Study On The Relationship Between PDG And Pancreatic Ductal Epithelium Regeneration In Mouse Model Of Pancreatitis

Objective:The models of acute and chronic inflammation of pancreas in mice were induced by intraperitoneal injection of caerulein.We observed the changes of pancreatic ductal epithelium by histopathological methods and studied the molecular expression of pancreatic ductal epithelium and PDG structure in immunohistochemical sections.We researched the regeneration of pancreatic ductal epithelium and the changes of PDG structure under the condition of inflammation,which provided an experimental basis for the relationship between the regeneration of pancreatic epithelium and PDG structure.Methods:Establishment of pancreatitis models in C57BL/6 mice:Group AP(n=6)received intraperitoneal injection of 50μg/kg dose of caerulein per hour for six times to induce acute pancreatitis.Group CP(n=14)received intraperitoneal injection of 50μg/kg dose of caerulein per hour for six times to induce chronic pancreatitis,and the mice were injected for six weeks(five days per week).Group Control(n=12)received intraperitoneal injection of normal saline per hour for six times.The mice were sacrificed 24 hours after the initial drug administration in group AP,and the tissues were taken every two weeks after initial drug administration in group CP.We evaluated the establishment of the pancreatitis models by calculating the body mass ratio and the histological scores in pathological sections.Researching the changes of PDG structure and pancreatic ductal epithelium:HE staining was used to observe the morphological changes of PDG structure and pancreatic ductal epithelium in acute and chronic pancreatitis models.AB-PAS staining was used to predict the secretion of mucins in PDG and pancreatic ductal structures.Immunohistochemistry of Ki67 was used to observe the proliferation of PDG and pancreatic ductal epithelial structures.Researching the expression of PDG protein markers in inflammatory models:We detected the expression of markers:Sox9,Ngn3 and Pdxl in the PDG by the methods of immunohistochemistry.Results:We successfully established models of acute and chronic pancreatitis through intraperitoneal injection of caerulein.Pancreatic body ratio of group AP was 1.10 ± 0.14%,and group Control was 0.66 ±0.02%(P value<0.01).We found pancreatic acinar edema,tissue congestion and inflammatory cell infiltration under the light microscope in group AP,and the pathological score of acute pancreatitis was 3.33 ±0.52.The pancreatic body ratio of group CP was 0.18 ±0.02%(P value<0.001).The pancreatic acinar atrophy,necrosis and fibrosis were observed under light microscope in group CP,and the pathological score of chronic pancreatitis was 8.50 ±0.54.In the models of acute pancreatitis,we found a few of PDG structures surrounding the pancreatic ductal epithelium and the pancreatic tissue edema was visible.In the models of chronic pancreatitis,much more PDG structures can be observed around the ductal epithelium,and there were pancreatic acinar atrophy,ductal epithelial hyperplasia.In the group CP,the AB-PAS staining of the pancreatic ducts was homogeneous red,while in the PDG structures,the staining was specific bluish violet.Besides,the immunohistochemical HIS scores of Ki67 were 3.5677±0.5854 in PDG and 1.1333 ±0.3266 in pancreatic ducts of group CP,and the score of Ki67 was 0.2667±0.1033 in PDG of group Control.There was obvious difference(P value<0.001),and has statistical significance.In the models of acute pancreatitis,the expression of Pdxl,CK19,Sox9 and Ngn3 protein markers had no significant difference with group Control in the PDG structures;while in the models of chronic pancreatitis,there were positive expression of Pdxl,CK19,Sox9 and Ngn3 protein markers in the PDG structures.The immunohistochemical HIS scores of Pdxl,CK19,Sox9 and Ngn3 in group CP were 1.9667±0.2338,1.0000±0.1789,0.7000±0.2098,0.9000±0.2098 in PDG,and the HIS scores in PDG were 0.0333±0.0817,0.4667±0.2422,0.0333±0.0817,0.0000±0.0000 in group Control.There were significant differences(P value<0.05),and statistically significant.Conclusions:This study successfully established mouse models of acute and chronic pancreatitis by intraperitoneal injection of caerulein.However,the pathologic histology of most acute pancreatitis models was acute edematous pancreatitis.Acinar necrosis was not obvious,and ductal epithelium was damaged slightly.But in the models of chronic pancreatitis,we can clearly find acinar atrophy and necrosis,and the ductal epithelial injury was serious.In the models of acute pancreatitis,pancreatic ductal epithelium was slightly injured,and the regeneration was weak.The proliferation of the PDG structures was not significant in group AP;while in the models of chronic pancreatitis,ductal epithelium was damaged seriously.The proliferation of the PDG structures surrounding ductal epithelial tissue was obvious,and both the duct and the PDG structures were able to secrete mucins.While the PDG structures could secrete specific bluish violet mucins of AB-PAS staining,and it could be concluded that PDG was involved in the repair and regeneration of pancreatic ductal epithelium.In the models of chronic pancreatitis,the expression of Pdxl,CK19,Sox9 and Ngn3 protein markers in PDG were positive.It was well known that these protein markers were closely linked with pancreatic tissue development and differentiation of pancreatic cell maturation.So it could be concluded that PDG may be the pancreatic stem cell nest distributing in the pancreas tissues.When the pancreatic ductal epithelium was injured,PDG may differentiate to ductal epithelial cells to repair the ductal epithelium.