Webb, Laura Ashley: Regulation of branched-chain amino acid metabolism in major metabolic tissues of dairy cows during late pregnancy and early lactation. - Bonn, 2020. - Dissertation, Rheinische Friedrich-Wilhelms-Universität Bonn.
Online-Ausgabe in bonndoc: https://nbn-resolving.org/urn:nbn:de:hbz:5-58127
urn: https://nbn-resolving.org/urn:nbn:de:hbz:5-58127,
author = {{Laura Ashley Webb}},
title = {Regulation of branched-chain amino acid metabolism in major metabolic tissues of dairy cows during late pregnancy and early lactation},
school = {Rheinische Friedrich-Wilhelms-Universität Bonn},
year = 2020,
month = apr,

note = {For dairy cows, the transition from late pregnancy to early lactation is characterized by dramatic changes in endocrine status, nutrient utilization as well as tissue metabolism. Specific metabolic processes, e.g., in adipose tissue (AT) thereby contribute to the physiological adaptation to the increased nutrient demands imposed by the onset of lactation. Even though AT is known to be a major site for regulating glucose and lipid metabolism, its role in systemic protein and amino acid metabolism in dairy cows is not clear. The branched-chain amino acids (BCAA) are taken up by the mammary gland in excess and are greatly used for the synthesis of (milk) protein as well as the supply of metabolic intermediates and energy. Their cellular transport and break-down are highly regulated key processes, involving the interaction of several metabolic tissues, one of them possibly AT. Yet, studies on the BCAA transporters or degrading enzymes in ruminant tissues are sparse. Thus, one aim of the present thesis was to characterize the potential capacity of bovine AT (along with liver, skeletal muscle and mammary gland) for BCAA metabolism during late gestation and early lactation by analyzing the tissue abundance (and activity) of the most relevant BCAA transporters and catabolic enzymes as well as the concentration of circulating BCAA on selected time points before and after parturition. Moreover, as high BCAA levels have been linked with obesity and certain metabolic dysfunctions such as impaired insulin sensitivity in mammals, we further aimed to investigate the effect of over-conditioning at calving on the aforementioned variables of BCAA metabolism. Overall, AT consistently had the greatest mRNA abundance of the BCAA transporters and the BCAA transaminating enzyme, branched-chain aminotransferase 2 (BCAT2) when compared to most other tissues, but expressed a rather low oxidative capacity for BCAA (more specifically their keto acids), indicating that AT could be an important site of BCAA uptake and initial degradation in dairy cows. Together with the marginal hepatic mRNA abundance of BCAA transporters and BCAT2 and the high mRNA and protein abundance as well as activity of the subsequent oxidative enzyme in liver, the branched-chain α-keto acid dehydrogenase, it seems that BCAA are only degraded in the liver after being deaminated in peripheral tissues, most likely AT. Furthermore, we detected a decrease in circulating BCAA levels around parturition in our studies, which was associated with the reduced feed intake during this time. Both observations were more pronounced for cows that were over-conditioned at calving. Interestingly, despite the lower feed intake, those cows appeared to have a greater ability than normal-conditioned cows to irreversibly catabolize BCAA in AT, especially before parturition. It is likely that, due to a nutrient oversupply, the over-conditioned cows were in a more anabolic situation during late pregnancy and might have used BCAA metabolites in addition to glycolytic metabolites for synthesizing even more body fat. The present thesis thus provides information about a possible anaplerotic link between BCAA and lipid metabolism in AT of over-conditioned dairy cows and might serve as basis for further studies investigating the role of AT in systemic protein and AA metabolism in cattle during different physiological and pathophysiological conditions.},
url = {http://hdl.handle.net/20.500.11811/8180}

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