Fatty acids are vital for the survival of eukaryotes, but when present in excess can have deleterious consequences. The AMP-activated protein kinase (AMPK) is an important regulator of multiple branches of metabolism. Studies in purified enzyme preparations and cultured cells have shown that AMPK is allosterically activated by small molecules as well as fatty acyl-CoAs through a mechanism involving Ser108 within the regulatory AMPK β1 isoform. However, the in vivo physiological significance of this residue has not been evaluated. In the current study, we generated mice with a targeted germline knock-in (KI) mutation of AMPKβ1 Ser108 to Ala (S108A-KI), which renders the site phospho-deficient. S108A-KI mice had reduced AMPK activity (50 to 75%) in the liver but not in the skeletal muscle. On a chow diet, S108A-KI mice had impairments in exogenous lipid-induced fatty acid oxidation. Studies in mice fed a high-fat diet found that S108A-KI mice had a tendency for greater glucose intolerance and elevated liver triglycerides. Consistent with increased liver triglycerides, livers of S108A-KI mice had reductions in mitochondrial content and respiration that were accompanied by enlarged mitochondria, suggestive of impairments in mitophagy. Subsequent studies in primary hepatocytes found that S108A-KI mice had reductions in palmitate- stimulated Cpt1a and Ppargc1a mRNA, ULK1 phosphorylation and autophagic/mitophagic flux. These data demonstrate an important physiological role of AMPKβ1 Ser108 phosphorylation in promoting fatty acid oxidation, mitochondrial biogenesis and autophagy under conditions of high lipid availability. As both ketogenic diets and intermittent fasting increase circulating free fatty acid levels, AMPK activity, mitochondrial biogenesis, and mitophagy, these data suggest a potential unifying mechanism which may be important in mediating these effects.

中文翻译：

---

AMPKβ1 的磷酸化对于增加自噬和维持线粒体对脂肪酸的稳态至关重要

脂肪酸对真核生物的生存至关重要，但如果脂肪酸含量过高，则会产生有害后果。AMP 活化蛋白激酶 (AMPK) 是多个代谢分支的重要调节因子。对纯化的酶制剂和培养细胞的研究表明，AMPK 被小分子以及脂肪酰基辅酶 A 通过涉及调节 AMPK β1 同工型内的 Ser108 的机制变构激活。然而，尚未评估该残留物的体内生理意义。在当前的研究中，我们生成了具有 AMPKβ1 Ser108 到 Ala (S108A-KI) 的靶向种系敲入 (KI) 突变的小鼠，这会导致该位点磷酸化缺陷。S108A-KI 小鼠肝脏中的 AMPK 活性降低（50% 至 75%），但骨骼肌中的 AMPK 活性没有降低。在松狮饮食中，S108A-KI 小鼠在外源性脂质诱导的脂肪酸氧化中存在损伤。对喂食高脂肪饮食的小鼠进行的研究发现，S108A-KI 小鼠有更严重的葡萄糖不耐受和肝甘油三酯升高的倾向。与肝脏甘油三酯增加一致，S108A-KI 小鼠的肝脏线粒体含量和呼吸减少，并伴有线粒体增大，表明线粒体自噬受损。随后对原代肝细胞的研究发现，S108A-KI 小鼠的棕榈酸酯刺激的 Cpt1a 和 Ppargc1a mRNA、ULK1 磷酸化和自噬/线粒体吞噬通量减少。这些数据证明了 AMPKβ1 Ser108 磷酸化在高脂质可用性条件下促进脂肪酸氧化、线粒体生物合成和自噬的重要生理作用。