Abstract #477

# 477
The effects of dietary niacin supplementation on FoxO1 and genes involved in hepatic glucose production in dairy cows during the transition period.
Asako Kinoshita*1, Kathrin Hansen3, Lena Locher1, Ulrich Meyer2, Sven Dänicke2, Korinna Huber3, Jürgen Rehage1, 1Clinic for cattle, University of Veterinary Medicine Hannover, Hannover, Lower Saxony, Germany, 2Institute of Animal Nutrition, Friedrich-Loeffler-Institute, Braunschweig, Lower Saxony, Germany, 3Department of Physiology, University of Veterinary Medicine Hannover, Hannover, Lower Saxony, Germany.

Forkhead box protein O1 (FoxO1) promotes the hepatic glucose production (HGP) by activating the transcription of gluconeogenic enzymes. As a main target of insulin signaling, FoxO1 is phosphorylated by insulin, leading to inhibition of HGP. Dietary niacin supplementation could affect HGP; for example, by modifying the expression of genes or by inhibiting lipolysis. The objective of this study was to investigate the effects of dietary niacin supplements on protein expression of hepatic FoxO1 and mRNA expression of genes involved in HGP in dairy cows during the transition period. Twenty-one pluriparous German Holstein cows were used for 2 × 2 factorial analysis. Cows received diets containing 0 g (C) or 24 g (N) niacin supplementation from −42 d related to calving (d −42) to d 24. Each group was further divided and received diets with 30% (L) or 60% (H) of concentrate on dry matter basis from d-42 to d0. Dietary concentrate proportion was set to 30% at d 0 for all, and then increased up to 50% within 16 d for CL and NL and within 24 d for CH and NH. Liver biopsies were taken at d −42, d 3, and d 21. Protein expression of FoxO1 and phosphorylated FoxO1 at serine 256 (pFoxO1) was measured semiquantitatively by Western blotting. Real-time RT-PCR was performed to measure the mRNA of FoxO1, glucose-6-phosphatase (G6P), pyruvate carboxylase (PC), cytosolic phosphoenolpyruvate carboxykinase (PCK1), propionyl CoA carboxylase (PCCA), glucose transporter 2 (GLUT2). Data were evaluated by mixed model for repeated measures to test the effect of time, niacin and prepartal concentrate proportion. The protein and mRNA expression of FoxO1 and the protein expression of pFoxO1 were affected neither by time nor by diet. In cows fed with niacin, the relative quantities of mRNA of G6P, GLUT2, PCCA were higher at d 21 and that of GLUT2 was lower at d1 (P < 0.05). Dietary niacin supplements altered the gene expression, increasing HGP in the transition period of cows. However, the regulation of HGP by FoxO1 seemed to be of less importance on the levels of mRNA, protein and phosphorylation.

Key Words: FoxO1, hepatic glucose production, cow