Prolonged Endoplasmic Reticulum Stress Research Articles

Tumour suppressor protein sMEK1 links to IRE1 signalling pathway to modulate its activity during ER stress

The Endoplasmic Reticulum is a pervasive, dynamic cellular organelle that performs a wide range of functions in the eukaryotic cell, including protein folding and maturation. Upon stress, ER activates an adaptive cellular pathway, namely Unfolded Protein Response, that transduces information from ER to nucleus, restoring homeostasis in the ER milieu. UPR consists of three membrane-tethered sensors; IRE1, PERK and ATF6. Among all the UPR sensors, the IRE1 branch acts as a central pathway that orchestrates several pathways to determine cell fate. However, the detailed knowledge underlying the whole process is not understood yet. Previously, we determined the sMEK1 as one of the interacting partners of IRE1. sMEK1 is a protein phosphatase, which has been indicated in a number of critical cellular functions like apoptosis, cell proliferation, and tumour suppression. In this study, we evaluated the role of sMEK1 on the IRE1 signalling pathway. Our data indicate that sMEK1 can inhibit IRE1 phosphorylation under ER stress. This inhibitory effect of sMEK1 could be reflected in its downstream effectors, Xbp1 and RIDD, which are downregulated in the presence of sMEK1. We also found that the repressing effect of sMEK1 was specific to the IRE1 signalling pathway and could be preserved even under prolonged ER stress. Our findings also indicate that sMEK1 can inhibit IRE1 and its downstream molecules under ER stress irrespective of other UPR sensors. These results help to draw the mechanistic details giving insights into different molecular connections of UPR with other pathways.

Insights into the Activation of Unfolded Protein Response Mechanism during Coronavirus Infection.

Coronaviruses represent a significant class of viruses that affect both animals and humans. Their replication cycle is strongly associated with the endoplasmic reticulum (ER), which, upon virus invasion, triggers ER stress responses. The activation of the unfolded protein response (UPR) within infected cells is performed from three transmembrane receptors, IRE1, PERK, and ATF6, and results in a reduction in protein production, a boost in the ER's ability to fold proteins properly, and the initiation of ER-associated degradation (ERAD) to remove misfolded or unfolded proteins. However, in cases of prolonged and severe ER stress, the UPR can also instigate apoptotic cell death and inflammation. Herein, we discuss the ER-triggered host responses after coronavirus infection, as well as the pharmaceutical targeting of the UPR as a potential antiviral strategy.

IRE1 signaling increases PERK expression during chronic ER stress

The Unfolded Protein Response (UPR) is an essential cellular process activated by the accumulation of unfolded proteins within the Endoplasmic Reticulum (ER), a condition referred to as ER stress. Three ER anchored receptors, IRE1, PERK and ATF6 act as ER stress sensors monitoring the health of the ER. Upon detection of ER stress, IRE1, PERK and ATF6 initiate downstream signaling pathways collectively referred to as the UPR. The overarching aim of the UPR is to restore ER homeostasis by reducing ER stress, however if that is not possible, the UPR transitions from a pro-survival to a pro-death response. While our understanding of the key signaling pathways central to the UPR is well defined, the same is not true of the subtle signaling events that help fine tune the UPR, supporting its ability to adapt to varying amplitudes or durations of ER stress. In this study, we demonstrate cross talk between the IRE1 and PERK branches of the UPR, wherein IRE1 via XBP1s signaling helps to sustain PERK expression during prolonged ER stress. Our findings suggest cross talk between UPR branches aids adaptiveness thereby helping to support the plasticity of UPR signaling responses.

Sinapic acid protects against lead acetate-induced lung toxicity by reducing oxidative stress, apoptosis, inflammation, and endoplasmic reticulum stress damage.

Lead acetate (PbAc) is a compound that produces toxicity in many tissues after exposure. Sinapic acid (SNP) possesses many biological and pharmacological properties. This study aimed to investigate the efficacy of SNP on the toxicity of PbAc in lung tissue. PbAc was administered orally at 30 mg/kg and SNP at 5 or 10 mg/kg for 7 days. Biochemical, genetic, and histological methods were used to investigate inflammatory, apoptotic, endoplasmic reticulum stress, and oxidative stress damage levels in lung tissue. SNP administration induced PbAc-reduced antioxidant (GSH, SOD, CAT, and GPx) and expression of HO-1 in lung tissue. It also reduced MDA, induced by PbAc, and thus alleviated oxidative stress. SNP decreased the inflammatory markers NF-κB, TNF-α and IL-1β levels induced by PbAc in lung tissue and exhibited anti-inflammatory effect. PbAc increased apoptotic Bax, Apaf-1, and Caspase-3 mRNA transcription levels and decreased anti-apoptotic Bcl-2 in lung tissues. SNP decreased apoptotic damage by reversing this situation. On the other hand, SNP regulated these markers and brought them closer to the levels of the control group. PbAc caused prolonged ER stress by increasing the levels of ATF6, PERK, IRE1α, GRP78 and this activity was stopped and tended to retreat with SNP. After evaluating all the data, While PbAc caused toxic damage in lung tissue, SNP showed a protective effect by reducing this damage.

Doxorubicin‑induced cardiomyopathy is mitigated by empagliflozin via the modulation of endoplasmic reticulum stress pathways.

Doxorubicin (Dox) exhibits a high efficacy in the treatment of numerous types of cancer. However, the beneficial cytotoxic effects of Dox are often accompanied by an increase in the risk of cardiotoxicity. Oxidative stress (OS) plays a key role in Dox‑induced cardiomyopathy (DIC). OS in cardiomyocytes disrupts endoplasmic reticulum (ER) function, leading to the accumulation of misfolded/unfolded proteins known as ER stress. ER stress acts as an adaptive mechanism; however, prolonged ER stress together with OS may lead to the initiation of cardiomyocyte apoptosis. The present study aimed to explore the potential of an anti‑diabetic drug, empagliflozin (EMPA), in mitigating Dox‑induced ER stress and cardiomyocyte apoptosis. In the present study, the effects of 1h pretreatment of EMPA on Dox‑treated cardiomyocytes isolated from Sprague‑Dawley rats were investigated. After 24h, EMPA pre‑treatment promoted cell survival in the EMPA + Dox group compared with the Dox group. Results of the present study also demonstrated that EMPA mitigated overall ER stress, as the increased expression of ER stress markers was reduced in the EMPA + Dox group. Additionally, OS, inflammation and expression of ER stress apoptotic proteins were also significantly reduced following EMPA pre‑treatment in the EMPA + Dox group. Thus, EMPA may exert beneficial effects on Dox‑induced ER stress and may exhibit potential changes that can be utilised to further evaluate the role of EMPA in mitigating DIC.

Understanding the Unfolded Protein Response (UPR) Pathway: Insights into Neuropsychiatric Disorders and Therapeutic Potentials.

The Unfolded Protein Response (UPR) serves as a critical cellular mechanism dedicated to maintaining protein homeostasis, primarily within the endoplasmic reticulum (ER). This pathway diligently responds to a variety of intracellular indicators of ER stress with the objective of reinstating balance by diminishing the accumulation of unfolded proteins, amplifying the ER's folding capacity, and eliminating slow-folding proteins. Prolonged ER stress and UPR irregularities have been linked to a range of neuropsychiatric disorders, including major depressive disorder, bipolar disorder, and schizophrenia. This review offers a comprehensive overview of the UPR pathway, delineating its activation mechanisms and its role in the pathophysiology of neuropsychiatric disorders. It highlights the intricate interplay within the UPR and its profound influence on brain function, synaptic perturbations, and neural developmental processes. Additionally, it explores evolving therapeutic strategies targeting the UPR within the context of these disorders, underscoring the necessity for precision and further research to effective treatments. The research findings presented in this work underscore the promising potential of UPR-focused therapeutic approaches to address the complex landscape of neuropsychiatric disorders, giving rise to optimism for improving outcomes for individuals facing these complex conditions.

MITOL deficiency triggers hematopoietic stem cell apoptosis via ER stress response.

Hematopoietic stem cell (HSC) divisional fate and function are determined by cellular metabolism, yet the contribution of specific cellular organelles and metabolic pathways to blood maintenance and stress-induced responses in the bone marrow remains poorly understood. The outer mitochondrial membrane-localized E3 ubiquitin ligase MITOL/MARCHF5 (encoded by the Mitol gene) is known to regulate mitochondrial and endoplasmic reticulum (ER) interaction and to promote cell survival. Here, we investigated the functional involvement of MITOL in HSC maintenance by generating MX1-cre inducible Mitol knockout mice. MITOL deletion in the bone marrow resulted in HSC exhaustion and impairment of bone marrow reconstitution capability in vivo. Interestingly, MITOL loss did not induce major mitochondrial dysfunction in hematopoietic stem and progenitor cells. In contrast, MITOL deletion induced prolonged ER stress in HSCs, which triggered cellular apoptosis regulated by IRE1α. In line, dampening of ER stress signaling by IRE1α inihibitor KIRA6 partially rescued apoptosis of long-term-reconstituting HSC. In summary, our observations indicate that MITOL is a principal regulator of hematopoietic homeostasis and protects blood stem cells from cell death through its function in ER stress signaling.

FBXO5-mediated RNF183 degradation prevents endoplasmic reticulum stress-induced apoptosis and promotes colon cancer progression

Endoplasmic reticulum (ER) stress induces the unfolded protein response (UPR), and prolonged ER stress leads to cell apoptosis. Despite increasing research in this area, the underlying molecular mechanisms remain unclear. Here, we discover that ER stress upregulates the UPR signaling pathway while downregulating E2F target gene expression and inhibiting the G2/M phase transition. Prolonged ER stress decreases the mRNA levels of E2F2, which specifically regulates the expression of F-Box Protein 5(FBXO5), an F-box protein that functions as an inhibitor of the anaphase-promoting complex/cyclosome (APC/C) ubiquitin ligase complex. Depletion of FBXO5 results in increased ER stress-induced apoptosis and decreased expression of proteins related to PERK/IRE1α/ATF6 signaling. Overexpression of FBXO5 wild-type (not its ΔF-box mutant) alleviates apoptosis and the expression of the C/EBP Homologous Protein (CHOP)/ATF. Mechanistically, we find that FBXO5 directly binds to and promotes the ubiquitin-dependent degradation of RNF183, which acts as a ubiquitin E3 ligase in regulating ER stress-induced apoptosis. Reversal of the apoptosis defects caused by FBXO5 deficiency in colorectal cancer cells can be achieved by knocking down RNF183 in FBXO5-deficient cells. Functionally, we observed significant upregulation of FBXO5 in colon cancer tissues, and its silencing suppresses tumor occurrence in vivo. Therefore, our study highlights the critical role of the FBXO5/RNF183 axis in ER stress regulation and identifies a potential therapeutic target for colon cancer treatment.

ER stress mediated inflammation in cancer pathogenesis

Inflammation is a complex process which is associated with the initiation and progression of cancer. Prolonged Endoplasmic Reticulum (ER) stress triggers inflammation which is a key factor associated with cancer pathogenesis. ER stress also contributes to immune suppression in inflammatory and tumor microenvironment. It stimulates the production of pro-inflammatory cytokines by regulating the activation of various transcription factors and inflammatory signalling pathways. Targeting ER stress is an exciting possibility that can be used as a therapeutic strategy for cancer treatment. This mini review focuses on the emerging link between ER stress-induced inflammatory responses in cancer development.

Endoplasmic reticulum stress caused by traumatic injury promotes cardiomyocyte apoptosis through acetylation modification of GRP78.

Cardiomyocyte apoptosis is an important cause of trauma-induced secondary cardiac injury (TISCI), in which the endoplasmic reticulum stress (ERS)-mediated apoptosis signaling pathway is known to be first activated, but the mechanism remains unclear. In this study, rat models of traumatic injury are established by using the Noble-Collip trauma device. The expression of glucose-regulating protein 78 (GRP78, a molecular chaperone of the cardiomyocyte ER), acetylation modification of GRP78 and apoptosis of cardiomyocytes are determined. The results show that ERS-induced GRP78 elevation does not induce cardiomyocyte apoptosis in the early stage of trauma. However, with prolonged ERS, the GRP78 acetylation level is elevated, and the apoptosis of cardiomyocytes also increases significantly. In addition, in the early stage of trauma, the expression of histone acetyl-transferase (HAT) P300 is increased and that of histone deacetylase 6 (HDAC6) is decreased in cardiomyocytes. Inhibition of HDAC function could induce the apoptosis of traumatic cardiomyocytes by increasing the acetylation level of GRP78. Our present study demonstrates for the first time that post-traumatic protracted ERS can promote cardiomyocyte apoptosis by increasing the acetylation level of GRP78, which may provide an experimental basis for seeking early molecular events of TISCI.

Naringin attenuates oxaliplatin-induced nephrotoxicity and hepatotoxicity: A molecular, biochemical, and histopathological approach in a rat model.

Oxaliplatin (OXL) is a significant therapy agent for the worldwide increase in cancer cases. Naringin (4',5,7-trihydroxy flavonon 7-rhamnoglucoside, NRG) has a wide range of biological and pharmacological activities, including antioxidant and anti-inflammatory potentials. This research aimed to investigate NRG activity in OXL-induced hepatorenal toxicity. Accordingly, OXL (4 mg/kg b.w.) in 5% glucose was injected intraperitoneally on the first, second, fifth, and sixth days, and NRG (50 and 100 mg/kg b.w.) was given orally 30 min before to treatment. Biochemical, genetic, and histological methods were utilized to investigate the function tests, oxidant/antioxidant status, inflammation, apoptosis, and endoplasmic reticulum (ER) stress pathways in kidney and liver tissues. Administration of NRG demonstrated an antioxidant effect by increasing the activities of OXL-induced reduced antioxidant enzymes (superoxide dismutase, catalase, and glutathione peroxidase) and decreasing the elevated lipid peroxidation parametermalondialdehyde levels. Nuclear factor-κB, tumor necrosis factor-α, interleukin-1β, andinducible nitric oxide synthase levels increased in OXL administered groups but reduced in NRG-treated groups. In the OXL-administered groups, NRG reduced the apoptosis-inducing factors Caspase-3 and B-cell lymphoma 2 (Bcl-2)-associated X protein levels, while elevating the antiapoptotic factor Bcl-2 levels. OXL triggered prolonged ER stress by increasing the levels of ER stress parameters activating transcription factor 6, protein kinase R-like ER kinase, inositol-requiring enzyme 1α, and glucose-regulated protein 78. Therefore, with the NRG administration, this activity was reduced and the ER stress level decreased. Taken together, it was found that OXL induced toxicity by increasing the levels of urea and creatinine, alanine transaminase, aspartate aminotransferase, andalkaline phosphatase activities, inflammation, apoptosis, ER stress, and oxidants in the liver and kidney tissue, and NRG had a protective effect by reversing the deterioration in these pathways.

The endoplasmic reticulum (ER) chaperone GRP78 is secreted during ER Stress and alleviates endothelial cell inflammation

Abstract Introduction Glucose-Regulated Protein 78kD (GRP78) is a chaperone and the main regulator of the ER-stress response which is triggered by a variety of conditions that disturb folding of proteins in the ER. Upon ER Stress, GRP78 activates the unfolded protein response (UPR), which aims to clear unfolded proteins and restore ER homeostasis. Recently, extracellular secretion of GRP78 was described. However, the pathophysiological relevance of secreted GRP78 in atherosclerosis and endothelial cell inflammation remains to be elucidated. Aim of this study is to investigate the role of GRP78 secretion in endothelial cells. Methods and Results First, we sought to investigate if vascular cells secrete GRP78 during ER Stress. Human coronary artery endothelial cells (HCAEC) were treated with the ER stress inductor tunicamycin for up to 48h. After ER Stress induction, Western Blot and ELISA experiments detected an increased intracellular GRP78 expression. Intriguingly, prolonged ER Stress also promoted extracellular secretion of GRP78. Unbiased proteomic analysis of the HCAEC secretome confirmed that after ER-Stress induction, GRP78 is one of the most highly upregulated extracellular proteins (2.43-fold). Co-incubation with Brefeldin A, an inhibitor of ER-Golgi protein transport, abolished extracellular secretion (Fig.1). Hence, ER-Stress-induced GRP78 secretion is an actively regulated process. Next, the effect of GRP78 containing conditioned medium (CM) on HCAEC was analyzed. For control, HCAEC were co-incubated with BFA, or GRP78-knockdown was performed by siRNA. Treatment with GRP78 containing CM decreased GRP78 mRNA expression in target cells (0.35-fold vs. control [+BFA], p<0.0001). Furthermore, it increased viability ( BFA: 93.0 % vs. 83%, p=0.002; GRP78-siRNA: 94% vs. 85%, p=0.01) and decreased the rate of apoptosis (e.g. BFA: 1.7-fold vs. 5.1, p=0.02). Moreover, expression of markers of vascular inflammation and ER Stress (e.g., NF-κB and CHOP) were decreased when compared to CM without GRP78 (Fig.2). Furthermore, increased H2O2-generation was measured (BFA: 1.4-fold, p>0.001, GRP78-siRNA:1.3-fold, p=0.004) (Fig. 2). To confirm that the beneficial effects of the CM are in fact caused by GRP78, we treated HCAEC with recombinant GRP78 and observed an increased cell viability in a dose-dependent manner (1000 ng/ml: p=0.02 vs. control). CRIPTO is a membrane-bound co-receptor for growth factors and was previously linked to GRP78-signalling. siRNA-Knockdown of CRIPTO reduces viability and leads to cell apoptosis, irrespective of GRP78-treatment. Thus, GRP78-mediated effects may be mediated by CRIPTO. Conclusion Endothelial ER Stress promotes GRP78 secretion. Presence of GRP78 in conditioned medium ameliorates subsequent ER Stress and endothelial inflammation, which play a critical role in atherogenesis. Further investigations are important to shed light on the mechanism of release and the effect on target cells.

Adaptive responses of neuronal cells to chronic endoplasmic reticulum (ER) stress

Accumulation of misfolded proteins or perturbation of calcium homeostasis leads to endoplasmic reticulum (ER) stress and is linked to the pathogenesis of neurodegenerative diseases. Hence, understanding the ability of neuronal cells to cope with chronic ER stress is of fundamental interest. Interestingly, several brain areas uphold functions that enable them to resist challenges associated with neurodegeneration. Here, we established novel clonal mouse hippocampal (HT22) cell lines that are resistant to prolonged (chronic) ER stress induced by thapsigargin (TgR) or tunicamycin (TmR) as in vitro models to study the adaption to ER stress. Morphologically, we observed a significant increase in vesicular und autophagosomal structures in both resistant lines and ‘giant lysosomes’, especially striking in TgR cells. While autophagic activity increased under ER stress, lysosomal function appeared slightly impaired; in both cell lines, we observed enhanced ER-phagy. However, proteomic analyses revealed that various protein clusters and signaling pathways were differentially regulated in TgR versus TmR cells in response to chronic ER stress. Additionally, bioenergetic analyses in both resistant cell lines showed a shift toward aerobic glycolysis (‘Warburg effect’) and a defective complex I of the oxidative phosphorylation (OXPHOS) machinery. Furthermore, ER stress-resistant cells differentially activated the unfolded protein response (UPR) comprising IRE1α and ATF6 pathways. These findings display the wide portfolio of adaptive responses of neuronal cells to chronic ER stress. ER stress-resistant neuronal cells could be the basis to uncover molecular modulators of adaptation, resistance, and neuroprotection as potential pharmacological targets for preventing neurodegeneration.

MTORC1 inhibition impairs activation of the unfolded protein response and induces cell death during ER stress in cardiomyocytes.

The mechanistic target of rapamycin complex 1 (mTORC1) is a central regulator of protein synthesis that senses and responds to a variety of stimuli to coordinate cellular metabolism with environmental conditions. To ensure that protein synthesis is inhibited during unfavorable conditions, translation is directly coupled to the sensing of cellular protein homeostasis. Thus, translation is attenuated during endoplasmic reticulum (ER) stress by direct inhibition of the mTORC1 pathway. However, residual mTORC1 activity is maintained during prolonged ER stress which is thought to be involved in translational reprogramming and adaption to ER stress. By analyzing the dynamics of mTORC1 regulation during ER stress, we unexpectedly found that mTORC1 is transiently activated in cardiomyocytes within minutes at the onset of ER stress before being inhibited during chronic ER stress. This dynamic regulation of mTORC1 appears to be mediated, at least in part, by ATF6, as its activation was sufficient to induce the biphasic control of mTORC1. We further showed that protein synthesis remains dependent on mTORC1 throughout the ER stress response and that mTORC1 activity is essential for posttranscriptional induction of several unfolded protein response elements. Pharmacological inhibition of mTORC1 increased cell death during ER stress, indicating that the mTORC1 pathway serves adaptive functions during ER stress in cardiomyocytes potentially by controlling the expression of the protective unfolded protein response.

Reducing erythroblast apoptosis in β-thalassemia via unfolded protein response (UPR) signaling

Apoptosis plays an important role in ineffective erythropoiesis in β-thalassemia. This early destruction causes severe anemia and contributes significantly to patient mortality. There are several treatment options for this disorder based on the use of drugs that inhibit the destruction of immature erythrocytes in the bone marrow. However, the clinical effectiveness of these drugs has yet to be proven. Therefore, new targets for more effective treatments are needed. The unfolded protein response (UPR) is a biological process that occurs in response to endoplasmic reticulum (ER) stress. To cope with ER stress, unfolded or misfolded proteins activate the UPR pathway, thereby activating a series of cell death pathways. Here, we propose that prolonged ER stress causes apoptosis via UPR signaling during erythroid development in β-thalassemia. Our proposed hypothesis is supported by 1) the involvement of UPR signaling in apoptotic cell death, 2) changes in UPR-related proteins in β-thalassemia, and 3) the availability of UPR signaling inhibitors. In vitro and in vivo studies should be conducted to identify the proteins that participate in the UPR pathway and identify molecular targets for therapy. The β-thalassemia mouse model could be used to evaluate the efficacy of UPR mimic drugs prior to clinical trials. If verified, gaining control over cell fate determination during UPR signaling in β-thalassemia may minimize erythroblast destruction.

Beyond UPR: cell-specific roles of ER stress sensor IRE1α in kidney ischemic injury and transplant rejection

Kidney damage due to ischemia or rejection results in the accumulation of unfolded and misfolded proteins in the endoplasmic reticulum (ER) lumen, a condition known as "ER stress." Inositol-requiring enzyme 1α (IRE1α), the first ER stress sensor found, is a type I transmembrane protein with kinase and endoribonuclease activity. On activation, IRE1α nonconventionally splices an intron from unspliced X-box-binding protein 1 (XBP1) mRNA to produce XBP1s mRNA that encodes the transcription factor, XBP1s, for the expression of genes encoding proteins that mediate the unfolded protein response. The unfolded protein response promotes the functional fidelity of ER and is required for secretory cells to sustain protein folding and secretory capability. Prolonged ER stress can lead to apoptosis, which may result in detrimental repercussions to organ health and has been implicated in the pathogenesis and progression of kidney diseases. The IRE1α-XBP1 signaling acts as a major arm of unfolded protein response and is involved in regulating autophagy, cell differentiation, and cell death. IRE1α also interacts with activator protein-1 and nuclear factor-κB pathways to regulate inflammatory responses. Studies using transgenic mouse models highlight that the roles of IRE1α differ depending on cell type and disease setting. This review covers these cell-specific roles of IRE1α signaling and the potential for therapeutic targeting of this pathway in the context of ischemia and rejection affecting the kidneys.

The role of Chinese herbal medicine in the treatment of diabetic nephropathy by regulating endoplasmic reticulum stress.

Diabetic nephropathy (DN), a prevalent microvascular complication of diabetes mellitus, is the primary contributor to end-stage renal disease in developed countries. Existing clinical interventions for DN encompass lifestyle modifications, blood glucose regulation, blood pressure reduction, lipid management, and avoidance of nephrotoxic medications. Despite these measures, a significant number of patients progress to end-stage renal disease, underscoring the need for additional therapeutic strategies. The endoplasmic reticulum (ER) stress response, a cellular defense mechanism in eukaryotic cells, has been implicated in DN pathogenesis. Moderate ER stress can enhance cell survival, whereas severe or prolonged ER stress may trigger apoptosis. As such, the role of ER stress in DN presents a potential avenue for therapeutic modulation. Chinese herbal medicine, a staple in Chinese healthcare, has emerged as a promising intervention for DN. Existing research suggests that some herbal remedies may confer renoprotective benefits through the modulation of ER stress. This review explores the involvement of ER stress in the pathogenesis of DN and the advancements in Chinese herbal medicine for ER stress regulation, aiming to inspire new clinical strategies for the prevention and management of DN.

Defining the role of endoplasmic reticulum in the initiation of paligenosis

Reprogramming is crucial for cellular renewal in adult organs that lack dedicated stem cells for replacement of cell loss after injury. Because such cell plasticity is likely to be executed by a conserved cellular program, we have begun to identify the conserved cellular-molecular features of the process in which differentiated cells are recruited as progenitors. We have characterized three successive stages by which this occur with differentiated cells: 1) the cells downscale their organelle contents, 2) cells activate a progenitor-like gene network, and 3) cells reenter the cell cycle. We have given this conserved process the name paligenosis. Here, we investigate upstream triggers of paligenosis. Using a high-dose tamoxifen (HD-TAM) injury model to induce paligenosis in zymogenic chief cells of the murine stomach corpus, we observed ultrastructural changes in the endoplasmic reticulum (ER) during paligenosis initiation (e.g., swelling of ER lamellae, liberation of ribosomes from rough ER, and overall loss of ER). This led us to hypothesize that dynamic changes in ER were an upstream event in paligenosis. ER functioning is in part monitored by the Integrated Stress Response (ISR) with the paramount ER stress sensor being PERK, which then autophosphorylates and in turn phosphorylates the α subunit of the eukaryotic initiation factor 2 (eIF2α). Phospho-eIF2α halts global translation while upregulating a specific set of genes to restore homeostasis. Here, we go on to show that HD-TAM activates the ISR in paligenotic gastric chief cells, triggering global attenuation of protein synthesis. However, this “ER stress” ISR pathway must occur in a critical, temporally limited window early in paligenosis, as pharmaceutically-induced prolonged ER stress caused paligenosis to halt in early stages with cells failing to proliferate. Blocking the ISR also halted paligenosis in early stages. Ongoing experiments include the use of the glycosylation-inhibiting drug tunicamycin to determine if inducing the ISR via ER stress is sufficient to initiate paligenosis; and deleting PERK in chief cells during paligenosis using Perk flox/flox ; Mist1 CreERT2 mice. Our results provide initial insights on the dynamic functionality of the ER and its role and necessity during cellular regeneration. This work was supported by funding from the NIH through the National Institute of Diabetes and Digestive and Kidney Diseases and the National Cancer Institute. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Ac-SDKP inhibits Tunicamycin-induced ER stress UPR's sensors and subsequently inflammation and fibrosis in human cardiac fibroblasts

Background: Endoplasmic Reticulum (ER) stress, chronic inflammation and cardiac fibrosis are very common pathophysiologic processes found in hypertension and other cardiovascular diseases. Prolonged ER stress disturbs ER functional capacity, resulting from accumulated unfolded or misfolded proteins in ER lumen. Thereby, cells activate an adaptive mechanism ‘unfolded protein response (UPR)’ to restore ER normal function. Consequently, a series of downstream signaling pathways are activated. N-acetyl-seryl-aspartyl-proline (Ac-SDKP) is an endogenous tetrapeptide released from its precursor thymosin-β4 and found in circulation and organs including heart and kidneys. Previously, our in-vivo studies showed that Ac-SDKP inhibits inflammation and fibrosis through the mechanism that remains elusive. Methods and Results: Quiescent human Cardiac Fibroblast (hCFB) cells were treated with tunicamycin (TM; 0.25 μg/mL) in absence or presence of Ac-SDKP (10 nM) and Tauroursodeoxycholic acid (TUDCA; 500 μg/mL). Ac-SDKP inhibited TM-induced expression of ER stress and downstream mediated UPRs sensors IRE1ɑ, XBP1, ATF4 and CHOP encoding molecular chaperons and protein processing enzymes, at the transcriptional and translational levels [ IRE1α; Ctl (1.0 ± 0.39)***, TM (2.99 ± 0.34), Ac-SDKP +TM (1.9 ± 0.10)*** Tudca +TM (2.5 ± 0.20)***. XBP1; Ctl (1.0 ± 0.36)***, TM (8.56 ± 0.77), Ac-SDKP +TM (4.57 ± 0.4)***, Tudca +TM (5.1 ± 0.6)***. ATF4; Ctl (1.0 ± 0.17)***, TM (5.35 ± 0.63), Ac-SDKP +TM (3.0 ± 0.31)**, Tudca +TM (2.9 ± 0.36)**. CHOP; Ctl (1.0 ± 0.17)***, TM (3.1 ± 0.21), Ac-SDKP +TM (1.75 ± 0.24)***, Tudca +TM (2.0 ± 0.18)**]. The inhibition of ER and UPRs sensors subsequently prevented proinflammatory mediator NF-kB activation, cytokine IL-6 and fibrotic Collagen-I (Coll I) expression [ NF-κB; Ctl (1.0 ± 0.10)*, TM (1.6 ± 0.13), Ac-SDKP +TM (1.08 ± 0.11)†, Tudca +TM (1.09 ± 0.14)†. IL-6; Ctl (1.0 ± 0.18)***, TM (6.8 ± 1.4), Ac-SDKP +TM (1.24 ± 0.23***), Tudca +TM (1.3 ± 0.35)***. Coll I; Ctl (1.0 ± 0.02)*** TM (2.5 ± 0.43), Ac-SDKP +TM (1.13 ± 0.13)***, Tudca +TM (1.22 ± 0.18)***]. TM also induced collagen production (Hydroxyproline assay), which was significantly inhibited by Ac-SDKP. The common ER stress inhibitor, TUDCA, exhibited similar inhibitory profile as Ac-SDKP. Conclusion: Ac-SDKP prevents inflammation and fibrosis in hCFB, likely by blocking the overexpressed detrimental ER stress UPRs sensors and its downstream molecular chaperon. Notes: Data are shown a mean ± SEM, p values were calculated using one-way ANOVA compared to CTL. All the experiments are representative of n = 5 – 8.***:p ≤ 0.0001 vs TM; **:p ≤ 0.001 vs TM; *: p ≤ 0.05 vs TM; †:p ≤ 0.05 vs TM. NIH This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Nebivolol Alleviates Vascular Endothelial Insulin Resistance by Inhibiting Endoplasmic Reticulum Stress.

Vascular endothelial insulin resistance (IR) is an important risk factor in the development of vascular complications in diabetes. Prolonged endoplasmic reticulum stress (ERS) contributes to the development and progression of endothelial IR. The current study assessed the effects and mechanism of nebivolol on vascular IR in Goto-Kakizaki (GK) rats and endothelial IR induced by high glucose (33.3 mmol/L) associated with high insulin (10-7 mol/L) in human aortic endothelial cells (HAECs). Rats were divided into Wistar, Wistar + Neb (Wistar rats treated with nebivolol, 10 mg/kg, ig), GK, and GK + Neb (GK rats treated with nebivolol, 10 mg/kg, ig). GK rats showed hyperglycemia, dyslipidemia, impaired glucose homeostasis, metabolic IR, reduced relaxation to insulin, and lower serum nitric oxide (NO) level. Treatment with nebivolol for 4 months ameliorated insulin's vasorelaxation and NO production, and relieved dyslipidemia in GK rats. Additionally, nebivolol increased glucose uptake and NO level in the endothelial IR group in vitro. Nebivolol increased aortic expressions of IRS-1/PI3K/Akt/eNOS relative proteins and GLUT4 and reduced expressions of ERS markers (ATF6, GRP78, and CHOP, p-JNK/JNK). Furthermore, both nebivolol and TUDCA (ERS inhibitor) alleviated the attenuated IRS-1PI3K/Akt/eNOS pathway and enhanced ERS in HAECs IR. Tunicamycin (ERS inducer) not only induced endothelial IR but also blocked nebivolol's alleviation on the IRS-1PI3K/Akt/eNOS pathway and ERS. Nebivolol ameliorated endothelial IR partially by inhibiting ERS and then regulating the IRS-1/PI3K/Akt/eNOS signal.