Transcriptional regulation in whole organ mammary gland culture mediated by the Liver X Receptor

OLSZANOWSKI E; GRINMAN DG; PECCI A

Mar del Plata

Congreso; LXIX Reunion Anual de SAIC; 2019

Liver X Receptors (LXRs) belong to the nuclear receptors superfamily of ligand activated transcription factors, being the oxysterols their endogenous ligands. They play a key role in the regulation of the cholesterol homeostasis, induce the expression on genes related to the de novo synthesis of triacylglycerides, and repress pro-inflammatory factors effects. During lactation, the mammary gland is endowed with an enormous capacity to synthesize and secrete lipid in the form of triglycerides and cholesterol esters. In previous studies, we found an increase in milk-cholesterol mediated by LXR activation in vivo. According to this founding, we aimed to study direct influence of LXR activation in the mammary epithelium. Mammary gland explants from C57BL/6JFCEN pregnant mice (15 days post coitum) were differentiated in culture in Waymouth?s MB 752/1 medium, in the presence of the lactogenic hormone mix of insulin, aldosterone, hydrocortisone and prolactin; in the presence of LXR agonist GW3965 1uM or DMSO (vehicle). Medium and additives were added fresh every second day. Lymph nodes were removed before culture. After 5 or 9 days of culture, mammary epithelial cells (MECs) were prepared using an enrichment protocol. Total RNA was extracted and RT-qPCR was performed. Both LXRα and LXRβ are expressed in MECs. In response of the LXR activation, there was an increase in the expression of LXR target genes SREBP1C and ABCA1, related to de novo synthesis of triacylglycerides and cholesterol transport, respectively. Also, the expression of ABCA7, another cholesterol membrane transporter, was augmented. In addition, PPAR expression was induced. The greatest differences in LXR dependent gene expression were found at day 5 concomitant an increase in the expression of milk protein B-casein, a marker of mammary gland lactogenic differentiation. Together these results suggest the direct relevance of LXRs in the control of lipid homeostasis and secretion into the milk during lactation.