Abstract
Abstract A central composite design (CCD) study was conducted to understand the relationship among dietary branched chain amino acid (BCAA) ratios and expression of proteins related to amino acid and protein metabolism in the liver of broilers. A total of 2,592 d-old Ross 344 × 708 male broilers were randomly placed in 144 floor pens. Each pen received 1 of 15 dietary treatments in a 23 CCD with 6 center points from 20 to 35 d of age, varying in digestible ratios of isoleucine:lysine (Ile:Lys; 52 to 75), valine:lysine (Val:Lys; 64 to 87), and leucine:lysine (Leu:Lys; 110 to 185). On d 35, 1 bird per pen was selected, euthanized, and liver tissue samples were collected for protein extraction and proteomic analysis via data independent acquisition protein sequencing with a timsTOF Pro 2 LC/MS/MS and Spectronaut 15 software. Dihydrolipoamide acetyltransferase (PDHX), aspartate aminotransferase (GOT2), branched-chain-amino-acid aminotransferase (BCAT1), diphosphomevalonate decarboxylase (MVD), acylamino-acid-releasing enzyme (APEH), and aspartate aminotransferase (GOT1) were identified and quantified. Protein quantification data were analyzed as a CCD using the RSREG procedure of SAS v. 9.4 with significance declared at P ≤ 0.10. When the individual AA effect in the response surface (RS) regression analysis was P ≤ 0.2, raw protein quantification data were analyzed as a 1-way ANOVA and the PDIFF option of SAS set at P ≤ 0.1 using the GLIMMIX procedure. The RS model for MVD and APEH expression were significant (P ≤ 0.0511). However, models for PDHX, GOT2, BCAT1, and GOT1 were not significant (P ≥ 0.1356) and the R2 values ≤ 0.25 for all proteins did not allow for prediction of protein expression means. No linear, quadratic, cross product, or individual BCAA ratio effects were observed for PDHX, GOT2, and BCAT1 (P ≥ 0.1977). A linear model for MVD and APEH protein expression (P ≤ 0.8030) and quadratic model for APEH (P ≤ 0.0552) were significant. MVD increased as Val:Lys ratio increased when Leu:Lys and Ile:Lys were fixed at 148 and 63 or 170 and 70, respectively (P ≤ 0.0926). Low Val:Lys ratio expressed the least hepatic APEH expression when Leu:Lys and Ile:Lys ratios were 148 and 63 or 125 and 70, respectably (P ≤ 0.0153). Hepatic MVD expression decreased as Leu:Lys ratio increased when Val:Lys and Ile:Lys were 75 and 63, respectably (P ≤ 0.0044). GOT1 expression was higher with 170 Leu:Lys ratio compared with 125, when Val:Lys and Ile:Lys ratio were 68 and 70, respectably (P ≤ 0.0460). APEH was greater with a low Ile:Lys ratio when Val:Lys and Leu:Lys were 68 and 125, respectably (P ≤ 0.0786). Varying concentrations of dietary BCAA and their interactions seem to alter hepatic protein expression and may help explain the mechanisms underlying their influence on broiler growth.
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