On the brotherhood of the mitochondrial chaperones mortalin and heat shock protein 60

The mitochondrial LONP1 protease: molecular targets and role in pathophysiology

Lon peptidase 1 (LONP1), a member of the AAA + family, is essential for maintaining mitochondrial function. Recent studies have revealed that LONP1 serves as a multifunctional enzyme, acting not only as a protease but also as a molecular chaperone, interacting with mitochondrial DNA (mtDNA), and playing roles in mitochondrial dynamics, oxidative stress, cellular respiration, and energy metabolism. LONP1 is evolutionarily highly conserved, and mutations or dysfunctions in LONP1 can lead to diseases. There is growing evidence linking LONP1 to various human diseases, such as tumors, neurodegenerative diseases, and heart diseases. This review discusses the discovery, molecular structure, subcellular localization, tissue distribution, and mitochondrial function of LONP1. Furthermore, it summarizes the associations between LONP1 and tumors, neurodegenerative diseases, and heart diseases, exploring its role in different diseases and potential molecular mechanisms. It also analyzes the regulatory effects of related inhibitors and agonists on LONP1. Considering the pleiotropic effects of LONP1, the study of LONP1 is crucial to understanding the relevant pathophysiological processes and developing strategies to modulate and control these related diseases.

Mitochondrial protein deacetylation by SIRT3 in osteoclasts promotes bone resorption with aging in female mice

OBJECTIVES

The mitochondrial deacetylase sirtuin-3 (SIRT3) is necessary for the increased bone resorption and enhanced function of mitochondria in osteoclasts that occur with advancing age; how SIRT3 drives bone resorption remains elusive.

METHODS

To determine the role of SIRT3 in osteoclast mitochondria, we used mice with conditional loss of Sirt3 in osteoclast lineage and mice with germline deletion of either Sirt3 or its known target Pink1.

RESULTS

SIRT3 stimulates mitochondrial quality in osteoclasts in a PINK1-independent manner, promoting mitochondrial activity and osteoclast maturation and function, thereby contributing to bone loss in female but not male mice. Quantitative analyses of global proteomes and acetylomes revealed that deletion of Sirt3 dramatically increased acetylation of osteoclast mitochondrial proteins, particularly ATPase inhibitory factor 1 (ATPIF1), an essential protein for mitophagy. Inhibition of mitophagy via mdivi-1 recapitulated the effect of deletion of Sirt3 or Atpif1 in osteoclast formation and mitochondrial function.

CONCLUSIONS

Decreasing mitophagic flux in osteoclasts may be a promising pharmacotherapeutic approach to treat osteoporosis in older adults.

Quantitative proteomics reveals cellular responses to individual mAb expression and tunicamycin in CHO cells

Chinese hamster ovary (CHO) cells are popular in the pharmaceutical industry for their ability to produce high concentrations of antibodies and their resemblance to human cells in terms of protein glycosylation patterns. Current data indicate the relevance of CHO cells in the biopharmaceutical industry, with a high number of product commendations and a significant market share for monoclonal antibodies. To enhance the production capabilities of CHO cells, a deep understanding of their cellular and molecular composition is crucial. Genome sequencing and proteomic analysis have provided valuable insights into the impact of the bioprocessing conditions, productivity, and product quality. In our investigation, we conducted a comparative analysis of proteomic profiles in high and low monoclonal antibody-producing cell lines and studied the impact of tunicamycin (TM)-induced endoplasmic reticulum (ER) stress. We examined the expression levels of different proteins including unfolded protein response (UPR) target genes by using label-free quantification techniques for protein abundance. Our results show the upregulation of proteins associated with protein folding mechanisms in low producer vs. high producer cell line suggesting a form of ER stress related to specific protein production. Further, Hspa9 and Dnaja3 are notable candidates activated by the mitochondria UPR and play important roles in protein folding processes in mitochondria. We identified significant upregulation of Nedd8 and Lgmn proteins in similar levels which may contribute to UPR stress. Interestingly, the downregulation of Hspa5/Bip and Pdia4 in response to tunicamycin treatment suggests a low-level UPR activation. KEY POINTS: • Proteome profiling of recombinant CHO cells under mild TM treatment. • Identified protein clusters are associated with the unfolded protein response (UPR). • The compared cell lines revealed noticeable disparities in protein expression levels.

Temporal Quantitative Proteomic and Phosphoproteomic Profiling of SH-SY5Y and IMR-32 Neuroblastoma Cells during All-Trans-Retinoic Acid-Induced Neuronal Differentiation

The human neuroblastoma cell lines SH-SY5Y and IMR-32 can be differentiated into neuron-like phenotypes through treatment with all-trans-retinoic acid (ATRA). After differentiation, these cell lines are extensively utilized as in vitro models to study various aspects of neuronal cell biology. However, temporal and quantitative profiling of the proteome and phosphoproteome of SH-SY5Y and IMR-32 cells throughout ATRA-induced differentiation has been limited. Here, we performed relative quantification of the proteomes and phosphoproteomes of SH-SY5Y and IMR-32 cells at multiple time points during ATRA-induced differentiation. Relative quantification of proteins and phosphopeptides with subsequent gene ontology analysis revealed that several biological processes, including cytoskeleton organization, cell division, chaperone function and protein folding, and one-carbon metabolism, were associated with ATRA-induced differentiation in both cell lines. Furthermore, kinase-substrate enrichment analysis predicted altered activities of several kinases during differentiation. Among these, CDK5 exhibited increased activity, while CDK2 displayed reduced activity. The data presented serve as a valuable resource for investigating temporal protein and phosphoprotein abundance changes in SH-SY5Y and IMR-32 cells during ATRA-induced differentiation.

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

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

Tat-heat shock protein 10 ameliorates age-related phenotypes by facilitating neuronal plasticity and reducing age-related genes in the hippocampus

We investigated the effects of heat shock protein 10 (HSP10) protein on memory function, hippocampal neurogenesis, and other related genes/proteins in adult and aged mice. To translocate the HSP10 protein into the hippocampus, the Tat-HSP10 fusion protein was synthesized, and Tat-HSP10, not HSP10, was successfully delivered into the hippocampus based on immunohistochemistry and western blotting. Tat-HSP10 (0.5 or 2.0 mg/kg) or HSP10 (control protein, 2.0 mg/kg) was administered daily to 3- and 21-month-old mice for 3 months, and observed the senescence maker P16 was significantly increased in aged mice and the treatment with Tat-HSP10 significantly decreased P16 expression in the hippocampus of aged mice. In novel object recognition and Morris water maze tests, aged mice demonstrated decreases in exploratory preferences, exploration time, distance moved, number of object contacts, and escape latency compared to adult mice. Treatment with Tat-HSP10 significantly improved exploratory preferences, the number of object contacts, and the time spent swimming in the target quadrant in aged mice but not adults. Administration of Tat-HSP10 increased the number of proliferating cells and differentiated neuroblasts in the dentate gyrus of adult and aged mice compared to controls, as determined by immunohistochemical staining for Ki67 and doublecortin, respectively. Additionally, Tat-HSP10 treatment significantly mitigated the reduction in sirtuin 1 mRNA level, N-methyl-D-aspartate receptor 1, and postsynaptic density 95 protein levels in the hippocampus of aged mice. In contrast, Tat-HSP10 treatment significantly increased sirtuin 3 protein levels in both adult and aged mouse hippocampus. These suggest that Tat-HSP10 can potentially reduce hippocampus-related aging phenotypes.

Insect Peptide CopA3 Mitigates the Effects of Heat Stress on Porcine Muscle Satellite Cells

Heat stress inhibits cell proliferation as well as animal production. Here, we aimed to demonstrate that 9-mer disulfide dimer peptide (CopA3) supplementation stabilizes porcine muscle satellite cell (PMSC) proliferation and heat shock protein (HSP) expression at different temperatures. Therefore, we investigated the beneficial effects of CopA3 on PMSCs at three different temperatures (37, 39, and 41 °C). Based on temperature and CopA3 treatment, PMSCs were divided into six different groups including treatment and control groups for each temperature. Cell viability was highest with 10 µg/mL CopA3 and decreased as the concentration increased in a dose-dependent manner. CopA3 significantly increased the cell viability at all temperatures at 24 and 48 h. It significantly decreased apoptosis compared to that in the untreated groups. In addition, it decreased the apoptosis-related protein, Bcl-2-associated X (BAX), expression at 41 °C. Notably, temperature and CopA3 had no effects on the apoptosis-related protein, caspase 3. Expression levels of HSP40, HSP70, and HSP90 were significantly upregulated, whereas those of HSP47 and HSP60 were not affected by temperature changes. Except HSP90, CopA3 did not cause temperature-dependent changes in protein expression. Therefore, CopA3 promotes cell proliferation, inhibits apoptosis, and maintains stable HSP expression, thereby enhancing the heat-stress-tolerance capacity of PMSCs.

Effects of heat stress exposure on porcine muscle satellite cells

Heat stress (HS) affects cell culture as well as animal production. Although there have been many reports on the disparate effects of heat stress, its effects on mammalian muscle stem cells are still unclear. In this study, we isolated porcine muscle satellite cells (PMSCs) from the femurs of 1-day-old piglets, and cultured them under three temperature conditions: 37 °C, 39 °C, and 41 °C. Exposure to HS not only decreased the viability and proliferation rates of PMSCs, but also regulated the cell cycle and induced apoptosis. High-temperature culture conditions decreased both protein and gene expression of Pax7, a proliferation and maintenance marker of muscle satellite cells, whereas it increased both protein and gene expression of MyoG, a differentiation marker, and promoted myotube formation in the early stage of differentiation induction. In addition, the protein and gene expression of several heat shock proteins (HSPs) in PMSCs increased due to heat treatment. In conclusion, HS induced the cell cycle arrest of PMSCs, thereby reducing the proliferation rate. In addition, high-temperature culture conditions promoted the formation of myotubes at the early stage of differentiation of PMSCs without additives.

Mortalin: Protein partners, biological impacts, pathological roles, and therapeutic opportunities

Mortalin (GRP75, HSPA9A), a heat shock protein (HSP), regulates a wide range of cellular processes, including cell survival, growth, and metabolism. The regulatory functions of mortalin are mediated through a diverse set of protein partners associated with different cellular compartments, which allows mortalin to perform critical functions under physiological conditions, including mitochondrial protein quality control. However, alteration of mortalin's activities, its abnormal subcellular compartmentalization, and its protein partners turn mortalin into a disease-driving protein in different pathological conditions, including cancers. Here, mortalin's contributions to tumorigenic pathways are explained. Pathology information based on mortalin's RNA expression extracted from The Cancer Genome Atlas (TCGA) transcriptomic database indicates that mortalin has an independent prognostic value in common tumors, including lung, breast, and colorectal cancer (CRC). Subsequently, the binding partners of mortalin reported in different cellular models, from yeast to mammalian cells, and its regulation by post-translational modifications are discussed. Finally, we focus on colorectal cancer and discuss how mortalin and its tumorigenic downstream protein targets are regulated by a ubiquitin-like protein through the 26S proteasomal degradation machinery. A broader understanding of the function of mortalin and its positive and negative regulation in the formation and progression of human diseases, particularly cancer, is essential for developing new strategies to treat a diverse set of human diseases critically associated with dysregulated mortalin.

Heat stress inhibits the proliferation and differentiation of myoblasts and is associated with damage to mitochondria

Introduction: Heat stress is harmful to the health of humans and animals, more and more common, as a consequence of global warming, while the mechanism that heat stress modulates skeletal development remains unknown. Hence, we conducted a model of heat stress in vitro. Methods: We used Hu sheep myoblasts as the research object, real-time quantitative PCR (RT-qPCR) and western blot (WB) were conducted to detect the expression of mRNA and protein in heat-stressed myoblasts. The would-healing assay was used to detect the migration of myoblasts. The mitochondria were observed by a transmission electron microscope. Results: mRNA and protein expression of HSP60 was significantly enriched in the heat-stressed myoblasts during proliferation and differentiation (p < 0.05). In our study, we indicated that heat stress enriched the intracellular ROS of the myoblasts (p < 0.001), leading to an increase in autophagy in the myoblasts to induce apoptosis. The results demonstrated that the protein expression of LC3B-1 and BCL-2 was significantly increased in myoblasts under heat stress during proliferation and differentiation (p < 0.05). Additionally, heat stress inhibited mitochondrial biogenesis and function and reduced the mitochondrial membrane potential and downregulated the expression of mtCo2, mtNd1 and DNM1L (p < 0.05) in myoblasts during proliferation and differentiation. Consequently, heat stress inhibited the proliferation and differentiation of the myoblasts, in accordance with the downregulation of the expression of PAX7, MYOD, MYF5, MYOG and MYHC (p < 0.05). Moreover, heat stress also inhibited the cell migration of the myoblasts. Discussion: This work demonstrates that heat stress inhibits proliferation and differentiation, and accelerates apoptosis by impairing mitochondrial function and promoting autophagy, which provides a mechanism to understand heat stress affects the development of the skeletal muscle.

Insights Into the Role of Mortalin in Alzheimer’s Disease, Parkinson’s Disease, and HIV-1-Associated Neurocognitive Disorders

Mortalin is a chaperone protein that regulates physiological functions of cells. Its multifactorial role allows cells to survive pathological conditions. Pharmacological, chemical, and siRNA-mediated downregulation of mortalin increases oxidative stress, mitochondrial dysfunction leading to unregulated inflammation. In addition to its well-characterized function in controlling oxidative stress, mitochondrial health, and maintaining physiological balance, recent evidence from human brain autopsies and cell culture–based studies suggests a critical role of mortalin in attenuating the damage seen in several neurodegenerative diseases. Overexpression of mortalin provides an important line of defense against accumulated proteins, inflammation, and neuronal loss, a key characteristic feature observed in neurodegeneration. Neurodegenerative diseases are a group of progressive disorders, sharing pathological features in Alzheimer’s disease, Parkinson’s disease, multiple sclerosis, and HIV-associated neurocognitive disorder. Aggregation of insoluble amyloid beta-proteins and neurofibrillary tangles in Alzheimer’s disease are among the leading cause of neuropathology in the brain. Parkinson’s disease is characterized by the degeneration of dopamine neurons in substantia nigra pars compacta. A substantial synaptic loss leading to cognitive decline is the hallmark of HIV-associated neurocognitive disorder (HAND). Brain autopsies and cell culture studies showed reduced expression of mortalin in Alzheimer’s, Parkinson’s, and HAND cases and deciphered the important role of mortalin in brain cells. Here, we discuss mortalin and its regulation and describe how neurotoxic conditions alter the expression of mortalin and modulate its functions. In addition, we also review the neuroprotective role of mortalin under neuropathological conditions. This knowledge showcases the importance of mortalin in diverse brain functions and offers new opportunities for the development of therapeutic targets that can modulate the expression of mortalin using chemical compounds.

Identification, expression analysis and functional verification of two genes encoding small heat shock proteins in the western flower thrips, Frankliniella occidentalis (Pergande)

Small heat shock proteins (sHSPs) help prevent the irreversible aggregation of denatured proteins that occurs in response to organismal stress. In this study, we identified two intron-free genes encoding sHSPs from Frankliniella occidentalis; these were designated FoHSP11.6 and FoHSP28.0 and belonged to an atypical and typical sHSP family, respectively. Both FoHSPs were transcribed in all developmental stages of F. occidentalis with the highest expression levels in pupae and adults and greater expression in males than females. Although the FoHSPs had different temperature-induced expression profiles, they were generally induced by both low and high temperatures and reached maximal expression levels after 0.5-1 h of temperature stress. The FoHSPs expression levels in pupae were induced by drought and high humidity, and higher expression levels were correlated with lower survival rates. The thermotolerance of F. occidentalis decreased when theFoHSPs were silenced by RNA interference. Our results show that FoHSP11.6 and FoHSP28.0 are involved in the response to temperature and drought and may also function in growth and development of F. occidentalis.

Mitochondrial chaperones in human health and disease

Molecular chaperones are a family of proteins that maintain cellular protein homeostasis through non-covalent peptide folding and quality control mechanisms. The chaperone proteins found within mitochondria play significant protective roles in mitochondrial biogenesis, quality control, and stress response mechanisms. Defective mitochondrial chaperones have been implicated in aging, neurodegeneration, and cancer. In this review, we focus on the two most prominent mitochondrial chaperones: mtHsp60 and mtHsp70. These proteins demonstrate different cellular localization patterns, interact with different targets, and have different functional activities. We discuss the structure and function of these prominent mitochondrial chaperone proteins and give an update on newly discovered regulatory mechanisms and disease implications.

HSP70 and HSP90 in Cancer: Cytosolic, Endoplasmic Reticulum and Mitochondrial Chaperones of Tumorigenesis

HSP70 and HSP90 are two powerful chaperone machineries involved in survival and proliferation of tumor cells. Residing in various cellular compartments, HSP70 and HSP90 perform specific functions. Concurrently, HSP70 and HSP90 homologs may also translocate from their primary site under various stress conditions. Herein, we address the current literature on the role of HSP70 and HSP90 chaperone networks in cancer. The goal is to provide a comprehensive review on the functions of cytosolic, mitochondrial and endoplasmic reticulum HSP70 and HSP90 homologs in cancer. Given that high expression of HSP70 and HSP90 enhances tumor development and associates with tumor aggressiveness, further understanding of HSP70 and HSP90 chaperone networks may provide clues for the discoveries of novel anti-cancer therapies.

Glucose 6-P dehydrogenase delays the onset of frailty by protecting against muscle damage

BACKGROUND

Frailty is a major age-associated syndrome leading to disability. Oxidative damage plays a significant role in the promotion of frailty. The cellular antioxidant system relies on reduced nicotinamide adenine dinucleotide phosphate (NADPH) that is highly dependent on glucose 6-P dehydrogenase (G6PD). The G6PD-overexpressing mouse (G6PD-Tg) is protected against metabolic stresses. Our aim was to examine whether this protection delays frailty.

METHODS

Old wild-type (WT) and G6PD-Tg mice were evaluated longitudinally in terms of frailty. Indirect calorimetry, transcriptomic profile, and different skeletal muscle quality markers and muscle regenerative capacity were also investigated.

RESULTS

The percentage of frail mice was significantly lower in the G6PD-Tg than in the WT genotype, especially in 26-month-old mice where 50% of the WT were frail vs. only 13% of the Tg ones (P < 0.001). Skeletal muscle transcriptomic analysis showed an up-regulation of respiratory chain and oxidative phosphorylation (P = 0.009) as well as glutathione metabolism (P = 0.035) pathways in the G6PD-Tg mice. Accordingly, the Tg animals exhibited an increase in reduced glutathione (34.5%, P < 0.01) and a decrease on its oxidized form (-69%, P < 0.05) and in lipid peroxidation (4-HNE: -20.5%, P < 0.05). The G6PD-Tg mice also showed reduced apoptosis (BAX/Bcl2: -25.5%, P < 0.05; and Bcl-xL: -20.5%, P < 0.05), lower levels of the intramuscular adipocyte marker FABP4 (-54.7%, P < 0.05), and increased markers of mitochondrial content (COX IV: 89.7%, P < 0.05; Grp75: 37.8%, P < 0.05) and mitochondrial OXPHOS complexes (CII: 81.25%, P < 0.01; CIII: 52.5%, P < 0.01; and CV: 37.2%, P < 0.05). Energy expenditure (-4.29%, P < 0.001) and the respiratory exchange ratio were lower (-13.4%, P < 0.0001) while the locomotor activity was higher (43.4%, P < 0.0001) in the 20-month-old Tg, indicating a major energetic advantage in these mice. Short-term exercise training in young C57BL76J mice induced a robust activation of G6PD in skeletal muscle (203.4%, P < 0.05), similar to that achieved in the G6PD-Tg mice (142.3%, P < 0.01).

CONCLUSIONS

Glucose 6-P dehydrogenase deficiency can be an underestimated risk factor for several human pathologies and even frailty. By overexpressing G6PD, we provide the first molecular model of robustness. Because G6PD is regulated by pharmacological and physiological interventions like exercise, our results provide molecular bases for interventions that by increasing G6PD will delay the onset of frailty.

Rapidly Growing Mycobacterium Species: The Long and Winding Road from Tuberculosis Vaccines to Potent Stress-Resilience Agents

Inflammatory diseases and stressor-related psychiatric disorders, for which inflammation is a risk factor, are increasing in modern Western societies. Recent studies suggest that immunoregulatory approaches are a promising tool in reducing the risk of suffering from such disorders. Specifically, the environmental saprophyte Mycobacterium vaccae National Collection of Type Cultures (NCTC) 11659 has recently gained attention for the prevention and treatment of stress-related psychiatric disorders. However, effective use requires a sophisticated understanding of the effects of M. vaccae NCTC 11659 and related rapidly growing mycobacteria (RGMs) on microbiome–gut–immune–brain interactions. This historical narrative review is intended as a first step in exploring these mechanisms and provides an overview of preclinical and clinical studies on M. vaccae NCTC 11659 and related RGMs. The overall objective of this review article is to increase the comprehension of, and interest in, the mechanisms through which M. vaccae NCTC 11659 and related RGMs promote stress resilience, with the intention of fostering novel clinical strategies for the prevention and treatment of stressor-related disorders.

Role of Heat Shock Proteins (HSP70 and HSP90) in Viral Infection

Heat shock proteins (HSPs) are a large group of chaperones found in most eukaryotes and bacteria. They are responsible for the correct protein folding, protection of the cell against stressors, presenting immune and inflammatory cytokines; furthermore, they are important factors in regulating cell differentiation, survival and death. Although the biological function of HSPs is to maintain cell homeostasis, some of them can be used by viruses both to fold their proteins and increase the chances of survival in unfavorable host conditions. Folding viral proteins as well as replicating many different viruses are carried out by, among others, proteins from the HSP70 and HSP90 families. In some cases, the HSP70 family proteins directly interact with viral polymerase to enhance viral replication or they can facilitate the formation of a viral replication complex and/or maintain the stability of complex proteins. It is known that HSP90 is important for the expression of viral genes at both the transcriptional and the translational levels. Both of these HSPs can form a complex with HSP90 and, consequently, facilitate the entry of the virus into the cell. Current studies have shown the biological significance of HSPs in the course of infection SARS-CoV-2. A comprehensive understanding of chaperone use during viral infection will provide new insight into viral replication mechanisms and therapeutic potential. The aim of this study is to describe the molecular basis of HSP70 and HSP90 participation in some viral infections and the potential use of these proteins in antiviral therapy.

PSPC1 is a new contextual determinant of aberrant subcellular translocation of oncogenes in tumor progression

Dysregulation of nucleocytoplasmic shuttling is commonly observed in cancers and emerging as a cancer hallmark for the development of anticancer therapeutic strategies. Despite its severe adverse effects, selinexor, a selective first-in-class inhibitor of the common nuclear export receptor XPO1, was developed to target nucleocytoplasmic protein shuttling and received accelerated FDA approval in 2019 in combination with dexamethasone as a fifth-line therapeutic option for adults with relapsed refractory multiple myeloma (RRMM). To explore innovative targets in nucleocytoplasmic shuttling, we propose that the aberrant contextual determinants of nucleocytoplasmic shuttling, such as PSPC1 (Paraspeckle component 1), TGIF1 (TGF-β Induced Factor Homeobox 1), NPM1 (Nucleophosmin), Mortalin and EBP50, that modulate shuttling (or cargo) proteins with opposite tumorigenic functions in different subcellular locations could be theranostic targets for developing anticancer strategies. For instance, PSPC1 was recently shown to be the contextual determinant of the TGF-β prometastatic switch and PTK6/β-catenin reciprocal oncogenic nucleocytoplasmic shuttling during hepatocellular carcinoma (HCC) progression. The innovative nucleocytoplasmic shuttling inhibitor PSPC1 C-terminal 131 polypeptide (PSPC1-CT131), which was developed to target both the shuttling determinant PSPC1 and the shuttling protein PTK6, maintained their tumor-suppressive characteristics and exhibited synergistic effects on tumor suppression in HCC cells and mouse models. In summary, targeting the contextual determinants of nucleocytoplasmic shuttling with cargo proteins having opposite tumorigenic functions in different subcellular locations could be an innovative strategy for developing new therapeutic biomarkers and agents to improve cancer therapy.

Adhesion-mediated mechanosignaling forces mitohormesis

Mitochondria control eukaryotic cell fate by producing the energy needed to support life and the signals required to execute programed cell death. The biochemical milieu is known to affect mitochondrial function and contribute to the dysfunctional mitochondrial phenotypes implicated in cancer and the morbidities of aging. However, the physical characteristics of the extracellular matrix are also altered in cancerous and aging tissues. Here, we demonstrate that cells sense the physical properties of the extracellular matrix and activate a mitochondrial stress response that adaptively tunes mitochondrial function via solute carrier family 9 member A1-dependent ion exchange and heat shock factor 1-dependent transcription. Overall, our data indicate that adhesion-mediated mechanosignaling may play an unappreciated role in the altered mitochondrial functions observed in aging and cancer.

Heat Shock Proteins in Lymphoma Immunotherapy

Immunotherapy harnessing the host immune system for tumor destruction revolutionized oncology research and advanced treatment strategies for lymphoma patients. Lymphoma is a heterogeneous group of cancer, where the central roles in pathogenesis play immune evasion and dysregulation of multiple signaling pathways. Immunotherapy-based approaches such as engineered T cells (CAR T), immune checkpoint modulators and NK cell-based therapies are now in the frontline of lymphoma research. Even though emerging immunotherapies showed promising results in treating lymphoma patients, low efficacy and on-target/off-tumor toxicity are of a major concern. To address that issue it is suggested to look into the emerging role of heat shock proteins. Heat shock proteins (HSPs) showed to be highly expressed in lymphoma cells. HSPs are known for their abilities to modulate immune responses and inhibit apoptosis, which made their successful entry into cancer clinical trials. Here, we explore the role of HSPs in Hodgkin and Non-Hodgkin lymphoma and their involvement in CAR T therapy, checkpoint blockade and NK cell- based therapies. Understanding the role of HSPs in lymphoma pathogenesis and the ways how HSPs may enhance anti-tumor responses, may help in the development of more effective, specific and safe immunotherapy.

Function and Fiber-Type Specific Distribution of Hsp60 and αB-Crystallin in Skeletal Muscles: Role of Physical Exercise

Simple Summary

Skeletal muscle represents about 40% of the body mass in humans and it is a copious and plastic tissue, rich in proteins that are subject to continuous rearrangements. Physical exercise is considered a physiological stressor for different organs, in particular for skeletal muscle, and it is a factor able to stimulate the cellular remodeling processes related to the phenomenon of adaptation. All cells respond to various stress conditions by up-regulating the expression and/or activation of a group of proteins called heat shock proteins (HSPs). Although their expression is induced by several stimuli, they are commonly recognized as HSPs due to the first experiments showing their increased transcription after application of heat shock. These proteins are molecular chaperones mainly involved in assisting protein transport and folding, assembling multimolecular complexes, and triggering protein degradation by proteasome. Among the HSPs, a special attention needs to be devoted to Hsp60 and αB-crystallin, proteins constitutively expressed in the skeletal muscle, where they are known to be important in muscle physiopathology. Therefore, here we provide a critical update on their role in skeletal muscle fibers after physical exercise, highlighting the control of their expression, their biological function, and their specific distribution within skeletal muscle fiber-types.

Abstract

Skeletal muscle is a plastic and complex tissue, rich in proteins that are subject to continuous rearrangements. Skeletal muscle homeostasis can be affected by different types of stresses, including physical activity, a physiological stressor able to stimulate a robust increase in different heat shock proteins (HSPs). The modulation of these proteins appears to be fundamental in facilitating the cellular remodeling processes related to the phenomenon of training adaptations such as hypertrophy, increased oxidative capacity, and mitochondrial activity. Among the HSPs, a special attention needs to be devoted to Hsp60 and αB-crystallin (CRYAB), proteins constitutively expressed in the skeletal muscle, where their specific features could be highly relevant in understanding the impact of different volumes of training regimes on myofiber types and in explaining the complex picture of exercise-induced mechanical strain and damaging conditions on fiber population. This knowledge could lead to a better personalization of training protocols with an optimal non-harmful workload in populations of individuals with different needs and healthy status. Here, we introduce for the first time to the reader these peculiar HSPs from the perspective of exercise response, highlighting the control of their expression, biological function, and specific distribution within skeletal muscle fiber-types.

Heat Shock Protein HSP60 in Left Ventricular Cardiomyocytes of Hypertensive Rats with and without Insulin-Dependent Diabetes Mellitus

In cardiomyocytes, high molecular ATP-dependent HSP70 and HSP90 play an important role in protecting the myocardium from abnormal proteins that appear, in particular, due to activation of oxidative stress. Molecular chaperone HSP60 is of particular importance for cardiomyocytes as it is responsible for assembly of mitochondrial matrix proteins. We studied the peculiarities of expression of HSP60 in left ventricular cardiomyocytes in hypertension, insulin-dependent diabetes mellitus, and their combination. The experiment was performed on 38-week-old male Wistar-Kyoto and SHR (spontaneously hypertensive) rats aged 38-57 weeks. Insulin-dependent diabetes mellitus was modeled by a single parenteral administration of 65 mg/kg streptozotocin. Expression of HSP60 in left ventricular cardiomyocytes was evaluated by immunohistochemical methods. It was found that hypertension, diabetes mellitus, and their combination are associated with a significant decrease in the content of HSP60 in left ventricular cardiomyocytes in comparison with the control. This finding can be considered as a pathogenetic mechanism of myocardial damage induced by hypertension and diabetes mellitus.

Mitochondrial Translocation of DJ-1 Is Mediated by Grp75: Implication in Cardioprotection of Resveratrol Against Hypoxia/Reoxygenation-Induced Oxidative Stress

Resveratrol (Res) was recently reported to ameliorate hypoxia/reoxygenation (H/R)-caused oxidative stress in H9c2 cardiomyocytes through promoting the mitochondrial translocation of DJ-1 protein and subsequently preserving the activity of mitochondrial complex I. However, it is noteworthy that DJ-1 possesses no mitochondria-targeting sequence. Therefore, how Res induces DJ-1 mitochondrial translocation is an important and interesting question for further exploration. Glucose-regulated protein 75 (Grp75), whose N-terminus contains a 51-amino acid long mitochondrial-targeting signal peptide, is a cytoprotective chaperone that partakes in mitochondrial import of several proteins. Here, the contribution of Grp75 to mitochondrial import of DJ-1 by Res was investigated in a cellular model of H/R. Our results showed that Res upregulated the expression of DJ-1 protein, enhanced the interaction of DJ-1 and Grp75, and promoted DJ-1 translocation to mitochondria from cytosol in H9c2 cardiomyocytes undergoing H/R. Importantly, knockdown of Grp75 markedly reduced the interaction of DJ-1 with Grp75 and subsequent DJ-1 mitochondrial translocation induced by Res. Furthermore, Res pretreatment promoted the association of DJ-1 with ND1 and NDUFA4 subunits of complex I, preserved the activity of complex I, decreased mitochondria-derived reactive oxygen species production, and eventually ameliorated H/R-caused oxidative stress damage. Intriguingly, these effects were largely prevented also by small interfering RNA targeting Grp75. Overall, these results suggested that Grp75 interacts with DJ-1 to facilitate its translocation from cytosol to mitochondria, which is required for Res-mediated preservation of mitochondria complex I and cardioprotection from H/R-caused oxidative stress injury.

Hypertrophic Adipocyte-Derived Exosomal miR-802-5p Contributes to Insulin Resistance in Cardiac Myocytes Through Targeting HSP60

OBJECTIVE

This study aimed to elucidate the mechanism by which hypertrophic adipocytes regulate insulin signaling in cardiac myocytes.

METHODS

Palmitate was used to induce hypertrophic 3T3-L1 adipocytes. Exosomes were purified from normal control or hypertrophic 3T3-L1 adipocyte-associated conditioned medium. Exosome-exposed neonatal rat ventricular myocytes were stimulated with insulin to investigate the effects of exosomes on insulin signaling. Small interfering RNA techniques were used to downregulate protein levels, and their efficiency was evaluated by Western blot.

RESULTS

Hypertrophic adipocyte-derived exosomes highly expressed miR-802-5p. Insulin sensitivity of neonatal rat ventricular myocytes was negatively regulated by miR-802-5p. TargetScan and luciferase reporter assays revealed that heat shock protein 60 (HSP60) was a direct target of miR-802-5p. HSP60 silencing was found to induce insulin resistance and to mitigate the insulin-sensitizing effects of adiponectin. In addition, HSP60 depletion significantly increased the expression levels of C/EBP-homologous protein and enhanced oxidative stress, accompanied by the increases in the phosphorylation of JNK and IRS-1 Ser307. Moreover, the effects of HSP60 knockdown on C/EBP-homologous protein and oxidative stress were abolished by the inhibition of either miR-802-5p or endocytosis.

CONCLUSIONS

Hypertrophic adipocyte-derived exosomal miR-802-5p caused cardiac insulin resistance through downregulating HSP60. These findings provide a novel mechanism by which epicardial adipose tissue impairs cardiac function.

Identification of miPEP133 as a novel tumor-suppressor microprotein encoded by miR-34a pri-miRNA

BACKGROUND

Very few proteins encoded by the presumed non-coding RNA transcripts have been identified. Their cellular functions remain largely unknown. This study identifies the tumor-suppressor function of a novel microprotein encoded by the precursor of miR-34a. It consists of 133 amino acid residues, thereby named as miPEP133 (pri-microRNA encoded peptide 133).

METHODS

We overexpressed miPEP133 in nasopharyngeal carcinoma (NPC), ovarian cancer and cervical cancer cell lines to determine its effects on cell growth, apoptosis, migration, or invasion. Its impact on tumor growth was evaluated in a xenograft NPC model. Its prognostic value was analyzed using NPC clinical samples. We also conducted western blot, immunoprecipitation, mass spectrometry, confocal microscopy and flow cytometry to determine the underlying mechanisms of miPEP133 function and regulation.

RESULTS

miPEP133 was expressed in normal human colon, stomach, ovary, uterus and pharynx. It was downregulated in cancer cell lines and tumors. miPEP133 overexpression induced apoptosis in cancer cells and inhibited their migration and invasion. miPEP133 inhibited tumor growth in vivo. Low miPEP133 expression was an unfavorable prognostic marker associated with advanced metastatic NPC. Wild-type p53 but not mutant p53 induced miPEP133 expression. miPEP133 enhanced p53 transcriptional activation and miR-34a expression. miPEP133 localized in the mitochondria to interact with mitochondrial heat shock protein 70kD (HSPA9) and prevent HSPA9 from interacting with its binding partners, leading to the decrease of mitochondrial membrane potential and mitochondrial mass.

CONCLUSION

miPEP133 is a tumor suppressor localized in the mitochondria. It is a potential prognostic marker and therapeutic target for multiple types of cancers.

EVEN-PLUS syndrome: A case report with novel variants in HSPA9 and evidence of HSPA9 gene dysfunction

EVEN-PLUS syndrome is a rare condition characterized by its involvement of the Epiphyses, Vertebrae, Ears, and Nose, PLUS other associated findings. We report here the fifth case of EVEN-PLUS syndrome with novel variants c.818 T > G (p.L273X) and c.955C > T (p.L319F) in the HSPA9 gene identified through whole-exome sequencing. The patient is the first male known to be affected and presented with additional features not previously described with EVEN-PLUS syndrome. These features include agenesis of the septum pellucidum, a short chest and sternum, 13 pairs of ribs, a single hemivertebra, laterally displaced nipples, hydronephrosis, unilateral cryptorchidism, unilateral single palmar crease, bilateral clubfoot, and hypotonia. qPCR analysis provides supporting evidence for a nonsense-mediated decay mechanism for the HSPA9 truncating variant. In silico 3D modeling supports the pathogenicity of the c.955C > T (p.L319F) missense variant. The study presented here further describes the syndrome and broadens its mutational and phenotypic spectrum. Our study also lends support to HSPA9 variants as the underlying etiology of EVEN-PLUS syndrome and ultimately provides a better understanding of the molecular basis of the condition.

Mitochondrial Protein Quality Control Mechanisms

Mitochondria serve as a hub for many cellular processes, including bioenergetics, metabolism, cellular signaling, redox balance, calcium homeostasis, and cell death. The mitochondrial proteome includes over a thousand proteins, encoded by both the mitochondrial and nuclear genomes. The majority (~99%) of proteins are nuclear encoded that are synthesized in the cytosol and subsequently imported into the mitochondria. Within the mitochondria, polypeptides fold and assemble into their native functional form. Mitochondria health and integrity depend on correct protein import, folding, and regulated turnover termed as mitochondrial protein quality control (MPQC). Failure to maintain these processes can cause mitochondrial dysfunction that leads to various pathophysiological outcomes and the commencement of diseases. Here, we summarize the current knowledge about the role of different MPQC regulatory systems such as mitochondrial chaperones, proteases, the ubiquitin-proteasome system, mitochondrial unfolded protein response, mitophagy, and mitochondria-derived vesicles in the maintenance of mitochondrial proteome and health. The proper understanding of mitochondrial protein quality control mechanisms will provide relevant insights to treat multiple human diseases.

Sex Differences in Biological Processes and Nitrergic Signaling in Mouse Brain

Nitric oxide (NO) represents an important signaling molecule which modulates the functions of different organs, including the brain. S-nitrosylation (SNO), a post-translational modification that involves the binding of the NO group to a cysteine residue, is a key mechanism of nitrergic signaling. Most of the experimental studies are carried out on male animals. However, significant differences exist between males and females in the signaling mechanisms. To investigate the sex differences in the SNO-based regulation of biological functions and signaling pathways in the cortices of 6–8-weeks-old mice, we used the mass spectrometry technique, to identify S-nitrosylated proteins, followed by large-scale computational biology. This work revealed significant sex differences in the NO and SNO-related biological functions in the cortices of mice for the first-time. The study showed significant SNO-induced enrichment of the synaptic processes in female mice, but enhanced SNO-related cytoskeletal processes in the male mice. Proteins, which were S-nitrosylated in the cortices of mice of both groups, were more abundant in the female brain. Finally, we investigated the shared molecular processes that were found in both sexes. This study presents a mechanistic insight into the role of S-nitrosylation in both sexes and provides strong evidence of sex difference in many biological processes and signalling pathways, which will open future research directions on sex differences in neurological disorders.

Heat Shock Protein 60 in Hepatocellular Carcinoma: Insights and Perspectives

Heat shock protein 60 (HSP60) is a mitochondrial chaperone that is implicated in physiological and pathological processes. For instance, it contributes to protein folding and stability, translocation of mitochondrial proteins, and apoptosis. Variations in the expression levels of HSP60 have been correlated to various diseases and cancers, including hepatocellular carcinoma (HCC). Unlike other HSPs which clearly increase in some cancers, data about HSP60 levels in HCC are controversial and difficult to interpret. In the current review, we summarize and simplify the current knowledge about the role of HSP60 in HCC. In addition, we highlight the possibility of its targeting, using chemical compounds and/or genetic tools for treatment of HCC.

Sunscreen-induced expression and identification of photosensitive marker proteins in human keratinocytes under UV radiation

Solar ultraviolet (UV) radiation is the main factor of photocarcinogenesis, photoaging, and photosensitivity; thus protection from biological damaging UV radiation is a concern. Sunscreens containing UV filters are the most preferred means of photoprotection but the safety and efficacy of UV filters are in question. Benzophenone (BP) and its derivatives, namely, benzophenone 1 (BP1), is commonly used in sunscreens as a UV blocker. The aim of this study was to assess the effects of BP and BP1 on the differential expression of proteins in human keratinocytes (HaCaT cells) under exposure to ultraviolet A radiation. Photosensitive proteins were screened from HaCaT cells by two-dimensional (2-D) gel electrophoresis, and identification of these differentially expressed proteins was performed by matrix-assisted laser desorption/ionization-time-of-flight (MALDI-TOF)/TOF mass spectrometry. Protein identification was performed using the search program MASCOT and a database made of SUMO and GhJMJ12 amino acid sequences. Our results showed that the proteins involved directly or indirectly in apoptosis are 70 kDa heat shock protein, long-chain specific acyl-CoA dehydrogenase, serine/threonine-protein kinase, and FAM78A protein, which were upregulated in comparison to control HaCaT cells. The expressions of binding immunoglobulin protein, podocalyxin-like protein, actin, cytoplasmic, and calreticulin precursors were downregulated. The altered protein expression indicated that cell growth arrest and apoptosis were potential mechanisms of cytotoxicity and genotoxicity of BPs. The results of 2-D gel electrophoresis followed by mass spectrometry showed expression of novel proteins involved in promoting or initiating apoptotic pathways. Hence, we conclude that BPs should be avoided as a UV blocker from sunscreens because of its potential to promote apoptotic proteins in human skin keratinocytes.

A Comprehensive Review of Alzheimer's Association with Related Proteins: Pathological Role and Therapeutic Significance

Alzheimer's is an insidious, progressive, chronic neurodegenerative disease which causes the devastation of neurons. Alzheimer's possesses complex pathologies of heterogeneous nature counting proteins as one major factor along with enzymes and mutated genes. Proteins such as amyloid precursor protein (APP), apolipoprotein E (ApoE), presenilin, mortalin, calbindin-D28K, creactive protein, heat shock proteins (HSPs), and prion protein are some of the chief elements in the foremost hypotheses of AD like amyloid-beta (Aβ) cascade hypothesis, tau hypothesis, cholinergic neuron damage, etc. Disturbed expression of these proteins results in synaptic dysfunction, cognitive impairment, memory loss, and neuronal degradation. On the therapeutic ground, attempts of developing anti-amyloid, anti-inflammatory, anti-tau therapies are on peak, having APP and tau as putative targets. Some proteins, e.g., HSPs, which ameliorate oxidative stress, calpains, which help in regulating synaptic plasticity, and calmodulin-like skin protein (CLSP) with its neuroprotective role are few promising future targets for developing anti-AD therapies. On diagnostic grounds of AD C-reactive protein, pentraxins, collapsin response mediator protein-2, and growth-associated protein-43 represent the future of new possible biomarkers for diagnosing AD. The last few decades were concentrated over identifying and studying protein targets of AD. Here, we reviewed the physiological/pathological roles and therapeutic significance of nearly all the proteins associated with AD that addresses putative as well as probable targets for developing effective anti-AD therapies.

Molecular Mechanism Underlying Hypoxic Preconditioning-Promoted Mitochondrial Translocation of DJ-1 in Hypoxia/Reoxygenation H9c2 Cells

DJ-1 was recently reported to be involved in the cardioprotection of hypoxic preconditioning (HPC) against hypoxia/reoxygenation (H/R)-induced oxidative stress damage, by preserving mitochondrial complex I activity and, subsequently, inhibiting mitochondrial reactive oxygen species (ROS) generation. However, the molecular mechanism by which HPC enables mitochondrial translocation of DJ-1, which has no mitochondria-targeting sequence, to preserve mitochondrial complex I, is largely unknown. In this study, co-immunoprecipitation data showed that DJ-1 was associated with glucose-regulated protein 75 (Grp75), and this association was significantly enhanced after HPC. Immunofluorescence imaging and Western blot analysis showed that HPC substantially enhanced the translocation of DJ-1 from cytosol to mitochondria in H9c2 cells subjected to H/R, which was mimicked by DJ-1 overexpression induced by pFlag-DJ-1 transfection. Importantly, knockdown of Grp75 markedly reduced the mitochondrial translocation of DJ-1 induced by HPC and pFlag-DJ-1 transfection. Moreover, HPC promoted the association of DJ-1 with mitochondrial complex I subunits ND1 and NDUFA4, improved complex I activity, and inhibited mitochondria-derived ROS production and subsequent oxidative stress damage after H/R, which was also mimicked by pFlag-DJ-1 transfection. Intriguingly, these effects of HPC and pFlag-DJ-1 transfection were also prevented by Grp75 knockdown. In conclusion, these results indicated that HPC promotes the translocation of DJ-1 from cytosol to mitochondria in a Grp75-dependent manner and Grp75 is required for DJ-1-mediated protection of HPC on H/R-induced mitochondrial complex I defect and subsequent oxidative stress damage.

Expression and localization of heat-shock proteins during skeletal muscle cell proliferation and differentiation and the impact of heat stress

Skeletal myogenesis is a coordinated sequence of events associated with dramatic changes in cell morphology, motility, and metabolism, which causes cellular stress and alters proteostasis. Chaperones, such as heat-shock proteins (HSPs), play important roles in limiting cellular stresses and maintaining proteostasis, but whether HSPs are specifically involved in myogenesis is not well understood. Here, we characterized gene and protein expression and subcellular localization of various HSPs in proliferating C2C12 myoblasts and differentiating myotubes under control conditions and in response to heat stress. Hsp25, Hsp40, and Hsp60 protein expression declined by 48, 35, and 83%, respectively, during differentiation. In contrast, Hsp70 protein levels doubled during early differentiation. Hsp25 was predominantly localized to the cytoplasm of myoblasts and myotubes but formed distinct aggregates in perinuclear spaces of myoblasts after heat-shock. Hsp40 was distributed diffusely throughout the cytoplasm and nucleus and, after heat-shock, translocated to the nucleus of myoblasts but formed aggregates in myotubes. Hsp60 localized to the perinuclear space in myoblasts but was distributed more diffusely across the cytoplasm in myotubes. Hsp70 was expressed diffusely throughout the cytoplasm and nucleus and translocated to the nucleus after heat-shock in myoblasts, but not in myotubes. Hsp90 was expressed diffusely across the cytoplasm in both myoblasts and myotubes under control conditions and did not change in response to heat-shock. These findings reveal distinct and different roles for HSPs in the regulation of myogenic cell proliferation and differentiation.

Modulation of Diacylglycerol-Induced Melanogenesis in Human Melanoma and Primary Melanocytes: Role of Stress Chaperone Mortalin

Skin color/pigmentation is regulated through melanogenesis process in specialized melanin-producing cells, melanocytes, involving multiple signaling pathways. It is highly influenced by intrinsic and extrinsic factors such as oxidative, ultraviolet radiations and other environmental stress conditions. Besides determining the color, it governs response and tolerance of skin to a variety of environmental stresses and pathological conditions including photodamage, hyperpigmentation, and skin cancer. Depigmenting reagents have been deemed useful not only for cosmetics but also for pigmentation-related pathologies. In the present study, we attempted modulation of 1-oleoyl-2-acetyl-glycerol- (OAG-) induced melanogenesis in human melanoma and primary melanocytes. In both cell types, OAG-induced melanogenesis was associated with increase in enhanced expression of melanin, tyrosinase, as well as stress chaperones (mortalin and HSP60) and Reactive Oxygen Species (ROS). Treatment with TXC (trans-4-(Aminomethyl) cyclohexanecarboxylic acid hexadecyl ester hydrochloride) and 5/40 natural compounds resulted in their reduction. The data proposed an important role of mortalin and oxidative stress in skin pigmentation and the use of TXC and natural extracts for modulation of pigmentation pathways in normal and pathological conditions.

Biophysical Consequences of EVEN-PLUS Syndrome Mutations for the Function of Mortalin

HSPA9, the gene coding for the mitochondrial chaperone mortalin, is involved in various cellular roles such as mitochondrial protein import, folding, degradation, Fe-S cluster biogenesis, mitochondrial homeostasis, and regulation of the antiapoptotic protein p53. Mutations in the HSPA9 gene, particularly within the region coding for the nucleotide-binding domain (NBD), cause the autosomal disorder known as EVEN-PLUS syndrome. The resulting mutants R126W and Y128C are located on the surface of the mortalin-NBD near the binding interface with the interdomain linker (IDL). We used differential scanning fluorimetry (DSF), biolayer interferometry, X-ray crystallography, ATP hydrolysis assays, and Rosetta docking simulations to study the structural and functional consequences of the EVEN-PLUS syndrome-associated R126W and Y128C mutations within the mortalin-NBD. These results indicate that the surface mutations R126W and Y128C have far-reaching effects that disrupt ATP hydrolysis, interdomain linker binding, and thermostability and increase the propensity for aggregation. The structural differences observed provide insight into how the conformations of mortalin differ from other heat shock protein 70 (Hsp70) homologues. Combined, our biophysical and structural studies contribute to the understanding of the molecular basis for how disease-associated mortalin mutations affect mortalin functionality and the pathogenesis of EVEN-PLUS syndrome.

The Hsp70/J-protein machinery of the African trypanosome, Trypanosoma brucei

The etiological agent of the neglected tropical disease African trypanosomiasis, Trypanosoma brucei, possesses an expanded and diverse repertoire of heat shock proteins, which have been implicated in cytoprotection, differentiation, as well as progression and transmission of the disease. Hsp70 plays a crucial role in proteostasis, and inhibition of its interactions with co-chaperones is emerging as a potential therapeutic target for numerous diseases. In light of genome annotations and the release of the genome sequence of the human infective subspecies, an updated and current in silico overview of the Hsp70/J-protein machinery in both T. brucei brucei and T. brucei gambiense was conducted. Functional, structural, and evolutionary analyses of the T. brucei Hsp70 and J-protein families were performed. The Hsp70 and J-proteins from humans and selected kinetoplastid parasites were used to assist in identifying proteins from T. brucei, as well as the prediction of potential Hsp70-J-protein partnerships. The Hsp70 and J-proteins were mined from numerous genome-wide proteomics studies, which included different lifecycle stages and subcellular localisations. In this study, 12 putative Hsp70 proteins and 67 putative J-proteins were identified to be encoded on the genomes of both T. brucei subspecies. Interestingly there are 6 type III J-proteins that possess tetratricopeptide repeat-containing (TPR) motifs. Overall, it is envisioned that the results of this study will provide a future context for studying the biology of the African trypanosome and evaluating Hsp70 and J-protein interactions as potential drug targets.

Hsp60 in Skeletal Muscle Fiber Biogenesis and Homeostasis: From Physical Exercise to Skeletal Muscle Pathology

Hsp60 is a molecular chaperone classically described as a mitochondrial protein with multiple roles in health and disease, participating to the maintenance of protein homeostasis. It is well known that skeletal muscle is a complex tissue, rich in proteins, that is, subjected to continuous rearrangements, and this homeostasis is affected by many different types of stimuli and stresses. The regular exercise induces specific histological and biochemical adaptations in skeletal muscle fibers, such as hypertrophy and an increase of mitochondria activity and oxidative capacity. The current literature is lacking in information regarding Hsp60 involvement in skeletal muscle fiber biogenesis and regeneration during exercise, and in disease conditions. Here, we briefly discuss the functions of Hsp60 in skeletal muscle fibers during exercise, inflammation, and ageing. Moreover, the potential usage of Hsp60 as a marker for disease and the evaluation of novel treatment options is also discussed. However, some questions remain open, and further studies are needed to better understand Hsp60 involvement in skeletal muscle homeostasis during exercise and in pathological condition.

Identification of a Shared Cytochrome p4502E1 Epitope Found in Anesthetic Drug-Induced and Viral Hepatitis

Cytochrome p4502E1 (CYP2E1) autoantibodies are biomarkers for drug-induced hepatitis and chronic hepatitis C. However, major histocompatibility-restricted CYP2E1 epitopes associated with these diseases have not been identified. We hypothesized that CYP2E1 epitopes associated with different types of hepatitis may be shared and may impact immune responses and metabolism. SYFPEITHI epitope prediction identified CYP2E1 candidate epitopes that would be recognized by MHC II haplotypes. Candidate epitopes were tested for induction of hepatitis and CYP2E1 autoantibodies in mice and recognition by sera from patients with anesthetic drug-induced and viral hepatitis. Human liver cells treated with epitope hybridoma serum were analyzed for mitochondrial stress. CYP2E1 activity was measured in human microsomes similarly treated. Epitope antibodies in viral hepatitis sera were analyzed using linear regression to uncover associations with liver pathology. A P value of <0.05 was considered significant. One epitope (Gly113-Leu135) induced hepatitis and CYP2E1 autoantibodies in mice after modification of Lys123 (P < 0.05). Gly113-Leu135 antiserum recognized mitochondria and endoplasmic reticula (P < 0.05), upregulated HSP27 (P < 0.01) and mitochondrial oxidative stress via complex 1 inhibition (P < 0.001), and inhibited CYP2E1 activity. Gly113-Leu135 IgG4 detected in viral hepatitis sera was associated with severe hepatic fibrosis (P = 0.0142). We found a novel CYP2E1 epitope that was detected in anesthetic and viral hepatitis and that triggered hepatitis in mice. Our findings may improve understanding of hepatic immune responses triggered by metabolism or viruses.IMPORTANCE Drug-induced hepatitis is the leading reason that an approved drug is removed from the commercial market. Halogenated anesthetics can induce hepatitis in susceptible persons, and cytochrome p4502E1 (CYP2E1) enzymes responsible for their metabolism induce antibodies in addition to hepatitis. CYP2E1 antibodies detected in anesthetic hepatitis patients have been detected in patients with viral hepatitis, suggesting that these different forms of hepatitis could develop immune reactions to a common segment or epitope of CYP2E1. We have found a common MHC-restricted CYP2E1 epitope in anesthetic and viral hepatitis that is a dominant epitope in anesthetic hepatitis and is significantly associated with fibrosis in patients with viral hepatitis. Along with conformational epitopes, our identification of MHC-restricted CYP2E1 epitopes can be used to develop specific diagnostic tests for drug-induced or viral hepatitis or associated fibrosis or to predict individuals at risk for developing these diseases or their sequelae.

UBXN2A enhances CHIP-mediated proteasomal degradation of oncoprotein mortalin-2 in cancer cells

Overexpression of oncoproteins is a major cause of treatment failure using current chemotherapeutic drugs. Drug-induced degradation of oncoproteins is feasible and can improve clinical outcomes in diverse types of cancers. Mortalin-2 (mot-2) is a dominant oncoprotein in several tumors, including colorectal cancer (CRC). In addition to inactivating the p53 tumor suppressor protein, mot-2 enhances tumor cell invasion and migration. Thus, mot-2 is considered a potential therapeutic target in several cancer types. The current study investigated the biological role of a ubiquitin-like protein called UBXN2A in the regulation of mot-2 turnover. An orthogonal ubiquitin transfer technology followed by immunoprecipitation, in vitro ubiquitination, and Magnetic Beads TUBE2 pull-down experiments revealed that UBXN2A promotes carboxyl terminus of the HSP70-interacting protein (CHIP)-dependent ubiquitination of mot-2. We subsequently showed that UBXN2A increases proteasomal degradation of mot-2. A subcellular compartmentalization experiment revealed that induced UBXN2A decreases the level of mot-2 and its chaperone partner, HSP60. Pharmacological upregulation of UBXN2A using a small molecule, veratridine (VTD), decreases the level of mot-2 in cancer cells. Consistent with the in vitro results, UBXN2A^+/- mice exhibited selective elevation of mot-2 in colon tissues. An in vitro Anti-K48 TUBE isolation approach showed that recombinant UBXN2A enhances proteasomal degradation of mot-2 in mouse colon tissues. Finally, we observed enhanced association of CHIP with the UBXN2A-mot-2 complex in tumors in an azoxymethane/dextran sulfate sodium-induced mouse CRC model. The existence of a multiprotein complex containing UBXN2A, CHIP, and mot-2 suggests a synergistic tumor suppressor activity of UBXN2A and CHIP in mot-2-enriched tumors. This finding validates the UBXN2A-CHIP axis as a novel and potential therapeutic target in CRC.

Heat acclimation increases inflammatory and apoptotic responses to subsequent LPS challenge in C2C12 myotubes

This work investigated the ability of a 6-day heat acclimation protocol to impart heat acclimation-mediated cross-tolerance (HACT) in C2C12 myotubes, as indicated by changes in inflammatory and apoptotic responses to subsequent lipopolysaccharide (LPS) challenge. Myotubes were incubated at 40 °C for 2 h/day over 6 days (HA) or maintained for 6 days at 37 °C (C). Following 24 h recovery, myotubes from each group received either no stimulation or 500 ng/ml LPS for 2 h (HA + LPS and C + LPS, respectively). Cell lysates were collected and analyzed for protein markers of the heat shock response, inflammation, and apoptosis. As compared to C, HA exhibited an elevated heat shock response [HSP70 (+ 99%); HSP60 (+ 216%); HSP32 (+ 40%); all p < 0.01] and reduced inflammatory and apoptotic signaling [p-NF-ĸB:NF-ĸB (- 99%%); p-JNK (- 49%); all p < 0.01]. When compared to C + LPS, HA + LPS also exhibited an elevated heat shock response [HSP70 (+ 68%); HSP60 (+ 32%); HSP32 (+ 38%); all p < 0.01]. However, inflammatory and apoptotic responses in HA + LPS were increased [p-IKBa:IKBa (+ 432%); p-NF-ĸB:NF-ĸB (+ 283%); caspase-8p18 (+ 53%); p-JNK (+ 41%); all p < 0.05]. This unanticipated finding may be due to increased TLR4-mediated signaling capacity in HA + LPS, as indicated by upregulation of TLR4 [(+ 24%); MyD88 (+ 308%); p-NIK (+ 199%); and p-IKKα/b (+ 81%); all p < 0.05]. Data suggest HA reduces inflammatory and apoptotic signaling in skeletal muscle cells that are maintained under basal conditions. However, HACT is selective and does not apply to TLR4 signaling in the present model.

The HSP90 Family: Structure, Regulation, Function, and Implications in Health and Disease

The mammalian HSP90 family of proteins is a cluster of highly conserved molecules that are involved in myriad cellular processes. Their distribution in various cellular compartments underlines their essential roles in cellular homeostasis. HSP90 and its co-chaperones orchestrate crucial physiological processes such as cell survival, cell cycle control, hormone signaling, and apoptosis. Conversely, HSP90, and its secreted forms, contribute to the development and progress of serious pathologies, including cancer and neurodegenerative diseases. Therefore, targeting HSP90 is an attractive strategy for the treatment of neoplasms and other diseases. This manuscript will review the general structure, regulation and function of HSP90 family and their potential role in pathophysiology.

Therapeutic potential of heat shock protein induction for muscular dystrophy and other muscle wasting conditions

Duchenne muscular dystrophy is the most common and severe of the muscular dystrophies, a group of inherited myopathies caused by different genetic mutations leading to aberrant expression or complete absence of cytoskeletal proteins. Dystrophic muscles are prone to injury, and regenerate poorly after damage. Remorseless cycles of muscle fibre breakdown and incomplete repair lead to progressive and severe muscle wasting, weakness and premature death. Many other conditions are similarly characterized by muscle wasting, including sarcopenia, cancer cachexia, sepsis, denervation, burns, and chronic obstructive pulmonary disease. Muscle trauma and loss of mass and physical capacity can significantly compromise quality of life for patients. Exercise and nutritional interventions are unlikely to halt or reverse the conditions, and strategies promoting muscle anabolism have limited clinical acceptance. Heat shock proteins (HSPs) are molecular chaperones that help proteins fold back to their original conformation and restore function. Since many muscle wasting conditions have pathophysiologies where inflammation, atrophy and weakness are indicated, increasing HSP expression in skeletal muscle may have therapeutic potential. This review will provide evidence supporting HSP induction for muscular dystrophy and other muscle wasting conditions.This article is part of the theme issue 'Heat shock proteins as modulators and therapeutic targets of chronic disease: an integrated perspective'.

Hsp70 Suppresses Mitochondrial Reactive Oxygen Species and Preserves Pulmonary Microvascular Barrier Integrity Following Exposure to Bacterial Toxins

Pneumonia is a leading cause of death in children and the elderly worldwide, accounting for 15% of all deaths of children under 5 years old. Streptococcus pneumoniae is a common and aggressive cause of pneumonia and can also contribute to meningitis and sepsis. Despite the widespread use of antibiotics, mortality rates for pneumonia remain unacceptably high in part due to the release of bacterial toxins. Pneumolysin (PLY) is a cholesterol-dependent toxin that is produced by Streptococcus, and it is both necessary and sufficient for the development of the extensive pulmonary permeability edema that underlies acute lung injury. The mechanisms by which PLY disrupts the pulmonary endothelial barrier are not fully understood. Previously, we found that reactive oxygen species (ROS) contribute to the barrier destructive effects of PLY and identified an unexpected but potent role of Hsp70 in suppressing ROS production. The ability of Hsp70 to influence PLY-induced barrier dysfunction is not yet described, and the goal of the current study was to identify whether Hsp70 upregulation is an effective strategy to protect the lung microvascular endothelial barrier from G⁺ bacterial toxins. Overexpression of Hsp70 via adenovirus-mediated gene transfer attenuated PLY-induced increases in permeability in human lung microvascular endothelial cells (HLMVEC) with no evidence of cytotoxicity. To adopt a more translational approach, we employed a pharmacological approach using geranylgeranylacetone (GGA) to acutely upregulate endogenous Hsp70 expression. Following acute treatment (6 h) with GGA, HLMVECs exposed to PLY displayed improved cell viability and enhanced endothelial barrier function as measured by both Electric Cell-substrate Impedance Sensing (ECIS) and transwell permeability assays compared to control treated cells. PLY promoted increased mitochondrial ROS, decreased mitochondrial oxygen consumption, and increased caspase 3 cleavage and cell death, which were collectively improved in cells pretreated with GGA. In mice, IP pretreatment with GGA 24 h prior to IT administration of PLY resulted in significantly less Evans Blue Dye extravasation compared to vehicle, indicating preserved endothelial barrier integrity and suggesting that the acute upregulation of Hsp70 may be an effective therapeutic approach in the treatment of lung injury associated with pneumonia.

Mitochondrial Quality Control in Neurodegenerative Diseases: Focus on Parkinson's Disease and Huntington's Disease

In recent years, several important advances have been made in our understanding of the pathways that lead to cell dysfunction and death in Parkinson's disease (PD) and Huntington's disease (HD). Despite distinct clinical and pathological features, these two neurodegenerative diseases share critical processes, such as the presence of misfolded and/or aggregated proteins, oxidative stress, and mitochondrial anomalies. Even though the mitochondria are commonly regarded as the "powerhouses" of the cell, they are involved in a multitude of cellular events such as heme metabolism, calcium homeostasis, and apoptosis. Disruption of mitochondrial homeostasis and subsequent mitochondrial dysfunction play a key role in the pathophysiology of neurodegenerative diseases, further highlighting the importance of these organelles, especially in neurons. The maintenance of mitochondrial integrity through different surveillance mechanisms is thus critical for neuron survival. Mitochondria display a wide range of quality control mechanisms, from the molecular to the organellar level. Interestingly, many of these lines of defense have been found to be altered in neurodegenerative diseases such as PD and HD. Current knowledge and further elucidation of the novel pathways that protect the cell through mitochondrial quality control may offer unique opportunities for disease therapy in situations where ongoing mitochondrial damage occurs. In this review, we discuss the involvement of mitochondrial dysfunction in neurodegeneration with a special focus on the recent findings regarding mitochondrial quality control pathways, beyond the classical effects of increased production of reactive oxygen species (ROS) and bioenergetic alterations. We also discuss how disturbances in these processes underlie the pathophysiology of neurodegenerative disorders such as PD and HD.

Targeting Hodgkin and Reed-Sternberg Cells with an Inhibitor of Heat-Shock Protein 90: Molecular Pathways of Response and Potential Mechanisms of Resistance

Classical Hodgkin lymphoma (cHL) cells overexpress heat-shock protein 90 (HSP90), an important intracellular signaling hub regulating cell survival, which is emerging as a promising therapeutic target. Here, we report the antitumor effect of celastrol, an anti-inflammatory compound and a recognized HSP90 inhibitor, in Hodgkin and Reed–Sternberg cell lines. Two disparate responses were recorded. In KM-H2 cells, celastrol inhibited cell proliferation, induced G0/G1 arrest, and triggered apoptosis through the activation of caspase-3/7. Conversely, L428 cells exhibited resistance to the compound. A proteomic screening identified a total of 262 differentially expressed proteins in sensitive KM-H2 cells and revealed that celastrol’s toxicity involved the suppression of the MAPK/ERK (extracellular signal regulated kinase/mitogen activated protein kinase) pathway. The apoptotic effects were preceded by a decrease in RAS (proto-oncogene protein Ras), p-ERK1/2 (phospho-extracellular signal-regulated Kinase-1/2), and c-Fos (proto-oncogene protein c-Fos) protein levels, as validated by immunoblot analysis. The L428 resistant cells exhibited a marked induction of HSP27 mRNA and protein after celastrol treatment. Our results provide the first evidence that celastrol has antitumor effects in cHL cells through the suppression of the MAPK/ERK pathway. Resistance to celastrol has rarely been described, and our results suggest that in cHL it may be mediated by the upregulation of HSP27. The antitumor properties of celastrol against cHL and whether the disparate responses observed in vitro have clinical correlates deserve further research.

Mitochondrial pathways to cardiac recovery: TFAM

Mitochondrial dysfunction underlines a multitude of pathologies; however, studies are scarce that rescue the mitochondria for cellular resuscitation. Exploration into the protective role of mitochondrial transcription factor A (TFAM) and its mitochondrial functions respective to cardiomyocyte death are in need of further investigation. TFAM is a gene regulator that acts to mitigate calcium mishandling and ROS production by wrapping around mitochondrial DNA (mtDNA) complexes. TFAM's regulatory functions over serca2a, NFAT, and Lon protease contribute to cardiomyocyte stability. Calcium- and ROS-dependent proteases, calpains, and matrix metalloproteinases (MMPs) are abundantly found upregulated in the failing heart. TFAM's regulatory role over ROS production and calcium mishandling leads to further investigation into the cardioprotective role of exogenous TFAM. In an effort to restabilize physiological and contractile activity of cardiomyocytes in HF models, we propose that TFAM-packed exosomes (TFAM-PE) will act therapeutically by mitigating mitochondrial dysfunction. Notably, this is the first mention of exosomal delivery of transcription factors in the literature. Here we elucidate the role of TFAM in mitochondrial rescue and focus on its therapeutic potential.

Mortalin deficiency suppresses fibrosis and induces apoptosis in keloid spheroids

Mortalin (Mot) is a mitochondrial chaperone of the heat shock protein 70 family and it’s pro-proliferative and anti-apoptosis functions could be associated with keloid pathogenesis, and blocking of mortalin and its interaction with p53 might be a potential novel target for the treatment of keloid. Therefore, we generated mortalin-specific small hairpin (sh) RNAs (dE1-RGD/GFP/shMot) and introduced into keloid spheroids for examination of its apoptotic and anti-fibrotic effect. On keloid tissues, mortalin expression was higher than adjacent normal tissues and it’s protein expressions were activated keloid fibroblasts (KFs). After primary keloid spheroid were transduced with dE1-RGD/GFP/shMot for knockdown of mortalin, expression of type I, III collagen, fibronectin, and elastin was significantly reduced and transforming growth factor-β1, epidermal growth factor receptor (EGFR), Extracellular Signal-Regulated Kinases 1 and 2 (Erk 1/2), and Smad 2/3 complex protein expression were decreased. In addition, increased TUNEL activities and cytochrome C were observed. Further, for examine of mortalin and p53 interaction, we performed immunofluorescence analysis. Knockdown of mortalin relocated p53 to the cell nucleus in primary keloid spheroids by dE1-RGD/GFP/shMot transduction. These results support the utility of knockdown of mortalin to induce apoptosis and reduce ECMs expression in keloid spheroid, which may be highly beneficial in treating keloids.

Protein quality control at the mitochondrion

Mitochondria are essential constituents of a eukaryotic cell by supplying ATP and contributing to many mayor metabolic processes. As endosymbiotic organelles, they represent a cellular subcompartment exhibiting many autonomous functions, most importantly containing a complete endogenous machinery responsible for protein expression, folding and degradation. This article summarizes the biochemical processes and the enzymatic components that are responsible for maintaining mitochondrial protein homoeostasis. As mitochondria lack a large part of the required genetic information, most proteins are synthesized in the cytosol and imported into the organelle. After reaching their destination, polypeptides must fold and assemble into active proteins. Under pathological conditions, mitochondrial proteins become misfolded or damaged and need to be repaired with the help of molecular chaperones or eventually removed by specific proteases. Failure of these protein quality control mechanisms results in loss of mitochondrial function and structural integrity. Recently, novel mechanisms have been identified that support mitochondrial quality on the organellar level. A mitochondrial unfolded protein response allows the adaptation of chaperone and protease activities. Terminally damaged mitochondria may be removed by a variation of autophagy, termed mitophagy. An understanding of the role of protein quality control in mitochondria is highly relevant for many human pathologies, in particular neurodegenerative diseases.

Mitochondrial CCAR2/DBC1 is required for cell survival against rotenone-induced mitochondrial stress

CCAR2 (cell cycle and apoptosis regulator protein 2; formerly DBC1, deleted in breast cancer 1) functions in diverse cellular processes including responses to genotoxic and metabolic stresses. However, its role in the mitochondrial stress response has not been fully elucidated. To investigate how CCAR2 regulates stress response, we purified CCAR2-containing complexes. Interestingly, the results revealed that CCAR2 localized to the mitochondria, and also bound Hsp60 (heat shock protein 60), a mitochondrial chaperone. The binding of CCAR2 to Hsp60 increased following rotenone-induced mitochondrial stress. The deficiencies in CCAR2 and Hsp60 also disrupted the mitochondrial membrane potential, thereby promoting apoptosis following mitochondrial stress. In summary, the CCAR2-Hsp60 complex promoted cell survival during mitochondrial stress-induced apoptosis. These data suggest that CCAR2 is critical for maintaining mitochondrial homeostasis in response to stress.