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

Abstract

Amyloid ␤ (A␤) damages neurons and triggers microglial inflammatory activation in the Alzheimer disease (AD) brain. BACE1 is the primary enzyme in A␤ generation. Neuroinflammation potentially up-regulates BACE1 expression and increases A␤ 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 p38␣ MAPK, a kinase sensitive to inflammatory and oxidative stimuli. Using immunological and biochemical methods, we observed that reduction of p38␣ MAPK expression facilitated the lysosomal degradation of BACE1, decreased BACE1 protein and activity, and subsequently attenuated A␤ generation in the AD mouse brain. Inhibition of p38␣ MAPK also enhanced autophagy. Blocking autophagy by treating cells with 3-methyladenine or overexpressing dominant-negative ATG5 abolished the deficiency of the p38␣ MAPK-induced BACE1 protein reduction in cultured cells. Thus, our study demonstrates that p38␣ MAPK plays a critical role in the regulation of BACE1 degradation and A␤ generation in AD pathogenesis. Alzheimer disease (AD)2 is pathologically characterized by the extracellular deposits of amyloid ␤ peptide (A␤). A␤ injures neurons in the neocortex and limbic system directly (1) and indirectly by triggering microglial release of various neurotoxic inflammatory mediators, including cytokines (tumor necrosis factor-␣ and interleukin-1␤ (IL-1␤)) and reactive oxygen species (2). A␤ is generated after serial digestion of Alzheimer amyloid precursor protein (APP) by the membrane-anchored ␤-site APP-cleaving enzyme (BACE1, ␤-secretase) and ␥-secretase (3). It has been observed that knock-out of BACE1 or administration of the BACE1 inhibitor dramatically decreases A␤ levels in the brain and attenuates behavioral and electrophysiological deficits in APP-transgenic mice (4 -6). Thus, extensive investigations have focused on the direct inhibition of BACE1 to reduce A␤ load in the AD brain; however, these studies have unfortunately not yet led to any efficacious therapy for AD patients due to the various physiological roles of BACE1 (7). Using alternative methods to inhibit BACE1 might be a preferable investigative approach.Inflammatory activation might lead to up-regulation of neuronal BACE1 expression in the AD brain, as NF-B signaling enhances (8), and PPAR␥ activation suppresses (9), the activity of bace1 gene promoter. Accumulating evidence has shown that posttranslational modification of BACE1 is extremely important for the activity, intracellular trafficking, and lysosomal degradation of BACE1. For example, phosphorylation of BACE1 at Thr-252 by p25/Cdk5 increases the secretase activity (10), and phosphorylation at Ser-498 facilitates retrograde transport of BACE1 from endosomes to the trans-Golgi network (11). Ubiquitination at Lys-501 targets BACE1 to late endosomes/lysosomes for degradation (12). Finally, bisecting N-acetylglucosamine modification blocks delivery of BACE1 to lysosomes (13).p38 mitogen-activated protei...

An exploratory clinical study of p38α kinase inhibition in Alzheimer's disease

“…In particular, as within subject variability in BP ND is less than 3% between two PET scans,21, 22 the three responder subjects in the 40 mg dose group are highly likely to have had significant reductions in brain amyloid plaque load during the study. We believe these reduction in brain amyloid plaque load are consistent with the scientific reports published during and after the conduct of the study that indicates neuronal p38 α through modulating autophagy‐lysosome protein degradation appears to play a “critical role” in amyloid beta generation and plaque production 28, 29. Moreover, a very recent publication indicates that genetic knockout of neuronal p38 α in AD‐transgenic mice prevents both the development of amyloid plaque pathothology and synaptic dysfunction and memory loss 30.…”

Stimulation of TLR4 Attenuates Alzheimer’s Disease–Related Symptoms and Pathology in Tau-Transgenic Mice

“…Lysosomes were isolated using our established protocol (35). The brain tissue was homogenized in 53 vol of ice-cold homogenization buffer (HB; 0.25 M sucrose, 10 mM HEPES, 1 mM EDTA [pH 7.4]) and centrifuged at 800 3 g for 10 min.…”

“…LC3-GFP-monomeric red fluorescence protein (mRFP)-transgenic autophagy reporter cell line mRFP, GFP, and LC3 fusion protein serially (37) and SH-SY5Y cell lines overexpressing wild-type (wt) and dominantnegative (DN) human ATG5 were established in our previous study (35).…”

“…To further examine the role of autophagy in p-Tau degradation, we used recently established SH-SY5Y cell lines overexpressing DN and wt human ATG5 (35,44). Overexpression of ATG5DN inhibits autophagy of SH-SY5Y cells (35).…”

“…Overexpression of ATG5DN inhibits autophagy of SH-SY5Y cells (35). We cocultured ATG5DN-and wt ATG5-transgenic SH-SY5Y cells with bone marrow-derived macrophages as we did in experiments shown in Fig.…”