Endoplasmic reticulum stress-induced IRE1α activation mediates cross-talk of GSK-3β and XBP-1 to regulate inflammatory cytokine production

Gsk3 Signalling and Redox Status in Bipolar Disorder: Evidence from Lithium Efficacy

Objective. To discuss the link between glycogen synthase kinase-3 (GSK3) and the main biological alterations demonstrated in bipolar disorder (BD), with special attention to the redox status and the evidence supporting the efficacy of lithium (a GSK3 inhibitor) in the treatment of BD. Methods. A literature research on the discussed topics, using Pubmed and Google Scholar, has been conducted. Moreover, a manual selection of interesting references from the identified articles has been performed. Results. The main biological alterations of BD, pertaining to inflammation, oxidative stress, membrane ion channels, and circadian system, seem to be intertwined. The dysfunction of the GSK3 signalling pathway is involved in all the aforementioned “biological causes” of BD. In a complex scenario, it can be seen as the common denominator linking them all. Lithium inhibition of GSK3 could, at least in part, explain its positive effect on these biological dysfunctions and its superiority in terms of clinical efficacy. Conclusions. Deepening the knowledge on the molecular bases of BD is fundamental to identifying the biochemical pathways that must be targeted in order to provide patients with increasingly effective therapeutic tools against an invalidating disorder such as BD.

Endoplasmic Reticulum Stress Is a Danger Signal Promoting Innate Inflammatory Responses in Bronchial Epithelial Cells

Endoplasmic reticulum (ER) stress is associated with chronic pulmonary inflammatory diseases. We hypothesized that the combined activation of both Toll-like receptor (TLR) signaling and ER stress might increase inflammatory reactions in otherwise tolerant airway epithelial cells. Indeed, ER stress resulted in an increased response of BEAS-2B and human primary bronchial epithelial cells to pathogen-associated molecular pattern stimulation with respect to IL6 and IL8 production. ER stress elevated p38 and ERK MAP kinase activation, and pharmacological inhibition of these kinases could inhibit the boosting effect. Knockdown of unfolded protein response signaling indicated that mainly PERK and ATF6 were responsible for the synergistic activity. Specifically, PERK and ATF6 mediated increased MAPK activation, which is needed for effective cytokine secretion. We conclude that within airway epithelial cells the combined activation of TLR signaling and ER stress-mediated MAPK activation results in synergistic proinflammatory activity. We speculate that ER stress, present in various chronic pulmonary diseases, boosts TLR signaling and therefore proinflammatory cytokine production, thus acting as a costimulatory danger signal.

The unfolded protein response in immunity and inflammation

The unfolded protein response (UPR) is a highly conserved pathway that allows the cell to manage endoplasmic reticulum (ER) stress that is imposed by the secretory demands associated with environmental forces. In this role, the UPR has increasingly been shown to have crucial functions in immunity and inflammation. In this Review, we discuss the importance of the UPR in the development, differentiation, function and survival of immune cells in meeting the needs of an immune response. In addition, we review current insights into how the UPR is involved in complex chronic inflammatory diseases and, through its role in immune regulation, antitumour responses.

The Unfolded Protein Response in Homeostasis and Modulation of Mammalian Immune Cells

The endoplasmic reticulum (ER) plays important roles in eukaryotic protein folding and lipid biosynthesis. Several exogenous and endogenous cellular sources of stress can perturb ER homeostasis leading to the accumulation of unfolded proteins in the lumen. Unfolded protein accumulation triggers a signal-transduction cascade known as the unfolded protein response (UPR), an adaptive mechanism which aims to protect cells from protein aggregates and to restore ER functions. Further to this protective mechanism, in immune cells, UPR molecular effectors have been shown to participate in a wide range of biological processes such as cell differentiation, survival and immunoglobulin and cytokine production. Recent findings also highlight the involvement of the UPR machinery in the maturational program and antigen presentation capacities of dendritic cells. UPR is therefore a key element in immune system homeostasis with direct implications on both adaptive and innate immune responses. The present review summarizes the knowledge on the emerging roles of UPR signaling cascades in mammalian immune cells as well as the consequences of their dysregulation in relation to the pathogenesis of several diseases.

Epithelial ER Stress in Crohn's Disease and Ulcerative Colitis

Research in the past decade has greatly expanded our understanding of the pathogenesis of inflammatory bowel disease, which includes Crohn's disease and ulcerative colitis. In addition to the sophisticated network of immune response, the epithelial layer lining the mucosa has emerged as an essential player in the development and persistence of intestinal inflammation. As the frontline of numerous environmental insults in the gut, the intestinal epithelial cells are subject to various cellular stresses. In eukaryotic cells, disturbance of endoplasmic reticulum homeostasis may lead to the accumulation of unfolded and misfolded proteins in the ER lumen, a condition called ER stress. This cellular process activates the unfolded protein response, which functions to enhance the ER protein folding capacity, alleviates the burden of protein synthesis and maturation, and activates ER-associated protein degradation. Paneth and goblet cells, 2 secretory epithelial populations in the gut, are particularly sensitive to ER stress on environmental or genetic disturbances. Recent studies suggested that epithelial ER stress may contribute to the pathogenesis of Crohn's disease and ulcerative colitis by compromising protein secretion, inducing epithelial cell apoptosis and activating proinflammatory response in the gut. Our knowledge of ER stress in intestinal epithelial function may open avenue to new inflammatory bowel disease therapies by targeting the ER protein folding homeostasis in the cells lining the intestinal mucosa.

The role of the endoplasmic reticulum stress in stemness, pluripotency and development

The molecular machinery of endoplasmic reticulum (ER) integrates various intracellular and extracellular cues to maintain homeostasis in diverse physiological or pathological scenarios. ER stress and the unfolded protein response (UPR) have been found to mediate molecular and biochemical mechanisms that affect cell proliferation, differentiation, and apoptosis. Although a number of reviews on the ER stress response have been published, comprehensive reviews that broadly summarize ER physiology in the context of pluripotency, embryonic development, and tissue homeostasis are lacking. This review complements the current ER literature and provides a summary of the important findings on the role of the ER stress and UPR in embryonic development and pluripotent stem cells.

Altered Expression of Endoplasmic Reticulum Stress Associated Genes in Hippocampus of Learned Helpless Rats: Relevance to Depression Pathophysiology

The unfolded protein response (UPR) is an evolutionarily conserved defensive mechanism that is used by cells to correct misfolded proteins that accumulate in the endoplasmic reticulum. These proteins are misfolded as a result of physical stress on a cell and initiate a host of downstream effects that govern processes ranging from inflammation to apoptosis. To examine whether UPR system plays a role in depression, we examined the expression of genes that are part of the three different pathways for UPR activation, namely GRP78, GRP94, ATF6, XBP-1, ATF4, and CHOP using an animal model system that distinguishes vulnerability (learned helpless, LH) from resistance (non-learned helpless, NLH) to develop depression. Rats were exposed to inescapable shock on days 1 and 7 and were tested for escape latency on day 14. Rats not given shock but tested for escape latency were used as tested control (TC). Plasma corticosterone (CORT) levels were measured. Expression levels of various UPR associated genes were determined in hippocampus using qPCR. We found that the CORT level was higher in LH rats compared with TC and NLH rats. Expression of GRP78, GRP94, ATF6, and XBP-1 were significantly upregulated in LH rats compared with TC or NLH rats, whereas NLH rats did not show such changes. Expression levels of ATF4 and CHOP showed trends toward upregulation but were not significantly altered in LH or NLH group. Our data show strong evidence of altered UPR system in depressed rats, which could be associated with development of depressive behavior.

Curcumin induces cell death of human papillary thyroid carcinoma BCPAP cells through endoplasmic reticulum stress

Curcumin induced cell death of BCPAP cells via ER stress with activation of the ATF6/XBP-1 signaling pathway and Ca²⁺ release.

Inhibition of osteolysis after local administration of osthole in a TCP particles-induced osteolysis model

PURPOSE

Wear debris-induced osteolysis and aseptic loosening are the most frequent late complications of total joint arthroplasty leading to revision of the prosthesis. However, no effective measures for the prevention and treatment of particles-induced osteolysis currently exist. Here, we investigated the efficacy of local administration of osthole on tricalcium phosphate (TCP) particles-induced osteolysis in a murine calvarial model.

METHODS

TCP particles were implanted over the calvaria of ICR mice, and established TCP particles-induced osteolysis model. On days one, four, seven, ten and thirteen post-surgery, osthole (10 mg/kg) or phosphate buffer saline (PBS) were subcutaneously injected into the calvaria of TCP particles-implanted or sham-operated mice. Two weeks later, blood, the periosteum and the calvaria were collected and processed for bone turnover markers, pro-inflammatory cytokine, histomorphometric and molecular analysis.

RESULTS

Osthole (10 mg/kg) markedly prevented TCP particles-induced osteoclastogenesis and bone resorption in a mouse calvarial model. Osthole also inhibited the decrease of serum osteocalcin level and calvarial alkaline phosphatase (ALP) activity, and prevented the increase in the activity of tartrate resistant acid phosphatase (TRAP) and cathepsin K in the mouse calvaria. Furthermore, osthole obviously reduced the release of tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) into the periosteum. Western blotting demonstrated TCP particles caused a remarkable endoplasmic reticulum (ER) stress response in the mouse calvaria, which was obviously blocked by osthole treatment.

CONCLUSION

These results suggest that local administration of osthole inhibits TCP particles-induced osteolysis in the mouse calvarial in vivo, which may be mediated by inhibition of the ER stress signaling pathway, and it will be developed as a new drug in the prevention and treatment of destructive diseases caused by prosthetic wear particles.

The Chondroprotective Role of TMF in PGE2-Induced Apoptosis Associating with Endoplasmic Reticulum Stress

Endoplasmic reticulum stress (ERS) has been demonstrated to exhibit a critical role in osteoarthritic chondrocytes. Whether 5,7,3′,4′-tetramethoxyflavone (TMF) plays the chondroprotective role in inhibition of PGE₂-induced chondrocytes apoptosis associating with ERS has not been reported. To investigate this, the activation of PERK, ATF6, and IRE1 signaling pathways in ERS in chondrocytes pretreated with PGE₂ was studied. By treatment with PGE₂, the chondrocytes apoptosis was significantly increased, the proapoptotic CHOP and JNK were upregulated, the prosurvival GRP78 and XBP1 were downregulated, and GSK-3β was also upregulated. However, TMF exhibited the effectively protective functions via counteracting these detrimental effects of PGE₂. Finally, the inflammatory cytokine PGE₂ can activate ERS signaling and promote chondrocytes apoptosis, which might be associated with upregulation of GSK-3β. TMF exhibits a chondroprotective role in inhibiting PGE₂-induced ERS and GSK-3β.