LEAP2 triggers retromer-mediated membrane trafficking of MOSPD2 to promote chemotaxis in teleost monocytes/macrophages.

Liver-expressed antimicrobial peptide 2 (LEAP2) is a key regulator of innate immune defense in teleosts, yet the molecular basis of its chemotactic function remains largely unidentified. Boleophthalmus pectinirostris MOSPD2 ( BpMOSPD2) was previously identified as a candidate receptor for BpLEAP2 in monocytes/macrophages (MO/MΦ). In the present study, BpLEAP2 stimulation was found to trigger a retromer-dependent intracellular trafficking program essential for BpMOSPD2-mediated chemotaxis. Exposure to BpLEAP2 significantly enhanced BpMO/MΦ migration and promoted the accumulation of BpMOSPD2 at the plasma membrane. Subcellular fractionation and immunofluorescence analyses revealed that BpMOSPD2 translocated from the endoplasmic reticulum (ER) to early endosomes upon BpLEAP2 stimulation, followed by redistribution to the cell surface. Blockade of ER export or knockdown of core retromer subunits ( BpVPS35, BpVPS26, or BpVPS29) abolished membrane localization and attenuated BpLEAP2-induced migration. Co-immunoprecipitation combined with mass spectrometry confirmed direct binding between BpMOSPD2 and BpVPS35, while domain-mapping indicated that this interaction was not exclusively dependent on MSP or CRAL-TRIO domains. Depletion of individual retromer components led to retention of BpMOSPD2 in early endosomes, establishing the necessity of the retromer complex for receptor recycling. Functionally, disruption of this complex eliminated the pro-migratory activity of BpLEAP2 on BpMO/MΦ. These findings identify the retromer complex as a critical regulator of BpMOSPD2 trafficking and uncover a previously unrecognized mechanism through which BpLEAP2 promotes MO/MΦ migration in teleosts.