Neuroinflammation alters cellular proteostasis by producing endoplasmic reticulum stress, autophagy activation and disrupting ERAD activation

Cristina Pintado,Helena Domínguez-Martín,Angélica Castaño,Diego Ruano,Sandra Macías

doi:10.1038/s41598-017-08722-3

Abstract

Proteostasis alteration and neuroinflammation are typical features of normal aging. We have previously shown that neuroinflammation alters cellular proteostasis through immunoproteasome induction, leading to a transient decrease of proteasome activity. Here, we further investigated the role of acute lipopolysaccharide (LPS)-induced hippocampal neuroinflammation in cellular proteostasis. In particular, we focused on macroautophagy (hereinafter called autophagy) and endoplasmic reticulum-associated protein degradation (ERAD). We demonstrate that LPS injection induced autophagy activation that was dependent, at least in part, on glycogen synthase kinase (GSK)-3β activity but independent of mammalian target of rapamycin (mTOR) inhibition. Neuroinflammation also produced endoplasmic reticulum (ER) stress leading to canonical unfolded protein response (UPR) activation with a rapid activating transcription factor (ATF) 6α attenuation that resulted in a time-dependent down-regulation of ERAD markers. In this regard, the time-dependent accumulation of unspliced X-box binding protein (XBP) 1, likely because of decreased inositol-requiring enzyme (IRE) 1α-mediated splicing activity, might underlie in vivo ATF6α attenuation. Importantly, lactacystin-induced activation of ERAD was abolished in both the acute neuroinflammation model and in aged rats. Therefore, we provide a cellular pathway through which neuroinflammation might sensitize cells to neurodegeneration under stress situations, being relevant in normal aging and other disorders where neuroinflammation is a characteristic feature.

Highlights

Neuroinflammation and proteostasis disruption are characteristics of normal aging and some age-related neurodegenerative diseases
Because IRE1α activation was observed for no longer than 3 hours, we further investigated whether the time-dependent reduction in the sXBP1 protein could be explained by a reduction in the amount of spliced Xbp[1] mRNA
To investigate whether nuclear depletion of both processed ATF6α (pATF6α) and sXBP1 could have functional relevance, we evaluated endoplasmic reticulum-associated protein degradation (ERAD) activation by analysing the expression of several ERAD-associated molecules involved in both recognition and retrotranslocation of misfolded and/or unfolded proteins

Summary

Introduction

Neuroinflammation and proteostasis disruption are characteristics of normal aging and some age-related neurodegenerative diseases. A consequence of proteostasis alteration is ER-stress Under this situation, cells activate the UPR, which is mediated by IRE1α, ATF6α and double-stranded RNA-dependent protein kinase-like endoplasmic reticulum kinase (PERK) signalling pathways[2]. Neuroinflammation, autophagy and UPR are three interrelated processes, which can influence each other depending on different factors and stressors[14, 15]. LPS injection produced a canonical but short UPR activation Both ATF6α and IRE-1α were quickly attenuated, leading to down-regulation of ERAD markers. The up-regulation of ERAD markers induced by proteasome inhibition was abolished in both aged rats and LPS-injected young animals. These results suggest that neuroinflammation-induced ERAD inactivation might increase cell vulnerability under proteasomal stress situations

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Results

Conclusion