The Mechanism Of The Regulation Of APAP-induced Liver Injury By ULK1/2

The Ser/Thr kinases ULK1 and ULK2 regulate autophagy initiation under various stress conditions.However,the physiological functions of these kinases are not well-characterized.In this thesis,we show that mice with liver-specific double knockout of Ulkl and Ulk2(Ulkl/2 LDKO)are viable but exhibit overt hepatomegaly phenotype.Surprisingly,Ulkl/2 LDKO mice display normal autophagic activity in hepatic cells upon overnight fasting but are strongly resistant to acetaminophen(APAP)-induced liver injury.Further studies revealed that Ulkl/2 are also dispensable for APAP-induced autophagy but are essential for the maximum activation of JNK signaling both in vivo and in isolated primary hepatic cells during APAP treatment.Mechanistically,APAP-mediated mTORC1 inhibition releases ULK1 from an inactive state.The activated ULK1 then directly phosphorylates and increases the kinase activity of MKK7,the upstream kinase and activator of JNK,and mediates APAP-induced liver injury.ULK1-dependent phosphorylation of MKK7 was further confirmed by a phosphorylation site-specific antibody.Moreover,the activation of JNK and APAP-inducted cell death were markedly attenuated in MKK4/7 double knockdown hepatocytes reconstituted with an ULK1-unphosphorylatable mutant of MKK7 compared with those expressing wild-type MKK7.Together,these findings reveal an important role of ULK1/2 for APAP-mediated JNK activation and liver injury,and understanding of this regulatory mechanism may offer us new strategies for prevention and treatment of human APAP hepatotoxicity.