The NOD-like receptor pyrin domain-containing protein 3 (NLRP3) inflammasome has been implicated as a crucial component in both neurodegeneration and diabetes. However, the role of metabolic ...signalling pathways and the NLRP3 inflammasome in frontotemporal dementia remain largely elusive. We therefore investigated the effects of an NLRP3 inhibitor (MCC950) in a murine tau knock-in (PLB2TAU) model vs. wild-type (PLBWT) control mice. In male PLB2TAU mice (4 months at start of study), MCC950 treatment (20 mg/kg, for 12 weeks) improved insulin sensitivity and reduced circulating plasma insulin levels. Further molecular analysis suggested normalisation in insulin signalling pathways in both liver and muscle tissue. Treatment also resulted in improvements in inflammation and ER stress signalling, both peripherally and centrally, alongside a partial normalisation of phospho-tau levels.
Overall, we provide evidence that MCC950 improved metabolic, inflammatory and frontotemporal dementia (FTD) relevant phenotypes in multiple tissues. NLRP3 inhibition may therefore offer a therapeutic approach to ameliorate FTD pathology.
•The metabolic role of NLRP3 was investigated in a murine tauopathy model, PLB2Tau.•The inhibitor MCC950 improved glucose tolerance and insulin signalling.•Inflammation and ER stress was ameliorated in brain and liver.•In the brain, a partial normalisation of phospho-tau levels was detected.•MCC950 partially recovered metabolic, inflammatory and FTD-relevant phenotypes.
Chlorpyrifos (CPF) is a typical organophosphate insecticide known to has serious toxicological effects on aquatic animals and causes many environmental contamination problems. To assess the effects ...of CPF on the epithelioma papulosum cyprini (EPC) cells of the common carps from the point of calcium ion (Ca2+) transport, the CPF-exposed EPC models were primarily established, and both AO/EB staining and Annexin V/PI assay with flow cytometry analysis were subsequently implemented to identify that CPF-induced EPC cell apoptosis, in consistent with the up-regulated expression of BAX, Cyt-c, CASP3 and CASP9, and down-regulated BCL-2 expression. Then, Mag-Fluo-4 AM, Fluo-4 AM and Rhod-2 AM staining probes were co-stained with ER-Tracker Red and Mito-Tracker Green applied to image cellular Ca2+ flux, illuminating Ca2+ depleted from ER and flux into mitochondria, resulting in ER stress and mitochondrial dysfunction. Additionally, 2-Aminoethyl Diphenylborinate (2-APB), 4-Phenylbutyric acid (4-PBA) and Dorsomorphin (Compound C) were performed as the inhibitor of Ca2+ transition, ER stress and AMPK phosphorylation, suggesting CPF-mediated Ca2+ overload triggered ER stress. And the over-generation of Mito-ROS intensified oxidative stress, promoting the phosphorylation of AMPK and deteriorating cell apoptotic death. The results of this study demonstrated Ca2+ overload-dependent mitochondrial dysfunction engages in the CPF-induced apoptosis, providing a novel concept for investigating the toxicity of CPF as environmental pollution on aquatic organisms.
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•CPF mediates Ca2+ dyshomeostasis.•Mitochondrial Ca2+ overload intensifies mitochondrial dysfunction.•The accumulation of ROS induces EPC cell apoptosis via AMPK/ULK1.
It has been reported that asprosin is a novel adipokine which is augmented in mice and humans with type 2 diabetes (T2DM). Asprosin stimulates hepatic gluconeogenesis under fasting conditions. ...However, the roles of asprosin in inflammation, endoplasmic reticulum (ER) stress, and insulin resistance in skeletal muscle has not been studied. In the currents study, elevated levels of asprosin expression were observed in adipocytes under hyperlipidemic conditions. Treatment of C2C12 myocytes with asprosin‐induced ER stress markers (phosphorylated inositol‐requiring enzyme 1 and eukaryotic initiation factor 2, and CHOP expression) as well as inflammation markers (interleukin‐6 expression, phosphorylated IκB, and nuclear translocated nuclear factor‐κβ). Finally, asprosin treatment promoted exacerbation of insulin sensitivity as determined by levels of insulin receptor substrate 1 and Akt phosphorylation as well as glucose uptake. Moreover, treatment of asprosin augmented protein kinase C‐δ (PKCδ) phosphorylation and nuclear translocation, but suppressed messenger RNA expression of sarcoplasmic reticulum Ca2+ ATPase 2b in both C2C12 myocytes and in mouse soleus skeletal muscle. These asprosin‐induced effects were markedly decreased in small interfering (si) RNA‐mediated PKCδ‐knockdown in C2C12 myocytes. These results suggest that asprosin results in impairment of insulin sensitivity in skeletal muscle through PKCδ‐associated ER stress/inflammation pathways and may be a valuable strategy for management of insulin resistance and T2DM.
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Palmitate and high‐fat diet induce asprosin expression in mouse adipocytes
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Recombinant asprosin induces inflammation and ER stress in skeletal muscle cells
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Recombinant asprosin induces impairment of insulin signaling in skeletal muscle cells
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Recombinant asprosin causes insulin resistance through PKCδ/ER stress or PKCδ/inflammation
Glucose-regulated protein 94 is the HSP90-like protein in the lumen of the endoplasmic reticulum and therefore it chaperones secreted and membrane proteins. It has essential functions in development ...and physiology of multicellular organisms, at least in part because of this unique clientele. GRP94 shares many biochemical features with other HSP90 proteins, in particular its domain structure and ATPase activity, but also displays distinct activities, such as calcium binding, necessitated by the conditions in the endoplasmic reticulum. GRP94's mode of action varies from the general HSP90 theme in the conformational changes induced by nucleotide binding, and in its interactions with co-chaperones, which are very different from known cytosolic co-chaperones. GRP94 is more selective than many of the ER chaperones and the basis for this selectivity remains obscure. Recent development of molecular tools and functional assays has expanded the spectrum of clients that rely on GRP94 activity, but it is still not clear how the chaperone binds them, or what aspect of folding it impacts. These mechanistic questions and the regulation of GRP94 activity by other proteins and by post-translational modification differences pose new questions and present future research avenues. This article is part of a Special Issue entitled: Heat Shock Protein 90 (HSP90).
► GRP94 is an endoplasmic reticulum resident chaperone that belongs to HSP90 family. ► GRP94 chaperones secreted and membrane proteins. ► GRP94 is essential in development and physiology of multi-cellular organisms. ► GRP94 shares biochemical features with HSP90 but displays distinct activities.
In obesity, plasma free fatty acids (FFAs) levels are elevated due to enlarged adipose tissue mass. Saturated fatty acids can induce prolonged ER stress and insulin resistance. Double-stranded ...RNA-dependent Protein Kinase (PKR) is activated under stress conditions in skeletal muscle. The current study aimed to investigate the effect of imoxin (IMX), a selective PKR inhibitor, on palmitate-induced ER stress and insulin resistance in C2C12 myotubes. Cells were treated with 5 μM imoxin and exposed to 0.5 mM bovine serum albumin (BSA)-conjugated PA for 24 h. A subset of cells was stimulated with 50 nM insulin for the last 15 min. Glucose uptake was monitored and protein levels involved in ER stress and insulin signaling were measured by Western blotting. Palmitate stimulated PKR phosphorylation, which was prevented by imoxin. Moreover, imoxin reduced protein levels of ER stress-related markers including glucose-regulating protein 78 (GRP78), CCAAT-enhancer-binding protein homologous protein (CHOP), activating transcription factor 6 (ATF6) and spliced X-box binding protein 1 (XBP-1s) which were induced by palmitate. Furthermore, imoxin ameliorated palmitate-induced suppression of phospho-insulin receptor beta (p-IRβ) and Akt phosphorylation in myotubes. In addition, imoxin promoted glucose uptake in response to insulin under palmitate exposure. Furthermore, imoxin reduced phospho-c-Jun N-terminal kinase (p-JNK) induced by palmitate treatment. These findings suggest that imoxin may protect against saturated fatty acid-induced ER stress and insulin resistance in skeletal muscle, which are potentially mediated by PKR.
Glycogen synthase kinase 3 (GSK-3) dysregulation plays an important role in the pathogenesis of numerous disorders, affecting the central nervous system (CNS) encompassing both neuroinflammation and ...neurodegenerative diseases. Several lines of evidence have illustrated a key role of the GSK-3 and its cellular and molecular signaling cascades in the control of neuroinflammation. Glycogen synthase kinase 3 beta (GSK-3β), one of the GSK-3 isomers, plays a major role in neuronal apoptosis and its inhibition decreases expression of alpha-Synuclein (α-Synuclein), which make this kinase an attractive therapeutic target for neurodegenerative disorders.
Parkinson's disease (PD) is a chronic neurodegenerative movement disorder characterized by the progressive and massive loss of dopaminergic neurons by neuronal apoptosis in the substantia nigra pars compacta and depletion of dopamine in the striatum, which lead to pathological and clinical abnormalities. Thus, understanding the role of GSK-3β in PD will enhance our knowledge of the basic mechanisms underlying the pathogenesis of this disorder and facilitate the identification of new therapeutic avenues. In recent years, GSK-3β has been shown to play essential roles in modulating a variety of cellular functions, which have prompted efforts to develop GSK-3β inhibitors as therapeutics.
In this review, we summarize GSK-3 signaling pathways and its association with neuroinflammation. Moreover, we highlight the interaction between GSK-3β and several cellular processes involved in the pathogenesis of PD, including the accumulation of α-Synuclein aggregates, oxidative stress and mitochondrial dysfunction. Finally, we discuss about GSK-3β inhibitors as a potential therapeutic strategy in PD.
B-cell receptor-associated protein 31 (BAP31 or BCAP31) is a ubiquitously expressed transmembrane protein found mainly in the endoplasmic reticulum (ER), including in mitochondria-associated ...membranes (MAMs). It acts as a broad-specificity membrane protein chaperone and quality control factor, which can promote different fates for its clients, including ER retention, ER export, ER-associated degradation (ERAD), or evasion of degradation, and it also acts as a MAM tetherer and regulatory protein. It is involved in several cellular processes – it supports ER and mitochondrial homeostasis, promotes proliferation and migration, plays several roles in metabolism and the immune system, and regulates autophagy and apoptosis. Full-length BAP31 can be anti-apoptotic, but can also mediate activation of caspase-8, and itself be cleaved by caspase-8 into p20-BAP31, which promotes apoptosis by mobilizing ER calcium stores at MAMs. BAP31 loss-of-function mutations is the cause of ‘deafness, dystonia, and central hypomyelination’ (DDCH) syndrome, characterized by severe neurological symptoms and early death. BAP31 is furthermore implicated in a growing number of cancers and other diseases, and several viruses have been found to target it to promote their survival or life cycle progression. The purpose of this review is to provide an overview and examination of the basic properties, functions, mechanisms, and roles in disease of BAP31.
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•Membrane protein chaperone and regulatory protein with growing list of interactors.•Found mainly in the ER – including in mitochondria-associated membranes (MAMs).•Functions in ER and mitochondrial homeostasis, apoptosis, proliferation, and more.•Implicated in diseases, including multiple cancer forms and viral infections.
AMPK mediates energetic stress‐induced liver GDF15 Townsend, Logan K.; Weber, Alyssa J.; Day, Emily A. ...
The FASEB journal,
January 2021, 2021-Jan, 2021-01-00, 20210101, Volume:
35, Issue:
1
Journal Article
Peer reviewed
Growth differentiating factor‐15 (GDF15) is an emerging target for the treatment of obesity and metabolic disease partly due to its ability to suppress food intake. GDF15 expression and secretion are ...thought to be regulated by a cellular integrated stress response, which involves endoplasmic reticulum (ER) stress. AMPK is another cellular stress sensor, but the relationship between AMPK, ER stress, and GDF15 has not been assessed in vivo. Wildtype (WT), AMPK β1 deficient (AMPKβ1−/−), and CHOP−/− mice were treated with three distinct AMPK activators; AICAR, which is converted to ZMP mimicking the effects of AMP on the AMPKγ isoform, R419, which indirectly activates AMPK through inhibition of mitochondrial respiration, or A769662, a direct AMPK activator which binds the AMPKβ1 isoform ADaM site causing allosteric activation. Following treatments, liver Gdf15, markers of ER‐stress, AMPK activity, adenine nucleotides, circulating GDF15, and food intake were assessed. AICAR and R419 caused ER and energetic stress, increased GDF15 expression and secretion, and suppressed food intake. Direct activation of AMPK β1 containing complexes by A769662 increased hepatic Gdf15 expression, circulating GDF15, and suppressed food intake, independent of ER stress. The effects of AICAR, R419, and A769662 on GDF15 were attenuated in AMPKβ1−/− mice. AICAR and A769662 increased GDF15 to a similar extent in WT and CHOP−/− mice. Herein, we provide evidence that AMPK plays a role in mediating the induction of GDF15 under conditions of energetic stress in mouse liver in vivo.
The heterogeneity of the N-linked glycan profile of therapeutic monoclonal antibodies (mAbs) derived from animal cells affects therapeutic efficacy and, therefore, needs to be appropriately ...controlled during the manufacturing process. In this study, we examined the effects of polyamines on the N-linked glycan profiles of mAbs produced by CHO DP-12 cells. Normal cell growth of CHO DP-12 cells and their growth arrest by α-difluoromethylornithine (DFMO), an inhibitor of the polyamine biosynthetic pathway, was observed when 0.5% fetal bovine serum was added to serum-free medium, despite the presence of cadaverine and aminopropylcadaverine, instead of putrescine and spermidine in cells. Polyamine depletion by DFMO increased IgG galactosylation, accompanied by β1,4-galactosyl transferase 1 (B4GAT1) mRNA elevation. Additionally, IgG production in polyamine-depleted cells was reduced by 30% compared to that in control cells. Therefore, we examined whether polyamine depletion induces an ER stress response. The results indicated increased expression levels of chaperones for glycoprotein folding in polyamine-depleted cells, suggesting that polyamine depletion causes ER stress related to glycoprotein folding. The effect of tunicamycin, an ER stress inducer that inhibits N-glycosylation, on the expression of B4GALT1 mRNA was examined. Tunicamycin treatment increased B4GALT1 mRNA expression. These results suggest that ER stress caused by polyamine depletion induces B4GALT1 mRNA expression, resulting in increased IgG galactosylation in CHO cells. Thus, introducing polyamines, particularly SPD, to serum-free CHO culture medium for CHO cells may contribute to consistent manufacturing and quality control of antibody production.
Adipocyte‐derived exosomes (Exos) serve as bioinformation‐containing messengers in cell‐to‐cell communications, and numerous reports demonstrate that resistin, an adipokine, is strongly associated ...with hepatic steatosis and other fatty liver diseases, suggesting that adipose dysfunction‐generated altered pattern of exosomal cytokines may contribute to shaping the physiological activities in liver. Admittedly, melatonin‐mediated positive effects on various tissues/organs have been respectively reported, but regulatory mechanisms of melatonin on the crosstalk between adipose tissue and liver have been investigated rarely. Overall, we hypothesize that the crosstalk originating from adipose tissue may be another worthy regulatory pathway for melatonin ameliorating of hepatic steatosis. Here, we first found the amount of adipocyte‐derived exosomal resistin to be significantly decreased by melatonin supplementation. Compared to mice with ExosHFD or Exosresistin treatment, ExosMT remarkably ameliorated hepatic steatosis. Further test demonstrated that resistin was a pivotal cytokine which repressed phosphorylation of 5′ adenosine monophosphate‐activated protein kinase α (pAMPKα Thr172) to trigger endoplasmic reticulum (ER) stress, resulting in hepatic steatosis, whereas ExosMT reversed these risks in hepatocytes. In adipocytes, we identified melatonin to reduce the production of resistin through the brain and muscle arnt‐like protein 1 (Bmal1) transcriptional inhibition. Notably, we also confirmed that melatonin enhanced N6‐Methyladenosine (m6A) RNA demethylation to degrade resistin mRNA in adipocytes. Overall, melatonin decreases traffic volume of adipocyte‐generated exosomal resistin from adipocytes to hepatocytes, which further alleviates ER stress‐induced hepatic steatosis. Our findings illustrate a novel melatonin‐mediated regulatory pathway from adipocytes to hepatocytes, indicating that adipocyte‐derived exosome is a new potential target for treating obesity and related hepatorenal syndrome.
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