C-Type Natriuretic Peptide/Natriuretic Peptide Receptor B Regulate the Expression and Secretion of Antibacterial Peptide S100A7 in Goat Mammary Gland Through PKG/JNK/c-Jun Signaling Pathway

Abstract

Background C- type natriuretic peptide (CNP) and its receptor natriuretic peptide receptor B (NPR-B) were members of natriuretic peptides system which were well known produced in cardiovascular and central nervous system. However, whether CNP/NPR-B is expressed in mammary gland, and what its role in mammary gland has not been reported. The antimicrobial peptide S100A7 is a critical component of the animal innate immune system and plays important roles to resist infection of pathogens in the mastitis. It is a hypothesis that CNP/NPR-B signaling pathway maybe induces the expression and secretion of S100A7 in mammary epithelial cells to take part in local mammary gland innate immune. In order to verify this hypothesis, goat mammary gland and isolated mammary epithelial cells (MECs) were used to explore the expression of CNP/NPR-B and their physiological roles in goat mammary gland. Results The results showed that goat mammary gland expressed NPR-B but not CNP. Activating NPR-B by treatment with CNP had no effect on synthesis of β-casein and lipid in goat MECs. But the expression and secretion of S100A7 in goat MECs were obviously induced by CNP/NPR-B signaling pathway. After treatment with CNP, the cGMP level in goat MECs were significantly up-regulated. Along with the up-regulation of cGMP level, the phosphorylation levels of JNK and its target c-Jun also increased gradually. KT-5823 is a specific inhibitor for PKG. KT5823 remarkably inhibited the phosphorylation of JNK and c-Jun induced by CNP. Correspondingly, KT5823 evidently inhibited the expression and secretion of S100A7 induced by CNP. On the other hand, the expression of NPR-B and S100A7 were up-regulated in mastitis goat mammary gland. But, there were no significant difference in expression of CNP between health and mastitis goat mammary gland tissues. Goat mastitis model was established in vitro using goat MECs treated by lipopolysaccharide (LPS). LPS treatment also could increase the expression of NPR-B and NPR-B. Conclusions Goat mammary gland expressed NPR-B, indicating mammary gland was target organ for natriuretic peptide system. Moreover, CNP, through NPR-B/JNK/c-Jun signaling pathway to regulate the expression and secretion of S100A7 in MECs, played an important role in mammary gland innate immune.