Associations between Forkhead Box O1 (FoxO1) Expression and Indicators of Hepatic Glucose Production in Transition Dairy Cows Supplemented with Dietary Nicotinic Acid

Forkhead box protein O1 (FoxO1) is a transcription factor which promotes hepatic glucose production (HGP) by up-regulating the transcription of gluconeogenic enzymes in monogastric species. The activity of FoxO1 is inhibited by insulin-induced phosphorylation. The aims of the present study were to find associations between FoxO1 expression and variables associated with HGP as affected by feeding regimen in dairy cows during the transition period. Twenty one healthy German Holstein cows were allocated to four groups (LC-CON, HC-CON, LC-NA with 5 cows/group and HC-NA with 6 cows/group, respectively). Cows received 0 (LC-CON and HC-CON) or 24 (LC-NA and HC-NA) g/d nicotinic acid with high (HC) or low (LC) concentrate proportion from -42 days (-41.8 + 4.8; mean + standard deviation) relative to expected calving date (d-42) to d24. Liver biopsy was taken at d-42, 1, 21, and 100. The total protein expression of FoxO1 (tFoxO1) and the extent of phosphorylation of FoxO1 at serine 256 (pFoxO1) were analysed semiquantitatively by Western Blotting. The expression of hepatic mRNA of FoxO1 and seven genes associated with HGP was measured by real-time RT-PCR. Mixed model and Pearson’s correlation were used for statistical evaluation with the level of significance at P<0.05. No dietary effect was observed either on feed intake, energy balance, or on the concentration of blood metabolites. Neither time nor diet affected the expression of FoxO1 total protein and mRNA. A NA × concentrate interaction was found in pFoxO1. However, no corresponding dietary effect was found in the mRNA expression of investigated genes. Different patterns of correlations between FoxO1-related variables and investigated indicators for HGP were found at d21 and 100. The results indicated that the regulation of HGP did not take place on the levels of mRNA and protein expression and the phosphorylation of FoxO1 in dairy cows in early lactation.

叉头框蛋白O1（Forkhead box protein O1, FoxO1）是一种转录因子，在单胃动物中可通过上调糖异生酶的转录来促进肝脏葡萄糖生成（hepatic glucose production, HGP）。FoxO1的活性可被胰岛素诱导的磷酸化所抑制。本研究旨在探究围产期奶牛中，FoxO1表达与受饲喂方案影响的肝脏葡萄糖生成相关变量之间的关联。本研究选取21头健康的德国荷斯坦奶牛，将其分为四组（每组奶牛数分别为：LC-CON、HC-CON、LC-NA组各5头，HC-NA组6头）。所有奶牛从相对于预期产犊日期的-42天（即-41.8±4.8天，均值±标准差）至产后24天，分别饲喂精料比例高（HC）或低（LC）的日粮，并同时添加0（LC-CON与HC-CON组）或24 g/d烟酸（LC-NA与HC-NA组）。分别在-42天、1天、21天及100天采集肝脏活检样本。通过蛋白质免疫印迹（Western Blotting）对FoxO1总蛋白表达量（tFoxO1）以及FoxO1在丝氨酸256位点的磷酸化水平（pFoxO1）进行半定量分析；通过实时荧光定量逆转录聚合酶链反应（real-time RT-PCR）检测肝脏中FoxO1 mRNA以及7个与肝脏葡萄糖生成相关基因的表达量。采用混合模型与皮尔逊相关分析进行统计学评估，显著性水平设定为P<0.05。试验未观察到日粮处理对采食量、能量平衡以及血液代谢物浓度产生显著影响。时间与日粮处理均未对FoxO1总蛋白及mRNA的表达量产生显著影响。在pFoxO1水平上发现了烟酸×精料的交互作用，但未在目标基因的mRNA表达中观察到对应的日粮效应。在21天与100天两个时间点，FoxO1相关变量与肝脏葡萄糖生成评估指标之间呈现出不同的相关模式。本研究结果表明，在泌乳早期的奶牛中，肝脏葡萄糖生成的调控并未发生在FoxO1的mRNA与蛋白表达水平以及其磷酸化修饰层面。