Streptococcus agalactiae Affects Milk Protein Synthesis in Bovine Mammary Epithelial Cells by Inhibiting Tyrosine Kinase/Signal Transduction and Transcriptional Activators and Mammalian Target of Rapamycin Signaling Pathways

  • YANG Delian ,
  • TONG Jinjin ,
  • SUN Mingwei ,
  • ZHANG Jie ,
  • ZHANG Hua ,
  • XIONG Benhai ,
  • JIANG Linshu
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  • 1. Key Laboratory for Dairy Cow Nutrition, College of Animal Science and Technology, Beijing University of Agriculture, Beijing 102206, China;
    2. Institute of Animal Science and Veterinary, Chinese Academy of Agricultural Science, Beijing 100193, China

Received date: 2019-01-23

  Online published: 2019-08-19

Abstract

The objective of this study was to explore the mechanism of the effects of Streptococcus agalactiae (GBS) on milk protein synthesis in bovine mammary epithelial cells (BMECs). Three different concentrations of GBS (MOI=100, 50 and 10) were used to infect BMECs for 1, 2, 4, 6, 8, 12, 18, and 24 h, and each time point was set up corresponding blank control. Then,the effects of GBS on the activity, morphology and apoptosis of BMECs were determined using lactate dehydrogenase (LDH) kit, scanning electron microscopy and flow cytometry. RT-PCR and Western blot were used to detect the mRNA and protein expression of related genes of β-casein and lactoprotein synthesis. The results showed as follows:1) the toxicity of GBS to BMECs was time-and dose-dependent. With the prolongation of infection time and the increase of bacterial concentration, LDH release amount was significantly or extremely significantly higher than that of the control group (P<0.05 or P<0.01). The cell morphology changed significantly after GBS infection. At 6 h of infection, the cell structure was broken and the cell morphology was severely damaged at 8 h of infection. Moreover, the apoptosis of BMECs was significant at 2 h (P<0.05) and extremely significant at 6 h of infection (P<0.01). 2) When the infecting time lasted for 6 h, GBS resulted that the mRNA expression levels of β-casein and the genes regulating lactoprotein expression like tyrosine kinase 2 (JAK2), signal transduction and transcription activator 5a (STAT5a), mammalian target of rapamycin (mTOR), serine/threonine protein kinase 1 (AKT1), ribosomal protein S6 (sRPS6), prolactin receptor (PRLR) and est domain transcription factor 5 (ELF5) in BMECs, were extremely significant down-regulated (P<0.01), while the mRNA expression level of negative regulatory gene eukaryotic translation initiation factor 4E binding protein 1 (EIF4E-BP1) was remarkably up-regulated (P<0.01). The protein expression levels of β-casein, STAT5a, p-STAT5a, mTOR, p-mTOR, and AKT1 in BMECs were dramatically down-regulated by GBS (P<0.01), while P-AKT1 protein expression was completely inhibited. At 8 h of infection, GBS completely inhibited the protein expression of β-casein, STAT5a, p-STAT5a. It can be concluded that GBS can damage the morphological structure of BMECs, promote apoptosis and decrease cell viability, at last having an adverse impact on the normal cell physiological functions. In addition, GBS inhibits the lactoprotein synthesis in BMECs mainly by inhibiting the function of the JAK/STAT and mTOR signaling pathways.

Cite this article

YANG Delian , TONG Jinjin , SUN Mingwei , ZHANG Jie , ZHANG Hua , XIONG Benhai , JIANG Linshu . Streptococcus agalactiae Affects Milk Protein Synthesis in Bovine Mammary Epithelial Cells by Inhibiting Tyrosine Kinase/Signal Transduction and Transcriptional Activators and Mammalian Target of Rapamycin Signaling Pathways[J]. Chinese Journal of Animal Nutrition, 2019 , 31(8) : 3706 -3718 . DOI: 10.3969/j.issn.1006-267x.2019.08.032

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