Different pathways of uptake and degradation of sphingomyelin by lymphoblastoid cells and the potential participation of the neutral sphingomyelinase.
The metabolism of sphingomyelin (SPM) was investigated in Epstein-Barr virus-transformed lymphoid cell lines from normal individuals and from patients with Niemann-Pick disease Type A (deficient in the acid, lysosomal sphingomyelinase) and familial hypercholesterolemia (lacking the low density lipoprotein receptor). Cells were incubated with the following radioactive or fluorescent SPMs: [choline-methyl-14C] SPM, [oleoyl-3H]SPM, pyrene-propenoyl-SPM (P3:1-SPM), pyrene-butanoyl-SPM (P4-SPM), pyrene-dodecanoyl-SPM (P12-SPM), and pyrene-sulfonylamino-undecanoyl-SPM (PSA11-SPM). Several pathways of uptake and subsequent metabolism of SPM in the lymphoblastoid cells were identified. [choline-methyl-14C]SPM and the P12-analog, administered to the cells in the presence of lipoproteins, were taken up through the apoB/E receptor-dependent pathway of endocytosis and degraded solely by the lysosomal sphingomyelinase. Under similar conditions, the other sphingomyelins, i.e. [oleoyl-3H]SPM, P3:1-SPM, P4-SPM, and PSA11-SPM, were taken up by a low density lipoprotein receptor-independent pathway and degraded mostly by a nonlysosomal sphingomyelinase which also catalyzed their hydrolysis in Niemann-Pick cells. In the absence of serum, all sphingomyelins were taken up by an apoB/E receptor-independent pathway and hydrolyzed by a nonlysosomal sphingomyelinase. Indeed, in vitro assays demonstrated the presence, in lymphoblastoid cells, of the neutral magnesium-activated sphingomyelinase, which was also fully active in the Niemann-Pick cells. In conclusion, our observations are consistent with: (i) the existence in lymphoblastoid cells of several pathways for the uptake and subsequent utilization of SPM; (ii) a major role of lipoproteins for the metabolic routing of the SPM; and (iii) the effect of the structure of the fatty acyl residue of SPM on its possible association with lipoproteins and/or cell membranes.
Levade
T
T
Laboratoire de Biochimie, C.H.U. Rangueil, Toulouse Cédex, France.
Gatt
S
S
Maret
A
A
Salvayre
R
R
D001769:Blood; D002413:Cations, Divalent; D002472:Cell Transformation, Viral; D002478:Cells, Cultured; D003470:Culture Media; D004789:Enzyme Activation; D004854:Herpesvirus 4, Human; D006801:Humans; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D008214:Lymphocytes / Q000378:metabolism*; D009542:Niemann-Pick Diseases / Q000378:metabolism; D011973:Receptors, LDL / Q000378:metabolism; D013108:Sphingomyelin Phosphodiesterase / Q000172:deficiency / Q000378:metabolism*; D013109:Sphingomyelins / Q000378:metabolism*; D013997:Time Factors
D002413:Cations, Divalent; D003470:Culture Media; D011973:Receptors, LDL; D013109:Sphingomyelins; D013108:Sphingomyelin Phosphodiesterase