BAG5 Promotes Alpha-Synuclein Oligomer Formation and Functionally Interacts With the Autophagy Adaptor Protein p62.

Erik L Friesen,Rebecca Earnshaw,Hien Chau,Yu Tong Zhang,Darren M O’Hara,Suneil K Kalia,Victoria Agapova,Sophie Ngana,Mitch L De Snoo,Lorraine V Kalia,Kevin S Chen

doi:10.3389/fcell.2020.00716

Abstract

Molecular chaperones are critical to maintaining intracellular proteostasis and have been shown to have a protective role against alpha-synuclein-mediated toxicity. Co-chaperone proteins regulate the activity of molecular chaperones and connect the chaperone network to protein degradation and cell death pathways. Bcl-2 associated athanogene 5 (BAG5) is a co-chaperone that modulates proteostasis by inhibiting the activity of Heat shock protein 70 (Hsp70) and several E3 ubiquitin ligases, resulting in enhanced neurodegeneration in models of Parkinson’s disease (PD). Here we identify a novel interaction between BAG5 and p62/sequestosome-1 (SQSTM1), suggesting that BAG5 may bridge the chaperone network to autophagy-mediated protein degradation. We found that BAG5 enhanced the formation of pathogenic alpha-synuclein oligomers and regulated the levels and subcellular distribution of p62. These results extend the role of BAG5 in alpha-synuclein processing and intracellular proteostasis.

Highlights

Parkinson’s disease (PD) is an incurable neurodegenerative disease which affects 1–2% of the population over the age of 60 (Kalia and Lang, 2015)
Heat shock protein 70 (Hsp70) family members, such as HSPA8 and HSPA1A, were more abundant in the Bcl-2 associated athanogene 5 (BAG5) IP condition relative to the GFP-BAG5DARA IP condition, as gauged by total spectral counts, providing internal validation of our technique. We focused on the latter since they represent proteins that interact with BAG5 but likely do not require Hsp70 to mediate the interaction
Using a mass spectrometry-based screen for BAG5 interacting proteins, we found that BAG5 interacts with a rich network of chaperones as well as numerous proteins that function within the ubiquitinproteasome system (UPS) and autophagy lysosome pathway (ALP)

Summary

Introduction

Parkinson’s disease (PD) is an incurable neurodegenerative disease which affects 1–2% of the population over the age of 60 (Kalia and Lang, 2015). PD is characterized by a significant loss of dopaminergic neurons within the substantia nigra pars compacta as well as the presence of Lewy bodies (LBs), intracellular inclusions comprised largely of aggregated alpha-synuclein (Kalia et al, 2013). Various factors modulate alpha-synuclein processing and aggregation including molecular chaperones. Heat shock protein 70 (Hsp70) is a chaperone which has been shown to be involved in alphasynuclein processing and preferentially binds to alpha-synuclein fibrils (Aprile et al, 2017). Hsp can reduce levels of misfolded and aggregated alpha-synuclein, and protect against alphasynuclein-mediated toxicity (Auluck et al, 2002; Klucken et al, 2004; Dedmon et al, 2005; Flower et al, 2005; Huang et al, 2006)

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