Abstract #W254

# W254
Longitudinal characterization of the gene expression of key components of the mTOR signaling and ubiquitin proteasome system in skeletal muscle of dairy cows during the periparturient period and subsequent lactation.
Yi Yang1, Helga Sauerwein*1, Sven Dänicke2, Jürgen Rehage3, Hassan Sadri1, 1Institute of Animal Science, Physiology and Hygiene Group, University of Bonn, Bonn, North Rhine-Westphalia, Germany, 2Institute of Animal Nutrition, Friedrich-Loeffler-Institute (FLI), Braunschweig, Lower Saxony, Germany, 3Clinic for Cattle, University for Veterinary Medicine, Foundation, Hannover, Lower Saxony, Germany.

At the onset of lactation when voluntary feed intake is insufficient to cover the total needs for maintenance and lactation, dairy cows need to mobilize body reserves. Besides fat, skeletal muscle protein is also degraded. Muscle is the main labile source of amino acids (AA) and may thus partition AA to protein syntheses in other organs, mainly the mammary gland, for gluconeogenesis and for generating ATP. The mammalian target of rapamycin (mTOR) and ubiquitin-proteasome system (UPS) are considered as the major regulators of protein synthesis and protein degradation, respectively. We hypothesized that the transcript abundance of key components of mTOR signaling and of 2 major muscle-specific E3 ubiquitin ligases, MuRF1 (muscle RING-finger protein-1) and atrogin-1 in skeletal muscle will change throughout late pregnancy and the subsequent lactation period. From 14 German Holstein cows, muscle tissue (M. semitendinosus) were obtained for biopsy on d −21, 1, 21, 70, 105, 182, 196, 224, and 252 relative to calving. The target mRNAs were quantified by qPCR. Data were analyzed by the MIXED procedure of SAS and results are reported as LSM with P-values adjusted by the method of Tukey-Kramer. The mRNA abundance of mTOR increased (P < 0.05) from d −21 to d 1, followed by a decline toward pre-partum values by d 180 and then increased thereafter. A 6-fold increase in eukaryotic initiation factor 4E-binding protein mRNA was observed from d −21 to d 1, and then a gradual decrease until d 105 with relatively stable values thereafter. The encoding ribosomal protein S6 kinase mRNA decreased (P < 0.0001) during lactation. The abundance of MuRF1 mRNA increased (3.6-fold) from d −21 to d 1, declined to nearly pre-partum values by d 105 and then remained unchanged. The mRNA abundance of atrogin-1 followed almost a similar trend as that of MuRF1; a 2.2 fold increase was noted from d −21 to d 1, and then a decrease until d 21 and unchanged values thereafter. In conclusion, our data show that key components of mTOR and UPS are upregulated at the level of the mRNA on d 1, suggesting a greater rate of protein turnover in muscle around calving.

Key Words: skeletal muscle, mTOR, ubiquitin-proteasome system