Activating Transcription Factor Research Articles

Herp regulates intracellular survival of Mycobacterium tuberculosis H37Ra in macrophages by regulating reactive oxygen species-mediated autophagy.

Several studies have suggested that endoplasmic reticulum (ER) stress is important in the pathogenesis of infectious diseases; however, the precise function of ER stress regulation and the role of Herp as a regulator in Mtb H37Ra-induced ER stress remain elusive. Therefore, our study investigated ER stress and autophagy associated with Herp expression in Mycobacterium tuberculosis-infected macrophages to determine the role of Herp in the pathogenesis of tuberculosis.

Resveratrol improves emamectin benzoate-induced pyroptosis and inflammation of Ctenopharyngodon idellus hepatic cells by alleviating oxidative stress/endoplasmic reticulum stress

Emamectin benzoate (EMB) is the most widely used pesticide in the world and contributes to water pollution. Owing to the lack of a specific antidote, EMB has a severe negative impact on the health of aquatic organisms. Resveratrol (RES), a substance with antioxidant capacity, is secreted by the fruits of many plants. This study was to explore the protection of RES against EMB-induced pyroptosis and inflammatory response in grass carp (Ctenopharyngodon idellus) hepatic liver (L8824) cells by oxidative stress/endoplasmic reticulum (ER) stress. The results showed that compared to the CON group, EMB induced oxidative stress in L8824 cells with the increase of reactive oxygen species (ROS), methane dicarboxylic aldehyde (MDA), and hydrogen peroxide (H2O2) contents and the decrease of total superoxide dismutase (t-sod) and glutathione peroxidase (gsh-px) activities (P < 0.05). In addition, EMB triggered ERS, increasing the relative mRNA expression of protein kinase R-like endoplasmic reticulum kinase (perk), inositol requiring enzyme 1 alpha (ire1α), glucose-regulated protein 78 (grp78), activating transcription factor 4 (atf4), activating transcription factor 6 (atf6), and CCAAT-enhancer-binding protein homologous protein (chop) and the protein expression of eukaryotic initiation factor 2α (eif2α), chop, atf6, and atf4. Meanwhile, EMB further induced pyroptosis by upregulating the mRNA and protein expression of nlrp3, aptamer protein (asc), caspase-1, gsdmd, interleukin-1β (il-1β), and interleukin-18 (il-18). EMB also induced inflammation in L8824 cells by increasing the mRNA expression of interleukin-2 (il-2), interleukin-6 (il-6), tumor necrosis factor-α (tnf-α), and ifn-γ and decreasing the content of interleukin-10 (il-10). However, compared to the EMB group, the oxidant indices and expression of genes related to ER stress, pyroptosis, and pro-inflammatory factors were significantly down-regulated (P < 0.05), whereas the antioxidant indicators and anti-inflammatory factor were significantly up-regulated in the EMB + RES group (P < 0.05). In conclusion, EMB caused hepatocytes pyroptosis and inflammation in grass carp, and RES could alleviate EMB-induced pyroptosis and inflammation in L8824 cells by ameliorating oxidative stress/ER stress.

Macrophage depletion attenuates degeneration of spiral ganglion neurons in kanamycin-induced unilateral hearing loss model

Pathological conditions in cochlea, such as ototoxicity, acoustic trauma, and age-related cochlear degeneration, induce cell death in the organ of Corti and degeneration of the spiral ganglion neurons (SGNs). Although macrophages play an essential role after cochlear injury, its role in the SGNs is limitedly understood. We analyzed the status of macrophage activation and neuronal damage in the spiral ganglion after kanamycin-induced unilateral hearing loss in mice. The number of ionized calcium-binding adapter molecule 1 (Iba1)-positive macrophages increased 3 days after unilateral kanamycin injection. Macrophages showed larger cell bodies, suggesting activation status. Interestingly, the number of activating transcription factor 3 (ATF3)-positive-neurons, an indicator of early neuronal damage, also increased at the same timing. In the later stages, the number of macrophages decreased, and the cell bodies became smaller, although the number of neuronal deaths increased. To understand their role in neuronal damage, macrophages were depleted via intraperitoneal injection of clodronate liposome 24 h after kanamycin injection. Macrophage depletion decreased the number of ATF3-positive neurons at day 3 and neuronal death at day 28 in the spiral ganglion following kanamycin injection. Our results suggest that suppression of inflammation by clodronate at early timing can protect spiral ganglion damage following cochlear insult.

Key role for Rac in the early transcriptional response to ECM stiffness and the stiffness-dependent repression of ATF3.

The Rho family GTPases, Rac and Rho, play critical roles in transmitting mechanical information contained within the extracellular matrix (ECM) to the cell. Rac and Rho have well described roles in regulating stiffness-dependent actin remodeling, proliferation and motility. However, much less is known about the relative roles of these GTPases in stiffness-dependent transcription, particularly at the genome-wide level. Here, we selectively inhibited Rac and Rho in mouse embryonic fibroblasts cultured on deformable substrata and used RNA sequencing to elucidate and compare the contribution of these GTPases to the early transcriptional response to ECM stiffness. Surprisingly, we found that the stiffness-dependent activation of Rac is dominant over Rho in the initial transcriptional response to ECM stiffness. We also identified Activating Transcription Factor 3 (ATF3) as a major target of stiffness/Rac-mediated signaling and show that ATF3 repression by ECM stiffness helps to explain how the stiffness-dependent activation of Rac results in the induction of cyclin D1.

Ring finger protein 146-mediated long-chain fatty-acid-coenzyme A ligase 4 ubiquitination regulates ferroptosis-induced neuronal damage in ischemic stroke.

Ischemic stroke (IS) is one of the leading causes of disability and death worldwide. Long-chain fatty-acid-coenzyme A ligase 4 (ACSL4) is a critical isozyme for ferroptosis that participates in the progression of IS. RING finger protein 146 (RNF146) is an E3 ligase predicted to interact with ACSL4 and regulated by activating transcription factor 3 (ATF3). The molecular mechanism of the RNF146/ACSL4 axis in IS is still unclear. Oxygen-glucose deprivation/reperfusion (OGD/R) treatment was used as the in vitro model, and middle cerebral artery occlusion (MCAO) mice were established for the in vivo model for IS. The protein level of ACSL4 was monitored by Western blot during ischemic injury. RNF146 was overexpressed in vitro and in vivo. The interaction of RNF146 and ACSL4 was determined by co-immunoprecipitation (Co-IP) assay. Chromatin immunoprecipitation (ChIP) assay and luciferase assay were utilized to determine the regulation of ATF3 on RNF146. Ferroptosis was evaluated by the levels of lactate dehydrogenase (LDH), malondialdehyde (MDA), Fe2+, and protein levels of related genes including ACSL4, SLC7A11, and GPX4. ACSL4 was downregulated upon OGD treatment and then increased by re-oxygenation. RNF146 was responsible for the ubiquitination and degradation of ACSL4 protein. RNF146 overexpression could prevent the stimulation of OGD/R-induced LDH, MDA, and Fe2+ levels and ferroptosis-related gene expression. ATF3 could activate the transcription and expression of RNF146, leading to the inhibition of OGD/R-induced neuron ferroptosis. The ATF3-mediated RNF146 could alleviate neuronal damage in IS by regulating ACSL4 ubiquitination and ferroptosis, providing a novel theoretical basis for exploring therapeutic targets and strategies.

N6 -methyladenosine-modified circSTX6 promotes hepatocellular carcinoma progression by regulating the HNRNPD/ATF3 axis and encoding a 144 amino acid polypeptide.

Circular RNAs (circRNAs) play a significant role in the initiation and progression of various cancers, including hepatocellular carcinoma (HCC). Circular syntaxin 6 (circSTX6, also known as hsa_circ_0007905) has been identified as a microRNA (miRNA) sponge in pancreatic adenocarcinoma. However, its full range of functions in terms of protein scaffold and translation remain largely unexplored in the context of HCC. The expression of circSTX6 and its encoded protein was examined in HCC tumour tissues. N6 -methyladenosine (m6 A) on circSTX6 was verified and quantified by methylated RNA immunoprecipitation (Me-RIP), RIP and dual luciferase reporter assays. The biological functions of circSTX6 and its encoded protein in HCC were clarified by in vitro and in vivo experiments. Mechanistically, the interaction between circSTX6 and heterogeneous nuclear ribonucleoprotein D (HNRNPD) was investigated by RNA pull-down, RIP and fluorescence in situ hybridization (FISH)/IF. The regulatory effects of circSTX6 and HNRNPD on activating transcription factor 3 (ATF3) mRNA were determined by mRNA stability and RIP assays. Furthermore, the presence of circSTX6-encoded protein was verified by mass spectrometry. CircSTX6 and its encoded 144 amino acid polypeptide, circSTX6-144aa, were highly expressed in HCC tumour tissues and served as independent risk factors for overall survival in HCC patients. The expression of circSTX6 was regulated by METTL14 in an m6 A-dependent manner. Functionally, circSTX6 accelerated HCC proliferation and tumourigenicity and reinforced tumour metastasis in vitro and in vivo. Mechanistically, circSTX6 acted as a sponge for HNRNPD protein, facilitating its binding to ATF3 mRNA, consequently promoting ATF3 mRNA decay. Meanwhile, circSTX6-144aa promoted HCC proliferation, migration and invasion independent of circSTX6 itself. Collectively, our study reveals that m6 A-modified circSTX6 drives malignancy in HCC through the HNRNPD/ATF3 axis, while its encoded circSTX6-144aa contributes to HCC progression independent of circSTX6. CirSTX6 and its encoded protein hold promise as potential biomarkers and therapeutic targets in HCC.

The Critical Role of The Piezo1/β-catenin/ATF4 Axis on The Stemness of Gli1+ BMSCs During Simulated Microgravity-Induced Bone Loss.

Disuse osteoporosis is characterized by decreased bone mass caused by abnormal mechanical stimulation of bone. Piezo1 is a major mechanosensitive ion channel in bone homeostasis. However, whether intervening in the action of Piezo1 can rescue disuse osteoporosis remains unresolved. In this study, a commonly-used hindlimb-unloading model is employed to simulate microgravity. By single-cell RNA sequencing, bone marrow-derived mesenchymal stem cells (BMSCs) are the most downregulated cell cluster, and coincidentally, Piezo1 expression is mostly enriched in those cells, and is substantially downregulated by unloading. Importantly, activation of Piezo1 by systemically-introducing yoda1 mimics the effects of mechanical stimulation and thus ameliorates bone loss under simulated microgravity. Mechanistically, Piezo1 activation promotes the proliferation and osteogenic differentiation of Gli1+ BMSCs by activating the β-catenin and its target gene activating transcription factor 4 (ATF4). Inhibiting β-catenin expression substantially attenuates the effect of yoda1 on bone loss, possibly due to inhibited proliferation and osteogenic differentiation capability of Gli1+ BMSCs mediated by ATF4. Lastly, Piezo1 activation also slightly alleviates the osteoporosis of OVX and aged mice. In conclusion, impaired function of Piezo1 in BMSCs leads to insufficient bone formation especially caused by abnormal mechanical stimuli, and is thus a potential therapeutic target for osteoporosis.

Primary pulmonary myxoid sarcoma: A case report and review of the literature

Background: Primary pulmonary myxoid sarcoma is a very rare tumor, with less than 25 cases being described in the literature. When found in the bronchial tree, an R0 resection with post-operative follow-up is sufficient for curative treatment. We present a case of primary pulmonary myxoid sarcoma in a middle-aged man with an associated review of the literature to highlight this rare tumor. Case presentation: A 62-year-old man with a 40-pack-year smoking history presented to the thoracic surgery clinic for evaluation of a suspicious lung nodule. Pre-operative testing revealed a spiculated mass in the left upper lobe and the biopsy was non-diagnostic. The patient was taken for left upper lobectomy tri-segmentectomy with mediastinal lymph node dissection. Final pathology of the nodule revealed primary pulmonary myxoid sarcoma with an Ewing sarcoma breakpoint region 1 on chromosome 22 with activating transcription factor 1 (EWSR-ATF1) fusion transcript consistent with the diagnosis. Conclusion: Primary pulmonary myxoid sarcoma is an exceedingly rare sarcoma of the lung with less than 25 reported cases in the literature. This case report highlights our experience treating primary pulmonary myxoid sarcoma in a middle-aged man, and a review of current treatment recommendations in the available published literature.

Signaling pathways upregulating glutathione‑specific γ‑glutamylcyclotransferase 1 by 3‑(5'‑hydroxymethyl‑2'‑furyl)‑1‑benzylindazole.

Glutathione‑specific γ‑glutamylcyclotransferase1 (CHAC1), is an unfolded protein response‑induced gene. Although it has been previously reported that CHAC1 transcription is regulated by activating transcription factor (ATF)4, ATF3 and CCAAT/enhancer‑binding protein β (C/EBPβ), the signaling pathways that regulate CHAC1 are largely unknown. It was revealed that 3‑(5'‑hydroxymethyl‑2'‑furyl)‑1‑benzylindazole (YC‑1; PubChem ID: 5712), a nitric oxide‑independent activator ofsoluble guanylyl cyclase (sGC), increases CHAC1 levels in cultured human kidney proximal tubular cells (HK‑2). Therefore, in the present study, the signaling pathways that induce CHAC1 by YC‑1 were investigated in HK‑2 cells. YC‑1 induced CHAC1 expression in a dose‑ and time‑dependent manner. KT5823, an inhibitor of cGMP‑dependent protein kinase (PKG), partially inhibited CHAC1 upregulation, indicating that the sGC‑cGMP‑PKG pathway participates in CHAC1 regulation. These results also suggested that other signaling pathways are involved in the regulation of CHAC1. Since antibody array analysis showed the activation of p38, mTOR and Akt, the involvement of these factors was further investigated. Although LY294002 and KU0063794 (inhibitors of Akt and mTOR, respectively) inhibited YC‑1‑induced CHAC1 expression, SB203580 (an inhibitor of p38) did not. These results indicated that CHAC1 is regulated by the Akt‑mTOR pathway. In addition, YC‑1 induced endoplasmic reticulum (ER) stress, a regulator of CHAC1 induction. These findings suggested that CHAC1 is regulated by YC‑1 through the sGC‑cGMP‑PKG, Akt‑mTOR and ER stress pathways. The present study demonstrated that CHAC1 induction reduced the intracellular glutathione concentration, indicating that CHAC1 plays an important role in intracellular redox homeostasis in tubular cells.

Linderalactone mitigates diabetic cardiomyopathy in mice via suppressing the MAPK/ATF6 pathway

Diabetic cardiomyopathy (DCM) is a challenging diabetic complication that manifests as chronic inflammation. Yet, the mechanism underlying diabetes-associated myocardial injury is not fully understood. We investigated the pharmacological effects and mechanisms of linderalactone, a natural compound that can prevent diabetes-induced cardiomyopathy in mice. Diabetes was induced by a single dose of streptozotocin (120 mg/kg, i.p.). Diabetic mice were administrated with linderalactone (2.5 or 5 mg/kg) by gavage for five weeks. Harvested heart tissues were then subjected to RNA-sequencing analysis to explore the potential mechanism of linderalactone. Linderalactone prevented heart dysfunction by inhibiting myocardial hypertrophy, fibrosis, and inflammation, without altering blood glucose. RNA-sequencing indicated that linderalactone exerted its cardioprotective effects mainly by affecting the mitogen-activated protein kinase (MAPK)/ activating transcription factor 6 (ATF6) pathway. Linderalactone also suppressed endoplasmic reticulum (ER) stress mediated by the diabetes-activated MAPKs/ATF6 pathway, thereby reducing myocardial hypertrophy and inflammation in heart tissues and in cultured cardiomyocytes. Inhibition of MAPKs or a deficiency of ATF6 in cardiomyocytes mimicked the linderalactone-associated decreases in high glucose-induced hypertrophy and inflammation. Linderalactone showed beneficial effects in alleviating diabetic cardiomyopathy, in part by modulating the MAPK/ATF6 signaling pathway to mitigate myocardial hypertrophy and inflammation. Linderalactone may have clinical utility in the treatment for diabetes-associated cardiomyopathy.

Endoplasmic reticulum stress in pancreatic β cells induces incretin desensitization and β-cell dysfunction via ATF4-mediated PDE4D expression.

Pancreatic β-cell dysfunction and eventual loss are key steps in the progression of type 2 diabetes (T2D). Endoplasmic reticulum (ER) stress responses, especially those mediated by the protein kinase RNA-like ER kinase and activating transcription factor 4 (PERK-ATF4) pathway, have been implicated in promoting these β-cell pathologies. However, the exact molecular events surrounding the role of the PERK-ATF4 pathway in β-cell dysfunction remain unknown. Here, we report our discovery that ATF4 promotes the expression of PDE4D, which disrupts β-cell function via a downregulation of cAMP signaling. We found that β-cell-specific transgenic expression of ATF4 led to early β-cell dysfunction and loss, a phenotype that resembles accelerated T2D. Expression of ATF4, rather than C/EBP homologous protein (CHOP), promoted PDE4D expression, reduced cAMP signaling, and attenuated responses to incretins and elevated glucose. Furthermore, we found that β-cells of leptin receptor-deficient diabetic (db/db) mice had elevated nuclear localization of ATF4 and PDE4D expression, accompanied by impaired β-cell function. Accordingly, pharmacological inhibition of the ATF4 pathway attenuated PDE4D expression in the islets and promoted incretin-simulated glucose tolerance and insulin secretion in db/db mice. Finally, we found that inhibiting PDE4 activity with selective pharmacological inhibitors improved β-cell function in both db/db mice and β-cell-specific ATF4 transgenic mice. In summary, our results indicate that ER stress causes β-cell failure via ATF4-mediated PDE4D production, suggesting the ATF4-PDE4D pathway could be a therapeutic target for protecting β-cell function during the progression of T2D.NEW & NOTEWORTHY Endoplasmic reticulum stress has been implied to cause multiple β-cell pathologies during the progression of type 2 diabetes (T2D). However, the precise molecular events underlying this remain unknown. Here, we discovered that elevated ATF4 activity, which was seen in T2D β cells, attenuated β-cell proliferation and impaired insulin secretion via PDE4D-mediated downregulation of cAMP signaling. Additionally, we demonstrated that pharmacological inhibition of the ATF4 pathway or PDE4D activity alleviated β-cell dysfunction, suggesting its therapeutic usefulness against T2D.

Maternal obstructive sleep apnea aggravates metabolic dysfunction-associated fatty liver disease via HMGB1-TLR4 signaling-mediated endoplasmic reticulum stress in male offspring rats

Aims/hypothesisMaternal obstructive sleep apnea (MOSA) may inflict long-term metabolic effects on offspring. We hypothesize that MOSA increases the propensity for metabolic dysregulation in offspring and thus facilitates the development of metabolic dysfunction-associated fatty liver disease (MAFLD). This study aims to test the hypothesis and explore the underlying mechanism. MethodsThe MOSA rat model of upper airway obstruction was established and fecundated. The postweaning male offspring (n = 171) from both the control group and MOSA group were randomly fed the normal chow diet (NCD, n = 89) or high-fat diet (HFD, n = 82) for the next 5 months. Liver function, lipid profile, glucose, and insulin levels were measured. Expression levels of fibrosis-related proteins and endoplasmic reticulum (ER) stress-related proteins in liver tissues were assessed using immunohistochemistry and western blotting. ResultsMOSA increased body and liver weight in male offspring, along with augmented liver organ coefficient. Serum levels of aminotransferases, low-density lipoprotein, high-density lipoprotein, triglycerides, total cholesterol, total bile acid, fasting glucose, and insulin increased significantly. MOSA exacerbated HFD-induced hepatic steatosis and fibrosis. These effects were driven by the overactivated double-stranded RNA-activated protein kinase (PKR)-like eukaryotic initiation factor 2(PERK)-activating transcription factor (ATF)4-C/EBP homologous protein (CHOP) signaling pathway-induced ER stress, and hyperacetylation and release of high mobility group box-1(HMGB1) elicited above signaling in a TLR4-dependent manner. ConclusionsThese findings indicate that MOSA can exert prolonged adverse effects manifested as metabolic dysfunction in male offspring. Therefore, surveillance and management of OSA during pregnancy may be necessary to prevent and alleviate MAFLD in offspring.

Intracellular Fusobacterium nucleatum infection attenuates antitumor immunity in esophageal squamous cell carcinoma

Currently, the influence of the tumor microbiome on the effectiveness of immunotherapy remains largely unknown. Intratumoural Fusobacterium nucleatum (Fn) functions as an oncogenic bacterium and can promote tumor progression in esophageal squamous cell carcinoma (ESCC). Our previous study revealed that Fn is a facultative intracellular bacterium and that its virulence factor Fn-Dps facilitates the intracellular survival of Fn. In this study, we find that Fn DNA is enriched in the nonresponder (NR) group among ESCC patients receiving PD-1 inhibitor and that the serum antibody level of Fn is significantly higher in the NR group than in the responder (R) group. In addition, Fn infection has an opposite impact on the efficacy of αPD-L1 treatment in animals. Mechanistically, we confirm that Fn can inhibit the proliferation and cytokine secretion of T cells and that Fn-Dps binds to the PD-L1 gene promoter activating transcription factor-3 (ATF3) to transcriptionally upregulate PD-L1 expression. Our results suggest that it may be an important therapeutic strategy to eradicate intratumoral Fn infection before initiating ESCC immunotherapies.

Abstract PO-088: TRPV1+ sensory neurons provide a tumor supportive environment through recruitment of MDSCs

Abstract Cancer neuroscience has become an increasing area of focus in cancer research as our understanding of the presence and function of intra-tumoral neurons continues to emerge, with studies indicating that tumor infiltrating neurons impact components of the tumor microenvironment promoting cancer initiation and progression. We have previously published that head and neck squamous cell carcinomas are innervated. We now focus on defining the contributions of intra-tumoral neurons to disease progression in HNSCC. Tumor implantation in a double transgenic mouse (TRPV1cre::DTAfl/wt) lacking the cancer-recruited TRPV1-expressing sensory neurons allows us to study the consequences of this neuronal loss on the local immune response. Importantly, comparison between wild type and TRPV1cre::DTAfl/wt mice demonstrated no significant immune population differences at baseline. Thus, wildtype and TRPV1cre::DTAfl/wt mice were orthotopically implanted with tumor and tumoral immune cell populations identified by flow cytometry. Cytokine and peptide concentrations were measured by ELISA. In vitro assays were preformed to molecularly define the neuronal signals and immune responses. Here, co-culture experiments of immortalized head and neck cancer cell lines and dorsal root ganglia (DRG) from wildtype mice were used to model tumor innervation in vitro. The media generated was applied to bone marrow derived (BMD) immune cells and the impact on immune cell phenotypes assayed by flow cytometry. Our orthotopic model demonstrates that the presence of HNSCC promotes a nerve-injury phenotype in ipsilateral trigeminal ganglion, demonstrated by increased expression of activating transcription factor 3 (ATF3). Utilizing a 12-color flow cytometry panel we show that tumors from TRPV1cre::DTAfl/wt mice harbor a significantly smaller population of myeloid derived suppressor cells (MDSCs) compared to those from wildtype animals. Further analysis demonstrates this population shift occurs primarily due to a decrease in the CD11b+ Ly6G+/Ly6Clo population. In vitro studies using BMD immune cells show that tumor cell-DRG co-culture conditioned media induces an expansion of the MDSC population compared to condition media from DRG or tumor cells alone. Additionally, transwell migration assays show that co-culture condition media also increases cellular migration compared to condition media from DRG or tumor cells alone. Moreover, ELISA analysis indicates that co-culture of tumor cells and DRG increases neuronal release of the neuropeptide, Substance P (SP), potentiating IL-6 release from tumor cells. In summary, we identified several mechanisms by which TRPV1-expressing intra-tumoral neurons promote MDSC infiltration at the tumor bed and promote disease progression. These mechanisms define targets for therapeutic intervention including SP and IL-6 signaling. Future studies will test the clinical utility of these targets. Together, our data suggests that intra-tumoral neurons contribute to cancer progression through generation of a tumor supportive microenvironment. Citation Format: Anthony C. Restaino, Maryam Ahmadi, Sebastien Talbot, Paola D. Vermeer. TRPV1+ sensory neurons provide a tumor supportive environment through recruitment of MDSCs [abstract]. In: Proceedings of the AACR-AHNS Head and Neck Cancer Conference: Innovating through Basic, Clinical, and Translational Research; 2023 Jul 7-8; Montreal, QC, Canada. Philadelphia (PA): AACR; Clin Cancer Res 2023;29(18_Suppl):Abstract nr PO-088.

Unfolded Protein Response Signaling in Liver Disorders: A 2023 Updated Review.

Endoplasmic reticulum (ER) is the site for synthesis and folding of secreted and transmembrane proteins. Disturbance in the functioning of ER leads to the accumulation of unfolded and misfolded proteins, which finally activate the unfolded protein response (UPR) signaling. The three branches of UPR-IRE1 (Inositol requiring enzyme 1), PERK (Protein kinase RNA-activated (PKR)-like ER kinase), and ATF6 (Activating transcription factor 6)-modulate the gene expression pattern through increased expression of chaperones and restore ER homeostasis by enhancing ER protein folding capacity. The liver is a central organ which performs a variety of functions which help in maintaining the overall well-being of our body. The liver plays many roles in cellular physiology, blood homeostasis, and detoxification, and is the main site at which protein synthesis occurs. Disturbance in ER homeostasis is triggered by calcium level imbalance, change in redox status, viral infection, and so on. ER dysfunction and subsequent UPR signaling participate in various hepatic disorders like metabolic (dysfunction) associated fatty liver disease, liver cancer, viral hepatitis, and cholestasis. The exact role of ER stress and UPR signaling in various liver diseases is not fully understood and needs further investigation. Targeting UPR signaling with drugs is the subject of intensive research for therapeutic use in liver diseases. The present review summarizes the role of UPR signaling in liver disorders and describes why UPR regulators are promising therapeutic targets.

Exosomes Derived from M2 Microglial Cells Modulated by 1070-nm Light Improve Cognition in an Alzheimer's Disease Mouse Model.

Near-infrared photobiomodulation has been identified as a potential strategy for Alzheimer's disease (AD). However, the mechanisms underlying this therapeutic effect remain poorly characterize. Herein, it is illustrate that 1070-nm light induces the morphological alteration of microglia from an M1 to M2 phenotype that secretes exosomes, which alleviates the β-amyloid burden to improve cognitive function by ameliorating neuroinflammation and promoting neuronal dendritic spine plasticity. The results show that 4Jcm-2 1070-nm light at a 10-Hz frequency prompts microglia with an M1 inflammatory type to switch to an M2 anti-inflammatory type. This induces secretion of M2 microglial-derived exosomes containing miR-7670-3p, which targets activating transcription factor 6 (ATF6) during endoplasmic reticulum (ER) stress. Moreover, it is found that miR-7670-3p reduces ATF6 expression to further ameliorate ER stress, thus attenuating the inflammatory response and protecting dendritic spine integrity of neurons in the cortex and hippocampus of 5xFAD mice, ultimately leading to improvements in cognitive function. This study highlights the critical role of exosomes derive from 1070-nm light-modulated microglia in treating AD mice, which may provide a theoretical basis for the treatment of AD with the use of near-infrared photobiomodulation.

P02.26.B METABOLIC PLASTICITY IN GLIOBLASTOMA TUMOR-INITIATING CELL AND RESISTANCE TO LSD1-DIRECTED THERAPY

Abstract BACKGROUND Glioblastoma (GBM), the most common primary brain tumor in adults, remains incurable despite multimodal therapy. There is a pressing unmet medical need for new therapeutic strategies, especially because patients experience only short-term benefit after primary treatment and the vast majority inevitably relapse. Adaptation to harsh microenvironmental conditions, including nutrient deprivation, proteostasis perturbation, hypoxia and drug treatment, induce molecular and metabolic changes in glioblastoma that lead to the acquisition of a tolerance to stress and resistance to drug. In this context, we demonstrated that Lysine-specific histone demethylase 1 (LSD1) is a regulator of tumor-initiating cell (TICs) survival, adaptation and recovery from stress. LSD1 pharmacological inhibition with a specific and brain penetrant inhibitor (LSD1i) induces a maladaptive integrated stress response (ISR) which leads to the death of TICs exposed to ER stress or nutrient deficiency. MATERIAL AND METHODS Given the high GBM heterogeneity, we analyzed different patient-derived TICs grown in vitro as sphere and characterized for their genetic landscape and in vitro/in vivo stem cell-like features. We applied mechanistically different strategies, including biological, metabolic and pharmacological approaches, as well as transcriptomic and proteomic profiling. Zebrafish and GBM xenografts have been exploited as in vivo models. RESULTS LSD1i treatment induces physical and functional rearrangements of mitochondria, culminating into their enhanced bioenergetic activity and ATP production that predispose to cell death. Interestingly, only a subset of patient-derived TICs benefits from LSD1i therapy. These samples are largely dependent on glycolysis and, upon LSD1i administration, they are unable to further enhance it when mitochondrial energy production is inhibited. The samples resistant to LSD1i maintain their cellular behavior unaltered even upon prolonged treatment. They display reduced susceptibility to the stressful cues represented by either LSD1i and the known ER stressors Thapsigargin and Tunicamycin, by efficiently restoring energy homeostasis and properly activating the Activating Transcription Factor 4 (ATF4)-dependent ISR. Remarkably, LSD1i resistant samples display metabolic flexibility and switch between glycolytic and oxidative metabolism to ensure their survival. CONCLUSION The identification of specific metabolic vulnerabilities could offer unique opportunities for therapeutic intervention: the selective LSD1i vulnerability relies on the preferential dependence on glycolysis, while the great metabolic plasticity of LSD1i resistant TICs coordinates changes that favor their adaptation to stressful microenvironments and therapeutic insults.

Lysosomes mediate the mitochondrial UPR via mTORC1-dependent ATF4 phosphorylation

Lysosomes are central platforms for not only the degradation of macromolecules but also the integration of multiple signaling pathways. However, whether and how lysosomes mediate the mitochondrial stress response (MSR) remain largely unknown. Here, we demonstrate that lysosomal acidification via the vacuolar H+-ATPase (v-ATPase) is essential for the transcriptional activation of the mitochondrial unfolded protein response (UPRmt). Mitochondrial stress stimulates v-ATPase-mediated lysosomal activation of the mechanistic target of rapamycin complex 1 (mTORC1), which then directly phosphorylates the MSR transcription factor, activating transcription factor 4 (ATF4). Disruption of mTORC1-dependent ATF4 phosphorylation blocks the UPRmt, but not other similar stress responses, such as the UPRER. Finally, ATF4 phosphorylation downstream of the v-ATPase/mTORC1 signaling is indispensable for sustaining mitochondrial redox homeostasis and protecting cells from ROS-associated cell death upon mitochondrial stress. Thus, v-ATPase/mTORC1-mediated ATF4 phosphorylation via lysosomes links mitochondrial stress to UPRmt activation and mitochondrial function resilience.

Activating transcription factor 3: A potential therapeutic target for inflammatory pulmonary diseases.

Activating transcription factor 3 (ATF3) is a nuclear protein that is widely expressed in a variety of cells. It is a stress-inducible transcription gene and a member of the activating transcription factor/cAMP responsive element-binding protein (ATF/CREB) family. The comprehensive literature review was conducted by searching PubMed and Google Scholar. Search terms used were "ATF3", "ATF3 and (ALI or ARDS)", "ATF3 and COPD", "ATF3 and PF", and "ATF3 and Posttranslational modifications". Recent studies have shown that ATF3 plays a critical role in many inflammatory pulmonary diseases, including acute lung injury (ALI)/acute respiratory distress syndrome (ARDS), chronic obstructive pulmonary disease (COPD), and pulmonary fibrosis (PF). ATF3 participates in many signaling pathways and complex pathophysiological processes, such as inflammation, immunity, endoplasmic reticulum stress, and cell proliferation. However, the role of ATF3 in current studies is controversial, and there are reports showing that ATF3 plays different roles in different pulmonary diseases. In this review, we first summarized the structure, function, and mechanism of ATF3 in various inflammatory pulmonary diseases. The impact of ATF3 on disease pathogenesis and the clinical implications was particularly focused on, with an overall aim to identify new targets for treating inflammatory pulmonary diseases.

ATF3 regulates SPHK1 in cardiomyocyte injury via endoplasmic reticulum stress.

Endoplasmic reticulum (ER) stress is common in different human pathologies, including cardiac diseases. Sphingosine kinase-1 (SPHK1) represents an important player in cardiac growth and function. Nevertheless, its function in cardiomyocyte ER stress remains vague. This study sought to evaluate the mechanism through which SPHK1 might influence ER stress during myocardial infarction (MI). MI-related GEO data sets were queried to screen differentially expressed genes. Murine HL-1 cells exposed to oxygen-glucose deprivation (OGD) and mice with MI were induced, followed by gene expression manipulation using short hairpin RNAs and overexpression vectors. The activating transcription factor 3 (ATF3) and SPHK1 expression was examined in cells and tissues. Cell counting kit-8, TUNEL, DHE, HE, and Masson's staining were conducted in vitro and in vivo. The inflammatory factor concentrations in mouse serum were measured using ELISA. Finally, the transcriptional regulation of SPHK1 by ATF3 was validated. ATF3 and SPHK1 were upregulated in vivo and in vitro. ATF3 downregulation reduced the SPHK1 transcription. ATF3 and SPHK1 downregulation increased the viability of OGD-treated HL-1 cells and decreased apoptosis, oxidative stress, and ER stress. ATF3 and SPHK1 downregulation narrowed the infarction area and attenuated myocardial fibrosis in mice, along with reduced inflammation in the serum and ER stress in the myocardium. In contrast, SPHK1 reduced the protective effect of ATF3 downregulation in vitro and in vivo. ATF3 downregulation reduced SPHK1 expression to attenuate cardiomyocyte injury in MI.