OBJECTIVE: To explore the mechanism by which estradiol modulates the immunophenotype of macrophages through the endoplasmic reticulum stress pathway. METHODS: Peritoneal macrophages isolated from C57 mice were cultured in the presence of 60 ng/mL interferon-γ (IFN-γ) followed by treatment with estradiol (1.0 nmol/L) alone, estradiol with estrogen receptor antagonist (Acolbifene, 4 nmol/L), estradiol with IRE1α inhibitor (4 μ 8 C), or estradiol with IRE1α agonist. After the treatments, the expression levels of MHC-Ⅱ, iNOS and endoplasmic reticulum stress marker proteins IRE1α, eIF2α and ATF6 in the macrophages were detected with Western blotting, and the mRNA levels of TGF-β, IL-6, IL-10 and TNF-α were detected with RT-PCR. RESULTS: Estrogen treatment of the macrophages significantly decreased the expressions of M1-related proteins MHC-Ⅱ (P=0.021) and iNOS (P < 0.001) and the mRNA expressions of TNF-α (P=0.003) and IL-6 (P=0.004), increased the mRNA expression of TGF-β (P=0.002) and IL-10 (P=0.008), and up-regulated the protein expressions of IRE1α (P < 0.001) and its downstream transcription factor XBP-1 (P < 0.001). Addition of the estrogen inhibitor obviously blocked the effect of estrogen. Compared with estrogen treatment alone, combined treatment of the macrophages with estrogen and the IRE1α inhibitor 4 μ 8 C significantly up-regulated the protein expressions of MHC-Ⅱ (P=0.002) and iNOS (P=0.003) and the mRNA expressions of TNF-α (P=0.003) and IL-6 (P=0.024), and obviously down-regulated the mRNA expression of TGF-β (P < 0.001) and IL-10 (P < 0.001); these changes were not observed in cells treated with estrogen and the IRE1α agonist. CONCLUSION Estrogen can inhibit the differentiation of murine macrophages into a pro-inflammatory phenotype by up-regulating the IRE1α-XBP-1 signaling axis, thereby producing an inhibitory effect on inflammatory response.
Animals ; Cell Differentiation/drug effects* ; Endoribonucleases/metabolism* ; Estradiol/pharmacology* ; Estrogens/metabolism* ; Interleukin-10 ; Interleukin-6/metabolism* ; Macrophages, Peritoneal/metabolism* ; Mice ; Phenotype ; Protein Serine-Threonine Kinases/metabolism* ; RNA, Messenger/metabolism* ; Signal Transduction/drug effects* ; Transforming Growth Factor beta/metabolism* ; Tumor Necrosis Factor-alpha/metabolism* ; Up-Regulation/drug effects* ; X-Box Binding Protein 1/metabolism*

The aim of this study was to investigate the role of S100 calcium binding protein A16 (S100A16) in lipid metabolism in hepatocytes and its possible biological mechanism. HepG2 cells (human hepatoma cell line) were cultured with fatty acid to establish fatty acid culture model. The control model was cultured without fatty acid. Each model was divided into three groups and transfected with S100a16 over-expression, shRNA and vector plasmids, respectively. The concentration of triglyceride (TG) in the cells was measured by kit, and the lipid droplets was observed by oil red O staining. Immunoprecipitation and mass spectrometry were used to find the interesting proteins interacting with S100A16, and the interaction was verified by immunoprecipitation. The further mechanism was studied by Western blot and qRT-PCR. The results showed that the intracellular lipid droplet and TG concentrations in the fatty acid culture model were significantly higher than those in the control model. The accumulation of intracellular fat in the S100a16 over-expression group was significantly higher than that in the vector plasmid transfection group. There was an interaction between heat shock protein A5 (HSPA5) and S100A16. Over-expression of S100A16 up-regulated protein expression levels of HSPA5, inositol-requiring enzyme 1α (IRE1α) and pIREα1, which belong to endoplasmic reticulum stress HSPA5/IRE1α-XBP1 pathway. Meanwhile, over-expression of S100A16 up-regulated the mRNA expression levels of adipose synthesis-related gene Srebp1c, Acc and Fas. In the S100a16 shRNA plasmid transfection group, the above-mentioned protein and mRNA levels were lower than those of vector plasmid transfection group. These results suggest that S100A16 may promote lipid synthesis in HepG2 cells through endoplasmic reticulum stress HSPA5/IRE1α-XBP1 pathway.
Endoplasmic Reticulum Stress ; Endoribonucleases ; physiology ; Heat-Shock Proteins ; physiology ; Hep G2 Cells ; Humans ; Lipid Metabolism ; Protein-Serine-Threonine Kinases ; physiology ; S100 Proteins ; physiology ; Triglycerides ; biosynthesis ; X-Box Binding Protein 1 ; physiology

OBJECTIVE: To investigate the effect of rosuvastatin on homocysteine (Hcy) induced mousevascular smooth muscle cells(VSMCs) dedifferentiation and endoplasmic reticulum stress(ERS). METHODS: VSMCs were co-cultured with Hcy and different concentration of rosuvastatin (0.1, 1.0 and 10 μmol/L). Cytoskeleton remodeling, VSMCs phenotype markers (smooth muscle actin-α, calponin and osteopontin) and ERS marker mRNAs (Herpud1, XBP1s and GRP78) were detected at predicted time. Tunicamycin was used to induce, respectively 4-phenylbutyrate(4-PBA) inhibition, ERS in VSMCs and cellular migration, proliferation and expression of phenotype proteins were analyzed. Mammalian target of rapamycin(mTOR)-P70S6 kinase (P70S6K) signaling agonist phosphatidic acid and inhibitor rapamycin were used in Rsv treated VSMCs. And then mTOR signaling and ERS associated mRNAs were detected. RESULTS: Compared with Hcy group, Hcy+ Rsv group (1.0 and 10 μmol/L) showed enhanced α-SMA and calponin expression (<0.01), suppressed ERS mRNA levels (<0.01) and promoted polarity of cytoskeleton. Compared with Hcy group, Hcy+Rsv group and Hcy+4-PBA group showed suppressed proliferation, migration and enhanced contractile protein expression (<0.01); while tunicamycin could reverse the effect of Rsv on Hcy treated cells. Furthermore, alleviated mTOR-P70S6K phosphorylation and ERS (<0.01)were observed in Hcy+Rsv group and Hcy+rapamycin group, compared with Hcy group; while phosphatidic acid inhibited the effect of Rsv on mTOR signaling activation and ERS mRNA levels (<0.01). CONCLUSIONS Rosuvastatin could inhibit Hcy induced VSMCs dedifferentiation suppressing ERS, which might be regulated by mTOR-P70S6K signaling.
Actins ; metabolism ; Animals ; Calcium-Binding Proteins ; metabolism ; Cell Dedifferentiation ; drug effects ; Cells, Cultured ; Endoplasmic Reticulum Stress ; drug effects ; Heat-Shock Proteins ; metabolism ; Homocysteine ; Membrane Proteins ; metabolism ; Mice ; Microfilament Proteins ; metabolism ; Muscle, Smooth, Vascular ; cytology ; Myocytes, Smooth Muscle ; cytology ; drug effects ; Ribosomal Protein S6 Kinases, 70-kDa ; metabolism ; Rosuvastatin Calcium ; pharmacology ; TOR Serine-Threonine Kinases ; metabolism ; X-Box Binding Protein 1 ; metabolism

BackgroundA high consumption of fructose leads to hepatic steatosis. About 20-30% of triglycerides are synthesized via de novo lipogenesis. Some studies showed that endoplasmic reticulum stress (ERS) is involved in this process, while others showed that a lipotoxic environment directly influences ER homeostasis. Here, our aim was to investigate the causal relationship between ERS and fatty acid synthesis and the effect of X-box binding protein-1 (XBP-1), one marker of ERS, on hepatic lipid accumulation stimulated by high fructose.

MethodsHepG2 cells were incubated with different concentrations of fructose. Upstream regulators of de novo lipogenesis (i.e., carbohydrate response element-binding protein [ChREBP] and sterol regulatory element-binding protein 1c [SREBP-1c]) were measured by polymerase chain reaction and key lipogenic enzymes (acetyl-CoA carboxylase [ACC], fatty acid synthase [FAS], and stearoyl-CoA desaturase-1 [SCD-1]) by Western blotting. The same lipogenesis-associated factors were then evaluated after exposure of HepG2 cells to high fructose followed by the ERS inhibitor tauroursodeoxycholic acid (TUDCA) or the ERS inducer thapsigargin. Finally, the same lipogenesis-associated factors were evaluated in HepG2 cells after XBP-1 upregulation or downregulation through cell transfection.

ResultsExposure to high fructose increased triglyceride levels in a dose- and time-dependent manner and significantly increased mRNA levels of SREBP-1c and ChREBP and protein levels of FAS, ACC, and SCD-1, concomitant with XBP-1 conversion to an active spliced form. Lipogenesis-associated factors induced by high fructose were inhibited by TUDCA and induced by thapsigargin. Triglyceride level in XBP-1-deficient group decreased significantly compared with high-fructose group (4.41 ± 0.54 μmol/g vs. 6.52 ± 0.38 μmol/g, P < 0.001), as mRNA expressions of SREBP-1c (2.92 ± 0.46 vs. 5.08 ± 0.41, P < 0.01) and protein levels of FAS (0.53 ± 0.06 vs. 0.85 ± 0.05, P = 0.01), SCD-1 (0.65 ± 0.06 vs. 0.90 ± 0.04, P = 0.04), and ACC (0.38 ± 0.03 vs. 0.95 ± 0.06, P < 0.01) decreased. Conversely, levels of triglyceride (4.22 ± 0.54 μmol/g vs. 2.41 ± 0.35 μmol/g, P < 0.001), mRNA expression of SREBP-1c (2.70 ± 0.33 vs. 1.00 ± 0.00, P < 0.01), and protein expression of SCD-1 (0.93 ± 0.06 vs. 0.26 ± 0.05, P < 0.01), ACC (0.98 ± 0.09 vs. 0.43 ± 0.03, P < 0.01), and FAS (0.90 ± 0.33 vs. 0.71 ± 0.02, P = 0.04) in XBP-1s-upregulated group increased compared with the untransfected group.

ConclusionsERS is associated with de novo lipogenesis, and XBP-1 partially mediates high-fructose-induced lipid accumulation in HepG2 cells through augmentation of de novo lipogenesis.

Endoplasmic Reticulum Stress ; physiology ; Fatty Liver ; Fructose ; metabolism ; Hep G2 Cells ; Humans ; Lipogenesis ; physiology ; Liver ; Sterol Regulatory Element Binding Protein 1 ; X-Box Binding Protein 1 ; physiology

Endoplasmic reticulum (ER) stress is involved in the process of kidney fibrosis. Spliced X-box binding protein 1 (XBP1S) is the key mediator of ER stress while its role in fibrosis is still poorly understood. This study was aimed to investigate the role of XBP1S in renal fibrosis and evaluate whether valsartan could alleviate fibrosis through XBP1S. Renal interstitial fibrosis was induced by unilateral ureteral obstruction (UUO) in C57BL/6 mice, and UUO mice were daily administered with valsartan (20 mg/kg) through oral gavage. After 7 days of UUO, at euthanasia, left kidney was collected to examine the histological alteration by using haematoxylin-eosin staining, Masson's trichrome staining, Sirius red staining and immunohistochemistry. Western blot was used to assess XBP1S, targets of XBP1S, fibronectin, α-SMA, BAX and BCL2 protein levels. Real-time polymerase chain reaction was performed to assess NADPH oxidase subunits p47-phox and p67-phox mRNA levels. The results showed that XBP1S expression was decreased by about 70% in the UUO mice compared with that in sham mice (P < 0.01), which was reversed by valsartan administration (P < 0.05). Meanwhile, UUO-induced renal interstitial fibrosis was attenuated by valsartan treatment. In addition, the protein levels of fibronectin and α-SMA were upregulated by UUO induction (P < 0.01), and valsartan administration inhibited the protein levels of fibronectin and α-SMA in UUO mice (P < 0.05). Western blot analysis showed that the ratio of BAX to BCL2 protein level was increased in UUO model compared with that in sham mice, and the increment also was diminished by valsartan treatment (P < 0.05). Finally, UUO-induced mRNA levels of p47-phox and p67-phox were significantly attenuated by valsartan administration (P < 0.05). These results showed that valsartan at least partly restores renal interstitial fibrosis by enhancing XBP1S activation through inhibiting oxidative stress and apoptosis in the UUO mice. These results suggest that XBP1S could be a potential therapeutic target for kidney fibrosis.
Animals ; Apoptosis ; Fibronectins ; Fibrosis ; Kidney ; Kidney Diseases ; Mice ; Mice, Inbred C57BL ; NADPH Oxidases ; Oxidative Stress ; Phosphoproteins ; Real-Time Polymerase Chain Reaction ; Ureteral Obstruction ; X-Box Binding Protein 1

OBJECTIVETo study the association between endoplasmic reticulum stress (ERS) pathway mediated by inositol-requiring kinase 1 (IRE1) and the apoptosis of type II alveolar epithelial cells (AECIIs) exposed to hyperoxia.

METHODSThe primarily cultured AECIIs from preterm rats were devided into an air group and a hyperoxia group. The model of hyperoxia-induced cell injury was established. The cells were harvested at 24, 48, and 72 hours after hyperoxia exposure. An inverted phase-contrast microscope was used to observe morphological changes of the cells. Annexin V/PI double staining flow cytometry was performed to measure cell apoptosis. RT-PCR and Western blot were used to measure the mRNA and protein expression of glucose-regulated protein 78 (GRP78), IRE1, X-box binding protein-1 (XBP-1), and C/EBP homologous protein (CHOP). An immunofluorescence assay was performed to measure the expression of CHOP.

RESULTSOver the time of hyperoxia exposure, the hyperoxia group showed irregular spreading and vacuolization of AECIIs. Compared with the air group, the hyperoxia group showed a significantly increased apoptosis rate of AECIIs and significantly increased mRNA and protein expression of GRP78, IRE1, XBP1, and CHOP compared at all time points (P<0.05). The hyperoxia group had significantly greater fluorescence intensity of CHOP than the air group at all time points. In the hyperoxia group, the protein expression of CHOP was positively correlated with the apoptosis rate of AECIIs and the protein expression of IRE1 and XBP1 (r=0.97, 0.85, and 0.88 respectively; P<0.05).

CONCLUSIONSHyperoxia induces apoptosis of AECIIs possibly through activating the IRE1-XBP1-CHOP pathway.

Animals ; Apoptosis ; Cells, Cultured ; Endoplasmic Reticulum Stress ; physiology ; Endoribonucleases ; physiology ; Epithelial Cells ; physiology ; Female ; Hyperoxia ; metabolism ; pathology ; Multienzyme Complexes ; physiology ; Protein-Serine-Threonine Kinases ; physiology ; Pulmonary Alveoli ; pathology ; Rats ; Rats, Sprague-Dawley ; Transcription Factor CHOP ; physiology ; X-Box Binding Protein 1 ; physiology

Serum palmitic acid (PA), a type of saturated fatty acid, causes lipid accumulation and induces toxicity in hepatocytes. Ethanol (EtOH) is metabolized by the liver and induces hepatic injury and inflammation. Herein, we analyzed the effects of EtOH on PA-induced lipotoxicity in the liver. Our results indicated that EtOH aggravated PA-induced apoptosis and lipid accumulation in primary rat hepatocytes in dose-dependent manner. EtOH intensified PA-caused endoplasmic reticulum (ER) stress response in vitro and in vivo, and the expressions of CHOP, ATF4, and XBP-1 in nucleus were significantly increased. EtOH also increased PA-caused cleaved caspase-3 in cytoplasm. In wild type and CHOP(-/-) mice treated with EtOH and high fat diet (HFD), EtOH worsened the HFD-induced liver injury and dyslipidemia, while CHOP knockout blocked toxic effects of EtOH and PA. Our study suggested that targeting UPR-signaling pathways is a promising, novel approach to reducing EtOH and saturated fatty acid-induced metabolic complications.
Activating Transcription Factor 4 ; drug effects ; metabolism ; Animals ; Apoptosis ; drug effects ; Caspase 3 ; drug effects ; Chemical and Drug Induced Liver Injury ; metabolism ; DNA-Binding Proteins ; drug effects ; metabolism ; Diet, High-Fat ; adverse effects ; Dose-Response Relationship, Drug ; Dyslipidemias ; chemically induced ; metabolism ; Endoplasmic Reticulum Stress ; drug effects ; Ethanol ; metabolism ; toxicity ; Fatty Liver ; chemically induced ; metabolism ; Gene Knockout Techniques ; Hepatocytes ; drug effects ; metabolism ; Lipid Metabolism ; drug effects ; Liver ; metabolism ; Male ; Mice ; Palmitic Acid ; toxicity ; Rats ; Rats, Sprague-Dawley ; Regulatory Factor X Transcription Factors ; Signal Transduction ; drug effects ; Transcription Factor CHOP ; drug effects ; genetics ; metabolism ; Transcription Factors ; drug effects ; metabolism ; Unfolded Protein Response ; drug effects ; X-Box Binding Protein 1

BACKGROUNDPrediabetes is an early stage of β-cell dysfunction presenting as insulin resistance. Evidences suggest that endoplasmic reticulum (ER) stress is involved in the pathogenesis of type 2 diabetes mellitus and prediabetes. In a Chinese population with prediabetes, we investigated single nucleotide polymorphisms (SNPs) in the genes of PERK, JNK, XBP1, BIP and CHOP which encode molecular proteins involved in ER stress pathways.

METHODSNine SNPs at the PERK, JNK, XBP1, BIP and CHOP loci were genotyped by mass spectrometry in 1 448 unrelated individuals. By using a 75 g oral glucose tolerance test (OGTT), 828 subjects were diagnosed as prediabetes and 620 subjects aged 55 years and over as normal controls based on WHO diagnostic criteria (1999) for diabetes mellitus.

RESULTSThe allele C of SNP rs867529 at PERK locus was a risk factor for prediabetes, with the carriers of C allele genotype at a higher risk of prediabetes compared to non-carriers (OR = 1.279, 95% CI: 1.013-1.614, P = 0.039, after adjustment for age, sex and body mass index (BMI). The SNPs rs6750998 at PERK locus was associated with homeostasis model assessments of insulin resistance (HOMA-IR) (P = 0.019), and rs17037621 with BMI (P = 0.044). The allele G of SNP rs10986663 in BIP gene was associated with a decreased risk of prediabetes (OR = 0.699, 95% CI: 0.539-0.907, P = 0.007). The SNP rs2076431 in JNK gene was associated with fasting plasma glucose levels (P = 0.006) and waist-hip ratios (P = 0.019). The SNP rs2239815 in XBP1 gene was associated with 2-hour plasma glucose levels after 75 g oral glucose load (P = 0.048) in the observed population.

CONCLUSIONCommon variants at PERK and BIP loci contributed to the risk of prediabetes, and the genetic variations in JNK and XBP1 genes are associated with diabetes-related clinical parameters in this Chinese population.

Aged ; DNA-Binding Proteins ; genetics ; Diabetes Mellitus, Type 2 ; genetics ; Female ; Genotype ; Humans ; MAP Kinase Kinase 4 ; genetics ; Male ; Middle Aged ; Polymorphism, Single Nucleotide ; genetics ; Prediabetic State ; genetics ; Regulatory Factor X Transcription Factors ; Transcription Factor CHOP ; genetics ; Transcription Factors ; genetics ; X-Box Binding Protein 1 ; eIF-2 Kinase ; genetics

The saturated free fatty acid (FFA), palmitate, could induce apoptosis in various cell types, but little is known about its effects on human umbilical cord-derived mesenchymal stem cells (hUC-MSCs). Here, we investigated whether palmitate induced apoptosis and endoplasmic reticulum (ER) stress in hUC-MSCs. hUC-MSCs were stained by labeled antibodies and identified by flow cytometry. After administration with palmitate, apoptotic cell was assessed by flow cytometry using the Annexin V-FITC/7-AAD apoptosis detection kit. Relative spliced XBP1 levels were analyzed using semi-quantitative RT-PCR. The mRNA of BiP, GRP94, ATF4 and CHOP were analyzed by real-time PCR. Relative BiP and CHOP protein were analyzed using Western blot analysis. The results showed that hUC-MSCs were homogeneously positive for MSC markers; palmitate increased apoptosis of hUC-MSCs and activated XBP1 splicing, BiP, GRP94, ATF4 and CHOP transcription. These findings suggest that palmitate induces apoptosis and ER stress in hUC-MSCs.
Activating Transcription Factor 4 ; metabolism ; Apoptosis ; DNA-Binding Proteins ; metabolism ; Endoplasmic Reticulum Stress ; Heat-Shock Proteins ; metabolism ; Humans ; Membrane Glycoproteins ; metabolism ; Mesenchymal Stromal Cells ; cytology ; drug effects ; Palmitates ; pharmacology ; Regulatory Factor X Transcription Factors ; Transcription Factor CHOP ; metabolism ; Transcription Factors ; metabolism ; Umbilical Cord ; cytology ; X-Box Binding Protein 1

The aim of this study was to explore the effect of 2 different spliceosomes of X-box binding protein 1 (XBP-1), the spliced form XBP-1s and unspliced form XBP-1u, on myeloma cell differentiation and its mechanism. The overexpression plasmids pcDNA3.1-C-XBP1u and pcDNA3.1-C-XBP1s were constructed and transfected into myeloma cell line U266, RPMI8226. The morphology of U266 and RPMI 8226 cells was observed by means of light microscope, the expression rate of CD49e on cell surface was detected by flow cytometry, the ELISA was used to determine the changes of light chain protein level in supernatants of cell culture, the Western blot was used to assay the expression changes of XBP1u and XBP1s. The results showed that the overexpression of XBP1u could promote the myeloma cell differentiation morphologically displaying the maturation of plasmocytes, the CD49e positive expression rates on surface of U266 and RPMI8226 cells were obviously up-regulated from 9.02±0.3% and 5.17±0.92% in control group to 27.7±1.14% and 13.97±1.79% respectively (p<0.01), the levels of light chain protein in supernatants of U266 and RPMI 8226 cell cultures increased from 474.75±19.52 ng/ml and 289.44±6.19 ng/ml in control group to 692.34±21.17 ng/ml and 401.55±13.7 ng/ml respectively (p<0.01, p<0.05), while the above-mentioned parameters in the overexpressed XBP-1s showed no significant changes, which indicated no promotive effect of overexpressed XBP1s on myeloma cell differentiation. It is concluded that the up-regulation of XBP-1u expression plays an important role in the differentiation of myeloma cells.
Cell Differentiation ; genetics ; Cell Line, Tumor ; DNA-Binding Proteins ; genetics ; Gene Expression Regulation, Neoplastic ; Humans ; Multiple Myeloma ; genetics ; pathology ; Regulatory Factor X Transcription Factors ; Spliceosomes ; genetics ; Transcription Factors ; genetics ; Transfection ; X-Box Binding Protein 1