The specific PKR inhibitor C16 prevents apoptosis and IL-1β production in an acute excitotoxic rat model with a neuroinflammatory component

Therapeutic application of circular RNA aptamers in a mouse model of psoriasis

Efforts to advance RNA aptamers as a new therapeutic modality have been limited by their susceptibility to degradation and immunogenicity. In a previous study, we demonstrated synthesized short double-stranded region-containing circular RNAs (ds-cRNAs) with minimal immunogenicity targeted to dsRNA-activated protein kinase R (PKR). Here we test the therapeutic potential of ds-cRNAs in a mouse model of imiquimod-induced psoriasis. We find that genetic supplementation of ds-cRNAs leads to inhibition of PKR, resulting in alleviation of downstream interferon-α and dsRNA signals and attenuation of psoriasis phenotypes. Delivery of ds-cRNAs by lipid nanoparticles to the spleen attenuates PKR activity in examined splenocytes, resulting in reduced epidermal thickness. These findings suggest that ds-cRNAs represent a promising approach to mitigate excessive PKR activation for therapeutic purposes.

PKR Inhibitor C16 Regulates HIV-gp120 Induced Neuronal Injury and Cognitive Impairment in Vivo and in Vitro Models

To study the neuronal protective effect and its potential mechanism of C16 against gp120-induced cognitive impairment in vitro and in vivo. The NORT method was used to evaluate the short-term memory abilities of rats, the morphological changes in hippocampus were observed by Nissl staining. Cell viability and damage degree were detected by MTT and LDH. The cell living/apoptosis status of PC12 cells was determined by AO/EB double staining and the relative mRNA expressions of PKR, IRE1α, JNK, GRP78, and CHOP were detected by RT-qPCR. In comparison with the gp120 + Memantine and gp120 + C16 groups, the rats in the gp120 group showed a significantly decreased discrimination index (P < 0.001), with disordered CA1 region cells and reduced neuron numbers. AO/EB double staining revealed morphological changes in the gp120 and NMDA groups, while cells in the gp120 + C16 and NMDA + C16 groups resembled the control group. And C16 can significantly down-regulate the mRNA expression levels of PKR, IRE1α, JNK, GRP78, and CHOP. (P < 0.05). C16 can reduce the cognitive impairment stimulated by gp120 or NMDA, the protective mechanism may be correlated with inhibiting the upregulation of PKR/IRE1α/JNK pathway and suppressing apoptosis induced by downstream proteins GRP78 and CHOP.

Calcium signaling from damaged lysosomes induces cytoprotective stress granules

Lysosomal damage induces stress granule (SG) formation. However, the importance of SGs in determining cell fate and the precise mechanisms that mediate SG formation in response to lysosomal damage remain unclear. Here, we describe a novel calcium-dependent pathway controlling SG formation, which promotes cell survival during lysosomal damage. Mechanistically, the calcium-activated protein ALIX transduces lysosomal damage signals to SG formation by controlling eIF2α phosphorylation after sensing calcium leakage. ALIX enhances eIF2α phosphorylation by promoting the association between PKR and its activator PACT, with galectin-3 inhibiting this interaction; these regulatory events occur on damaged lysosomes. We further find that SG formation plays a crucial role in promoting cell survival upon lysosomal damage caused by factors such as SARS-CoV-2ORF3a, adenovirus, malarial pigment, proteopathic tau, or environmental hazards. Collectively, these data provide insights into the mechanism of SG formation upon lysosomal damage and implicate it in diseases associated with damaged lysosomes and SGs.

PKR activation-induced mitochondrial dysfunction in HIV-transgenic mice with nephropathy

HIV disease remains prevalent in the USA and chronic kidney disease remains a major cause of morbidity in HIV-1-positive patients. Host double-stranded RNA (dsRNA)-activated protein kinase (PKR) is a sensor for viral dsRNA, including HIV-1. We show that PKR inhibition by compound C16 ameliorates the HIV-associated nephropathy (HIVAN) kidney phenotype in the Tg26 transgenic mouse model, with reversal of mitochondrial dysfunction. Combined analysis of single-nucleus RNA-seq and bulk RNA-seq data revealed that oxidative phosphorylation was one of the most downregulated pathways and identified signal transducer and activator of transcription (STAT3) as a potential mediating factor. We identified in Tg26 mice a novel proximal tubular cell cluster enriched in mitochondrial transcripts. Podocytes showed high levels of HIV-1 gene expression and dysregulation of cytoskeleton-related genes, and these cells dedifferentiated. In injured proximal tubules, cell-cell interaction analysis indicated activation of the pro-fibrogenic PKR-STAT3-platelet-derived growth factor (PDGF)-D pathway. These findings suggest that PKR inhibition and mitochondrial rescue are potential novel therapeutic approaches for HIVAN.

A mechanism that transduces lysosomal damage signals to stress granule formation for cell survival

Lysosomal damage poses a significant threat to cell survival. Our previous work has reported that lysosomal damage induces stress granule (SG) formation. However, the importance of SG formation in determining cell fate and the precise mechanisms through which lysosomal damage triggers SG formation remains unclear. Here, we show that SG formation is initiated via a novel calcium-dependent pathway and plays a protective role in promoting cell survival in response to lysosomal damage. Mechanistically, we demonstrate that during lysosomal damage, ALIX, a calcium-activated protein, transduces lysosomal damage signals by sensing calcium leakage to induce SG formation by controlling the phosphorylation of eIF2α. ALIX modulates eIF2α phosphorylation by regulating the association between PKR and its activator PACT, with galectin-3 exerting a negative effect on this process. We also found this regulatory event of SG formation occur on damaged lysosomes. Collectively, these investigations reveal novel insights into the precise regulation of SG formation triggered by lysosomal damage, and shed light on the interaction between damaged lysosomes and SGs. Importantly, SG formation is significant for promoting cell survival in the physiological context of lysosomal damage inflicted by SARS-CoV-2 ORF3a, adenovirus infection, Malaria hemozoin, proteopathic tau as well as environmental hazard silica.

Activation of protein kinase receptor (PKR) plays a pro-viral role in mammarenavirus-infected cells

Many viruses, including mammarenaviruses, have evolved mechanisms to counteract different components of the host cell innate immunity, which is required to facilitate robust virus multiplication. The double-stranded RNA (dsRNA) sensor protein kinase receptor (PKR) pathway plays a critical role in the cell anti-viral response. Whether PKR can restrict the multiplication of the Old World mammarenavirus lymphocytic choriomeningitis virus (LCMV) and the mechanisms by which LCMV may counteract the anti-viral functions of PKR have not yet been investigated. Here we present evidence that LCMV infection results in very limited levels of PKR activation, but LCMV multiplication is enhanced in the absence of PKR. In contrast, infection with a recombinant LCMV with a mutation affecting the 3'-5' exonuclease (ExoN) activity of the viral nucleoprotein resulted in robust PKR activation in the absence of detectable levels of dsRNA, which was associated with severely restricted virus multiplication that was alleviated in the absence of PKR. However, pharmacological inhibition of PKR activation resulted in reduced levels of LCMV multiplication. These findings uncovered a complex role of the PKR pathway in LCMV-infected cells involving both pro- and anti-viral activities.IMPORTANCEAs with many other viruses, the prototypic Old World mammarenavirus LCMV can interfere with the host cell innate immune response to infection, which includes the dsRNA sensor PKR pathway. A detailed understanding of LCMV-PKR interactions can provide novel insights about mammarenavirus-host cell interactions and facilitate the development of effective anti-viral strategies against human pathogenic mammarenaviruses. In the present work, we present evidence that LCMV multiplication is enhanced in PKR-deficient cells, but pharmacological inhibition of PKR activation unexpectedly resulted in severely restricted propagation of LCMV. Likewise, we document a robust PKR activation in LCMV-infected cells in the absence of detectable levels of dsRNA. Our findings have revealed a complex role of the PKR pathway during LCMV infection and uncovered the activation of PKR as a druggable target for the development of anti-viral drugs against human pathogenic mammarenaviruses.

Redox-associated changes in healthy individuals at risk of Alzheimer's disease. A ten-year follow-up study

Carrying an allele 4 of the apolipoprotein E (ApoE) is the best-established genetic risk factor to develop Alzheimer's disease (AD). Fifty percent of ApoE4/4 individuals develop the disease at 70 years of age. ApoE3/4 carriers have a lower risk of developing the disease, still 50% of them suffer AD at around 80 years. In a previous study we showed that healthy young individuals, who had a parent with AD and were carriers of at least one ApoE4 allele displayed reductive stress. This was evidenced as a decrease in oxidative markers, such as oxidized glutathione, p-p38, and NADP+/NADPH ratio, and an increase of antioxidant enzymes, such as glutathione peroxidase (Gpx1) and both the catalytic and regulatory subunits of glutamyl-cysteinyl (GCLM and GCLC). Moreover, we found an increase in stress-related proteins involved in tau physiopathology. Now, 10 years later, we have conducted a follow-up study measuring the same parameters in the same cohort. Our results show that reductive stress has reversed, as we could now observe an increase in lipid peroxidation and in the oxidation of glutathione along with a decrease in the expression of Gpx1 and SOD1 antioxidant enzymes in ApoE4 carriers. Furthermore, we found an increase in plasma levels of IL1β levels and in PKR (eukaryotic translation initiation factor 2 alpha kinase 2) gene expression in isolated lymphocytes. Altogether, our results suggest that, in the continuum of Alzheimer's disease, people at risk of developing the disease go through different redox phases, from stablished reductive stress to oxidative stress.

Microglial NLRP3 inflammasome activation mediates diabetes-induced depression-like behavior via triggering neuroinflammation

BACKGROUND

Abundant evidence suggests that the prevalence and risk of depression in people with diabetes is high. However, the pathogenesis of diabetes-related depression remains unclear. Since neuroinflammation is associated with the pathophysiology of diabetic complications and depression, this study aims to elucidate the neuroimmune mechanism of diabetes-related depression.

METHODS

Male C57BL/6 mice were injected with streptozotocin to establish a diabetes model. After screening, diabetic mice were treated with the NLRP3 inhibitor MCC950. Then, metabolic indicators and depression-like behaviors were evaluated in these mice, as well as their central and peripheral inflammation. To explore the mechanism of high glucose-induced microglial NLRP3 inflammasome activation, we performed in vitro studies focusing on its canonical upstream signal I (TLR4/MyD88/NF-κB) and signal II (ROS/PKR/P2X7R/TXNIP).

RESULTS

Diabetic mice exhibited depression-like behaviors and activation of NLRP3 inflammasome in hippocampus. In vitro high-glucose (50 mM) environment primed microglial NLRP3 inflammasome by promoting NF-κB phosphorylation in a TLR4/MyD88-independent manner. Subsequently, high glucose activated the NLRP3 inflammasome via enhancing intracellular ROS accumulation, upregulating P2X7R, as well as promoting PKR phosphorylation and TXNIP expression, thereby facilitating the production and secretion of IL-1β. Inhibition of NLRP3 with MCC950 significantly restored hyperglycemia-induced depression-like behavior and reversed the increase in IL-1β levels in the hippocampus and serum.

CONCLUSION

The activation of NLRP3 inflammasome, probably mainly in hippocampal microglia, mediates the development of depression-like behaviors in STZ-induced diabetic mice. Targeting the microglial inflammasome is a feasible strategy for the treatment of diabetes-related depression.

Cryptosporidium uses CSpV1 to activate host type I interferon and attenuate antiparasitic defenses

Cryptosporidium infects gastrointestinal epithelium and is a leading cause of infectious diarrhea and diarrheal-related death in children worldwide. There are no vaccines and no fully effective therapy available for the infection. Type II and III interferon (IFN) responses are important determinants of susceptibility to infection but the role for type I IFN response remains obscure. Cryptosporidium parvum virus 1 (CSpV1) is a double-stranded RNA (dsRNA) virus harbored by Cryptosporidium spp. Here we show that intestinal epithelial conditional Ifnar1^-/- mice (deficient in type I IFN receptor) are resistant to C. parvum infection. CSpV1-dsRNAs are delivered into host cells and trigger type I IFN response in infected cells. Whereas C. parvum infection attenuates epithelial response to IFN-γ, loss of type I IFN signaling or inhibition of CSpV1-dsRNA delivery can restore IFN-γ-mediated protective response. Our findings demonstrate that type I IFN signaling in intestinal epithelial cells is detrimental to intestinal anti-C. parvum defense and Cryptosporidium uses CSpV1 to activate type I IFN signaling to evade epithelial antiparasitic response.

Luteolin protects DYT-PRKRA cells from apoptosis by suppressing PKR activation

DYT-PRKRA is a movement disorder caused by mutations in the PRKRA gene, which encodes for PACT, the protein activator of interferon-induced, double-stranded RNA (dsRNA)-activated protein kinase PKR. PACT brings about PKR's catalytic activation by a direct binding in response to stress signals and activated PKR phosphorylates the translation initiation factor eIF2α. Phosphorylation of eIF2α is the central regulatory event that is part of the integrated stress response (ISR), an evolutionarily conserved intracellular signaling network essential for adapting to environmental stresses to maintain healthy cells. A dysregulation of either the level or the duration of eIF2α phosphorylation in response to stress signals causes the normally pro-survival ISR to become pro-apoptotic. Our research has established that the PRKRA mutations reported to cause DYT-PRKRA lead to enhanced PACT-PKR interactions causing a dysregulation of ISR and an increased sensitivity to apoptosis. We have previously identified luteolin, a plant flavonoid, as an inhibitor of the PACT-PKR interaction using high-throughput screening of chemical libraries. Our results presented in this study indicate that luteolin is markedly effective in disrupting the pathological PACT-PKR interactions to protect DYT-PRKRA cells against apoptosis, thus suggesting a therapeutic option for using luteolin to treat DYT-PRKRA and possibly other diseases resulting from enhanced PACT-PKR interactions.

Salvianolic acid A regulates pyroptosis of endothelial cells via directly targeting PKM2 and ameliorates diabetic atherosclerosis

Rescuing endothelial cells from pyroptotic cell death emerges as a potential therapeutic strategy to combat diabetic atherosclerosis. Salvianolic acid A (SAA) is a major water-soluble phenolic acid in the Salvia miltiorrhiza Bunge, which has been used in traditional Chinese medicine (TCM) and health food products for a long time. This study investigated whether SAA-regulated pyruvate kinase M2 (PKM2) functions to protect endothelial cells. In streptozotocin (STZ)-induced diabetic ApoE-/- mice subjected to a Western diet, SAA attenuated atherosclerotic plaque formation and inhibited pathological changes in the aorta. In addition, SAA significantly prevented NLRP3 inflammasome activation and pyroptosis of endothelial cells in the diabetic atherosclerotic aortic sinus or those exposed to high glucose. Mechanistically, PKM2 was verified to be the main target of SAA. We further revealed that SAA directly interacts with PKM2 at its activator pocket, inhibits phosphorylation of Y105, and hinders the nuclear translocation of PKM2. Also, SAA consistently decreased high glucose-induced overproduction of lactate and partially lactate-dependent phosphorylation of PKR (a regulator of the NLRP3 inflammasome). Further assay on Phenylalanine (PKM2 activity inhibitor) proved that SAA exhibits the function in high glucose-induced pyroptosis of endothelial cells dependently on PKM2 regulation. Furthermore, an assay on c16 (inhibitor of PKR activity) with co-phenylalanine demonstrated that the regulation of the phosphorylated PKR partially drives PKM2-dependent SAA modulation of cell pyroptosis. Therefore, this article reports on the novel function of SAA in the pyroptosis of endothelial cells and diabetic atherosclerosis, which provides important insights into immunometabolism reprogramming that is important for diabetic cardiovascular disease complications therapy.

Protein kinase RNA-activated controls mitotic progression and determines paclitaxel chemosensitivity through B-cell lymphoma 2 in ovarian cancer

Anti-tubulin agents, such as paclitaxel, have been used extensively for treatment of several types of cancer, including ovarian, lung, breast, and pancreatic cancers. Despite their wide use in cancer treatment, however, patient response is highly variable and drug resistance remains a major clinical issue. Protein kinase RNA-activated (PKR) plays a critical role in immune response to viral infection. We identified PKR as a phospho-protein in response to anti-tubulin agents and this phosphorylation occurs independent of its own kinase activity. PKR is phosphorylated by cyclin-dependent kinase 1 (CDK1) during anti-tubulin treatment and unperturbed mitosis and that PKR regulates mitotic progression in a phosphorylation-dependent manner. Furthermore, inactivation of PKR confers resistance to paclitaxel in ovarian and breast cancer cells in vitro and in vivo. PKR expression levels and activity are decreased in chemotherapeutic recurrent ovarian cancer patients. Mechanistically, our findings suggest that PKR controls paclitaxel chemosensitivity through repressing Bcl2 expression. Pharmacological inhibition of Bcl2 with FDA-approved agent venetoclax overcomes paclitaxel resistance in preclinical animal models of ovarian cancer. Our results suggest that PKR is a critical determinant of paclitaxel cytotoxicity and that PKR-Bcl2 axis as a potential therapeutic target for the treatment of recurrent drug-resistant ovarian tumors.

Exocyst protein subnetworks integrate Hippo and mTOR signaling to promote virus detection and cancer

The exocyst is an evolutionarily conserved protein complex that regulates vesicular trafficking and scaffolds signal transduction. Key upstream components of the exocyst include monomeric RAL GTPases, which help mount cell-autonomous responses to trophic and immunogenic signals. Here, we present a quantitative proteomics-based characterization of dynamic and signal-dependent exocyst protein interactomes. Under viral infection, an Exo84 exocyst subcomplex assembles the immune kinase Protein Kinase R (PKR) together with the Hippo kinase Macrophage Stimulating 1 (MST1). PKR phosphorylates MST1 to activate Hippo signaling and inactivate Yes Associated Protein 1 (YAP1). By contrast, a Sec5 exocyst subcomplex recruits another immune kinase, TANK binding kinase 1 (TBK1), which interacted with and activated mammalian target of rapamycin (mTOR). RALB was necessary and sufficient for induction of Hippo and mTOR signaling through parallel exocyst subcomplex engagement, supporting the cellular response to virus infection and oncogenic signaling. This study highlights RALB-exocyst signaling subcomplexes as mechanisms for the integrated engagement of Hippo and mTOR signaling in cells challenged by viral pathogens or oncogenic signaling.

Protein Kinase R in Bacterial Infections: Friend or Foe?

The global antimicrobial resistance crisis poses a significant threat to humankind in the coming decades. Challenges associated with the development of novel antibiotics underscore the urgent need to develop alternative treatment strategies to combat bacterial infections. Host-directed therapy is a promising new therapeutic strategy that aims to boost the host immune response to bacteria rather than target the pathogen itself, thereby circumventing the development of antibiotic resistance. However, host-directed therapy depends on the identification of druggable host targets or proteins with key functions in antibacterial defense. Protein Kinase R (PKR) is a well-characterized human kinase with established roles in cancer, metabolic disorders, neurodegeneration, and antiviral defense. However, its role in antibacterial defense has been surprisingly underappreciated. Although the canonical role of PKR is to inhibit protein translation during viral infection, this kinase senses and responds to multiple types of cellular stress by regulating cell-signaling pathways involved in inflammation, cell death, and autophagy - mechanisms that are all critical for a protective host response against bacterial pathogens. Indeed, there is accumulating evidence to demonstrate that PKR contributes significantly to the immune response to a variety of bacterial pathogens. Importantly, there are existing pharmacological modulators of PKR that are well-tolerated in animals, indicating that PKR is a feasible target for host-directed therapy. In this review, we provide an overview of immune cell functions regulated by PKR and summarize the current knowledge on the role and functions of PKR in bacterial infections. We also review the non-canonical activators of PKR and speculate on the potential mechanisms that trigger activation of PKR during bacterial infection. Finally, we provide an overview of existing pharmacological modulators of PKR that could be explored as novel treatment strategies for bacterial infections.

Inhibition of Protein Kinase R by C16 Protects the Retinal Ganglion Cells from Hypoxia-induced Oxidative Stress, Inflammation, and Apoptosis

AIM/PURPOSE

Individually, hypoxia and protein kinase R (PKR) induce retinal ganglion cells (RGCs) damage by aggravating reactive oxygen species (ROS), oxidative stress, inflammation, and apoptosis. However, it is still not established in hypoxia mediates such damaging effect by modulating PKR. This study investigated the expression and activation of PKR in hypoxic RGCs and tested if suppression of PKR by C16 is protective.

MATERIALS AND METHODS

Isolated RGCs were under normoxic or hypoxic conditions for 12 h. In some cases, hypoxic cells were pre-treated with C16, a PKR inhibitor, or n-acetyl cysteine (NAC) a glutathione (GSH) precursor for 1 h and then exposed to hypoxia for the next 12 h.

RESULTS

Hypoxia increased cell death, lactate dehydrogenase (LDH) levels, and levels of single-stranded DNA (ssDNA). It also increased levels of ROS, the activity of the nuclear factor-kappa beta (NF-κB), JNK, and p38 MAPK, expression of Bax, p53, and cleaved caspase-3, levels of tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6), and cytoplasmic levels of cytochrome-c. It concomitantly suppressed levels of GSH and Bcl-2. All these events were associated with increased phosphorylation (activation) of PKR and its target eukaryotic initiation factor 2 (eIF2). Pre-incubating the cells with NAC completely prevented all these effects in hypoxic cells. Similar protective effects without affecting levels of ROS and GSH levels were also seen in hypoxic cells pre-treated with C16.

CONCLUSION

Hypoxia induces oxidative stress, inflammation, and apoptosis in the RGCs mainly by ROS induced activation of PKR, whereas scavenging ROS by NAC or suppressing PKR by C16 is a novel protective mechanism.

Double-Stranded RNA Dependent Kinase R Regulates Antibacterial Immunity in Sepsis

Double-stranded RNA dependent kinase R (PKR) is originally identified as an intracellular sensor of viral infection, but its role in bacterial infection remains largely unknown. Here we report that PKR was an important regulator of antibacterial immunity in sepsis. Genetic deletion of PKR or pharmacological inhibition of its kinase activity markedly increased bacterial loads, organ injury, and mortality in polymicrobial infection induced by cecal ligation and puncture (CLP). In contrast, PKR deficiency or inhibition did not affect bacterial loads, organ injury, or mortality when mice were systemically challenged with Escherichia coli, an abundant microbe in the gastrointestinal tract. PKR deficiency or inhibition markedly decreased the release of interleukin (IL)-1β after CLP. Defect in IL-1 signaling phenocopied PKR deficiency or inhibition in CLP-induced bacterial sepsis. Taken together, these findings identified a critical role of the PKR signaling pathway in antibacterial immunity.

Role of CGRP in Neuroimmune Interaction via NF-κB Signaling Genes in Glial Cells of Trigeminal Ganglia

Activation of the trigeminal system causes the release of various neuropeptides, cytokines, and other immune mediators. Calcitonin gene-related peptide (CGRP), which is a potent algogenic mediator, is expressed in the peripheral sensory neurons of trigeminal ganglion (TG). It affects the inflammatory responses and pain sensitivity by modulating the activity of glial cells. The primary aim of this study was to use array analysis to investigate the effect of CGRP on the glial cells of TG in regulating nuclear factor kappa B (NF-κB) signaling genes and to further check if CGRP in the TG can affect neuron-glia activation in the spinal trigeminal nucleus caudalis. The glial cells of TG were stimulated with CGRP or Minocycline (Min) + CGRP. The effect on various genes involved in NF-κB signaling pathway was analyzed compared to no treatment control condition using a PCR array analysis. CGRP, Min + CGRP or saline was directly injected inside the TG and the effect on gene expression of Egr1, Myd88 and Akt1 and protein expression of cleaved Caspase3 (cleav Casp3) in the TG, and c-Fos and glial fibrillary acidic protein (GFAP) in the spinal section containing trigeminal nucleus caudalis was analyzed. Results showed that CGRP stimulation resulted in the modulation of several genes involved in the interleukin 1 signaling pathway and some genes of the tumor necrosis factor pathway. Minocycline pre-treatment resulted in the modulation of several genes in the glial cells, including anti-inflammatory genes, and neuronal activation markers. A mild increase in cleav Casp3 expression in TG and c-Fos and GFAP in the spinal trigeminal nucleus of CGRP injected animals was observed. These data provide evidence that glial cells can participate in neuroimmune interaction due to CGRP in the TG via NF-κB signaling pathway.

The Integrated Stress Response and Phosphorylated Eukaryotic Initiation Factor 2α in Neurodegeneration

The proposed molecular mechanisms underlying neurodegenerative pathogenesis are varied, precluding the development of effective therapies for these increasingly prevalent disorders. One of the most consistent observations across neurodegenerative diseases is the phosphorylation of eukaryotic initiation factor 2α (eIF2α). eIF2α is a translation initiation factor, involved in cap-dependent protein translation, which when phosphorylated causes global translation attenuation. eIF2α phosphorylation is mediated by 4 kinases, which, together with their downstream signaling cascades, constitute the integrated stress response (ISR). While the ISR is activated by stresses commonly observed in neurodegeneration, such as oxidative stress, endoplasmic reticulum stress, and inflammation, it is a canonically adaptive signaling cascade. However, chronic activation of the ISR can contribute to neurodegenerative phenotypes such as neuronal death, memory impairments, and protein aggregation via apoptotic induction and other maladaptive outcomes downstream of phospho-eIF2α-mediated translation inhibition, including neuroinflammation and altered amyloidogenic processing, plausibly in a feed-forward manner. This review examines evidence that dysregulated eIF2a phosphorylation acts as a driver of neurodegeneration, including a survey of observations of ISR signaling in human disease, inspection of the overlap between ISR signaling and neurodegenerative phenomenon, and assessment of recent encouraging findings ameliorating neurodegeneration using developing pharmacological agents which target the ISR. In doing so, gaps in the field, including crosstalk of the ISR kinases and consideration of ISR signaling in nonneuronal central nervous system cell types, are highlighted.

The integrated stress response: From mechanism to disease

Protein quality control is essential for the proper function of cells and the organisms that they make up. The resulting loss of proteostasis, the processes by which the health of the cell's proteins is monitored and maintained at homeostasis, is associated with a wide range of age-related human diseases. Here, we highlight how the integrated stress response (ISR), a central signaling network that responds to proteostasis defects by tuning protein synthesis rates, impedes the formation of long-term memory. In addition, we address how dysregulated ISR signaling contributes to the pathogenesis of complex diseases, including cognitive disorders, neurodegeneration, cancer, diabetes, and metabolic disorders. The development of tools through which the ISR can be modulated promises to uncover new avenues to diminish pathologies resulting from it for clinical benefit.

Synergistic activation of p53 by actinomycin D and nutlin-3a is associated with the upregulation of crucial regulators and effectors of innate immunity

Actinomycin D and nutlin-3a (A + N) activate p53, partly through induction of phosphorylation on Ser392. The death of A549 cells induced by A + N morphologically resembles inflammation-inducing pyroptosis - cell destruction triggered by activated caspase-1. The treatment with A + N (or camptothecin) strongly upregulated caspase-1 and its two activators: IFI16 and NLRP1, however, caspase-1 activation was not detected. A549 cells may have been primed for pyroptosis, with the absence of a crucial trigger. The investigation of additional innate immunity elements revealed that A + N (or camptothecin) stimulated the expression of NLRX1, STING (stimulator of interferon genes) and two antiviral proteins, IFIT1 and IFIT3. IFI16 and caspase-1 are coded by p53-regulated genes which led us to investigate regulation of NLRP1, NLRX1, STING, IFIT1 and IFIT3 in p53-dependent mode. The upregulation of NLRP1, NLRX1 and STING was attenuated in p53 knockdown cells. The upsurge of the examined genes, and activation of p53, was inhibited by C16, an inhibitor of PKR kinase. PKR was tested due to its ability to phosphorylate p53 on Ser392. Surprisingly, C16 was active even in PKR knockdown cells. The ability of C16 to prevent activation of p53 and expression of innate immunity genes may be the source of its strong anti-inflammatory action. Moreover, cells exposed to A + N can influence neighboring cells in paracrine fashion, for instance, they shed ectodomain of COL17A1 protein and induce, in p53-dependent mode, the expression of gene for interleukin-7. Further, the activation of p53 also spurred the expression of SOCS1, an inhibitor of interferon triggered STAT1-dependent signaling. We conclude that, stimulation of p53 primes cells for the production of interferons (through upregulation of STING), and may activate negative-feedback within this signaling system by enhancing the production of SOCS1.

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Actinomycin D and nutlin-3a strongly and synergistically activate p53 protein

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Strongly activated p53 promotes expression of innate immunity genes

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Strong activation of innate immunity genes can be prevented by C16 compound

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By inducing SOCS1 protein p53 can prevent overactivation of interferon signaling

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Strongly activated p53 can send signal to nearby immune cells through interleukin-7

PKR suppress NLRP3-pyroptosis pathway in lipopolysaccharide-induced acute lung injury model of mice

To explore the effect of double-stranded RNA-dependent kinase (PKR) in acute lung injury (ALI) and resultant acute respiratory distress syndrome (ARDS). A mouse model of lipopolysaccharide (LPS)-induced ALI was used to evaluate the levels of phosphorylated (p)-PKR and NLRP3 in lung tissue, and the protective effects of a PKR inhibitor on lung injury. And in vitro, macrophages were incubated with LPS, with or without PKR inhibitor pre-treatment. It was observed that the levels of p-PKR protein and NLRP3 protein were significantly increased compared with those in control tissues after LPS administration. Meanwhile, treatment with PKR inhibitor decreased inflammation, injury score, wet/dry weight ratio, bronchoalveolar lavage fluid (BALF) protein levels, neutrophil count in BALF, myeloperoxidase activity and expression of high-mobility group box1(HMGB1) and interleukin(IL)-1β in the lungs of LPS-challenged mice. In vitro, we demonstrated that the levels of p-PKR and NLRP3, and cell mortality rate were increased in macrophages which were incubated with LPS compared with those without LPS administration, and PKR inhibitor significantly suppressed the level of NLRP3, caspase-1, HMGB1 and IL-1β. These results indicate that PKR plays a key role in ALI through NLRP3-pyrotosis pathway and pharmacological inhibition of PKR may have potential therapeutic effects in the treatment of patients with ALI and ARDS.

Epac1 inhibits PKR to reduce NLRP3 inflammasome proteins in retinal endothelial cells

Purpose: Inflammation has been strongly associated with retinal damage in diseases such as diabetic retinopathy. Several studies have reported that high glucose exposure induces damage to the retinal vasculature. We and others have shown that high glucose can activate the NOD-like receptor family, pyrin domain containing family member 3 (NLRP3) pathway, leading to increased levels of cleaved caspase 1 and IL-1β to activate a number of inflammatory pathways in the retina.

Methods: We used retinal endothelial cells grown in normal (5 mM) or high (25 mM) glucose or retinal lysates from endothelial cell-specific knockout mice for exchange protein activated by cAMP 1 (Epac1). Human recombinant protein kinase R (PKR) or C16, a PKR inhibitor, was used on the cells to dissect PKR and NLRP3 signaling.

Results: Using retinal endothelial cells (REC) in high glucose and whole retinal lysates from endothelial cell-specific knockout of Epac1, we demonstrate that Epac1 regulates PKR phosphorylation. Using an Epac1 agonist or PKR inhibition with C16, we demonstrated that loss of PKR resulted in reduced NLRP3, cleaved caspase 1, and IL-1β levels. Furthermore, despite the addition of recombinant human PKR, Epac1 was still able to significantly reduce NLRP3 signaling.

Conclusion: Overall, these studies demonstrated that PKR regulates the NLRP3 inflammasome in REC, and that Epac1 inhibition of PKR can reduce activation of the NLRP3 inflammasome.

PKR knockout in the 5xFAD model of Alzheimer's disease reveals beneficial effects on spatial memory and brain lesions

Brain lesions in Alzheimer's disease (AD) include amyloid plaques made of Aβ peptides and neurofibrillary tangles composed of hyperphosphorylated tau protein with synaptic and neuronal loss and neuroinflammation. Aβ oligomers can trigger tau phosphorylation and neuronal alterations through activation of neuronal kinases leading to progressive cognitive decline. PKR is a ubiquitous pro-apoptotic serine/threonine kinase, and levels of activated PKR are increased in AD brains and AD CSF. In addition, PKR regulates negatively memory formation in mice. To assess the role of PKR in an AD in vivo model, we crossed 5xFAD transgenic mice with PKR knockout (PKRKO) mice and we explored the contribution of PKR on cognition and brain lesions in the 5xFAD mouse model of AD as well as in neuron-microglia co-cultures exposed to the innate immunity activator lipopolysaccharide (LPS). Nine-month-old double-mutant mice revealed significantly improved memory consolidation with the new object location test, starmaze test, and elevated plus maze test as compared to 5xFAD mice. Brain amyloid accumulation and BACE1 levels were statistically decreased in double-mutant mice. Apoptosis, neurodegeneration markers, and synaptic alterations were significantly reduced in double-mutant mice as well as neuroinflammation markers such as microglial load and brain cytokine levels. Using cocultures, we found that PKR in neurons was essential for LPS microglia-induced neuronal death. Our results demonstrate the clear involvement of PKR in abnormal spatial memory and brain lesions in the 5xFAD model and underline its interest as a target for neuroprotection in AD.

PKR: A Kinase to Remember

Aging is a major risk factor for many diseases including metabolic syndrome, cancer, inflammation, and neurodegeneration. Identifying mechanistic common denominators underlying the impact of aging is essential for our fundamental understanding of age-related diseases and the possibility to propose new ways to fight them. One can define aging biochemically as prolonged metabolic stress, the innate cellular and molecular programs responding to it, and the new stable or unstable state of equilibrium between the two. A candidate to play a role in the process is protein kinase R (PKR), first identified as a cellular protector against viral infection and today known as a major regulator of central cellular processes including mRNA translation, transcriptional control, regulation of apoptosis, and cell proliferation. Prolonged imbalance in PKR activation is both affected by biochemical and metabolic parameters and affects them in turn to create a feedforward loop. Here, we portray the central role of PKR in transferring metabolic information and regulating cellular function with a focus on cancer, inflammation, and brain function. Later, we integrate information from open data sources and discuss current knowledge and gaps in the literature about the signaling cascades upstream and downstream of PKR in different cell types and function. Finally, we summarize current major points and biological means to manipulate PKR expression and/or activation and propose PKR as a therapeutic target to shift age/metabolic-dependent undesired steady states.

Imoxin attenuates LPS-induced inflammation and MuRF1 expression in mouse skeletal muscle

The double-stranded RNA-dependent protein kinase (PKR) contributes to inflammatory cytokine expression and disease pathogenesis in many conditions. Limited data are available on the efficacy of the PKR inhibitor imoxin to prevent lipopolysaccharide (LPS)-induced inflammation in skeletal muscle in vivo. The aim of this study was to evaluate the effect of imoxin, a PKR inhibitor, on inflammatory and atrophy signaling in skeletal muscle in response to an acute inflammatory insult with LPS. Six-week old C57BL/6J mice received vehicle (saline) or 0.5 mg/kg imoxin 24 and 2 h prior to induction of inflammation via 1 mg/kg LPS. Gastrocnemius muscles were collected 24 h post-LPS and mRNA and protein expression were assessed. LPS lead to a loss of body weight, which was similar in Imoxin+LPS. There were no differences in muscle weight among groups. LPS increased gastrocnemius mRNA expression of TNF-α and IL-1β, and protein levels of NLRP3, all of which were attenuated by imoxin. Similarly, IL-6 mRNA and IL-1β protein were suppressed in Imoxin+LPS compared to LPS alone. LPS increased mRNA of the atrogenes, MuRF1 and MAFbx, and imoxin attenuated the LPS-induced increase in MuRF1 mRNA, and lowered MuRF1 protein. Imoxin+LPS increased p-Akt compared to saline or LPS, whereas p-mTOR was unaltered. FoxO1 was upregulated and p-FoxO1/FoxO1 reduced by LPS, both of which were prevented by imoxin. Both LPS and Imoxin+LPS had diminished p-FoxO3/FoxO3 compared to control. These results demonstrate the potential anti-inflammatory and anti-atrophy effects of imoxin on skeletal muscle in vivo.

Double-stranded RNA-dependent kinase PKR activates NF-κB pathway in acute pancreatitis

The activation of transcription factor nuclear factor kappa B (NF-κB) occurs early in acute pancreatitis (AP) simultaneously with intracellular trypsinogen activation. Double-stranded RNA-dependent kinase (PKR) promotes the activation of NF-κB and the production of pro-inflammatory factors including tumor necrosis factor alpha (TNF-α) and interleukin 6 (IL-6). The rat and rat pancreatic AR42J cells were treated by cerulein to establish AP models, showing PKR increased. TNF-α, IL-6 and lactate dehydrogenase (LDH) in AP pancreatic tissues and cerulein-treated AR42J cells increased, while PKR knockdown in AR42J cells reversed cerulein-induced inflammatory response and pancreatic cell injury. In addition, inhibitor of kappa B kinase α (IKKα), phosphorylated P65 (p-P65), P65 increased in cerulein-treated AR42J cells. Meanwhile, in cerulein-treated AR42J cells, interaction between PKR and IKKα, as well as the co-localization and nuclear accumulation of PKR and P65, were detected. Furthermore, cerulein induced the phosphorylation and nuclear translocation of P65, which indicated the activation of NF-κB, while PKR knockdown hindered NF-κB activation to alleviate pancreatic cell injury. In summary, PKR might promote NF-κB activation via facilitating its phosphorylation and nuclear translocation, thus accelerated inflammatory response and pancreatic cell injury in AP, implying a novel molecular target for the treatment of AP.

Neuronal Regulation of eIF2α Function in Health and Neurological Disorders

A key site of translation control is the phosphorylation of the eukaryotic translation initiation factor 2α (eIF2α), which reduces the rate of GDP to GTP exchange by eIF2B, leading to altered translation. The extent of eIF2α phosphorylation within neurons can alter synaptic plasticity. Phosphorylation of eIF2α is triggered by four stress-responsive kinases, and as such eIF2α is often phosphorylated during neurological perturbations or disease. Moreover, in some cases decreasing eIF2α phosphorylation mitigates neurodegeneration, suggesting that this could be a therapeutic target. Mutations in the γ subunit of eIF2, the guanine exchange factor eIF2B, an eIF2α phosphatase, or in two eIF2α kinases can cause disease in humans, demonstrating the importance of proper regulation of eIF2α phosphorylation for health.

Microtubule affinity-regulating kinases are potential druggable targets for Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder that affects normal functions of the brain. Currently, AD is one of the leading causes of death in developed countries and the only one of the top ten diseases without a means to prevent, cure, or significantly slow down its progression. Therefore, newer therapeutic concepts are urgently needed to improve survival and the quality of life of AD patients. Microtubule affinity-regulating kinases (MARKs) regulate tau-microtubule binding and play a crucial role in neurons. However, their role in hyperphosphorylation of tau makes them potential druggable target for AD therapy. Despite the relevance of MARKs in AD pathogenesis, only a few small molecules are known to have anti-MARK activity and not much has been done to progress these compounds into therapeutic candidates. But given the diverse role of MARKs, the specificity of novel inhibitors is imperative for their successful translation from bench to bedside. In this regard, a recent co-crystal structure of MARK4 in association with a pyrazolopyrimidine-based inhibitor offers a potential scaffold for the development of more specific MARK inhibitors. In this manuscript, we review the biological role of MARKs in health and disease, and draw attention to the largely unexplored area of MARK inhibitors for AD.

PKR involvement in Alzheimer's disease

BACKGROUND

Brain lesions in Alzheimer's disease (AD) are characterized by Aβ accumulation, neurofibrillary tangles, and synaptic and neuronal vanishing. According to the amyloid cascade hypothesis, Aβ1-42 oligomers could trigger a neurotoxic cascade with kinase activation that leads to tau phosphorylation and neurodegeneration. Detrimental pathways that are associated with kinase activation could also be linked to the triggering of direct neuronal death, the production of free radicals, and neuroinflammation.

RESULTS

Among these kinases, PKR (eukaryotic initiation factor 2α kinase 2) is a pro-apoptotic enzyme that inhibits translation and that has been implicated in several molecular pathways that lead to AD brain lesions and disturbed memory formation. PKR accumulates in degenerating neurons and is activated by Aβ1-42 neurotoxicity. It might modulate Aβ synthesis through BACE 1 induction. PKR is increased in cerebrospinal fluid from patients with AD and mild cognitive impairment and can induce the activation of pro-inflammatory pathways leading to TNFα and IL1-β production. In addition, experimentally, PKR seems to down-regulate the molecular processes of memory consolidation. This review highlights the major findings linking PKR and abnormal brain metabolism associated with AD lesions.

CONCLUSIONS

Studying the detrimental role of PKR signaling in AD could pave the way for a neuroprotective strategy in which PKR inhibition could reduce neuronal demise and alleviate cognitive decline as well as the cumbersome burden of AD for patients.

Inhibition of PKR ameliorates lipopolysaccharide-induced acute lung injury by suppressing NF-κB pathway in mice

Acute lung injury (ALI) is characterized by dramatic lung inflammation and alveolar epithelial cell death. Although protein kinase R (PKR) (double-stranded RNA-activated serine/threonine kinase) has been implicated in inflammatory response to bacterial cell wall components, whether it plays roles in lipopolysaccharide (LPS)-induced ALI remains unclear. This study was aimed to reveal whether and how PKR was involved in LPS-induced ALI pathology and the potential effects of its specific inhibitor, C16 (C₁₃H₈N₄OS). During the experiment, mice received C16 (100 or 500 ug/kg) intraperitoneally 1 h before intratracheal LPS instillation. Then, whole lung lavage was collected for analysis of total protein levels and proinflammatory cytokines, including tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β) and IL-6. The lungs were tested for Western blot, transferase-mediated dUTP nick-end labeling (TUNEL) stain and immunohistochemistry. Results showed that PKR phosphorylation increased significantly after LPS instillation. Furthermore, PKR specific inhibition attenuated LPS-induced lung injury (hematoxylin and eosin stain), reduced lung protein permeability (total protein levels in whole lung lavage) and suppressed proinflammatory cytokines (TNF-α, IL-1β and IL-6) and lung apoptosis (TUNEL stain and caspase3 activation). Moreover, mechanism-study showed that C16 significantly suppressed I kappa B kinase (IKK)/I kappa B alpha (IκBα)/NF-κB signaling pathway after LPS challenge. These findings suggested that PKR inhibition ameliorated LPS-induced lung inflammation and apoptosis in mice by suppressing NF-κB signaling pathway.

Protein Kinase R Mediates the Inflammatory Response Induced by Hyperosmotic Stress

High extracellular osmolarity results in a switch from an adaptive to an inflammatory gene expression program. We show that hyperosmotic stress activates the protein kinase R (PKR) independently of its RNA-binding domain. In turn, PKR stimulates nuclear accumulation of nuclear factor κB (NF-κB) p65 species phosphorylated at serine-536, which is paralleled by the induction of a subset of inflammatory NF-κB p65-responsive genes, including inducible nitric oxide synthase (iNOS), interleukin-6 (IL-6), and IL-1β. The PKR-mediated hyperinduction of iNOS decreases cell survival in mouse embryonic fibroblasts via mechanisms involving nitric oxide (NO) synthesis and posttranslational modification of proteins. Moreover, we demonstrate that the PKR inhibitor C16 ameliorates both iNOS amplification and disease-induced phenotypic breakdown of the intestinal epithelial barrier caused by an increase in extracellular osmolarity induced by dextran sodium sulfate (DSS) in vivo Collectively, these findings indicate that PKR activation is an essential part of the molecular switch from adaptation to inflammation in response to hyperosmotic stress.

The Specific Protein Kinase R (PKR) Inhibitor C16 Protects Neonatal Hypoxia-Ischemia Brain Damages by Inhibiting Neuroinflammation in a Neonatal Rat Model

BACKGROUND Brain injuries induced by hypoxia-ischemia in neonates contribute to increased mortality and lifelong neurological dysfunction. The specific PKR inhibitor C16 has been previously demonstrated to exert a neuroprotective role in adult brain injuries. However, there is no recent study available concerning its protective role in hypoxia-ischemia-induced immature brain damage. Therefore, we investigated whether C16 protects against neonatal hypoxia-ischemia injuries in a neonatal rat model. MATERIAL AND METHODS Postnatal day 7 (P7) rats were used to establish classical hypoxia-ischemia animal models, and C16 postconditioning with 100 ug/kg was performed immediately after hypoxia. Western blot analysis was performed to quantify the phosphorylation of the PKR at 0 h, 3 h, 6 h, 12 h, 24 h, and phosphorylation of NF-κB 24h after hypoxia exposure. The TTC stain for infarction area and TUNEL stain for apoptotic cells were assayed 24 h after the brain hypoxia. Gene expression of IL-1β, IL-6, and TNF-α was performed at 3 h, 6 h, 12 h, and 24 h. RESULTS The level of PKR autophosphorylation was increased dramatically, especially at 3 h (C16 group vs. HI group, P<0.01). Intraperitoneal C16 administration reduced the infarct volume and apoptosis ratio after this insult (C16 group vs. HI group<0.01), and C16 reduced proinflammatory cytokines mRNA expression, partly through inhibiting NF-κB activation (C16 group vs. HI group<0.05). CONCLUSIONS C16 can protect immature rats against hypoxia-ischemia-induced brain damage by modulating neuroinflammation.

PKM2-dependent glycolysis promotes NLRP3 and AIM2 inflammasome activation

Sepsis, severe sepsis and septic shock are the main cause of mortality in non-cardiac intensive care units. Immunometabolism has been linked to sepsis; however, the precise mechanism by which metabolic reprogramming regulates the inflammatory response is unclear. Here we show that aerobic glycolysis contributes to sepsis by modulating inflammasome activation in macrophages. PKM2-mediated glycolysis promotes inflammasome activation by modulating EIF2AK2 phosphorylation in macrophages. Pharmacological and genetic inhibition of PKM2 or EIF2AK2 attenuates NLRP3 and AIM2 inflammasomes activation, and consequently suppresses the release of IL-1β, IL-18 and HMGB1 by macrophages. Pharmacological inhibition of the PKM2-EIF2AK2 pathway protects mice from lethal endotoxemia and polymicrobial sepsis. Moreover, conditional knockout of PKM2 in myeloid cells protects mice from septic death induced by NLRP3 and AIM2 inflammasome activation. These findings define an important role of PKM2 in immunometabolism and guide future development of therapeutic strategies to treat sepsis.

Design and synthesis of novel protein kinase R (PKR) inhibitors

Protein kinase RNA-activated (PKR) plays an important role in a broad range of intracellular regulatory mechanisms and in the pathophysiology of many human diseases, including microbial and viral infections, cancer, diabetes and neurodegenerative disorders. Recently, several potent PKR inhibitors have been synthesized. However, the enzyme's multifunctional character and a multitude of PKR downstream targets have prevented the successful transformation of such inhibitors into effective drugs. Thus, the need for additional PKR inhibitors remains. With the help of computer-aided drug-discovery tools, we designed and synthesized potential PKR inhibitors. Indeed, two compounds were found to inhibit recombinant PKR in pharmacologically relevant concentrations. One compound, 6-amino-3-methyl-2-oxo-N-phenyl-2,3-dihydro-1H-benzo[d]imidazole-1-carboxamide, also showed anti-apoptotic properties. The novel molecules diversify the existing pool of PKR inhibitors and provide a basis for the future development of compounds based on PKR signal transduction mechanism.

Discovery of Diverse Small-Molecule Inhibitors of Mammalian Sterile20-like Kinase 3 (MST3)

Increasing evidence suggests key roles for members of the mammalian Sterile20-like (MST) family of kinases in many aspects of biology. MST3 is a member of the STRIPAK complex, the deregulation of which has recently been associated with cancer cell migration and metastasis. Targeting MST3 with small-molecule inhibitors may be beneficial for the treatment of certain cancers, but little information exists on the potential of kinase inhibitor scaffolds to engage with MST3. In this study we screened MST3 against a library of 277 kinase inhibitors using differential scanning fluorimetry and confirmed 14 previously unknown MST3 inhibitors by X-ray crystallography. These compounds, of which eight are in clinical trials or FDA approved, comprise nine distinct chemical scaffolds that inhibit MST3 enzymatic activity with IC50 values between 0.003 and 23 μm. The structure-activity relationships explain the differential inhibitory activity of these compounds against MST3 and the structural basis for high binding potential, the information of which may serve as a framework for the rational design of MST3-selective inhibitors as potential therapeutics and to interrogate the function of this enzyme in diseased cells.

PKR deficiency alters E. coli-induced sickness behaviors but does not exacerbate neuroimmune responses or bacterial load

Background

Systemic inflammation induces neuroimmune activation, ultimately leading to sickness (e.g., fever, anorexia, motor impairments, exploratory deficits, and social withdrawal). In this study, we evaluated the role of protein kinase R (PKR), a serine-threonine kinase that can control systemic inflammation, on neuroimmune responses and sickness.

Methods

Wild-type (WT) PKR+/+ mice and PKR−/− mice were subcutaneously injected with live Escherichia coli (E. coli) or vehicle. Food consumption, rotarod test performance, burrowing, open field activity, object investigation, and social interaction were monitored. Plasma TNF-α and corticosterone were measured by ELISA. The percentage of neutrophils in blood was deduced from blood smears. Inflammatory gene expression (IL-1β, TNF-α, IL-6, cyclooxygenase (COX)-2, iNOS) in the liver and the brain (hypothalamus and hippocampus) were quantified by real-time PCR. Blood and lavage fluid (injection site) were collected for microbiological plate count and for real-time PCR of bacterial 16S ribosomal DNA (rDNA). Corticotrophin-releasing hormone (CRH) expression in the hypothalamus was also determined by real-time PCR.

Results

Deficiency of PKR diminished peripheral inflammatory responses following E. coli challenge. However, while the core components of sickness (anorexia and motor impairments) were similar between both strains of mice, the behavioral components of sickness (reduced burrowing, exploratory activity deficits, and social withdrawal) were only observable in PKR−/− mice but not in WT mice. Such alteration of behavioral components was unlikely to be caused by exaggerated neuroimmune activation, by an impaired host defense to the infection, or due to a dysregulated corticosterone response, because both strains of mice displayed similar neuroimmune responses, bacterial titers, and plasma corticosterone profiles throughout the course of infection. Nevertheless, the induction of hypothalamic corticotrophin-releasing hormone (CRH) by E. coli was delayed in PKR−/− mice relative to WT mice, suggesting that PKR deficiency may postpone the CRH response during systemic inflammation.

Conclusions

Taken together, our findings show that (1) loss of PKR could alter E. coli-induced sickness behaviors and (2) this was unlikely to be due to exacerbated neuroimmune activation, (3) elevated bacterial load, or (4) dysregulation in the corticosterone response. Further studies can address the role of PKR in the CRH response together with its consequence on sickness.

Hepatocyte Nicotinamide Adenine Dinucleotide Phosphate Reduced Oxidase 4 Regulates Stress Signaling, Fibrosis, and Insulin Sensitivity During Development of Steatohepatitis in Mice

BACKGROUND & AIMS

Reactive oxidative species (ROS) are believed to be involved in the progression of nonalcoholic steatohepatitis (NASH). However, little is known about the sources of ROS in hepatocytes or their role in disease progression. We studied the effects of nicotinamide adenine dinucleotide phosphate reduced oxidase 4 (NOX4) in liver tissues from patients with NASH and mice with steatohepatitis.

METHODS

Liver biopsy samples were obtained from 5 patients with NASH, as well as 4 patients with simple steatosis and 5 patients without steatosis (controls) from the University of California, Davis Cancer Center Biorepository. Mice with hepatocyte-specific deletion of NOX4 (NOX4(hepKO)) and NOX4(floxp+/+) C57BL/6 mice (controls) were given fast-food diets (supplemented with high-fructose corn syrup) or choline-deficient l-amino acid defined diets to induce steatohepatitis, or control diets, for 20 weeks. A separate group of mice were given the NOX4 inhibitor (GKT137831). Liver tissues were collected and immunoblot analyses were performed determine levels of NOX4, markers of inflammation and fibrosis, double-stranded RNA-activated protein kinase, and phospho-eIF-2α kinase-mediated stress signaling pathways. We performed hyperinsulinemic-euglycemic clamp studies and immunoprecipitation analyses to determine the oxidation and phosphatase activity of PP1C.

RESULTS

Levels of NOX4 were increased in patients with NASH compared with controls. Hepatocyte-specific deletion of NOX4 reduced oxidative stress, lipid peroxidation, and liver fibrosis in mice with diet-induced steatohepatitis. A small molecule inhibitor of NOX4 reduced liver inflammation and fibrosis and increased insulin sensitivity in mice with diet-induced steatohepatitis. In primary hepatocytes, NOX4 reduced the activity of the phosphatase PP1C, prolonging activation of double-stranded RNA-activated protein kinase and phosphorylation of extracellular signal-regulated kinase-mediated stress signaling. Mice with hepatocyte-specific deletion of NOX4 and mice given GKT137831 had increased insulin sensitivity.

CONCLUSIONS

NOX4 regulates oxidative stress in the liver and its levels are increased in patients with NASH and mice with diet-induced steatohepatitis. Inhibitors of NOX4 reduce liver inflammation and fibrosis and increase insulin sensitivity, and might be developed for treatment of NASH.

Neuroinflammation and Aβ accumulation linked to systemic inflammation are decreased by genetic PKR down-regulation

Alzheimer's disease (AD) is a neurodegenerative disorder, marked by senile plaques composed of amyloid-β (Aβ) peptide, neurofibrillary tangles, neuronal loss and neuroinflammation. Previous works have suggested that systemic inflammation could contribute to neuroinflammation and enhanced Aβ cerebral concentrations. The molecular pathways leading to these events are not fully understood. PKR is a pro-apoptotic kinase that can trigger inflammation and accumulates in the brain and cerebrospinal fluid of AD patients. The goal of the present study was to assess if LPS-induced neuroinflammation and Aβ production could be altered by genetic PKR down regulation. The results show that, in the hippocampus of LPS-injected wild type mice, neuroinflammation, cytokine release and Aβ production are significantly increased and not in LPS-treated PKR knock-out mice. In addition BACE1 and activated STAT3 levels, a putative transcriptional regulator of BACE1, were not found increased in the brain of PKR knock-out mice as observed in wild type mice. Using PET imaging, the decrease of hippocampal metabolism induced by systemic LPS was not observed in LPS-treated PKR knock-out mice. Altogether, these findings demonstrate that PKR plays a major role in brain changes induced by LPS and could be a valid target to modulate neuroinflammation and Aβ production.