Functional LCAT is not required for macrophage cholesterol efflux to human serum

ObjectivesTo evaluate the capacity of serum from carriers of LCAT gene mutations to promote cell cholesterol efflux through the ABCA1, ABCG1, and SR-BI pathways.MethodsSerum was obtained from 41 carriers of mutant LCAT alleles (14 carriers of two mutant LCAT alleles and 27 heterozygotes) and 10 non-carrier relatives (controls). The capacity of serum to promote cholesterol efflux was tested in pathway-specific cell models.ResultsLCAT deficient sera were significantly more efficient than control sera in promoting cell cholesterol efflux via ABCA1 (3.1 ± 0.3% for carriers of two mutant LCAT alleles and 2.6 ± 0.2% for heterozygotes vs. 1.5 ± 0.4% for controls), and less efficient in promoting ABCG1- and SR-BI-mediated cholesterol efflux. The enhanced capacity of LCAT deficient serum for ABCA1 efflux is explained by the increased content of preβ-HDL, as indicated by the significant positive correlation between ABCA1 efflux and serum preβ-HDL content (R = 0.468, P < 0.001). Moreover, chymase treatment of LCAT deficient serum selectively degraded preβ-HDL and completely abolished ABCA1 efflux. Despite the remarkable reductions in serum HDL levels, LCAT deficient sera were as effective as control sera in removing mass cholesterol from cholesterol-loaded macrophages.ConclusionsSerum from carriers of LCAT gene mutations has the same capacity of control serum to decrease the cholesterol content of cholesterol-loaded macrophages due to a greater cholesterol efflux capacity via ABCA1.