Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.1.1.34 (lipoprotein lipase)
 7,025 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

It has been postulated that lipoprotein lipase, an enzyme important in the uptake of fatty acids into tissues, is bound to the vascular endothelial cell surface and that this binding occurs through attachment to heparinlike glycosaminoglycans. Furthermore, it is thought that heparin releases the enzyme from its attachment to the endothelium into the circulation. These hypotheses have never been tested directly in cell systems in vitro. In the present study we have directly evaluated the interaction of lipoprotein lipase, purified from bovine skim milk with monolayer cultures of endothelial cells, isolated from bovine pulmonary artery. Endothelial cells in primary culture had no intrinsic lipoprotein lipase activity but were able to bind lipoprotein lipase quantitatively. The binding reached equilibrium and was saturable at 0.24 nmol of lipoprotein lipase/mg of cell protein. The concentration of lipoprotein lipase at half-maximal binding was 0.52 microM. Bound lipoprotein lipase could be detached from cultured cells by increasing concentrations of heparin, and at and above 0.6 microgram/ml of heparin, 90% of the cell-bound lipoprotein lipase activity was released. Heparan sulfate and dermatan sulfate released the enzyme to a lesser extent and chondroitin sulfate caused little, if any, release of lipoprotein lipase. The release of lipoprotein lipase with heparin was not associated with a release of [3S]glycosaminoglycans from 35S-prelabeled cells. Reductions of lipoprotein lipase binding to endothelial cells and of cell surface-associated [3S]glycosaminoglycans in 35S-prelabeled cells occurred in parallel both when cells were pretreated with crude Flavobacterium heparinum enzyme before lipoprotein lipase binding and when cells were treated with this enzyme after lipoprotein lipase binding. The removal of heparan sulfate from the cell surface by purified heparinase totally inhibited the binding of lipoprotein lipase by endothelial cells, but the removal of chondroitin sulfate by chondroitin ABC lyase had no effect on this binding. These results provide direct evidence for lipoprotein lipase attachment to endothelial cells through heparan sulfate on the cell surface, and provide evidence for the release of lipoprotein lipase by heparin through a detachment from this binding site.
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PMID:Involvement of cell surface heparin sulfate in the binding of lipoprotein lipase to cultured bovine endothelial cells. 645 61

Prominent features of atheromata include smooth muscle cells, cholesteryl ester-loaded macrophage foam cells, extracellular matrix, extracellularly trapped and aggregated lipoproteins, and various enzymes including lipoprotein lipase (LpL) and sphingomyelinase (SMase). The interplay of these factors was investigated in cell culture. Incubation of bovine aortic smooth muscle cells for 18 h at 37 degrees C with low density lipoprotein (LDL) in the presence of LpL and SMase led to massive aggregation of LDL on the surface of the cells as viewed by phase, fluorescence (using 1,1'-dioctadecyl-3,3,3',3'-tetramethyl-indocarbocyanine perchlorate-LDL), and electron microscopy. This aggregation required both enzymes. Studies with 125I-LDL confirmed these observations: 125I-LDL cell association in the presence of LpL plus SMase was 50-100-fold greater than in the absence of the two enzymes and was 10-fold greater than in the presence of either enzyme alone. A similar effect (68-fold enhancement) was seen with 125I-labeled lipoprotein(a) (Lp(a)), another atherogenic lipoprotein. In all cases, 125I-lipoprotein degradation was relatively low (< 5% of cell-associated material). LpL/SMase-mediated association of 125I-LDL with smooth muscle cells was still observed when enzymatically inactive LpL was used. The effect was markedly diminished when the smooth muscle cells were treated with a combination of chondroitin ABC lyase and heparitinase or when mutant Chinese hamster ovary cells that lack cell-surface proteoglycans were used, indicating a specific role for cellular proteoglycans. When smooth muscle cells with 125I-LDL or 125I-Lp(a) aggregates were rinsed and then coincubated with mouse peritoneal macrophages for a further 24 h, visible aggregates disappeared, and there was marked 125I-lipoprotein degradation. Electron micrographs after 24 h of co-culture showed lipid-laden, foamy macrophages situated on top of smooth muscle cells, suggesting that the macrophages phagocytosed and metabolized the smooth muscle cell-associated LDL aggregates. Last, 125I-LDL association with smooth muscle cell extracellular matrix was also synergistically enhanced by LpL and SMase, to a level that was 19-fold greater than in the absence of the two enzymes. Thus, the interaction of LDL and Lp(a) with four atheroma components, namely, smooth muscle cells, extracellular matrix, LpL, and SMase, represents a physiologically plausible mechanism for massive, focal retention and aggregation of atherogenic lipoproteins in the arterial wall with subsequent macrophage foam cell formation.
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PMID:Lipoprotein lipase and sphingomyelinase synergistically enhance the association of atherogenic lipoproteins with smooth muscle cells and extracellular matrix. A possible mechanism for low density lipoprotein and lipoprotein(a) retention and macrophage foam cell formation. 837 99