Increased sphingomyelin content impairs HDL biogenesis and maturation in human Niemann-Pick disease type B.
We previously reported that human Niemann-Pick Disease type B (NPD-B) is associated with low HDL. In this study, we investigated the pathophysiology of this HDL deficiency by examining both HDL samples from NPD-B patients and nascent high density lipoprotein (LpA-I) generated by incubation of lipid-free apolipoprotein A-I (apoA-I) with NPD-B fibroblasts. Interestingly, both LpA-I and HDL isolated from patient plasma had a significant increase in sphingomyelin (SM) mass ( approximately 50-100%). Analysis of LCAT kinetics parameters (V(max) and K(m)) revealed that either LpA-I or plasma HDL from NPD-B, as well as reconstituted HDL enriched with SM, exhibited severely decreased LCAT-mediated cholesterol esterification. Importantly, we documented that SM enrichment of NPD-B LpA-I was not attributable to increased cellular mass transfer of SM or unesterified cholesterol to lipid-free apoA-I. Finally, we obtained evidence that the conditioned medium from HUVEC, THP-1, and normal fibroblasts, but not NPD-B fibroblasts, contained active secretory sphingomyelinase (S-SMase) that mediated the hydrolysis of [(3)H]SM-labeled LpA-I and HDL(3). Furthermore, expression of mutant SMase (DeltaR608) in CHO cells revealed that DeltaR608 was synthesized normally but had defective secretion and activity. Our data suggest that defective S-SMase in NPD leads to SM enrichment of HDL that impairs LCAT-mediated nascent HDL maturation and contributes to HDL deficiency. Thus, S-SMase and LCAT may act in concert and play a crucial role in the biogenesis and maturation of nascent HDL particles.
Lee
Ching Yin
CY
Cardiovascular Genetics Laboratory, Department of Medicine, Division of Cardiology, McGill University Health Centre/Royal Victoria Hospital, Montréal, Québec, Canada.
Lesimple
Alain
A
Denis
Maxime
M
Vincent
Jérôme
J
Larsen
Asmund
A
Mamer
Orval
O
Krimbou
Larbi
L
Genest
Jacques
J
Marcil
Michel
M
D000328:Adult; D000818:Animals; D016466:CHO Cells; D002478:Cells, Cultured; D002784:Cholesterol / Q000378:metabolism; D006224:Cricetinae; D005260:Female; D005347:Fibroblasts / Q000378:metabolism; D006801:Humans; D008075:Lipoproteins, HDL / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D009542:Niemann-Pick Diseases / Q000097:blood / Q000378:metabolism*; D010743:Phospholipids / Q000378:metabolism; D013108:Sphingomyelin Phosphodiesterase / Q000378:metabolism; D013109:Sphingomyelins / Q000378:metabolism* / Q000494:pharmacology; D014162:Transfection
D008075:Lipoproteins, HDL; D010743:Phospholipids; D013109:Sphingomyelins; D002784:Cholesterol; D013108:Sphingomyelin Phosphodiesterase