Constitutive Overexpression of Acyloxyacyl Hydrolase in Mus Musculus
Acyloxyacyl hydrolase (AOAH) is a highly conserved host lipase that selectively removes the secondary acyl chains from lipid A, the bioactive center of Gram negative bacterial lipopolysaccharide (LPS). Deacylated LPS has a marked reduction in bioactivity and antagonizes the LPS signaling pathway. Thus, AOAH deacylation of LPS may represent a mechanism by which animals control responses to Gram-negative bacteria. Prior to the experiments described in this study, mice deficient in AOAH were found to be susceptible to the long-term effects of LPS. Aoah-/- mice developed long-lasting hepatomegaly, exaggerated antibody responses, and prolonged immunosuppression in response to small doses of LPS. In the studies described here, AOAH was overexpressed in mice by using CD68 promoter sequences which have been shown by others to drive transgene expression in macrophages. CD68p-AOAH transgenic mice had constitutive overexpression of AOAH in macrophages, dendritic cells and tissues rich in these cells (liver, spleen and lung). They also secreted the enzyme into blood and deacylated LPS at a faster rate both in vitro and in vivo. Importantly, constitutive overexpression of AOAH did not interfere with the initial pro-inflammatory responses to LPS, in keeping with prior observations that AOAH-mediated inactivation of LPS occurs over several hours and does not moderate acute reactions to LPS in vivo. The protective role of constitutive AOAH overexpression was determined by two test systems. First, after an intraperitoneal dose of LPS, CD68p-AOAH transgenic mice returned to their pre-challenge weights more rapidly than did the wildtype mice. Secondly, CD68p-AOAH transgenic mice were less susceptible to LPS and Gram-negative bacteria induced hepatosplenomegaly. These results suggest that overexpression of AOAH in macrophages could accelerate recovery from Gram-negative bacterial infections in animals, including humans.