Endotoxin Detoxification

National Institute Of Allergy And Infectious Diseases

Investigators

Linked publications & trials

Abstract

During the 12 years of its existence, the AHDL has worked to solidify and extend our observations that uncovered a previously unappreciated aspect of innate immunity: the requirement that a potent microbial stimulus, lipopolysaccharide (LPS), be inactivated by a host enzyme before homeostasis can be restored following Gram-negative bacterial diseases. We discovered the enzyme, acyloxyacyl hydrolase (AOAH), purified the low-abundance protein to homogeneity, cloned its cDNA, made knockout and transgenic mice, and studied the enzymes properties for almost 30 years before moving to the NIAID in 2009. We showed, with confirmation by others, that AOAH is required for mice to recover from parenteral exposure to LPS; none of the many better-known LPS inhibitors (immunoglobulins, BPI, lipoproteins, etc.) can compensate for the absence of AOAH in Aoah-/- mice. At NIH we showed that AOAH effectively inactivates LPS before it can enter the bloodstream from a subcutaneous tissue inoculation site and that bioactive LPS can persist for many weeks in the peritoneal cavity of an AOAH-/- mouse. Since staff scientist Mingfang Lu returned to China in 2014 we have collaborated with her and shown that AOAH can also inactivate oxidized phospholipids (published in 2021), prevent atherosclerosis in LPS-challenged mice (published in 2020), and influence pulmonary allergy by inactivating intestinal LPS (published by Lu lab in 2018). Encouraged by leadership to study a topic more closely related to the LCIMs interests, we embarked on a study of the pathogenesis of lipid-laden macrophages in CGD. We found that LPS induces fat retention to the same extent in both normal and CGD mouse macrophages and characterized the enzymology involved; in a follow-up study we made the surprising finding that the major determinant of triglyceride retention was the pH of the medium, not LPS or even the oxygen concentration. This prompted us to investigate the impact of low extracellular pH (pHe) on macrophage longevity, realizing that tissue macrophages often encounter an acidic environment and manage to survive and recover. This investigation led us to study mitochondrial fission, oxidative phosphorylation, the utilization of lactate and glutamine, and conversion to a M2 phenotype; the experiments have been finished and a manuscript is nearing submission. This work was done largely at NIH with the help of a student from the Lu-Fudan lab who visited NIH for 3 months in 2018-2019. The absence of a metabolomics resource slowed our progress. Our results were published in 2021.