MRNA Expression Of Integrin α_vβ₃and Leukemia Inhibitory Factor And DNA Methylation After Pregnant Mice Exposed To Carbon Disulfide

BackgroundOur previous studies revealed that the number of embryos reduced obviously when mice exposed to carbon disulfide (CS2) during the process of embryo implantation. And the reducing embryos numbers is found to be related with the expression of adhesion molecules such as integrin αvβ3and leukemia inhibitory factor (LIF). Integrin αvβ3and LIF, which were the markers of endometrial receptivity, are supposed to be reduced evidently during the embryo implantation period when exposed to CS2. However, the mechanism of the reducing expression remains unidentified. Thus it is of significant importance to study the reason of, in order to discuss the mechanism of embryo toxicity.Previous epidemiology studies showed that the integrin αvβ3expression may be one of the reasons leading to infertility. Other studies found that the low level of LIF mRNA express may be related to female implantation failure. Previous studies revealed that exogenous compounds exposure can affect the efficiency of gene transcription and then influence the protein expression. We can infer that the mRNA expression of integrin αvβ3and LIF may be affected when exposed to CS2during the embryo implantation period. Thus it will be of significant importance to reveal the cause of protein abnormalities and the mechanism of CS2embryotoxicity through investigating the possible mechanism of expression pattern of integrin αvβ3and LIF mRNA during the embryo implantation period.DNA methylation as one the most major epigenetic form, which is the important mechanism to regulate the expression of genes and play an important role in the development of embryonic development. Methylation cytosine mainly located in CpG island in the promoter region, and the CH3was added to cytosine under the catalysis of DNMT(DNA methyltransferase). Recent studies found that DNA methylation influenced the HOX expression and endometrium receptivity. Thus testing the methylation status in the gene promoter region on the basis of research on the mRNA expression of integrin αvβ3and LIF can not only clarify the correlation of DNA methylation and integrin αvβ3and LIF mRNA expression, but also discussion the possible cause of integrin αvβ3and LIF protein abnormalities in depth.Therefore, this study was designed to detect the mRNA expression and methylation status of integrin αvβ3and LIF in order to explore the mechanism of embryotoxicity caused by CS2, to provide a theoretical reference for CS2exposure.ObjectiveThe animal models of embryo development and implantation defects were established to observe the condition of mice embryo development in order to find the pattern of change, then to detect the mRNA expression of Integrin αvβ3and LIF in uterus at different time points, to determine the methylation pattern of CpG islands in gene promoter region of integrin αvβ3and LIF in different exposed groups, to analyze the internal relationship of methylation change and protein expression, in order to reveal the mRNA expression of integrin αvβ3and LIF and DNA methylation on the decrease of integrin αvβ3and LIF protein in uterus of mice exposed to carbon disulfide during embryo implantation.Methods1. Establishment of animal modelDesign for the exposure:Pregnant mice were intraperitoneal injection to CS2for one time at different time points (GD3,GD4, GD5, GD6) during embryo implantation and sacrificed on the corresponding endpoints (GD4, GD5, GD6, GD7) respectively. The day that the female mice mated successfully was identified as the first day of gestation (GD1). Dosage of CS2was designed to be631.4mg/kg (0.4LD50) and the injection volume was0.1ml/10g body weight. Mice in the control group were injected with the corn oil.2. Detection of mRNA expression in murine uterusThe mRNA expressions of integrin αvβ3and LIF in endometrium were measured by reverse transcription-polymerase chain reaction.3. Detection of DNMT1mRNA expression in murine uterusThe mRNA expressions of DNMT1in endometrium were measured by reverse transcription-polymerase chain reaction.4. Detection of methylation pattern of CpG islands in promoter region of integrin αvβ3and LIFThe detection of methylation pattern of CpG islands in promter region of integrin αvβ3and LIF were measures by bisulfite sequencing polymerase chain reaction (BSP) and methylation-specific polymerase chain reaction (MSP).Results1. Embryotoxicity induced by CS2exposure during implantationCompared to control group, nonsignificant differences were observed for the weights of uterus, ovary, liver, spleen, kidney in each exposed groups.Non-parametric test showed that uterus coefficient and ovary coefficient are both smaller in each exposed groups compared to the control group. And the differences are significant. However, the significant differences of liver coefficient, spleen coefficient, kidney coefficient were not detected in each exposed groups. This revealed that reproductive system of mouse will suffer a lot when exposed to CS2during the embryo implantation period.2. Effects of CS2exposure on integrin αvβ3mRNA expressionCompared to control group, the integrinαvβ3mRNA expression on GD4and GD5endpoint for GD3group were reduced evidently by33.21%and35.65%respectively, with significant difference. The GD5and GD6endpoint for GD4group were reduced markedly by44.08%and28.06%respectively, also with significant difference. The above results indicated that exposure to CS2during embryo implantation (GD3,4,5,6) reduced the integrin αvβ3mRNA expression of in uterine tissue on each first endpoint (P<0.05).3. Effects of CS2exposure on LIF mRNA expressionThe LIF expression declined obviously on GD4endpoints when the exposure time was on GD3(P<0.05), nosignificant differences was found for the other endpoints (GD5, GD6, GD7). For the GD4group, the later GD5, GD6and GD7endpoints were reduced by39.98%,17.13%and18.11%respectively, compared to their control groups, with significant difference (P<0.05). For the GD5group, the later GD6endpoint was reduced markedly by29.92%, also with significant difference. However, for the GD6group, significant difference was not found in GD7group. The above results revealed that exposure to CS2on GD4group may cause the expression of LIF on the latter endpoints reduced evidently, which indicated that the GD4may be sensitive exposed point.4. Effects of CS2exposure on DNMT1mRNA expressionThe LIF expression declined obviously on GD4endpoints when the exposure time was on GD3(P<0.05). For the GD4group, the later GD5endpoint was reduced by33.60%. The above results revealed that exposure to CS2may influence the expression of DNMT1.5. Detection of methylation in the promoter region of CpG island of integrin αvβ3and LIFTest results from the Methprimer software showed that there is one CpG island in the promoter region of the integrin αvβ3gene, with14methylation cites. And the fragment length is200bp. On the grounds of the results from mRNA expression detection, we firstly choose the group whose mRNA expression decreased mostly significantly and its control group and then use the bisulfite sequencing polymerase chain reaction (BSP) method to test the methylation status of Integrin αvβ3gene. Each sample was tested for5clones. Finally, the sequencing results showed that there is no methylation occurred in the exposed group and so was the control group. There is nosignificant difference for the methylation status in the14cites in the two groups. We can infer from this that the other exposed group didn’t occur methylation either. BSP sequencing results were same between the exposure groups and control group. the14CpG sites on CpG islands remained in the state of unmethylated. We also used the Methprimer software to detect the CpG islands in the promoter region of the LIF gene. The results showed that there is no CpG island there.Therefore according to the results of methylation detection, the probability of methylation in the promoter region of CpG island of LIF is very small. This suggested that there is no significant association between gene methylation status and mRNA expression of LIF and integrin αvβ3Conclusion 1. Exposure to CS2during embryo implantation reduced the mRNA expression of LIF and integrin αvβ3, which indicates that the low level of mRNA expression of LIF and integrin αvβ3may be one of the main reasons of expression of LIF and integrin αvβ3protein, which may be an important mechanism of embryo implantation disorder.2. Exposure to CS2during embryo implantation didn’t alter the methylation status of integrin αvβ3gene, which indicates that there is no significant association between the CpG islands methylation status and integrin αvβ3mRNA expression, and there is no CpG island in the LIF gene and the probability of methylation in the promoter region for LIF is very small, suggesting that methylation does not participate in LIF and integrin αvβ3gene expression decrease, other effect mechanisms still need to be investigated.