Abstract
Matrix metalloproteinase-9 (MMP-9) is a zinc-dependent enzyme, and plays a crucial role in extracellular matrix degeneration, inflammation and tissue remodeling. However, the relationship between MMP-9 and somatic cell count (SCC) in goat milk and the role of MMP-9 in the regulation of mastitis are still unknown. In this study, we found MMP-9 was predominantly expressed in the spleen, intestine and mammary gland. The SCC in goat milk was positively correlated with MMP-9 expression, and staphylococcus aureus could markedly increase MMP-9 expression in goat mammary epithelial cells (GMEC) in dosage and time dependent manner. We also demonstrated that SB-3CT, an inhibitor of MMP-9, promoted apoptosis and inhibited proliferation in GMEC. Thus, MMP-9 may emerge as an easily measurable and sensitive parameter that reflects the number of somatic cells present in milk and a regulatory factor of apoptosis in GMEC.
Highlights
Matrix metalloproteinase-9 (MMP-9) is a multifunctional protein that is synthesized and secreted widely in various cells, such as capillary endothelial cell, neutrophils and macrophages, and plays important roles in degradation of extracellular matrix, cell migration, cell apoptosis and inflammation [1,2,3,4]
The goat MMP-9 was widely expressed in different tissues, with the highest messenger RNA levels were observed in spleen, followed by intestine and mammary gland, and the lowest levels were detected in heart (Fig 1A)
We propose that the somatic cells count (SCC) in goat milk was positively correlated with MMP-9 messenger RNA (mRNA) expression, and staphylococcus aureus could markedly increase MMP-9
Summary
Matrix metalloproteinase-9 (MMP-9) is a multifunctional protein that is synthesized and secreted widely in various cells, such as capillary endothelial cell, neutrophils and macrophages, and plays important roles in degradation of extracellular matrix, cell migration, cell apoptosis and inflammation [1,2,3,4]. The somatic cells in goat milk consist of mammary epithelial cells and leukocytes including neutrophils, lymphocytes and macrophages [5]. The proportion of leukocytes is about 90% and only 10% of somatic cells are mammary epithelial cells in milk [6, 7]. When breast tissue infected by pathogenic microorganisms, a large number of white blood cells is recruited to the milk, which markedly increases milk somatic cells count (SCC) and activates the immune response [8, 9]. Previous research showed that age, parity, lactation stage and bacterial infection could impact the SCC in milk [13, 14]. Mastitis, caused by bacterial infection, has a profound impact on milk yield and leads to great financial losses. Studies have suggested that somatic cells in PLOS ONE | DOI:10.1371/journal.pone.0160989 August 12, 2016
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