Cited by 214Lipid metabolism and disordersCholesterol and Lipid MetabolismLipoproteins and Cardiovascular Health

The DOI matches its Crossref record; 31 of the 31 references it cites were found in a registry or an index; none of the 6 sources its claims cite is checked for support yet.

Low density lipoprotein receptor internalizes low density and very low density lipoproteins that are bound to heparan sulfate proteoglycans via lipoprotein lipase

Open access
Mulder, M., Lombardi, P., Jansen, H., van Berkel, T.J., Frants, R.R., Havekes, L.M.·1993·Journal of Biological Chemistry

Abstract

It has previously been shown that lipoprotein lipase (LPL) enhances the binding of low density lipoproteins (LDL) and very low density lipoproteins (VLDL) to HepG2 cells and fibroblasts, up to 80-fold. This increase in binding is LDL receptor-independent and is due to a bridging of LPL between extracellular heparan sulfate proteoglycans (HSPG) and the lipoproteins. In the present paper, we show that preincubation of the cells with LPL, followed by washing prior to the binding experiment, increased binding to the same extent as occurs when the binding is performed in the presence of LPL. This indicates that the formation of a complex of LPL with the lipoproteins is not a prerequisite of binding. Binding curves and Scatchard analyses reveal that both the number of binding sites and the affinity of the binding are increased 20-30-fold by the addition of 3.4 micrograms/ml LPL. The addition of LPL also resulted in an enhanced uptake and subsequent lysosomal degradation of both LDL and VLDL when compared with binding, although to a lesser extent (up to 25-fold when measured after 5 h at 37 degrees C). Strikingly, enhanced uptake did not occur in LDL receptor-negative fibroblasts. In addition, down-regulation of the LDL receptor activity by preincubation of the cells for 48 h with either LDL or beta-VLDL resulted in a parallel decrease in the uptake of LPL-mediated HSPG-bound LDL, whereas the LPL-mediated binding itself was not diminished. These observations indicate that the uptake of LPL-mediated HSPG-bound LDL and VLDL mainly proceeds via the LDL receptor. Binding of labeled LDL to the cells at 4 degrees C for 2 h followed by a chase period at 37 degrees C revealed that in absolute terms, the initial rate of internalization of HSPG-bound LDL is comparable with that of LDL receptor-bound LDL (0.58 and 0.44 ng/min/mg of cell protein, respectively). We conclude that in LDL receptor-positive cells, the LPL-mediated binding of LDL and VLDL to HSPG is followed by internalization of the lipoproteins mainly through the rapid process of the classical LDL receptor recycling system, whereas only a minor portion is internalized via the much slower process of HSPG uptake.

Overview

AI snapshot

Written from the paper’s full text.

TL;DR

LPL bridges LDL and VLDL to cell-surface heparan sulfate proteoglycans (HSPG), and the major portion of these HSPG-bound lipoproteins is subsequently internalized via the classical LDL receptor rather than by slow HSPG uptake. The paper concludes that LPL-mediated binding is LDL receptor-independent, but LPL-mediated uptake and lysosomal degradation are mainly LDL receptor-dependent.

Key findings

  • Preincubating cells with LPL followed by washing increased LDL binding as much as adding LPL during the binding assay, indicating that LPL–lipoprotein complex formation is not required for enhanced binding.
  • Binding curves and Scatchard analyses showed that LPL increased both the number of binding sites and binding affinity about 20–30-fold; the abstract reports this with 3.4 pg/ml LPL, and Fig. 2 reports an approximately 20-fold higher maximum LDL binding after preincubation with 1.7 pg/ml LPL.
  • LPL enhanced uptake and lysosomal degradation of LDL and VLDL, though less than binding: the abstract states up to 25-fold after 5 h at 37 °C, while Fig. 3 reports internalization increases of 6-fold for LDL and 23-fold for VLDL after 4 h with heat-inactivated LPL.
  • Down-regulation of LDL receptor activity decreased uptake of LPL-mediated HSPG-bound LDL in parallel with reduced LDL receptor-bound LDL uptake, while LPL-mediated binding itself was not diminished; the initial internalization rate of HSPG-bound LDL was comparable to LDL receptor-bound LDL (0.58 versus 0.44 ng/min/mg cell protein).

Methods

  • Cultured HepG2 cells, normal fibroblasts, and LDL receptor-negative fibroblasts from a patient with homozygous familial hypercholesterolemia were used; LDL, VLDL, and β-VLDL were isolated by ultracentrifugation, iodinated, and incubated with cells in the presence or absence of bovine LPL from skimmed milk or heat-inactivated LPL.
  • Binding was measured at 0–4 °C with 10 µg/ml ¹²⁵I-labeled lipoprotein; uptake, intracellular content, and degradation were measured at 37 °C, with trypsin treatment to separate surface-bound from internalized lipoprotein, and with heparinase, chloroquine, or NH₄Cl treatments as indicated.
  • Main analyses included binding curves, Scatchard plots, degradation assays, LDL receptor down-regulation by preincubation with LDL or β-VLDL, and chase experiments to measure internalization rates.

Limitations

  • The paper states that the relevance of these cell-culture data to the in vivo fate of lipoproteins is still unclear, and that most experiments used LPL concentrations more than 100 times the physiological range of 8–25 ng/ml, although 25 ng/ml LPL still increased LDL binding about 1.5-fold.
  • The discussion notes discrepancies with other studies, attributing them to differences in measuring total cell association versus discriminating bound and internalized lipoprotein, different sampling times, and expressing internalization as percent of total radioactivity rather than absolute ng/min/mg cell protein.
  • The text itself contains an apparent inconsistency: the abstract says enhanced uptake did not occur in LDL receptor-negative fibroblasts, whereas the discussion says internalization was increased considerably in those cells but was much less efficient than in control fibroblasts.

Model-written summary. Check it against the paper before relying on it.

Integrity signals

Registry

Crossref · 10.1016/s0021-9258(18)98359-6

Cites

31 of 31 references verified0 citation errors · 0 not checkable

Statistics

Nothing to recompute.

Verification

Claims the paper makes

0 of 6 cited sources checked · 0 supported · 0 flagged

  • Findingown data

    LPL-mediated binding of LDL is already evident at more physiological concentrations of LPL (ng/ml range).

    “In Fig. lB, it is shown that the LPL-mediated binding of LDL is already evident at more physiological concentrations of LPL (ng/ml range).”
    Quote in the paperNot a substantial claim
  • Findingown data
    § Low Density Lipoprotein Receptor Internalizes Low Density and Very Low Density Lipoproteins That Are Bound to Heparan Sulfate Proteoglycans via Lipoprotein Lipase*

    Preincubation of cells with LPL followed by washing prior to the binding experiment increased binding to the same extent as occurs when binding is performed in the presence of LPL.

    “In the present paper, we show that preincubation of the cells with LPL, followed by washing prior to the binding experiment, increased binding to the same extent as occurs when the binding is performed in the presence of LPL.”
    Quote in the paperSubstantial claim
  • Findingown data

    Treatment of cells with heparinase inhibited LPL-mediated binding and internalization of both LDL and VLDL.

    “Fig, 3 shows that besides the inhibition of the LPLmediated binding of LDL and VLDL, treatment of the cells with heparinase also resulted in inhibition of the LPL-mediated internalization of both lipoproteins.”
    Quote in the paperSubstantial claim
  • Findingown data
    § Low Density Lipoprotein Receptor Internalizes Low Density and Very Low Density Lipoproteins That Are Bound to Heparan Sulfate Proteoglycans via Lipoprotein Lipase*

    Initial rate of internalization of HSPG-bound LDL is comparable with that of LDL receptor-bound LDL (0.58 and 0.44 ng/min/mg of cell protein, respectively).

    “Binding of labeled LDL to the cells at 4”
    Quote in the paperSubstantial claim
  • Findingown data

    Parallel results were obtained for the uptake of LPL-mediated HSPG-bound LDL (50 and 45% of the control value, respectively).

    “Strikingly, parallel results were obtained for the uptake of LPL-mediated HSPG-bound LDL (50 and 45% of the control value, respectively) (D).”
    Quote in the paperSubstantial claim
  • It may state two separate claims as one. 10
  • The quote only partly states this claim. 1
  • Probably not a substantial claim. 2
  • It may state two separate claims as one.

    Findingown data

    Most LDL receptor-bound LDL has been internalized within 10-15 min, which is in accordance with the recycling time reported earlier for the classical LDL receptor.

    “As shown in Fig. 6, most of the LDL receptor-bound LDL has been internalized within 10-15 min, which is in accordance with the recycling time reported earlier for the classical LDL receptor (28).”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [28]

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  • It may state two separate claims as one.

    Findingown data

    In the presence of heat-inactivated LPL, binding of LDL and VLDL is enhanced (about 14- and 31-fold for LDL and VLDL, respectively) and internalization is increased to a lesser extent (6- and 23-fold for LDL and VLDL, respectively).

    “In Fig. 3, it is shown that in the presence of heat-inactivated LPL, not only the binding of LDL and VLDL is enhanced (about 14and 31-fold for LDL and VLDL, respectively) but also the internalization (expressed as the amount of intracellular plus degraded lipoprotein) is increased, although to a lesser extent (6-and 23-fold for LDL and VLDL, respectively).”
    Quote in the paperSubstantial claim
  • It may state two separate claims as one.

    Findingown data
    § Low Density Lipoprotein Receptor Internalizes Low Density and Very Low Density Lipoproteins That Are Bound to Heparan Sulfate Proteoglycans via Lipoprotein Lipase*

    Down-regulation of LDL receptor activity by preincubation of cells for 48 h with either LDL or beta-VLDL resulted in a parallel decrease in uptake of LPL-mediated HSPG-bound LDL, whereas LPL-mediated binding itself was not diminished.

    “In addition, down-regulation of the LDL receptor activity by preincubation of the cells for 48 h with either LDL or 8-VLDL resulted in a parallel decrease in the uptake of LPL-mediated HSPG-bound LDL, whereas the LPL-mediated binding itself was not diminished.”
    Quote in the paperSubstantial claim
  • It may state two separate claims as one.

    Premisecitation
    § Low Density Lipoprotein Receptor Internalizes Low Density and Very Low Density Lipoproteins That Are Bound to Heparan Sulfate Proteoglycans via Lipoprotein Lipase*

    The increase in binding is LDL receptor-independent and is due to bridging of LPL between extracellular HSPG and lipoproteins.

    “This increase in binding is LDL receptor-independent and is due to a bridging of LPL between extracellular heparan sulfate proteoglycans (HSPG) and the lipoproteins.”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [15]

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  • It may state two separate claims as one. The quote only partly states this claim.

    Interpretationown data
    § Low Density Lipoprotein Receptor Internalizes Low Density and Very Low Density Lipoproteins That Are Bound to Heparan Sulfate Proteoglycans via Lipoprotein Lipase*

    At 37C, most of the LPL-mediated binding and LPL-mediated internalization of LDL and VLDL could be inhibited by heparinase, indicating that the LPL-mediated increases in both binding and internalization are dependent on the presence of HSPG on the plasma membrane.

    “At 37”
    Quote in the paperSubstantial claim
  • It may state two separate claims as one.

    Interpretationown data

    Although LPL-mediated binding of LDL and VLDL occurs via HSPG, the major part of the subsequent internalization of these lipoproteins is mediated via the LDL receptor.

    “Thus, although the LPL-mediated binding of LDL and VLDL occurs via HSPG, the major part of the subsequent internalization of these lipoproteins is mediated via the LDL receptor.”
    Quote in the paperSubstantial claim
  • Probably not a substantial claim.

    Premisecitation
    § Low Density Lipoprotein Receptor Internalizes Low Density and Very Low Density Lipoproteins That Are Bound to Heparan Sulfate Proteoglycans via Lipoprotein Lipase*

    LPL enhances the binding of LDL and VLDL to HepG2 cells and fibroblasts up to 80-fold.

    “It has previously been shown that lipoprotein lipase (LPL) enhances the binding of low density lipoproteins (LDL) and very low density lipoproteins (VLDL) to HepG2 cells and fibroblasts, up to 80-fold.”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [15]

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  • It may state two separate claims as one.

    Premisecitation

    Trypsin removes both cell-bound lipoproteins and cell-bound lipoprotein lipase.

    “Trypsin removes both cell-bound lipoproteins and cell-bound lipoprotein lipase (26).”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [26]

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  • Probably not a substantial claim.

    Premisecitation

    LDL receptor-negative fibroblasts were obtained from a patient with homozygous familial hypercholesterolemia.

    “LDL receptornegative fibroblasts were obtained from a patient with homozygous familial hypercholesterolemia (25).”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [25]

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  • It may state two separate claims as one.

    Interpretationown data
    § Low Density Lipoprotein Receptor Internalizes Low Density and Very Low Density Lipoproteins That Are Bound to Heparan Sulfate Proteoglycans via Lipoprotein Lipase*

    In LDL receptor-positive cells, LPL-mediated binding of LDL and VLDL to HSPG is followed by internalization mainly through the rapid process of the classical LDL receptor recycling system, whereas only a minor portion is internalized via the much slower process of HSPG uptake.

    “We conclude that in LDL receptor-positive cells, the LPL-mediated binding of LDL and VLDL to HSPG is followed by internalization of the lipoproteins mainly through the rapid process of the classical LDL receptor recycling system, whereas only a minor portion is internalized via the much slower process of HSPG uptake.”
    Quote in the paperSubstantial claim
  • It may state two separate claims as one.

    Interpretationreasoning

    In normal cells, the uptake of LPL-mediated HSPG-bound LDL continues up to 60 min, indicating that the LDL-receptor recycling system is saturated during 4-6 LDL receptor cycles and is consequently the rate-limiting step in this process.

    “The fact that in normal cells the uptake of LPL-mediated HSPG-bound LDL continues up to 60 min indicates that the LDL-receptor recycling system is saturated during 4-6 LDL receptor cycles and, consequently, the rate-limiting step in this process.”
    Quote in the paperSubstantial claim
  • It may state two separate claims as one.

    Interpretationown data

    LPL-mediated HSPG-bound LDL and VLDL are taken up and directed to the lysosomes for degradation.

    “From these results, we conclude that the LPL-mediated HSPG-bound LDL and VLDL are also taken up and directed to the lysosomes for degradation.”
    Quote in the paperSubstantial claim
12 of 12
  • The authors state this as an assumption.

    The LRP binds only apoE-containing lipoproteins.

    “while the LRP is assumed to bind only apoE-containing lipoproteins.”
  • The authors state this as an assumption.

    The LRP contains no heparan sulfate side chains.

    “whereas the LRP is assumed to contain no heparan sulfate side chains.”
2 of 2

Claims other papers make about this one

Each is checked against this paper’s own text: does it say what the citing paper says it does?

Self-check

Percentages, sums and reported differences re-computed from the paper’s own numbers.

Each contradiction between two passages listed here was confirmed by an independent check.

  • Abstract denies uptake increase in receptor-negative fibroblasts

    Major

    The abstract says enhanced uptake did not occur in LDL receptor-negative fibroblasts, but the discussion says LPL considerably increased their internalization of both LDL and VLDL.

  • Conflicting preincubation times for receptor down-regulation

    Minor

    The abstract gives a 48-hour preincubation with LDL or β-VLDL, whereas the description of the down-regulation experiment gives 24 hours.

2 of 2

Citations

Cites

Flagged first, then by citations

Research works printed but not linked: 5

  1. De Water, 1992, Biochem. J., 281, 62
  2. Tajima, 1984, J. Biol. Chem., 96, 1753
  3. Olivecrona, 1989, Curr. Opin. Lipid., 1, 112
  4. Villeli, 1991, Med. Sei. Res., 19, 111
  5. Vilaro, 1988, Am. J. Physiol., 254, G711

Cited by

Sorted by citations

Metadata

Authors
Mulder, M., Lombardi, P., Jansen, H., van Berkel, T. J., Frants, R. R., & Havekes, L. M.
Affiliations
Netherlands Organisation for Applied Scientific Research (NL)
Venue
Journal of Biological Chemistry
Publisher
Elsevier BV
Published
1993-05
Volume
268
Issue
13
Pages
9369-9375
ISSN
0021-9258 (ISSN-L)
OpenAlex
W1525062280
Cited by
214
References
31
Citations by year
2025: 3 · 2024: 1 · 2023: 1 · 2022: 1 · 2021: 5 · 2020: 2 · 2019: 1 · 2018: 1 · 2017: 2 · 2016: 1 · 2015: 5 · 2014: 5 · 2013: 6 · 2012: 5
FWCI
15.93
Type
journal article
Language
en
Open access
Locations
  • Journal of Biological Chemistry (publishedVersion, cc-by)
  • PubMed (publishedVersion)
  • TNO Repository (submittedVersion)
  • Repository hosted by TU Delft Library (TU Delft) (submittedVersion)
  • Data Archiving and Networked Services (DANS) (submittedVersion, other-oa)
Topics
  • Health Sciences › Medicine › Cardiology and Cardiovascular Medicine › Lipid metabolism and disorders
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Biochemistry › Cholesterol and Lipid Metabolism
  • Health Sciences › Medicine › Cardiology and Cardiovascular Medicine › Lipoproteins and Cardiovascular Health
Keywords
heparan sulfate proteoglycans, lipoprotein lipase, low-density lipoprotein, VLDL, LDL receptor, receptor internalization, lipoprotein uptake, lysosomal degradation, LDL receptor recycling, receptor down-regulation, hepatic lipoprotein metabolism, fibroblasts, HepG2 cells, lipoprotein binding
MeSH terms
Animals, Biological Transport, Cattle, Female, Fibroblasts, Heparan Sulfate, Carcinoma, Hepatocellular, Humans, Kinetics, Lipoprotein Lipase, Lipoproteins, LDL, Lipoproteins, VLDL, Liver Neoplasms, Milk, Models, Biological, Polysaccharide-Lyases, Protein Binding, Proteoglycans, Receptors, LDL, Tumor Cells, Cultured, Heparin Lyase, Heparan Sulfate Proteoglycans

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