Involvement of Noxa in mediating cellular ER stress responses to lytic virus infection

Noxa is a Bcl-2 homology domain-containing pro-apoptotic mitochondrial protein. Noxa mRNA and protein expression are upregulated by dsRNA or virus, and ectopic Noxa expression enhances cellular sensitivity to virus or dsRNA-induced apoptosis. Here we demonstrate that Noxa null baby mouse kidney (BMK) cells are deficient in normal cytopathic response to lytic viruses, and that reconstitution of the knockout cells with wild-type Noxa restored normal cytopathic responses. Noxa regulation by virus mirrored its regulation by proteasome inhibitors or ER stress inducers and the ER stress response inhibitor salubrinal protected cells against viral cytopathic effects. Noxa mRNA and protein were synergistically upregulated by IFN or dsRNA when combined with ER stress inducers, leading to Noxa/Mcl-1 interaction, activation of Bax and pro-apoptotic caspases, degradation of Mcl-1, loss of mitochondrial membrane potential and initiation of apoptosis. These data highlight the importance of ER stress in augmenting the expression of Noxa following viral infection.     

Salubrinal对大鼠脑缺血再灌注模型LC3-ⅡmRNA及LC3-Ⅱ/LC3-ⅠmRNA的影响

目的 探讨Salubrinal对大鼠脑缺血再灌注模型LC3-ⅡmRNA及LC3-Ⅱ/LC3-ⅠmRNA表达的影响.方法 用线栓法建立大鼠大脑中动脉脑缺血(MCAO)缺血再灌注模型.大鼠随机分为假手术组、模型组、Salubrinal组(Sal组),各组又分为再灌6、12、24、72 h 4个亚组.各组于再灌相应时间点行神经功能缺损评分,并断头取脑行HE染色及Real time-PCR检测.结果 神经功能缺损:与假手术组比较,模型组、Sal组各时间点均有神经功能缺损(P<0.01);与模型组比较,再灌24、72 h Sal组神经功能缺损评分降低(P<0.05).HE染色:模型组神经元减少、缺失,细胞肿胀,部分破裂,细胞核固缩、偏移、深染,胶质细胞增生,经Salubrinal干预后,再灌各时间点神经元增多,胞膜较完整,核固缩现象较轻,水肿轻微.Real time-PCR检测:与假手术组比较,模型组、Sal组各指标于再灌各时间点均增高(P<0.01).与模型组比,Sal组LC3-ⅡmRNA表达于再灌12、24、72 h下降明显(P<0.05);Sal组LC3-Ⅱ/LC3-ⅠmRNA于再灌后各时间点下降均明显(P<0.01).结论 Salubrinal通过下调LC3-ⅡmRNA及LC3-Ⅱ/LC3-ⅠmRNA比值,对大鼠脑缺血再灌注损伤起保护作用.     

Salubrinal protects against tunicamycin and hypoxia induced cardiomyocyte apoptosis via the PERK-eIF2α signaling pathway

Objectives This study examined the protective effect of salubrinal and the mechanism underlying this protection on tunicamycin (TM)- and hypoxia-induced apoptosis in rat cardiomyocytes. Methods Neonatal rat cardiomyocytes were cultured from the ventricles of 1-day-old Wistar rats. Cells were exposed to different concentrations of salubrinal (10, 20, and 40 μmol/L) for 30 minutes followed by TM treatment or hypoxia for 36 hours. Apoptosis was measured by a multiparameter HCS (high content screening) apoptosis assay, TUNEL assay and flow cytometry. The phosphorylation of eukaryotic translation initiation factor 2 subunit alpha (p-eIF2α) and the expression of cleaved caspase-12 were determined by western blotting. C/EBP homologous protein (CHOP) was detected by immunocytochemistry. Results HCS, TUNEL assays and flow cytometry showed that salubrinal protected against apoptosis induced by TM or hypoxia. Western blotting showed that salubrinal protected cardiomyocytes against apoptosis by inducing eIF2α phosphorylation and down-regulating the expression of the endoplasmic reticulum stress-mediated apoptotic proteins, CHOP and cleaved caspase-12. Conclusions Our study suggests that salubrinal protects rat cardiomyocytes against TM- or hypoxia-associated apoptosis via a mechanism involving the inhibition of ER stress-mediated apoptosis.     

Mechanical and hypoxia stress can cause chondrocytes apoptosis through over-activation of endoplasmic reticulum stress

ObjectiveTo examine the role of mechanical force and hypoxia on chondrocytes apoptosis and osteoarthritis (OA)-liked pathological change on mandibular cartilage through over-activation of endoplasmic reticulum stress (ERS).MethodsWe used two in vitro models to examine the effect of mechanical force and hypoxia on chondrocytes apoptosis separately. The mandibular condylar chondrocytes were obtained from three-week-old male Sprague–Dawley rats. Flexcell 5000T apparatus was used to produce mechanical forces (12%, 0.5 Hz, 24 h vs 20%, 0.5 Hz, 24 h) on chondrocytes. For hypoxia experiment, the concentration of O₂ was down regulated to 5% or 1%. Cell apoptosis rates were quantified by annexin V and propidium iodide (PI) double staining and FACS analysis. Quantitative real-time PCR and western blot were performed to evaluate the activation of ERS and cellular hypoxia. Then we used a mechanical stress loading rat model to verify the involvement of ERS in OA-liked mandibular cartilage pathological change. Histological changes in mandibular condylar cartilage were assessed via hematoxylin & eosin (HE) staining. Immunohistochemistry of GRP78, GRP94, HIF-1α, and HIF-2α were performed to evaluate activation of the ERS and existence of hypoxia. Apoptotic cells were detected by the TUNEL method.ResultsTunicamycin, 20% mechanical forces and hypoxia (1% O₂) all significantly increased chondrocytes apoptosis rates and expression of ERS markers (GRP78, GRP94 and Caspase 12). However, 12% mechanical forces can only increase the apoptotic sensitivity of chondrocytes. Mechanical stress resulted in OA-liked pathological change on rat mandibular condylar cartilage which included thinning cartilage and bone erosion. The number of apoptotic cells increased. ERS and hypoxia markers expressions were also enhanced. Salubrinal, an ERS inhibitor, can reverse these effects in vitro and in vivo through the down-regulation of ERS markers and hypoxia markers.ConclusionWe confirmed that mechanical stress and local hypoxia both contributed to the chondrocytes apoptosis. Mechanical stress can cause OA-like pathological change in rat mandibular condylar cartilage via ERS activation and hypoxia existed in the meantime. Both mechanical forces and hypoxia can induce ERS and cause chondrocytes apoptosis only if the stimulate was in higher level. Salubrinal can protect chondrocytes from apoptosis, and relieve OA-liked pathological change on mandibular condylar cartilage under mechanical stress stimulation.     

Salubrinal通过调节破骨细胞发育改善骨关节炎 胫骨平台不均匀沉降

摘要：目的 观察Salubrinal对早期骨关节炎（OA）小鼠胫骨平台不均匀沉降的治疗作用。方法 30只小鼠随机 分为对照（Sham）组、OA组和OA+Salubrinal（OA+Sal）组。采用手术切除小鼠膝关节内侧半月板建立OA模型,Sham 组只切开关节内侧皮肤;OA+Sal组小鼠皮下注射Salubrinal （1 mg/kg）2周,Sham组及OA组给予等量的生理盐水。采 用番红O和抗酒石酸酸性磷酸酶（TRAP）染色,观察胫骨平台内侧和外侧的组织形态学改变以及破骨细胞活性变化。 使用骨髓细胞的破骨细胞形成、迁移、黏附实验检测破骨细胞发育情况。结果 与Sham组相比,OA组破骨细胞发育 显著激活,软骨下骨的破骨细胞活性也明显增高;关节软骨OARSI评分、钙化软骨比例（CC/TAC）均显著升高（P＜ 0.05）;胫骨平台内侧软骨下骨的骨面积分数（B.Ar/T.Ar）明显增加（P＜0.05）,但外侧B.Ar/T.Ar、软骨下骨板（SBP）厚 度均显著降低（P＜0.05）。与OA组相比,OA+Sal组破骨细胞发育及软骨下骨破骨细胞活性被抑制,OARSI评分、CC/ TAC 均有所降低（P＜0.05）;而且,内外侧胫骨平台软骨下骨 B.Ar/T.Ar 和 SBP 厚度的不均匀改变均明显恢复（P＜ 0.05）。结论 Salubrinal通过调控破骨细胞发育对早期OA胫骨平台的骨重建和不均匀沉降有明显的改善作用。     

内质网应激在慢性间歇低氧幼鼠脑损害中的作用

目的:探讨内质网应激在慢性间歇低氧幼鼠脑损害中的作用机制及salubrinal的干预作用。方法:取SPF级健康雄性SD幼鼠64只,随机分为8组:间歇低氧(intermittent hypoxia,IH)2、4周组(2IH、4IH),对照(control,C)2、4周组(2C、4C),Salubrinal(SAL)干预2、4周组(2SAL、4SAL),二甲基亚砜(DMSO)溶剂对照2、4周组(2DMSO、4DMSO),每组8只。八臂迷宫测试各组幼鼠参考记忆错误(RME)、工作记忆错误(WME)及总错误(TE)次数,观察海马神经元凋亡变化,测定超氧化物歧化酶(SOD)活性,及内质网应激标志物C/EBP同源蛋白(CHOP)、磷酸化真核翻译起始因子2α(p-e IF2α)和磷酸化蛋白激酶R样内质网激酶(p-PERK)的蛋白水平。结果:与相应对照2C、4C组比较,间歇低氧2IH、4IH组幼鼠的RME、WME和TE升高(P0.01),海马神经元凋亡指数(AI)升高(P0.01),SOD活性下降(P0.01),p-PERK和CHOP蛋白水平升高(P0.01),p-e IF2α蛋白水平下降(P0.05),4周组最明显;与对应间歇性低氧2IH、4IH组比较,药物干预组2SAL、4SAL组RME、WME和TE次数下降(P0.05),AI下降(P0.01),SOD活性升高(P0.01),p-e IF2α的蛋白水平升高(P0.01),CHOP表达下降(P0.01)。结论:慢性间歇低氧可上调记忆相关脑区p-PERK表达,启动内质网应激,从而诱导CHOP所介导的细胞凋亡,可能在慢性间歇低氧所致脑损伤中起重要作用。Salubrinal选择性抑制e IF2α去磷酸化,下调CHOP蛋白的水平,提高SOD活性,从而缓解内质网应激,减轻氧化应激,减少细胞凋亡。     

Protective Effects of Salubrinal on Liver Injury in Rat Models of Brain Death

Background:

Previous studies have indicated that endoplasmic reticulum stress participates in and mediates liver injury and apoptosis in brain-dead (BD) rats. In this study, we observed the effect of salubrinal (Sal, Sigma, USA) on liver cells in BD rats and explored its relevant mechanisms.

Methods:

Thirty Sprague–Dawley rats were equally randomized into three groups: BD group, Sal group, and DMSO group. The BD models were established by increasing intracranial pressure in a modified, slow, and intermittent way. In the drug groups, Sal was administered 1 h before the induction of BD. After modeling was completed, the blood and liver samples were harvested. CHOP and Caspase-12 mRNA expression was detected using quantitative polymerase chain reaction. PKR-like ER kinase (PERK), P-eukaryotic translation initiation factor 2α (eIF2α), eIF2α, CHOP and caspase-12 expression was detected using western blotting (WB). CHOP and caspase-12 distribution and expression in liver tissues were determined using immunohistochemistry (IHC). Alanine aminotransferase and aspartate aminotransferase level were detected using an automatic biochemical analyzer. Hepatic cell apoptosis was detected using TUNEL. The results were analyzed using Quantity-one v4.62 software (Bio-Rad, USA).

Results:

CHOP and caspase-12 expression and PERK, eIF2α, and P-eIF2α protein expression showed no significant difference between BD group and DMSO group. Compared with BD group, Sal group had a significantly higher P-eIF2C level and a lower P-PERK level 2 h and 6 h after BD (P < 0.05). However, eIF2α expression showed no significant difference (P > 0.05). After the Sal treatment, CHOP and caspase-12 mRNA expression significantly decreased 4 h after BD (P < 0.05). WB and IHC indicated that CHOP and caspase-12 expression also significantly decreased after Sal treatment. Sal was associated with improved liver function and decreased hepatic cell apoptosis.

Conclusions:

Sal can significantly reduce apoptosis in hepatic cells of BD rats. This protective effect may be achieved via the PERK-eIF2α signaling pathway.     

Inhibition of the dephosphorylation of eukaryotic initiation factor 2α ameliorates murine experimental pancreatitis

BackgroundEndoplasmic reticulum (ER) stress in the pancreas is closely associated with the development of acute pancreatitis. However, the role of the protein kinase RNA-like ER kinase (PERK) in this disease is not fully understood. We investigated whether an inhibitor of the dephosphorylation of eukaryotic initiation factor 2α, salubrinal, could improve murine experimental pancreatitis through the amelioration of ER stress.MethodsAcute pancreatitis was induced by the intraperitoneal administration of cerulein (50 μg/kg) six times at 1-h intervals followed by lipopolysaccharide (10 mg/kg). Salubrinal was administered intraperitoneally immediately after lipopolysaccharide injection and 3 h later. Mice were sacrificed 24 h after the first injection of cerulein, and serum amylase and proinflammatory cytokines were measured. The severity of pancreatitis was evaluated histologically using a scoring system. The expression levels of ER stress-related proteins were evaluated by Western blotting.ResultsThe administration of salubrinal significantly attenuated the increase in serum amylase levels and improved histologically assessed pancreatitis. The serum levels of proinflammatory cytokines were significantly suppressed in salubrinal-treated mice, as was the expression of glucose-regulated protein 78, CCAAT/enhancer-binding protein homologous protein, and cleaved caspase-3.ConclusionsThe amelioration of ER stress through augmentation of the PERK-signaling pathway may be a therapeutic target for the treatment of acute pancreatitis.     

ICP34.5-dependent and -independent activities of salubrinal in herpes simplex virus-1 infected cells

The small molecule salubrinal has antiviral activity against herpes simplex virus-1 (HSV-1) and inhibits dephosphorylation of eIF2α mediated by the HSV-1 protein ICP34.5. We investigated whether salubrinal's activities in infected cells depend on ICP34.5. An ICP34.5 deletion mutant was as sensitive as wild type HSV-1 to salubrinal inhibition of plaque formation in Vero cells. However, salubrinal induced formation of syncytia in infected Vero cells, which was enhanced by ICP34.5 mutations. Expression of HSV-1 US11 with immediate early kinetics, which is known to suppress the effects of ICP34.5 mutations, resulted in slight resistance to salubrinal in murine embryonic fibroblasts, and substantial resistance in those cells when ICP34.5 was additionally mutated. ICP34.5 mutations, but not immediate early expression of US11, prevented salubrinal's ability to increase phosphorylation of eIF2α during HSV-1 infection of Vero cells. Taken together, our data indicate that salubrinal has both ICP34.5-dependent and -independent activities in HSV-1 infected cells.