| Intestinal epithelial cell renewal play an important role in the digestion of food,absorption of nutrients,and protection of animal from microbial infections,and others.The small intestine consists mainly of a single layer of columnar epithelial cells covering the villus and crypts.Intestinal epithelial cells are mainly composed of absorber cells,goblet cells,endocrine cells,stem cells,transient expansion(TA)cells,and Paneth cells.Intestinal epithelial cells are renewed every 3–5 days from intestinal stem cells in the steady state,and they continuously migrate and mature along crypt-villus axis and are eventually shed at the apical region of the villi.Fatty acids can provide energy for the body and are important components of subcellular organelles such as cell membrane and mitochondria.According to the number of carbon atoms(C)contained in the carbon chain,fatty acids are divided into three categories of short-chain fatty acids(less than 6 carbons),medium-chain fatty acids(6-12 carbons),and long-chain fatty acids(14 or more carbons).Saturated fatty acids with different chain lengths have different characteristics and functions.In this study,we examined the effects of fatty acids with different carbon chain length on the intestinal epithelial cell regeneration of weaned piglets.Butyric acid(C4),lauric acid(C12),and stearic acid(C18)were used for short-chain,medium-chain and long-chain fatty acids,respectively.Experiment 1: 21 day weaned piglets were randomly divided into 4groups and fed them separately: basic diet + 0.3% soybean oil,basic diet+ 0.3% sodium butyrate,and basic diet + 0.3% lauric acid,basic diet +0.3% stearic acid.All piglets were slaughtered for tissue sampling after having been fed experimental diets for 28 d after weaning.Supplementation with butyrate led to a rise in gain:feed(P = 0.006)compared with the piglets that were fed the control diet from day 15 to 28.However,the average daily gain and feed intake were unaffected among groups.Both ileal villus height and the ratio of villus height/crypt depth were higher in pigs supplemented with butyrate(P = 0.035,P = 0.007)or lauric acid(P = 0.015,P = 0.049)compared with the control diets.Diets supplemented with stearic acid promoted ileal villus height(P = 0.039)compared with the control diets.Further,jejunal crypt depth increased in butyrate supplemented pigs compared with that of those fed on the control diets.Diets supplemented with butyrate,lauric acid,or stearic acid all tended to promote jejunum proliferation(positive cells for Ki67/crypt)compared with the control.The Ki67-labeled cell number per crypt of ileum were significantly increased in piglets that were fed butyrate(P =0.001)or stearic acid(P = 0.002)compared with that of those fed on the control diets.Furthermore,in jejunum,the expression levels of activated caspase 3 and villin were increased in piglets fed butyrate(P = 0.001,P =0.004),lauric acid(P = 0.001,P = 0.0003),or stearic acid(P = 0.001,P =0.016)diets as compared to those on control diets.However,these three fatty acids had no effect on caspase 3 activation and villin protein expression level in the ileum.Experiment 2: Procine jejuna epitheial cells(IPEC-J2)were treated with different concentrations of butyric acid,lauric acid or stearic acid for 24,48 and 72 hours,respectively.It was found that three fatty acids promoted intestinal epithelial cell differentiation at low concentrations.Meanwhile,three fatty acids inhibited cell proliferation and induced cell death in dose-and time-dependent manner.We investigated the mechanism of intestinal epithelial cell death induced by three different fatty acids,respectively.Our results revealed that butyrate induced IPEC-J2 cells apoptosis through the caspase signaling pathway and partially depended on the p38 MAPK signaling pathway.Medium-chain fatty acids and long-chain fatty acids are absorbed into intestinal epithelial cells and form triglycerides with diglycerides.Our results showed that lauric acid and stearic acid significantly promoted triglyceride formation in IPEC-J2 cells.And lauric acid induced apoptosis by promoting the accumulation of triglycerides in cells partly dependent on the p38 MAPK signaling pathway.However,the accumulation of triglycerides in stearic acid-treated cells may alleviate the toxic effects of stearic acid on the cells.In addition,our results indicated that stearic acid induced apoptosis by triggering endoplasmic reticulum stress.In summary,our results showed that lauric acid or stearic acid did not effect the growth performance of weaned piglets and butyrate improved weaned piglets intestinal digestibility.In addition,fatty acids with different chain lengths may promoted the intestinal epithelial cell regeneration by significantly promoting the cell differentiation and apoptosis and tending to increase the cell proliferation.This result was further confirmed by the research results that fatty acids with different chain length promoted IPEC-J2 cells differentiation at low concentrations.The above research provide a basis for future application of fatty acids in the production of weaned piglets.Furthermore,this study found that fatty acids with different chain lengths induced IPEC-J2 cell apoptosis and its mechanism at high concentrations.This research provides a basis for the application of fatty acids in the treatment of intestinal diseases in the future. |
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