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Tau aggregation is a common feature of neurodegenerative diseases such as Alzheimer's disease, and hyperphosphorylation of tau has been implicated as a fundamental pathogenic mechanism in this process. To examine the impact of cdk5 in tau aggregation and tangle formation, we crossed transgenic mice overexpressing the cdk5 activator p25, with transgenic mice overexpressing mutant (P301L) human tau. Tau was hyperphosphorylated at several sites in the double transgenics, and there was a highly significant accumulation of aggregated tau in brainstem and cortex. This was accompanied by increased numbers of silver-stained neurofibrillary tangles (NFTs). Insoluble tau was also associated with active GSK. Thus, cdk5 can initiate a major impact on tau pathology progression that probably involves several kinases. Kinase inhibitors may thus be beneficial therapeutically.

Amyloid-β (Aβ) peptides, found in Alzheimer's disease brain, accumulate rapidly after traumatic brain injury (TBI) in both humans and animals. Here we show that blocking either β-or γ-secretase, enzymes required for production of Aβ from amyloid precursor protein (APP), can ameliorate motor and cognitive deficits and reduce cell loss after experimental TBI in mice. Thus, APP secretases are promising targets for treatment of TBI.TBI is the leading cause of mortality and disability among young individuals in developed countries, and globally the incidence of TBI is rising sharply 1 . TBI is a disease process, with an initial injury that induces biochemical and cellular changes that contribute to continuing neuronal damage and death over time. This continuing damage is known as secondary injury, and multiple apoptotic and inflammatory pathways are activated as part of this process (for reviews, see refs. 2,3 ). TBI is a major risk factor for the development of Alzheimer's disease 4,5 , and post-mortem studies show that 30% of TBI fatalities have Aβ deposits 6,7 . Remarkably, these deposits may occur less than 1 d after injury 8 . Not only does Aβ accumulate after TBI 9,10 , but also do the necessary APP enzymes responsible for Aβ production: β-APPcleaving enzyme-1 (BACE1) and presenilin-1, a γ-secretase complex protein [11][12][13][14] . Although the role of the APP secretases in secondary injury is unknown, multiple lines of evidence show that Aβ can cause cell death, activate inflammatory pathways [15][16][17][18] and prime proapoptotic pathways for activation by other insults 19 . The APP secretases may also be directly involved in secondary injury, as over-expressed BACE1 alone has been shown to cause neuronal cell loss in the absence of Aβ accumulation 20 . These facts make the APP secretases a potential therapeutic target for TBI.In our initial experiments, we characterized the TBI-induced protein changes in a nontransgenic mouse. We performed TBI by controlled cortical impact (CCI) of the left parietal cortex. This model induces both necrotic and apoptotic cell death, causing brain lesion and the development of behavioral deficits 21 . It has recently been reported that interstitial fluid Aβ concentrations correlate with neurological function in the injured human brain, with Aβ accumulating as neurological function improved in the days after trauma 22 . Exposure to experimental TBI resulted in accumulation of endogenous mouse Aβ x-40 peptide in the ipsilateral cortex within 1 d (Fig. 1a). Aβ levels increased by almost 120% at 3 d after injury before normalizing by 7 d (Fig. 1a) NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author ManuscriptBace1 and presenilin-1 (Fig. 1b), as has been previously reported in other animal models and humans 9-14 . Soluble APP-α, which is purported to be neuroprotective 23 , was also increased after injury. Functionally, this model of TBI causes deficits in fine motor coordination (beam walk test, Supplementary Fig. 1a online) in the absence of gross motor def...

Plaques containing beta-amyloid (Abeta) peptides are one of the pathological features of Alzheimer's disease, and the reduction of Abeta is considered a primary therapeutic target. Amyloid clearance by anti-Abeta antibodies has been reported after immunization, and recent data have shown that the antibodies may act as a peripheral sink for Abeta, thus altering the periphery/brain dynamics. Here we show that peripheral treatment with an agent that has high affinity for Abeta (gelsolin or GM1) but that is unrelated to an antibody or immune modulator reduced the level of Abeta in the brain, most likely because of a peripherally acting effect. We propose that in general, compounds that sequester plasma Abeta could reduce or prevent brain amyloidosis, which would enable the development of new therapeutic agents that are not limited by the need to penetrate the brain or evoke an immune response.

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Mutations in the amyloid precursor protein (APP) and presenilin-1 and -2 genes (PS-1, -2) cause Alzheimer's disease (AD). Mice carrying both mutant genes (PS/APP) develop AD-like deposits composed of beta-amyloid (Abeta) at an early age. In this study, we have examined how Abeta deposition is associated with immune responses. Both fibrillar and nonfibrillar Abeta (diffuse) deposits were visible in the frontal cortex by 3 months, and the amyloid load increased dramatically with age. The number of fibrillar Abeta deposits increased up to the oldest age studied (2.5 years old), whereas there were less marked changes in the number of diffuse deposits in mice over 1 year old. Activated microglia and astrocytes increased synchronously with amyloid burden and were, in general, closely associated with deposits. Cyclooxygenase-2, an inflammatory response molecule involved in the prostaglandin pathway, was up-regulated in astrocytes associated with some fibrillar deposits. Complement component 1q, an immune response component, strongly colocalized with fibrillar Abeta, but was also up-regulated in some plaque-associated microglia. These results show: i) an increasing proportion of amyloid is composed of fibrillar Abeta in the aging PS/APP mouse brain; ii) microglia and astrocytes are activated by both fibrillar and diffuse Abeta; and iii) cyclooxygenase-2 and complement component 1q levels increase in response to the formation of fibrillar Abeta in PS/APP mice.

Numerous cytoplasmic adaptor proteins, including JIP1, FE65, and X11␣, affect amyloid precursor protein (APP) processing and A␤ production. Dab1 is another adaptor protein that interacts with APP as well as with members of the apoE receptor family. We examined the effect of Dab1 on APP and apoEr2 processing in transfected cells and primary neurons. Dab1 interacted with APP and apoEr2 and increased levels of their secreted extracellular domains and their cytoplasmic C-terminal fragments. These effects depended on the NPXY domains of APP and apoEr2 and on the phosphotyrosine binding domain of Dab1 but did not depend on phosphorylation of Dab1. Dab1 decreased the levels of APP ␤-C-terminal fragment and secreted A␤. Full-length Dab1 or its phosphotyrosine binding domain alone increased surface levels of APP, as determined by surface protein biotinylation and live cell staining. A ligand for apoEr2, the extracellular matrix protein Reelin, significantly increased the interaction of apoEr2 with Dab1. Surprisingly, we also found that Reelin treatment significantly increased the interaction of APP and Dab1. Moreover, Reelin treatment increased cleavage of APP and apoEr2 and decreased production of the ␤-C-terminal fragment of APP and A␤. Together, these data suggest that Dab1 alters trafficking and processing of APP and apoEr2, and this effect is influenced by extracellular ligands. Proteolysis of the amyloid precursor protein (APP)2 results in production of the A␤ peptide, found in plaques of Alzheimer disease. The cytoplasmic domain of APP contains an NPTY sequence that serves as a binding motif for adaptor proteins that possess a phosphotyrosine binding domain (PTB), such as members of the Fe65, X11, JIP, and Dab protein families. Such adaptor proteins play critical roles in tyrosine kinase-mediated signal transduction, protein trafficking and localization, phagocytosis, cell fate determination, and neuronal development (1). Most importantly for Alzheimer disease, interactions between these cytoplasmic proteins and APP also lead to altered processing of APP.The effects of several of these adaptor proteins on APP trafficking and processing have been studied. The Fe65 family (FE65, FE65L1 (2), and FE65L2 (3)) is expressed at high levels in neurons (4). Co-expression of FE65 and APP promotes secreted APP and A␤ secretion in H4 cells and Madin-Darby canine kidney cells (2). However, co-expression of FE65 and APP in HEK293 cells stabilizes immature APP and inhibits APPs formation and A␤ secretion (5). The X11 family (X11␣, -␤, and -␥; also called Mint1, -2, and -3) are important in neuronal synaptic function (6). X11␣ slows cellular APP processing and reduces A␤40 and A␤42 secretion, perhaps through preventing trafficking of APP to subcellular compartments containing active ␥-secretase (7). X11␤ reduces A␤ levels and amyloid plaque formation in the brains of transgenic APP mice (8). Similar to X11␣ and -␤, JIP-1b interaction with APP stabilizes immature APP and inhibits APPs, A␤40, and A␤42 secretion in vitro (9).In contr...

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