Effects Of Different Dietary Protein Sources On Growth,Blood Metabolic Items,Liver Transcriptomics And Proteomics Of Rats

Apart for providing a source of amino acids (AA) for protein synthesis, dietary protein also exerts a wide range of biological functions. An example is the soy plant protein which has been recognized as having a hypocholesterolemic effect. Meat protein is an important dietary source of animal protein for human nutritional requirements. Compared to plant protein, meat protein distinguishes itself for its richness in all the essential amino acids. Meat protein from different species have different protein and amino acid composition, therefore intake of different meat protein sources may have different influences on physiology and metabolism. This study was designed to investigate and compare the impacts of different meat protein and soy protein sources on growth and blood metabolic profiles, and liver transcriptomics and proteomics were analyzed to find its molecular evidence. This study will provide novel evidence and suggestions for the health effects of different dietary protein sources in human diets. This study includes three parts:1. Effects of dietary meat protein, soy protein, and casein on growth and blood metabolic profiles of ratsRats were fed synthetic diets for 1 wk that differed only regarding protein source,including casein (as reference protein), soy, pork, beef, chicken and fish proteins. Feed intake,body weight, body adiposity, and blood lipid, glucose, amino acid profiles and insulin were detected. The results showed that 1) compared to casein, intake of soy protein reduced daily body weight gain (reduced by 65%) and blood methionine concentrations (reduced by 53.3%),but increased blood urea concentrations (increased by 53.7%). In addition, compared to casein, intake of soy protein reduced adipose tissue mass (reduced by 22.0%), liver triacylglycerol contents (reduced by 35%) and insulin resistance index (reduced by 69.4%).Therefore, soy protein has a positive effect on regulating lipid metabolism and insulin resistance, but it will cause negative nitrogen balance and inhibit the growth of rats due to the restriction of methionine. 2) Compared to casein, four meat proteins had no effects on body weight gain of rats, but changed blood amino acid concentrations and insulin levels.Compared to casein, intake of pork protein reduced blood leucine, valine and methionine concentrations, while intake of beef, chicken and fish proteins increased blood total amino acid concentrations. Except pork protein, other 3 kinds of meat proteins reduced blood insulin levels (reduced by > 44%) and insulin resistance index (reduced by > 49%). In addition,intake of the four meat protens decreased the body fat level of rats in different degrees:compared to casein, intake of pork and chicken protein reduced adipose tissue mass (reduced by 18.6% and 11.9%) and liver triacylglycerol contents (reduced by 68.2% and 37.1%);Intake of beef protein reduced liver triacylglycerol contents (reduced by 44.9%); Intake of fish protein reduced blood cholesterol concentrations (reduced by 20.4%). Therefore, intake of meat protein elicite a positive effect on regulating lipid metabolism and insulin resistance,and the changes of blood insulin and amino acid concentrations were in agreement.2. Effects of dietary meat protein, soy protein, and casein on liver transcriptomics of ratsAccoding to the results of the first experiment, intake of soy and meat proteins elicite distinct effects on growth and blood biochemical items of rats. Liver is the core organ in regulating substance metabolism. In this study, liver transcriptomes of rats fed soy protein,meat protein and casein (as reference protein) were analyed using RNA-seq method.Upstream regulators of differentially expressed genes were predicted using software. The results show showed that 1) compared to casein, the expression of 1571, 1258, 1172, 1076 and 609genes were altered by soy, chicken, fish, beef, and pork protein, respectively. 2)Functional classification revealed that compared with the casein, both soy and meat proteins increased gene sets describing (control of) the cell cycle, mRNA translation, oxidoreductive transformation and immune system, and reduced gene sets describing lipid metabolism and signaling transduction. Differently, soy protein increased gene sets relating to energy metabolism (oxidative phosphorylation/electron transport chain) and metabolism of non-essential and sulfer-containing amino acids, while except pork protein, other 3 kinds of meat protein reduced gene sets relating to essential amino acids metabolism and increased gene sets relating to amino acid transport. All 4 kinds of meat proteins reduced gene sets relating to insulin signaling pathway. 3) Upstream regulators predicted for soy and all meat protein groups is Nfe212 (nuclear factor erythroid 2-like 2). Upstream regulators predicted for all 4 meat protein groups is Rxra (Retinoid X receptor alpha). Upstream regulators predicted for soy, beef and chicken protein groups is Rictor (rapamycin-insensitive companion of TOR complex 2). Upstream regulators predicted for soy and fish protein groups is Srebfl (sterol regulatory element-binding transcription factor 1). Upstream regulators Srebf2 (sterol regulatory element-binding transcription factor 2) and Scap (sterol regulatory element-binding protein cleavage-activating protein) are specific for fish protein group. Upstream regulators Atf4 (activating transcription factor 4) and Trib3 (tribbles pseudokinase are specific for soy protein group. The above results show that intake of soy and different meat proteins have different effects on liver mRNA expression profiles of rats..3. Effects of dietary soy protein, meat protein and casein on liver proteomics of rats.Accoding to the results of the front two experiments, intake of soy plant and different meat proteins elicite distinct effects on growth, blood biochemical items and liver mRNA expression profiles of rats. In addition to mRNA expression changes, physiological changes are also related to protein expression changes. Liver proteomes of rats fed casein (as reference protein), soy, pork, chicken and fish proteins were detected using iTRAQ method. Upstream regulators of differentially expressed genes were predicted using software. At last, gene functional results from iTRAQ proteomics and RNA-seq transcriptomics data were compared. The results show showed that 1) compared to casein, the abundance of 308, 53,10, and 9 proteins was significantly changed by isolated chicken, soy, fish, and pork proteins,respectively. Very few significantly regulated proteins were located in the overlapping areas.2) Functional classification revealed that compared with the casein, all dietary proteins inhibited the cluster of protein sets relating to fatty acid oxidation and Ppara signaling pathway. Except by chicken protein, protein sets relating to oxidoreductive transformation were increased and energy metabolism and essential amino acid metabolism were inhibited by soy, fish, and pork proteins. Only soy protein increased protein expression of sulfurcontaining and nonessential amino acid metabolism. In addition, soy and fish protein increased protein sets relating to mRNA processing and translation. Only chicken protein increased TCA cycle but reduced protein sets related to immune system. 3) Upstream regulators predicted for the differentially expressed proteins of chicken protein group includedAdipoq (adiponectin, C1Q, and collagen-domain containing), Pten (phosphatase and tensin homologue) and Mknkl (MAP kinase-interacting serine/threonine-protein kinase 1).Upstream regulators predicted for the differentially expressed proteins of soy protein group included Pparg,Ppargcla (peroxisome proliferator-activated receptor gamma coactivator 1-alpha), Ppara (peroxisome proliferator-activated receptor alpha), Srebf2, Nrli2 (nuclear receptor subfamily 1, group I, member 2) and Adipoq. 4) When comparing the protein expression changes with our previous mRNA expression results, consistent changes were observed for: soy protein or fish protein changed AA and fatty acid metabolism,oxidoreductive transformation, and mRNA translation; pork protein increased oxidoreductive transformation and chicken protein reduced Ppar? signaling pathway. The above results show that intake of soy and meat proteins have distinct effects on liver protein expression profiles and these findings are partially in line with our RNA-seq transcriptome results and further show the distinct physiological functions of soy and different meat proteins.