Gene networks driving bovine milk fat synthesis during the lactation cycle

Abstract

Background: The molecular events associated with regulation of milk fat synthesis in the bovine mammary gland remain largely unknown. Our objective was to study mammary tissue mRNA expression via quantitative PCR of 45 genes associated with lipid synthesis (triacylglycerol and phospholipids) and secretion from the late pre-partum/non-lactating period through the end of subsequent lactation. mRNA expression was coupled with milk fatty acid (FA) composition and calculated indexes of FA desaturation and de novo synthesis by the mammary gland.

Role of trans fatty acids in the nutritional regulation of mammary lipogenesis in ruminants

“…abundance correspond with increases in mammary acetyl CoA synthesis suggesting that the protein encoded by this gene supplies activated acetate for de novo synthesis in the bovine (Bionaz and Loor, 2008b). Long chain fatty acids containing 16 or more carbon atoms inhibit mammary fatty acid synthesis in bovine or caprine mammary epithelial cells in vitro with the effects being more potent during incubations with fatty acids containing a longer carbon chain and/ or higher degree of unsaturation (Barber et al, 1997).…”

“…Studies using rodent models suggest that the VLDL receptor (VLDLR) is an essential component of mammary LPL activity (Tacken et al, 2001). Expression of VLDLR has been shown to be upregulated in the bovine mammary gland throughout lactation, particularly during the first month postpartum (Bionaz and Loor, 2008b).…”

“…Activation of fatty acids occurs primarily via an ATP-dependent mechanism involving the action of ACSL isoforms (Watkins et al, 2007). Measurements in lactating cows have shown that several ACSL (ACSL1, 3, 4 and 5) and FABP (FABP 1,3,4,5 and 6) isoforms are transcribed in mammary tissue (Bionaz and Loor, 2008a) and demonstrated that the expression of ACSL1, FABP3, FABP4 and FABP5 increases several-fold during lactation, whereas changes in the relative abundance of ACBP mRNA are much lower suggesting a minor role in mammary lipogenesis in the bovine (Bionaz and Loor 2008b). Passive diffusion is thought to play only a minor role in the transport of fatty acids across cell membranes compared with protein-mediated uptake, which in non-ruminants involves CD36 and SLC27A (Doege and Stahl, 2005).…”

“…Passive diffusion is thought to play only a minor role in the transport of fatty acids across cell membranes compared with protein-mediated uptake, which in non-ruminants involves CD36 and SLC27A (Doege and Stahl, 2005). Studies in cows have revealed the occurrence of transcripts encoding for CD36 (Bionaz and Loor, 2008b) and several SLC27A isoforms (1, 2, 3, 5 and 6; Bionaz and Loor, 2008a) in mammary tissue and demonstrated that CD36 and SLC27A6 mRNA abundance increases during the first months of lactation (Bionaz and Loor, 2008b). Even though the mechanisms responsible for the transport of fatty acids across the capillary endothelium and interstitial space are not well characterized (Barber et al, 1997;Bernard et al, 2008), it has been suggested that SLC27A6, ACSL1 and FABP3 are involved in the coordinate regulation of channelling fatty acids towards milk fat TAG synthesis in the bovine mammary gland (Bionaz and Loor, 2008a).…”

“…Several studies have demonstrated the involvement of SREBP1 and/or PPAR during diet-induced changes in mammary lipogenic gene expression in lactating cows (Peterson et al, 2004;Bionaz and Loor, 2008b), or in response to 3-to 5-day intravenous infusions of trans-10, cis-12 CLA Gervais et al, 2009) with the implication that these transcription factors are central elements in the overall regulation of milk fat synthesis. Two isoforms of SREBP1 (a and c) can be differentially expressed in various tissues.…”