bims-unfpre Biomed News
on Unfolded protein response
Issue of 2020‒06‒28
eight papers selected by
Susan Logue
University of Manitoba

  1. Gastroenterology. 2020 Jun 20. pii: S0016-5085(20)34831-9. [Epub ahead of print]
    Dasgupta D, Nakao Y, Mauer AS, Thompson JM, Sehrawat TS, Liao CY, Krishnan A, Lucien F, Guo Q, Liu M, Xue F, Fukushima M, Katsumi T, Bansal A, Pandey MK, Maiers JL, DeGrado T, Ibrahim SH, Revzin A, Pavelko KD, Barry MA, Kaufman RJ, Malhi H.
      BACKGROUND & AIMS: Endoplasmic reticulum to nucleus signaling 1 (ERN1, also called IRE1A) is a sensor of the unfolded protein response that is activated in livers of patients with nonalcoholic steatohepatitis (NASH). Hepatocytes release ceramide-enriched inflammatory extracellular vesicles (EVs) following activation of IRE1A. We studied the effects of inhibiting IRE1A on release of inflammatory EVs in mice with diet-induced steatohepatitis.METHODS: C57BL/6J mice and mice with hepatocyte-specific disruption of Ire1a (IRE1αΔhep) mice were fed a diet high in fat, fructose, and cholesterol (FFC) to induce development of steatohepatitis or a standard chow diet (controls). Some mice were given intraperitoneal injections of the IRE1A inhibitor 4μ8C. Mouse liver and primary hepatocytes were transduced with adenovirus or adeno-associated virus that expressed IRE1A. Livers were collected from mice and analyzed by quantitative PCR and chromatin immunoprecipitation assays; plasma samples were analyzed by ELISA. EVs were derived from hepatocytes and injected intravenously into mice. Plasma EVs were characterized by nanoparticle-tracking analysis, electron microscopy, immunoblots, and nanoscale flow cytometry; we used a membrane-tagged reporter mouse to detect hepatocyte-derived EVs. Plasma and liver tissues from patients with NASH and without NASH (controls) were analyzed for EV concentration and by RNAscope and gene expression analyses.
    RESULTS: Disruption of Ire1a in hepatocytes or inhibition of IRE1A reduced release of EVs and liver injury, inflammation, and accumulation of macrophages in mice on the FFC diet. Activation of IRE1A, in livers of mice, stimulated release of hepatocyte-derived EVs, and also from cultured primary hepatocytes. Mice given intravenous injections of IRE1A-stimulated, hepatocyte-derived EVs accumulated monocyte-derived macrophages in liver. IRE1A-stimulated EVs were enriched in ceramides. Chromatin immunoprecipitation showed that IRE1A activated X-box binding protein 1 (XBP1) to increase transcription of serine palmitoyltransferase genes, which encode the rate-limiting enzyme for ceramide biosynthesis. Administration of a pharmacological inhibitor of serine palmitoyltransferase to mice reduced the release of EVs. Levels of XBP1 and serine palmitoyltransferase were increased in liver tissues, and numbers of EVs were increased in plasma, from patients with NASH compared with controls and correlated with the histologic features of inflammation.
    CONCLUSIONS: In mouse hepatocytes, activated IRE1A promotes transcription of serine palmitoyltransferase genes via XBP1, resulting in ceramide biosynthesis and release of EVs. The EVs recruit monocyte-derived macrophages to liver, resulting in inflammation and injury in mice with diet-induced steatohepatitis. Levels of XBP1, serine palmitoyltransferase, and EVs are all increased in liver tissues from patients with NASH. Strategies to block this pathway might be developed to reduce liver inflammation in patients with NASH.
    Keywords:  ER stress; exosome; lipotoxicity; macrophage
  2. Oncol Lett. 2020 Jul;20(1): 589-600
    He C, Hua W, Liu J, Fan L, Wang H, Sun G.
      Previous studies have shown that endoplasmic reticulum (ER) stress serves an important role in shaping the immunosuppressive microenvironment by modulating resident immune cells. However, the communication between ER-stressed tumor cells and immune cells is not fully understood. Exosomes have been reported to play a vital role in intercellular communication. Therefore, in order to investigate the role of ER stress-related exosomes in liver cancer cells mediated macrophage function remodeling, immunohistochemical analysis, western-blotting immunofluorescence and cytokine bead array analyses were performed. The results demonstrated that glucose-regulated protein 78 (GRP78) expression was upregulated in human liver cancer tissue. Moreover, 69.09% of GRP78-positive liver cancer tissues possessed macrophages expressing CD68+ (r=0.55; P<0.001). In addition to these CD68+ macrophages, interleukin (IL)-10 and IL-6 expression levels were increased in liver cancer tissues. It was also demonstrated that exosomes released by ER-stressed HepG2 cells significantly enhanced the expression levels of several cytokines, including IL-6, monocyte chemotactic protein-1, IL-10 and tumor necrosis factor-α in macrophages. Furthermore, incubation of cells with ER stress-associated exosomes resulted inactivation of the Janus kinase 2/STAT3 pathway, and inhibition of STAT3 using S3I-201 in RAW264.7 cells significantly reduced cytokine production. Collectively, the present study identified a novel function of ER stress-associated exosomes in mediating macrophage cytokine secretion in the liver cancer microenvironment, and also indicated the potential of treating liver cancer via an ER stress-exosomal-STAT3 pathway.
    Keywords:  endoplasmic reticulum stress; exosome; inflammation; liver cancer; macrophage
  3. Sci Rep. 2020 Jun 23. 10(1): 10188
    Tavernier Q, Legras A, Didelot A, Normand C, Gibault L, Badoual C, Le Pimpec-Barthes F, Puig PL, Blons H, Pallet N.
      Proteostasis imbalance is emerging as a major hallmark of cancer, driving tumor growth and aggressiveness. Endoplasmic Reticulum (ER) stress has been documented in most major cancers, and the ability to tolerate persistent ER stress through an effective unfolded protein response enhances cancer cell survival, angiogenesis, metastasis, drug resistance and immunosuppression. The ER stress sensor IRE1α contributes to tumor progression through XBP1 mRNA splicing and regulated IRE1α-dependent decay of mRNA and miRNA. The aim of this study was to perform a molecular characterization of series of tumor samples to explore the impact of intratumoral IRE1 signaling in non-small cell lung cancer characteristics. To monitor IRE1 splicing activity, we adopted a fragment length analysis to detect changes in the length of the XBP1 mRNA before and after splicing as a method for measuring sXBP1 mRNA levels in tumors because sXBP1 mRNA is not probed by standard transcriptomic analyses. We demonstrate for the first time that XBP1 splicing is a valuable marker of lung cancer aggressiveness, and our results support a model in which IRE1 downstream signaling could act as a regulator of Epithelial to Mesenchymal Transition (EMT). Our findings study highlights the role of IRE1α downstream signaling in non-small cell lung cancer and opens a conceptual framework to determine how IRE1α endoribonuclease activity shapes the EMT program.
  4. FASEB J. 2020 Jun 27.
    Jiang M, Wang H, Liu Z, Lin L, Wang L, Xie M, Li D, Zhang J, Zhang R.
      Exposure to microgravity results in vascular remodeling and cardiovascular dysfunction. To elucidate the mechanism involved in this condition, we investigated whether endoplasmic reticulum (ER) stress during simulated microgravity induced endothelial inflammation and apoptosis in human umbilical vein endothelial cells (HUVECs). Microgravity was simulated by clinorotation in the current study. We examined markers of ER stress, inducible nitric oxide (NO) synthase (iNOS)/NO content, proinflammatory cytokine production, nuclear factor kappa B (NF-κB)/IκB signaling, NLRP3 inflammasome, and detected apoptosis in HUVECs. We found that the levels of C/EBP homologous protein and glucose-regulated protein 78, pro-inflammatory cytokines (IL-6, TNF-α, IL-8, and IL-1β), and iNOS/NO content were upregulated by clinorotation. ER stress inhibition with tauroursodeoxycholic acid or 4-phenylbutyric acid and iNOS inhibition with 1400 W dramatically suppressed activation of the NF-κB/IκB pathway and the NLRP3 inflammasome, and decreased the production of pro-inflammatory cytokines. The increase of apoptosis in HUVECs during clinorotation was significantly suppressed by inhibiting ER stress, iNOS activity, NF-κB/IκB, and the NLRP3 inflammasome signaling pathway. Therefore, simulated microgravity causes ER stress in HUVECs, and subsequently activates iNOS/NO-NF-κB/IκB and the NLRP3 inflammasome signaling pathway, which have key roles in the induction of endothelial inflammation and apoptosis.
    Keywords:  apoptosis; endoplasmic reticulum stress; endothelial cells; inflammation; microgravity
  5. Hepatology. 2020 Jun 22.
    Xu H, Tian Y, Tang D, Zou S, Liu G, Song J, Zhang G, Du X, Huang W, He B, Lin W, Jin L, Huang W, Yang J, Fu X.
      Endoplasmic reticulum (ER) stress is an adaptive response to excessive ER demand and contributes to the development of numerous diseases, including nonalcoholic fatty liver disease (NAFLD) that is hallmarked by the accumulation of lipid within hepatocytes. However, the underlying mechanisms remain elusive. MicroRNAs (miRNAs) play an indispensable role in various stress responses, but their implications in ER stress have not yet been systemically investigated. In this study, we identify a negative feedback loop comprising hepatic ER stress and miR-26a in NAFLD pathogenesis. Combining miRNA dot blot array and quantitative polymerase chain reaction, we find that miR-26a is specifically induced by ER stress in liver cells. This induction of miR-26a is critical for cells to cope with ER stress. In human hepatoma cells and murine primary hepatocytes, overexpression of miR-26a markedly alleviates chemical-induced ER stress, as well as palmitate-triggered ER stress and lipid accumulation. Conversely, deficiency of miR-26a exhibits opposite effects. Mechanistically, miR-26a directly targets the eukaryotic initiation factor 2α (eIF2α), a core ER stress effector controlling cellular translation. Intriguingly, miR-26a is reduced in the livers of NAFLD patients. Hepatocyte-specific restoration of miR-26a in mice significantly mitigates high-fat diet (HFD)-induced ER stress and hepatic steatosis. In contrast, deficiency of miR-26a in mice exacerbates HFD-induced ER stress, lipid accumulation, inflammation and hepatic steatosis. Conclusion: Our findings suggest ER stress-induced miR-26a upregulation as a regulator for hepatic ER stress resolution, and highlight the ER stress/miR-26a/eIF2α cascade as a promising therapeutic strategy for NAFLD.
    Keywords:  EIF2α; Insulin Resistance; Lipid Metabolism; Noncoding RNA; Obesity
  6. Cell Stress Chaperones. 2020 Jun 22.
    Anand RS, Ganesan D, Rajasekaran S, Jayavelu T.
      Structures of cellular organelles are intertwined with their functions that undergo alterations once the organelles are stressed. Since organelle functions are dependent on each other, an organelle-specific stress possibly influences the structure and function of its associated organelles. In this perspective, our study demonstrated that endoplasmic reticulum (ER)-specific stress induced by tunicamycin in primary astroglial culture is associated with altered mitochondrial dynamics and matched with the changes as observed in the aging rat brain. However, the exogenous addition of biotin, a highly lipogenic and mitochondrial vitamin, ameliorates ER stress even though its direct targets are not known within ER. Alternatively, the increased biotinylation of mitochondrial carboxylases preserves its basal respiratory capacity by upregulating mitofusin 2 (Mfn2) and, possibly, its associated role on mitochondrial fusion. Furthermore, the Mfn2 increase by biotin augments physical interaction between ER and functional mitochondria to exchange biomolecules as a part of ER stress resolution. This suggests an increased demand for micronutrient biotin under ER stress resolves the same by undergoing appropriate structural and metabolic contacts between ER and mitochondria. These findings provide a paradigm to resolve stress in one organelle by sustaining the metabolic commitments of another interdependent organelle. The findings also highlight a novel role of biotin in inducing Mfn2 expression and localization under ER stress in addition to its known role as a co-enzyme.
    Keywords:  Biotin; ER stress; Mitochondrial dynamics; Mitochondrial respiration
  7. Sci Rep. 2020 Jun 22. 10(1): 10028
    Onoda A, Kawasaki T, Tsukiyama K, Takeda K, Umezawa M.
      Nano-particulate air pollution threatens developing brains and is epidemiologically related to neurodegenerative diseases involving deposition of misfolded proteins. However, the mechanism underlying developmental neurotoxicity by nanoparticles remains unknown. Here, we report that maternal exposure to low doses of carbon black nanoparticle (CB-NP) induces endoplasmic reticulum (ER) stress associated with accumulation of misfolded proteins. Notably, offspring specifically showed high induction of ER stress in perivascular macrophages and reactive astrocytes only around brain blood vessels, along with accumulation of β-sheet-rich proteins regarded as misfolded proteins. Our results suggest that maternal CB-NP exposure induced ER stress in PVMs and reactive astrocytes around blood vessels in the brain of offspring in mice. The induction of ER stress accompanied by the perivascular accumulation of misfolded proteins is likely to be associated with perivascular abnormalities and neurodegeneration, and development of neurodegenerative diseases related to particulate air pollution.
  8. Cell Stress Chaperones. 2020 Jun 23.
    Zhang Y, Chatzistamou I, Kiaris H.
      The unfolded protein response (UPR) is an adaptive response that is implicated in multiple metabolic pathologies, including hepatic steatosis. In the present study, we analyzed publicly available RNAseq data to explore how the execution of the UPR is orchestrated in specimens that exhibit hepatocyte ballooning, a landmark feature of steatosis. By focusing on a panel of well-established UPR genes, we assessed how the UPR is coordinated with the whole transcriptome in specimens with or without hepatocyte ballooning. Our analyses showed that neither average levels nor correlation in expression between major UPR genes such as HSPA5 (BiP/GRP78), HSP90b1 (GRP94), or DDIT3 (CHOP) is altered in different groups. However, a panel of transcripts depending on the stringency of the analysis ranged from 16 to 372 lost its coordination with HSPA5, the major UPR chaperone, when hepatocyte ballooning occurred. In 13 genes, the majority of which is associated with metabolic processes, and the coordination with the HSPA5 was reversed from positive to negative in livers with ballooning hepatocytes. In order to examine if during ballooning, UPR genes abolish established and acquire novel functionalities, we performed gene ontology analyses. These studies showed that among the various UPR genes interrogated, only DDIT3 was not associated with conventional functions linked to endoplasmic reticulum stress during ballooning, while HSPA90b1 exhibited the highest function retention between the specimens with or without ballooning. Our results challenge conventional notions on the impact of specific genes in disease and suggest that besides abundance, the mode of coordination of UPR may be more important for disease development.
    Keywords:  Correlation network; ER stress; Liver; Pathogenesis