Grass-fed and grain-fed Angus cattle differ in the diet regimes. However, the intricate mechanisms of different beef quality and other phenotypes induced by diet differences are still unclear. Diet affects mitochondrial function and dynamic behavior in response to changes in energy demand and supply. In this study, we examined the mtDNA copy number, mitochondria-related genes expression, and metabolic biomarkers in grass-fed and grain-fed Angus cattle. We found that the grass-fed group had a higher mtDNA copy number than the grain-fed group. Among different tissues, the mtDNA copy number was the highest in the liver than muscle, rumen, and spleen. Based on the transcriptome of the four tissues, a lower expression of mtDNA-encoded genes in the grass-fed group compared to the grain-fed group was discovered. For the mitochondria-related nuclear genes, however, most of them were significantly down-regulated in the muscle of the grass-fed group and up-regulated in the other three tissues. In which, COX6A2, POLG2, PPIF, DCN, and NDUFA12, involving in ATP synthesis, mitochondrial replication, transcription, and maintenance, might contribute to the alterations of mtDNA copy number and gene expression. Meanwhile, 40 and 23 metabolic biomarkers were identified in the blood and muscle of the grain-fed group compared to a grass-fed group, respectively. Integrated analysis of the altered metabolites and gene expression revealed the high expression level of MDH1 in the grain-fed group might contribute to the mitochondrial NADH oxidation and spermidine metabolism for adapting the deletion mtDNA copy number. Overall, the study may provide further deep insight into the adaptive and regulatory modulations of the mitochondrial function in response to different feeding systems in Angus cattle.

中文翻译：

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饮食诱导安格斯牛mtDNA拷贝数和代谢的变化。

草饲和谷饲安格斯牛的饮食方式不同。然而，由饮食差异引起的不同牛肉品质和其他表型的复杂机制仍不清楚。饮食影响线粒体功能和动态行为以响应能量需求和供应的变化。在这项研究中，我们检测了草饲和谷饲安格斯牛的 mtDNA 拷贝数、线粒体相关基因表达和代谢生物标志物。我们发现草食组的 mtDNA 拷贝数高于谷物喂养组。在不同组织中，肝脏中的mtDNA拷贝数高于肌肉、瘤胃和脾脏。基于四种组织的转录组，发现与谷物喂养组相比，草饲组中 mtDNA 编码基因的表达较低。对于线粒体相关的核基因，然而，它们中的大多数在草食组的肌肉中显着下调，而在其他三个组织中上调。其中，COX6A2、POLG2、PPIF、DCN 和 NDUFA12 参与 ATP 合成、线粒体复制、转录和维持，可能有助于 mtDNA 拷贝数和基因表达的改变。同时，与草饲组相比，谷物喂养组的血液和肌肉中分别鉴定出 40 和 23 种代谢生物标志物。对改变的代谢物和基因表达的综合分析表明，谷物喂养组中 MDH1 的高表达水平可能有助于线粒体 NADH 氧化和亚精胺代谢以适应缺失的 mtDNA 拷贝数。总体，