Liver X receptor α promotes milk fat synthesis in buffalo mammary epithelial cells by regulating the expression of FASN

摘要

Liver X receptor α (LXRα; NR1H3) is an importanttranscription factor that can facilitate milk fat synthesisby regulating the transcription of FASN in miceand goats. Nevertheless, the lipid synthesis related toLXRα and its regulation on FASN in the buffalo mammarygland remain elusive. Here, we demonstrated thatthe mRNA and protein expression of LXRα in buffalomammary tissue increased in lactation compared withthat in the dry-off period. Overexpression of NR1H3enhanced the lipid droplet formation and triacylglycerolconcentration in buffalo mammary epithelial cells (Bu-MEC), whereas the knockdown of NR1H3 resulted in adecrease in the number of lipid droplets. At the sametime, NR1H3 also affected the expression of regulatoryfactors (INSIG1, INSIG2, SREBF1, and PPARG) relatedto milk fat synthesis and that of genes involvedin de novo synthesis (FASN, ACACA, and SCD), anduptake and transport (LPL, CD36, and FABP3) offatty acids as well as triacylglycerol synthesis (GPAM,APGAT6, and DGAT1). Luciferase reporter assays indicatedthat overexpression of NR1H3 resulted in anincrease in the activity of FASN promoter, whereas theknockdown of NR1H3 had an opposite effect. WhenNR1H3 was overexpressed, mutations in LXRE or SREcould decrease the promoter activity of FASN. Furthermore,mutagenesis of both LXRE and SRE withinthe FASN promoter completely eliminated the inducedactivity of LXRα. Our results reveal that buffalo LXRαpromotes milk fat synthesis through regulating the expressionof FASN by directly interacting with FASNpromoter and affecting the SREBF1 expression. Thisstudy underscores a crucial role of LXRα in regulatinglipid synthesis of the buffalo mammary gland.