A Western-Fed Diet Increases Plasma HDL and LDL-Cholesterol Levels in ApoD–/– Mice

Objective Plasma apolipoprotein (apo)D, a ubiquitously expressed protein that binds small hydrophobic ligands, is found mainly on HDL particles. According to studies of human genetics and lipid disorders, plasma apoD levels positively correlate with HDL-cholesterol and apoAI levels. Thus, we tested the hypothesis that apoD was a regulator of HDL metabolism. Methods & Results We compared the plasma lipid and lipoprotein profiles of wild-type (WT) C57BL/6 mice with apoD−/− mice on a C57BL/6 background after receiving a high fat-high cholesterol diet for 12 weeks. ApoD−/− mice had higher HDL-cholesterol levels (61±13-apoD−/− vs. 52±10-WT-males; 37±11-apoD−/− vs. 22±2 WT-female) than WT mice with sex-specific changes in total plasma levels of cholesterol and other lipids. Compared to WT, the HDL of apoD−/− mice showed an increase in large, lipid-rich HDL particles and according to size various quantities and sizes of LDL particles. Plasma levels of lecithin:cholesterol acyltransferase in the control and apoD−/− mice were not different, however, plasma phospholipid transfer protein activity was modestly elevated (+10%) only in male apoD−/− mice. An in vivo HDL metabolism experiment with isolated Western-fed apoD−/− HDL particles showed that female apoD−/− mice had a 36% decrease in the fractional catabolic rate of HDL cholesteryl ester. Hepatic SR-BI and LDLR protein levels were significantly decreased; accordingly, LDL-cholesterol and apoB levels were increased in female mice. Conclusion In the context of a high fat-high cholesterol diet, apoD deficiency in female mice is associated with increases in both plasma HDL and LDL-cholesterol levels, reflecting changes in expression of SR-BI and LDL receptors, which may impact diet-induced atherosclerosis

Decrease in the relative protein expression of SRBI and LDLR in female apoD−/− mice but opposite pattern for mRNA expression.

<p>Liver levels of A) Cholesterol and B) Triglyceride C) Relative expression of genes and D) Protein expression levels of LDLR and SRBI after 12 weeks on a Western diet. n = 5–7 per group, mean±SD, *p<0.05, **p<0.01.</p

ApoE-HDL enrichment and lipids content changes in HDL particles.

<p>Size exclusion chromatography lipid profiles (total cholesterol, free cholesterol, phospholipids) of pooled plasma from A) female and B) male WT and apoD−/− mice after 12 weeks on a Western diet.</p

Up-regulation of plasma apoD levels in Western-fed WT mice.

<p>Western blot and semi-quantitative analyses of apoD levels in WT mice fed a 12-week chow and Western diets. Data is representative of both sexes, n = 4–5 per group, mean±SD, *p<0.05.</p

Lipoprotein particle size and concentrations (nmol/L) analyzed by IM methodology from pooled plasma of WT and apoD−/− mice fed a Western diet for 12 weeks.

<p>Lipoprotein particle size and concentrations (nmol/L) analyzed by IM methodology from pooled plasma of WT and apoD−/− mice fed a Western diet for 12 weeks.</p

Increased PLTP activity.

<p>A) Plasma LCAT and B) PLTP activities from female and male WT and apoD−/− mice on a Western diet for 12 weeks. n = 7–14, values are mean±SD, *p<0.05.</p

No change in plasma apoAI, but changes in apolipoproteins content in HDL-size exclusion chromatography fractions.

<p>A) Western blot analysis of apoAI levels from the SEC-HDL fractions. B) Semi-quantitative analysis of plasma apoAI levels. C) SimpleStain and Western blotting for apolipoprotein levels of pooled SEC-HDL fractions (10–20 µg).</p