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Lpcat3-dependent production of arachidonoyl phospholipids is a key determinant of triglyceride secretion.

Rong X, Wang B, Dunham MM, Hedde PN, Wong JS, Gratton E, Young SG, Ford DA, Tontonoz P - Elife (2015)

Bottom Line: Mice lacking Lpcat3 in the intestine fail to thrive during weaning and exhibit enterocyte lipid accumulation and reduced plasma TGs.Mice lacking Lpcat3 in the liver show reduced plasma TGs, hepatosteatosis, and secrete lipid-poor very low-density lipoprotein (VLDL) lacking arachidonoyl PLs.Mechanistic studies indicate that Lpcat3 activity impacts membrane lipid mobility in living cells, suggesting a biophysical basis for the requirement of arachidonoyl PLs in lipidating lipoprotein particles.

View Article: PubMed Central - PubMed

Affiliation: Department of Pathology and Laboratory Medicine, Howard Hughes Medical Institute, University of California, Los Angeles, Los Angeles, United States.

ABSTRACT
The role of specific phospholipids (PLs) in lipid transport has been difficult to assess due to an inability to selectively manipulate membrane composition in vivo. Here we show that the phospholipid remodeling enzyme lysophosphatidylcholine acyltransferase 3 (Lpcat3) is a critical determinant of triglyceride (TG) secretion due to its unique ability to catalyze the incorporation of arachidonate into membranes. Mice lacking Lpcat3 in the intestine fail to thrive during weaning and exhibit enterocyte lipid accumulation and reduced plasma TGs. Mice lacking Lpcat3 in the liver show reduced plasma TGs, hepatosteatosis, and secrete lipid-poor very low-density lipoprotein (VLDL) lacking arachidonoyl PLs. Mechanistic studies indicate that Lpcat3 activity impacts membrane lipid mobility in living cells, suggesting a biophysical basis for the requirement of arachidonoyl PLs in lipidating lipoprotein particles. These data identify Lpcat3 as a key factor in lipoprotein production and illustrate how manipulation of membrane composition can be used as a regulatory mechanism to control metabolic pathways.

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Loss of Lpcat3 from liver impairs hepatic TG secretion.(A) ApoB protein in livers from Lpcat3fl/fl (Flox/Flox) and Lpcat3fl/flAlbumin-Cre (L-Lpcat3 KO) mice fed on a chow diet was analyzed by western blot (n = 3). (B) VLDL-TG secretion in Lpcat3fl/fl mice transduced with adenoviral expressed Cre (Ad-Cre), compared to control GPF (Ad-GFP) for 4 weeks. Mice were fasted for 6 hr followed by intravenous injection of tyloxapol. Plasma TG was measured at indicated durations after tyloxapol injection. Values are means ± SEM. (C) Plasma VLDL particle size in Lpcat3fl/flAlbumin-Cre mice. Isolated VLDL particles from Lpcat3fl/fl (Fl/Fl) and Lpcat3fl/flAlbumin-Cre (L-Lpcat3 KO) mice fed on a western diet were stained with 2.0% uranyl acetate and visualized by electron microscopy (EM) (left) and their size quantified (right). Statistical analysis was performed using two-way ANOVA with Bonferroni post hoc tests (B). **p < 0.01.DOI:http://dx.doi.org/10.7554/eLife.06557.018
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fig8: Loss of Lpcat3 from liver impairs hepatic TG secretion.(A) ApoB protein in livers from Lpcat3fl/fl (Flox/Flox) and Lpcat3fl/flAlbumin-Cre (L-Lpcat3 KO) mice fed on a chow diet was analyzed by western blot (n = 3). (B) VLDL-TG secretion in Lpcat3fl/fl mice transduced with adenoviral expressed Cre (Ad-Cre), compared to control GPF (Ad-GFP) for 4 weeks. Mice were fasted for 6 hr followed by intravenous injection of tyloxapol. Plasma TG was measured at indicated durations after tyloxapol injection. Values are means ± SEM. (C) Plasma VLDL particle size in Lpcat3fl/flAlbumin-Cre mice. Isolated VLDL particles from Lpcat3fl/fl (Fl/Fl) and Lpcat3fl/flAlbumin-Cre (L-Lpcat3 KO) mice fed on a western diet were stained with 2.0% uranyl acetate and visualized by electron microscopy (EM) (left) and their size quantified (right). Statistical analysis was performed using two-way ANOVA with Bonferroni post hoc tests (B). **p < 0.01.DOI:http://dx.doi.org/10.7554/eLife.06557.018

Mentions: We next investigated the etiology of reduced VLDL TG levels in mice lacking Lpcat3. Protein levels of apoB in liver were not different between control and L-Lpcat3 KO mice (Figure 8A). Together with the preserved levels of apoB in plasma (Figures 2, 3), these data suggest that a defect in production or secretion of apoB alone cannot explain the change in plasma VLDL. We directly assessed hepatic TG secretion by treating mice with the lipase inhibitor Tyloxapol and measuring TG accumulation in fasted mice. L-Lpact3 KO mice showed a markedly reduced rate of TG secretion (Figure 8B), suggesting that reduced incorporation of TGs into lipoproteins was the likely cause of the reduced VLDL TG levels. Consistent with this hypothesis, negative staining of plasma VLDL fractions by EM revealed markedly smaller VLDL particles in L-Lpcat3 KO mice compared to controls (Figure 8C).10.7554/eLife.06557.018Figure 8.Loss of Lpcat3 from liver impairs hepatic TG secretion.


Lpcat3-dependent production of arachidonoyl phospholipids is a key determinant of triglyceride secretion.

Rong X, Wang B, Dunham MM, Hedde PN, Wong JS, Gratton E, Young SG, Ford DA, Tontonoz P - Elife (2015)

Loss of Lpcat3 from liver impairs hepatic TG secretion.(A) ApoB protein in livers from Lpcat3fl/fl (Flox/Flox) and Lpcat3fl/flAlbumin-Cre (L-Lpcat3 KO) mice fed on a chow diet was analyzed by western blot (n = 3). (B) VLDL-TG secretion in Lpcat3fl/fl mice transduced with adenoviral expressed Cre (Ad-Cre), compared to control GPF (Ad-GFP) for 4 weeks. Mice were fasted for 6 hr followed by intravenous injection of tyloxapol. Plasma TG was measured at indicated durations after tyloxapol injection. Values are means ± SEM. (C) Plasma VLDL particle size in Lpcat3fl/flAlbumin-Cre mice. Isolated VLDL particles from Lpcat3fl/fl (Fl/Fl) and Lpcat3fl/flAlbumin-Cre (L-Lpcat3 KO) mice fed on a western diet were stained with 2.0% uranyl acetate and visualized by electron microscopy (EM) (left) and their size quantified (right). Statistical analysis was performed using two-way ANOVA with Bonferroni post hoc tests (B). **p < 0.01.DOI:http://dx.doi.org/10.7554/eLife.06557.018
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fig8: Loss of Lpcat3 from liver impairs hepatic TG secretion.(A) ApoB protein in livers from Lpcat3fl/fl (Flox/Flox) and Lpcat3fl/flAlbumin-Cre (L-Lpcat3 KO) mice fed on a chow diet was analyzed by western blot (n = 3). (B) VLDL-TG secretion in Lpcat3fl/fl mice transduced with adenoviral expressed Cre (Ad-Cre), compared to control GPF (Ad-GFP) for 4 weeks. Mice were fasted for 6 hr followed by intravenous injection of tyloxapol. Plasma TG was measured at indicated durations after tyloxapol injection. Values are means ± SEM. (C) Plasma VLDL particle size in Lpcat3fl/flAlbumin-Cre mice. Isolated VLDL particles from Lpcat3fl/fl (Fl/Fl) and Lpcat3fl/flAlbumin-Cre (L-Lpcat3 KO) mice fed on a western diet were stained with 2.0% uranyl acetate and visualized by electron microscopy (EM) (left) and their size quantified (right). Statistical analysis was performed using two-way ANOVA with Bonferroni post hoc tests (B). **p < 0.01.DOI:http://dx.doi.org/10.7554/eLife.06557.018
Mentions: We next investigated the etiology of reduced VLDL TG levels in mice lacking Lpcat3. Protein levels of apoB in liver were not different between control and L-Lpcat3 KO mice (Figure 8A). Together with the preserved levels of apoB in plasma (Figures 2, 3), these data suggest that a defect in production or secretion of apoB alone cannot explain the change in plasma VLDL. We directly assessed hepatic TG secretion by treating mice with the lipase inhibitor Tyloxapol and measuring TG accumulation in fasted mice. L-Lpact3 KO mice showed a markedly reduced rate of TG secretion (Figure 8B), suggesting that reduced incorporation of TGs into lipoproteins was the likely cause of the reduced VLDL TG levels. Consistent with this hypothesis, negative staining of plasma VLDL fractions by EM revealed markedly smaller VLDL particles in L-Lpcat3 KO mice compared to controls (Figure 8C).10.7554/eLife.06557.018Figure 8.Loss of Lpcat3 from liver impairs hepatic TG secretion.

Bottom Line: Mice lacking Lpcat3 in the intestine fail to thrive during weaning and exhibit enterocyte lipid accumulation and reduced plasma TGs.Mice lacking Lpcat3 in the liver show reduced plasma TGs, hepatosteatosis, and secrete lipid-poor very low-density lipoprotein (VLDL) lacking arachidonoyl PLs.Mechanistic studies indicate that Lpcat3 activity impacts membrane lipid mobility in living cells, suggesting a biophysical basis for the requirement of arachidonoyl PLs in lipidating lipoprotein particles.

View Article: PubMed Central - PubMed

Affiliation: Department of Pathology and Laboratory Medicine, Howard Hughes Medical Institute, University of California, Los Angeles, Los Angeles, United States.

ABSTRACT
The role of specific phospholipids (PLs) in lipid transport has been difficult to assess due to an inability to selectively manipulate membrane composition in vivo. Here we show that the phospholipid remodeling enzyme lysophosphatidylcholine acyltransferase 3 (Lpcat3) is a critical determinant of triglyceride (TG) secretion due to its unique ability to catalyze the incorporation of arachidonate into membranes. Mice lacking Lpcat3 in the intestine fail to thrive during weaning and exhibit enterocyte lipid accumulation and reduced plasma TGs. Mice lacking Lpcat3 in the liver show reduced plasma TGs, hepatosteatosis, and secrete lipid-poor very low-density lipoprotein (VLDL) lacking arachidonoyl PLs. Mechanistic studies indicate that Lpcat3 activity impacts membrane lipid mobility in living cells, suggesting a biophysical basis for the requirement of arachidonoyl PLs in lipidating lipoprotein particles. These data identify Lpcat3 as a key factor in lipoprotein production and illustrate how manipulation of membrane composition can be used as a regulatory mechanism to control metabolic pathways.

Show MeSH
Related in: MedlinePlus