Deficiency of Neuronal p38α MAPK Attenuates Amyloid Pathology in Alzheimer Disease Mouse and Cell Models through Facilitating Lysosomal Degradation of BACE1

Laura Schnöder,Wenlin Hao,Yiren Qin,Shirong Liu,Inge Tomic,Xu Liu,Klaus Fassbender,Yang Liu

doi:10.1074/jbc.m115.695916

Laura Schnöder, Wenlin Hao + Show 6 more

Open Access

https://doi.org/10.1074/jbc.m115.695916

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Abstract

Amyloid β (Aβ) damages neurons and triggers microglial inflammatory activation in the Alzheimer disease (AD) brain. BACE1 is the primary enzyme in Aβ generation. Neuroinflammation potentially up-regulates BACE1 expression and increases Aβ production. In Alzheimer amyloid precursor protein-transgenic mice and SH-SY5Y cell models, we specifically knocked out or knocked down gene expression of mapk14, which encodes p38α MAPK, a kinase sensitive to inflammatory and oxidative stimuli. Using immunological and biochemical methods, we observed that reduction of p38α MAPK expression facilitated the lysosomal degradation of BACE1, decreased BACE1 protein and activity, and subsequently attenuated Aβ generation in the AD mouse brain. Inhibition of p38α MAPK also enhanced autophagy. Blocking autophagy by treating cells with 3-methyladenine or overexpressing dominant-negative ATG5 abolished the deficiency of the p38α MAPK-induced BACE1 protein reduction in cultured cells. Thus, our study demonstrates that p38α MAPK plays a critical role in the regulation of BACE1 degradation and Aβ generation in AD pathogenesis.

Highlights

In the brain and attenuates behavioral and electrophysiological deficits in APP-transgenic mice (4 – 6)
Deletion of p38␣ MAPK in Neurons Reduces A␤ Load in the Alzheimer Mouse Model—To confirm that p38 MAPK is activated in the Alzheimer disease (AD) mouse brain, we compared the phosphorylation levels of p38␣ MAPK in 4-month-old APP/PS1-transgenic mice and their wild-type littermate controls and observed that phosphorylation levels were significantly higher in the APP/ PS1-transgenic mice (Fig. 1, A and B; t test, p Ͻ 0.05)
Our study demonstrates for the first time that partial deletion of the inflammation-sensitive kinase, p38␣ MAPK, in neurons reduces A␤ generation and decreases cerebral A␤ load by promoting macroautophagy-associated BACE1 degradation

Summary

Experimental Procedures

Animal Models and Cross-breeding—APP/PS1 double transgenic mice over-expressing human mutated APP (KM670/ 671NL) and PS1 (L166P) under Thy-1 promoters [27] were kindly provided by M. Western Blot Analysis of A␤ Pathology—For detection of A␤, C99, and APP in the mouse brain, frozen brain tissues derived from p38␣ MAPK-deficient and wild-type mice were homogenized in 5 ml/g of tissue in radioimmunoprecipitation assay buffer (RIPA; 50 mM Tris, 150 mM NaCl, 0.1% SDS, 0.5% sodium deoxycholate, 1% Nonidet P-40, and 5 mM EDTA (pH 8.0)) supplemented with protease inhibitor mixture (Roche Applied Science, Mannheim, Germany) on ice and centrifuged at 16,100 ϫ g for 30 min at 4 °C to collect the supernatants. Western Blot Analysis of p38␣ MAPK, BACE1, and Autophagy—The frozen brain or cell pellets were homogenized in RIPA buffer. The cells were first stained with mouse monoclonal antibody (clone number 137612; R&D Systems) or rabbit polyclonal antibody (catalog number ab10716, Abcam) against BACE1 and Alexa 488-conjugated second antibodies (Life Technologies).

Results

Discussion

Fassbender and Yang Liu