One hallmark of Alzheimer disease is the accumulation of amyloid beta-peptide in the brain and its deposition as plaques. Mice transgenic for an amyloid beta precursor protein (APP) mini-gene driven by a platelet-derived (PD) growth factor promoter (PDAPP mice), which overexpress one of the disease-linked mutant forms of the human amyloid precursor protein, show many of the pathological features of Alzheimer disease, including extensive deposition of extracellular amyloid plaques, astrocytosis and neuritic dystrophy. Active immunization of PDAPP mice with human amyloid beta-peptide reduces plaque burden and its associated pathologies. Several hypotheses have been proposed regarding the mechanism of this response. Here we report that peripheral administration of antibodies against amyloid beta-peptide, was sufficient to reduce amyloid burden. Despite their relatively modest serum levels, the passively administered antibodies were able to enter the central nervous system, decorate plaques and induce clearance of preexisting amyloid. When examined in an ex vivo assay with sections of PDAPP or Alzheimer disease brain tissue, antibodies against amyloid beta-peptide triggered microglial cells to clear plaques through Fc receptor-mediated phagocytosis and subsequent peptide degradation. These results indicate that antibodies can cross the blood-brain barrier to act directly in the central nervous system and should be considered as a therapeutic approach for the treatment of Alzheimer disease and other neurological disorders.

Transgenic PDAPP mice, which express a disease-linked isoform of the human amyloid precursor protein, exhibit CNS pathology that is similar to Alzheimer's disease. In an age-dependent fashion, the mice develop plaques containing ␤-amyloid peptide (A␤) and exhibit neuronal dystrophy and synaptic loss. It has been shown in previous studies that pathology can be prevented and even reversed by immunization of the mice with the A␤ peptide. Similar protection could be achieved by passive administration of some but not all monoclonal antibodies against A␤. In the current studies we sought to define the optimal antibody response for reducing neuropathology. Immune sera with reactivity against different A␤ epitopes and monoclonal antibodies with different isotypes were examined for efficacy both ex vivo and in vivo. The studies showed that: (i) of the purified or elicited antibodies tested, only antibodies against the N-terminal regions of A␤ were able to invoke plaque clearance; (ii) plaque binding correlated with a clearance response and neuronal protection, whereas the ability of antibodies to capture soluble A␤ was not necessarily correlated with efficacy; (iii) the isotype of the antibody dramatically influenced the degree of plaque clearance and neuronal protection; (iv) high affinity of the antibody for Fc receptors on microglial cells seemed more important than high affinity for A␤ itself; and (v) complement activation was not required for plaque clearance. These results indicate that antibody Fc-mediated plaque clearance is a highly efficient and effective process for protection against neuropathology in an animal model of Alzheimer's disease.I mmunization of the transgenic PDAPP mice with ␤-amyloid peptide (A␤)-derived immunogens results in an antibody response that facilitates the clearance of plaques within the central nervous system (CNS) (1-4). Although a number of mechanisms are likely to operate in this clearance response (5, 6), our previous findings strongly indicate that antibodymediated, Fc-dependent phagocytosis by microglial cells and͞or macrophages is important to the process (7). Importantly, a T cell response was not required for amyloid plaque clearance. When peripherally administered, antibodies against A␤ entered the CNS of PDAPP transgenic mice, decorated amyloid plaques, and induced plaque clearance. Comparing different antibodies in an ex vivo assay with sections of PDAPP or Alzheimer's disease (AD) brain, there was a strong correlation between those that produced ex vivo efficacy and those that were efficacious in vivo. Fc receptors on microglial cells were found to be key for the clearance response in this assay. However, it has been reported that antibody efficacy can also be obtained in vivo by mechanisms that are independent of Fc interactions (8). Studies have indicated that an antibody directed against the midportion of A␤, which cannot recognize amyloid plaques, appears to bind to soluble A␤ and reduce plaque deposition (6). In addition, it has been reported recently that short-term...

The authors report a patient with Alzheimer disease (AD) without encephalitis who was immunized with AN-1792 (an adjuvanted formulation of Abeta-42). There were no amyloid plaques in the frontal cortex and abundant Abeta-immunoreactive macrophages, but tangles and amyloid angiopathy were present. The white matter appeared normal and minimal lymphocytic infiltration in the leptomeninges was observed. This case illustrates the effects of an Abeta-based immunization on AD pathogenesis in the absence of overt meningoencephalitis and leukoencephalopathy.

Alzheimer's disease (AD) is characterized by progressive neurodegeneration and cerebral accumulation of the β-amyloid peptide (Aβ), but it is unknown what makes neurons susceptible to degeneration. We report that the TGF-β type II receptor (TβRII) is mainly expressed by neurons, and that TβRII levels are reduced in human AD brain and correlate with pathological hallmarks of the disease. Reducing neuronal TGF-β signaling in mice resulted in age-dependent neurodegeneration and promoted Aβ accumulation and dendritic loss in a mouse model of AD. In cultured cells, reduced TGF-β signaling caused neuronal degeneration and resulted in increased levels of secreted Aβ and β-secretase-cleaved soluble amyloid precursor protein. These results show that reduced neuronal TGF-β signaling increases age-dependent neurodegeneration and AD-like disease in vivo. Increasing neuronal TGF-β signaling may thus reduce neurodegeneration and be beneficial in AD. IntroductionAlzheimer's disease (AD) is a progressive neurodegenerative disease that leads to loss of cognitive function in a large number of elderly people. The human AD brain is characterized by the accumulation of β-amyloid peptide (Aβ) in extracellular plaques and hyperphosphorylated tau in intracellular neurofibrillary tangles. In addition, there is degeneration of synapses and dendrites and a progressive loss of neurons involved in memory processes (1). The cause of this degeneration in AD remains unknown, and no effective treatments are available.Survival of neurons is dependent on extracellular signals from neurotrophic factors and related factors with trophic activity (reviewed in ref.2). Levels of the neurotrophin nerve growth factor (NGF) and its receptor, tropomyosin receptor kinase A (TRKA), as well as levels of brain-derived neurotrophic factor (BDNF) and its receptor, TRKB, are lower in human AD brains than in nondemented controls (2-5). It was therefore proposed that a deficiency in neurotrophic factor signaling would promote neurodegeneration and cognitive dysfunction in AD, but this hypothesis has not been tested using specific genetic inhibition of neurotrophic factor signaling in a mouse model for AD (reviewed in refs. 2, 6).

Several neurological diseases, includingThe importance of ␣-synuclein to the pathogenesis of Parkinson disease (PD) 4 and the related disorder, dementia with Lewy bodies (DLB), is suggested by its association with Lewy bodies and Lewy neurites, the inclusions that characterize these diseases (1)(2)(3), and demonstrated by the existence of mutations that cause syndromes mimicking sporadic PD and DLB (4 -6). Furthermore, three separate mutations cause early onset forms of PD and DLB. It is particularly telling that duplications or triplications of the gene (7-9), which increase levels of ␣-synuclein with no alteration in sequence, also cause PD or DLB.␣-Synuclein has been reported to be phosphorylated on serine residues, at Ser-87 and Ser-129 (10), although to date only the Ser-129 phosphorylation has been identified in the central nervous system (11,12). Phosphorylation at tyrosine residues has been observed by some investigators (13,14) but not by others (10 -12). Phosphorylation at Ser-129 (p-Ser-129) is of particular interest because the majority of synuclein in Lewy bodies contains this modification (15). In addition, p-Ser-129 was found to be the most extensive and consistent modification in a survey of synuclein in Lewy bodies (11). Results have been mixed from studies investigating the function of phosphorylation using S129A and S129D mutations to respectively block and mimic the modification. Although the phosphorylation mimic was associated with pathology in studies in Drosophila (16) and in transgenic mouse models (17, 18), studies using adeno-associated virus vectors to overexpress ␣-synuclein in rat substantia nigra found an exacerbation of pathology with the S129A mutation, whereas the S129D mutation was benign, if not protective (19). Interpretation of these studies is complicated by a recent study showing that the S129D and S129A mutations themselves have effects on the aggregation properties of ␣-synuclein independent of their effects on phosphorylation, with the S129A mutation stimulating fibril formation (20). Clearly, determination of the role of p-Ser-129 phosphorylation would be helped by identification of the responsible kinase. In addition, identification will provide a pathologically relevant way to increase phosphorylation in a cell or animal model.Several kinases have been proposed to phosphorylate ␣-synuclein, including casein kinases 1 and 2 (10, 12, 21) and members of the G-protein-coupled receptor kinase family (22). In this report, we offer evidence that a member of the polo-like kinase (PLK) family, PLK2 (or serum-inducible kinase, SNK), functions as an ␣-synuclein kinase. The ability of PLK2 to directly phosphorylate ␣-synuclein at Ser-129 is established by overexpression in cell culture and by in vitro reaction with the purified kinase. We show that PLK2 phosphorylates ␣-synuclein in cells, including primary neuronal cultures, using a series of kinase inhibitors as well as inhibition of expression with RNA interference. In addition, inhibitor and knock-out studies in mouse brai...

Leucine-rich repeat kinase-2 (LRRK2) mutations are the most important cause of familial Parkinson's disease and non-selective inhibitors are protective in rodent disease models. Due to their poor potency and selectivity, the neuroprotective mechanism of these tool compounds has remained elusive so far and it is still unknown whether selective LRRK2 inhibition can attenuate mutant LRRK2-dependent toxicity in human neurons. Here, we employ a chemoproteomics strategy to identify potent, selective and metabolically stable LRRK2 inhibitors. We demonstrate that CZC-25146 prevents mutant LRRK2-induced injury of cultured rodent and human neurons with mid-nanomolar potency. These precise chemical probes further validate this emerging therapeutic strategy. They will enable more detailed studies of LRRK2-dependent signaling and pathogenesis and accelerate drug discovery.

Transgenic mice mimicking certain features of Alzheimer's disease (AD)-pathology, namely amyloid plaques and neurofibrillary tangles, have been developed in an effort to better understand the mechanism leading to the formation of these characteristic cerebral lesions. More recently, these animal models have been widely used to investigate emergent therapies aimed at the reduction of the cerebral amyloid load. Several studies have shown that immunotherapy targeting the amyloid peptide (Abeta) is efficacious at clearing the amyloid plaques or preventing their formation, and at reducing the memory/behavior impairment observed in these animals. In AD, different types of plaques likely have different pathogenic significance, and further characterization of plaque pathology in the PDAPP transgenic mice would enhance the evaluation of potential therapeutics. In the present study, a morphological classification of amyloid plaques present in the brains of PDAPP mice was established by using Thioflavin-S staining. Neuritic dystrophy associated with amyloid plaques was also investigated. Finally, the efficacy of passive immunization with anti-Abeta antibodies on the clearance of Thio-S positive amyloid plaques was studied. Our results show that distinct morphological types of plaques are differentially cleared depending upon the isotype of the antibody.

TH17 cells enter tissues to facilitate pathogenic autoimmune responses, including multiple sclerosis (MS). However, the adhesion molecules involved in the unique migratory capacity of TH17 cells, into both inflamed and uninflamed tissues remain unclear. Herein, we characterize MCAM (CD146) as an adhesion molecule that defines human TH17 cells in the circulation; following in vitro restimulation of human memory T cells, nearly all of the capacity to secrete IL-17 is contained within the population of cells expressing MCAM. Furthermore, we identify the MCAM ligand as laminin 411, an isoform of laminin expressed within the vascular endothelial basement membranes under inflammatory as well as homeotstatic conditions. Purified MCAM-Fc binds to laminin 411 with an affinity of 27 nM, and recognizes vascular basement membranes in mouse and human tissue. MCAM-Fc binding was undetectable in tissue from mice with targeted deletion of laminin 411, indicating that laminin 411 is a major tissue ligand for MCAM. An anti-MCAM monoclonal antibody, selected for inhibition of laminin binding, as well as soluble MCAM-Fc, inhibited T cell adhesion to laminin 411 in vitro. When administered in vivo, the antibody reduced TH17 cell infiltration into the CNS and ameliorated disease in an animal model of MS. Our data suggest that MCAM and laminin 411 interact to facilitate TH17 cell entry into tissues and promote inflammation.