Mastitis, the inflammation of mammary glands resulting from bacterial infection, disrupts milk production in lactating mammary glands. In this study, we injected lipopolysaccharide (LPS), one of the endotoxins from Escherichia coli into mouse mammary glands to disrupt milk production, and we investigated the influence of LPS on nutrient uptake, synthesis, and secretion processes for milk component production in alveolar epithelial cells (AEC). The expression of genes relevant to the three-staged milk component production process (nutrient uptake, synthesis, and secretion of milk components) were down-regulated within 12 h after LPS injection in AEC. The internalization of glucose transporter 1 (GLUT-1) from the basolateral membrane to the cytoplasm occurred in accordance with the down-regulation of gene expression 3 h after LPS injection. The abnormal localization of adipophilin and beta-casein was also observed in the LPS-injected mammary glands. SLC7A1, an amino acid transporter, was up-regulated 3 and 6 h after LPS injection. Furthermore, the inactivation of signal transducer and activator of transcription 5 (STAT5) and the activation of STAT3 and nuclear factor-kappa B (NFkappaB) occurred 3 h after LPS injection. These results indicate that the nutrient uptake, synthesis, and secretion of milk components in AEC are rapidly shut down in the lactating mammary glands after LPS injection.

Bovine lactoferrin (bLf) is a multifunctional iron-binding glycoprotein secreted mainly in milk and other secretory fluids. Bovine lactoferrin is reported to promote the growth of bifidobacteria and binding of bLf to bifidobacteria cell is thought to be involved. After separation of bLf half molecule and extraction of surface proteins from bifidobacteria, binding profiles were observed by immunoblotting. No binding was appeared when bLf C-lobe was being reacted with cell surface proteins on PVDF membrane. Conversely, a 50-kDa band was appeared when reacted with either intact bLf or nicked bLf. This result strongly suggests that binding region could be N-lobe.Moreover, blot, probed with nicked bLf, reacted with anti-lactoferricin antibody also produced a 50-kDa band that indicates the binding occurred at lactoferricin region of bLf molecule. Interestingly, despite absence of binding, bLf C-lobe can stimulate the growth of bifidobacteria.