Characterization of lipoprotein lipase activity, secretion, and degradation at different sites of post-translational processing in primary cultures of rat adipocytes

Characterization of lipoprotein lipase storage vesicles in 3T3-L1 adipocytes

Lipoprotein lipase (LPL) is a secreted triglyceride lipase involved in the clearance of very-low-density lipoproteins and chylomicrons from circulation. LPL is expressed primarily in adipose and muscle tissues and transported to the capillary lumen. LPL secretion is regulated by insulin in adipose tissue; however, few studies have examined the regulatory and trafficking steps involved in secretion. Here, we describe the intracellular localization and insulin-dependent trafficking of LPL in 3T3-L1 adipocytes. We compared LPL trafficking to the better characterized trafficking pathways taken by leptin and GLUT4 (also known as SLC2A4). We show that the LPL trafficking pathway shares some characteristics of these other pathways, but that LPL subcellular localization and trafficking are distinct from those of GLUT4 and leptin. LPL secretion occurs slowly in response to insulin and rapidly in response to the Ca2+ ionophore ionomycin. This regulated trafficking is dependent on Golgi protein kinase D and the ADP-ribosylation factor GTPase ARF1. Together, these data give support to a new trafficking pathway for soluble cargo that is active in adipocytes.

Endoplasmic reticulum quality control in lipoprotein metabolism

Lipids play a critical role in energy metabolism, and a suite of proteins is required to deliver lipids to tissues. Several of these proteins require an intricate endoplasmic reticulum (ER) quality control (QC) system and unique secondary chaperones for folding. Key examples include apolipoprotein B (apoB), which is the primary scaffold for many lipoproteins, dimeric lipases, which hydrolyze triglycerides from circulating lipoproteins, and the low-density lipoprotein receptor (LDLR), which clears cholesterol-rich lipoproteins from the circulation. ApoB requires specialized proteins for lipidation, dimeric lipases lipoprotein lipase (LPL) and hepatic lipase (HL) require a transmembrane maturation factor for secretion, and the LDLR requires several specialized, domain-specific chaperones. Deleterious mutations in these proteins or their chaperones may result in dyslipidemias, which are detrimental to human health. Here, we review the ER quality control systems that ensure secretion of apoB, LPL, HL, and LDLR with a focus on the specialized chaperones required by each protein.

Angiopoietin-like 4 promotes intracellular degradation of lipoprotein lipase in adipocytes

LPL hydrolyzes triglycerides in triglyceride-rich lipoproteins along the capillaries of heart, skeletal muscle, and adipose tissue. The activity of LPL is repressed by angiopoietin-like 4 (ANGPTL4) but the underlying mechanisms have not been fully elucidated. Our objective was to study the cellular location and mechanism for LPL inhibition by ANGPTL4. We performed studies in transfected cells, ex vivo studies, and in vivo studies with Angptl4(-/-) mice. Cotransfection of CHO pgsA-745 cells with ANGPTL4 and LPL reduced intracellular LPL protein levels, suggesting that ANGPTL4 promotes LPL degradation. This conclusion was supported by studies of primary adipocytes and adipose tissue explants from wild-type and Angptl4(-/-) mice. Absence of ANGPTL4 resulted in accumulation of the mature-glycosylated form of LPL and increased secretion of LPL. Blocking endoplasmic reticulum (ER)-Golgi transport abolished differences in LPL abundance between wild-type and Angptl4(-/-) adipocytes, suggesting that ANGPTL4 acts upon LPL after LPL processing in the ER. Finally, physiological changes in adipose tissue ANGPTL4 expression during fasting and cold resulted in inverse changes in the amount of mature-glycosylated LPL in wild-type mice, but not Angptl4(-/-) mice. We conclude that ANGPTL4 promotes loss of intracellular LPL by stimulating LPL degradation after LPL processing in the ER.

Transgenic mice expressing lipoprotein lipase in adipose tissue. Absence of the proximal 3'-untranslated region causes translational upregulation

Lipoprotein lipase (LPL) is a key enzyme in lipoprotein and adipocyte metabolism. Defects in LPL can lead to hypertriglyceridemia and the subsequent development of atherosclerosis. The mechanisms of regulation of this enzyme are complex and may occur at multiple levels of gene expression. Because the 3'-untranslated region (UTR) is involved in LPL translational regulation, transgenic mice were generated with adipose tissue expression of an LPL construct either with or without the proximal 3'-UTR and driven by the aP2 promoter. Both transgenic mouse colonies were viable and expressed the transgene, resulting in a 2-fold increase in LPL activity in white adipose tissue. Neither mouse colony exhibited any obvious phenotype in terms of body weight, plasma lipids, glucose, and non-esterified fatty acid levels. In the mice expressing hLPL with an intact 3'-UTR, hLPL mRNA expression approximately paralleled hLPL activity. However in the mice without the proximal 3'-UTR, hLPL mRNA was low in the setting of large amounts of hLPL protein and LPL activity. In previous studies, the 3'-UTR of LPL was critical for the inhibitory effects of constitutively expressed hormones, such as thyroid hormone and catecholamines. Therefore, these data suggest that the absence of the 3'-UTR results in a translationally unrepressed LPL, resulting in a moderate overexpression of adipose LPL activity.

VLDL-induced triglyceride accumulation in human macrophages is mediated by modulation of LPL lipolytic activity in the absence of change in LPL mass

Mixed dyslipidemia of phenotype IIB is characterized by elevated levels of very low density lipoprotein (VLDL)-1 and VLDL-2 subfractions and of low density lipoprotein (LDL), which are associated with premature formation of atherosclerotic plaques, characterized by the presence of lipid-rich macrophage foam cells. Lipoprotein lipase (LPL) is a key factor in mediating macrophage lipid accumulation and foam-cell formation from native VLDL particles. The action of macrophage-derived LPL in the induction of intracellular lipid accumulation from triglyceride-rich lipoprotein (TRL) subfractions (VLDL-1, VLDL-2) is, however, indeterminate, as is the potential role of VLDL-1 and VLDL-2 in modulating macrophage LPL expression. We evaluated the role of LPL in the interaction of type IIB VLDL-1 and VLDL-2 with human macrophages. Both VLDL-1 and VLDL-2 subfractions induced significant accumulation of triglyceride (9.8-fold, P<0.0001, and 4.8-fold, P<0.0001, respectively) and of free cholesterol content (1.4-fold, P<0.001, and 1.2-fold, P=0.02, respectively). Specific inhibition (90%) of the lipolytic activity of endogenous LPL by tetrahydrolipstatin (THL) in the presence of VLDL-1 or VLDL-2 resulted in marked reduction in cellular loading of both triglycerides (-89%, P=0.008, and -89%, P=0.015, respectively) and free cholesterol (-76%, P=0.02, and -55%, P=0.06 respectively). Furthermore, VLDL-1 and VLDL-2 induced marked increase in macrophage-derived LPL enzyme activity (+81%, P=0.002, and +45%, P=0.02), but did not modulate macrophage-derived LPL mRNA and protein expression; consequently, LPL specific activity was significantly increased from 1.6 mU/microg at baseline to 4.1 mU/microg (P=0.01) and 3.1 mU/microg (P=0.05), in the presence of VLDL-1 and VLDL-2, respectively. We conclude that type IIB VLDL-1 and VLDL-2 induce triglyceride accumulation in human monocyte-macrophages primarily via the lipolytic action of LPL, which may involve stabilization and activation of the macrophage-secreted enzyme, rather than via modulation of enzyme production.

Maturation of lipoprotein lipase in the endoplasmic reticulum. Concurrent formation of functional dimers and inactive aggregates

The maturation of lipoprotein lipase (LPL) into a catalytically active enzyme was believed to occur only after its transport from the endoplasmic reticulum (ER) to the Golgi apparatus. To test this hypothesis, LPL located in these two subcellular compartments was separated and compared. Heparin affinity chromatography resolved low affinity, inactive LPL displaying ER characteristics from a high affinity, active fraction exhibiting both ER and Golgi forms. The latter forms were further separated by beta-ricin chromatography and were found to have comparable activities per unit of LPL mass. Thus, LPL must reach a functional conformation in the ER. Active LPL, regardless of its cellular location, exhibited the expected dimer conformation. However, inactive LPL, found only in the ER, was highly aggregated. Kinetic analysis indicated a concurrent formation of LPL dimer and aggregate and indicated that the two forms have dissimilar fates. Whereas the dimer remained stable even when confined to the ER, the aggregate was degraded. Degradation rates were not affected by proteasomal or lysosomal inhibitors but were markedly reduced by ATP depletion. Lowering the redox potential in the ER by dithiothreitol caused the dimer to associate with calnexin, BiP, and protein-disulfide isomerase to form large, inactive complexes; dithiothreitol removal induced complex dissociation with restoration of the functional LPL dimer. In contrast, the LPL aggregate was only poorly associated with ER chaperones, appearing to be trapped in an irreversible, inactive conformation destined for ER degradation.

Resistance of adipose tissue lipoprotein lipase to insulin action in rats fed an obesity-promoting diet

This study aimed to assess whether adipose lipoprotein lipase (LPL) becomes resistant to insulin in a nutritional model of resistance of glucose metabolism to insulin. Sprague-Dawley rats were fed for 4 wk chow or a purified high-sucrose, high-fat (HSHF) diet that induced overt insulin resistance. Rats were fasted for 24 h and then refed chow for 1, 3, or 6 h. The postprandial rise in insulinemia was similar in both dietary cohorts, whereas glycemia was higher in HSHF-fed than in chow-fed animals, indicating glucose intolerance and insulin resistance. In chow-fed rats, adipose LPL activity increased two- to fourfold postprandially, but only minimally (30%) in HSHF-fed rats. Muscle LPL decreased postprandially in HSHF-fed rats, suggesting intact sensitivity to insulin, but it increased in chow-fed animals. Peak postprandial triglyceridemia was higher (+70%) in insulin-resistant than in control rats. The postprandial rate of appearance of triglycerides in the circulation was similar in control and insulin-resistant rats, indicating that hypertriglyceridemia of the latter was the result of impaired clearance. These results demonstrate that adipose LPL becomes resistant to insulin in diet-induced IR and further suggest that, under certain nutritional conditions, modifications in adipose LPL modulation associated with insulin resistance, along with low muscle LPL, heightens postprandial hypertriglyceridemia through attenuated triglyceride clearance.

The atherogenic plasma remnant-like particle cholesterol concentration is increased in the fasting and postprandial state in active acromegalic patients

BACKGROUND

Premature atherosclerosis is a clinical feature in untreated acromegaly. Increased postprandial lipoprotein remnant levels are associated with premature atherosclerosis. In most studies, remnants have been measured indirectly using retinyl esters (RE) as a chylomicron core label. Remnants can also be directly quantified by immunoseparation using monoclonal antibodies to apolipoprotein (apo) AI and apo B100 to remove nonremnant lipoproteins. Cholesterol is quantified in the remaining apo E-rich remnant fraction (RLP-C).

OBJECTIVE

The aim of the present study was to investigate the role of postprandial lipaemia in patients with acromegaly to further define abnormalities leading to increased susceptibility for atherosclerosis.

PATIENTS

In a case-control study, the plasma postprandial lipoprotein remnant fraction (RLP-C and RE) were analysed in six patients with active acromegaly [two females, four males; aged 53 +/- 9 years; body mass index (BMI), 29 +/- 4 kg/m2] and in six normolipidaemic control subjects (matched for age, gender, BMI and apo E genotype). They underwent an oral vitamin A fat loading test.

RESULTS

Baseline plasma triglycerides (TG) were not significantly different in patients (1.75 +/- 0.71 mM) and controls (1.15 +/- 0.46 mM). Lipoprotein lipase activity was significantly lower in patients than in controls (108 +/- 21 vs. 141 +/- 19 U/l, respectively; P < 0.05). Baseline plasma apo E levels were higher in patients (60.8 +/- 7.9 mg/l) than in controls (48.3 +/- 5.9 mg/l; P < 0.05). No differences were found in the area under the postprandial TG curve (AUC-TG), the incremental AUC-TG (DeltaAUC-TG) and AUC-RE in the Sf < 1000 remnant fraction. However, fasting plasma RLP-C concentrations, isolated by immunoseparation, were increased in patients with active acromegaly (0.41 +/- 0.13 mM) compared to control subjects (0.20 +/- 0.07 mM; P < 0.05). Incremental postprandial RLP-C response (corrected for fasting values) was also significantly elevated in patients (2.14 +/- 1.19 mM/h/l) compared to controls (0.86 +/- 0.34 mM/h/l; P < 0.05). In both groups, the maximal RLP-C concentration was reached between 2 and 4 h.

CONCLUSIONS

In conclusion, the atherogenic postprandial remnants, represented by RLP-C, were significantly elevated at baseline and in the postprandial period, whereas the larger-sized remnants, represented by retinyl esters (Sf < 1000), were not different from controls. The disturbances in the postprandial RLP-C response increased the susceptibility for premature atherosclerosis as observed in patients with acromegaly.

Partial hepatectomy and/or surgical stress provoke changes in the expression of lipoprotein lipase and actin in liver and extrahepatic tissues

The expression of lipoprotein lipase (LPL) and actin genes was examined in heart, muscle and white adipose tissue (WAT) and the expression of albumin and actin genes was examined in regenerating liver after 2/3 hepatectomy. Both surgical stress and partial hepatectomy (PH) affected LPL and actin mRNA levels in muscle and WAT, but not in heart. The changes in LPL mRNA suggest transcriptional regulation of the enzyme during hepatic regeneration. Our results show for the first time that the LPL gene expression in the different tissues studied is altered not only by the surgical stress, but also by PH per se. Actin expression is also affected in some tissues. In liver, PH and surgical stress altered the expression of albumin and total mRNA. The total mRNA of the other tissues studied did not change. The changes observed in LPL in different tissues, especially in WAT and muscle, may be responsible for some of the changes in lipidic metabolism, thus allowing for some plasma lipoproteins to be used as substrates by the LPL activity that arises in the liver during hepatic regeneration. The fatty acids derived from these lipoproteins would constitute not only an energy source but also the building material needed in the process of restoration of the lost hepatic mass. It is suggested that hormonal changes taking place after surgery are responsible for the variation in the levels of the different mRNAs studied.

Antagonistic effects of vitamin D and parathyroid hormone on lipoprotein lipase in cultured adipocytes

The effects of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) (calcitriol) and parathyroid hormone (PTH) on synthesis and secretion of lipoprotein lipase (LPL) were studied in 3T3-L1 adipocytes. Expression of the vitamin D receptor was demonstrated by saturation kinetics with radiolabeled calcitriol. Incubation with calcitriol (10(-8) M) for up to 4 d resulted in a time-dependent significant increase in heparin-releasable LPL activity (LPLa) accompanied by a significant increase in LPL mRNA. In contrast, incubation with intact (1-84) PTH (10(-6) to 10(-9) M) produced a time- and dose-dependent significant decrease in LPLa, but no change in LPL mRNA. The effect of PTH (24-h incubation, 10(-8) M) could be prevented by the calcium channel blocker verapamil. Coincubation with both calcitriol and PTH at equimolar concentration (10(-8) M) resulted in an increase in LPLa and LPL mRNA. These data indicate an antagonistic role for calcitriol and PTH in the regulation of LPL, possibly mediated by intracellular calcium, which may contribute to the alterations in lipoprotein metabolism occurring in uremia.

Dengue virus type 1 nonstructural glycoprotein NS1 is secreted from mammalian cells as a soluble hexamer in a glycosylation-dependent fashion

Nonstructural glycoprotein NS1, specified by dengue virus type 1 (Den-1), is secreted from infected green monkey kidney (Vero) cells in a major soluble form characterized by biochemical and biophysical means as a unique hexameric species. This noncovalently bound oligomer is formed by three dimeric subunits and has a molecular mass of 310 kDa and a Stokes radius of 64.4 A. During protein export, one of the two oligosaccharides of NS1 is processed into an endo-beta-N-acetylglucosaminidase F-resistant complex-type sugar while the other remains of the polymannose type, protected in the dimeric subunit from the action of maturation enzymes. Complete processing of the complex-type sugar appears to be required for efficient release of soluble NS1 into the culture fluid of infected cells, as suggested by the repressive effects of the N-glycan processing inhibitors swainsonine and deoxymannojyrimicin. These results, together with observations related to the absence of secretion of NS1 from Den-infected insect cells, suggest that maturation and secretion of hexameric NS1 depend on the glycosylation status of the host cell.

Effect of increased afterload on cardiac lipoprotein lipase and VLDL receptor expression

Fatty acids are a major source of fuel for energy production by myocytes. Lipoprotein lipase (LPL) and very low density lipoprotein (VLDL) receptor are abundantly expressed by the heart and skeletal muscles. LPL and possibly VLDL receptor represent the primary route of access to fatty acids contained in circulating triglyceride-rich lipoproteins. Physical exercise and thyroid hormone, which promote energy consumption, upregulate LPL expression in skeletal muscles. This study tested the hypothesis that increased cardiac workload might modulate myocardial LPL and/or VLDL receptor expressions. Accordingly, cardiac tissue LPL activity, LPL and VLDL receptor proteins and mRNA abundance were studied in Sprague-Dawley rats 4 weeks after induction of severe thoracic aorta constriction or sham operation. Elevation of afterload with thoracic aortic constriction led to a significant cardiomegaly and a marked upregulation of cardiac LPL activity, LPL mRNA and LPL protein abundance, but did not modify VLDL receptor mRNA or protein abundance. Thus, increased cardiac workload in this model results in upregulation of myocardial LPL expression which can enhance fatty acid availability to accommodate the heart's increased energy requirement.

Thiazolidinediones inhibit lipoprotein lipase activity in adipocytes

The thiazolidinediones troglitazone and BRL 49653 improve insulin sensitivity in humans and animals with insulin resistance. Adipose tissue lipoprotein lipase is an insulin-sensitive enzyme. We examined the effects of thiazolidinediones on lipoprotein lipase expression in adipocytes. When added to 3T3-F442A, 3T3-L1, and rat adipocytes in culture, troglitazone and BRL 49653 inhibited lipoprotein lipase activity. This inhibition was observed at concentrations as low as 0.1 microM and within 2 h after addition of the drug. Lipoprotein lipase activity was inhibited in differentiated adipocytes as well as the differentiating cells. Despite this decrease in enzyme activity, these drugs increased mRNA levels in undifferentiated 3T3-F442A and 3T3-L1 cells and had no effect on mRNA expression or synthesis of lipoprotein lipase in differentiated cells. Western blot analysis showed that these drugs did not affect the mass of the enzyme protein. Lipoprotein lipase activity in cultured Chinese hamster ovary cells was not inhibited by troglitazone. Glucose transport, biosynthesis of lipids from glucose or the biosynthesis of proteins were unaffected by thiazolidinediones in differentiated cells, whereas glucose transport and lipid biosynthesis were increased when these drugs were added during differentiation. These results show that troglitazone and BRL 49653 have a specific, post-translational inhibitory effect on lipoprotein lipase in adipocytes, yet they promote lipid accumulation and differentiation in preadipocytes.

Mechanisms of decreased lipoprotein lipase activity in adipocytes of starved rats depend on duration of starvation

The aim of this study was to delineate the mechanisms by which varying periods of starvation decrease lipoprotein lipase (LPL) activity in rat adipose tissue. LPL mRNA levels and rates of LPL synthesis, degradation and secretion were compared in adipocytes from male rats that had been fed or starved for 1 or 3 d. The decreased LPL activity after 3 d of starvation (-76%) was explained mainly by a 50% decrease in the relative abundance of LPL mRNA levels (P < 0.05) and a parallel 50% decrease in relative rates of LPL biosynthesis (P < 0.05). In contrast, starvation for 1 d decreased total LPL activity by 47% (P < 0.05) but did not affect LPL mRNA levels or relative rates of LPL biosynthesis. Pulse-chase studies demonstrated that 1 d of starvation increased the rate of degradation of newly synthesized LPL (P < 0.05) and markedly decreased its secretion into the medium (P < 0.05). A decrease in overall protein synthesis also contributed to the decreased LPL activity after 1 and 3 d of starvation. We conclude that the relative importance of pre- and post-translational mechanisms in regulating adipose tissue LPL activity depends on the duration of starvation. During short-term starvation, degradation of newly synthesized LPL is an important determinant to its secretion from the adipocyte and hence its functional activity at the capillary endothelium.

Defects of lipoprotein metabolism in familial combined hyperlipidaemia

Familial combined hyperlipidaemia is the most common inherited hyperlipidaemia and is found in up to 10% of patients with premature myocardial infarction. The genetic and metabolic bases of the disorder have not yet been defined. This review discusses the important advances in the past year in our understanding of the different metabolic pathways contributing to the pathogenesis of familial combined hyperlipidaemia.

Gene expression of lipoprotein lipase in experimental nephrosis

Nephrotic syndrome (NS) is commonly associated with marked hypertriglyceridemia, impaired triglyceride-laden lipoprotein clearance, and reduced peripheral tissue uptake of triglycerides from chylomicrons. Lipoprotein lipase (LPL) is the rate-limiting step in triglyceride-rich lipoprotein metabolism. Earlier studies have demonstrated a marked reduction of plasma post-heparin lipolytic activity and LPL protein in NS. However, the effect of NS on gene expression of LPL has not been elucidated. We studied rats with puromycin aminonucleoside-induced NS and the placebo-injected control animals. Heart, soleus muscle, and fat body LPL activity, protein mass, and mRNA were measured and plasma lipid levels were quantitated. The NS group exhibited marked proteinuria, hypoalbuminemia, and hypertriglyceridemia. This was associated with significant reductions of LPL activity and immunodetectable protein in the heart, adipose tissue, and soleus muscle in the NS group. The reduction in LPL protein mass in the tissues tested was accompanied by a parallel reduction in LPL mRNA of the heart but not of either adipose tissue or skeletal muscle, suggesting translational or posttranslational modifications. A negative correlation was found between plasma triglyceride concentration and the LPL, activities of the tissues tested in the study population. Thus this study has revealed a significant down-regulation of tissue LPL protein in experimental NS. This phenomenon can, in part, account for hypertriglyceridemia, impaired catabolism of chylomicrons, and very low-density lipoprotein by peripheral tissues and decreased postheparin lipolytic activity in NS.

Effects of exercise training and feeding on lipoprotein lipase gene expression in adipose tissue, heart, and skeletal muscle of the rat

Lipoprotein lipase (LPL) is found in adipose tissue and muscle, and is important for the uptake of triglyceride-rich lipoproteins from plasma. This study examined the regulation of LPL in adipose tissue and muscle by exercise training in combination with the fed or fasted state. After training male rats on a treadmill for 6 weeks, LPL activity, mass, and mRNA levels were measured in adipose tissue, heart, soleus, and extensor digitorum longus (EDL) muscles and compared with levels in sedentary rats. Tissue LPL was measured as the heparin-released (HR) and cellular-extracted (EXT) fractions 16 hours following the last bout of exercise, during which time some animals were fasted and others were allowed free access to food. Training led to an increase in HR LPL activity and LPL protein mass in soleus and EDL, but had no effort on adipose tissue and heart LPL. The increase in soleus LPL with exercise was in the HR fraction only, whereas the increase in EDL LPL with training was in both the HR and EXT fractions. All these changes in LPL activity were accompanied by similar changes in LPL immunoreactive mass. However, there were no changes in LPL mRNA levels with training. Feeding induced a large increase in adipose tissue LPL activity and mass in both the HR and EXT fractions: however, there was no change in mRNA levels. In heart, feeding yielded a decrease in HR but no consistent change in EXT activity or mass, and a consistent decrease in mRNA levels. As compared with control rats, trained rats demonstrated different responses to feeding in all tissues, especially in soleus and EDL. Whereas feeding had no effect on LPL in soleus and EDL of control rats, feeding induced a decrease in HR and EXT LPL in the soleus of trained rats. In addition, feeding yielded a significant decrease in EXT LPL of the EDL of trained rats. Thus, these data demonstrate that adipose tissue and heart LPL are highly regulated by feeding and are not responsive to long-term exercise training. On the other hand, skeletal muscle LPL is increased in trained rats, but this increase is blunted considerably by feeding following the last bout of exercise. These changes in LPL activity and mass are mostly unaccompanied by changes in LPL mRNA levels, demonstrating that much physiologic regulation occurs posttranscriptionally.

Role of processing of the oligosaccharide chains in the affinity of lipoprotein lipase for heparin

The role of processing of the oligosaccharide chains in the affinity of lipoprotein lipase (LPL) for heparin was examined in 3T3-L1 adipocytes. 43% of 35S-labeled LPL subunits in tunicamycin (TUN)-treated cells did not bind to a heparin-Sepharose column and 46% was eluted with 0.6 M NaCl. 11% of LPL subunits in castanospermine (CSTP)-treated cells did not bind to the column and 38% was eluted with 0.6 M NaCl. In contrast, as in untreated cells, LPL subunits in 1-deoxymannojirimycin (dMM)-treated and swainsonine (SW)-treated cells almost all bound to the column and over 93% of the subunits bound were eluted with 1.5 M NaCl. Thus, core glycosylation and subsequent removal of the distal glucose residue from oligosaccharide chains of LPL in the endoplasmic reticulum (ER) is required for acquisition of a higher affinity for heparin.