Hepatocyte-specific deletion of XBP1 sensitizes mice to liver injury through hyperactivation of IRE1α. Cell death and differentiation X-box binding protein-1 (XBP1) is a transcription factor that plays a central role in controlling cellular responses to endoplasmic reticulum (ER) stress. Under stress conditions, the transcriptionally active form of XBP1 is generated via splicing of Xbp1 mRNA by the ER-resident protein inositol-requiring enzyme-1 (IRE1α). Genetic deletion of XBP1 has multiple consequences: some resulting from the loss of the transcription factor per se, and others related to compensatory activation of IRE1α. The objective of the current study was to investigate the effects of XBP1 deletion in adult mouse liver and determine to what extent they are direct or indirect. XBP1 was deleted from hepatocytes in adult Xbp1 mice using AAV8-Transthyretin-Cre (Xbp1). Xbp1 mice exhibited no liver disease at baseline, but developed acute biochemical and histologic liver injury in response to a dietary challenge with fructose for 4 weeks. Fructose-mediated liver injury in Xbp1 mice coincided with heightened IRE1α activity, as demonstrated by Xbp1 mRNA splicing, JNK activation, and regulated IRE1α-dependent RNA decay (RIDD). Activation of eIF2α was also evident, with associated up-regulation of the pro-apoptotic molecules CHOP, BIM, and PUMA. To determine whether the adverse consequences of liver-specific XBP1 deletion were due to XBP1 loss or heightened IRE1α activity, we repeated a fructose challenge in mice with liver-specific deletion of both XBP1 and IRE1α (Xbp1;Ire1a). Xbp1;Ire1a mice were protected from fructose-mediated liver injury and failed to exhibit any of the signs of ER stress seen in mice lacking XBP1 alone. The protective effect of IRE1α deletion persisted even with long-term exposure to fructose. Xbp1 mice developed liver fibrosis at 16 weeks, but Xbp1;Ire1a mice did not. Overall, the results indicate that the deleterious effects of hepatocyte-specific XBP1 deletion are due primarily to hyperactivation of IRE1α. They support further exploration of IRE1α as a contributor to acute and chronic liver diseases. 10.1038/s41418-020-00671-1

Involvement of the IRE1α-XBP1 pathway and XBP1s-dependent transcriptional reprogramming in metabolic diseases. Wu Rong,Zhang Qing-Hai,Lu Yan-Ju,Ren Kun,Yi Guang-Hui DNA and cell biology The X-box binding protein 1 (XBP1) is not only an important component of the unfolded protein response (UPR), but also an important nuclear transcription factor. Upon endoplasmic reticulum stress, XBP1 is spliced by inositol-requiring enzyme 1 (IRE1), thereby generating functional spliced XBP1 (XBP1s). XBP1s functions by translocating into the nucleus to initiate transcriptional programs that regulate a subset of UPR- and non-UPR-associated genes involved in the pathophysiological processes of various diseases. Recent reports have implicated XBP1 in metabolic diseases. This review summarizes the effects of XBP1-mediated regulation on lipid metabolism, glucose metabolism, obesity, and atherosclerosis. Additionally, for the first time, we present XBP1s-dependent transcriptional reprogramming in metabolic diseases under different conditions, including pathology and physiology. Understanding the function of XBP1 in metabolic diseases may provide a basic knowledge for the development of novel therapeutic targets for ameliorating these diseases. 10.1089/dna.2014.2552

KIRA8 attenuates non-alcoholic steatohepatitis through inhibition of the IRE1α/XBP1 signalling pathway. Biochemical and biophysical research communications Endoplasmic reticulum (ER) stress is enhanced in non-alcoholic steatohepatitis (NASH). Among three signalling pathways, the IRE1α/XBP1 signalling pathway is strongly implicated in the pathogenesis of NASH but its significance is still largely uncharacterised. In this report, we constructed a hepatocyte-specific XBP1-Luciferase knock-in mouse model that allows in vivo monitoring of the IRE1α/XBP1 activity in hepatocytes. Using this mouse model, we found that IRE1α/XBP1 was activated within hepatocytes during the pathogenesis of NASH. Significantly, a specific IRE1α kinase-inhibiting RNase attenuator, KIRA8, attenuated NASH in mice. In conclusion, our hepatocyte-specific XBP1 splicing reporter mouse represents a valid model for research and drug development of NASH, which showed that the IRE1α-induced XBP splicing is potentiated in hepatocytes during pathogenesis of NASH. Furthermore, we carried out the proof-of-concept study to demonstrate that the allosteric IRE1α RNase inhibitor serves as a promising therapeutic agent for the treatment of NASH. 10.1016/j.bbrc.2022.09.098

Empagliflozin Attenuates Non-Alcoholic Fatty Liver Disease (NAFLD) in High Fat Diet Fed ApoE Mice by Activating Autophagy and Reducing ER Stress and Apoptosis. International journal of molecular sciences AIMS/HYPOTHESIS:SGLT-2 inhibitors (SGLT-2i) have been studied as potential treatments against NAFLD, showing varying beneficial effects. The molecular mechanisms mediating these effects have not been fully clarified. Herein, we investigated the impact of empagliflozin on NAFLD, focusing particularly on ER stress, autophagy and apoptosis. METHODS:Five-week old ApoE mice were switched from normal to a high-fat diet (HFD). After five weeks, mice were randomly allocated into a control group (HFD + vehicle) and Empa group (HFD + empagliflozin 10 mg/kg/day) for five weeks. At the end of treatment, histomorphometric analysis was performed in liver, mRNA levels of , , , , , , , , , , , , , , , , , , , , , and were measured by qRT-PCR, and protein levels of p-EIF2α, EIF2a, CHOP, LC3II, P62, BECLIN-1 and cleaved CASPASE-8 were assessed by immunoblotting. RESULTS:Empagliflozin-treated mice exhibited reduced fasting glucose, total cholesterol and triglyceride serum levels, as well as decreased NAFLD activity score, decreased expression of lipogenic enzymes (, and ) and inflammatory molecules ( and ), compared to the Control group. Empagliflozin significantly decreased the expression of ER stress molecules , , , , , , , and ; whilst activating autophagy via increased AMPK phosphorylation, decreased and increased expression. Finally, empagliflozin increased the ratio and inhibited CASPASE-8 cleavage, reducing liver cell apoptosis. Immunoblotting analysis confirmed the qPCR results. CONCLUSION:These novel findings indicate that empagliflozin treatment for five weeks attenuates NAFLD progression in ApoE mice by promoting autophagy, reducing ER stress and inhibiting hepatic apoptosis. 10.3390/ijms22020818

Targeting the IRE1α/XBP1 Endoplasmic Reticulum Stress Response Pathway in -Mutant Ovarian Cancers. Cancer research The SWI/SNF chromatin-remodeling complex is frequently altered in human cancers. For example, the SWI/SNF component is mutated in more than 50% of ovarian clear cell carcinomas (OCCC), for which effective treatments are lacking. Here, we report that ARID1A transcriptionally represses the IRE1α-XBP1 axis of the endoplasmic reticulum (ER) stress response, which confers sensitivity to inhibition of the IRE1α-XBP1 pathway in -mutant OCCC. mutational status correlated with response to inhibition of the IRE1α-XBP1 pathway. In a conditional genetic mouse model, knockout significantly improved survival of mice bearing OCCCs. Furthermore, the IRE1α inhibitor B-I09 suppressed the growth of ARID1A-inactivated OCCCs in orthotopic xenograft, patient-derived xenograft, and the genetic mouse models. Finally, B-I09 synergized with inhibition of HDAC6, a known regulator of the ER stress response, in suppressing the growth of -inactivated OCCCs. These studies define the IRE1α-XBP1 axis of the ER stress response as a targetable vulnerability for -mutant OCCCs, revealing a promising therapeutic approach for treating -mutant ovarian cancers. SIGNIFICANCE: These findings indicate that pharmacological inhibition of the IRE1α-XBP1 pathway alone or in combination with HDAC6 inhibition represents an urgently needed therapeutic strategy for -mutant ovarian cancers. 10.1158/0008-5472.CAN-21-1545