Expression Localization of Angiotensin Converting Enzyme 2(ACE 2)in Dairy Cow Mammary Gland and Its Anti-inflammation Effect

LIU Xiao-qian;LIU Ying;RONG Chao;WANG Kun;XIAO Hang;ZHANG Yuan-shu;Key Laboratory of Animal Physiology and Biochemistry,Ministry of Agriculture,Nanjing Agricultural University;

renin-angiotensin system(RAS);;angiotensin angiotensin converting enzyme 2(ACE 2);;mammary tissue of dairy cows;;expression;;anti-injury

The aim of this study is to gain a clear understanding of the expression distribution of ACE 2through both in vivo and in vitro experiments and also to study ACE 2's anti-injury effect in dairy cow mastitis induced by long-term high concentrate feeding.In vitro,mammary tissues samples from the lactating Holstein cows and Mac-T cells were used.The mRNA and protein expression of ACE 2in bovine mammary gland was determined using RT-PCR and Western blotting.The location of ACE 2protein in Mac-T cell was determined using immune fluorescence method.In vivo,6healthy lactating Holstein cows were divided into 2groups:normal feeding group(40% concentrate,dry matter basis)and high concentrate feeding group(60% concen-trate).After 20 weeks' feeding,mammary biopsy samples and milk samples were collected.Milk LPS content,somatic cell number,as well as some inflammatory indicators including NAGase,AKP and MPO were tested.Histopathological test was also performed.The mRNA expression level of ACE2,ACEand their receptors AT1 and MasRin mammary tissues were analysed using RT-qPCR.The contents of AngII and Ang1-7 were also determined using ELISA.The results showed that both mRNA and protein expression of ACE2 were found in dairy cow mammary gland,ACE 2was located in the cytoplasm and on the membrane of the Mac-T cell.With a long-term high concentrate feeding,somatic cell number and LPS content in milk significantly increased(P<0.01);the activities of NAGase and AKP were significantly higher than those in the control group(P<0.05),MPO activity had no significant differences between the 2groups;mammary gland tissues in the high concentrate group cows found inflammatory injury changes.The mRNA expression level of ACE,ACE2,AT1,MasRincreased,and the mRNA ratio of ACE2/ACE was higher than the control group.Ang1-7content was significantly higher in breast tissue(P<0.05),AngII content was significantly lower(P<0.05).Conclusion:It is the first time that the presence of ACE2 in bovine mammary gland has been confirmed.When mammary inflammatory injuries are induced by long-tern high concentrate feeding,the local RAS in mammary is activated,ratio of ACE/ACE2 varies and the ACE 2-Ang1-7-MasR pathway takes the dominat position,that is to say that the anti-injury effect of ACE 2becomes significant.ACE2 helps to protect the mammary from inflammatory injuries by degrading Ang II to Ang1-7.