AIG1 and ADTRP are endogenous hydrolases of fatty acid esters of hydroxy fatty acids (FAHFAs) in mice

Abstract

Keywords: fatty acid ester of hydroxy fatty acid (FAHFA), threonine hydrolase, metabolism, androgeninduced gene 1(AIG1), androgen-dependent TFPI-regulating protein (ADTRP), lipid ester, enzyme inhibitor, diabetes, lipid signaling, glucose metabolism. AbstractFatty acid esters of hydroxy fatty acids (FAHFAs) are a newly discovered class of signaling lipids with anti-inflammatory and antidiabetic properties. However, the endogenous regulation of FAHFAs remains a pressing but unanswered question. Here, using MS-based FAHFA hydrolysis assays, LC-MS-based lipidomics analyses, and activity-based protein profiling, we found that androgen-induced gene 1 (AIG1) and androgen-dependent TFPI-regulating protein (ADTRP), two threonine hydrolases, control FAHFA levels in vivo in both genetic and pharmacologic mouse models. Tissues from mice lacking ADTRP (Adtrp-KO), or both AIG1 and ADTRP (DKO) had higher concentrations of FAHFAs particularly isomers with the ester bond at the 9 th carbon due to decreased FAHFA hydrolysis activity. The levels of other lipids were unaltered indicating that AIG1 and ADTRP specifically hydrolyze FAHFAs. Complementing these genetic studies, we also identified a dual AIG1/ADTRP inhibitor, ABD-110207, that is active in vivo. Acute treatment of wild-type mice with ABD-110207 resulted in elevated FAHFA levels, further supporting the notion that AIG1 and ADTRP activity control endogenous FAHFA levels. However, loss of AIG1/ADTRP did not mimic the changes associated with pharmacologically administered FAHFAs on circulating and tissue FAHFA levels, glucose tolerance or insulin sensitivity in mice, indicating that therapeutic strategies should continue to focus on FAHFA administration. Together, these findings identify AIG1 and ADTRP as the first endogenous FAHFA hydrolases identified and provide critical genetic and chemical tools for further characterization of these enzymes and endogenous FAHFAs to unravel their physiological functions and roles in health and disease.https://www.jbc.org/cgi/

Insights into the Functional Role of ADTRP (Androgen-Dependent TFPI-Regulating Protein) in Health and Disease

“…The mRNA expression of Adtrp increased significantly (3–4 times) during embryogenesis [ 39 ]. Another group also reported localization of mouse ADTRP in the liver, adipose tissue, kidney, and duodenum [ 40 ].…”

“…Neo-/perinatal mortality of ~35% in Adtrp −/− mice correlated with the degree of phenotype severity. In independently generated Adtrp mutant mice, another group [ 40 ] found that mice lacking ADTRP developed normally with the expected Mendelian ratio. The discrepancy between our mice and theirs can be attributed to different strategies applied to generate ADTRP-deficient mice.…”

“…The discrepancy between our mice and theirs can be attributed to different strategies applied to generate ADTRP-deficient mice. Whereas we specifically deleted ~37 kb of the Adtrp gene between exons 2 and 6, Erikci Ertunc and colleagues [ 40 ] targeted only exon 2 using CRISPR/Cas9 technology, which resulted in the removal of 13-bases from the Adtrp gene locus. Further studies are warranted to understand the differences in these two mouse strains.…”

“…In a recent study, Erikci Ertunc and colleagues used a combination of genetic loss-of-function and chemical approaches to demonstrate that ADTRP and AIG1 are major contributors to endogenous FAHFA hydrolysis [ 40 ]. They used global Aig1 , Adtrp , and double knockout (DKO) mice and a small molecule inhibitor (ABD-110207) of ADTRP and AIG1 to show that both proteins are responsible for regulating FAHFA hydrolysis primarily in the adipose tissue.…”

“…Interestingly, tissues from DKO mice showed decreased hydrolytic activity towards 9-PAHSA added exogenously but no change in the overall endogenous FAHFA levels. In parallel, a significant residual 9-PAHSA hydrolytic activity was observed in the liver and kidney of DKO mice [ 40 ]. Together, these data indicate that other endogenous enzymes, such as carboxyl ester lipase [ 67 ] can compensate for loss of ADTRP and/or AIG1 to hydrolyze FAHFAs in vivo.…”