Complementary transcriptomic and proteomic analyses reveal regulatory mechanisms of milk protein production in dairy cows consuming different forages

Abstract

Forage plays a critical role in the milk production of dairy cows; however, the mechanisms regulating bovine milk synthesis in dairy cows fed high forage rations with different basal forage types are not well-understood. In the study, rice straw (RS, low-quality) and alfalfa hay (AH, high-quality) diets were fed to lactating cows to explore how forage quality affected the molecular mechanisms regulating milk production using RNA-seq transcriptomic method with iTRAQ proteomic technique. A total of 554 transcripts (423 increased and 131 decreased) and 517 proteins (231 up-regulated and 286 down-regulated) were differentially expressed in the mammary glands of the two groups. The correlation analysis demonstrated seven proteins (six up-regulated and one down-regulated) had consistent mRNA expression. Functional analysis of the differentially expressed transcripts/proteins suggested that enhanced capacity for energy and fatty acid metabolism, increased protein degradation, reduced protein synthesis, decreased amino acid metabolism and depressed cell growth were related to RS consumption. The results indicated cows consuming RS diets may have had depressed milk protein synthesis because these animals had decreased capacity for protein synthesis, enhanced proteolysis, inefficient energy generation and reduced cell growth. Additional work evaluating RS- and AH-based rations may help better isolate molecular adaptations to low nutrient availability during lactation.

Seryl-tRNA synthetase-mediated essential amino acids regulate β-casein synthesis via cell proliferation and mammalian target of rapamycin (mTOR) signaling pathway in bovine mammary epithelial cells

“…To date, potential functional roles of AARS involved in AA regulating milk protein synthesis have been identified in humans (Han et al, 2012) and dairy cows (Wang et al, 2014). Furthermore, SARS has been shown to be closely related to lactation in dairy cows that were fed different roughages (Dai et al, 2017a) or during varying lactation periods (Dai et al, 2017b(Dai et al, , 2018. Therefore, the present find- Figure 3.…”

“…Protein lysates were centrifuged at 12,000 × g for 5 min and the supernatants were collected and measured for the protein concentration using the bicinchoninic acid (BCA) protein assay kit (Beyotime, Jiangsu, China). Protein levels were analyzed by Western blotting according to previously described procedures (Dai et al, 2017a). Approximately 40 μg of protein per sample was separated on 12% SDS polyacrylamide gels.…”

“…Corresponding roles of AARS in BMEC were subsequently identified (Wang et al, 2014). Additionally, transcriptomic and proteomic studies have demonstrated that seryl-tRNA synthetase (SARS) was the most abundantly and significantly expressed gene at both the mRNA and protein levels when comparing mammary gland tissues from dairy cows fed varying roughages (corn stover vs. alfalfa hay) or dairy cows during different stages of lactation (dry period vs. mid lactation; Dai et al, 2017aDai et al, ,b, 2018. Collectively, the previous studies suggest that SARS may play a vital role in milk protein synthesis.…”

Essential oil-bearing supplementation of dairy cows – <i>in vivo</i> experiments elucidating factors and co-factors influencing parameters of feed efficiency

“…Nowadays, the in vivo effects of EO supplementation on parameters of feed efficiency (FE, milk yield/ DMI) in dairy cows are of great importance, as rising global competition forces agriculture to increase efficiency to maintain profitability (Socha et al, 2007). While in vitro results provide evidence that EOMs have the potential to improve energy utilization in ruminants by positively shifting the propionate:acetate ratio in the rumen, in vivo results are inconsistent (Thao et al, 2014;Dai et al, 2017). One of the reasons for the lack of consistent positive in vivo effects might be the adaptation of rumen bacteria to EO in long-term applications (Benchaar et al, 2008).…”

Seryl-tRNA synthetase is involved in methionine stimulation of β-casein synthesis in bovine mammary epithelial cells

“…Moreover, Wang et al uncovered a role of leucyl-tRNA synthetase in the promotion of mammary casein production through activating mTOR pathway in primary BMEC and MG explants (23) . Recent studies in our laboratory identified a differential expression of seryl-tRNA synthetase (SARS) in the lactating MG of dairy cows fed low-quality v. high-quality forages (24,25) and during different stages of lactation (26,27) . These observations have implicated a potential regulatory role of SARS in AA-stimulated milk protein synthesis in the MG.…”