Niacin, an innovative protein kinase-C-dependent endoplasmic reticulum stress reticence in murine Parkinson's disease.

AIMS: Niacin (NIA) supplementation showed effectiveness against Parkinson's disease (PD) in clinical trials. The depletion of NAD and endoplasmic reticulum stress response (ERSR) are implicated in the pathogenesis of PD, but the potential role for NAD precursors on ERSR is not yet established. This study was undertaken to decipher NIA molecular mechanisms against PD-accompanied ERSR, especially in relation to PKC. METHODS: Alternate-day-low-dose-21 day-subcutaneous exposure to rotenone (ROT) in rats induced PD. Following the 5th ROT injection, rats received daily doses of either NIA alone or preceded by the PKC inhibitor tamoxifen (TAM). Extent of disease progression was assessed by behavioral, striatal biochemical and striatal/nigral histopathological/immunohistochemical analysis. KEY FINDINGS: Via activating PKC/LKB1/AMPK stream, NIA post-treatment attenuated the ERSR reflected by the decline in ATF4, ATF6 and XBP1s to downregulate the apoptotic markers, CHOP/GADD153, p-JNK and active caspase-3. Such amendments congregated in motor activity/coordination improvements in open field and rotarod tasks, enhanced grid test latency and reduced overall PD scores, while boosting nigral/striatal tyrosine hydroxylase immunoreactivity and increasing intact neurons (Nissl stain) in both SNpc and striatum that showed less neurodegeneration (H&E stain). To different extents, TAM reverted all the NIA-related actions to prove PKC as a fulcrum in conveying the drug neurotherapeutic potential. SIGNIFICANCE: PKC activation is a pioneer mechanism in the drug ERSR inhibitory anti-apoptotic modality to clarify NIA promising clinical and potent preclinical anti-PD efficacy. This kinase can be tagged as a druggable target for future add-on treatments that can assist dopaminergic neuronal aptitude against this devastating neurodegenerative disease.

Irisin Ameliorate Acute Pancreatitis and Acinar Cell Viability through Modulation of the Unfolded Protein Response (UPR) and PPARγ-PGC1α-FNDC5 Pathways.

Acute pancreatitis (AP) entails pancreatic inflammation, tissue damage and dysregulated enzyme secretion, including pancreatic lipase (PL). The role of irisin, an anti-inflammatory and anti-apoptotic cytokine, in AP and exocrine pancreatic stress is unclear. We have previously shown that irisin regulates PL through the PPARγ-PGC1α-FNDC5 pathway. In this study, we investigated irisin and irisin's pathway on AP in in vitro (AR42J-B13) and ex vivo (rat primary acinar) models using molecular, biochemical and immunohistochemistry methodology. Pancreatitis induction (cerulein (cer)) resulted in a significant up-regulation of the PPARγ-PGC1α-FNDC5 axis, PL expression and secretion and endoplasmic reticulum (ER) stress unfolded protein response (UPR) signal-transduction markers (CHOP, XBP-1 and ATF6). Irisin addition in the cer-pancreatitis state resulted in a significant down-regulation of the PPARγ-PGC1α-FNDC5 axis, PPARγ nucleus-translocation and inflammatory state (TNFα and IL-6) in parallel to diminished PL expression and secretion (in vitro and ex vivo models). Irisin addition up-regulated the expression of pro-survival UPR markers (ATF6 and XBP-1) and reduced UPR pro-apoptotic markers (CHOP) under cer-pancreatitis and induced ER stress (tunicamycin), consequently increasing cells viability. Irisin's pro-survival effect under cer-pancreatitis state was abolished under PPARγ inhibition. Our findings suggest irisin as a potential therapeutic option for AP via its ability to up-regulate pro-survival UPR signals and activate the PPARγ-PGC1α-FNDC5 pathway.

The total xanthones extracted from Gentianella acuta alleviates HFpEF by activating the IRE1α/Xbp1s pathway.

Heart failure with preserved ejection fraction (HFpEF) is a clinical syndrome characterized by pulmonary and systemic congestion resulting from left ventricular diastolic dysfunction and increased filling pressure. Currently, however, there is no evidence on effective pharmacotherapy for HFpEF. In this study, we aimed to investigate the therapeutic effect of total xanthones extracted from Gentianella acuta (TXG) on HFpEF by establishing an high-fat diet (HFD) + L-NAME-induced mouse model. Echocardiography was employed to assess the impact of TXG on the cardiac function in HFpEF mice. Haematoxylin and eosin staining, wheat germ agglutinin staining, and Masson's trichrome staining were utilized to observe the histopathological changes following TXG treatment. The results demonstrated that TXG alleviated HFpEF by reducing the expressions of genes associated with myocardial hypertrophy, fibrosis and apoptosis. Furthermore, TXG improved cardiomyocyte apoptosis by inhibiting the expression of apoptosis-related proteins. Mechanistic investigations revealed that TXG could activate the inositol-requiring enzyme 1α (IRE1α)/X-box-binding protein 1 (Xbp1s) signalling pathway, but the knockdown of IRE1α using the IRE1α inhibitor STF083010 or siRNA-IRE1α impaired the ability of TXG to ameliorate cardiac remodelling in HFpEF models. In conclusion, TXG alleviates myocardial hypertrophy, fibrosis and apoptosis through the activation of the IRE1α/Xbp1s signalling pathway, suggesting its potential beneficial effects on HFpEF patients.

Overactivation of XBP1 in plasma cells implies worse survival through innate immunity in esophageal squamous cell carcinoma.

To maintain protein homeostasis, X-box binding protein 1 (XBP1) undergoes splicing following the activation of the unfolded protein response (UPR) in response to endoplasmic reticulum (ER) stress. Although targeting ER stress represents a promising therapeutic strategy, a comprehensive understanding of XBP1 at the cellular level and the link between XBP1 and the innate nervous system is lacking. Here, TCGA pancancer datasets from 33 cancer types, scRNA pancancer datasets from 454 patients and bulk RNA-seq datasets from 155 paired esophageal squamous cell carcinoma (ESCC) patients were analyzed. To cope with ER stress, plasma cells tend to activate XBP1 after undergoing bacterial infection and inflammatory signaling from the innate immune system. Patients with high XBP1 expression in their plasma cells have a higher tumor grade and worse survival. However, activation of the innate immune system with increased XBP1 expression in plasma cells correlates with an increased lymphocyte ratio, indicative of a more robust immune response. Moreover, XBP1 activation appears to initiate leukocyte migration at the transcriptional level. Our study revealed that the XBP1-induced UPR could mediate the crosstalk between optimal acquired humoral immune responses and innate immunity in ESCC.

UFL1 regulates cellular homeostasis by targeting endoplasmic reticulum and mitochondria in NEFA-stimulated bovine mammary epithelial cells via the IRE1α/XBP1 pathway.

Elevated levels of NEFA caused by negative energy balance in transition cows induce cellular dyshomeostasis. Ubiquitin-like modifier 1 ligating enzyme 1 (UFL1) can maintain cellular homeostasis and act as a critical regulator of stress responses besides functioning in the ubiquitin-like system. The objective of this study was to elucidate the UFL1 working mechanism on promoting cellular adaptations in bovine mammary epithelial cells (BMECs) in response to NEFA challenge, with an emphasis on the ER and mitochondrial function. The results showed that exogenous NEFA and UFL1 depletion resulted in the disorder of ER and mitochondrial homeostasis and the damage of BMEC integrity, overexpression of UFL1 effectively alleviated the NEFA-induced cellular dyshomeostasis. Mechanistically, our study found that UFL1 had a strong interaction with IRE1α and could modulate the IRE1α/XBP1 pathway of unfolded protein response in NEFA-stimulated BMECs, thereby contributing to the modulation of cellular homeostasis. These findings imply that targeting UFL1 may be a therapeutic alternative to relieve NEB-induced metabolic changes in perinatal dairy cows.

Kaempferol attenuates particle-induced osteogenic impairment by regulating ER stress via the IRE1α-XBP1s pathway.

Periprosthetic osteolysis and subsequent aseptic loosening are the primary causes of failure following total joint arthroplasty. Wear particle-induced osteogenic impairment is recognized as an important contributing factor in the development of osteolysis, with endoplasmic reticulum (ER) stress emerging as a pivotal underlying mechanism. Hence, searching for potential therapeutic targets and agents capable of modulating ER stress in osteoblasts is crucial for preventing aseptic loosening. Kaempferol (KAE), a natural flavonol compound, has shown promising osteoprotective effects and anti-ER stress properties in diverse diseases. However, the influence of KAE on ER stress-mediated osteogenic impairment induced by wear particles remains unclear. In this study, we observed that KAE effectively relieved TiAl6V4 particles-induced osteolysis by improving osteogenesis in a mouse calvarial model. Furthermore, we demonstrated that KAE could attenuate ER stress-mediated apoptosis in osteoblasts exposed to TiAl6V4 particles, both in vitro and in vivo. Mechanistically, our results revealed that KAE mitigated ER stress-mediated apoptosis by upregulating the IRE1α-XBP1s pathway while concurrently partially inhibiting the IRE1α-regulated RIDD and JNK activation. Collectively, our findings suggest that KAE is a prospective therapeutic agent for treating wear particle-induced osteolysis and highlight the IRE1α-XBP1s pathway as a potential therapeutic target for preventing aseptic loosening.

The role of the ER stress sensor IRE1 in cardiovascular diseases.

Despite enormous advances in the treatment of cardiovascular diseases, including I/R injury and heart failure, heart diseases remain a leading cause of mortality worldwide. Inositol-requiring enzyme 1 (IRE1) is an evolutionarily conserved sensor endoplasmic reticulum (ER) transmembrane protein that senses ER stress. It manages ER stress induced by the accumulation of unfolded/misfolded proteins via the unfolded protein response (UPR). However, if the stress still persists, the UPR pathways are activated and induce cell death. Emerging evidence shows that, beyond the UPR, IRE1 participates in the progression of cardiovascular diseases by regulating inflammation levels, immunity, and lipid metabolism. Here, we summarize the recent findings and discuss the potential therapeutic effects of IRE1 in the treatment of cardiovascular diseases.

Changes in Oxidised Phospholipids in Response to Oxidative Stress in Microtubule-Associated Protein Tau (MAPT) Mutant Dopamine Neurons.

Microtubule-associated protein Tau (MAPT) is strongly associated with the development of neurodegenerative diseases. In addition to driving the formation of neurofibrillary tangles (NFT), mutations in the MAPT gene can also cause oxidative stress through hyperpolarisation of the mitochondria. This study explores the impact that MAPT mutation is having on phospholipid metabolism in iPSC-derived dopamine neurons, and to determine if these effects are exacerbated by mitochondrial and endoplasmic reticulum stress. Neurons that possessed a mutated copy of MAPT were shown to have significantly higher levels of oxo-phospholipids (Oxo-PL) than wild-type neurons. Oxidation of the hydrophobic fatty acid side chains changes the chemistry of the phospholipid leading to disruption of membrane function and potential cell lysis. In wild-type neurons, both mitochondrial and endoplasmic reticulum stress increased Oxo-PL abundance; however, in MAPT mutant neurons mitochondrial stress appeared to have a minimal effect. Endoplasmic reticulum stress, surprisingly, reduced the abundance of Oxo-PL in MAPT mutant dopamine neurons, and we postulate that this reduction could be modulated through hyperactivation of the unfolded protein response and X-box binding protein 1. Overall, the results of this study contribute to furthering our understanding of the regulation and impact of oxidative stress in Parkinson's disease pathology.

XBP1s activates METTL3/METTL14 for ER-phagy and paclitaxel sensitivity regulation in breast cancer.

Cancer cells employ the unfolded protein response (UPR) or induce autophagy, especially selective removal of certain ER domains via reticulophagy (termed ER-phagy), to mitigate endoplasmic reticulum (ER) stress for ER homeostasis when encountering microenvironmental stress. N6-methyladenosine (m6A) is one of the most abundant epitranscriptional modifications and plays important roles in various biological processes. However, the molecular mechanism of m6A modification in the ER stress response is poorly understood. In this study, we first found that ER stress could dramatically elevate m6A methylation levels through XBP1s-dependent transcriptional upregulation of METTL3/METTL14 in breast cancer (BC) cells. Further MeRIP sequencing and relevant validation results confirmed that ER stress caused m6A methylation enrichment on target genes for ER-phagy. Mechanistically, METTL3/METTL14 increased ER-phagy machinery formation by promoting m6A modification of the ER-phagy regulators CALCOCO1 and p62, thus enhancing their mRNA stability. Of note, we further confirmed that the chemotherapeutic drug paclitaxel (PTX) could induce ER stress and increase m6A methylation for ER-phagy. Furthermore, the combination of METTL3/METTL14 inhibitors with PTX demonstrated a significant synergistic therapeutic effect in both BC cells and xenograft mice. Thus, our data built a novel bridge on the crosstalk between ER stress, m6A methylation and ER-phagy. Most importantly, our work provides novel evidence of METTL3 and METTL14 as potential therapeutic targets for PTX sensitization in breast cancer.

Correlation Between Low Cytoplasmic Expression of XBP1 and the Likelihood of Surviving Hepatocellular Carcinoma.

BACKGROUND/AIM: Our objectives in this study were to (i) evaluate the clinical significance of X-box-binding protein 1 (XBP1) expression in cases of hepatocellular carcinoma (HCC) and (ii) assess the potential of XBP1 to be used as a prognostic biomarker. PATIENTS AND METHODS: The expression of XBP1 protein in 267 HCC tissue specimens was measured using immunohistochemistry in order to characterize the associations among XBP1 expression, clinicopathological factors and survival outcomes. Survival analysis using follow-up data was used to assess the prognostic value of XBP1 in cases of HCC. Immunohistochemistry revealed a significant decrease in cytoplasmic XBP1 protein expression in HCC tumor tissue. RESULTS: Immunoreactivity results showed that low cytoplasmic XBP1 expression was significantly associated with vascular invasion, as well as poor 5-year overall survival and long-term disease-specific (DSS) and disease-free (DFS) survival rates. Kaplan-Meier survival curves further confirmed a significant association between low cytoplasmic XBP1 protein expression and poor DSS and DFS. Univariate and multivariate analyses revealed that XBP1 expression, tumor differentiation, vascular invasion, tumor stage, and the rate of recurrence were linked to DSS, while low cytoplasmic XBP1 expression remained an independent predictor of poor DSS. Our analysis also revealed that XBP1 expression, tumor differentiation, vascular invasion, and T classification were linked to DFS, while low cytoplasmic XBP1 expression remained an independent predictor of poor DFS. CONCLUSION: Low cytoplasmic XBP1 protein expression may play an important role in the pathogenesis of HCC, which suggests that XBP1 could potentially be targeted to benefit therapeutic strategies for HCC.

The inositol-requiring enzyme 1 (IRE1) endoplasmic reticulum stress pathway promotes MDA-MB-231 cell survival and renewal in response to the aryl-ureido fatty acid CTU.

Current treatment options for triple-negative breast cancer (TNBC) are limited to toxic drug combinations of low efficacy. We recently identified an aryl-substituted fatty acid analogue, termed CTU, that effectively killed TNBC cells in vitro and in mouse xenograft models in vivo without producing toxicity. However, there was a residual cell population that survived treatment. The present study evaluated the mechanisms that underlie survival and renewal in CTU-treated MDA-MB-231 TNBC cells. RNA-seq profiling identified several pro-inflammatory signaling pathways that were activated in treated cells. Increased expression of cyclooxygenase-2 and the cytokines IL-6, IL-8 and GM-CSF was confirmed by real-time RT-PCR, ELISA and Western blot analysis. Increased self-renewal was confirmed using the non-adherent, in vitro colony-forming mammosphere assay. Neutralizing antibodies to IL-6, IL-8 and GM-CSF, as well as cyclooxygenase-2 inhibition suppressed the self-renewal of MDA-MB-231 cells post-CTU treatment. IPA network analysis identified major NF-κB and XBP1 gene networks that were activated by CTU; chemical inhibitors of these pathways and esiRNA knock-down decreased the production of pro-inflammatory mediators. NF-κB and XBP1 signaling was in turn activated by the endoplasmic reticulum (ER)-stress sensor inositol-requiring enzyme 1 (IRE1), which mediates the unfolded protein response. Co-treatment with an inhibitor of IRE1 kinase and RNase activities, decreased phospho-NF-κB and XBP1s expression and the production of pro-inflammatory mediators. Further, IRE1 inhibition also enhanced apoptotic cell death and prevented the activation of self-renewal by CTU. Taken together, the present findings indicate that the IRE1 ER-stress pathway is activated by the anti-cancer lipid analogue CTU, which then activates secondary self-renewal in TNBC cells.

Xbp1 promotes odontoblastic differentiation through modulating mitochondrial homeostasis.

Odontoblast differentiation depends on the orderly recruitment of transcriptional factors (TFs) in the transcriptional regulatory network. The depletion of crucial TFs disturbs dynamic alteration of the chromatin landscape and gene expression profile, leading to developmental defects. Our previous studies have revealed that the basic leucine zipper (bZIP) TF family is crucial in odontoblastic differentiation, but the function of bZIP TF family member XBP1 is still unknown. Here, we showed the stage-specific expression patterns of the spliced form Xbp1s during tooth development. Elevated Xbp1 expression and nuclear translocation of XBP1S in mesenchymal stem cells (MSCs) were induced by differentiation medium in vitro. Diminution of Xbp1 expression impaired the odontogenic differentiation potential of MSCs. The further integration of ATAC-seq and RNA-seq identified Hspa9 as a direct downstream target, an essential mitochondrial chaperonin gene that modulated mitochondrial homeostasis. The amelioration of mitochondrial dysfunction rescued the impaired odontogenic differentiation potential of MSCs caused by the diminution of Xbp1. Furthermore, the overexpression of Hspa9 rescued Xbp1-deficient defects in odontoblastic differentiation. Our study illustrates the crucial role of Xbp1 in odontoblastic differentiation via modulating mitochondrial homeostasis and brings evidence to the therapy of mitochondrial diseases caused by genetic defects.

Peste des petits ruminants virus infection induces endoplasmic reticulum stress and apoptosis via IRE1-XBP1 and IRE1-JNK signaling pathways.

BACKGROUND: Peste des petits ruminants (PPR) is a contagious and fatal disease of sheep and goats. PPR virus (PPRV) infection induces endoplasmic reticulum (ER) stress-mediated unfolded protein response (UPR). The activation of UPR signaling pathways and their impact on apoptosis and virus replication remains controversial. OBJECTIVES: To investigate the role of PPRV-induced ER stress and the IRE1-XBP1 and IRE1-JNK pathways and their impact on apoptosis and virus replication. METHODS: The cell viability and virus replication were assessed by 3-(4,5-Dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide assay, immunofluorescence assay, and Western blot. The expression of ER stress biomarker GRP78, IRE1, and its downstream molecules, PPRV-N protein, and apoptosis-related proteins was detected by Western blot and quantitative reverse transcription-polymerase chain reaction, respectively. 4-Phenylbutyric acid (4-PBA) and STF-083010 were respectively used to inhibit ER stress and IRE1 signaling pathway. RESULTS: The expression of GRP78, IRE1α, p-IRE1α, XBP1s, JNK, p-JNK, caspase-3, caspase-9, Bax and PPRV-N were significantly up-regulated in PPRV-infected cells, the expression of Bcl-2 was significantly down-regulated. Due to 4-PBA treatment, the expression of GRP78, p-IRE1α, XBP1s, p-JNK, caspase-3, caspase-9, Bax, and PPRV-N were significantly down-regulated, the expression of Bcl-2 was significantly up-regulated. Moreover, in PPRV-infected cells, the expression of p-IRE1α, p-JNK, Bax, and PPRV-N was significantly decreased, and the expression of Bcl-2 was increased in the presence of STF-083010. CONCLUSIONS: PPRV infection induces ER stress and IRE1 activation, resulting in apoptosis and enhancement of virus replication through IRE1-XBP1s and IRE1-JNK pathways.

S-nitrosylation-triggered unfolded protein response maintains hematopoietic progenitors in Drosophila.

The Drosophila lymph gland houses blood progenitors that give rise to myeloid-like blood cells. Initially, blood progenitors proliferate, but later, they become quiescent to maintain multipotency before differentiation. Despite the identification of various factors involved in multipotency maintenance, the cellular mechanism controlling blood progenitor quiescence remains elusive. Here, we identify the expression of nitric oxide synthase in blood progenitors, generating nitric oxide for post-translational S-nitrosylation of protein cysteine residues. S-nitrosylation activates the Ire1-Xbp1-mediated unfolded protein response, leading to G2 cell-cycle arrest. Specifically, we identify the epidermal growth factor receptor as a target of S-nitrosylation, resulting in its retention within the endoplasmic reticulum and blockade of its receptor function. Overall, our findings highlight developmentally programmed S-nitrosylation as a critical mechanism that induces protein quality control in blood progenitors, maintaining their undifferentiated state by inhibiting cell-cycle progression and rendering them unresponsive to paracrine factors.

Fatostatin promotes anti-tumor immunity by reducing SREBP2 mediated cholesterol metabolism in tumor-infiltrating T lymphocytes.

Aberrant lipid metabolism impacts intratumoral T cell-mediated immune response and tumor growth. Fatostatin functions as an inhibitor of sterol regulatory element binding protein (SREBP) activation. However, the complex effects of fatostatin on cholesterol metabolism in the tumor microenvironment (TME) and its influence on T cell anti-tumor immunity remain unclear. In this study, fatostatin effectively suppressed B16 melanoma, MC38 colon cancer, and Lewis lung cancer (LLC) transplanted tumor growth in immunocompetent mice by reducing SREBPs-mediated lipid metabolism, especially cholesterol levels. Mechanistically, fatostatin decreased intracellular cholesterol accumulation and inhibited X-box binding protein 1 (XBP1)-mediated endoplasmic reticulum (ER) stress, reducing Treg cells and alleviating CD8+ T cell exhaustion in the TME, exerting anti-tumor activity. Nevertheless， this effect was impaired in immunodeficient nude mice, suggesting fatostatin's anti-tumor efficacy in transplanted tumors partly relies on T cell-mediated anti-tumor immunity. Our study highlights SREBP2-mediated cholesterol metabolism as a potential strategy for anti-tumor immunotherapy, and confirms fatostatin's promise in tumor immunotherapy.

Inhibition of keloid fibroblast proliferation by artesunate is mediated by targeting the IRE1α/XBP1 signaling pathway and decreasing TGF-ß1.

BACKGROUND: Keloid is a benign hyperplastic dermatosis with high recurrence rate and complex pathogenesis. There is no universally effective treatment yet. New therapies and elucidation of pathogenesis are urgently required. AIMS: To explore the function of IRE1α/XBP1 in keloid fibroblasts and to investigate the potential mechanism of artesunate in inhibiting keloid hyperplasia. METHODS: Human keloid fibroblasts (KFs) were cultured, and the expressions of XBP1 and TGF-ß1 were detected by immunohistochemistry. The expression of IRE1 was interfered with through cell transfection and the effects of IRE1 interference on cell proliferation and the cell cycle were assessed using MTS, colony formation assays, and flow cytometry. Detection of the expressions of XBP1 and TGF-ß1 by qRT-PCR and Western blot. Then artesunate was applied to a subset of the cells, and its effects on cell viability and the expression of related proteins using the same methods. RESULTS: The IRE1α/XBP1 pathway was activated in KFs. Knocking out the gene IRE1α can inhibit the expression of TGF-ß1, in addition, the cell viability and cell cycle progression of KFs were also significantly affected. After artesunate treatment, there was a remarkable reduction in cell proliferation. Meanwhile, the cell cycle of KFs treated with artesunate was blocked in G1 phase.After upregulating the expression of IRE1α and treating KFs with artesunate, both cell cycle and proliferation showed inhibitory effects, and related proteins also exhibited suppressed expression. CONCLUSIONS: The IRE1α/XBP1 pathway is activated in keloid, and inhibiting the expression of this pathway can affect the cell proliferation activity. In addition, artesunate also has a significant effect on fibroblast proliferation, and the IRE1α/XBP1 pathway may participate in this process. These findings suggest that IRE1α/XBP1 signal pathway may be a potential target for scar treatment, and artesunate could also be a powerful candidate for keloid treatment.

Genetic and pharmacological targeting of XBP1 alleviates hepatic ischemia reperfusion injury by enhancing FoxO1-dependent mitophagy.

Hepatic ischemia reperfusion (I/R) injury is a common clinical complication. X-box binding protein 1 (XBP1), as a critical regulator of the endoplasmic reticulum stress, has been implicated in a variety of diseases. In this study, we aimed to investigate the effects and the underlying mechanism of XBP1 in the progression of hepatic I/R injury. Hepatocyte-specific XBP1 knockout mice, multiple viral delivery systems and specific pharmacological inhibitors were applied in vivo in a partial hepatic I/R injury mouse model and in vitro in a cell model of hypoxia-reoxygenation (H/R) injury. Mitophagy and autophagic flux were evaluated and fluorescence resonance energy transfer (FRET) as well as immunoprecipitation were performed. The results demonstrated that reperfusion for 6 h represented a critical timepoint in hepatic I/R injury and resulted in significant intracellular mitochondrial dysfunction; led to the breakdown of hepatocytes accompanied by the highest expression levels of XBP1. Hepatocyte-specific XBP1 knockout alleviated hepatic I/R injury via enhanced mitophagy, as demonstrated by the reduction in hepatocellular damage/necrosis and increased expression of mitophagy markers. Mechanistically, XBP1 interacted with FoxO1 directly and catalyzed the ubiquitination of FoxO1 for proteasomal degradation. Targeting XBP1 by genetic or pharmacological techniques potentiated the protein levels of FoxO1, further promoting the activity of the PINK1/Parkin signaling pathway, thus augmenting mitophagy and exerting hepatoprotective effects upon I/R injury. In conclusion, the inhibition of XBP1 potentiated FoxO1-mediated mitophagy in hepatic I/R injury. Specific genetic and pharmacological treatment targeting XBP1 in the perioperative 6 h prior to reperfusion exerted beneficial effects, thus providing a novel therapeutic approach.

Transcriptomics analysis of LINC02202/XBP1 axis in melanoma: Implications for drug targeting and PD-1 monoclonal antibody efficacy.

Malignant melanoma (MM) is a highly aggressive and deadly form of skin cancer, primarily caused by recurrence and metastasis. Therefore, it is crucial to investigate the regulatory mechanisms underlying melanoma recurrence and metastasis. Our study has identified a potential targeted regulatory relationship between LINC02202, miR-526b-3p and XBP1 in malignant melanoma. Through the regulation of the miR-526b-3p/XBP1 signalling pathway, LINC02202 may play a role in tumour progression and immune infiltration and inhibiting the expression of LINC02202 can increase the efficacy of immunotherapy for melanoma. Our findings shed light on the impact of LINC02202/XBP1 on the phenotype and function of malignant melanoma cells. Furthermore, this study provides a theoretical foundation for the development of novel immunotherapy strategies for malignant melanoma.

A Study of Alternative TrkA Splicing Identifies TrkAIII as a Novel Potentially Targetable Participant in PitNET Progression.

Pituitary neuroendocrine tumors (PitNETs) are generally benign but comprise an aggressive, invasive, therapy-resistant, metastatic subset, underpinning a need for novel therapeutic targets. PitNETs exhibit low mutation rates but are associated with conditions linked to alternative splicing, an alternative oncogene pathway activation mechanism. PitNETs express the neurotrophin receptor TrkA, which exhibits oncogenic alternative TrkAIII splicing in other neuroendocrine tumors. We, therefore, assessed whether TrkAIII splicing represents a potential oncogenic participant in PitNETs. TrkAIII splicing was RT-PCR assessed in 53 PitNETs and TrkA isoform(s) expression and activation were assessed by confocal immunofluorescence. TrkAIII splicing was also compared to HIF1α, HIF2α, SF3B1, SRSF2, U2AF1, and JCPyV large T antigen mRNA expression, Xbp1 splicing, and SF3B1 mutation. TrkAIII splicing was detected in all invasive and most non-invasive PitNETs and was significantly elevated in invasive cases. In PitNET lineages, TrkAIII splicing was significantly elevated in invasive PIT1 PitNETs and high in invasive and non-invasive SF1 and TPIT lineages. Immunoreactivity consistent with TrkAIII activation characterized PitNET expressing TrkAIII mRNA, and invasive Pit1 PitNETs exhibited elevated HIF2α expression. TrkAIII splicing did not associate with SF3B1 mutations, altered SF3B1, SRSF2, and U2AF1 or JCPyV large T antigen expression, or Xbp1 splicing. Therefore, TrkAIII splicing is common in PitNETs, is elevated in invasive, especially PIT1 tumors, can result in intracellular TrkAIII activation, and may involve hypoxia. The data support a role for TrkAIII splicing in PitNET pathogenesis and progression and identify TrkAIII as a novel potential target in refractory PitNETs.

Enhancing Antibody-Specific Productivity: Unraveling the Impact of XBP1s Overexpression and Glutamine Availability in SP2/0 Cells.

Augmentation of glycoprotein synthesis requirements induces endoplasmic reticulum (ER) stress, activating the unfolded protein response (UPR) and triggering unconventional XBP1 splicing. As a result, XBP1s orchestrates the expression of essential genes to reduce stress and restore homeostasis. When this mechanism fails, chronic stress may lead to apoptosis, which is thought to be associated with exceeding a threshold in XBP1s levels. Glycoprotein assembly is also affected by glutamine (Gln) availability, limiting nucleotide sugars (NS), and preventing compliance with the increased demands. In contrast, increased Gln intake synthesizes ammonia as a by-product, potentially reaching toxic levels. IgA2m(1)-producer mouse myeloma cells (SP2/0) were used as the cellular mammalian model. We explored how IgA2m(1)-specific productivity (qIgA2m(1)) is affected by (i) overexpression of human XBP1s (h-XBP1s) levels and (ii) Gln availability, evaluating the kinetic behavior in batch cultures. The study revealed a two and a five-fold increase in qIgA2m(1) when lower and higher levels of XBP1s were expressed, respectively. High h-XBP1s overexpression mitigated not only ammonia but also lactate accumulation. Moreover, XBP1s overexpressor showed resilience to hydrodynamic stress in serum-free environments. These findings suggest a potential application of h-XBP1s overexpression as a feasible and cost-effective strategy for bioprocess scalability.