The Establishment Of Esophageal Precancerous Lesion Model By Using P53 Conditional Knockout Mouse In Esophageal Epithelium

Esophageal cancer?EC?is a common malignant tumor of digestive tract.It is the sixth most common cause of death from cancer in the world.The annual death toll of EC is more than 400,000,which is a serious threat to human life and health.China is a country with a high incidence of esophageal cancer,especially Linzhou in Henan Province which is an endemic region of esophageal cancer in China.Esophageal squamous cell cancer?ESCC?is the main type in China,which has high morbility and mortality,poor prognosis and lack of effective clinical diagnosis and treatment methods.Therefore,establishing precancerous lesion ESCC model to study the pathogenesis of EC deeply,identify specific early markers,and develop chemical prophylaxis drugs is currently one of the important strategies to promote the prevention and treatment of ESCC.Tumorigenesis and progression are mainly caused by activation of oncogenes or inactivation of tumor suppressor genes.At present,p53 is one of the most important tumor suppressor genes in cells.Studies have shown that nearly half of human tumors are associated with p53 mutation or deletion.P53 mutation is common in ESCC,which is an early event.Although p53 as a tumor suppressor gene is closely related to ESCC,its specific molecular mechanism is still unclear.Animal models can imitate the development of disease and reveal the characteristics of disease.Transgenic animals are the important models to study the role of specific genes in the carcinogenesis and development of tumor,especially conditional knockout transgenic mice.At present,mouse models of conditional knockout of p53 gene in lung,uterus,stomach,mouth,tongue and forebrain have been successfully established,but there are no reports on the mouse model with specific p53 knockout in esophageal epithelium.The occurrence and development of EC is a complex biological process which is related to multi-factor involvement,multi-stage progression,and multiple gene abnormal expressions.Study has confirmed that the occurrence of ESCC is a result of the gene changes accumulation combined with environmental factors.However the N-methyl-N-benzyl nitrosamine?NMBzA?is widespread in water,soil and food in the high incidence of esophageal cancer area,which is a kind of nitrosamines and is now recognized as ESCC carcinogen.This study firstly established esophageal epithelial tissue specific p53 knockout mice?KO mice?model,and then established KO mice precancerous lesion model induced by NMBzA.The establishment of the model provides a good platform for further studying the pathogenesis of ESCC and screening effective inhibitors.Part?:Establishment of a mouse model with p53 knockout on esophageal epitheliumMethods1.Breeding of KO mice The mice with genotype B6.p53^flox/flox were mated with ED-L2-Cre^+/-mice,KO mice and control loxp mice of the same litter could be obtained after two generations of hybridization using Cre/loxp system.2.Identification of mouse genotypes by PCR When mice were born 21 days,the tail tip was cut,the genomic DNA was extracted by protease K method,PCR amplification was carried out,then the genotypes were identified by agarose gel electrophoresis.3.Real-time fluorescence quantitative PCR assay The esophagus of KO mice and loxp mice were taken,the mucosal layer was separated from the muscular layer,and the homogenate was ground separately.And the total RNA were extracted by Trizol method,reverse transcriptional reaction was performed.cDNA samples were prepared and used as a template for qPCR detection for p53 mRNA expression of mouse esophageal mucosa.4.Immunohistochemical staining method The expression of P53 protein in esophageal mucosa of KO mice and loxp mice was detected respectively by immunohistochemical method.5.Observation of histopathology Histological changes of esophageal mucosal cells in KO mice and control mice were observed by hematoxylin and eosin staining.Results1.Genotypic identification After two generations of hybridization,mice that were p53 conditional knockout mice of esophageal epithelium with genotype B6.p53^flox/floxED-L2-Cre^+/-were obtained.2.qPCR detection The level of p53 mRNA in the esophageal epithelium of KO mice was significantly lower than that of loxp mice,and the difference was statistically significant?P<0.05?.3.Immunohistochemical staining method The expression of P53 protein in the esophageal epithelium of mice with KO was significantly lower than that of loxp mice by immunohistochemistry?P<0.05?.4.Pathological examination The esophageal epithelium of KO mice was thicker,the basal cells were increased and disordered,and the nuclear polarity was changed,compared with loxp mice.Part?:The precancerous lesion model of KO mouse induced by NMBzA was established and the mechanism P53 involved was studied.Methods1.Experimental animals and groups The mice were divided into two groups according to their genotypes,sex and nest type.All of them were injected subcutaneously with 1 mg/kg of NMBzA,3 times per week for 5 weeks,and then routinely observed and measured their weights.Three mice from the non-knockout group and five mice from the knockout group were euthanized when feeding up to16 weeks,and the remaining mice in each group were killed after 48 weeks of feeding.1.Pathological diagnosis At the 16 th and 48 th week,the mouse esophagus was taken and fixed,4?m sections for HE staining.The pathological changes of the esophageal epithelium were observed under optical microscope,and the pathological grades were done.The number of pathological changes in two groups of mice was recorded and statistically analyzed.2.Immunohistochemical staining Immunohistochemical method was used to detect the expression of Ki67,P21,Bcl-2 and Bax protein in the esophageal tissues of mice in each experimental group.3.Western blotting The expression of P53 protein in human immortalized normal esophageal epithelial cells?SHEE cell?treated with p53 siRNA was detected by western blotting.4.Soft-agar colony formation assay The effect of p53 knockdown and NMBA?25?g/ml?on the transformation of SHEE cells was evaluated.Results1.The monitoring results of mouse body weight showed that both the body weights of the p53 non-knockout mice treated with NMBzA and p53 knockout mice treated with NMBzA had a smooth increase and no difference between the two groups.2.Pathological findings showed that there were hyperplasia lesions in both p53knockout group and non-knockout group treated with NMBzA at 16 weeks.The number of lesions in knockout group was significantly higher than that in non-knockout group,and there were simple hyperplasias in the non-knockout group,while there were mild atypical hyperplasias in the knockout group.After 48 weeks,there were only mild atypical hyperplasias in p53 non-knockout group treated with NMBzA,while there were severe atypical hyperplasias in p53 knockout group treated with NMBzA.And the number of lesions at all levels in p53 knockout group was significantly more than that in p53 non-knockout group?P<0.05?.3.The results of immunohistochemical staining showed that the positive rate of Ki67and Bcl-2 in the esophageal epithelium of the p53 knockout group was significantly higher than that of the non-knockout group,while the positive cell rate of P21 and Bax was significantly decreased in the esophageal epithelium of the p53 knockout group,compared with the non-knockout group.4.The results of detecting the expression of P53 protein in SHEE cell by western blotting showed that the expression of P53 protein was decreased and successfully constructed the p53 knockdown cell line compared with the control group.5.Soft-agar colony formation assay showed that the transformation ability of p53knockdown cells treated with NMBzA was enhanced,compared with the control group.Conclusion1.The mouse model of p53 knockout in esophageal epithelium is successfully established.2.The model of precancerous lesion in esophageal epithelium of the p53 knockout mouse induced by NMBzA is successfully established,and at the cellular level,it is preliminarily proved that the effect of NMBzA and p53 knockdown promote the transformation of esophageal epithelial cells.