Endoplasmic Reticulum Stress-related Signaling Pathways Research Articles

ER stress in mouse serotonin neurons triggers a depressive phenotype alleviated by ketamine targeting eIF2α signaling

Depression is a devastating mood disorder that causes significant disability worldwide. Current knowledge of its pathophysiology remains modest and clear biological markers are lacking. Emerging evidence from human and animal models reveals persistent alterations in endoplasmic reticulum (ER) homeostasis, suggesting that ER stress-related signaling pathways may be targets for prevention and treatment. However, the neurobiological basis linking the pathways involved in depression-related ER stress remains unknown. Here, we report that an induced model of ER stress in mouse serotonin (5-HT) neurons is associated with reduced Egr1-dependent 5-HT cellular activity and 5-HT neurotransmission, resulting in neuroplasticity deficits in forebrain regions and a depressive-like phenotype. Ketamine administration engages downstream eIF2α signaling to trigger rapid neuroplasticity events that rescue the depressive-like effects. Collectively, these data identify ER stress in 5-HT neurons as a cellular pathway involved in the pathophysiology of depression and show that eIF2α is critical in eliciting ketamine's fast antidepressant effects.

Inhibition of SK2 and ER stress ameliorated inflammation and apoptosis in liver ischemia-reperfusion injury.

Ischemia-reperfusion injury (IRI) remains a major cause of mortality and morbidity after liver surgery. Endoplasmic reticulum (ER) stress is a critical mechanism of inflammatory injury during hepatic IRI. In this study, we investigated the effect of sphingosine kinases 2 (SK2) on ER stress and hepatic IRI. We established hepatic IRI mice and hepatocellular hypoxia/reoxygenation in vitro model. We observed the SK2 and ER stress protein IRE1α expression. Then, we used an SK2 inhibitor and knocked down IRE1α/SK2, to observe the effect of SK2 during IRI. Our results showed that the expression of ER stress and SK2 was significantly elevated during hepatic IRI. Inhibition of SK2 ameliorated liver inflammation and reduced cell apoptosis in hepatic IRI mice. Consistently, we found that the inhibition of IRE1α also downregulated SK2 expression and reduced mitochondrial membrane permeability. Furthermore, the knockdown of SK2 could also reduce cell damage and reduce the expression of inflammatory factors but did not influence ER stress-related signaling pathway. Taken together, our results suggested that ER stress and SK2 played important and regulatory roles in hepatic IRI. Inhibition of ER stress and SK2 could significantly improve liver function after hepatic IRI.

Role of estrogen receptors in thyroid toxicity induced by mono (2-ethylhexyl) phthalate via endoplasmic reticulum stress: An in vitro mechanistic investigation

Mono(2-ethylhexyl) phthalate (MEHP) can influence the expression of estrogen receptors (ERs) and induce thyroid injury. The expression of ERs can be related to thyroid disease and abnormal expression of ERs has been associated with activation of endoplasmic reticulum stress. This study aimed to clarify the role of ERs in MEHP-induced thyroid damage via endoplasmic reticulum stress. We exposed Nthy-ori 3–1 cells to different doses of MEHP. We found that after the exposure, the cell viability and the expression levels of thyroid hormone metabolism-related proteins decreased, while the apoptosis level and the expression levels of ERs (ERα and GPR30) increased. Three endoplasmic reticulum stress-related signaling pathways were activated by MEHP. After ERα and GPR30 were knocked down, these three pathways were inhibited and the thyroid toxicity was alleviated. Taken together, our results indicate that MEHP can induce thyroid toxicity by upregulating the expression of ERs, further activating endoplasmic reticulum stress.

Narrative Review: Phytocannabinoids and their Potential Use as a Phytochemotherapy

Cannabis sativa L. has been used as an herbal medicine for centuries. This plant is a natural source of cannabinoids, including Δ-9-tetrahydrocannabinol (THC) and cannabidiol (CBD), the two major phytocannabinoids that have been a recently interested research topic on their therapeutic properties. The human endocannabinoid system generally consists of receptors, endogenous ligands, and metabolizing enzymes, and plays an important role in various physiological and pathological effects. Based on cancer therapy, phytocannabinoids have mainly been used for palliative care treatment, i.e. relieving nausea and vomiting caused by chemotherapy and stimulating appetite. Additionally, in many preclinical experiments, including in vitro and in vivo studies, cannabinoids have exhibited anticancer effects against numerous cancer cell lines through various mechanisms. For example, THC induced apoptosis of cancer cells via cannabinoid receptors by a stimulation of ceramide synthesis led to an activation of the endoplasmic reticulum stress-related signaling pathway, and the induction of autophagy through a calmodulin-activated kinase kinase β. In contrast, the anticancer activity of CBD is related to other types of receptors, i.e. orphan G-protein coupled receptor 55 (GPR55), transient receptor potential vanilloid receptor 1 (TRPV1), transient receptor potential melastatin 8 (TRPM8), which mainly relied on the stimulation of reactive oxygen species (ROS) production, leading to induced cancer cell death. Although, there are many reports on anticancer properties of phytocannabinoids, in vitro and in vivo, high quality clinical trials concerning their efficacy and safety are still essential to approve their potential use as a phytochemotherapy.

Research Progress on Mechanism of Podocyte Depletion in Diabetic Nephropathy.

Diabetic nephropathy (DN) together with glomerular hyperfiltration has been implicated in the development of diabetic microangiopathy in the initial stage of diabetic diseases. Increased amounts of urinary protein in DN may be associated with functional and morphological alterations of podocyte, mainly including podocyte hypertrophy, epithelial-mesenchymal transdifferentiation (EMT), podocyte detachment, and podocyte apoptosis. Accumulating studies have revealed that disruption in multiple renal signaling pathways had been critical in the progression of these pathological damages, such as adenosine monophosphate-activated kinase signaling pathways (AMPK), wnt/β-catenin signaling pathways, endoplasmic reticulum stress-related signaling pathways, mammalian target of rapamycin (mTOR)/autophagy pathway, and Rho GTPases. In this review, we highlight new molecular insights underlying podocyte injury in the progression of DN, which offer new therapeutic targets to develop important renoprotective treatments for DN over the next decade.

Cantharidin Induced Oral Squamous Cell Carcinoma Cell Apoptosis via the JNK-Regulated Mitochondria and Endoplasmic Reticulum Stress-Related Signaling Pathways.

Oral cancer is a subtype of head and neck cancer which represents 2.65% of all human malignancies. Most of oral cancer is histopathologically diagnosed as oral squamous cell carcinoma (OSCC). OSCC is characterized by a high degree of local invasion and a high rate of metastasis to the cervical lymph nodes. How to prevention and treatment of OSCC is important and imperative. Here, we investigated the therapeutic effect and molecular mechanism of cantharidin, an active compound isolated from blister beetles, on OSCC in vitro. Results showed that cantharidin significantly decreased cell viability in human tongue squamous carcinoma-derived SAS, CAL-27, and SCC-4 cell lines. The further mechanistic studies were carried out in SAS cells. Cantharidin also significantly increased apoptosis-related signals, including caspase-9, caspase-7 and caspase-3 proteins. Besides, cantharidin decreased mitochondrial transmembrane potential (MMP) and induced cytochrome c and apoptosis inducing factor (AIF) release. Cantharidin also increased Bax, Bid, and Bak protein expressions and decreased Bcl-2 protein expression. Cantharidin could also increase the endoplasmic reticulum (ER) stress signals, including the expressions of phosphorylated eIF-2α and CHOP, but not Grp78 and Grp94. Furthermore, cantharidin reduced pro-caspase-12 protein expression. In signals of mitogen-activated protein kinases, cantharidin increased the phosphorylation of JNK, but not ERK and p38. Transfection of shRNA-JNK to OSCC cells effectively reversed the cantharidin-induced cell apoptotic signals, including the mitochondrial and ER stress-related signaling molecules. Taken together, these findings suggest that cantharidin induces apoptosis in OSCC cells via the JNK-regulated mitochondria and ER stress-related signaling pathways.

YiQiFuMai Powder Injection Ameliorates Cerebral Ischemia by Inhibiting Endoplasmic Reticulum Stress-Mediated Neuronal Apoptosis.

YiQiFuMai (YQFM) powder injection as a modern preparation derived from Sheng Mai San, a traditional Chinese medicine, has been widely used in the treatment of cardiovascular and cerebrovascular diseases. However, its neuroprotective effect and underlying mechanism in cerebral ischemia remain to be explored. The present study was designed to investigate the neuroprotective effect of YQFM on endoplasmic reticulum (ER) stress-mediated neuronal apoptosis in the permanent middle cerebral artery occlusion- (MCAO-) injured mice and the oxygen-glucose deprivation- (OGD-) induced pheochromocytoma (PC12) cells. The results showed that single administration of YQFM (1.342 g/kg, i.p.) could reduce the brain infarction and improve the neurological deficits and the cerebral blood flow (CBF) after MCAO for 24 h in mice. Moreover, incubation with YQFM (100, 200, and 400 μg/mL) could increase the cell viability, decrease the caspase-3 activity, and inhibit the cell apoptosis in OGD-induced PC12 cells for 12 h. In addition, YQFM treatment could significantly modulate cleaved caspase-3 and Bcl-2 expressions and inhibit the expressions of ER stress-related marker proteins and signaling pathways in vivo and in vitro. In conclusion, our findings provide the first evidence that YQFM ameliorates cerebral ischemic injury linked with modulating ER stress-related signaling pathways, which provided some new insights for its prevention and treatment of cerebral ischemia diseases.

C-Jun Regulates ER Stress Signaling to Promote Chemotherapy Resistance in Acute Myeloid Leukemia

The first-line treatment for acute myeloid leukemia (AML) patients is a combination of cytarabine (Ara-C) and an antracycline, such as daunorubicin (Dnr). However, one third of AML patients are refractory to first-line therapy and 35-60% of those who do initially respond to chemotherapy relapse with resistant disease. Therefore, identifying and deciphering the molecular abnormalities that contribute to chemotherapy resistance in AML is the critical first step for developing new therapies that overcome chemotherapy resistance. In our study, we found that expression of the proto-oncogene c-JUN is elevated in patient-derived AML samples compared with normal hematopoietic progenitor cells. Additionally, expression and phosphorylation of c-JUN further increased in human AML cells exposed to Ara-C or Dnr. Confirming functional functional importance of c-JUN in human AML cells, we found that short hairpin RNAs (shRNAs) that specifically target c-JUN suppress cell growth and induce apoptosis in several genetically distinct human AML cell lines (Kasumi-1, MOLM-14, MV4-11, NOMO-1, OCI-AML3, SKM-1, THP-1 and U937). Furthermore, we have observed that shRNA-mediated inhibition of c-JUN also significantly potentiated the cytotoxic effects of Ara-C (p<0.05), suggesting that c-JUN is required for AML cell survival and may play a critical role in chemotherapy resistance.To elucidate the molecular mechanism by which c-JUN promotes AML cell survival and chemotherapy resistance, we performed global gene expression analyses (RNA-seq) of THP-1 cells expressing either non-targeting control or c-JUN shRNAs. From these analyses, we found that c-JUN inhibition results in decreased expression of numerous genes that are activated in response to endoplasmic reticulum (ER) stress, including a significant reduction in the expression of genes regulated by the ER stress-activated transcription factors ATF4 and DDIT3 (p=2.44x10-20).We therefore hypothesized that c-JUN may control ER stress signaling pathways to promote cell survival and chemotherapy resistance in AML. In support of this hypothesis, we have found that c-JUN inhibition blunts the activation of ER-stress related pathways stimulated by chemical inducers of ER stress, thapsigargin and tunicamycin. Additionally, we found that Ara-C treatment activates ER stress-related signaling pathways and that this activation can be reversed by c-JUN inhibition, which correlates with the increased death of c-JUN shRNA-expressing AML cells exposed to Ara-C.To further elucidate the role of ER-stress related pathways in AML, we focused on the serine/threonine kinase, PERK (encoded by EIF2AK3), which activates signaling pathways that aim to ameliorate ER stress and promote cell survival. Similar to c-JUN inhibition, shRNA-mediated inhibition of PERK not only increased cell death but also enhanced the cytotoxicity of Ara-C in AML cells, indicating that this ER stress pathway is a potential therapeutic target to increase the effectiveness of standard chemotherapy.To investigate the therapeutic potential of targeting the PERK pathway, we treated human AML cells with a chemical inhibitor of PERK, GSK2656157, in combination with Ara-C and found that certain concentrations of the two drugs synergistically increased AML cell killing versus each drug alone. Using leukemia cells derived from a mouse model of AML driven by the leukemogenic fusion allele MLL-AF9 alone or in combination with a FLT3 internal tandem duplication, we observed that the combination of GSK2656157 and Ara-C significantly reduced colony growth in methylcellulose by 80% compared with each drug alone (p<0.05).These findings suggest that c-JUN plays a vital role in mitigating ER stress in AML cells and that targeting c-JUN and/or ER stress signaling pathways is a novel potential therapeutic approach for improving the effectiveness of current first-line AML therapies. DisclosuresNo relevant conflicts of interest to declare.

PERK Activation Preserves the Viability and Function of Remyelinating Oligodendrocytes in Immune-Mediated Demyelinating Diseases

Remyelination occurs in multiple sclerosis (MS) lesions but is generally considered to be insufficient. One of the major challenges in MS research is to understand the causes of remyelination failure and to identify therapeutic targets that promote remyelination. Activation of pancreatic endoplasmic reticulum kinase (PERK) signaling in response to endoplasmic reticulum stress modulates cell viability and function under stressful conditions. There is evidence that PERK is activated in remyelinating oligodendrocytes in demyelinated lesions in both MS and its animal model, experimental autoimmune encephalomyelitis (EAE). In this study, we sought to determine the role of PERK signaling in remyelinating oligodendrocytes in MS and EAE using transgenic mice that allow temporally controlled activation of PERK signaling specifically in oligodendrocytes. We demonstrated that persistent PERK activation was not deleterious to myelinating oligodendrocytes in young, developing mice or to remyelinating oligodendrocytes in cuprizone-induced demyelinated lesions. We found that enhancing PERK activation, specifically in (re)myelinating oligodendrocytes, protected the cells and myelin against the detrimental effects of interferon-γ, a key proinflammatory cytokine in MS and EAE. More important, we showed that enhancing PERK activation in remyelinating oligodendrocytes at the recovery stage of EAE promoted cell survival and remyelination in EAE demyelinated lesions. Thus, our data provide direct evidence that PERK activation cell-autonomously enhances the survival and preserves function of remyelinating oligodendrocytes in immune-mediated demyelinating diseases.

Endoplasmic reticulum stress mediates aristolochic acid I-induced apoptosis in human renal proximal tubular epithelial cells

Aristolochic acid (AA), derived from the Aristolochia species, has been associated with aristolochic acid nephropathy (AAN), which has emerged as a worldwide disease. Aristolochic acid I (AAI) is the main ingredient of AA, and the underlying mechanisms for AAI-induced nephrotoxicity are still unclear. In this study, we investigated whether endoplasmic reticulum (ER) stress was involved in AAI-induced nephrotoxicity. The results showed that treatment of HK-2 cells (a human proximal tubular epithelial cell line) with AAI caused an increase in eukaryotic initiation factor-2α (eIF2α) phosphorylation, X-box binding protein 1 (XBP1) mRNA splicing and the expression of glucose-regulated protein (GRP) 78 and CAAT/enhancer-binding protein-homologous protein (CHOP). These events represent typical markers of the ER stress-related signaling pathway. Pretreatment with 4-phenylbutyrate (4-PBA) or salubrinal (Sal) significantly inhibited AAI-induced apoptosis, indicating the role of ER stress in AAI-induced apoptosis. In addition, AAI-induced cell death followed an increase of reactive oxygen species (ROS) formation in HK-2 cells. Pretreatment with N-acetyl cysteine (NAC) or glutathione (GSH) significantly inhibited AAI-induced ER stress proteins and cell death, suggesting that ROS mediate AAI-induced ER stress. Taken together, these results suggest that the ER stress response is involved in apoptosis induced by AAI in HK-2 cells, thus offering a new insight into the nephrotoxicity of AAI.

Increased Expression of Endoplasmic Reticulum Stress-Related Signaling Pathway Molecules in Multiple Sclerosis Lesions

Activation of endoplasmic reticulum (ER) stress-related cell signals has been reported in several neurologic disorders and may contribute to neurodegeneration. Endoplasmic reticulum stress is also linked to ischemic injury. However, activation of an ER stress response has not been investigated in multiple sclerosis (MS) lesions. We detected increased expression of ER stress-associated C/EBP homologous protein, immunoglobulin heavy chain-binding protein, and X-box-binding protein 1 in multiple cell types, including oligodendrocytes, astrocytes, T cells, and microglia in active MS lesions. Semiquantitative analysis of expression in active, chronic active, and chronic inactive lesions indicated that levels of immunoglobulin heavy chain-binding protein were significantly higher in acute lesions than in non-MS controls or MS normal-appearing white matter, and that ER stress-associated C/EBP homologous protein was upregulated to the greatest extent at the edges of chronic active lesions. Because demyelination may be triggered by a tissue response to ischemia-like conditions, changes in the hypoxia-related antigen D-110 were also investigated, and it was found that increased ER stress-associated C/EBP homologous protein expression can occur in either the presence or absence of D-110. A possible link between a perturbed ER and lesion development in MS suggests a signaling pathway that may represent a new therapeutic target in MS.