Branched-chain amino acids: Abundance of their transporters and metabolizing enzymes in adipose tissue, skeletal muscle, and liver of dairy cows at high or normal body condition
Branched-chain amino acids: Abundance of their transporters and metabolizing enzymes in adipose tissue, skeletal muscle, and liver of dairy cows at high or normal body condition
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DOI：
10.3168/jds.2019-17147
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发表时间：
2020-03-01
影响因子：
3.5
通讯作者：
Sauerwein, H.
中科院分区：
文献类型：
--
作者：
Webb, L. A.;Sadri, H.;Sauerwein, H.
支链氨基酸是乳蛋白的主要成分，也是合成非必需氨基酸的重要前体。因此，支链氨基酸的转运和分解在代谢适应哺乳期的高营养需求中起着关键作用。然而，在单胃动物中，支链氨基酸水平的增加与肥胖和某些代谢紊乱有关，如胰岛素敏感性受损。本研究的目的是研究产犊时过度调节对妊娠晚期和哺乳期奶牛血浆支链氨基酸水平以及最相关支链氨基酸转运体和降解酶组织丰度的影响。将38头荷斯坦奶牛随机分为正常(NBCS)组和过度调理(HBCS)组，在哺乳后期分别摄入6.8或7.2MJ的NEL/kg DM，以达到体况评分(BCS)和背脂厚度(UT；NBCS：BCS 1.4 cm)的目标差异，直到产后干涸。在干奶期和下一次哺乳期，奶牛饲喂相同的日粮，以保持BCS和BFT的差异：产前平均值为3.16+/-0.06和1.03+/-0.07厘米(NBCS)比3.77+/-0.08和1.89+/-0.11厘米(HBCS)，产后平均值2.89+/-0.06和0.81+/-0.05厘米(NBCS)比3.30+/-0.06和1.38+0.08厘米(HBCS)。分别在产前19天、产后3天、21天和84天从肝脏、半腱肌肌和皮下脂肪组织(SCAT)采集血液和活检标本。测定溶质载体家族1成员5(SLC1A5)、SLC7A5、SLC38A2以及支链转氨酶2(BCAT2)、支链酮酸脱氢酶E1α(BCKDHA)和支链α-酮酸脱氢酶E1β(BCK-DHB)的mRNA丰度以及BCKDHA的蛋白丰度。所有BCAA的浓度都随时间变化，在HBCS奶牛中最明显，在产犊前后达到最低点。除ILE外，个体支链氨基酸和总支链氨基酸均不存在组间差异。与NBCS奶牛相比，HBCS组SCAT中BCKDHA mRNA和产前BCKDHA蛋白丰度更高，这表明在过度条件下的SCAT中，HBCS组奶牛SCAT中BCAA转氨基产物的不可逆降解具有更大的氧化能力。HBCS奶牛产前肝脏BCKDHA蛋白丰度低于NBCS奶牛。SLC1A5、SLC7A5和BCAT2在SCAT中含量最高，SLC38A2在SCAT和肌肉中含量高于肝脏，BCKDHA和BCKDHB在肝脏和肌肉中含量最高。我们的结果表明，SCAT可能是奶牛BCAA摄取和初始分解代谢的主要部位，但前者与奶牛的BCS和产犊时间无关。
Branched-chain amino acids (BCAA) are major components of milk protein and important precursors for nonessential AA. Thus, the BCAA transport and break-down play a key role in the metabolic adaptation to the high nutrient demands in lactation. However, in monogastrics, increased BCAA levels have been linked with obesity and certain metabolic disorders such as impaired insulin sensitivity. Our objective was to study the effect of over-conditioning at calving on plasma BCAA levels as well as the tissue abundance of the most relevant BCAA transporters and degrading enzymes in dairy cows during late pregnancy and early lactation. Thirty-eight Holstein cows were allocated 15 wk antepartum to either a normal- (NBCS) or overconditioned (HBCS) group, receiving 6.8 or 7.2 MJ of NEL/kg of DM, respectively, during late lactation to reach the targeted differences in body condition score (BCS) and back fat thickness (UT; NBCS: BCS 1.4 cm) until dry-off. During the dry period and next lactation, cows were fed the same diets, whereby differences in BCS and BFT were maintained: prepartum means were 3.16 +/- 0.06 and 1.03 +/- 0.07 cm (NBCS) vs. 3.77 +/- 0.08 and 1.89 +/- 0.11 cm (HBCS), postpartum means were 2.89 +/- 0.06 and 0.81 +/- 0.05 cm (NBCS) vs. 3.30 +/- 0.06 and 1.38 + 0.08 cm (HBCS). Blood and biopsies from liver, semitendinosus muscle, and subcutaneous adipose tissue (scAT) were sampled at d 19 antepartum, 3, 21, and 84 postpartum. Free BC:AA were analyzed and the mRNA abundance of solute carrier family 1 member 5 (SLC1A5), SLC7A5, and SLC38A2 as well as branchedchain aminotransferase 2 (BCAT2), branched-chain oc-keto acid dehydrogenase E1 alpha (BCKDHA), and branched-chain alpha-keto acid dehydrogenase E1 beta (BCK-DHB) as well as the protein abundance of BCKDHA were assessed. Concentrations of all BCAA changed with time, most markedly in HBCS cows, with a nadir around calving. Apart from Ile, neither individual nor total BCAA differed between groups. The HBCS group had greater BCKDHA mRNA as well as higher prepartum BCKDHA protein abundance in scAT than NBCS cows, pointing to a greater oxidative capacity for the irreversible degradation of BCAA transamination products in scAT of over-conditioned cows. Prepartum hepatic BCKDHA protein abundance was lower in HBCS than in NBCS cows. In both groups, SLC1A5, SLC7A5, and BCAT2 mRNA were most abundant in scAT, whereas SLC38A2 was higher in scAT and muscle compared with liver, and BCKDHA and BCKDHB mRNA were greatest in liver and muscle, respectively. Our results indicate that scAT may be a major site of BCAA uptake and initial catabolism, with the former, however, being independent of BCS and time relative to calving in dairy cows.