Activation of the AMPK-ULK1 pathway plays an important role in autophagy during prion infection.

Xue-Yu Fan,Xiao-Ping Dong,Ge Meng,Hui Wang,Qi-Xiang Shao,Chen Gao,Bao-Yun Zhang,Yin Xu,Ke Ren,Yang-Jing Zhao,Qi Shi,Lu-Bin Zhang,Chan Tian

doi:10.1038/srep14728

Abstract

AMPK is a serine/threonine protein kinase that acts as a positive regulator of autophagy, by phosphorylating ULK1 at specific sites. A previous study demonstrated activation of the macroautophagic system in scrapie-infected experimental rodents and in certain human prion diseases, in which the essential negative regulator mTOR is severely inhibited. In this study, AMPK and ULK1 in the brains of hamsters infected with scrapie strain 263 K and in the scrapie-infected cell line SMB-S15 were analysed. The results showed an up-regulated trend of AMPK and AMPK-Thr172, ULK1 and ULK1-Ser555. Increases in brain AMPK and ULK1 occurred at an early stage of agent 263 K infection. The level of phosphorylated ULK1-Ser757 decreased during mid-infection and was only negligibly present at the terminal stage, a pattern that suggested a close relationship of the phosphorylated protein with altered endogenous mTOR. In addition, the level of LKB1 associated with AMPK activation was selectively increased at the early and middle stages of infection. Knockdown of endogenous ULK1 in SMB-S15 cells inhibited LC3 lipidation. These results showed that, in addition to the abolishment of the mTOR regulatory pathway, activation of the AMPK-ULK1 pathway during prion infection contributes to autophagy activation in prion-infected brain tissues.

Highlights

Are macroautophagy, microautophagy and chaperone-mediated autophagy[7,8,9]
We showed that the macroautophagic system is activated in scrapie-infected experimental animals and in certain subtypes of human prion diseases, in which the essential negative regulator mammalian target of rapamycin (mTOR) is severely inhibited[15]
To observe potential changes in the endogenous kinase AMPKα 1/2 and its phosphorylated form AMPK-Thr[172] in prion-diseased brain tissue, 10% brain homogenates from four hamsters infected with scrapie strain 263 K were evaluated

Summary

Introduction

Are macroautophagy, microautophagy and chaperone-mediated autophagy[7,8,9]. The mammalian target of rapamycin (mTOR)[10] is a negative regulator of autophagy while the BECN1-PIK3C3/Vps[34] (vacuolar sorting protein34)-Vps[15] (vacuolar sorting protein15) class III phosphatidylinositol 3-kinase core complex is a positive regulator[11]. We showed that the macroautophagic system is activated in scrapie-infected experimental animals and in certain subtypes of human prion diseases, in which the essential negative regulator mTOR is severely inhibited[15]. As one of the important elements in autophagy induction, both ULK1 and ULK1-Ser[555] are increased in hamsters infected with scrapie agent-263 K and in SMB-S15 cells. Since ULK1-Ser[555] is a target of AMPK, alterations in the former suggest that multi-kinase cross-talk and protein turnover pathways participate in the regulation of autophagy during prion infection. We analysed AMPK and ULK1 in the brains of hamsters infected with scrapie agent[263] K and in the scrapie infected cell line SMB-S15. Together with the abolishment of the mTOR regulatory pathway, activation of the AMPK-ULK1 pathway contributes to autophagy activation in prion-infected brain tissues

Methods

Results

Conclusion