Methionyl-Methionine Promotes α-s1 Casein Synthesis in Bovine Mammary Gland Explants by Enhancing Intracellular Substrate Availability and Activating JAK2-STAT5 and mTOR-Mediated Signaling Pathways.

BACKGROUND: Interest is increasing in the role of peptide-bound amino acids (AAs) in milk protein synthesis because studies have found that the uptake of some essential AAs by the mammary gland cannot meet the requirements for milk protein synthesis. Although the role of dipeptides in milk protein synthesis is clearly established, little is known about the underlying mechanisms. OBJECTIVE: The objective of this study was to determine whether small peptides can be taken up intact by the peptide transporters in mammary tissue explants and the underlying mechanisms of the effects of methionyl-methionine (Met-Met) supplementation on milk protein synthesis. METHODS: Mammary tissue explants were cultured in conditional medium and then treated with different concentrations of Met-Met that replaced 0%, 5%, 10%, 15%, 20%, and 25% of free Met for another 24 h. In some experiments, explants were cultured with an optimal dose of Met-Met with or without the inhibitors of peptide transporter 2 [PepT2; diethylpyrocarbonate (DEPC), 0.1 mmol/L] and aminopeptidase N (APN; bestatin, 20 µmol/L) for 24 h. RESULTS: The substitutions of 15% free Met with Met-Met significantly promoted α-s1 casein (αs1-CN) expression in the mammary explants (P < 0.05). The inhibition of the PepT2 by DEPC or APN by bestatin significantly decreased the Met-Met-stimulated increase of αs1-CN expression (P < 0.05). Compared with the control group (0% Met-Met), absorption of Val, Met, Leu, Phe, Lys, and His was improved, and mRNA abundance of the neutral and basic AA transporter was increased in the 15% Met-Met group (P < 0.05). In addition, the mRNA abundance of the mammalian target of rapamycin (mTOR), p70 ribosomal S6 kinase 1 gene, eukaryotic initiation factor 4E binding protein 1 gene , Janus kinase 2 (JAK2), and signal transducer and activator of transcription 5 (STAT5) was increased in the 15% Met-Met-treated group (P < 0.05). CONCLUSION: Met-Met promoted αs1-CN synthesis in cultured bovine mammary gland explants, and this stimulation may be mediated by enhanced intracellular substrate availability and by activating JAK2-STAT5 and mTOR signaling pathways.

[Distribution characteristics of soil heavy metals in bamboo forest of Phyllostachys edulis on lead-zinc orefield].

The woodland and farmland soil nearby lead-zinc mine has been polluted seriously due to the mining. Bamboo forest of Phyllostachys edulis has high economic value and is distributed widely in China. The Phyllostachys edulis forest nearby lead-zinc mine was selected, and the distribution characteristics of main heavy metal Cu, Zn, Pb and Cd in soil were studied. The result showed that the concentration of Cu, Zn, Pb and Cd in bamboo rhizome zone reached 38.10-50.87, 92.24-137.75, 32.04-46.22 and 0.03-0.35 mg x kg(-1) respectively, which was lower than that in non-rhizome zone soil significantly. This result indicated that the distribution and concentration of heavy metals in soil were influenced partly by bamboo developed rhizome-root system and human frequent tending management. About the influence of distance from pollution source and slope position, the heavy metals content in soil showed a decreasing trend as the distance increased, and for most elements, the content in soil of the middle slope position was high, and was a little lower in upper slope position.

Translocation of gut microbes to epididymal white adipose tissue drives lipid metabolism disorder under heat stress.

Heat stress induces multi-organ damage and serious physiological dysfunction in mammals, and gut bacteria may translocate to extra-intestinal tissues under heat stress pathology. However, whether gut bacteria translocate to the key metabolic organs and impair function as a result of heat stress remains unknown. Using a heat stress-induced mouse model, heat stress inhibited epididymal white adipose tissue (eWAT) expansion and induced lipid metabolic disorder but did not damage other organs, such as the heart, liver, spleen, or muscle. Microbial profiling analysis revealed that heat stress shifted the bacterial community in the cecum and eWAT but not in the inguinal white adipose tissue, blood, heart, liver, spleen, or muscle. Notably, gut-vascular barrier function was impaired, and the levels of some bacteria, particularly Lactobacillus, were higher in the eWAT, as confirmed by catalyzed reporter deposition fluorescence in situ hybridization (CARD-FISH) staining when mice were under heat stress. Moreover, integrated multi-omics analysis showed that the eWAT microbiota was associated with host lipid metabolism, and the expression of genes involved in the lipid metabolism in eWAT was upregulated under heat stress. A follow-up microbial supplementation study after introducing Lactobacillus plantarum to heat-stressed mice revealed that the probiotic ameliorated heat stress-induced loss of eWAT and dyslipidemia and reduced gut bacterial translocation to the eWAT by improving gut barrier function. Overall, our findings suggest that gut bacteria, particularly Lactobacillus spp., play a crucial role in heat stress-induced lipid metabolism disorder and that there is therapeutic potential for using probiotics, such as Lactobacillus plantarum.

Duodenum has the greatest potential to absorb soluble non-ammonia nitrogen in the nonmesenteric gastrointestinal tissues of dairy cows.

In cattle, dietary protein is gradually degraded into peptide-bound amino acids (PBAAs), free amino acids (FAAs), and ultimately into ammonia by the rumen microbes. Both PBAA and FAA are milk protein precursors, and the rumen and small intestines are the main sites where such precursors are produced and absorbed. This work was designed to investigate the expression of the peptide transporter PepT1 and the AA transporters ASCT2, y(+)LAT1, and ATB(0,+), and the concentrations of PBAA, FAA, and soluble protein in the rumen, omasum, and duodenum of dairy cows. Tissues and digesta were collected from six healthy Chinese Holstein dairy cows immediately after the animals were slaughtered. The expression of transporters was analyzed by real-time quantitative polymerase chain reaction (PCR). The FAA concentration was assessed using an amino acid (AA) analyzer, PBAA concentration by quantification of AA before and after acid-hydrolysis by 6 mol/L HCl, and soluble protein concentration by quantification of the bicinchoninic acid content. The results showed that the relative abundance of mRNA of the transporters and the soluble non-ammonia nitrogen (SNAN) concentration of each fraction were greater in the duodenum than in the rumen or omasum. These results indicate that the duodenum is the predominant location within the nonmesenteric digestive tract for producing milk protein precursors. In addition, PBAA was the largest component of SNAN in the digesta from the rumen, omasum, and duodenum. In conclusion, the duodenum has the greatest concentrations of SNAN and PBAA, and the greatest potential for absorption of SNAN in the form of PBAA in the nonmesenteric gastrointestinal tissues of dairy cows.