FLT4/VEGFR3 activates AMPK to coordinate glycometabolic reprogramming with autophagy and inflammasome activation for bacterial elimination

Macrophages rapidly undergo glycolytic reprogramming in response to macroautophagy/autophagy, inflammasome activation and pyroptosis for the clearance of bacteria. Identification the key molecules involved in these three events will provide critical potential therapeutic applications. Upon <i>S. typhimurium</i> infection, FLT4/VEGFR3 and its ligand VEGFC were inducibly expressed in macrophages, and FLT4 signaling inhibited CASP1 (caspase 1)-dependent inflammasome activation and pyroptosis but enhanced MAP1LC3/LC3 activation for elimination of the bacteria. Consistently, FLT4 mutants lacking the extracellular ligand-binding domain increased production of the proinflammatory metabolites such as succinate and lactate, and reduced antimicrobial metabolites including citrate and NAD(P)H in macrophages and liver upon infection. Mechanistically, FLT4 recruited AMP-activated protein kinase (AMPK) and phosphorylated Y247 and Y441/442 in the PRKAA/alpha subunit for AMPK activation. The AMPK agonist AICAR could rescue glycolytic reprogramming and inflammasome activation in macrophages expressing the mutant FLT4, which has potential translational application in patients carrying <i>Flt4</i> mutations to prevent recurrent infections. Collectively, we have elucidated that the FLT4-AMPK module in macrophages coordinates glycolytic reprogramming, autophagy, inflammasome activation and pyroptosis to eliminate invading bacteria.

巨噬细胞在响应巨自噬/自噬（macroautophagy/autophagy）、炎性小体激活与细胞焦亡以清除细菌时，会快速发生糖酵解重编程。鉴定参与上述三大事件的关键分子，将为相关治疗应用提供重要潜力。在<i>S. typhimurium</i>感染后，FMS样酪氨酸激酶4/血管内皮生长因子受体3（FLT4/VEGFR3）及其配体血管内皮生长因子C（VEGFC）可在巨噬细胞中被诱导表达，且FLT4信号通路可抑制半胱氨酸天冬氨酸蛋白酶1（CASP1/caspase 1）依赖的炎性小体激活与细胞焦亡，但增强微管相关蛋白1轻链3（MAP1LC3/LC3）的激活以清除细菌。与之相符的是，缺失细胞外配体结合结构域的FLT4突变体，可在感染后增加巨噬细胞与肝脏中琥珀酸、乳酸等促炎代谢产物的生成，并减少柠檬酸、烟酰胺腺嘌呤二核苷酸（磷酸，NAD(P)H）等抗菌代谢产物的水平。从机制上讲，FLT4可招募AMP激活的蛋白激酶（AMPK），并对PRKAA/α亚基（PRKAA/alpha subunit）中的Y247以及Y441/442位点进行磷酸化以激活AMPK。AMPK激动剂氨基咪唑甲酰胺核苷（AICAR）可挽救表达突变型FLT4的巨噬细胞的糖酵解重编程与炎性小体激活，这为携带<i>Flt4</i>基因突变的患者预防复发性感染提供了潜在的转化应用价值。综上，本研究阐明了巨噬细胞中的FLT4-AMPK信号模块可协调糖酵解重编程、自噬、炎性小体激活与细胞焦亡过程，以清除入侵的细菌。