Influence of low protein diets on gene expression of digestive enzymes and hormone secretion in the gastrointestinal tract of young weaned piglets

To investigate dietary protein level effects on digestive mechanisms, weaned piglets were fed for 45 d with diets containing 20%, 17%, or 14% crude protein （CP） supplemented to meet requirements for essential amino acids. This article describes the influence of dietary protein on gastrointestinal hormones and expression of an array of digestive enzymes in the gastrointestinal tract and pancreas. Results indicated that there were no significant differ- ences in expression of enzymes involved in carbohydrate digestion, except for maltase in the duodenum. In the je- junum, amylase expression in pigs fed 20% CP was much higher than that in pigs fed other diets （P〈0.05） and maltase expression in those fed 17% CP was higher than that in other treatments （P〈0.05）. Although there were no remarkable differences in expression of aminopeptidase in the small intestine or carboxypeptidase in the pancreas （P〉0.05）, there was a trend towards higher expression of various proteases in pigs fed 17% CP. The duodenal expression of en- teropeptidase in diets with 14% and 17% CP was significantly higher than that with 20% CP （P〈0.05）, but treatment differences did not existed in jejunum （P〉0.05）. The expression of GPR93 as a nutrient-responsive G protein-coupled receptor in 14% and 17% CP diets was significantly higher than that in 20% CP diet in the small intestine （P〈0.05）. The expressions of genes for pancreatic enzymes, lipase and elastase, were significantly higher in pigs fed diets with low CP, while similar trends occurred for carboxypeptidase, chymotrypsin and amylase. Conversely, the gastric expres- sions of pepsinogen A and progastricsin were lower with the 17% CP diet. Differences between treatments were found in the gastric antral contents of cholecystokinin and somatostatin： both increased in pigs fed 17% CP, accompanied by decreased content of motilin, which was also seen in plasma concentrations. These patterns were not reflected in duodenal contents. In general, 17% dietary CP was beneficial to the digestion of nutrient substance in the gastroin- testinal tract.

A high-fat diet increases body fat mass and up-regulates expression of genes related to adipogenesis and inflammation in a genetically lean pig

Because of their physiological similarity to humans, pigs provide an excellent model for the study of obesity. This study evaluated diet-induced adiposity in genetically lean pigs and found that body weight and energy intake did not differ between controls and pigs fed the high-fat （HF） diet for three months. However, fat mass percentage, adi- pocyte size, concentrations of total cholesterol （TC）, triglyceride （TG）, high-density lipoprotein cholesterol （HDL-C） and low-density lipoprotein cholesterol （LDL-C）, insulin, and leptin in plasma were significantly higher in HF pigs than in controls. The HF diet increased the expression in backfat tissue of genes responsible for cholesterol synthesis such as Insig-1 and Insig-2. Lipid metabolism-related genes including sterol regulatory element binding protein lc （SREBP-lc）, fatty acid synthase 1 （FASN1）, diacylglycerol O-acyltransferase 2 （DGAT2）, and fatty acid binding protein 4 （FABP4） were significantly up-regulated in backfat tissue, while the expression of proliferator-activated receptor-α（PPAR-α） and carnitine palmitoyl transferase 2 （CPT2）, both involved in fatty acid oxidation, was reduced. In liver tissue, HF feeding significantly elevated the expression of SREBP-lc, FASN1, DGAT2, and hepatocyte nuclear factor-4α （HNF-4α） mRNAs. Microarray analysis further showed that the HF diet had a significant effect on the expression of 576 genes. Among these, 108 genes were related to 21 pathways, with 20 genes involved in adiposity deposition and 26 related to immune response. Our results suggest that an HF diet can induce genetically lean pigs into obesity with body fat mass expansion and adipose-related inflammation.

CIDE gene expression in adipose tissue,liver,and skeletal muscle from obese and lean pigs

The expression of the cell death-inducing DNA fragmentation factorα-like effector（CIDE）family including Cidea,Cideb,and Cidec was significantly increased in mouse and human models of obesity.However,there was less information on these genes’expression in pigs.Here,we hypothesized that different fat accumulation between lean（Duroc×Landrace×Yorkshire gilts,DLY）and obese（Lantang）pigs was attributed to porcine CIDE-modulating lipid metabolism.Our data showed that Cidea and Cidec were expressed at a high level in adipose tissue,and at a relatively high level in skeletal muscle,whereas Cideb was mainly expressed in the liver in both breeds of pig.Lantang pigs had higher white adipose and skeletal muscle Cidea and Cidec mR NA abundance,and hepatic and muscle Cideb mR NA than DLY pigs.Lipid metabolism-related genes including sterol regulatory element binding protein 1c（SREBP-1c）,hepatocyte nuclear factor-4α（HNF-4α）,peroxisome proliferator-activated receptorγcoactivator-1α（PGC-1α）,fatty acid synthase（FASN）,diacylglycerol O-acyltransferase 1（DGAT1）,and DGAT2 showed a higher expression level in adipose tissue from obese pigs than in that from lean pigs.Lantang pigs exhibited higher mR NA abundance for liver SREBP-1c,HNF-4α,and PGC-1α,and higher skeletal muscle SREBP-1c,HNF-4α,PGC-1α,and DGAT2 expression,as compared with DLY pigs.However,the perlipin2 mR NA levels in adipose tissues,liver,and skeletal muscle were significantly lower in obese pigs than in their lean counterparts.Furthermore,plasma non-esterified fatty acid（NEFA）,glucose,and triacylglycerol（TAG）levels were greater in obese pigs than in lean pigs.Finally,data from correlation analysis further found that CIDE mR NA expression was positively correlated with back fat thickness（BFT）,abdominal fat mass（AFM）,and the levels of NEFA,TAG,and glucose in the two breeds.Collectively,these data revealed that the porcine CIDEs possibly modulated lipid metabolism and contributed to the development of fat deposition and obesity in Lantang pigs.