Reactive astrocytes and microglia in Alzheimer's disease surround amyloid plaques and secrete proinflammatory cytokines that affect neuronal function. Relationship between cytokine signaling and amyloid-␤ peptide (A␤) accumulation is poorly understood. Thus, we generated a novel Swedish ␤-amyloid precursor protein mutant (APP) transgenic mouse in which the interferon (IFN)-␥ receptor type I was knocked out (APP/GRKO). IFN-␥ signaling loss in the APP/GRKO mice reduced gliosis and amyloid plaques at 14 months of age. Aggregated A␤ induced IFN-␥ production from co-culture of astrocytes and microglia, and IFN-␥ elicited tumor necrosis factor (TNF)-␣ secretion in wild type (WT) but not GRKO microglia co-cultured with astrocytes. Both IFN-␥ and TNF-␣ enhanced A␤ production from APP-expressing astrocytes and cortical neurons. TNF-␣ directly stimulated ␤-site APP-cleaving enzyme (BACE1) expression and enhanced ␤-processing of APP in astrocytes. The numbers of reactive astrocytes expressing BACE1 were increased in APP compared with APP/GRKO mice in both cortex and hippocampus. IFN-␥ and TNF-␣ activation of WT microglia suppressed A␤ degradation, whereas GRKO microglia had no changes. These results support the idea that glial IFN-␥ and TNF-␣ enhance A␤ deposition through BACE1 expression and suppression of A␤ clearance. Taken together, these observations suggest that proinflammatory cytokines are directly linked to Alzheimer's disease pathogenesis. Accumulating evidence supports the idea that neuroinflammation plays a significant role in the neuropathogenesis of Alzheimer's disease (AD).1,2 Amyloid-␤ peptide (A␤) aggregation and accumulation, a principal part of AD neuropathology, is linked directly to disease progression 3 and is regulated and directly affected by innate immune responses. 4 -6 Indeed, A␤ modulates microglial inflammatory responses and abilities and speed at which microglia digest and clear this protein from brain underlines disease severity. 7A␤ is processed from the ␤-amyloid precursor protein (APP). This is accomplished by processing enzymes (secretases), which include the ␤-site APP-cleaving enzyme (BACE1, a ␤-secretase) 8 as well as the ␥-secretase complexes of presenilin (PS)-1, aph-1, pen-2, and nicastrin. 9 Mutant forms of PS-1, PS-2, and APP genes are transmitted as autosomal dominants in early onset familial AD (FAD) and are linked to A␤ aggregation and deposition.10 Transgenic mice expressing Swedish FAD APP mutant (Tg2576) 11 mimic pathobiological features of human disease including neural dysfunction, amyloid deposition, and neuroinflammation.12-14 Each disease component affects one another. Indeed, for neuroinflammation, chronic expression of monocyte chemotactic protein-1/CCL2, a major mononuclear phagocyte chemoattractant, recruits monocytes and macrophages into the brain and enhances diffuse plaque formation in APP/CCL2 bigenic mice. 15 Moreover, proinflammatory cytokines, such as interferon (IFN)-␥, interleukin (IL)-1␤, transforming growth factor (TGF)-1␤, and tumor necrosis factor (TNF...

Neurofibrillary tangles, which are major pathological hallmarks of Alzheimer's disease (AD), are composed of paired helical filaments (PHFs) containing hyperphosphorylated tau. Specific kinases regulate tau phosphorylation and are closely linked to the pathogenesis of AD. We have characterized a human tau-tubulin kinase 1 (TTBK1) gene located on chromosome 6p21.1. TTBK1 is a serine/threonine/tyrosine kinase that is conserved among species and belongs to the casein kinase 1 superfamily. It is specifically expressed in the brain, especially in the cytoplasm of cortical and hippocampal neurons. TTBK1 phosphorylates tau proteins in both a Mg 2+-and a Mn 2+ -dependent manner. Phosphopeptide mapping and immunoblotting analysis confirmed a direct tau phosphorylation by TTBK1 at Ser198, Ser199, Ser202 and Ser422, which are also phosphorylated in PHFs. TTBK1 also induces tau aggregation in human neuronal cells in a dose-dependent manner. We conclude that TTBK1 is a neuron-specific dual kinase involved in tau phosphorylation at AD-related sites and is also associated with tau aggregation.

Microglia accumulation at the site of amyloid plaques is a strong indication that microglia play a major role in Alzheimer's disease pathogenesis. However, how microglia affect amyloid-beta peptide (Abeta) deposition remains poorly understood. To address this question, we developed a novel bigenic mouse that overexpresses both amyloid precursor protein (APP) and monocyte chemotactic protein-1 (MCP-1; CCL2 in systematic nomenclature). CCL2 expression, driven by the glial fibrillary acidic protein promoter, induced mononuclear phagocyte (MP; monocyte-derived macrophage and microglial) accumulation in the brain. When APP/CCL2 transgenic mice were compared to APP mice, a fivefold increase in Abeta deposition was present despite increased MP accumulation around hippocampal and cortical amyloid plaques. Levels of full-length APP, its C-terminal fragment, and Abeta-degrading enzymes (insulin-degrading enzyme and neprilysin) in APP/CCL2 and APP mice were indistinguishable. Sodium dodecyl sulfate-insoluble Abeta (an indicator of fibrillar Abeta) was increased in APP/CCL2 mice at 5 months of age. Apolipoprotein E, which enhances Abeta deposition, was also increased (2.2-fold) in aged APP/CCL2 as compared to APP mice. We propose that although CCL2 stimulates MP accumulation, it increases Abeta deposition by reducing Abeta clearance through increased apolipoprotein E expression. Understanding the mechanisms underlying these events could be used to modulate microglial function in Alzheimer's disease and positively affect disease outcomes.

Elucidation of the factors involved in host defense against human immunodeficiency viral infection remains pivotal if viral control may be achieved. Toward these ends, we investigated the function of a putative antiretroviral factor, OTK18, isolated by differential display of mRNA from HIV type 1-infected primary human monocyte-derived macrophages. Molecular and immunohistochemical analyses showed that the OTK18 nucleotide sequence contains 13 adjacent C2H2-type zinc finger motifs, a Krüppel-associated box, and is localized to both cytosol and nucleus. Mutational analyses revealed that both the Krüppel-associated box and zinc finger regions of OTK18 are responsible for the transcriptional suppressive activities of this gene. OTK18 was copiously expressed in macrophages following HIV type I infection and diminished progeny virion production. A mechanism for this antiretroviral activity was by suppression of HIV type 1 Tat-induced viral long terminal repeat promoter activity. Our findings suggest that one possible function of OTK18 is as a HIV type 1-inducible transcriptional suppresser.

Increasing evidence strongly supports the role of glial immunity in the pathogenesis of Alzheimer's disease (AD). To investigate such events we have developed cell systems mimicking the interactions between b-amyloid precursor protein (APP)-expressing neurons and brain mononuclear phagocytes (MP; macrophages and microglia). MP were co-cultured with neuronal cells expressing wild type APP or familial AD-linked APP mutants. The latter was derived from recombinant adenoviral constructs. Neuronal APP processing products induced MP activation, reactive oxygen species, and neurotoxic activities. These occurred without the addition of pro-inflammatory cytokines and were reversed by depletion of amyloid b-peptide (Ab) and secreted APP (sAPP). Neurotoxic activities were diminished by superoxide dismutase mimetics and NMDA receptor inhibitors. Microglial glutamate secretion was suppressed by the cystine-glutamate antiporter inhibitor and its levels paralleled the depletion of sAPP and Ab from conditioned media prepared from APP-expressing neurons. The excitotoxins from activated MP were potent enough to evoke recombinant NMDA receptor-mediated inward currents expressed in vitro in the Xenopus oocytes. These results demonstrate that neuronal APP-processing products can induce oxidative neurotoxicity through microglial activation.