LEAP2 triggers retromer-mediated membrane trafficking of MOSPD2 to drive chemotaxis in teleost monocyte/macrophages

The immune peptide liver-expressed antimicrobial peptide 2 (LEAP2) plays a critical role in regulating innate immune responses in teleosts, yet the molecular mechanisms underlying its chemotactic activity remain largely unknown. Our previous studies identified Boleophthalmus pectinirostris MOSPD2 (BpMOSPD2) as a candidate receptor for BpLEAP2 in monocytes/macrophages (MO/MΦ). In this study, we demonstrate that BpLEAP2 stimulation triggers a retromer-dependent intracellular trafficking program that is essential for BpMOSPD2-mediated chemotaxis. BpLEAP2 treatment significantly enhanced BpMO/MΦ migration and promoted the plasma membrane accumulation of BpMOSPD2. Subcellular fractionation and immunofluorescence analyses revealed that BpMOSPD2 translocates from the endoplasmic reticulum to early endosomes upon BpLEAP2 stimulation, followed by redistribution to the plasma membrane. Inhibition of ER export or knockdown of core retromer subunits (BpVPS35, BpVPS26, or BpVPS29) disrupted this membrane localization and impaired BpLEAP2-induced migration. Mass spectrometry and co-immunoprecipitation confirmed the interaction between BpMOSPD2 and BpVPS35. Further domain-mapping analyses indicated that this interaction is not purely dependent of the MSP or CRAL-TRIO domains. Knockdown of individual retromer components led to BpMOSPD2 retention in early endosomes, demonstrating that the retromer complex is essential for its recycling to the cell surface. Functionally, impairment of the retromer complex abolished the pro-migratory effects of BpLEAP2 on BpMO/MΦ. Collectively, these findings identify the retromer complex as a critical regulator of BpMOSPD2 trafficking and reveal a novel mechanism by which BpLEAP2 promotes MO/MΦ migration in teleosts.