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l-Lactate Dehydrogenase B Chain Associated with Milk Protein Content in Dairy Cows

1
Department of Animal Science and Technology, College of Animal Bioscience and Technology, Konkuk University, Seoul 143-701, Korea
2
Department of Animal Nutrition and Feed Science, College of Animal Science and Technology, Jilin Agricultural University, Changchun 130118, China
*
Author to whom correspondence should be addressed.
These Authors contributed equally to this work.
Animals 2019, 9(7), 442; https://doi.org/10.3390/ani9070442
Received: 25 April 2019 / Revised: 5 July 2019 / Accepted: 8 July 2019 / Published: 15 July 2019
(This article belongs to the Section Animal Genetics and Genomics)
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Simple Summary

The aim of this study was to explore the genes associated with milk protein content in dairy cows. Seven down-regulated and three up-regulated proteins were found in isolated milk epithelial cells (MECs) from dairy cows with high milk protein level (group High). l-leucine depletion not only decreased the proteins synthesis (p < 0.05), but also decreased l-lactate dehydrogenase B chain (LDH-B) mRNA expression in bovine mammary alveolar cells MAC-T cells (p < 0.05). This study suggested that LDH-B is negatively associated with the milk protein content of dairy cows and has a positive relationship with l-leucine. These findings may provide some theoretical basis to study individual differences in the milk protein synthesis ability of dairy cows.

Abstract

This study aimed to explore genes associated with milk protein content in dairy cows and their relationships with l-leucine. Ten primiparous Holstein cows (93.8 ± 11.56 milking days) fed the same diet were divided into two groups depending on their milk protein contents (group High, 3.34 ± 0.10%; and group Low, 2.86 ± 0.05%). Milk epithelial cells (MECs) were isolated from the collected morning milk and differentially expressed proteins in MECs were explored by two-dimensional gel electrophoresis (2-DE). Then, the mRNA expression of these proteins was detected by real time PCR in MAC-T cells incubated with three different media named positive control (PC), negative control (NC), and l-leucine depletion (NO-leu). Results showed that ten proteins were differentially expressed in MECs from cows in group High. They included seven down-regulated ones (heat shock protein beta-1 (HSPB1), 78 kDa glucose-regulated protein (GRP-78), l-lactate dehydrogenase B chain (LDH-B), malate dehydrogenase, cytoplasmic (MDH1), annexin I (ANXA1), cytokeratin-7 (CK-7), and glyceraldehyde-3-phosphate dehydrogenase (GAPDH)), and three up-regulated ones (prohibitin (PHB), beta casein (CSN2), and alpha S1 casein (CSN1S1)). When l-leucine was depleted from the medium, not only proteins content was lowered (p < 0.05), but also the LDH-B mRNA expression was decreased in MAC-T cells (p < 0.05). In conclusion, LDH-B is negatively associated with the milk protein content of dairy cows and has a positive association with l-leucine. View Full-Text
Keywords: milk epithelial cells; l-leucine; MAC-T cells; milk protein content; l-lactate dehydrogenase B chain milk epithelial cells; l-leucine; MAC-T cells; milk protein content; l-lactate dehydrogenase B chain
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MDPI and ACS Style

Wang, T.; Jeon, S.W.; Jung, U.S.; Kim, M.J.; Lee, H.G. l-Lactate Dehydrogenase B Chain Associated with Milk Protein Content in Dairy Cows. Animals 2019, 9, 442.

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