Expression And Localization Of Glucose Transporter In Porcine Liver At Different Growth Stages

Objective: The morphological parameters of porcine hepatic lobule have been reported in several studies,but due to the improvement of modern pig breeds and the development of microscopic measurement technology,these parameters need to be measured again.In present study,the diameter and area of porcine liver lobules at different growth stages,as well as the diameter of hepatocytes and nuclei were measured,which provide a data reference for constructing the computer three-dimensional virtual simulation model.The liver was the main organ to maintain blood glucose stability.Glucose uptake by hepatocytes depends on glucose transporters on cell membrane.Studies have been reported that GLUT1,GLUT2,GLUT3,GLUT5 and GLUT8 are highly expressed in human and rat livers,but few studies have been reported on the expression of glucose transporters in pig livers.In this study,the expression and localization of GLUT1,GLUT2,GLUT3,GLUT5 and GLUT8 in pig liver at different growth stages were detected to provide morphological basis for studing the glucose uptake by hepatocytes to maintain the homeostasis of blood glucose metabolism.Methods: The experimental animals in this study were raised in the experimental animal base of College of Animal Science and Technology,Shanxi Agricultural University.Three healthy Landrace sows were selected respectively from different stages: fetal pigs(about 100 days after late gestation),3 weeks(lactation),7 weeks(weaning),11 weeks(growth period),16 weeks(growth period),22 weeks(fattening period)and 26 weeks(fattening period).The liver tissues of the animals were partially placed in Bouin′s solution for histomorphological observation,partially placed in liquid nitrogen for detection of protein and m RNA expression.The expression and localization of GLUT1,GLUT2,GLUT3,GLUT5 and GLUT8 in pig liver at different growth stages were tested by immunohistochemistry,Western Blot and q RT-PCR,and compared with those in rat liver.Results:1.Histological changes of porcine hepatic lobules and hepatocytes at different growth stagesThe morphological structure showed that the boundary of fetal porcine hepatic lobules was not obvious,less interlobular connective tissue.At the age of about 3 weeks after birth,interlobular connective tissue around the portal area began to form,and hepatic lobules were not completely separated.At the age of about 7 weeks after birth,the boundary of hepatic lobules was clear and interlobular connective tissue was completely formed.It suggested that interlobular connective tissue gradually formed with age after birth.The measurement results of hepatic lobule showed that the diameter and area of hepatic lobule increased with age after birth.The morphological structure of liver cells showed that fetal porcine hepatocytes were large in size,round in shape,clear in boundary,closely arranged,and vacuolated in cytoplasm.At about 3 w after birth,hepatocytes were arranged in cord shape,and the cell boundary was not obvious.The results of hepatocytes measurement showed that the diameter of fetal porcine hepatocytes and cell nuclei was large.The diameter of hepatocytes after birth gradually increased with age,while cell nuclei gradually decreased with age.2.Expression and localization of glucose transporters in pig liver at different growth stagesImmunohistochemical results showed that GLUT1 and GLUT5 proteins were mainly located in the cytoplasm and membrane of porcine hepatocytes at different growth stages.GLUT2 and GLUT8 are located at the junction surface of adjacent hepatocytes and the bile duct membrane side,and GLUT8 was also expressed in the cytoplasm.GLUT3 was mainly expressed in cytoplasm around hepatocyte membrane.Western Blot and q RT-PCR results showed that GLUT1,GLUT2,GLUT3,GLUT5 and GLUT8 protein and m RNA were expressed in pig liver at different growth stages.Fetal pigs rely on placenta to obtain glucose and nutrients from maternal blood,while suckling piglets mainly obtain the required nutrients from milk due to underdeveloped digestive organs.In suckling piglets,the expression of GLUT3,GLUT5 and GLUT8 increased,but the expression of GLUT1 and GLUT2 decreased compared with those of fetal pigs.Weaned piglets were obtain nutrient entirely by feeding.The digestive system of weaned piglets were not fully developed and can not adapt to the change of feed.Thus the weaning stage was the most critical stage in pig growth and development.The GLUT1,GLUT2,GLUT3,GLUT5 and GLUT8 expression levels in weaned piglets liver were significantly increased compared with those of fetal pigs.Growing fattening pigs have basically adapted to feed changes,the mainly characters are protein and fat deposition,declined growth.GLUT1,GLUT2,GLUT3,GLUT5 and GLUT8 expression levels in growing and fattening pigs liver were basically at a stable level compared with those of fetal pigs.Therefore,the relative expression levels of GLUT1,GLUT2,GLUT3,GLUT5 and GLUT8 gradually increased during lactation and weaning,while they were basically at a stable level during growth and fattening.3.Location of glucose transporter in rats liver at different agesImmunohistochemical results showed that GLUT1,GLUT5 and GLUT8 were expressed in the cytoplasm and membrane of rat hepatocytes at different ages.GLUT2 was mainly located in the lateral basement membrane of hepatocytes near the hepatic sinusoid.GLUT3 was expressed in cytoplasm around hepatocyte membrane,and the expression in the cytoplasm near the bile duct was more abundant than that in the blood sinus.Conclusion:The content of protein in feed of suckling and weaned piglets was high,but the content of energy feed was relatively low.Therefore,piglets have high energy demand,strong ability to uptake glucose and high expression of glucose transporters.In the growth and fattening stage,the energy feed content was high,the demand for glucose was relatively low,and the expression of glucose transporter was at a stable level.It is suggested that different diets can affect the expression of glucose transporter in liver of pigs at different growth stages,which provides morphological basis and theoretical guidance for modern pig production.