Association between liver X receptor-a and neuron-derived orphan nuclear receptor-1 in Kupffer cells of C57BL/6 mice during inflammation

Abstract

The liver X receptor (LXR) isoform LXR-a has a significant role in lipid metabolism and innate immunity. Overexpression of neuron-derived orphan nuclear receptor-1 (NOR-1) in macrophages reduces the synthesis of inflammatory cytokines and chemokines. However, to date, the mechanisms via which NOR-1 inhibits lipopolysaccharide (LPS)-induced inflammation in Kupffer cells (KCs) via LXR-a have not been elucidated. T0901317 is the most potent LXR-a ligand, leading to its activation. In the present study, KCs were isolated from C57BL/6 mice and randomly divided into five groups: Control, T0901317, LPS, LPS + T0901317 and LPS + T0901317 + NOR-1 small hairpin (sh)RNA groups. In order to investigate the role of NOR-1 in inflammation, shRNA targeting NOR-1 was used to specifically knock down NOR-1 mRNA in KCs. The expression levels of LXR-a and NOR-1 in KCs were determined by reverse transcription quantitative polymerase chain reaction and western blot analyses. The protein levels of tumor necrosis factor (TNF)-a and interleukin (IL)-10 in the supernatant of KCs were evaluated by ELISA. The results revealed that LXR-a expression in the T0901317 group was higher than that in the control group; furthermore, LXR-a expression was higher in KCs treated with LPS + T0901317 compared with that in KCs treated with LPS only. The expression levels of NOR-1 in each group showed a similar trend. shRNA targeting of NOR-1 suppressed the mRNA expression of NOR-1, but had no influence on LXR-a mRNA expression. NOR-1 protein expression was augmented in the LPS + T0901317 group compared with that in the LPS + T09 + shRNA group. In the supernatant of KCs, the TNF-a levels in the LPS + T0901317 group were lower than those in the LPS group, whereas the IL-10 levels were higher in the LPS + T0901317 group compared with those in the LPS group. The results of the present study suggested that ligand T0901317 promotes LXR-a expression, which consequently suppresses LPS-induced inflammation by elevating NOR-1 expression in KCs.