2529-P: A Brown Adipose Tissue–Derived Lipokine Signals through a Novel GPCR to Regulate Macrophage Recruitment during Cold Exposure

Introduction and Objective: Brown adipose tissue (BAT) is a promising target for metabolic diseases due to its thermogenic and endocrine functions. Beyond heat production, BAT secretes signaling molecules such as the lipokine, 12,13-dihydroxy-9Z-octadecenoic acid (12,13-diHOME), which is induced by cold and exercise. 12,13-diHOME exerts metabolic benefits, yet the molecular signaling mechanisms mediating these effects remain elusive. Methods: To identify signaling pathways for 12,13-diHOME, we performed a G protein-coupled receptor (GPCR) screen to identify candidate receptors. We then analyzed single-cell RNA sequencing (scRNA-seq) data from BAT of mice housed at thermoneutrality or cold environment to determine cell-type-specific receptor expression. Guided by these findings, we conducted complementary in vivo and ex vivo experiments using bone marrow (BM) chimeric mice, flow cytometric profiling, and migration assays with BM-derived macrophages (BMDM) to investigate the functional role of this signaling axis. Results: We identified a previously uncharacterized GPCR with high specificity for 12,13-diHOME. scRNA-seq analysis revealed that cold exposure increased BAT macrophages enriched for this receptor. Using BM transplantation, we demonstrated that cold-induced macrophage accumulation in BAT originated from circulating BM-derived cells. Importantly, mice receiving BM lacking the GPCR failed to exhibit enhanced macrophage recruitment to BAT after cold exposure. Additionally, 12,13-diHOME and co-culture with brown adipocytes promoted BMDM migration, an effect that was absent in the receptor-deficient cells. Conclusion: These findings uncover a novel ligand-receptor signaling pathway through which the BAT-derived lipokine 12,13-diHOME drives macrophage recruitment during cold exposure, providing new insight into metabolite-mediated cell-cell communication that shapes BAT function and its metabolic impact. Disclosure B.I. Park: None. S. Chen: None. Y. Tseng: Consultant; Ended; Paratus Sciences. Consultant; Current; Sofinova Partners. F. Alvarez-Gallego: None. J.I. Senfeld: Employee; Current; Eli Lilly and Company. Funding NIH Training Grant (T32 DK007260), Joslin Diabetes Center DRC (NIDDK P30 DK036836)