Ceramide in Lipid Particles Enhances Heparan Sulfate Proteoglycan and Low Density Lipoprotein Receptor-related Protein-mediated Uptake by Macrophages

Abstract

Arterial wall sphingomyelinase (SMase) has been proposed to be involved in atherogenesis. SMase modification of lipoproteins has been shown to occur in atherosclerotic lesions and to facilitate their uptake by macrophages and foam cell formation. To investigate the mechanism of macrophage uptake enhanced by SMase, we prepared lipid emulsions containing sphingomyelin (SM) or ceramide (CER) as model particles of lipoproteins. SMase remarkably increased the uptake of SM-containing emulsions by J774 macrophages without apolipoproteins. The emulsion uptake was negatively correlated with the degree of particle aggregation by pretreatment with SMase, whereas the uptake of CERcontaining emulsions was significantly larger than SMcontaining emulsions, indicating that enhancement of uptake is due to the generation of CER molecules in particles but not to the aggregation by SMase. Heparan sulfate proteoglycans (HSPGs) and low density lipoprotein receptor-related protein (LRP) were crucial for CER-enhanced emulsion uptake, because heparin or lactoferrin inhibited the emulsion uptake. Confocal microscopy also showed that SMase promoted both binding and internalization of emulsions by J774 macrophages, which were almost abolished by lactoferrin. Apolipoprotein E further increased the uptake of CERcontaining emulsions compared with SM-containing emulsions. These findings suggest the generation of CER in lipoproteins by SMase facilitates the macrophage uptake via HSPG and LRP pathways and plays a crucial role in foam cell formation. Thus, CER may act as an important atherogenic molecule.

Metabolism and Modification of Apolipoprotein B-Containing Lipoproteins Involved in Dyslipidemia and Atherosclerosis

“…61,74,284) I have shown that SMase promotes the aggregation and fusion of lipid emulsions depending on ceramide formation. 287,288) I have also confirmed the existence of ceramide-enriched domains in emulsion particles by confocal fluorescence microscopy 288) (Fig. 4).…”

“…287) Ceramide formed in the particles by SMase enhances their uptake into J774 macrophages, although the increase in size or particle aggregation decreases their uptake. HSPGs and LRP are crucial for the ceramide-enhanced emulsion uptake, because heparin or lactoferrin inhibit the emulsion uptake.…”

“…HSPGs and LRP are crucial for the ceramide-enhanced emulsion uptake, because heparin or lactoferrin inhibit the emulsion uptake. 287) LRP is largely confined to clathrin-coated pits, which measure 180-240 nm in diameter. 296,297) It is likely that large particles are restricted to enter clathrin-coated pits, and thus the interaction of large particles with LRP is impaired.…”

Increase in Secretory Sphingomyelinase Activity and Specific Ceramides in the Aorta of Apolipoprotein E Knockout Mice during Aging

“…11) Elevated ceramide levels were recently shown to correlate with atherogenetic processes such as low-density lipoprotein (LDL) aggregation, 12) and form cell migration. 13) In relation to atherogenesis, we previously reported that the ceramide level in human plasma was positively correlated with both total cholesterol and oxidized apolipoprotein B-100 (oxLDL) levels. 14) Deevska et al 15) reported that LDL-SM content and sSMase activity in LDL receptor knockout mice, which were fed an atherogenic diet, were increased.…”

Peculiaries of interactions between proteins of the macroglobulin family and with the endocytic receptors (a possible mechanism of transmembrane transfer)

“…Очевидно, что направленность реализуемых процессов определяется типом эффектора в составе комплекса, а также тем, какой именно представитель семейства МГ является доминирующим в общем пуле комплексов. Необходимо также отметить, что система представляет собой саморегулирующийся механизм, поскольку известно, что экспрессия ЛРП регулируется транспортируемыми МГ субстанциями -интерлейкином-10, интерфероном-g, и лактоферином [13,14]. We have conducted a series of experiments, for specification of mechanisms which proteins of the macroglobulin family deliver regulatory substances inside of a cells.…”