Lack of LCAT reduces the LPS-neutralizing capacity of HDL and enhances LPS-induced inflammation in mice

Abstract HDL has important immunomodulatory properties, including the attenuation of lipopolysaccharide (LPS)-induced inflammatory response. As lecithin–cholesterol acyltransferase (LCAT) is a critical enzyme in the maturation of HDL we investigated whether LCAT-deficient ( Lcat −/− ) mice present an increased LPS-induced inflammatory response. LPS (100 μg/kg body weight)-induced cytokine response in Lcat −/− mice was markedly enhanced and prolonged compared to wild-type mice. Importantly, reintroducing LCAT expression using adenovirus-mediated gene transfer reverted their phenotype to that of wild-type mice. Ex vivo stimulation of whole blood with LPS (1–100 ng/mL) showed a similar enhanced pro-inflammatory phenotype. Further characterization in RAW 264.7 macrophages in vitro showed that serum and HDL, but not chylomicrons, VLDL or the lipid-free protein fraction of Lcat −/− mice, had a reduced capacity to attenuate the LPS-induced TNFα response. Analysis of apolipoprotein composition revealed that LCAT-deficient HDL lacks significant amounts of ApoA-I and ApoA-II and is primarily composed of ApoE, while HDL from Apoa1 −/− mice is highly enriched in ApoE and ApoA-II. ApoA-I-deficiency did not affect the capacity of HDL to neutralize LPS, though Apoa1 −/− mice showed a pronounced LPS-induced cytokine response. Additional immunophenotyping showed that Lcat −/− , but not Apoa1 −/− mice, have markedly increased circulating monocyte numbers as a result of increased Cd11b + Ly6C med monocytes, whereas ‘pro-inflammatory’ Cd11b + Ly6C hi monocytes were reduced. In line with this observation, peritoneal macrophages of Lcat −/− mice showed a markedly dampened LPS-induced TNFα response. We conclude that LCAT-deficiency increases LPS-induced inflammation in mice due to reduced LPS-neutralizing capacity of immature discoidal HDL and increased monocyte number.