The Effect And Mechanism Of Epidermal Growth Factor On Intestinal Function And Epithelial Cell Turnover In Weaning Piglets

This study determined the effect and mechanism of epidermal growth factor(EGF)on intestinal function and epithelial cell turnover in weaning piglets.Forty-two piglets(Landrace×Yorkshire×Duroc;initial body weight of 6.44 ± 0.12 kg)were weaned at 21-day-old age and randomly assigned to one of three treatment groups:(1)basal diet(control group),(2)basal diet + 200 ?g/kg EGF or(3)basal diet + 400 ?g/kg EGF.There were 14 piglets each group for a 14-day experimental period.In the first 7 day of experiment,7 piglets from each group were randomly selected to sacrifice.By day 14,all animals were killed to collect samples for analyzing piglet growth performance,nutrient digestibility,intestinal morphology,digestive enzymes activities,nutrient transporters expression,the proliferation and differentiation of intestinal epithelial cells as well as the activation of EGFR,Wnt/?-catenin and mTOR signaling pathways.Results showed:(1)Piglet growth performance did not significantly differ among the treatment groups during the overall experimental period(P>0.05).On day 14,supplementing 200 ?g/kg EGF into the piglet diet increased the total tract apparent digestibility(TTAD)of crude protein(P<0.05)and tended to increase the TTAD of phosphorus(P=0.094).The 400 ?g/kg EGF group showed an increased the TTAD of calcium(P<0.05).(2)On day 7,the 200 ?g/kg EGF tended to increase villus height(VH)in the distal small intestine(P=0.069),and villus height: crypt depth(VH:CD;P=0.060)in the proximal small intestine(P<0.05),but decreased(P<0.05)the villus width in the middle segment of small intestine.By day 14,the VH,CD and VH: CD in the middle small intestine were higher(P<0.05)on the 200 ?g/kg EGF group.(3)Dietary supplementation with 400 ?g/kg EGF tended to decrease the small intestinal mucosal sucrase activity on day 7(P=0.06)and day 14(P=0.098).The 200 ?g/kg EGF group increased(P<0.05)the mRNA levels of nutrient transporters Slc2a2(glucose transporter 2),Slc6a19(neutral amino acid transporter)and Slc15a1(peptide transporter 1)as well as the protein abundances of sodium/glucose cotransporter 1(SGLT-1)and peptide transporter 1(PEPT-1).The mRNA levels of nutrient transporters Slc5a1(sodium-glucose linked transporter 1),Slc7a1(L-arginine transporter),Slc1a1(neuronal glutamate transporter),VDR(vitamin D receptor),and TRPV6(transient receptor potential vanilloid type 6)did not significantly differ(P<0.05)among treatment groups.The mRNA expression of calcium transporter S100 G was enhanced on the 400 ?g/kg EGF group(P<0.05).(4)Animals receiving diets supplemented with 200 ?g/kg EGF had a significantly increased Ki-67 positive cell numbers in the proximal,middle and distal parts of small intestine(P<0.01).In the first 7 day of treatment,feeding 200 ?g/kg EGF to piglets decreased the protein abundance of intestinal fatty acid binding protein(I-FABP;P<0.05).By day 14,dietary EGF at 400 ?g/kg concentration increased the intestinal alkaline phosphatase(IAP)mRNA level(P<0.05).However,the addition of 200 ?g/kg EGF tended to increase the mRNA level of proliferating cell nuclear antigen(PCNA;P=0.066).(5)The supplementation of 200 ?g/kg EGF increased the numbers of goblet and enteroendocrine cells in the proximal,middle and distal parts of small intestine(P<0.05).The protein abundance and mRNA level of lysozyme were up-regulated in the 400 ?g/kg EGF group(P<0.05).(6)Dietary supplementation with 200 ?g/kg EGF increased the mRNA levels of genes mucin2 and ITF3(Intestinal trefoil factor;P<0.05).This supplementation also enhanced(P<0.05)the mRNA level of transcription factor Atoh1(atonal homologue 1 gene).The mRNA abundances of transcription factors Gif1(growth factor-independent 1),SPDEF(SAM pointed domain containing ETS transcription factor),and Pdx1(pancreatic and duodenal homeobox 1)were increased in the both 200 and 400 ?g/kg EGF groups(P<0.05),but the Elf3(E74 like ETS transcription factor 3)mRNA level was decreased(P<0.05)on EGF groups.(7)The supplementation of 200 ?g/kg EGF upregulated the EGFR mRNA abundance and the ratio of non-p-?-catenin/?-catenin in villus epithelial cells(P<0.05).The EGFR mRNA expression in crypt epithelial cells was not significantly different among treatment groups(P>0.10).However,dietary supplementation with 200 or 400 ?g/kg EGF increased the mTOR phosphorylation level in intestinal mucosa and the ratio of non-p-?-catenin/?-catenin in crypt epithelial cells(P<0.05).These results demonstrated that low dose EGF(200 ?g/kg)improved the intestinal morphology and the digestive and absorptive function in weaning piglets.Dietary EGF also promoted the proliferation and differentiation of intestinal epithelial cells by affecting EGFR,Wnt/?-catenin and mTOR signaling pathways.Therefore,EGF can be used as a feed additive to promote intestinal development of weaning piglets.