Goat liver X receptor α, molecular cloning, functional characterization and regulating fatty acid synthesis in epithelial cells of goat mammary glands

The liver X receptor alpha (LXR alpha) is a nuclear receptor of the transcription factor and is known to play a crucial role in lipid metabolism processes such as bile acid and fatty acid synthesis in humans and rodents. However, very little information is available on the role of LXR alpha in the regulation of fatty acid synthesis in the goat mammary gland. In this investigation, a cDNA was isolated from the mammary gland of Xinong Saanen dairy goats and designated as goat LXR alpha. RT-PCR and RACE gave rise to the full-length cDNA of LXR alpha, which was comprised of 1654 bp and characterized by an ORF of 1344 bp and 5'- and 3'-UTR regions of 150 and 160 bp, respectively. The deduced amino acid sequence encodes 477 amino acids with a predicted molecular weight (MW) of 50.4 kDa and a theoretical isoelectric point (pl) of 6.3. Additionally, homology search and sequence multi-alignment indicated that the putative goat LXR alpha amino acid sequence is very similar to those of cattle, mice, rats, swine, and humans. Bioinformatic predictions demonstrated that the LXR alpha protein is located in the nucleus, containing characteristic signatures of a nuclear receptor with DNA-binding domain (DBD) and ligand-binding domain (LBD). Real-time quantitative PCR suggested that LXR alpha was predominantly expressed in the small intestine, liver, spleen and mammary gland. Treatment of goat mammary gland epithelial cells (GMEC) with different concentrations (i.e., 0.01, 0.1, 1 mu M) of T0901317, a synthetic agonist of LXR alpha, resulted in elevated sterol regulatory element binding protein 1 (SREBP1) and fatty acid synthase (FASN) mRNA levels in response to LXR alpha activation. The association between different 10901317 concentrations and fatty acid composition in GMEC also was examined using gas chromatography (GC). The results showed that activation of LXR alpha significantly increased GMEC C18:1 and C18:2 contents, but did not affect levels of saturated fatty acids (SFA). These discoveries are consistent with the notion that LXR alpha plays a key role in controlling lipogenesis and regulating synthesis of unsaturated fatty acids (UFA) in the mammary gland of goats, which may prove useful in regulation of milk fat production. Crown Copyright (C) 2012 Published by Elsevier B.V. All rights reserved.