Transcriptional adaptation of adipose tissue in dairy cows in response to energy overfeeding

In experiment 1, 18 multiparous non-pregnant non-lactating Holstein dairy cows were fed either moderate energy diet (MoE, NEL = 1.62 Mcal/kg DM) or controlled energy diet (LoE, NEL = 1.35 Mcal/kg DM) for 8 weeks and sacrificed. Compared with LoE animals, MoE cows had markedly increased visceral adipose mass (Nikkhah et al., unpublished data). Higher dietary energy plane significantly increased lipogenic gene expression in both visceral and subcutaneous adipose tissue (AT). Visceral AT (including mesenteric and omental fat; MES and OAT) exhibited higher mRNA profile for genes associated with utilization of long-chain fatty acid (LCFA), whereas subcutaneous AT (SUBQ) had greater gene expression related with de novo FA synthesis. Visceral AT, particularly MES, showed greater mRNA expression of pro-inflammatory cytokines, chemokines, and acute-phase protein. In conclusion, overfeeding energy may increase visceral AT secretion of pro-inflammatory cytokines by stimulating fat accumulation in visceral AT depots. (For the contents in chapter 3 and 4) In experiment 2, mRNA samples of MES and SUBQ collected from a subset of animals (5 cows from each treatment) that used in experiment 1 was utilized to conduct transcriptomic study through microarray technique. The microarray platform contains 13k annotated bovine oligonucleotides. A FDR value of 0.2 was used as the cut-off threshold for determination of differentially expressed genes (DEG). Totally 409 and 310 DEGs were identified due to either adipose depot effect or dietary energy effect. Bioinformatics analysis revealed that gene sets associated with extracellular matrix, vasculature development and cytoskeleton formation were differentially expressed between MES and SUBQ. Overfeeding energy had significant impact on the genes in the pathway of MAPK signaling and apoptosis, and response to external stimuli. (For the contents in chapter 5) In experiment 3, 14 Holstein dairy cows (≥ 2 parity, a subset from another study) were fed the same controlled energy diet during far-off dry period (-50 to -22 d) and randomly assigned to either moderate energy diet (Overfed, NEL = 1.47 Mcal/kg DM) or controlled energy diet (Controlled, NEL = 1.24 Mcal/kg DM) during close-up dry period (-21 d until parturition). Compared with Controlled group, Overfed animals had lower and higher serum NEFA in pre- and postpartum respectively, higher prepartal insulin and close-up DMI, and greater postpartal hepatic lipid storage and BHBA production. No difference in milking performance was found between the two groups. AT biopsy was carried out on -10, 7 and 21 d relative to parturition date for RNA extraction and gene expression analysis through quantitative PCR (qPCR). Energy overfeeding increased prepartal lipogenic genes and pre- and early postpartal lipolytic related gene (ATGL and ABHD5) expression in subcutaneous AT, but decreased PDE3B expression during periparturient period. Part of AT from biopsy of -10 and 7 d was used for tissue explant and challenged with hyperphysiological bovine insulin in vitro. Over-consumption of dietary energy increased and decreased insulin-stimulated IRS1 tyrosine phosphorylation in AT in pre- and postpartum, respectively, which may contribute to differentially regulated lipolysis in these overfed animals. (For contents in chapter 6