Role of activating transcription factor 3 （ATF3） in sublytic C5b-9-induced glomerular mesangial cell apoptosis

Sublytic complement C5b-9 complexes can cause cell apoptosis, but the mechanism of glomerular mesangial cell （GMC） apoptosis mediated by these complexes has not been well defined. The activating transcription factor 3 （ATF3） gene is an immediate early gene for the cell to cope with a variety of stress signals and can promote apoptosis of some cells. In this study, ATF3 expression and cell apoptosis in GMCs induced by sublytic C5b-9 were measured, and then the effects of ATF3 gene over-expression or knockdown on GMC apoptosis induced by sublytic C5b-9 were examined at a fixed time. The results showed that both ATF3 expression and GMC apoptosis were markedly increased and ATF3 over-expression obviously increased sublytic C5b-9-induced GMC apoptosis, whereas ATF3 gene silencing had a significant opposite effect. Collectively, these findings indicate that upregulation of ATF3 gene expression is involved in regulating GMC apoptosis induced by sublytic C5b-9 complexes.

Cardiac Fibroblast-Specific Activating Transcription Factor 3 Promotes Myocardial Repair after Myocardial Infarction

Background：Myocardial ischemia injury is one of the leading causes of death and disability worldwide.Cardiac fibroblasts （CFs） have central roles in modulating cardiac function under pathophysiological conditions.Activating transcription factor 3 （ATF3） plays a self-protective role in counteracting CF dysfunction.However,the precise function of CF-specific ATF3 during myocardial infarction （MI） injury/repair remains incompletely understood.The aim of this study was to determine whether CF-specific ATF3 affected cardiac repair after MI.Methods：Fifteen male C57BL/6 wild-type mice were performed with MI operation to observe the expression of ATF3 at 0,0.5,1.0,3.0,and 7.0 days postoperation.Model for MI was constructed in ATF3TGfl/flColla2-Cre＋ （CF-specific ATF3 overexpression group,n =5） and ATF3TGfl/flColla2-Cre-male mice （without CF-specific ATF3 overexpression group,n =5）.In addition,five mice of ATF3TGfl/flCol1a2-Cre＋ and ATF3TGfl/flCol 1 a2-Cre-were subjected to sham MI operation.Heart function was detected by ultrasound and left ventricular remodeling was observed by Masson staining （myocardial fibrosis area was detected by blue collagen deposition area） at the 28th day after MI surgery in ATF3TGfl/flColla2-Cre＋ and ATF3TGfl/flColla2-Cre-mice received sham or MI operation.Quantitative real-time polymerase chain reaction （qRT-PCR） was used to detect cell proliferation/cell cycle-related gene expression in cardiac tissue.BrdU staining was used to detect fibroblast proliferation.Results：After establishment of an MI model,we found that ATF3 proteins were increased in the heart of mice after MI surgery and dominantly expressed in CFs.Genetic overexpression of ATF3 in CFs （ATF3TGfl/flCol1a2-Cre＋ group） resulted in an improvement in the heart function as indicated by increased cardiac ejection fraction （41.0% vs.30.5%,t =8.610,P =0.001） and increased fractional shortening （26.8% vs.18.1%,t =7.173,P =0.002）,which was accompanied by a decrease in cardiac scar area （23.1% vs.11.0%,t =8.610,P =0.001）.qRT-PCR analysis of CFs isolated from ATF3TGfl/flCol1a2-Cre＋ and ATF3TGfl/flCol1a2-Cre-ischemic hearts revealed a distinct transcriptional profile in ATF3-overexpressing CFs,displaying pro-proliferation properties.BrdU-positive cells significantly increased in ATF3-overexpressing CFs than control CFs under angiotensin Ⅱ stimuli （11.5% vs.6.8%,t =31.599,P =0.001） or serum stimuli （31.6% vs.20.1%,t =31.599,P =0.001）.The 5（6）-carboxyfluorescein N-hydroxysuccinimidyl ester assay showed that the cell numbers of the P2 and P3 generations were higher in the ATF3-overexpressing CFs at 24 h （P2：91.6% vs.71.8%,t =8.465,P=0.015） and 48 h （P3：81.6% vs.51.1%,t =9.029,P =0.012） after semm stimulation.Notably,ATF3 overexpression-induced CF proliferation was clearly increased in the heart after MI injury.Conclusions：We identify that CF-specific ATF3 might contribute to be MI repair through upregulating the expression of cell cycle/proliferation-related genes and enhancing cell proliferation.

Activating transcription factor 3 in immune response and metabolic regulation

Activating transcription factor 3(ATF3)is a member of the ATF/cyclic adenosine monophosphate(cAMP)-response element binding protein(CREB)family of transcription factors.In response to stress stimuli,ATF3 forms dimers to activate or repress gene expression.Further,ATF3 modulates the immune response,atherogenesis,cell cycle,apoptosis,and glucose homeostasis.Recent studies have shown that ATF3 may also be involved in pathogenesis of other diseases.However,more studies are needed to determine the role of ATF3 in metabolic regulation.

Silencing of signal transducer and activator of transcription 3 expression by RNA interference suppresses growth of human hepatocellular carcinoma in tumor-bearing nude mice

AIM： To explore the effect of silencing of signal transducer and activator of transcription 3 （STAT3） expression by RNA interference （RNAi） on growth of human hepatocellular carcinoma （HCC） in tumorbearing nude mice in vivo.METHODS： To construct the recombinant plasmid of pSilencer 3.0-H1-STAT3-siRNA-GFP （pSHI-siRNA- STAT3） and establish the tumor-bearing nude mouse model of the HCC cell line SMMC7721, we used intratumoral injection together with electroblotting to transfect the recombinant plasmid pSHI-siRNA- STAT3 into the transplanted tumor. The weight of the nude mice and tumor volumes were recorded. STAT3 gene transcription was detected by semi-quantitative reverse transcription polymerase chain reaction （RT- PCR）. Level of protein expression and location of STAT3 were determined by Western blotting and immunohistochemical staining. STAT3-related genes such as survivin, c-myc, VEGF, p53 and caspase3 mRNA and protein expression were detected in tumor tissues at the same time. The terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling （TUNEL） assay was used to detect apoptosis of tumor cells.RESULTS： The weight of the treated nude mice increased, and the tumor volume decreased markedly compared with those of the mock-treated and negative control groups （P 〈 0.01）. The results of RT-PCR and Western blotting showed that mRNA and protein levels of STAT3 declined markedly in the treated group. The change in STAT3-related gene expression in tumor tissues at the mRNA and protein level also varied, the expression of survivin, VEGF and c-myc were obviously reduced, and expression of p53 and caspase3 increased （P 〈 0.01）. Most of the tumor tissue ceils in the treated group developed apoptosis that was detected by TUNEL assay.CONCLUSION： Silencing of STAT3 expression by RNAi significantly inhibits expression of STAT3 mRNA and protein, and suppresses growth of human HCC in tumor-bearing nude mice. The mechanism may be related to down-regulation of survivin, VEGF and c-myc and up-regulation of p53 and caspase3 expression. Accordingly, the STAT3 gene may act as an important and effective target in gene therapy of HCC.

Alternate day fasting aggravates atherosclerosis through the suppression of hepatic ATF3 in Apoe^(-/-)mice

Atherosclerosis is the major contributor to cardiovascular mortality worldwide.Alternate day fasting(ADF)has gained growing attention due to its metabolic benefits.However,the effects of ADF on atherosclerotic plaque formation remain inconsistent and controversial in atherosclerotic animal models.The present study was designed to investigate the effects of ADF on atherosclerosis in apolipoprotein E-deficient(Apoe^(-/-))mice.Eleven-week-old male Apoe^(-/-)mice fed with Western diet(WD)were randomly grouped into ad libitum(AL)group and ADF group,and ADF aggravated both the early and advanced atherosclerotic lesion formation,which might be due to the disturbed cholesterol profiles caused by ADF intervention.ADF significantly altered cholesterol metabolism pathways and down-regulated integrated stress response(ISR)in the liver.The hepatic expression of activating transcription factor 3(ATF3)was suppressed in mice treated with ADF and hepatocyte-specific overexpression of Aft3 attenuated the effects of ADF on atherosclerotic plaque formation in Apoe^(-/-)mice.Moreover,the expression of ATF3 could be regulated by Krüppel-like factor 6(KLF6)and both the expressions of ATF3 and KLF6 were regulated by hepatic cellular ISR pathway.In conclusion,ADF aggravates atherosclerosis progression in Apoe^(-/-)mice fed on WD.ADF inhibits the hepatic ISR signaling pathway and decreases the expression of KLF6,subsequently inhibiting ATF3 expression.The suppressed ATF3 expression in the liver mediates the deteriorated effects of ADF on atherosclerosis in Apoe^(-/-)mice.The findings suggest the potentially harmful effects when ADF intervention is applied to the population at high risk of atherosclerosis.

Edaravone protects against oxygen-glucose-serum deprivation/restoration-induced apoptosis in spinal cord astrocytes by inhibiting integrated stress response

We previously found that oxygen-glucose-serum deprivation/restoration（OGSD/R） induces apoptosis of spinal cord astrocytes, possibly via caspase-12 and the integrated stress response, which involves protein kinase R-like endoplasmic reticulum kinase（PERK）, eukaryotic initiation factor 2-alpha（eIF2α） and activating transcription factor 4（ATF4）. We hypothesized that edaravone, a low molecular weight, lipophilic free radical scavenger, would reduce OGSD/R-induced apoptosis of spinal cord astrocytes. To test this, we established primary cultures of rat astrocytes, and exposed them to 8 hours/6 hours of OGSD/R with or without edaravone（0.1, 1, 10, 100 μM） treatment. We found that 100 μM of edaravone significantly suppressed astrocyte apoptosis and inhibited the release of reactive oxygen species. It also inhibited the activation of caspase-12 and caspase-3, and reduced the expression of homologous CCAAT/enhancer binding protein, phosphorylated（p）-PERK, p-eIF2α, and ATF4. These results point to a new use of an established drug in the prevention of OGSD/R-mediated spinal cord astrocyte apoptosis via the integrated stress response.