血管新生性ソニックヘッジホッグ含有超大型細胞外小胞の非慣習的放出はPI3K-Rab18-GDPシグナル伝達によって駆動される

Extra-large extracellular vesicles (XLEVs), with diameters > 600 nm, are increasingly recognised as mediators of specialized modes of intercellular communication; however, the molecular mechanisms governing their biogenesis and functional regulation remain poorly understood. Here, we show that PI3K-Rab18-GDP signalling promotes the secretion of XLEVs from human mesenchymal stem cells (hMSCs) and fibroblasts. These vesicles are highly enriched in sonic hedgehog (SHH) and display potent pro-angiogenic activity. We further demonstrate that Rab18 functions as a key regulator of this pathway specifically in its GDP-bound form, which can be enriched by the Rab inhibitor CID1067700 or by pharmacological activation of PI3K using SF1670. Rab18-GDP preferentially accumulates in the perinuclear region, where it promotes the formation of SHH-XLEV precursors from endosomal compartments. Mechanistically, PI3K-Rab18-GDP signalling recruits heat shock protein 90α (Hsp90α) and neutral sphingomyelinase 2 (nSMase2), facilitating polarized release of SHH-XLEVs from the perinuclear-plasma membrane interface, accompanied by an Hsp90α-enriched extracellular assembly. Together, these findings identify a PI3K-Rab18-GDP-dependent secretory pathway for SHH-XLEVs and provide a framework for understanding how XLEV biogenesis is coupled to SHH-associated angiogenic signalling in developmental and regenerative contexts.