bims-unfpre 2022-01-02 papers

Issue of 2022–01–02
five papers selected by
Susan Logue, University of Manitoba

Plant Signal Behav. 2021 Dec 30. 2018857

The interplay of GTP-binding protein AGB1 with ER stress sensors IRE1a and IRE1b modulates Arabidopsis unfolded protein response and bacterial immunity.

Taiaba Afrin, Caitlin N Costello, Amber N Monella, Camilla J Kørner, Karolina M Pajerowska-Mukhtar.

In eukaryotic cells, the accumulation of unfolded or misfolded proteins in the endoplasmic reticulum (ER) results in ER stress that induces a cascade of reactions called the unfolded protein response (UPR). In Arabidopsis, the most conserved UPR sensor, Inositol-requiring enzyme 1 (IRE1), responds to both abiotic- and biotic-induced ER stress. Guanine nucleotide-binding proteins (G proteins) constitute another universal and conserved family of signal transducers that have been extensively investigated due to their ubiquitous presence and diverse nature of action. Arabidopsis GTP-binding protein β1 (AGB1) is the only G-protein β-subunit encoded by the Arabidopsis genome that is involved in numerous signaling pathways. Mounting evidence suggests the existence of a crosstalk between IRE1 and G protein signaling during ER stress. AGB1 has previously been shown to control a distinct UPR pathway independently of IRE1 when treated with an ER stress inducer tunicamycin. Our results obtained with combinatorial knockout mutants support the hypothesis that both IRE1 and AGB1 synergistically contribute to ER stress responses chemically induced by dithiothreitol (DTT) as well as to the immune responses against a phytopathogenic bacterium Pseudomonas syringae pv. tomato strain DC3000. Our study highlights the crosstalk between the plant UPR transducers under abiotic and biotic stress.

Keywords: Arabidopsis thaliana; GTP-binding Protein B1; Inositol-Requiring Enzyme 1; Pseudomonas syringae pv. tomato DC3000; Unfolded Protein Response

DOI: https://doi.org/10.1080/15592324.2021.2018857

Alzheimers Dement. 2021 Dec;17 Suppl 2 e058717

CHOP is not a main contributor to tau-mediated toxicity.

Marangelie Criado-Marrero, Laura J Blair.

BACKGROUND: In Alzheimer's disease (AD), the accumulation of the microtubule associated protein tau is linked with neuronal loss, but the major cell death pathway remains to be identified. Pathogenic tau promotes endoplasmic reticulum (ER) stress and subsequent unfolded protein response (UPR) activation. However, the contribution of ER stress to tau-mediated toxicity in neurons is unknown. A previous study demonstrated that mice lacking CHOP/Ddit3, an important regulator of ER stress-induced cell death, were protected from ER stress induced neuronal loss. We hypothesized that silencing CHOP would prevent tau toxicity through the ER stress pathway and reveal the contribution of tau toxicity that is mediated through this pathway.
METHOD: To investigate this, we generated a mouse-targeting CHOP/Ddit3 shRNA AAV9 that also expresses GFP by a separate promoter. We injected shCHOP AAV9 or a shScrambled control AAV9 in the brains of 8-month-old male and female rTg4510 tau transgenic mice and harvested them at 12-months of age, when ER stress is activated, and neuronal loss is occurring in these mice. We performed behavioral studies using the Y-Maze, Open field, and 2-day Radial-Arm water maze task with a reversal paradigm. Unbiased stereology was used to determine neuronal health and effect of CHOP shRNA on CHOP levels was evaluated by immunofluorescence.
RESULT: AAV9 CHOP shRNA did not alter spatial learning and memory in tau transgenic mice. Evaluation of the tissue revealed a modest, but non-significant increase in neuronal loss from CHOP knock down, while the DG shows a non-significant decrease in neuronal loss. Tissue volume was unchanged in both regions. Very surprising to us, and opposite of what was expected, we found that in these regions of interest the CHOP levels increased in the animal expressing the CHOP.
CONCLUSION: Overall, this suggests that shCHOP AAV9 does not alter tau-modified behaviors such as learning and memory particularly at this timepoint. Our results also suggest that there may be a compensatory increase in CHOP signaling in neighboring cells, suggesting that the activation of the UPR in the brains of these mice may be a protective mechanism.

DOI: https://doi.org/10.1002/alz.058717

J Biol Chem. 2021 Dec 22. pii: S0021-9258(21)01342-9. [Epub ahead of print] 101532

The ER stress sensor inositol-requiring enzyme 1α in Kupffer cells promotes hepatic ischemia-reperfusion injury.

Jie Cai, Xiaoge Zhang, Peng Chen, Yang Li, Songzi Liu, Qian Liu, Hanyong Zhang, Zhuyin Wu, Ke Song, Jianmiao Liu, Bo Shan, Yong Liu.

Hepatic ischemia/reperfusion (I/R) injury is an inflammation-mediated process arising from ischemia/reperfusion-elicited stress in multiple cell types, causing liver damage during surgical procedures and often resulting in liver failure. Endoplasmic reticulum (ER) stress triggers the activation of the unfolded protein response (UPR) and is implicated in tissue injuries, including hepatic I/R injury. However, the cellular mechanism that links the UPR signaling to local inflammatory responses during hepatic I/R injury remains largely obscure. Here, we report that IRE1α, a critical ER-resident transmembrane signal transducer of the UPR, plays an important role in promoting Kupffer cell-mediated liver inflammation and hepatic I/R injury. Utilizing a mouse model in which IRE1α is specifically ablated in myeloid cells, we found that abrogation of IRE1α markedly attenuated necrosis and cell death in the liver, accompanied by reduced neutrophil infiltration and liver inflammation following hepatic I/R injury. Mechanistic investigations in mice as well as in primary Kupffer cells revealed that loss of IRE1α in Kupffer cells not only blunted the activation of the NLRP3 inflammasome and IL-1β production, but also suppressed the expression of the inducible nitric oxide synthase (iNos) and pro-inflammatory cytokines. Moreover, pharmacological inhibition of IRE1α's RNase activity was able to attenuate inflammasome activation and iNos expression in Kupffer cells, leading to alleviation of hepatic I/R injury in mice. Collectively, these results demonstrate that Kupffer cell IRE1α mediates local inflammatory damage during hepatic I/R injury. Our findings suggest that IRE1α RNase activity may serve as a promising target for therapeutic treatment of ischemia/reperfusion-associated liver inflammation and dysfunction.

Keywords: ER stress; Hepatic ischemia/reperfusion injury; IRE1α; Inflammation; Kupffer cells

DOI: https://doi.org/10.1016/j.jbc.2021.101532

Gut Microbes. 2022 Jan-Dec;14(1):14(1): 2015238

Autophagy mediates ER stress and inflammation in Helicobacter pylori-related gastric cancer.

M C Mommersteeg, I Simovic, B Yu, S A V van Nieuwenburg, I M J Bruno, M Doukas, E J Kuipers, M C W Spaander, M P Peppelenbosch, N Castaño-Rodríguez, G M Fuhler.

Autophagy is a cellular degradation mechanism, which is triggered by the bacterium Helicobacter pylori. A single nucleotide polymorphism (SNP) in the autophagy gene ATG16L1 (rs2241880, G-allele) has been shown to dysregulate autophagy and increase intestinal endoplasmic reticulum (ER) stress. Here, we investigate the role of this SNP in H. pylori-mediated gastric carcinogenesis and its molecular pathways. ATG16L1 rs2241880 was genotyped in subjects from different ethnic cohorts (Dutch and Australian) presenting with gastric (pre)malignant lesions of various severity. Expression of GRP78 (a marker for ER stress) was assessed in gastric tissues. The effect of ATG16L1 rs2241880 on H. pylori-mediated ER stress and pro-inflammatory cytokine induction was investigated in organoids and CRISPR/Cas9 modified cell lines. Development of gastric cancer was associated with the ATG16L1 rs2241880 G-allele. Intestinal metaplastic cells in gastric tissue of patients showed increased levels of ER-stress. In vitro models showed that H. pylori increases autophagy while reducing ER stress, which appeared partly mediated by the ATG16L1 rs2241880 genotype. H. pylori-induced IL-8 production was increased while TNF-α production was decreased, in cells homozygous for the G-allele. The ATG16L1 rs2241880 G-allele is associated with progression of gastric premalignant lesions and cancer. Modulation of H. pylori-induced ER stress pathways and pro-inflammatory mediators by ATG16L1 rs2441880 may underlie this increased risk.

Keywords: ATG16L1; ER stress; Helicobacter pylori; Intestinal metaplasia; atrophic gastritis; autophagy; gastric cancer; inflammation

DOI: https://doi.org/10.1080/19490976.2021.2015238

J Biol Chem. 2021 Dec 24. pii: S0021-9258(21)01350-8. [Epub ahead of print] 101540

p53 regulates skeletal muscle mitophagy and mitochondrial quality control following denervation-induced muscle disuse.

Jonathan M Memme, Ashley N Oliveira, David A Hood.

Persistent inactivity promotes skeletal muscle atrophy, marked by mitochondrial aberrations that affect strength, mobility, and metabolic health leading to the advancement of disease. Mitochondrial quality control (MQC) pathways include biogenesis (synthesis), mitophagy/lysosomal turnover, and the mitochondrial unfolded protein response (UPRmt) which serve to maintain an optimal organelle network. Tumor suppressor p53 has been implicated in regulating muscle mitochondria in response to cellular stress; however, its role in the context of muscle disuse has yet to be explored, and whether p53 is necessary for MQC remains unclear. To address this, we subjected p53 muscle-specific knockout (mKO) and wild-type (WT) mice to unilateral denervation. Transcriptomic and pathway analyses revealed dysregulation of pathways pertaining to mitochondrial function, and especially turnover, in mKO muscle following denervation. Protein and mRNA data of the MQC pathways indicated activation of the UPRmt and mitophagy-lysosome systems along with reductions in mitochondrial biogenesis and content in WT and mKO tissue following chronic denervation. However, p53 ablation also attenuated the expression of autophagy/mitophagy machinery, reduced autophagic flux, and enhanced lysosomal dysfunction. While similar reductions in mitochondrial biogenesis and content were observed between genotypes, MQC dysregulation exacerbated mitochondrial dysfunction in mKO fibers, evidenced by elevated reactive oxygen species (ROS). Moreover, acute experiments indicate that p53 mediates the expression of transcriptional regulators of MQC pathways as early as 1 day following denervation. Together, our data illustrate exacerbated mitochondrial dysregulation with denervation stress in p53 mKO tissue, thus indicating that p53 contributes to organellar maintenance via regulation of MQC pathways during muscle atrophy.

Keywords: lysosome; mitochondria; mitochondrial biogenesis; mitochondrial quality control; mitophagy; muscle atrophy; p53; skeletal muscle; transcriptomics; unfolded protein response (UPR)

DOI: https://doi.org/10.1016/j.jbc.2021.101540