M. Azhar Chishti

Aβ peptide immunization reduces behavioural impairment and plaquesin a model of Alzheimer's disease

Much evidence indicates that abnormal processing and extracellular deposition of amyloid-β peptide (Aβ), a proteolytic derivative of the β-amyloid precursor protein (βAPP), is central to the pathogenesis of Alzheimers disease (reviewed in ref. 1). In the PDAPP transgenic mouse model of Alzheimers disease, immunization with Aβ causes a marked reduction in burden of the brain amyloid. Evidence that Aβ immunization also reduces cognitive dysfunction in murine models of Alzheimers disease would support the hypothesis that abnormal Aβ processing is essential to the pathogenesis of Alzheimers disease, and would encourage the development of other strategies directed at the ‘amyloid cascade’. Here we show that Aβ immunization reduces both deposition of cerebral fibrillar Aβ and cognitive dysfunction in the TgCRND8 murine model of Alzheimers disease without, however, altering total levels of Aβ in the brain. This implies that either a ∼50% reduction in dense-cored Aβ plaques is sufficient to affect cognition, or that vaccination may modulate the activity/abundance of a small subpopulation of especially toxic Aβ species.

In vivo reduction of amyloid-β by a mutant copper transporter

Cu ions have been suggested to enhance the assembly and pathogenic potential of the Alzheimers disease amyloid-β (Aβ) peptide. To explore this relationship in vivo, toxic-milk (txJ) mice with a mutant ATPase7b transporter favoring elevated Cu levels were analyzed in combination with the transgenic (Tg) CRND8 amyloid precursor protein mice exhibiting robust Aβ deposition. Unexpectedly, TgCRND8 mice homozygous for the recessive txJ mutation examined at 6 months of age exhibited a reduced number of amyloid plaques and diminished plasma Aβ levels. In addition, homozygosity for txJ increased survival of young TgCRND8 mice and lowered endogenous CNS Aβ at times before detectable increases in Cu in the CNS. These data suggest that the beneficial effect of the txJ mutation on CNS Aβ burden may proceed by a previously undescribed mechanism, likely involving increased clearance of peripheral pools of Aβ peptide.

Transgenic mouse models of Alzheimer’s disease

1. IntroductionAlzheimer’s disease has a well-de¢ned neuropatho-logic pro¢le which includes a surfeit of extracellularamyloid deposits (comprised mainly of the AL pep-tide derived by endoproteolysis of the L-amyloid pre-cursor protein (APP)), accretion of intracellular neu-ro¢brillary tangles (NFTs), comprised mainly ofhyperphosphorylated forms of the microtubule-asso-ciated protein tau (d), reduced synaptic density, andloss of cholinergic neurons of the basal forebrain(reviewed in [1]). The disease clearly has a complexetiology, existing in early- and late-onset familialforms (‘FAD’, familial Alzheimer’s disease) in addi-tion to manifestation in a common sporadic (idio-pathic) form. Linkage and positional cloning strat-egies exploiting FAD kindreds have so far de¢nedthree genes associated with FAD, the substrates fortransgenic modelling of AD. These are APP on chro-mosome 21 [2], presenilin 1 (PS1) on chromosome 14[3] and presenilin 2 (PS2) on chromosome 1 [4,5]. Afourth FAD locus is believed to be located on chro-mosome 12, with the alpha 2 macroglobulin genebeing a locus under consideration [6]. The O4 alleleof the apoE gene [7], a modi¢er associated with late-onset AD, is located on chromosome 19. Together,these observations have been taken to indicate bothenvironmental and genetic risk factors triggering achain of events which converge at a ¢nal pathogenicpathway leading to the stereotypic neuropathology[8].The relative importance of amyloid deposition andtangle formation in AD pathogenesis have been in-tensely debated, with proponents of two campsdubbed as ‘baptists’ and ‘tauists’, respectively. Muta-tions in the APP gene in FAD kindreds, early accu-mulation of amyloid deposits in Down’s syndromepatients (where the APP gene is triplicated) prior tothe onset of frank dementia [9], and toxic eiects ofAL in cell culture paradigms [10] comprised earlydata in favor of the baptists. Additionally, the in-creased level of AL during normal aging is correlatedwith cognitive deterioration in rodents (rats [11],mice [12^15]), non-human primates [16,17], and hu-mans [18,19]. Conversely, tauists have cited poor cor-relations between amyloid burden and cognitive de-cline in the elderly and a good correlation with tangleformation [20]. As described below, recent biochem-ical and genetic studies have continued to provideevidence in favor of AL peptide as a key player inAD pathogenesis, with the corollary that transgenicapproaches to AD have been highly skewed towardsAPP and interacting genes (i.e. presenilins). On theother hand, the concept of an important pathological

Accumulation of Filamentous Tau in the Cerebral Cortex of Human Tau R406W Transgenic Mice

Missense mutations of the tau gene cause autosomal dominant frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17), an illness characterized by progressive personality changes, dementia, and parkinsonism. There is prominent frontotemporal lobe atrophy of the brain accompanied by abundant tau accumulation with neurofibrillary tangles and neuronal cell loss. Using a hamster prion protein gene expression vector, we generated several independent lines of transgenic (Tg) mice expressing the longest form of the human four-repeat tau with the R406W mutation associated with FTDP-17. The TgTauR406W 21807 line showed tau accumulation beginning in the hippocampus and amygdala at 6 months of age, which subsequently spread to the cortices and subcortical areas. The accumulated tau was phosphorylated, ubiquitinated, conformationally changed, argyrophilic, and sarcosyl-insoluble. Activation of GSK-3beta and astrocytic induction of mouse tau were observed. Astrogliosis and microgliosis correlated with prominent tau accumulation. Electron microscopic examination revealed the presence of straight filaments. Behavioral tests showed motor disturbances and progressive acquired memory loss between 10 to 12 months of age. These findings suggested that TgTauR406W mice would be a useful model in the study of frontotemporal dementia and other tauopathies such as Alzheimers disease (AD).

Brain levels of CDK5 activator p25 are not increased in Alzheimer's or other neurodegenerative diseases with neurofibrillary tangles

Elevated levels of p25 and constitutive activation of CDK5 have been observed in AD brains. This has led to the hypothesis that increased p25 levels could promote neurofibrillary tangles (NFT) through CDK5‐mediated hyperphosphorylation of tau, the principal component of NFTs. We examined p25 immunoreactivity in brains from sporadic and familial AD cases, as well as other neurologic diseases that exhibit NFT, such as Downs syndrome (DS), Picks disease (Pick), corticobasal degeneration (CBD), progressive supranuclear palsy (PSP), frontotemporal dementia (FTD). Neither the p25 immunoreactivity nor the p25/p35 ratio was elevated in the AD brains or in the other tauopathies (n = 34) compared with controls (n = 11). Although Aβ peptides have been suggested to activate calpain‐mediated cleavage of p35 to p25 in cultured neurons, p25 levels in brains of TgCRND8 mice, which express high levels of brain Aβ peptides, were similar to those of non‐Tg littermates. Our data suggest that high Aβ levels in brain do not activate p35 proteolysis, and p25 is unlikely to be a causative agent for NFT formation in AD or other tauopathies.

Syrian hamster prion protein (PrPC) is expressed in photoreceptor cells of the adult retina

PrP(C), the cellular isoform of the prion protein (PrP) serves as a precursor to abnormal PrP isoforms which accumulate in diseases such as scrapie in sheep, and Creutzfeldt-Jakob disease in humans. Since prions can replicate in photoreceptors we surmised that PrP(C) must be expressed in these cells. Accordingly, monoclonal antisera directed against two epitopes of hamster PrP(C) produced retinal immunostaining in hamsters, and in mice bearing a hamster PrP transgene. Immunostaining was most prominent in the inner and outer segments of rod photoreceptors, coinciding with the earliest site of pathologic changes in scrapie-infected hamsters. These data define PrP(C) expression in an experimentally-accessible population of neurons and suggest that the retina may comprise a useful system for studying the biology of wild-type and mutant prion proteins.

Mouse Model for Alzheimer’s Disease

Transgenic mouse models for Alzheimer’s disease (AD) are now extensively used to understand the physiological and biochemical mechanisms of the disease as well as to discover new potential therapeutics. The identification of disease-causing mutations in proteins such as amyloid precursor protein (APP) and presenilins (PS1 and PS2) as well as pathogenic mutations in the tau protein has led to the creation of several transgenic mice including those expressing bigenic and trigenic constructs. Each model has unique pathologies that provide insight into disease mechanisms and features of neuropathologies and cognitive functions. Therapeutic hypotheses are now testable in these transgenic mice and the effectiveness of these therapeutics is testable in preclinical and clinical trials in AD patients. A number of therapeutic approaches including active and passive immunization, small molecule monoclonal antibodies, and nonviral DNA vaccines are available. It is hoped that in the near future a treatment for AD will be available as a result of these advancements.

Aβ vaccination of a genetic model of Alzheimer's disease

Abstract Alzheimers disease (AD), the pathological hallmarks of which are amyloid plaques, neurofibrillary tangles and neuronal loss, is the most common dementia in elderly persons. To date, much evidence supports the hypothesis that the excess extracellular deposition of amyloid β-peptide (Aβ) is the most likely initiator of the pathogenesis of the disease. Recently, immunization of Aβ in PDAPP transgenic mouse model of AD was reported to reduce the burden of amyloid in the central nervous system. We show here that immunization results in an ∼50% reduction in dense-core amyloid plaques and an improvement in cognitive impairment in both the young and old TgCRND8 murine model of AD, without changing the total amount of Aβ in the brain. The induced sera had strong immunoreactivity with dense-cored Aβ plaques, not with the amyloid precursor protein, and reduced Aβ fibril formation and cytotoxicity of Aβ in vitro. These findings suggest that immunization may be a potential therapy, although undesirable immune reactions must be avoided.