T cell mediated cerebral hemorrhages and microhemorrhages during passive Aβ immunization in APPPS1 transgenic mice

<p>Abstract</p> <p>Background</p> <p>Immunization against amyloid-β (Aβ), the peptide that accumulates in the form of senile plaques and in the cerebrovasculature in Alzheimer's disease (AD), causes a dramatic immune response that prevents plaque formation and clears accumulated Aβ in transgenic mice. In a clinical trial of Aβ immunization, some patients developed meningoencephalitis and hemorrhages. Neuropathological investigations of patients who died after the trial showed clearance of amyloid pathology, but also a powerful immune response involving activated T cells probably underlying the negative effects of the immunization.</p> <p>Results</p> <p>To define the impact of T cells on this inflammatory response we used passive immunization and adoptive transfer to separate the effect of IgG and T cell mediated effects on microhemorrhage in APPPS1 transgenic mice. Neither anti Aβ IgG nor adoptively transferred T cells, alone, led to increased cerebrovascular damage. However, the combination of adoptively transferred T cells and passive immunization led to massive cerebrovascular bleeding that ranged from multiple microhemorrhages in the parenchyma to large hematomas.</p> <p>Conclusions</p> <p>Our results indicate that vaccination can lead to Aβ and T cell induced cerebral micro-hemorrhages and acute hematomas, which are greatly exacerbated by T cell mediated activity.</p

A reporter of local dendritic translocation shows plaque- related loss of neural system function in APP-transgenic mice

Although neuronal communication is thought to be summated within local dendritic segments, no technique is currently available to monitor activity in vivo at this level of resolution. To overcome this challenge, we developed an optical reporter of neuronal activity utilizing the coding sequence of Venus, flanked by short stretches of the 5' and 3' untranslated regions from CAMKIIα. This reporter takes advantage of the fact that CAMKIIα mRNA is transported to the dendrite and locally translated in an activity dependent manner (Aakalu et al., 2001). Using adeno associated virus (AAV), we used this reporter to study neuronal activity in adult mice. Exposure of the mice to an enriched environment led to enhancement of Venus expression in dendritic segments of somatosensory cortex, demonstrating in vivo that dendritic mRNA translocation and local transcription occur in response to physiologically relevant stimuli. We then utilized this system to examine the impact of Alzheimer related local amyloid-β deposits on neural system function, to test the hypothesis that plaques are toxic. In APPswe/PS1d9 (APP/PS1) mice, neurons close to plaques, and dendritic segments close to plaques, both showed diminished fluorescent intensity and therefore neuronal activity. In contrast to wildtype mice, fluorescent intensity in neurons near plaques in transgenic mice did not increase after environmental enrichment. These data indicate that neuronal activity in dendritic segments and neurons in the vicinity of a plaque is decreased compared to wildtype mice, supporting the idea that plaques are a focal lesion leading to impaired neural system function

Rapid appearance and local toxicity of amyloid-beta plaques in a mouse model of Alzheimer's disease

Senile plaques accumulate over the course of decades in the brains of patients with Alzheimer’s disease. A fundamental tenet of the amyloid hypothesis of Alzheimer’s disease is that the deposition of amyloid-β precedes and induces the neuronal abnormalities that underlie dementia(1). This idea has been challenged, however, by the suggestion that alterations in axonal trafficking and morphological abnormalities precede and lead to senile plaques(2). The role of microglia in accelerating or retarding these processes has been uncertain. To investigate the temporal relation between plaque formation and the changes in local neuritic architecture, we used longitudinal in vivo multiphoton microscopy to sequentially image young APPswe/PS1d9xYFP (B6C3-YFP) transgenic mice(3). Here we show that plaques form extraordinarily quickly, over 24 h. Within 1–2 days of a new plaque’s appearance, microglia are activated and recruited to the site. Progressive neuritic changes ensue, leading to increasingly dysmorphic neurites over the next days to weeks. These data establish plaques as a critical mediator of neuritic pathology

Impaired spine stability underlies plaque-related spine loss in an Alzheimer's disease mouse model

Dendritic spines, the site of most excitatory synapses in the brain, are lost in Alzheimer’s disease and in related mouse models, undoubtedly contributing to cognitive dysfunction. We hypothesized that spine loss results from plaque-associated alterations of spine stability, causing an imbalance in spine forma-tion and elimination. To investigate effects of plaques on spine stability in vivo, we observed cortical neu-rons using multiphoton microscopy in a mouse model of amyloid pathology before and after extensive plaque deposition. We also observed age-matched non-transgenic mice to study normal effects of aging on spine plasticity. We found that spine density and struc-tural plasticity are maintained during normal aging. Tg2576 mice had normal spine density and plasticity before plaques appeared, but after amyloid pathology is established, severe disruptions were observed. In con-trol animals, spine formation and elimination were equivalent over 1 hour of observation (5 % of observed spines), resulting in stable spine density. However, in aged Tg2576 mice spine elimination increased, specifi-cally in the immediate vicinity of plaques. Spine forma-tion was unchanged, resulting in spine loss. These data show a small population of rapidly changing spines in adult and even elderly mouse cortex; further, in the vicinity of amyloid plaques, spine stability is markedly impaired leading to loss of synaptic structural in

Piezo1 integration of vascular architecture with physiological force

The mechanisms by which physical forces regulate endothelial cells to determine the complexities of vascular structure and function are enigmatic¹⁻⁵. Studies of sensory neurons have suggested Piezo proteins as subunits of Ca²⁺-permeable non-selective cationic channels for detection of noxious mechanical impact⁶⁻⁸. Here we show Piezo1 (Fam38a) channels as sensors of frictional force (shear stress) and determinants of vascular structure in both development and adult physiology. Global or endothelial-specific disruption of mouse Piezo1 profoundly disturbed the developing vasculature and was embryonic lethal within days of the heart beating. Haploinsufficiency was not lethal but endothelial abnormality was detected in mature vessels. The importance of Piezo1 channels as sensors of blood flow was shown by Piezo1 dependence of shear-stress-evoked ionic current and calcium influx in endothelial cells and the ability of exogenous Piezo1 to confer sensitivity to shear stress on otherwise resistant cells. Downstream of this calcium influx there was protease activation and spatial reorganization of endothelial cells to the polarity of the applied force. The data suggest that Piezo1 channels function as pivotal integrators in vascular biology

Passive immunotherapy rapidly increases structural plasticity in a mouse model of Alzheimer disease

Senile plaque-associated changes in neuronal connectivity such as altered neurite trajectory, dystrophic swellings, and synapse and dendritic spine loss are thought to contribute to cognitive dysfunction in Alzheimer’s disease and mouse models. Immunotherapy to remove amyloid beta is a promising therapy that causes recovery of neurite trajectory and dystrophic neurites over a period of days. The acute effects of immunotherapy on neurite morphology at a time point when soluble amyloid has been cleared but dense plaques are not yet affected are unknown. To examine whether removal of soluble amyloid β (Aβ) has a therapeutic effect on dendritic spines, we explored spine dynamics within one hour of applying a neutralizing anti Aβ antibody. This acute treatment caused a small but significant increase in dendritic spine formation in PDAPP brain far from plaques, without affecting spine plasticity near plaques or average dendritic spine density. These data support the hypothesis that removing toxic soluble forms of amyloid-beta rapidly increases structural plasticity possibly allowing functional recovery of neural circuits

Monitoring protein aggregation and toxicity in Alzheimer's disease mouse models using in vivo imaging

Aggregation of amyloid beta peptide into senile plaques and hyperphosphorylated tau protein into neurofibrillary tangles in the brain are the pathological hallmarks of Alzheimer’s disease. Despite over a century of research into these lesions, the exact relationship between pathology and neurotoxicity has yet to be fully elucidated. In order to study the formation of plaques and tangles and their effects on the brain, we have applied multiphoton in vivo imaging of transgenic mouse models of Alzheimer’s disease. This technique allows longitudinal imaging of pathological aggregation of proteins and the subsequent changes in surrounding neuropil neurodegeneration and recovery after therapeutic interventions

Rare coding variants in PLCG2, ABI3, and TREM2 implicate microglial-mediated innate immunity in Alzheimer's disease

We identified rare coding variants associated with Alzheimer’s disease (AD) in a 3-stage case-control study of 85,133 subjects. In stage 1, 34,174 samples were genotyped using a whole-exome microarray. In stage 2, we tested associated variants (P<1×10-4) in 35,962 independent samples using de novo genotyping and imputed genotypes. In stage 3, an additional 14,997 samples were used to test the most significant stage 2 associations (P<5×10-8) using imputed genotypes. We observed 3 novel genome-wide significant (GWS) AD associated non-synonymous variants; a protective variant in PLCG2 (rs72824905/p.P522R, P=5.38×10-10, OR=0.68, MAFcases=0.0059, MAFcontrols=0.0093), a risk variant in ABI3 (rs616338/p.S209F, P=4.56×10-10, OR=1.43, MAFcases=0.011, MAFcontrols=0.008), and a novel GWS variant in TREM2 (rs143332484/p.R62H, P=1.55×10-14, OR=1.67, MAFcases=0.0143, MAFcontrols=0.0089), a known AD susceptibility gene. These protein-coding changes are in genes highly expressed in microglia and highlight an immune-related protein-protein interaction network enriched for previously identified AD risk genes. These genetic findings provide additional evidence that the microglia-mediated innate immune response contributes directly to AD development