Endoplasmic Reticulum Stress Responses and Apoptosis

Endoplasmic Reticulum (ER) Stress Inhibitor or Antioxidant Treatments during Micromanipulation Can Inhibit Both ER and Oxidative Stresses in Porcine SCNT Embryos

We investigated the effects of endoplasmic reticulum (ER) stress inhibitor and antioxidant treatments during the micromanipulation of somatic cell nuclear transfer (SCNT) on in vitro development of SCNT embryos. Tauroursodeoxycholic acid (TUDCA), an ER stress inhibitor and vitamin C (Vit. C), an antioxidant, were treated by alone or in combination, then, the level of X-box binding protein 1 (Xbp1) splicing and the expressions of ER stress-associated genes, oxidative stress-related genes, and apoptotic genes were confirmed in the 1-cell and blastocyst stages. In the 1-cell stage, the levels of Xbp1 splicing were significantly decreased in TUDCA and Vit. C treatment groups compared to the control (p<0.05). In addition, the expression levels of most ER stress-associated genes and oxidative stress-related genes were significantly lower in all treatment groups than the control (p<0.05), and the transcript levels of apoptotic genes were also significantly lower in all treatment groups than the control (p<0.05). In the blastocyst stage, decreased expression of ER stress-, oxidative stress-, and apoptosis-related genes were observed only in some treatments. However, the blastocyst formation rates in TUDCA and Vit. C treatment groups (24.8% and 22.0%, respectively) and mean blastocyst cell number in all treatment groups (59.7±4.3 to 63.5±3.3) were significantly higher (p<0.05) than those of control. The results showed that the TUDCA or Vit. C treatment during micromanipulation inhibited both ER and oxidative stresses in the early stage of SCNT embryos, thereby reducing cell damage and promoting in vitro development.

Reactive oxygen species-mediated endoplasmic reticulum stress response induces apoptosis of Mycobacterium avium-infected macrophages by activating regulated IRE1-dependent decay pathway

Mycobacterium avium, a slow‐growing nontuberculous mycobacterium, causes fever, diarrhoea, loss of appetite, and weight loss in immunocompromised people. We have proposed that endoplasmic reticulum (ER) stress‐mediated apoptosis plays a critical role in removing intracellular mycobacteria. In the present study, we investigated the role of the regulated IRE1‐dependent decay (RIDD) pathway in macrophages during M. avium infection based on its role in the regulation of gene expression. The inositol‐requiring enzyme 1 (IRE1)/apoptosis signal‐regulating kinase 1 (ASK1)/c‐Jun N‐terminal kinase (JNK) signalling pathway was activated in macrophages after infection with M. avium. The expression of RIDD‐associated genes, such as Bloc1s1 and St3gal5, was decreased in M. avium‐infected macrophages. Interestingly, M. avium‐induced apoptosis was significantly suppressed by pretreatment with irestatin (inhibitor of IRE1α) and 4μ8c (RIDD blocker). Macrophages pretreated with N‐acetyl cysteine (NAC) showed decreased levels of reactive oxygen species (ROS), IRE1α, and apoptosis after M. avium infection. The expression of Bloc1s1 and St3gal5 was increased in NAC‐pretreated macrophages following infection with M. avium. Growth of M. avium was significantly increased in irestatin‐, 4μ8c‐, and NAC‐treated macrophages compared with the control. The data indicate that the ROS‐mediated ER stress response induces apoptosis of M. avium‐infected macrophages by activating IRE1α‐RIDD. Thus, activation of IRE1α suppresses the intracellular survival of M. avium in macrophages.

Effect of Endoplasmic Reticulum (ER) Stress Inhibitor Treatment during Parthenogenetic Activation on the Apoptosis and In Vitro Development of Parthenogenetic Porcine Embryos

We investigate the effect of endoplasmic reticulum (ER) stress inhibitor treatment during parthenogenetic activation of oocytes on the ER stress generation, apoptosis, and in vitro development of parthenogenetic porcine embryos. Porcine in vitro matured oocytes were activated by 1) electric stimulus (E) or 2) E+10 μM Ca-ionophore (A23187) treatment (EC). Oocytes were then treated by ER stress inhibitors such as salubrinal (200 nM) and tauroursodeoxychloic acid (TUDCA, 100 μM) for 3 h prior to in vitro culture. Parthenogenetic embryos were sampled to analyze ER stress and apoptosis at the 1-cell and blastocyst stages. The x-box binding protein 1 (Xbp1) mRNA and ER stress-associated genes were analyzed by RT-PCR or RT-qPCR. Apoptotic gene expression was analyzed by RT-PCR. At the 1-cell stage, although no difference was observed in Xbp1 splicing among treatments, BiP transcription level in the E group was significantly reduced by salubrinal treatment, and GRP94 and ATF4 transcription levels in EC group were significantly reduced by all treatments (p<0.05) compared to control. In the EC group, both apoptotic genes were reduced by ER stress inhibitor treatments compared to control (p<0.05) except Caspase-3 gene by TUDCA treatment. These results suggest that the treatment of ER stress inhibitor during parthenogenetic activation can reduce ER stress, and thereby reduce apoptosis and promote in vitro development of porcine parthenogenetic embryos.

Mycobacterium tuberculosis 38-kDa antigen induces endoplasmic reticulum stress-mediated apoptosis via toll-like receptor 2/4

Endoplasmic reticulum (ER) stress responses play critical roles in the pathogenesis of tuberculosis. To investigate the regulatory role of the ER stress response in 38-kDa antigen-induced apoptosis, we examined the relationship between the ER stress response and apoptosis in bone marrow-derived macrophages (BMDMs) stimulated with Mycobacterium tuberculosis antigen (38-kDa Ag). The expression of ER molecular chaperones, including C/EBP homologous protein (CHOP), glucose-regulated protein (Bip) and phosphorylated alpha subunit of eukaryotic initiation factor 2, was induced in BMDMs stimulated with the 38-kDa Ag. Interestingly, 38-kDa Ag-stimulation induced apoptosis via activation of caspase-12, -9 and -3. However, 38-kDa Ag-induced apoptosis was significantly reduced in TLR2- and TLR4-deficient macrophages. Because toll-like receptors (TLRs) initiate the activation of mitogen-activated protein kinase (MAPK) signaling cascades, we evaluated the effect of MAPK activation on ER stress. The 38-kDa Ag activated Jun N-terminal kinase, extracellular signal-regulated kinase and p38 phosphorylation. MAPK signaling induced the secretion of proinflammatory cytokines such as MCP-1, TNF-α and IL-6. The 38-kDa Ag-induced MCP-1 was especially associated with the induction of MCP-1-induced protein (MCPIP), which increased the generation of reactive oxygen species (ROS) and ER stress. To investigate the role of MCPIP in ROS-induced ER stress by 38-kDa Ag stimulation, we transfected MCPIP siRNA into RAW264.7 cells before 38-kDa Ag stimulation, and measured the generation of ROS and expression of ER molecular chaperones. ROS production and CHOP expression were decreased by the silencing of MCPIP induction. Our results demonstrate that the expression of MCPIP by 38-kDa Ag stimulation is increased through a TLR-MAPK-dependent signaling pathway, and leads to ER stress-induced apoptosis. In conclusion, MCPIP is important for host defense mechanisms in mycobacterial pathogenesis.

Helicobacter pylori vacuolating cytotoxin induces apoptosis via activation of endoplasmic reticulum stress in dendritic cells

BACKGROUND AND AIM

Dendritic cells (DCs) are observed on the Helicobacter pylori-infected gastric mucosa. DCs generally play an important role in the regulation of inflammation. Although stimulation of gastric epithelial cells with H. pylori vacuolating cytotoxin (VacA) has been reported to induce apoptosis and endoplasmic reticulum (ER) stress, the effects of VacA on the DC apoptotic response have not been well elucidated. This study was conducted to investigate the role of H. pylori VacA on the apoptotic process and ER stress in DCs.

METHODS

Murine and human DCs were generated from specific pathogen-free C57BL/6 mice and human peripheral blood mononuclear cells, respectively. DCs were incubated with purified VacA, after which Bax activation, cytochrome c release, and DNA fragmentation for apoptosis were measured by fluorescent microscopy, immunoblot, and ELISA. ER stress-related molecules such as GRP78 and CHOP were analyzed by immunoblot.

RESULTS

Treatment of DCs with purified H. pylori VacA resulted in the induction of apoptosis. DC stimulation with VacA led to the translocation of cytoplasmic Bax to mitochondria and cytochrome c release from mitochondria. H. pylori VacA induced signals for ER stress early during the stimulation process in DCs. Furthermore, suppression of ER stress resulted in a significant inhibition of the VacA-induced apoptosis in DCs.

CONCLUSION

These results suggest that ER stress is critical for regulation of DC apoptotic process in response to VacA stimulation.

Mycobacterium kansasii-induced death of murine macrophages involves endoplasmic reticulum stress responses mediated by reactive oxygen species generation or calpain activation

Although pathogenic mechanisms of tuberculosis have been extensively studied, little is known about the pathogenic mechanisms of Mycobacterium kansasii. In this work the influence of virulence and ER-stress mediated apoptosis of macrophages during two different strains of M. kansasii infection was investigated. We show that M. kansasii infection is associated with ER stress-mediated apoptosis in the murine macrophage cell line RAW 264.7. Infection of RAW 264.7 cells in vitro with apoptosis-inducing a clinical isolate of M. kansasii SM-1 (SM-1) resulted in strong induction of ER stress responses compared with M. kansasii type strain (ATCC 12478)-infected RAW 264.7 cells. Interestingly, inhibition of calpain prevented the induction of CHOP and Bip in ATCC 12478-infected RAW 264.7 cells but not in RAW 264.7 cells infected with SM-1. In contrast, reactive oxygen species (ROS) were significantly increased only in RAW 264.7 cells infected with SM-1. We propose that ROS generation is important for triggering ER stress-mediated apoptosis during SM-1 infection, whereas ATCC 12478-induced, ER stress-mediated apoptosis is associated with calpain activation. Our results demonstrate that the ER stress pathway plays important roles in the pathogenesis of M. kansasii infections, and that different strains of M. kansasii induce different patterns of ER stress-mediated apoptosis.