Families bearing mutations in the presenilin 1 (PS1) gene develop Alzheimer's disease. Previous studies have shown that the Alzheimer-associated mutations in PS1 increase production of amyloid ␤ protein (A␤ 1-42 ). We now show that PS1 also regulates phosphorylation of the microtubule-associated protein tau. PS1 directly binds tau and a tau kinase, glycogen synthase kinase 3␤ (GSK-3␤). Deletion studies show that both tau and GSK-3␤ bind to the same region of PS1, residues 250-298, whereas the binding domain on tau is the microtubule-binding repeat region. The ability of PS1 to bring tau and GSK-3␤ into close proximity suggests that PS1 may regulate the interaction of tau with GSK-3␤. Mutations in PS1 that cause Alzheimer's disease increase the ability of PS1 to bind GSK-3␤ and, correspondingly, increase its tau-directed kinase activity. We propose that the increased association of GSK-3␤ with mutant PS1 leads to increased phosphorylation of tau.The neuropathological diagnosis of Alzheimer's disease (AD) requires the presence of both senile plaques and neurofibrillary tangles (NFT) (1). Senile plaques are largely composed of amyloid ␤ protein (A␤), whereas NFT are composed of hyperphosphorylated tau organized into filamentous structures termed paired helical filaments (2-4). Mutations on the presenilin 1 (PS1) gene cause an early onset form of AD with an autosomal dominant inheritance pattern (5-7). The role of PS1 in AD is particularly interesting because it has a strong causal relationship to the disease; genetic studies show that mutations for PS1 exhibit 100% penetrance in causing AD (8). Although, the mechanism through which PS1 causes AD is unclear. Mutations in presenilins affect A␤ processing. Recent studies indicate that cell lines, transgenic mice, or patients expressing mutant forms of PS1 show a selective increase in production of A␤ 1-42 (9-12). Mutations in the presenilins also activate apoptotic pathways and render neurons more vulnerable to stressors, such as A␤ neurotoxicity (13-16). The ability of PS1 to potentiate A␤ toxicity raises the possibility that PS1 interacts with glycogen synthase kinase 3␤ (GSK-3␤), which we previously have shown to be involved in A␤-mediated cell death (17-20). The enzyme GSK-3␤ also has been implicated in AD because this kinase is one of a group of proline-directed kinases that can phosphorylate the microtubule-associated protein tau, to generate a precursor to NFTs, termed paired helical filaments-tau (21,22). PS1 (23-26) and GSK-3␤ (27, 28) can be found in association with NFTs in the Alzheimer brain, which further suggests that there may be a physiological connection between PS1, GSK-3␤, and tau. To pursue these intriguing connections, we investigated whether PS1 might directly associate with GSK-3␤ and tau. MATERIALS AND METHODSPreparation of Brain Samples. Human brain cortex was obtained at autopsy from patients ranging in age from 44 to 88 years old. Twenty-one samples, from donors age 44-79, showed no evidence of neurological disorders, whereas two sa...

Deposition of amyloid ss-protein (Ass), a hallmark of Alzheimer's disease, occurs to some extent in the brains of most elderly individuals. We sought to learn when Ass deposition begins and how deposition is affected by apolipoprotein E allele epsilon4, a strong risk factor for late-onset Alzheimer's disease. Using an improved extraction protocol and specific enzyme-linked immunosorbent assay, we quantified the levels of Ass40 and Ass42 in the insoluble fractions of brains from 105 autopsy cases, aged 22 to 81 years at death, who showed no signs of dementia. Ass40 and Ass42 were detected in the insoluble fractions from all of the brains examined; low levels were even found in the brains of patients as young as 20 to 30 years of age. The incidence of significant Ass accumulation increased age-dependently, with Ass42 levels beginning to rise steeply in some patients in their late 40's, accompanied by much smaller increases in Ass40 levels. The presence of the apolipoprotein E epsilon4 allele was found to significantly enhance the accumulation of Ass42 and, to a lesser extent, that of Ass40. These findings strongly suggest that the presence of epsilon4 allele results in an earlier onset of Ass42 accumulation in the brain.

The present study was undertaken to investigate the relationship of microglial activation to amyloid beta protein (A beta) deposition, particularly at the early stage. Using single and double immunostaining methods with a panel of microglia markers and antibodies against A beta and amyloid beta protein precursor (APP), we examined the cerebrum and cerebella of both Alzheimer's disease (AD) and non-demented subjects obtained at autopsy. In nondemented, middle-aged subjects that had small amounts of cerebral A beta deposits, approximately 70% of the diffuse plaques contained ramified microglia. However, no evidence of microglial activation was found in diffuse plaques in any of the non-demented subjects. Dual immunostaining of sections of cerebral cortex using antibodies against A beta and major histocompatibility complex class II antigen showed that in AD subjects, approximately 20% of total diffuse plaques contained a few, activated microglia. Most of these plaques were defined as a transitional from between diffuse and primitive plaques. Both primitive and classic plaques in the cerebral cortex of AD subjects consistently contained clusters of activated microglia. Subpial A beta deposits without neuritic changes lacked microglial activation. In the cerebellum, all of the diffuse plaques lacked microglial activation, and activated microglia in the compact plaques were not as hypertrophic as those in cerebral primitive/classic plaques. Our findings indicate that microglial reactions are absent in the early stages of A beta deposition, and it occurs during the transition from diffuse to primitive plaques, when amounts of A beta deposits and the degree of neuritic changes increase.