Abstract
(1) Background: The effects of a high-concentrate (HC) diet in inducing mammary epithelial cell apoptosis in dairy cows via the NOD1/Caspase-8 pathway have never been investigated before the current study. (2) Methods: Twelve Holstein Frisian cows at mid-lactation were selected to conduct this research. The animals were randomly allocated to two groups (n = 6), and both groups received one of two diets: a low-concentrate (LC) (forage: concentrate 6:4) or a high-concentrate (HC) (forage: concentrate 4:6) diet. Furthermore, an enzyme activity assay, tunnel cell assay, RT-qPCR, western blotting, and an immunofluorescence antibody (IFA) assay were performed to elucidate the effect of an HC diet in the mammary gland of dairy cows. (3) Results: The tunnel cell assay revealed a significant number of apoptotic cells in HC group, and the concentration of Caspase-3, and Caspase-8 was higher in the HC group than in the LC group. NOD1, Rip-2, Caspase-3, Caspase-8, Caspase-9, and Bax mRNA expressions, and NOD1, Caspase-3, Caspase-8, and Bax protein expressions, in the HC group were markedly higher than those in the LC group. Furthermore, Bcl-2 mRNA and protein expressions were markedly decreased in the HC compared to those in the LC group. (4) Conclusions: A HC diet fed to dairy cows incites subacute ruminal acidosis (SARA), which increases the iE-DAP concentration and induces apoptosis in the mammary gland via the NOD1/Caspase-8 pathway.
Highlights
Dairy ruminants are regularly nourished with high-grain forage to produce a higher milk yield in dairy farming industries. In ruminants, this high-grain forage is associated with subacute ruminal acidosis (SARA)
We studied NOD1-dependent Caspase-8 pathway activation and Bcl-2 regulation to confer the cell apoptosis induced by an HC diet via the translocation of iE-DAP in the mammary gland of dairy cows
Immuno-labeling further confirmed the localization of NOD1 and Caspase-8 in mammary gland tissue epithelial cells, and we found more positive CY3 staining in the HC group, which showed a similar trend to that observed in the case of western blot analysis
Summary
Dairy ruminants are regularly nourished with high-grain forage to produce a higher milk yield in dairy farming industries. In ruminants, this high-grain forage is associated with subacute ruminal acidosis (SARA). A decline in rumen pH leads to the lysis of rumen microorganisms and enhances the permeation ability of the rumen wall, which may allow substantial bacterial components to translocate into the blood circulation [4]. Many micro molecules, such as lipopolysaccharides (LPS) and D-glutamyl-meso-diaminopimelic acid (iE-DAP), are well-known to induce mammary cell inflammation [5]. The facts regarding how iE-DAP induces cellular apoptosis in the mammary gland tissue of dairy cows because of an HC diet are not well-established
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