1241
Effects of Arginase Inhibition on Casein Expression and Proliferation of Bovine Mammary Epithelial Cells
Reviews of the ruminant literature concluded that the uptake of Arg by the mammary gland greatly exceeds its output in milk. Furthermore, milk protein yield was increased by post-ruminal infusion of Arg compared with a control treatment that included infusion of water and a mixture of essential amino acids (AA) excluding Arg. Those results indicated that Arg might have an important role on casein synthesis regulation. Our previous research subsequently revealed that excess Arg has a regulatory function on the casein synthesis via effects on transcription of the casein gene. Whether Arg regulates the synthesis of casein by the metabolism of enzymes is not very clear. The specific objective of this work was to elucidate the effect of arginase on the regulation of casein expression using an arginase inhibitor in vitro. Primary bovine mammary epithelial cells (The mammary epithelial cell were isolated from 3 healthy multiparous dairy cow at lactation stage) were cultured with different concentrations (0, 0.5, 1, 2 µmol/L) of the arginase inhibitor nor-NOHA. The casein expression and the proliferation of mammary epithelial cells were determined after 24-h of in vitroculture (triplicate/treatment). Statistical analysis was done using the One-Way Analysis of Variance (ANOVA) with multiple comparison test of Duncan using SPSS v16.0. And the P values less than 0.05 were declared to be significant (P < 0.05). The results showed that the concentration of arginase-1 in different groups dropped (P < 0.05) when the concentrations of nor-NOHA increased, and was quite small in the cells incubated with 1 and 2 µmol nor-NOHA /L. The different concentrations of nor-NOHA had no effect (P>0.05) on the proliferation of mammary epithelial cells. Compared with the control group (0 µmol/L), the expression of casein was lower (P<0.05) in other groups and was lowest in the group with the nor-NOHA concentration of 2 µmol/L. Additionally, in cells incubated with 0.5 µmol/L nor-NOHA the expression level of OTC and ODC was significantly lower (P<0.05) than other treatments. The expression of eNOS was lowest (P<0.05) in the group with the nor-NOHA concentration of 1 µmol/L. In conclusion, the activity of arginase can be inhibited by nor-NOHA. Furthermore, nor-NOHA affected expression of casein and some arginine metabolism-related enzymes. With the increase of nor-NOHA concentration, the inhibitory effects on casein increased.
Keywords: arginine, casei expression