The Role Of PINK1 And Parkin Mediated Mitophagy In The Pathogenesis Of Ulcerative Colitis

Ulcerative colitis(UC)is a chronic and relapsing non-specific inflammatory disease.The main clinical manifestations consist of abdominal pain,diarrhea and bloody mucopurulent stool.In recent years,as the incidence of UC in our country is increasing,it can however,greatly diminish the patients’ quality of life and increase its financial burden,and the risk of canceration increases.At present,the etiology and pathogenesis of UC remains unclear,oxidative stress(OS)and mitochondrial dysfunction are associated with the pathogenesis of UC.Since Lemasters coined the term “mitophagy” in 2005,many studies have shown that it is related to many diseases,such as Parkinson’s disease,idiopathic pulmonary fibrosis(IPF)and so on.At present,most research are focusing on investigating the PINK1 and Parkin.In normal circumstance,PINK1 located in mitochondria.Then,get into the inner mitochondrial membrane(IMM)with the help of the translocator of the outer mitochondrial membrane(TOM)complex and the translocator of the inner mitochondrial membrane(TIM)complex,and finally degradated by mitochondrial protease.However,as a components of the major impact on oxidative stress,mitochondrial will be damaged to depolarization under oxidative stress.Then the degradation of PINK1 is blocked in mitochondrial,accumulating on the outer mitochondrial membrane(OMM).Subsequently PINK1 make Parkin phosphorylation and recruit it to the OMM,which initiate mitophagy.Mitophagy can not only eliminate damaged mitochondria to maintain the mitochondrial homeostasis,but also reduced the excess reactive oxygen species(ROS)which produced by damaged mitochondria,which protect cells from injury.Autophagy is considered as a protective mechanism that against inflammatory damage in UC.Mitophagy is also believed to be related to IBD.At present,there is no research on the role of PINK1/Parkin in the regulation of mitophagy in UC.Objective: This study aims to figure out whether the patients with UC is involved in mitophagy,the expression of mitophagy related protein PINK1 and Parkin,and its correlation with the severity of UC.Method:1 Collect 33 cases of UC patients as experimental subjects.Divide the subjects into three groups according to modified Mayo disease activity index: mild,moderate and sever.Each group contains 11 cases.Collect 11 cases of patients with colonic polyps as control group.2 Collect 4 pieces of colonic mucosal at rectum-sigmoid junction under colonoscope.Observe the histopathology of colonic mucosa with HE staining and watch the ultrastructure of mitochondria through transmission electron microscopy.Detect the expression of PINK1 and Parkin protein by immunohistochemistry and Western Blot method.Use the SPSS13.0,in the method of the analysis of variance(ANOVA)to analyze the dates.Result:1 HE staining The structure of colonic mucosal epithelial is integrity in control group,and glandular cells arranged in neat rows,contained numbers of goblet cells,and a small amount of inflammatory cell infiltration.There were a large number of inflammatory cells infiltration in UC groups mucosa,the structure of crypts are disordered,in the crypts and crypt epithelium presented a large number of neutrophils infiltration,the glands showe deformation,the arrangement are disorderd and the number is less,goblet cells are decreased,and emerge epithelial exfoliation or deletion.2 Transmission electron microscopyDestruction of mitochondria and mitophagy phenomenon are found in the colonic mucosa of UC patients,while in the normal control group the mitochondria morphology and structure are normal and mitochondrial autophagy are not found.3 The expression of PINK1 and Parkin in colonic mucosa by immunohistochemistry stainingPINK1 and Parkin was brown in the cytoplasm of colon mucosa in control group,but was dark brown in UC group and the expression were higher than that in control group.Statistical analysis the integrated optical density(IOD)of PINK1 are mild group(92372 ±17550)>moderate group(71405±1922)> severe group(54203 ± 3574)>control group(31944±25323),comparison of any two group show that P < 0.05,the differences are statistically significant.Statistical analysis the integrated optical density(IOD)of Parkin showed mild group(58435±1114)>moderate group(42160 ± 7798)>severe group(24262±1140)>control group(16274±2463),comparison of any two group show that P < 0.05,the differences are statistically significant.4 The expression of PINK1 and Parkin in colonic mucosa by Western BlotThe expression of PINK1 and Parkin were upregulated in UC group compared with control group.The statistical results of PINK1 expression are mild group(0.3795±0.0108)>moderate group(0.3484±0.0104)>severe group(0.3249 ±0.0180)>control group(0.2832±0.0479),comparison of any two group show that P < 0.05,the differences are statistically significant.The statistical results of Parkin expression are mild group(0.3319±0.0039)> moderate group(0.2910±0.0132)>sever group(0.2448±0.0381)>control group(0.1906± 0.0100),comparison of any two group show that P < 0.05,the differences are statistically significant.Conclusion:1 Mitochondria is damaged and mitophagy occur in UC patients.2 The expression of PINK1 and Parkin,which are mitophagy related protein,increases in colonic mucosa of UC patients,and decreased accompanied with the increase of disease severity.It showed that the mitophagy which regulated by PINK1/Parkin played a key role in the occurrence and development of UC,and the expression level correlation with severity of UC.