Alteration of alanine-327 in LXRα to LXRβ-type histidine deteriorates its subtype-selective activation by riccardin C

Liver X receptors (LXRα and LXRβ) are nuclear receptors critical for lipid homeostasis and inflammation regulation, making them potential therapeutic targets for atherosclerosis and inflammatory diseases. While LXR agonists hold promise, their use is limited by adverse effects on hepatic lipogenesis. Riccardin C (RC) has shown promise as an LXRα partial agonist/ LXRβ antagonist with cell-type-selective properties. This study investigates the molecular mechanisms behind RC-induced LXRα activation. A series of LXRα/β chimera and point-mutated receptors was generated to identify the domains and residues required for RC-induced transactivation. Functional analysis revealed that mutating alanine-327 of LXRα to LXRβ-type histidine in helix 6 impaired RC-induced association with coactivator peptides, reducing transactivation. Conversely, mutating histidine-341 of LXRβ or the inactive chimera to the LXRα-type alanine partially restored the response to RC, highlighting the significance of the A327H mutation in selective LXRα activation by RC. Furthermore, in vivo experiments revealed that when administered orally to mice, RC selectively induced hepatic and intestinal Abca1 expression without stimulating hepatic lipogenic gene expression, thereby elevating HDL levels without increasing plasma and hepatic triglycerides. These findings offer valuable insights for the development of novel therapeutic agents.