AR12 increases BAG3 expression which is essential for Tau and APP degradation via LC3-associated phagocytosis and macroautophagy

Abstract

We defined the mechanisms by which the chaperone ATPase inhibitor AR12 and the multi-kinase inhibitor neratinib interacted to reduce expression of Tau and amyloid-precursor protein (APP) in microglia and neuronal cells. AR12 and neratinib interacted to increase the phosphorylation of eIF2A S51 and the expression of BAG3, Beclin1 and ATG5, and in parallel, enhanced autophagosome formation and autophagic flux. Knock down of BAG3, Beclin1 or ATG5 abolished autophagosome formation and significantly reduced degradation of p62, LAMP2, Tau, APP, and GRP78 (total and plasma membrane). Knock down of Rubicon, a key component of LC3-associated phagocytosis (LAP), significantly reduced autophagosome formation but not autophagic flux and prevented degradation of Tau, APP, and cell surface GRP78, but not ER-localized GRP78. Knock down of Beclin1, ATG5 or Rubicon or over-expression of GRP78 prevented the significant increase in eIF2A phosphorylation. Knock down of eIF2A prevented the increase in BAG3 expression and significantly reduced autophagosome formation, autophagic flux, and it prevented Tau and APP degradation. We conclude that AR12 has the potential to reduce Tau and APP levels in neurons and microglia via the actions of LAP, endoplasmic reticulum stress signaling and macroautophagy. We hypothesize that the initial inactivation of GRP78 catalytic function by AR12 facilitates an initial increase in eIF2A phosphorylation which in turn is essential for greater levels of eIF2A phosphorylation, greater levels of BAG3 and macroautophagy and eventually leading to significant amounts of APP/Tau degradation.

PSEN1M146Vand PSEN1A246Emutations associated with Alzheimer’s disease impair proper microglia differentiation

“…5D ). Finally, the ADAD group of genes presented a strong correlation with the “ADAD” microglia cells characterized by Brase et al ( Fig.5E ), and notably supported by the presence of the genes BAG3 (chaperone protein, described as essential for Tau and APP degradation via phagocytosis 26 ), SYNDIG1 (considered as a central regulator of excitatory synapse development 27 , but also described as being over-expressed in microglia 28 ), or MLXIPL (a glucose-responsive transcription factor also known as ChREBP), a gene for which previous GWAS studies revealed significant association of single nucleotide polymorphisms (SNPs) in the context of AD 29 . SYNDIG1 and MLXIPL were also identified in a recent single-nuclei RNA-seq study covering ∼120,000 microglia isolated from 12 AD and 10 control donors 30 ( Fig.5F ).…”