Nrf2-Mediated Antioxidant Defense and Peroxiredoxin 6 Are Linked to Biosynthesis of Palmitic Acid Ester of 9-Hydroxystearic Acid

Abstract

Fatty acid esters of hydroxy fatty acids (FAHFAs) are lipid mediators with promising antidiabetic and anti-inflammatory properties that are formed in white adipose tissue (WAT) via de novo lipogenesis, but their biosynthetic enzymes are unknown. Using a combination of lipidomics in WAT, quantitative trait locus mapping, and correlation analyses in rat BXH/HXB recombinant inbred strains, as well as response to oxidative stress in murine models, we elucidated the potential pathway of biosynthesis of several FAHFAs. Comprehensive analysis of WAT samples identified ∼160 regioisomers, documenting the complexity of this lipid class. The linkage analysis highlighted several members of the nuclear factor, erythroid 2 like 2 ()-mediated antioxidant defense system (), lipid-handling proteins (), and the family of flavin containing monooxygenases () as the positional candidate genes. Transgenic expression of and deletion of genes resulted in reduction of palmitic acid ester of 9-hydroxystearic acid (9-PAHSA) and 11-PAHSA levels, while oxidative stress induced by an inhibitor of glutathione synthesis increased PAHSA levels nonspecifically. Our results indicate that the synthesis of FAHFAs via carbohydrate-responsive element-binding protein-driven de novo lipogenesis depends on the adaptive antioxidant system and suggest that FAHFAs may link activity of this system with insulin sensitivity in peripheral tissues.

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

“…FAHFAs are emerging bioactive lipids that have anti-inflammatory and glucoregulatory properties, but, as newly discovered lipids, little is known about how their levels in tissues are controlled (1,31). Using ABPP, we previously identified AIG1 and ADTRP as hydrolytic enzymes; in vitro assays revealed that AIG1 and ADTRP hydrolyzed FAHFAs in vitro (13).…”

Triacylglycerol‐Rich Oils of Marine Origin are Optimal Nutrients for Induction of Polyunsaturated Docosahexaenoic Acid Ester of Hydroxy Linoleic Acid (13‐DHAHLA) with Anti‐Inflammatory Properties in Mice

“…So far, the most complex FAHFA‐ome has been found in subcutaneous WAT of mice where multiple positional isomers were detected. [ 1,39 ] The experiment with omega‐3 PUFAs gavage highlighted the difference between systemic and eWAT FAHFAs levels. Although no other organs are available from that experiment, we could speculate that FAHFAs built on 9‐ and 13‐HLA backbone are synthesized outside of WAT.…”

“…Although no other organs are available from that experiment, we could speculate that FAHFAs built on 9‐ and 13‐HLA backbone are synthesized outside of WAT. A set of largely unknown enzymes in WAT is needed to synthesize acyl chains hydroxylated at specific positions, [ 39 ] but 9‐ or 13‐HLA could be synthesized either enzymatically (by 15‐lipoxygenase in immune cells, kidney, small intestine etc.) or non‐enzymatically nearly anywhere.…”

Methodological Issues in Studying PAHSA Biology: Masking PAHSA Effects

“…The LC-MS protocol used by Pflimlin et al to measure PAHSA levels did not recapitulate any of the protocols published by three independent groups (Brezinova et al, 2018; Kolar et al, 2018; Kuda et al, 2018; Ma et al, 2015; Syed et al, 2018; Zhang et al, 2016; Yore et al, 2014) (Table S2) or more recently by an additional group (Zhu et al, 2018). Furthermore, no information is provided comparing their protocol to any of the reported procedures to validate their results.…”

“…An in silico analysis predicted that >1,000 FAHFAs could exist in nature (Ma et al, 2015), and >20 FAHFA families have been identified in mammalian tissues (Kuda et al, 2016, 2018; Ma et al, 2015; Yore et al, 2014), with many additional families in plants (Zhu et al, 2018). These families differ by their acyl-chain composition and consist of multiple isomers distinguished by the position of the ester bond between acyl chains.…”