Acyloxyacyl hydrolase, also known as AOAH, is a eukaryotic protein encoded by the AOAHgene.[5]
AOAH is produced by macrophages (including Kupffer cells and microglia), dendritic cells (especially in the colon), NK cells, ILC1 cells, neutrophils and renal proximal tubule cells.[6]
The AOAH gene has been found in many invertebrates and in all vertebrates studied to date except fish. Although mice have other well-established mechanisms for preventing LPS signaling, none of these has prevented long-term persistence of stimulatory LPS in animals that lack AOAH.[7][8]
The enzyme's 2 disulfide-linked subunits are encoded by a single mRNA. The smaller subunit is a member of the saposin-like (SAPLIP) protein family and the larger subunit, which contains the active site serine, is a GDSL lipase. The enzyme's 3D structure and catalytic mechanism were reported by Gorelik et al.[9]
Acyloxyacyl hydrolase (AOAH) is a lipase that selectively releases the secondary (acyloxyacyl-linked) fatty acyl chains from the hexaacyl lipid A moiety found in many bacterial lipopolysaccharides (LPSs, also called endotoxins).[5][6] The resulting tetraacyl LPS is non-stimulatory and can be a potent inhibitor of LPS sensing via the MD-2--Toll-like Receptor 4 (TLR4). The enzyme's other known substrates include bacterial lipopeptides and several host glycerolipids, including lyso-and oxidized phospholipids.[6][10]
Absence of the enzyme in genetically engineered mice has been associated with distinctive phenotypes. AOAH-deficient animals are unable to inactivate even small amounts of LPS in most tissues; the LPS remains bioactive and may pass from cell to cell in vivo for many weeks. The LPS-injected mice develop strikingly high titers of polyclonal antibodies, prolonged hepatomegaly, and innate immune "tolerance" that results in slow and inadequate responses to a bacterial challenge. Absence of the enzyme renders mice more likely to develop severe lung injury and die if they are challenged with intratracheal LPS, Gram-negative bacteria, or acid (AOAH may also inactivate oxidized phospholipids).[10][11] Other studies have found that AOAH reduces the stimulatory potency of LPS that translocates from the gastrointestinal tract to the liver and other organs.[12] AOAH may also prevent LPS-induced arterial foam cell formation in vivo.[13]
^Gorelik A, Illes K, Nagar B (January 2018). "Crystal structure of the mammalian lipopolysaccharide detoxifier". Proceedings of the National Academy of Sciences of the United States of America. 115 (5): E896 –E905. Bibcode:2018PNAS..115E.896G. doi:10.1073/pnas.1719834115. PMC5798384. PMID29343645.E896 -E905&rft.date=2018-01&rft_id=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5798384#id-name=PMC&rft_id=info:pmid/29343645&rft_id=info:doi/10.1073/pnas.1719834115&rft_id=info:bibcode/2018PNAS..115E.896G&rft.aulast=Gorelik&rft.aufirst=A&rft.au=Illes, K&rft.au=Nagar, B&rft_id=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5798384&rfr_id=info:sid/en.wikipedia.org:AOAH" class="Z3988">
