Effect of milk yield genotype on gene expression in liver and adipose tissue from periparturient Holsteins

Abstract Text: Multiparous cows from unselected (stable milk yield since 1964; UH; n = 5) and contemporary CH; n = 6) Holsteins that differed in milk yield (6,200 and 11,100 kg milk/305 d) were fed the same diet ad lib, milked 2X/d, and exposed to the same management and environmental conditions.  Liver and adipose biopsies were collected at -14, 3, 14, and 35 days in milk (DIM).  RNA was extracted and expression of 38 genes (focused on the somatotropic axis, glucose and lipid metabolism) and 12 possible internal control genes determined by digital multiplexed analysis (nanoString nCounter). Expression was normalized to the positive control and the geometric mean of 5 internal control genes.  Data were transformed (square root) and analyzed by repeated measures using PROC MIXED (SAS) with DIM as the repeated effect.  Means differed when P < 0.05.  Expression of 23 genes in liver and 20 in adipose was altered by DIM.  Liver and adipose expression of 6 and 8 genes was greater in CH and of 8 and 7 genes was greater in UH, respectively. There were line by day interactions for IGFBP2 and IGF-ALS in liver and DGAT2, HNF4a, IGF2 in adipose. Hepatic GHRtot and GHR-1A were greater in UH than CH. GHR-1A decreased at 3 but recovered by 14 DIM.  Adipose GHRtot was greater in CH.  Hepatic IGFBP2 was greater in CH than UH, increased at 3 DIM and although decreasing, remained increased through 35 DIM. Hepatic IGF-ALS was greater in UH, decreased at 3 DIM in both lines and returned to prepartum values by 14 and 35 DIM in UH and CH, respectively.  Hepatic FGF21 was greater in CH than UH and peaked at 3 DIM in both lines.  FGF21 was not detected in adipose. DGAT1 was similar in UH and CH liver and greater in CH adipose.  Liver DGAT1 increased at 3 DIM but was not altered by DIM in adipose. DGAT2 was similar in UH and CH liver and greater in UH adipose.  Liver DGAT2 decreased through 35 DIM in both lines.  Adipose DGAT2 decreased at 3 DIM and recovered by 35 DIM in UH but not in CH cows.  Results are consistent with a prolonged postpartum reduction in hepatic sensitivity to somatotropin and in triglyceride synthesis from de novo fatty acids in adipose of contemporary Holsteins.

Keywords: gene expression; liver; adipose