NR4A1-mediated regulation of lipid droplets in progesterone synthesis in goat luteal cells

Nuclear receptor NR4A1 is a key factor in glycolipid metabolism and steroidogenesis, while lipid droplets serve as crucial dynamic organelles for lipid metabolism in luteal cells. To investigate the effects of NR4A1 on lipid droplet metabolism and progesterone (P4) synthesis in goat corpus luteum in vitro, luteal cells from the middle-cyclic corpus luteum were isolated and treated with Cytosporone B (CSNB, an agonist) or siRNA of NR4A1. Results showed that both low (1 µM) and high (50 µM) concentrations of CSNB promoted lipid droplet accumulation, while NR4A1 knockdown reduced lipid droplet content. CSNB increased while siNR4A1 decreased total cholesterol content; however, CSNB and siNR4A1 did not change triglyceride content. CSNB increased the expression of perilipins at mRNA and protein levels, also increased LDLR, SCARB1, SREBFs, and HMGCR mRNA abundance. Treatment with siNR4A1 revealed opposite results of CSNB, except for HMCGR and SREBF2. For steroidogenesis, 1 µM CSNB increased, but 50 µM CSNB inhibited P4 synthesis, NR4A1 knockdown also reduced the P4 level. Further analysis demonstrated that 1 µM CSNB increased the protein levels of StAR, HSD3B, and P-HSL, while 50 µM CSNB decreased StAR, HSD3B, and CYP11A1 protein levels. Moreover, 50 µM CSNB impaired active mitochondria, reduced the BCL2, and increased DRP1, Caspase 3, and cleaved-Caspase 3 protein levels. siNR4A1 consistently downregulated the P-HSL/HSL ratio and the steroidogenic protein levels. In conclusion, NR4A1-mediated lipid droplets are involved in the regulation of progesterone synthesis in goat luteal cells. Graphical Abstract