Abstract
Background: Neuronal death is a major hallmark of Alzheimer's disease (AD). Necroptosis, as a programmed necrotic process, is activated in AD. However, what signals and factors initiate necroptosis in AD is largely unknown.Methods: We examined the expression levels of critical molecules in necroptotic signaling pathway by immunohistochemistry (IHC) staining and immunoblotting using brain tissues from AD patients and AD mouse models of APP/PS1 and 5×FAD. We performed brain stereotaxic injection with recombinant TNF-α, anti-TNFR1 neutralizing antibody or AAV-mediated gene expression and knockdown in APP/PS1 mice. For in vitro studies, we used TNF-α combined with zVAD-fmk and Smac mimetic to establish neuronal necroptosis models and utilized pharmacological or molecular biological approaches to study the signaling pathways.Results: We find that activated neuronal necroptosis is dependent on upstream TNF-α/TNFR1 signaling in both neuronal cell cultures and AD mouse models. Upon TNF-α stimulation, accumulated p62 recruits RIPK1 and induces its self-oligomerization, and activates downstream RIPK1/RIPK3/MLKL cascade, leading to neuronal necroptosis. Ectopic accumulation of p62 is caused by impaired autophagy flux, which is mediated by UVRAG downregulation during the TNF-α-promoted necroptosis. Notably, UVRAG overexpression inhibits neuronal necroptosis in cell and mouse models of AD.Conclusions: We identify a finely controlled regulation of neuronal necroptosis in AD by coordinated TNF-α signaling, RIPK1/3 activity and autophagy machinery. Strategies that could fine-tune necroptosis and autophagy may bring in promising therapeutics for AD.
Highlights
Neuronal death is a major hallmark of Alzheimer’s disease (AD)
We find that activated neuronal necroptosis is dependent on upstream tumor necrosis factor-α (TNF-α)/Tumor necrosis factor receptor 1 (TNFR1) signaling in both neuronal cell cultures and AD mouse models
We further reveal that ectopic accumulation of p62 is caused by impaired autophagy flux, which is mediated by downregulation of UV Radiation Resistance Associated (UVRAG) during the TNF-α-promoted necroptosis
Summary
Neuronal death is a major hallmark of Alzheimer’s disease (AD). Necroptosis, as a programmed necrotic process, is activated in AD. Despite continuing debates about hypotheses for the cause(s) of AD, Aβ-induced neuronal death and brain dystrophy has emerged as the most extensively accepted theory [5]. Evidence has shown that extracellular Aβ plaques are directly toxic to adjacent neurons [6], and soluble or aggregated Aβ can induce inflammatory processes and secondary cell death [7]. Among the various forms of cell death, neuronal apoptosis and necrosis are believed to be the two major death pathways for neuronal loss in AD, but recent findings have implicated necroptosis, a programmed cell necrosis [8,9,10]. The mechanism initiating necroptosis in AD is not known
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