Crosstalk between activating transcription factor 6 and the inositol-requiring enzyme 1 - X-box binding protein 1 pathway in oxygen-glucose deprivation/reoxygenation-injured HT22 cells / 中华危重病急救医学

Objective:To study the crosstalk between the activating transcription factor 6 (ATF6) and inositol-requiring enzyme 1 (IRE1) - X-box binding protein 1 (XBP1) pathway in oxygen-glucose deprivation/reoxygenation (OGD/R)-injured mouse hippocampal neuronal cell line HT22.Methods:The OGD/R-injured HT22 cell model was used to observe the changes of the indicators of endoplasmic reticulum stress (ERS), cell viability, and apoptosis at different OGD/R time points (0, 3, 6, 12, and 24 hours). HT22 cells in the logarithmic growth phase were randomized into blank control group, control+ATF6 activator (AA147) group, control+IRE1 inhibitor (4μ8c) group, OGD/R model group, OGD/R+AA147 group and OGD/R+4μ8c group (10 μmol/L AA147 or 16 μmol/L 4μ8c was given during the whole process in the AA147 group and 4μ8c group). Western blotting was used to detect the expression of ERS-related proteins [glucose-regulated protein 78 (GRP78), phosphorylated-inositol-requiring enzyme 1 (p-IRE1), and phosphorylated-eukaryotic translation initiation factor-2α (p-eIF2α)], and apoptosis-related proteins (Bcl-2, Bax, caspase-3, and cleaved caspase-3). The mRNA of ERS-related genes, and ATF6 [homocysteine-inducible, endoplasmic reticulum stress-inducible, ubiquitin-like domain member 1 (Herpud1), protein disulfide isomerase associated 4 (Pdia4) and Sel-1 suppressor of lin-12-like (Sel1L)] and spliced XBP1 [XBP1s, include DnaJ heat shock protein family member B9 (Erdj4), Sec24 related gene family, member D (Sec24d) and signal sequence receptor, gamma (Ssr3)] induced transcriptional response-related genes were measured by real-time quantitative polymerase chain reaction (RT-qPCR). A cell counting kit-8 (CCK-8) assay was used to detect the viability of HT22 cells. Immunofluorescence was utilized to test the expression of cleaved caspase-3.Results:Compared with the blank control group, the expression of ERS-related proteins p-IRE1 and p-eIF2α were significantly increased at 12 hours and 3 hours following OGD/R, respectively (p-IRE1/β-actin: 2.09±0.10 vs. 1.00±0.00, p-eIF2α/β-actin: 1.39±0.11 vs. 1.00±0.00, both P < 0.01). The mRNA expressions of ERS-related genes [ATF6, XBP1s, unspliced XBP1 (XBP1u), activating transcription factor 4 (ATF4), CCAAT/EBP homologous protein (CHOP)] were also upregulated in different OGD/R timepoint in HT22 cells, which indicated ERS was activated in OGD/R-stimulated HT22 cells. Compared with the OGD/R model group, the expression of protein p-IRE1 was not changed, but the mRNA of XBP1s and XBP1u were obviously downregulated in the OGD/R+AA147 group [XBP1s (2 -ΔΔCt): 0.76 (0.71, 0.92) vs. 1.13 (1.03, 1.29), XBP1u (2 -ΔΔCt): 0.29±0.05 vs. 0.52±0.04, both P < 0.01], whereas the expressions of XBP1s-induced transcriptional response downstream genes did not change significantly. Compared with the OGD/R model group, the protein of short-form ATF6 (sATF6) and GRP78 were not changed after administration of 4μ8c, neither was the mRNA expression of ATF6-induced transcriptional response-related genes. These results showed that the mRNA expression of XBP1s and XBP1u were inhibited by AA147-induced activation of ATF6, but no crosstalk was observed between the transcriptional response induced by ATF6 and XBP1s. Compared with the blank control group, the cell viability decreased significantly at OGD/R 3 hours [(44.64±5.12) % vs. (99.13±5.76) %, P < 0.01], the ratios of apoptosis-related proteins Bax/Bcl-2 and cleaved caspase-3/caspase-3 were significantly increased at OGD/R 3 hours and OGD 0 hour, respectively (Bax/Bcl-2: 6.15±1.65 vs. 1.00±0.00, cleaved caspase-3/caspase-3: 17.48±2.75 vs. 1.00±0.00, both P < 0.01), which indicated that apoptosis was activated in OGD/R-treated HT22 cells. Compared with the OGD/R model group, the cell viability decreased significantly [(36.52±17.78)% vs. (69.90±9.43)%, P < 0.01], and the ratios of Bax/Bcl-2 and cleaved caspase-3/caspase-3 were significantly upregulated in the OGD/R+AA147 group in HT22 cells (Bax/Bcl-2: 2.06±0.31 vs. 1.10±0.25, cleaved caspase-3/caspase-3: 3.35±0.59 vs. 0.55±0.09, both P < 0.01). Conclusion:Under our experimental conditions, no obvious crosstalk between the transcriptional response induced by ATF6 and XBP1s was observed, while ATF6 activation induced by AA147 suppressed mRNA expression of XBP1s and XBP1u and promoted cell death in OGD/R-treated HT22 cells.

A cyclodextrin-based nanoformulation achieves co-delivery of ginsenoside Rg3 and quercetin for chemo-immunotherapy in colorectal cancer

The immune checkpoint blockade therapy has profoundly revolutionized the field of cancer immunotherapy. However, despite great promise for a variety of cancers, the efficacy of immune checkpoint inhibitors is still low in colorectal cancer (CRC). This is mainly due to the immunosuppressive feature of the tumor microenvironment (TME). Emerging evidence reveals that certain chemotherapeutic drugs induce immunogenic cell death (ICD), demonstrating great potential for remodeling the immunosuppressive TME. In this study, the potential of ginsenoside Rg3 (Rg3) as an ICD inducer against CRC cells was confirmed using in vitro and in vivo experimental approaches. The ICD efficacy of Rg3 could be significantly enhanced by quercetin (QTN) that elicited reactive oxygen species (ROS). To ameliorate in vivo delivery barriers associated with chemotherapeutic drugs, a folate (FA)-targeted polyethylene glycol (PEG)-modified amphiphilic cyclodextrin nanoparticle (NP) was developed for co-encapsulation of Rg3 and QTN. The resultant nanoformulation (CD-PEG-FA.Rg3.QTN) significantly prolonged blood circulation and enhanced tumor targeting in an orthotopic CRC mouse model, resulting in the conversion of immunosuppressive TME. Furthermore, the CD-PEG-FA.Rg3.QTN achieved significantly longer survival of animals in combination with Anti-PD-L1. The study provides a promising strategy for the treatment of CRC.

Research progress of the unfolded protein response-activating transcription factor 6 pathway in ischemia-reperfusion injury post cardiac arrest / 中华危重病急救医学

Ischemia/reperfusion (I/R) caused by cardiac arrest (CA) and subsequent cardiopulmonary resuscitation (CPR) was the primary cause of post-cardiac arrest syndrome (PCAS), including post-cardiac arrest myocardial dysfunction and post-cardiac arrest brain injury. Disturbance of endoplasmic reticulum proteostasis, so-called endoplasmic reticulum stress (ERS) was one of the pathological changes induced by I/R injury. The unfolded protein response (UPR) was an adaptive response triggered by ERS in cells. Modulating the UPR arms to alleviate ERS to promote cell survival was promising for attenuating I/R injury. Activating the activating transcription factor6 (ATF6) signaling pathway, one of the arms of the UPR, confers protection against I/R injury in multiple tissues by restoring endoplasmic reticulum proteostasis and reducing oxygen free radicals. This article reviewed the structural characteristics and biological function of ATF6 and focused on its essential role in cardiac and cerebral I/R injury as well as potential therapeutic targets, hoping to provide new ideas for the effective treatment of PCAS.

Natural compounds modulate the autophagy with potential implication of stroke

Stroke is considered a leading cause of mortality and neurological disability, which puts a huge burden on individuals and the community. To date, effective therapy for stroke has been limited by its complex pathological mechanisms. Autophagy refers to an intracellular degrading process with the involvement of lysosomes. Autophagy plays a critical role in maintaining the homeostasis and survival of cells by eliminating damaged or non-essential cellular constituents. Increasing evidence support that autophagy protects neuronal cells from ischemic injury. However, under certain circumstances, autophagy activation induces cell death and aggravates ischemic brain injury. Diverse naturally derived compounds have been found to modulate autophagy and exert neuroprotection against stroke. In the present work, we have reviewed recent advances in naturally derived compounds that regulate autophagy and discussed their potential application in stroke treatment.

SMYD3-PARP16 axis accelerates unfolded protein response and mediates neointima formation

Neointimal hyperplasia after vascular injury is a representative complication of restenosis. Endoplasmic reticulum (ER) stress-induced unfolded protein response (UPR) is involved in the pathogenesis of vascular intimal hyperplasia. PARP16, a member of the poly(ADP-ribose) polymerases family, is correlated with the nuclear envelope and the ER. Here, we found that PERK and IRE1

POST1/C12ORF49 regulates the SREBP pathway by promoting site-1 protease maturation

Sterol-regulatory element binding proteins (SREBPs) are the key transcriptional regulators of lipid metabolism. The activation of SREBP requires translocation of the SREBP precursor from the endoplasmic reticulum to the Golgi, where it is sequentially cleaved by site-1 protease (S1P) and site-2 protease and releases a nuclear form to modulate gene expression. To search for new genes regulating cholesterol metabolism, we perform a genome-wide CRISPR/Cas9 knockout screen and find that partner of site-1 protease (POST1), encoded by C12ORF49, is critically involved in the SREBP signaling. Ablation of POST1 decreases the generation of nuclear SREBP and reduces the expression of SREBP target genes. POST1 binds S1P, which is synthesized as an inactive protease (form A) and becomes fully mature via a two-step autocatalytic process involving forms B'/B and C'/C. POST1 promotes the generation of the functional S1P-C'/C from S1P-B'/B (canonical cleavage) and, notably, from S1P-A directly (non-canonical cleavage) as well. This POST1-mediated S1P activation is also essential for the cleavages of other S1P substrates including ATF6, CREB3 family members and the α/β-subunit precursor of N-acetylglucosamine-1-phosphotransferase. Together, we demonstrate that POST1 is a cofactor controlling S1P maturation and plays important roles in lipid homeostasis, unfolded protein response, lipoprotein metabolism and lysosome biogenesis.

A small molecule UPR modulator for diabetes identified by high throughput screening

Unfolded protein response (UPR) is a stress response that is specific to the endoplasmic reticulum (ER). UPR is activated upon accumulation of unfolded (or misfolded) proteins in the ER's lumen to restore protein folding capacity by increasing the synthesis of chaperones. In addition, UPR also enhances degradation of unfolded proteins and reduces global protein synthesis to alleviate additional accumulation of unfolded proteins in the ER. Herein, we describe a cell-based ultra-high throughput screening (uHTS) campaign that identifies a small molecule that can modulate UPR and ER stress in cellular and

Endoplasmic Reticulum Stress Induces MUC5AC and MUC5B Expression in Human Nasal Airway Epithelial Cells

OBJECTIVES: Endoplasmic reticulum (ER) stress is known to be associated with inflammatory airway diseases, and three major transmembrane receptors: double-stranded RNA-activated protein kinase-like ER kinase, inositol requiring enzyme 1, and activating transcription factor 6 (ATF6) play important roles in ER stress-related proinflammatory signaling. However, the effects of ER stress and these three major signaling pathways on the regulation of the production of airway mucins in human nasal airway epithelial cells have not been elucidated. METHODS: In primary human nasal epithelial cells, the effect of tunicamycin (an ER stress inducer) and 4-phenylbutyric acid (4-PBA, ER stress inhibitor) on the expression of MUC5AC and MUC5B was investigated by reverse transcriptasepolymerase chain reaction, real-time polymerase chain reaction, enzyme immunoassay, and immunoblot analysis. Small interfering RNA (siRNA) transfection was used to identify the mechanisms involved. RESULTS: Tunicamycin increased the expressions of MUC5AC and MUC5B and the mRNA expressions of ER stress-related signaling molecules, including spliced X-box binding protein 1 (XBP-1), transcription factor CCAAT-enhancer-binding protein homologous protein (CHOP), and ATF6. In addition, 4-PBA attenuated the tunicamycin-induced expressions of MUC5AC and MUC5B and the mRNA expressions of ER stress-related signaling molecules. Furthermore, siRNA knockdowns of XBP-1, CHOP, and ATF6 blocked the tunicamycin-induced mRNA expressions and glycoprotein productions of MUC5AC and MUC5B. CONCLUSION.: These results demonstrate that ER stress plays an important role in the regulation of MUC5AC and MUC5B via the activations of XBP-1, CHOP, and ATF6 in human nasal airway epithelial cells.

Effects of metformin on the expressions of ATF6 and Caspase12 in hippocampus of type 2 diabetic rats / 中华内分泌代谢杂志

Objective@#To investigate the effect of metformin on the expressions of activating transcription factor-6(ATF6)and Caspase12 in hippocampus of type 2 diabetic rats.@*Methods@#GK male rats with random blood glucose≥11.1 mmol/L were orally administrated with normal saline(DM group)and metformin(MET group, 85 mg·kg-1·d-1)for 8 weeks(n=10 each group). Wistar male rats were selected as normal contorl group(NC, n=10). After 8 weeks of continuous medication, body weight and fasting plasma glucose(FPG)were measured, and the morphology of HE stained cells and the expressions of ATF6 and Caspase12 by immunohistochemistry staining in the CA1 area of hippocampus were detected.@*Results@#Compared with NC group, the body weight of DM and MET groups decreased(P<0.05), but there was no significant difference between DM and MET groups(P>0.05). In comparison with NC group, FPG levels in DM and MET groups were markedly increased(P<0.05)while FPG level in MET group was significantly lower than that in DM group(P<0.05). The normal nerve cells in the CA1 region of hippocampal were lower in DM and MET groups than those in NC group, especially in DM group. The protein expressions of ATF6 and Caspase12 in DM and MET groups were higher than that in NC group(all P<0.05), and the expressions of the two protein in MET group were significantly decreased as compared with DM group(P<0.05).@*Conclusion@#Metformin reduces the expressions of ATF6 and Caspase12 in hippocampus of type 2 diabetic rats, which may be related to its protective effect on brain. (Chin J Endocrinol Metab, 2018, 34: 594-597)

Tannic acid enhances cisplatin-induced apoptosis of hepatocellular carcinoma HepG2 cells by activating ATF6-CHOP pathway / 实用医学杂志

Objective To detect the activation levels of endoplasmic reticulum stress ATF6-CHOP pathway,and to investigate the molecular mechanism of tannic acid (TA) combined with cisplatin (CDDP) against hepatocellular carcinoma.Methods HepG2 cells were cultured with 180 μM TA or/and 0.9 μg/ml CDDP for 24 h or 48 h.The levels of ATF6 (ATF6α),ATF6B (ATF6β) and CHOP were analyzed by real-time fluorescence quantitative PCR (q-RT-PCR) and western blot.Results We found that after 24 h or 48 h,compared with the control group,ATF6 mRNA and protein levels,ATF6B protein level,CHOP mRNA and protein levels were significantly increased in the TA group,CDDP group or combination group (P ＜ 0.01 or P ＜ 0.05).Conclusion TA can combine with CDDP to increase the levels of endoplasmic reticulum stress ATF6-CHOP pathway,and the ATF6-CHOP pathway may be one of the molecular mechanisms synergistic anti-hepatocellular carcinoma effect of TA and CDDP on HepG2 cells.

Inhibitory effects of L-carnitine on high glucose-induced apoptosis of HAECs by suppressing ATF6 signaling / 中国病理生理杂志

AIM: To investigate the inhibitory effect of L-carnitine on high glucose-induced apoptosis of human aortic endothelial cells (HAECs) and the molecular mechanisms.METHODS: The apoptosis of HAECs was induced by high-glucose incubation.HAECs were treated with L-carnitine at different concentrations (50, 100 and 200 μmol/L).The cell viability was measured by MTT assay.The cell apoptosis was assessed by Hoechst 33258 staining and flow cytometry.Colorimetric method was employed to detect the caspase-3 activity in the HAECs.The protein expression and phosphorylation levels were determined by Western blot.RESULTS: High-glucose incubation dramatically decreased the cell viability and induced apoptosis.The protein kinase R-like endoplasmic reticulum kinase (PERK), inositol-requiring enzyme-1 (IRE1) and activating transcription factor 6 (ATF6) signaling pathways of endoplasmic reticulum stress were activated to induce cell apoptosis via down-stream caspase-4/3 cascade.However, L-carnitine treatment significantly attenuated the cell apoptosis and increased the cell viability in a concentration-dependent manner.L-carnitine also significantly suppressed endoplasmic reticulum stress and ATF6 signaling in high glucose-incubated HAECs without attenuating PERK and IRE1 signaling.The expression of site-1 protease (S1P) and site-2 protease (S2P) was inhibited by L-carnitine treatment, thus decreasing pro-apoptotic factor ATF6 p50 produced by ATF6 cleavage.CONCLUSION: L-carnitine inhibits high glucose-induced apoptosis of HAECs by inhibiting ATF6 signaling.

Investigation on association of activating transcription factor 6 Ala145Pro variant with glucose and lipid metabolism in Chinese / 中华内分泌代谢杂志

Objective To investigate the association of activating transcription factor 6(ATF6)gene Ala145Pro(GCG→CCG)variant with glucose and lipid metabolism in Chinese.Methods The genotypes were determined by PCR-RFLP in 689 Chinese in Shanghai.Among them,361 subjects showed normal glucose regulation,250 cases were newly-diagnosed diabetic patients without taking any drug and 78 cases were probands of early-onset type 2 diabetes pedigrees.The following phenotypes were measured:body height and weight to calculate BMI;waist,hip and femoral circumference to calculate waist-to-hip ratio and waist-to-femoral ratio;blood pressure;plasma glucose levels obtained at 0 and 120 minute during 75 g oral glucose tolerance test;fasting serum lipid profile including total cholesterol,triglyceride,high density lipoprotein-cholesterol and low density lipoprotein-cholesterol;body fat percentage and distribution.Results(1)The frequency of C allele is significantly lower in probands from early-onset type 2 diabetes patients compared with subjects with normal glucose regulation(P=0.035).(2)In subjects with normal glucose regulation,the CC+CG genotype had a significantly lower level of high density lipoprotein cholesterol as compared with GG genotype(P=0.014).(3)In type 2 diabetic patients,the CC+CG genotype had a significantly higher level of low density lipoprotein-cholesterol as compared with GG genotype(P=0.041).Conclusion These findings suggest that variant of ATF6 plays a role in glucose and lipid metabolism in Chinese.