The Effect And Mechanism Of TGF-β1 On The Susceptibility Of Bovine Mammary Epithelial Cells And Bovine Mammary Fibroblasts To Staphylococcus Aureus

Alfalfa which has a higher nutritional value is the main roughage for the cows in developed countries.However,we are riching in crop straw resources,our cows’ main roughage is crop straw which has low nutrition.Therefore,the lacking of high quality roughage is an important factor for restricting the dairy industry in China.In particular,protein nutrition deficiency is an important factor in the high incidence and mortality of infectious diseases.The level of TGF-β1 in PBMCs of cows which fed with straw was significantly higher than that of the alfalfa group.TGF-β1 is a multifunctional cytokine that plays an important role in regulating immunity and cell susceptibility.Therefore,we hypothesized that TGF-β1 has a significant effect on the cow mastitis.Bovine mammary epithelial cells(BMECs)are the first infected cells by exogenous pathogens.Bovine mammary fibroblasts(BMFBs)are stromal cells of mammary gland,which primarily support BMECs and regulate BMECs functions.Therefore,we investigate the effect of TGF-β1 on the susceptibility of BMECs and BMFBs to S.aureus and its mechanism.For this purpose we carry out the following two aspects of work:Firstly,the S.aureus infection model of BMECs was established to detect the susceptibility of S.aureus to BMECs under TGF-β1 treatment.It was found that TGF-β1 significantly promoted S.aureus adhere to and invade into BMECs.The expression of fibronectin(Fn),integrin β1 and Fas m RNA was significantly up-regulated when BMECs treated with TGF-β1 by q RT-PCR detection.The expression of Fn,integrin β1 and Fas at the protein level was also up-regulated by Western blot detection.The adhesion ability of S.aureus to cells significantly increased when expression level of Fn and integrin β1 were up-regulated.Blocking Fn,integrin β1 and Fas function can significantly inhibit the adhesion and invasion of S.aureus to BMECs.TGF-β1 promotes BMECs apoptosis which induced by S.aureus and inhibited the expression of TNF-α and IL-8 after S.aureus infection.Secondly,to determine the relationship between breast fibrosis and S.aureus mammary gland infection,we use anti-α-smooth muscle actin(α-SMA)and anti-I Collagen to block their function.We found that the adhesion and invasion of BMFBs by S.aureus was significantly decreased.When ERK1/2 signaling pathway was blocked,the expression of α-SMA and I Collagen were significantly inhibited and S.aureus’ s ability of adhere to and invade into BMFBs was also decreased.The mouse model of mastitis caused by S.aureus infection was established to detect the effect of TGF-β1 on the colonization of S.aureus in the mammary gland and blood.The results showed that the colonization of S.aureus in the mammary gland and blood of the TGF-β1 treated group was significantly up-regulated.In summary,TGF-β1 promotes the expression of Fn,integrin β1 and Fas on the surface of BMECs and promote S.aureus to adhere to and invade into BMECs.And TGF-β1 enhanced S.aureus induceing BMECs apoptosis and inhibited the expression of TNF-α and IL-8.In the process of TGF-β1-induced fibrosis of BMFBs,S.aureus enhances the adhesion and invasion of BMFBs through α-SMA and I Collagen,and the mechanism is mediated by ERK pathway.TGF-β1 also can promote S.aureus to colonize in the mouse mastitis and blood.So the high level of TGF-β1 in the vitro may be a key factor of the cow mastitis.These results indicate the cytokines were related with the susceptibility of BMECs and BMFBs to S.aureus.It provides new thought for proventing and controling of intensive dairy cow mastitis.