Intercellular adhesion molecule 1 engagement modulates sphingomyelinase and ceramide, supporting uptake of drug carriers by the vascular endothelium.
OBJECTIVE
Engagement of intercellular adhesion molecule 1 (ICAM-1) on endothelial cells by ICAM-1-targeted carriers induces cell adhesion molecule-mediated endocytosis, providing intraendothelial delivery of therapeutics. This pathway differs from classical endocytic mechanisms and invokes aspects of endothelial signaling during inflammation. ICAM-1 interacts with Na(+)/H(+) exchanger NHE1 during endocytosis, but it is unclear how this regulates plasmalemma and cytoskeletal changes. We studied such aspects in this work.


RESULTS
We used fluorescence and electron microscopy, inhibitors and knockout tools, cell culture, and mouse models. ICAM-1 engagement by anti-ICAM carriers induced sphingomyelin-enriched engulfment structures. Acid sphingomyelinase (ASM), an acidic enzyme that hydrolyzes sphingomyelin into ceramide (involved in plasmalemma deformability and cytoskeletal reorganization), redistributed to ICAM-1-engagement sites at ceramide-enriched areas. This induced actin stress fibers and carrier endocytosis. Inhibiting ASM impaired ceramide enrichment, engulfment structures, cytoskeletal reorganization, and carrier uptake, which was rescued by supplying this enzyme activity exogenously. Interfering with NHE1 rendered similar outcomes, suggesting that Na(+)/H(+) exchange might provide an acidic microenvironment for ASM at the plasmalemma.


CONCLUSIONS
These findings are consistent with the ability of endothelial cells to internalize relatively large ICAM- 1--targeted drug carriers and expand our knowledge on the regulation of the sphingomyelin/ceramide pathway by the vascular endothelium.
Department of Cell Biology and Molecular Genetics, Biological Sciences Graduate Program, University of Maryland, College Park, MD 20742, USA.
Daniel
D
Serrano
Tridib
T
Bhowmick
Rishi
R
Chadha
Carmen
C
Garnacho
Silvia
S
Muro
D000818:Animals; D002478:Cells, Cultured; D002518:Ceramides / Q000378:metabolism*; D004337:Drug Carriers / Q000378:metabolism*; D004705:Endocytosis / Q000502:physiology*; D004730:Endothelium, Vascular / Q000378:metabolism* / Q000648:ultrastructure; D006801:Humans; D018799:Intercellular Adhesion Molecule-1 / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D008854:Microscopy, Electron; D015398:Signal Transduction; D013108:Sphingomyelin Phosphodiesterase / Q000378:metabolism*
D002518:Ceramides; D004337:Drug Carriers; D018799:Intercellular Adhesion Molecule-1; D013108:Sphingomyelin Phosphodiesterase