Background: Platelet-activating factor (PAF)-induced pulmonary endothelial barrier failure is mediated by acid sphingomyelinase (ASM) translocation to caveolae. ASM, however, lacks a transmembrane domain for anchoring inside caveolae. We hypothesized that ASM may anchor to cation-independent mannose-6-phosphate receptor (CI-M6PR) in caveolae from where it can be competitively released by M6P.

Methods: We probed for ASM-CI-M6PR interaction by co-immunoprecipitation (Co-IP) and proximity ligation assay (PLA) in isolated lungs and human pulmonary microvascular endothelial cells (hPMVECs). ASM release by M6P was determined in hPMVECs, isolated lungs and . Effects of M6P i) on PAF-induced lung edema formation and endothelial Ca concentration ([Ca]), and ii) lung injury in acid instilled, overventilated mouse lungs were tested. ASM levels were measured in serum and bronchoalveolar lavage fluid (BALF) of ARDS patients. The TriNetX database was probed for the association of ASM-inhibiting tricyclic antidepressants (TCA) with outcome.

Results: Co-IP and PLA revealed ASM interaction with CI-M6PR in endothelial caveolae, which was further increased by PAF. M6P, but not glucose-6-phosphate (Glu6P) caused ASM release, thereby decreasing ASM content and activity in caveolae , and . Analogously, M6P, yet not Glu6P attenuated PAF-induced endothelial [Ca] signaling and lung edema , and acute lung injury . ASM levels were increased in serum, yet not BALF in ARDS patients. Use of TCA was associated with better outcome in patients with severe respiratory infections.

Conclusions: CI-M6PR anchors ASM in caveolae. M6P may hence present a promising strategy against ASM-related lung injury and edema.

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http://dx.doi.org/10.1183/13993003.00003-2024DOI Listing

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