Insulin signaling, inflammation, and lipolysis in subcutaneous adipose tissue of transition dairy cows either overfed energy during the prepartum period or fed a controlled-energy diet
Insulin signaling, inflammation, and lipolysis in subcutaneous adipose tissue of transition dairy cows either overfed energy during the prepartum period or fed a controlled-energy diet
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DOI：
10.3168/jds.2016-10969
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发表时间：
2016-08-01
影响因子：
3.5
通讯作者：
Wakshlag, J. J.
中科院分区：
文献类型：
--
作者：
Mann, S.;Nydam, D. V.;Wakshlag, J. J.
脂肪组织动员是奶牛过渡期的标志。在干奶期过度饲喂能量的奶牛，与饲喂能量受控日粮的奶牛相比，非酯化脂肪酸（NEFA）和β-羟基丁酸（BHB）浓度更高。在能量摄入过量的奶牛中，脂肪组织水平的血液NEFA浓度升高的原因尚未完全阐明。一种假设是BHB浓度高的奶牛患有脂肪组织特异性胰岛素抵抗，导致产后脂肪组织动员率较高。为了检验这一假设，使用了干奶期能量超过预期需求50%的奶牛皮下脂肪组织活检，以及产后血液BHB浓度高的奶牛（H组; n = 12）。将结果与饲喂能量控制饮食和产后BHB浓度低的奶牛（C组; n = 12）的活检结果进行比较，以形成BHB浓度的最大对比。皮下脂肪组织活检前和60分钟后静脉注射葡萄糖挑战（0.25 g/kg的葡萄糖），在28和10天前预期产犊，以及在第4和21天产后。蛋白质激酶B、细胞外信号调节激酶和葡萄糖敏感性脂肪酶的磷酸化在葡萄糖输注之前和之后通过蛋白质印迹法测定。蛋白质印迹法也用于评估过氧化物酶体增殖物激活受体γ和胰岛素受体β亚基的基线蛋白质丰度。此外，脂肪酸合成酶，脂联素，单核细胞趋化蛋白1和肿瘤坏死因子α的基因表达通过实时定量逆转录PCR测定。通过超声检查确定臀部区域的背膘厚度。H组奶牛产后脂肪生成量显著高于C组，但脂肪分解酶活性与C组无显著差异。H组产后基础血浆胰岛素浓度降低，血清NEFA浓度升高。通过蛋白激酶B、胰岛素受体数量、炎症标志物和脂肪组织中过氧化物酶体增殖物激活受体γ的胰岛素信号传导在各组之间没有差异，但在围产期，H组奶牛脂肪组织中脂联素的表达增加。总之，牛过度饲喂能量饲料和高血药浓度BHB之间NEFA血清浓度的差异可能是由于产后更大的负能量平衡，反映在较低的葡萄糖和胰岛素循环浓度以及动员的脂肪组织质量总量增加，而不是由于脂肪组织胰岛素信号传导的变化。
Adipose tissue mobilization is a hallmark of the transition period in dairy cows. Cows overfed energy during the dry period have higher concentrations of non-esterified fatty acids (NEFA) and beta-hydroxybutyrate (BHB) compared with cows fed a controlled-energy diet prepartum. The reason for an increase in blood NEFA concentrations at the level of adipose tissue in cows overfed energy has not been fully elucidated. One hypothesis is that cows with high BHB concentrations suffer from adipose tissue-specific insulin resistance, leading to higher rates of adipose tissue mobilization in the postpartum period. To test this hypothesis, subcutaneous adipose tissue biopsies of cows overfed energy in excess of predicted requirements by 50% in the dry period, and that had high concentrations of blood BHB postpartum (group H; n = 12), were used. Findings were compared with results of biopsies from cows fed a controlled-energy diet and with low BHB concentrations postpartum (group C; n = 12) to create the biggest contrast in BHB concentrations. Subcutaneous adipose tissue biopsies were obtained before and 60 min after an intravenous glucose challenge (0.25 g/kg of glucose) at 28 and 10 d before expected calving as well as on d 4 and 21 postpartum. Phosphorylation of protein kinase B, extracellular signal-regulated kinase, and hormone-sensitive lipase was determined before and after glucose infusion by Western blot. Western blot was also used to assess the baseline protein abundance of peroxisome proliferator-activated receptor gamma and insulin receptor beta-subunit. In addition, gene expression of fatty acid synthase, adiponectin, monocyte chemoattractant protein 1, and tumor necrosis factor alpha was determined by real-time quantitative reverse-transcription PCR. Backfat thickness was determined in the thurl area by ultrasonography. Cows in group H showed a greater degree of lipogenesis prepartum, but no differences were found in lipolytic enzyme activity postpartum compared with cows in group C. Baseline plasma insulin concentrations were decreased and serum NEFA concentrations increased postpartum in group H. Insulin signaling through protein kinase B, quantity of insulin receptor, markers of inflammation, and peroxisome proliferator-activated receptor gamma in adipose tissue were not different between the groups, but expression of adiponectin was increased in adipose tissue of cows in group H during the immediate peripartum period. In conclusion, differences in serum concentrations of NEFA between cows overfed energy prepartum and high blood concentrations of BHB are likely due to greater negative energy balance postpartum reflected in lower circulating concentrations of glucose and insulin and an increase in the total amount of mobilized adipose tissue mass rather than due to changes in adipose tissue insulin signaling.