Study Of The Effect Of LAT1 On Milk Protein Synthesis In Mammary Gland Of Dairy Cow

Dairy cow is an important animal and milk quantity and quality of dairy cow is used to evaluate animal husbandry. Although there is a lot of dairy farming in our country,the average yield of dairy cow is still lower than other country. The milk protein percentage is lower and not enough to people’s demand. Milk is produced from secretory epithelial cells,which compose of mammary acinus. Screening and identification some genes which regulate mammary gland development and lactation is important to improve milk performance,and promote milk industry.L-type amino acid transporter 1(LAT1) is neutralamino acid transporter,which is charge to transport aromatic amino acid and branched chain amino acid. LAT1 has been detected in liver,bone marrow,brain,musc le,placenta,testis,and spleen. There is some research on LAT1 in breast cancer. But few studies were reported on normal mammary gland.In order to clarify the relationship between LAT1 expression and lactation,we detected the expr ession of LAT1 in lactating mammary glands with high quality milk,lactating mammary glands with low quality milk and mammary glands in dry cows by fluorescence quantitative PCR,western blot,and immunof luorescence. We also detected the effect of LAT1 on milk protein synthesis in cultured mammary epithelial cells by RNA interference and gene overexpression technologies. The results showed that LAT1 express ion was significant higher in lactating mammary glands with high quality milk compared with mammary glands with low quality milk and dry cows. The levels of LAT1 in mammary gland with low quality milk were also significant higher than mammary gland in dry cows. In lactating cows,LAT1 was localized in mammary epithelial cells of ac inus. LAT1 was also detected in connectivetissue and adipose tissue around acinus with lower fluor escence. In dry cows,LAT1 was localized inductal epithelial cells. In LAT1 overexpr essed mammar y epithelial cells,LAT1 increased β-cas einexpression. On the contrary,β-casein expression was decreased when LAT1 was knocked down. But the expression of 4F2 hcdid not changed when LAT1 expression was overexpressed or knocked down in cultural mammary epithelial cells.mTOR signal pathway is participated in regulating protein translation. In order to clarifyif LAT1 expression is regulated by mTOR signal pathway in mammary epithelial cell,rapamycin was used to inhibit mTOR signal pathway and western blot was used to detected the express ion of LAT1,4F 2hc,β-casein,as well as mTOR,4E- BP1,P70S6K in cultural mammary epithelial cells. The results showed that the expression of p-mTOR,p-4E-BP1,p-P70S6K,as well as LAT 1,4F2 hc,and β-casein were decreased when cells were treated with rapamycin. But the expression of mTOR,4E-BP1,P70S6K did not changed compared with control.Over all,LAT1 expression is associated with lactation ability of dairy cow. LAT1 mediates milk protein synthes is in cultured mammary epithelial cells and its expression was regulated by mTOR signal pathway. All thes eresults provide the experimental theory to improve milk yield and quality,which is important to our milk industry.