Alterations in cell surface glycosphingolipids and other lipid classes of fibroblasts in familial hypercholesterolemia.

Abstract

The glycosphingolipids (GSL) and other major lipid classes were studied in cultured fibroblasts from a family with familial hypercholesterolemia. The GSL content in cells grown in medium containing fetal calf serum was increased 5-fold in the homozygote and 2-to 3-fold in both heterozygous parents. Cell surface labeling experiments, using the membrane probe galactose oxidase followed by reduction with KB3H4, showed an increased incorporation of 3H by the homozygous cells into GL4 (4-fold), GM3 (2-to 3-fold), and GL3a and GD3 (1-to 2-fold); the amount of 3H incorporated by the heterozygous cells was in between that of the homozygous and normal fibroblasts. The specific radioactivity of each of the GSL, except GL2a, was lower in the mutant cells. This unlabeled pool of GSL may be buried in the membrane matrix (less exposure), or located intracellularly, or both. The phospholipids were most markedly elevated (3-fold) in homozygous cells, with a disproportionate increase in phosphatidic acid and sphingomyelin (5-to 6-fold). The content of the GSL, except GL2a, and of the phospholipids was reduced about one-half in the homozygous fibroblasts grown in lipoprotein-deficient medium for 24 hr; by 5 days the GSL content was reduced to only 1.3 times normal and phospholipids to below normal. Incubation of normal fibroblasts in lipoprotein-deficient medium 24 hr had no effect on the GSL or phospholipid content; at 5 days, there was a 50% increase in both GL3a and GL4 with a 25% increase in GM3; there was no change in the phospholipid content. These data suggest that the defective regulation of lipid metabolism in this syndrome may be more extensive than previously realized.Familial hypercholesterolemia (FH) is a disorder of lipid and low-density lipoprotein (LDL) metabolism which is inherited as an autosomal dominant trait and associated with premature atherosclerosis (1, 2). Goldstein and coworkers (3) have demonstrated a lack of functional LDL receptors (receptor-negative) or an alteration in the LDL receptors (receptor-defective) on the cell membrane of cultured fibroblasts from patients with FH. This inability to bind LDL is associated with several abnormalities of lipid and lipoprotein metabolism, which include a lack of feedback inhibition of the rate-limiting enzyme of cholesterol biosynthesis, hydroxymethylglutaryl-CoA reductase (NADPH) [mevalonate:NADP+ oxidoreductase (CoA-acylating), EC 1.1.1.34], decreased conversion of cholesterol to cholesteryl ester, and deficient proteolysis of LDL (4). The mo-

Lactosylceramide Mediates Tumor Necrosis Factor-α-induced Intercellular Adhesion Molecule-1 (ICAM-1) Expression and the Adhesion of Neutrophil in Human Umbilical Vein Endothelial Cells

“…11 LacCer is a ubiquitous glycosphingolipid and plays a pivotal role in the biosynthesis of complex glycosphingolipids (16). Moreover, LacCer may contribute to proliferative diseases such as polycystic kidney disease, atherosclerosis (17), and familial hypercholesterolemia (18,19). The biological function of LacCer was illustrated previously with two examples.…”

“…LacCer is also elevated in atherosclerotic plaque intima (20,21) and in patients with familial hypercholesterolemia (18,19), it is tempting to speculate that this GSL may serve as a lipid second messenger that may be required to stimulate O 2 . generation and ICAM-1 expression in atherosclerosis.…”

“…Moreover, the level of this GSL is elevated in several proliferative diseases including human polycystic kidney disease (17), familial hypercholesterolemia (18,19), and atherosclerosis (20,21). In addition, recently, there has been a surge in reports suggesting that sphingolipids may be implicated as second messengers in mediating diverse molecular events, including cell proliferation (22)(23)(24) and programmed cell death (apoptosis) (25), and as adhesive molecules (16).…”

Redox-regulated Signaling by Lactosylceramide in the Proliferation of Human Aortic Smooth Muscle Cells

“…Our laboratory has reported a close relationship between increased levels of LacCer and hyperproliferation in diverse human diseases. For example, in human atherosclerotic plaque (6), familial hypercholesterolemia (36,37), and human polycystic kidney disease, an increased cellular/tissue level of LacCer was accompanied by cell hyperproliferation (38). Among several GSLs investigated, we found that LacCer exerts the highest stimulation in H-ASMC proliferation (1), and LacCer from human atherosclerotic plaque tissue was significantly more effective in stimulating H-ASMC proliferation than LacCer from the unaffected aorta (6).…”

Localization of urinary lactosylceramide in cytoplasmic vesicles of renal tubular cells in homozygous familial hypercholesterolemia.

“…Our previous work in cultured fibroblasts indicated that there was an alteration of GSL metabolism in certain FH receptornegative homozygotes (4,5). Recently, Verdery and Theolis (6) showed that the synthesis of sphingosine, a long-chain base and a precursor of the ceramide component of GSL, was inhibited by LDL in cultured human fibroblasts.…”