ABCA1 Promotes the de Novo Biogenesis of Apolipoprotein CIII-Containing HDL Particles in Vivo and Modulates the Severity of Apolipoprotein CIII-Induced Hypertriglyceridemia

Abstract

In this study, the ability of the lipid transporter ABCA1 and apolipoprotein CIII (apoCIII) to promote the de novo biogenesis of apoCIII-containing HDL in vivo and the role of this HDL in apoCIII-induced hypertriglyceridemia were investigated, using adenovirus-mediated gene transfer in apoE (-/-) x apoA-I (-/-) mice or ABCA1 (-/-) mice. Injection of apoE (-/-) x apoA-I (-/-) mice with 8 x 10 (8) pfu of an adenovirus expressing the wild-type human apoCIII (AdGFP-CIII g) generated HDL-like particles and triggered only a modest increase in plasma cholesterol and triglyceride levels of these mice, 3-5 days postinfection. Plasma human apoCIII was distributed among HDL, VLDL/IDL, and LDL in these mice. In contrast, ABCA1 (-/-) mice treated similarly failed to form HDL particles and developed severe hypertriglyceridemia which could be alleviated by coinfection with an adenovirus expressing human LpL, while their plasma cholesterol levels remained unchanged 3-5 days postinfection with AdGFP-CIII g. Human apoCIII in these mice accumulated exclusively on VLDL. Control experiments confirmed that the differences between apoE (-/-) x apoA-I (-/-) and ABCA1 (-/-) mice expressing human apoCIII were not due to differences in apoCIII expression. Overall, these data show that ABCA1 and human apoCIII promote the formation of apoCIII-containing HDL-like particles that are distinct from classical apoE- or apoA-I-containing HDL. Formation of apoCIII-containing HDL prevents excess accumulation of plasma apoCIII on VLDL and allows for the efficient lipolysis of VLDL triglycerides by LpL. Furthermore, the data establish that ABCA1 and apoCIII-containing HDL play key roles in the prevention of apoCIII-induced hypertriglyceridemia in mice.

Targeted Deletion of Hepatocyte ABCA1 Leads to Very Low Density Lipoprotein Triglyceride Overproduction and Low Density Lipoprotein Hypercatabolism

“…For example, Wang et al (10) showed that VLDL from TD subjects was enriched with apoA-II and apoC-III, compared with VLDL from normolipidemic subjects, resulting in a reduced lipase accessibility. Consistent with this notion, Kyreos et al (41) recently showed that adenoviral overexpression of human apoC-III in apoE KO and ABCA1 KO mice induces hypertriglyceridemia due to low LPL reactivity of apoC-III-enriched VLDL. In addition to possible effects on VLDL substrate, our mouse model also showed that both HL and LPL were markedly reduced upon deletion of hepatic ABCA1 (Fig.…”

Apolipoprotein A-I Modulates Processes Associated with Diet-Induced Nonalcoholic Fatty Liver Disease in Mice

“…The mutagenic primers used were: 5′-TTGGC CGCGC GCCTT GAG-3′ (forward) and 5′-CTGGC GCAGC TCGTC GCT-3′ (reverse) with the pCA13-AIgN vector (23), which contains the genomic human apoA-I sequence, as template. The recombinant adenoviruses were constructed as described previously (24). The titer of the virus preparation was 2 × 10 10 pfu/mL.…”

“…Western blot analysis for apoA-I was performed as described previously (24), using a goat anti-human apoA-I antibody (cat# K45252G; Biodesign International, Saco, ME, USA) as primary, and a rabbit anti-goat antibody (cat # sc-2768; Santa-Cruz Biotechnology, Sant Cruz, CA, USA) as secondary. For analysis of culture medium, 100 μL of medium was extensively dialyzed in H 2 0 and then lyophilized.…”

“…Plasma cholesterol, triglyceride and free fatty acid levels were measured as described previously (24).…”

Quantitative analysis of intact apolipoproteins in human HDL by top-down differential mass spectrometry

“…Apolipoprotein C-III is mainly involved in modulating plasma triglyceride levels by the catabolism of triglyceride-rich particles, but plasma apolipoprotein C-III levels have been suggested to be linked to other conditions associated with metabolic syndrome (29). Apolipoprotein C-III-containing HDL may play a key role in the prevention of apolipoprotein C-III-induced hypertriglyceridemia (30). Recently, SELDI-TOF (surface-enhanced laser desorption ionization time of flight) analysis suggests a link between an ion species at m∕z 8,697 of apolipoprotein C-III and papillary thyroid carcinoma (31).…”