Branched fatty acid (FA) esters of hydroxy FAs (HFAs; FAHFAs) are recently discovered lipids that are conserved from yeast to mammals^1,2. A subfamily, palmitic acid esters of hydroxy stearic acids (PAHSAs), are anti-inflammatory and anti-diabetic^1,3. Humans and mice with insulin resistance have lower PAHSA levels in subcutaneous adipose tissue and serum¹. PAHSA administration improves glucose tolerance and insulin sensitivity and reduces inflammation in obesity, diabetes and immune-mediated diseases^1,4,5,6,7. The enzyme(s) responsible for FAHFA biosynthesis in vivo remains unknown. Here we identified adipose triglyceride lipase (ATGL, also known as patatin-like phospholipase domain containing 2 (PNPLA2)) as a candidate biosynthetic enzyme for FAHFAs using chemical biology and proteomics. We discovered that recombinant ATGL uses a transacylation reaction that esterifies an HFA with a FA from triglyceride (TG) or diglyceride to produce FAHFAs. Overexpression of wild-type, but not catalytically dead, ATGL increases FAHFA biosynthesis. Chemical inhibition of ATGL or genetic deletion of Atgl inhibits FAHFA biosynthesis and reduces the levels of FAHFA and FAHFA-TG. Levels of endogenous and nascent FAHFAs and FAHFA-TGs are 80–90 per cent lower in adipose tissue of mice in which Atgl is knocked out specifically in the adipose tissue. Increasing TG levels by upregulating diacylglycerol acyltransferase (DGAT) activity promotes FAHFA biosynthesis, and decreasing DGAT activity inhibits it, reinforcing TGs as FAHFA precursors. ATGL biosynthetic transacylase activity is present in human adipose tissue underscoring its potential clinical relevance. In summary, we discovered the first, to our knowledge, biosynthetic enzyme that catalyses the formation of the FAHFA ester bond in mammals. Whereas ATGL lipase activity is well known, our data establish a paradigm shift demonstrating that ATGL transacylase activity is biologically important.

羟基 FA 的支链脂肪酸 (FA) 酯（HFAs；FAHFAs）是最近发现的从酵母到哺乳动物都保守的脂质^1,2 。羟基硬脂酸棕榈酸酯 (PAHSA) 是一个亚家族，具有抗炎和抗糖尿病作用^1,3 。患有胰岛素抵抗的人和小鼠的皮下脂肪组织和血清中 PAHSA 水平较低¹ 。 PAHSA 给药可改善葡萄糖耐量和胰岛素敏感性，并减少肥胖、糖尿病和免疫介导疾病的炎症^1,4,5,6,7 。体内负责 FAHFA 生物合成的酶仍然未知。在这里，我们利用化学生物学和蛋白质组学鉴定了脂肪甘油三酯脂肪酶（ATGL，也称为含马铃薯蛋白样磷脂酶结构域 2 (PNPLA2)）作为 FAHFA 的候选生物合成酶。我们发现重组 ATGL 使用转酰基反应，将 HFA 与甘油三酯 (TG) 或甘油二酯中的 FA 酯化，产生 FAHFA。 ATGL 野生型（但未催化死亡）的过度表达会增加 FAFFA 的生物合成。 ATGL 的化学抑制或Atgl的基因缺失会抑制 FAHFA 生物合成并降低 FAHFA 和 FAHFA-TG 的水平。 Atgl在脂肪组织中被特异性敲除的小鼠脂肪组织中，内源性和新生 FAHFA 和 FAHFA-TG 的水平降低了 80-90%。通过上调二酰基甘油酰基转移酶 (DGAT) 活性来提高 TG 水平可促进 FAHFA 生物合成，而降低 DGAT 活性则可抑制其生物合成，从而增强 TG 作为 FAHFA 前体的作用。 ATGL 生物合成转酰基酶活性存在于人类脂肪组织中，强调了其潜在的临床相关性。 总之，据我们所知，我们发现了第一个催化哺乳动物中 FAHFA 酯键形成的生物合成酶。尽管 ATGL 脂肪酶活性众所周知，但我们的数据建立了范式转变，证明 ATGL 转酰基酶活性具有重要的生物学意义。