Calreticulin translocation aggravates endoplasmic reticulum stress-associated apoptosis during cardiomyocyte hypoxia/reoxygenation

The role of taurine through endoplasmic reticulum in physiology and pathology

Taurine is a sulfur-containing amino acid found in many cell organelles that plays a wide range of biological roles, including bile salt production, osmoregulation, oxidative stress reduction, and neuromodulation. Taurine treatments have also been shown to ameliorate the onset and development of many diseases, including hypertension, fatty liver, neurodegenerative diseases and ischemia-reperfusion injury, by exerting antioxidant, anti-inflammatory, and antiapoptotic effects. The endoplasmic reticulum (ER) is a dynamic organelle involved in a wide range of cellular functions, including lipid metabolism, calcium storage and protein stabilization. Under stress, the disruption of the ER environment leads to the accumulation of misfolded proteins and a characteristic stress response called the unfolded protein response (UPR). The UPR protects cells from stress and helps to restore cellular homeostasis, but its activation promotes cell death under prolonged ER stress. Recent studies have shown that ER stress is closely related to the onset and development of many diseases. This article reviews the beneficial effects and related mechanisms of taurine by regulating the ER in different physiological and pathological states, with the aim of providing a reference for further research and clinical applications.

Cytoplasmic vacuolation with endoplasmic reticulum stress directs sorafenib induced non-apoptotic cell death in hepatic stellate cells

The activated hepatic stellate cells (HSCs) are the major cells that secrete the ECM proteins and drive the pathogenesis of fibrosis in chronic liver disease. Targeting of HSCs by modulating their activation and proliferation has emerged as a promising approach in the development of anti-fibrotic therapy. Sorafenib, a multi-kinase inhibitor has shown anti-fibrotic properties by inhibiting the survival and proliferation of HSCs. In present study we investigated sorafenib induced cytoplasmic vacuolation mediated decreased cell viability of HSCs in dose and time dependent manner. In this circumstance, sorafenib induces ROS and ER stress in HSCs without involvement of autophagic signals. The protein synthesis inhibitor cycloheximide treatment significantly decreased the sorafenib-induced cytoplasmic vacuolation with increasing cell viability. Antioxidant human serum albumin influences the viability of HSCs by reducing sorafenib induced vacuolation and cell death. However, neither caspase inhibitor Z-VAD-FMK nor autophagy inhibitor chloroquine could rescue the HSCs from sorafenib-induced cytoplasmic vacuolation and cell death. Using TEM and ER organelle tracker, we conclude that the cytoplasmic vacuoles are due to ER dilation. Sorafenib treatment induces calreticulin and GPR78, and activates IRE1α-XBP1s axis of UPR pathway, which eventually trigger the non-apoptotic cell death in HSCs. This study provides a notable mechanistic insight into the ER stress directed non-apoptotic cell death with future directions for the development of efficient anti-fibrotic therapeutic strategies.

PERK-Dependent Activation of the JAK2/STAT3 Pathway Contributes to High Glucose-Induced Extracellular Matrix Deposition in Renal Tubular Epithelial Cells

BACKGROUND

Although the deposition of extracellular matrix (ECM) is critical leading to tubular damage in diabetic kidney disease (DKD), the mechanism still remains unclear. The purpose of this study was to demonstrate a role for protein kinase R-like endoplasmic reticulum kinase (PERK) (a protein located in the endoplasmic reticulum membrane) in this pathologic process.

METHODS

NRK-52E cells were grown in the media containing different concentrations of glucose or thapsigargin for different durations. Cells were subsequently incubated with or without AG490, a selective inhibitor of Janus kinase 2 (JAK2) or GSK2606414 (a selective PERK inhibitor). We evaluated the production of TGF-β1, fibronectin, and collagen I proteins by ELISA. The levels of 78 kD-glucose-regulated protein (GRP78) and PERK, as well as the phosphorylation statues of PERK and JAK2/signal transducer and activator of transcription (STAT3), were determined by western blotting analysis.

RESULTS

We showed that the increased phosphorylation of JAK2 and STAT3 was accompanied by overexpression of TGF-β1 and ECM deposition in high glucose medium. Disruption of the JAK2/STAT3 pathway with AG490 significantly prevents the high glucose-induced increase in TGF-β1, fibronectin, and collagen I. High glucose induced the overproduction of GRP78 and phosphorylation of PERK, which indicated that endoplasmic reticulum stress (ERS) was triggered in NRK-52E cells cultured under high glucose condition. Inhibition of PERK phosphorylation with GSK2606414, however, blocked the effect of JAK2/STAT3 on the production of TGF-β1 and ECM components in NRK-52E cells.

CONCLUSION

Our data indicated that the ECM accumulation induced by high glucose arouse via the PERK-dependent JAK2/STAT3-signaling pathway in renal tubular epithelial cells.

The Attenuating Effect of the Intraovarian Bone Morphogenetic Protein 4 on Age-Related Endoplasmic Reticulum Stress in Chicken Follicular Cells

In the poultry, only less than 5% primordial follicles in the ovary can develop into the prehierarchical follicles (PHFs) leading to progressive development, ovulation, and egg formation. This low rate of recruitment indicates a huge potential for improvement of the laying performance. A great reduction in egg production is caused by aging with extensive follicular atresia. In this study, age-related changes in the laying performance and ovarian status were compared between the peak-lay (D280) and aged (D580) chickens. Subsequently, a cross coculture of PHFs and granulosa cells (GCs) from D280 or D580 hens was adopted to reveal the mechanism of declined follicle development. Results showed that persistent endoplasmic reticulum (ER) stress in GCs of the aged hens was accompanied with intensified apoptosis. Bone morphogenetic protein 4 (BMP4) secreted by GCs of PHFs in D280 hens was capable of relieving ER stress and improving follicular dominance for selection in D580 hens. During this action, BMP4 reduced free calreticulin (CALR, an ER marker) content and attenuated cell apoptosis in PHFs of D580 hens via the PERK-CHOP-BCL2/caspase3 or CALR-Ca²⁺-BCL2-caspase12 pathway. Furthermore, BMP4 prevented follicular atresia by promoting production of steroid hormones to improve survival of GCs in PHFs from the aged hens. In conclusion, intensified ER stress and apoptosis occurred in GCs of PHFs in aged chickens, while BMP4 secreted by GCs was capable of improving follicular viability by alleviating ER stress to promote follicular development.

Changes in blood-brain barrier permeability and ultrastructure, and protein expression in a rat model of cerebral hypoperfusion

Cerebral hypoperfusion involved a reduction in cerebral blood flow, leading to neuronal dysfunction, microglial activation and white matter degeneration. The effects on the blood-brain barrier (BBB) however, have not been well-documented. Here, two-vessel occlusion model was adopted to mimic the condition of cerebral hypoperfusion in Sprague-Dawley rats. The BBB permeability to high and low molecular weight exogenous tracers i.e. Evans blue dye and sodium fluorescein respectively, showed marked extravasation of the Evans blue dye in the frontal cortex, posterior cortex and thalamus-midbrain at day 1 following induction of cerebral hypoperfusion. Transmission electron microscopy revealed brain endothelial cell and astrocyte damages including increased pinocytotic vesicles and formation of membrane invaginations in the endothelial cells, and swelling of the astrocytes' end-feet. Investigation on brain microvessel protein expressions using two-dimensional (2D) gel electrophoresis coupled with LC-MS/MS showed that proteins involved in mitochondrial energy metabolism, transcription regulation, cytoskeleton maintenance and signaling pathways were differently expressed. The expression of aconitate hydratase, heterogeneous nuclear ribonucleoprotein, enoyl Co-A hydratase and beta-synuclein were downregulated, while the opposite observed for calreticulin and enhancer of rudimentary homolog. These findings provide insights into the BBB molecular responses to cerebral hypoperfusion, which may assist development of future therapeutic strategies.

Origin and Consequences of Necroinflammation

When cells undergo necrotic cell death in either physiological or pathophysiological settings in vivo, they release highly immunogenic intracellular molecules and organelles into the interstitium and thereby represent the strongest known trigger of the immune system. With our increasing understanding of necrosis as a regulated and genetically determined process (RN, regulated necrosis), necrosis and necroinflammation can be pharmacologically prevented. This review discusses our current knowledge about signaling pathways of necrotic cell death as the origin of necroinflammation. Multiple pathways of RN such as necroptosis, ferroptosis, and pyroptosis have been evolutionary conserved most likely because of their differences in immunogenicity. As the consequence of necrosis, however, all necrotic cells release damage associated molecular patterns (DAMPs) that have been extensively investigated over the last two decades. Analysis of necroinflammation allows characterizing specific signatures for each particular pathway of cell death. While all RN-pathways share the release of DAMPs in general, most of them actively regulate the immune system by the additional expression and/or maturation of either pro- or anti-inflammatory cytokines/chemokines. In addition, DAMPs have been demonstrated to modulate the process of regeneration. For the purpose of better understanding of necroinflammation, we introduce a novel classification of DAMPs in this review to help detect the relative contribution of each RN-pathway to certain physiological and pathophysiological conditions.

Involvement of miR-455 in the protective effect of H2S against chemical hypoxia-induced injury in BEAS-2B cells

The protective effect of hydrogen sulfide (H₂S) against hypoxia-induced injury via anti-apoptosis is well established, but the underlying mechanism remains unclear. The present study aimed to investigate whether miR-455 participated in the H₂S protection of lung epithelial cells against CoCl₂-induced apoptosis by regulating endoplasmic reticulum stress (ERS)-related genes. Human lung epithelial cells BEAS-2B were subjected to hypoxia injury with or without H₂S preconditioning. It was found that hypoxia injury increased apoptosis of BEAS-2B cells, down-regulated the expression of miR-455, and upregulated the expression of calreticulin (Calr). H₂S preconditioning attenuated lung epithelial cells apoptosis, enhanced cell viability, up-regulated the expression of miR-455, as well as down-regulated the expression of Calr following hypoxia injury. In addition, Calr, GRP78, C/EBP homologous protein (CHOP) and Caspase-12 protein was down-regulated by the miR-455 mimic and up-regulated by the miR-455 inhibitor. These results implicate miR-455 regulated H₂S protection of lung epithelial cells against hypoxia-induced apoptosis by stimulating Calr.

Silencing calreticulin gene might protect cardiomyocytes from angiotensin II-induced apoptosis

AIMS

Calreticulin (CRT), as a chaperone, contributes to protein folding and quality control cycle. CRT is an important factor regulating Ca²⁺ that participates in cell apoptosis. However, the function of CRT in the heart is still controversial. Therefore, we aimed to investigate the potential role of CRT in angiotensin II-induced cardiomyocytes apoptosis.

MAIN METHODS

Primary cultured neonatal cardiomyocytes were stimulated with angiotensin II to induce the apoptosis. Expression of CRT and endoplasmic reticulum (ER) stress associated protein was detected by western blotting after angiotensin II stimulation for 24 h. The reactive oxygen species (ROS) production and mitochondrial membrane potential (MMP) were also detected. Additionally, the function of CRT on cardiomyocytes apoptosis and ER stress/unfolded protein response signaling pathway was investigated by transfecting specific CRT-targeting siRNA.

KEY FINDINGS

Cardiomyocytes apoptosis was induced by angiotensin II. The protein level of CRT was elevated after angiotensin -II stimulation for 24 h. Additionally, the protein levels of GRP78, ATF4, C-ATF6, CHOP and the ROS production were elevated, but the Bcl-2 expression and the level of MMP were down-regulated. After silencing CRT gene in the process of angiotensin II-induced cardiomyocytes apoptosis, cardiomyocytes apoptosis rate decreased, meanwhile the protein expression of CRT, GRP78, ATF4, C-ATF6 and CHOP were down-regulated. However, the Bcl-2 expression was up-regulated, and the increase of ROS and the loss of MMP were alleviated.

SIGNIFICANCE

Our study demonstrated that CRT might protect cardiomyocytes from apoptosis induced by angiotensin II, in which ER stress and mitochondria function were identified as possible underlying molecular bases.

Endoplasmic reticulum stress-mediated membrane expression of CRT/ERp57 induces immunogenic apoptosis in drug-resistant endometrial cancer cells

OBJECTIVE

To investigate the role of endoplasmic reticulum (ER) stress-mediated CRT/ERp57 complex expression underlying the mechanism of resistance to doxorubicin (DOX) in endometrial carcinoma (EC) in vivo and in vitro.

METHODS

The expression of CRT, ERp57, p-PERK, eIF2α, p-eIF2α in EC patients and EC cells was detected by Western blots and by immunofluorescence assay. MTT assay was used to determine the LC50 of EC cells to DOX and cell viability. Apoptosis was assayed using flow cytometer. The protein expression of PERK, cleaved-caspase-8, p-eIF2α and CHOP were detected by Western blot, and the expression of VAMP-1, SNAP23 and PERK was knockdown by siRNA and/or shRNA. The expression of CRT/ERp57 complex was detected by flow cytometry. In addition, the expression of eIF2α and p-eIF2α was detected by Western blot analysis after drug-resistant EC cells were transfected with lentivirus overexpressing CRT, treated with GADD34 inhibitor and ES stress inducer. MTT assay was used to detect the phagocytic activity of T cells induced by maturation of dendritic cells in drug-resistant EC cells.

RESULTS

The expression of CRT, ERp57, p-PERK and p-eIF2α was significantly decreased in the drug-resistant patients in EC patients. The IC₅₀ of the drug-resistant EC cells was 10 times higher than that of the wild type cells. In the drug-resistant EC cells the expression of CRT, ERp57, p-PERK, p-eIF2α, caspase-8 and CHOP was significantly lower than in the wild type cells. After treatment with DOX, CRT and ER stress-related proteins p-PERK, p-eIF2α, caspase-8 and apoptosis were significantly increased in wild-type EC cells, but not in drug-resistant EC cells. The increased expressions led to inhibition of cell growth and apoptosis. The knockdown of PERK gene and addition of DOX resulted in significant decrease of cleaved-caspase 8 and p-eIF2α in sensitive EC cells. The expression of CRT/ERp57 in sensitive EC cells was further significantly decreased by blocking VAMP and SNAP23. In addition, transfection with CRT overexpressing lentivirus and addition of GADD34 inhibitor and ER stress inducer in drug-resistant EC cells revealed a significant increase in the expression of CRT/ERp57 complex and p-eIF2α when DOX was added simultaneously, which promoted the maturation and chemotaxis of T lymphocytes to phagocytose drug-resistant EC cells.

CONCLUSION

DOX can induce the death of tumor cells by ER stress-mediated CRT/ERp57 expression in EC cells. Induction of ER stress in drug-resistant EC cells up-regulates the membrane expression of CRT/ERp57, enhances phagocytosis, induces immunogenic apoptosisand sensitizes the cells to DOX.

Pim-1 Kinase Regulating Dynamics Related Protein 1 Mediates Sevoflurane Postconditioning-induced Cardioprotection

BACKGROUND

It is well documented that sevoflurane postconditioning (SP) has a significant myocardial protection effect. However, the mechanisms underlying SP are still unclear. In the present study, we investigated the hypothesis that the Pim-1 kinase played a key role in SP-induced cardioprotection by regulating dynamics-related protein 1 (Drp1).

METHODS

A Langendorff model was used in this study. Seventy-two rats were randomly assigned into six groups as follows: CON group, ischemia reperfusion (I/R) group, SP group , SP+proto-oncogene serine/threonine-protein kinase 1 (Pim-1) inhibitor II group, SP+dimethylsufoxide group, and Pim-1 inhibitor II group (n = 12, each). Hemodynamic parameters and infarct size were measured to reflect the extent of myocardial I/R injury. The expressions of Pim-1, B-cell leukemia/lymphoma 2 (Bcl-2) and cytochrome C (Cyt C) in cytoplasm and mitochondria, the Drp1 in mitochondria, and the total Drp1 and p-Drp1ser637 were measured by Western blotting. In addition, transmission electron microscope was used to observe mitochondrial morphology. The experiment began in October 2014 and continued until July 2016.

RESULTS

SP improved myocardial I/R injury-induced hemodynamic parametric changes, cardiac function, and preserved mitochondrial phenotype and decreased myocardial infarct size (24.49 ± 1.72% in Sev group compared with 41.98 ± 4.37% in I/R group; P< 0.05). However, Pim-1 inhibitor II significantly (P < 0.05) abolished the protective effect of SP. Western blotting analysis demonstrated that, compared with I/R group, the expression of Pim-1 and Bcl-2 in cytoplasm and mitochondria as well as the total p-Drp1ser637 in Sev group (P < 0.05) were upregulated. Meanwhile, SP inhibited Drp1 compartmentalization to the mitochondria followed by a reduction in the release of Cyt C. Pretreatment with Pim-1 inhibitor II significantly (P < 0.05) abolished SP-induced Pim-1/p-Drp1ser637 signaling activation.

CONCLUSIONS

These findings suggested that SP could attenuate myocardial ischemia-reperfusion injury by increasing the expression of the Pim-1 kinase. Upregulation of Pim-1 might phosphorylate Drp1 and prevent extensive mitochondrial fission through Drp1 cytosolic sequestration.

Calreticulin attenuated microwave radiation-induced human microvascular endothelial cell injury through promoting actin acetylation and polymerization

Recent work reveals that actin acetylation modification has been linked to different normal and disease processes and the effects associated with metabolic and environmental stressors. Herein, we highlight the effects of calreticulin on actin acetylation and cell injury induced by microwave radiation in human microvascular endothelial cell (HMEC). HMEC injury was induced by high-power microwave of different power density (10, 30, 60, 100 mW/cm2, for 6 min) with or without exogenous recombinant calreticulin. The cell injury was assessed by lactate dehydrogenase (LDH) activity and Cell Counting Kit-8 in culture medium, migration ability, intercellular junction, and cytoskeleton staining in HMEC. Western blotting analysis was used to detected calreticulin expression in cytosol and nucleus and acetylation of globular actin (G-actin). We found that HMEC injury was induced by microwave radiation in a dose-dependent manner. Pretreatment HMEC with calreticulin suppressed microwave radiation-induced LDH leakage and increased cell viability and improved microwave radiation-induced decrease in migration, intercellular junction, and cytoskeleton. Meanwhile, pretreatment HMEC with exogenous calreticulin upregulated the histone acetyltransferase activity and the acetylation level of G-actin and increased the fibrous actin (F-actin)/G-actin ratio. We conclude that exogenous calreticulin protects HMEC against microwave radiation-induced injury through promoting actin acetylation and polymerization.

Madecassic Acid protects against hypoxia-induced oxidative stress in retinal microvascular endothelial cells via ROS-mediated endoplasmic reticulum stress

Madecassic acid (MA) is an abundant triterpenoid in Centella asiatica (L.) Urban. (Apiaceae) that has been used as a wound-healing, anti-inflammatory and anti-cancer agent. Up to now, the effects of MA against oxidative stress remain unclear. In this study, we investigated the effect of MA and its mechanisms on hypoxia-induced human Retinal Microvascular Endothelial Cells (hRMECs). hRMECs were pre-treated with different concentrations of MA (0-50μM) for 30min before being incubated under hypoxia condition (37°C, 5% CO₂ and 95% N₂). Cell apoptosis was evaluated with MTT assay and TUNEL staining, and the expression of apoptosis- and endoplasmic reticulum (ER) stress-related molecules was assessed with western blotting and RT-PCR analysis. Intracellular ROS level was evaluated using DCFH-DA. Intracellular malondialdehyde (MDA), dehydrogenase (LDH), glutathione peroxidase (GSH-PX) and superoxide dismutase (SOD) were evaluated using related Kits. Activating transcription factor 4 (ATF4) nuclear translocation was assessed with western blotting analysis and immunofluorescence staining. MA significantly reduced oxidative stress in hypoxia-induced hRMECs, as shown by increased cell viability, SOD and GSH-PX leakage, decreased TUNEL- and ROS-positive cell ratio, LDH and MDA leakage, caspase-3 and -9 activity, and Bax/Bcl-2 ratio. In addition, MA also attenuated hypoxia-induced ER stress in hRMECs, as shown by reduced mRNA levels of glucose-regulated protein 78 (GRP78), C/EBP homologous transcription factor (CHOP), protein levels of cleaved activating transcription factor 6 (ATF6) and inositol-requiring kinase/endonuclease 1 alpha (IRE1α), phosphorylation of pancreatic ER stress kinase (PERK) and eukaryotic initiation factor 2 alpha (eIF2α), cleaved caspase-12 and ATF4 translocation to nucleus. The current study indicated that the regulation of oxidative stress and ER stress by MA would be a promising therapy to reverse the process and development of hypoxia-induced hRMECs dysfunction.