. In this study, we used skeletal muscle-derived cells, from healthy controls and IIM patients to determine mitochondrial function and mitochondrial ability to adapt to a metabolic stress when deprived of glucose. We hypothesized that mitochondria would be dysfunctional in IIM samples, which was partially true in normal glucose rich growing medium as determined by oxygen consumption rate. However, in the glucose-free and galactose supplemented condition, a medium that forced mitochondria to function, IIM cells increased their respiration, reaching values matching normal derived cells. Unexpectedly, cell death significantly increased in IIM cells under this condition. Our findings show that mitochondria in IIM is functional and the decrease respiration observed is part of an adaptative response to improve survival. The increased metabolic function obtained after forcing IIM cells to rely on mitochondrial synthesized ATP is detrimental to the cell's viability. Thus, therapeutic interventions that activate mitochondria, could be detrimental in IIM cell physiology, and must be avoided in patients with IIM.