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Impaired LDL receptor-related protein 1 translocation correlates with improved dyslipidemia and atherosclerosis in apoE-deficient mice.

Gordts PL, Bartelt A, Nilsson SK, Annaert W, Christoffersen C, Nielsen LB, Heeren J, Roebroek AJ - PLoS ONE (2012)

Bottom Line: Postprandial lipoprotein improvement was explained by increased hepatic clearance of triglyceride-rich remnant lipoproteins and accompanied by a compensatory 1.6-fold upregulation of LDLR expression in hepatocytes.These findings demonstrate that the NPxYxxL motif in LRP1 is important for insulin-mediated translocation and slow perinuclear endosomal recycling.These LRP1 impairments correlated with reduced atherogenesis and cholesterol levels in apoE-deficient mice, likely via compensatory LDLR upregulation.

View Article: PubMed Central - PubMed

Affiliation: Laboratory for Experimental Mouse Genetics, Center for Human Genetics, KU Leuven, Leuven, Belgium.

ABSTRACT

Objective: Determination of the in vivo significance of LDL receptor-related protein 1 (LRP1) dysfunction on lipid metabolism and atherosclerosis development in absence of its main ligand apoE.

Methods and results: LRP1 knock-in mice carrying an inactivating mutation in the NPxYxxL motif were crossed with apoE-deficient mice. In the absence of apoE, relative to LRP1 wild-type animals, LRP1 mutated mice showed an increased clearance of postprandial lipids despite a compromised LRP1 endocytosis rate and inefficient insulin-mediated translocation of the receptor to the plasma membrane, likely due to inefficient slow recycling of the mutated receptor. Postprandial lipoprotein improvement was explained by increased hepatic clearance of triglyceride-rich remnant lipoproteins and accompanied by a compensatory 1.6-fold upregulation of LDLR expression in hepatocytes. One year-old apoE-deficient mice having the dysfunctional LRP1 revealed a 3-fold decrease in spontaneous atherosclerosis development and a 2-fold reduction in LDL-cholesterol levels.

Conclusion: These findings demonstrate that the NPxYxxL motif in LRP1 is important for insulin-mediated translocation and slow perinuclear endosomal recycling. These LRP1 impairments correlated with reduced atherogenesis and cholesterol levels in apoE-deficient mice, likely via compensatory LDLR upregulation.

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VLDL production, postprandial triglyceride response, intestinal lipid absorption and TRL clearance in apoE−/− (Δ or □) and ApoE−/−LRP1n2/n2 (▪) mice.A–C, VLDL production after a Tyloxapol injection to inhibit lipolysis (A), postprandial triglyceride response after gastric olive oil load (B) and lipid absorption and chylomicron production after a combined gastric olive oil load and Tyloxapol injection (C) (n = 6–10 per genotype). D, Postprandial accumulation of 3H-Triolein in liver, white adipose tissue (WAT) and proximal (Prox.), medial (Med.) and distal (Dist.) intestine 2 h after a gastric load with olive oil mixed with 3H-Triolein (E) (n = 5 per genotype). Data are mean±SEM. *P<0.05, **P<0.001.
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pone-0038330-g002: VLDL production, postprandial triglyceride response, intestinal lipid absorption and TRL clearance in apoE−/− (Δ or □) and ApoE−/−LRP1n2/n2 (▪) mice.A–C, VLDL production after a Tyloxapol injection to inhibit lipolysis (A), postprandial triglyceride response after gastric olive oil load (B) and lipid absorption and chylomicron production after a combined gastric olive oil load and Tyloxapol injection (C) (n = 6–10 per genotype). D, Postprandial accumulation of 3H-Triolein in liver, white adipose tissue (WAT) and proximal (Prox.), medial (Med.) and distal (Dist.) intestine 2 h after a gastric load with olive oil mixed with 3H-Triolein (E) (n = 5 per genotype). Data are mean±SEM. *P<0.05, **P<0.001.

Mentions: When crossing LRP1n2/n2 mice into an apoE−/− background, the LRP1 NPxYxxL-motif inactivating mutation had no significant effect on total cholesterol levels in the absence of apoE (Figure 1A). Plasma triglyceride levels, however, were significantly 1.3-fold reduced in the apoE−/−LRP1n2/n2 mice compared to the apoE−/− control mice (Figure 1A). Analysis of plasma apolipoprotein content revealed a decrease of apoB48 concentrations in apoE−/−LRP1n2/n2 mice (Figure 1B–C). While cholesterol distribution was similar between the two mouse genotypes (Figure 1D), triglyceride content was strongly decreased in the CR/VLDL fraction in apoE−/−LRP1n2/n2 mice when fasted (Figure 1F). Similar decreased triglyceride content in the CR/VLDL fractions was observed in the lipoprotein profile of apoE−/−LRP1n2/n2 mice 2 hours after receiving a fat load mimicking the postprandial state (Figure 1E & 1G). The decrease in TRLs seen for apoE−/−LRP1n2/n2 mice could not be linked to a reduction in hepatic VLDL-triglyceride production, as this was almost identical for both groups after Tyloxapol injection to inhibit lipolysis (Figure 2A). The postprandial triglyceride response after an oral fat load was, in contrast to control apoE−/− mice, almost undetectable in apoE−/−LRP1n2/n2 mice (Figure 2B). When mice were given an oral fat load together with injection of Tyloxapol, we could see that apoE−/−LRP1n2/n2 and apoE−/− mice had a similar postprandial triglyceride accumulation in the circulation (Figure 2C). These results exclude a possible contribution of both impaired lipid absorption and/or chylomicron production. To evaluate if accelerated clearance of TRLs could be a possible explanation, mice were given an oral load of a mixture of olive oil and a radioactive triglyceride, 3H-triolein, and sacrificed two hours later to harvest organs. Quantification revealed a significant 1.8-fold increase in the uptake of 3H-triolein in the liver for apoE−/−LRP1n2/n2 mice compared to apoE−/− controls, while no significant differences were seen for adipose tissue and the small intestine (Figure 2D). The data suggest that apoE−/−LRP1n2/n2 mice have enhanced postprandial hepatic clearance of TRLs.


Impaired LDL receptor-related protein 1 translocation correlates with improved dyslipidemia and atherosclerosis in apoE-deficient mice.

Gordts PL, Bartelt A, Nilsson SK, Annaert W, Christoffersen C, Nielsen LB, Heeren J, Roebroek AJ - PLoS ONE (2012)

VLDL production, postprandial triglyceride response, intestinal lipid absorption and TRL clearance in apoE−/− (Δ or □) and ApoE−/−LRP1n2/n2 (▪) mice.A–C, VLDL production after a Tyloxapol injection to inhibit lipolysis (A), postprandial triglyceride response after gastric olive oil load (B) and lipid absorption and chylomicron production after a combined gastric olive oil load and Tyloxapol injection (C) (n = 6–10 per genotype). D, Postprandial accumulation of 3H-Triolein in liver, white adipose tissue (WAT) and proximal (Prox.), medial (Med.) and distal (Dist.) intestine 2 h after a gastric load with olive oil mixed with 3H-Triolein (E) (n = 5 per genotype). Data are mean±SEM. *P<0.05, **P<0.001.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3368875&req=5

pone-0038330-g002: VLDL production, postprandial triglyceride response, intestinal lipid absorption and TRL clearance in apoE−/− (Δ or □) and ApoE−/−LRP1n2/n2 (▪) mice.A–C, VLDL production after a Tyloxapol injection to inhibit lipolysis (A), postprandial triglyceride response after gastric olive oil load (B) and lipid absorption and chylomicron production after a combined gastric olive oil load and Tyloxapol injection (C) (n = 6–10 per genotype). D, Postprandial accumulation of 3H-Triolein in liver, white adipose tissue (WAT) and proximal (Prox.), medial (Med.) and distal (Dist.) intestine 2 h after a gastric load with olive oil mixed with 3H-Triolein (E) (n = 5 per genotype). Data are mean±SEM. *P<0.05, **P<0.001.
Mentions: When crossing LRP1n2/n2 mice into an apoE−/− background, the LRP1 NPxYxxL-motif inactivating mutation had no significant effect on total cholesterol levels in the absence of apoE (Figure 1A). Plasma triglyceride levels, however, were significantly 1.3-fold reduced in the apoE−/−LRP1n2/n2 mice compared to the apoE−/− control mice (Figure 1A). Analysis of plasma apolipoprotein content revealed a decrease of apoB48 concentrations in apoE−/−LRP1n2/n2 mice (Figure 1B–C). While cholesterol distribution was similar between the two mouse genotypes (Figure 1D), triglyceride content was strongly decreased in the CR/VLDL fraction in apoE−/−LRP1n2/n2 mice when fasted (Figure 1F). Similar decreased triglyceride content in the CR/VLDL fractions was observed in the lipoprotein profile of apoE−/−LRP1n2/n2 mice 2 hours after receiving a fat load mimicking the postprandial state (Figure 1E & 1G). The decrease in TRLs seen for apoE−/−LRP1n2/n2 mice could not be linked to a reduction in hepatic VLDL-triglyceride production, as this was almost identical for both groups after Tyloxapol injection to inhibit lipolysis (Figure 2A). The postprandial triglyceride response after an oral fat load was, in contrast to control apoE−/− mice, almost undetectable in apoE−/−LRP1n2/n2 mice (Figure 2B). When mice were given an oral fat load together with injection of Tyloxapol, we could see that apoE−/−LRP1n2/n2 and apoE−/− mice had a similar postprandial triglyceride accumulation in the circulation (Figure 2C). These results exclude a possible contribution of both impaired lipid absorption and/or chylomicron production. To evaluate if accelerated clearance of TRLs could be a possible explanation, mice were given an oral load of a mixture of olive oil and a radioactive triglyceride, 3H-triolein, and sacrificed two hours later to harvest organs. Quantification revealed a significant 1.8-fold increase in the uptake of 3H-triolein in the liver for apoE−/−LRP1n2/n2 mice compared to apoE−/− controls, while no significant differences were seen for adipose tissue and the small intestine (Figure 2D). The data suggest that apoE−/−LRP1n2/n2 mice have enhanced postprandial hepatic clearance of TRLs.

Bottom Line: Postprandial lipoprotein improvement was explained by increased hepatic clearance of triglyceride-rich remnant lipoproteins and accompanied by a compensatory 1.6-fold upregulation of LDLR expression in hepatocytes.These findings demonstrate that the NPxYxxL motif in LRP1 is important for insulin-mediated translocation and slow perinuclear endosomal recycling.These LRP1 impairments correlated with reduced atherogenesis and cholesterol levels in apoE-deficient mice, likely via compensatory LDLR upregulation.

View Article: PubMed Central - PubMed

Affiliation: Laboratory for Experimental Mouse Genetics, Center for Human Genetics, KU Leuven, Leuven, Belgium.

ABSTRACT

Objective: Determination of the in vivo significance of LDL receptor-related protein 1 (LRP1) dysfunction on lipid metabolism and atherosclerosis development in absence of its main ligand apoE.

Methods and results: LRP1 knock-in mice carrying an inactivating mutation in the NPxYxxL motif were crossed with apoE-deficient mice. In the absence of apoE, relative to LRP1 wild-type animals, LRP1 mutated mice showed an increased clearance of postprandial lipids despite a compromised LRP1 endocytosis rate and inefficient insulin-mediated translocation of the receptor to the plasma membrane, likely due to inefficient slow recycling of the mutated receptor. Postprandial lipoprotein improvement was explained by increased hepatic clearance of triglyceride-rich remnant lipoproteins and accompanied by a compensatory 1.6-fold upregulation of LDLR expression in hepatocytes. One year-old apoE-deficient mice having the dysfunctional LRP1 revealed a 3-fold decrease in spontaneous atherosclerosis development and a 2-fold reduction in LDL-cholesterol levels.

Conclusion: These findings demonstrate that the NPxYxxL motif in LRP1 is important for insulin-mediated translocation and slow perinuclear endosomal recycling. These LRP1 impairments correlated with reduced atherogenesis and cholesterol levels in apoE-deficient mice, likely via compensatory LDLR upregulation.

Show MeSH
Related in: MedlinePlus