Recent developments have greatly improved the sensitivity of optical sensors based on metal nanoparticle arrays and single nanoparticles. We introduce the localized surface plasmon resonance (LSPR) sensor and describe how its exquisite sensitivity to size, shape and environment can be harnessed to detect molecular binding events and changes in molecular conformation. We then describe recent progress in three areas representing the most significant challenges: pushing sensitivity towards the single-molecule detection limit, combining LSPR with complementary molecular identification techniques such as surface-enhanced Raman spectroscopy, and practical development of sensors and instrumentation for routine use and high-throughput detection. This review highlights several exceptionally promising research directions and discusses how diverse applications of plasmonic nanoparticles can be integrated in the near future.

Biosensing with plasmonic nanosensors

Alzheimer's disease constitutes a rising threat to public health. Despite extensive research in cellular and animal models, identifying the pathogenic agent present in the human brain and showing that it confers key features of Alzheimer's disease has not been achieved. We extracted soluble amyloid-beta protein (Abeta) oligomers directly from the cerebral cortex of subjects with Alzheimer's disease. The oligomers potently inhibited long-term potentiation (LTP), enhanced long-term depression (LTD) and reduced dendritic spine density in normal rodent hippocampus. Soluble Abeta from Alzheimer's disease brain also disrupted the memory of a learned behavior in normal rats. These various effects were specifically attributable to Abeta dimers. Mechanistically, metabotropic glutamate receptors were required for the LTD enhancement, and N-methyl D-aspartate receptors were required for the spine loss. Co-administering antibodies to the Abeta N-terminus prevented the LTP and LTD deficits, whereas antibodies to the midregion or C-terminus were less effective. Insoluble amyloid plaque cores from Alzheimer's disease cortex did not impair LTP unless they were first solubilized to release Abeta dimers, suggesting that plaque cores are largely inactive but sequester Abeta dimers that are synaptotoxic. We conclude that soluble Abeta oligomers extracted from Alzheimer's disease brains potently impair synapse structure and function and that dimers are the smallest synaptotoxic species.

/pdf/amyloid-beta-protein-dimers-isolated-directly-from-alzheimer-52u9yp8r4h.pdf

Amyloid-beta protein dimers isolated directly from Alzheimer's brains impair synaptic plasticity and memory.

The neuropathological hallmarks of Alzheimer disease (AD) include “positive” lesions such as amyloid plaques and cerebral amyloid angiopathy, neurofibrillary tangles, and glial responses, and “negative” lesions such as neuronal and synaptic loss. Despite their inherently cross-sectional nature, postmortem studies have enabled the staging of the progression of both amyloid and tangle pathologies, and, consequently, the development of diagnostic criteria that are now used worldwide. In addition, clinicopathological correlation studies have been crucial to generate hypotheses about the pathophysiology of the disease, by establishing that there is a continuum between “normal” aging and AD dementia, and that the amyloid plaque build-up occurs primarily before the onset of cognitive deficits, while neurofibrillary tangles, neuron loss, and particularly synaptic loss, parallel the progression of cognitive decline. Importantly, these cross-sectional neuropathological data have been largely validated by longitudinal in vivo studies using modern imaging biomarkers such as amyloid PET and volumetric MRI.

/pdf/neuropathological-alterations-in-alzheimer-disease-2zexumi6x1.pdf

Neuropathological Alterations in Alzheimer Disease

Converging lines of evidence suggest that progressive accumulation of the amyloid beta-protein (A beta) plays a central role in the genesis of Alzheimer's disease, but it was long assumed that A beta had to be assembled into extracellular amyloid fibrils to exert its cytotoxic effects. Over the past decade, data have emerged from the use of synthetic A beta peptides, cell culture models, beta-amyloid precursor protein transgenic mice and human brain to suggest that pre-fibrillar, diffusible assemblies of A beta are also deleterious. Although the precise molecular identity of these soluble toxins remains unsettled, accumulating evidence suggests that soluble forms of A beta are indeed the proximate effectors of synapse loss and neuronal injury. Here we review recent progress in understanding the role of soluble oligomers in Alzheimer's disease.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1471-4159.2006.04426.x

A beta oligomers - a decade of discovery.

A pathological hallmark of Alzheimer's disease is an accumulation of insoluble plaque containing the amyloid-beta peptide of 40-42 amino acid residues. Prefibrillar, soluble oligomers of amyloid-beta have been recognized to be early and key intermediates in Alzheimer's-disease-related synaptic dysfunction. At nanomolar concentrations, soluble amyloid-beta oligomers block hippocampal long-term potentiation, cause dendritic spine retraction from pyramidal cells and impair rodent spatial memory. Soluble amyloid-beta oligomers have been prepared from chemical syntheses, transfected cell culture supernatants, transgenic mouse brain and human Alzheimer's disease brain. Together, these data imply a high-affinity cell-surface receptor for soluble amyloid-beta oligomers on neurons-one that is central to the pathophysiological process in Alzheimer's disease. Here we identify the cellular prion protein (PrP(C)) as an amyloid-beta-oligomer receptor by expression cloning. Amyloid-beta oligomers bind with nanomolar affinity to PrP(C), but the interaction does not require the infectious PrP(Sc) conformation. Synaptic responsiveness in hippocampal slices from young adult PrP null mice is normal, but the amyloid-beta oligomer blockade of long-term potentiation is absent. Anti-PrP antibodies prevent amyloid-beta-oligomer binding to PrP(C) and rescue synaptic plasticity in hippocampal slices from oligomeric amyloid-beta. Thus, PrP(C) is a mediator of amyloid-beta-oligomer-induced synaptic dysfunction, and PrP(C)-specific pharmaceuticals may have therapeutic potential for Alzheimer's disease.

/pdf/cellular-prion-protein-mediates-impairment-of-synaptic-3z7d4gecnb.pdf

Cellular prion protein mediates impairment of synaptic plasticity by amyloid-β oligomers

The basis for memory loss in early Alzheimer9s disease (AD) seems likely to involve synaptic damage caused by soluble Aβ-derived oligomers (ADDLs). ADDLs have been shown to build up in the brain and CSF of AD patients and are known to interfere with mechanisms of synaptic plasticity, acting as gain-of-function ligands that attach to synapses. Because of the correlation between AD dementia and synaptic degeneration, we investigated here the ability of ADDLs to affect synapse composition, structure, and abundance. Using highly differentiated cultures of hippocampal neurons, a preferred model for studies of synapse cell biology, we found that ADDLs bound to neurons with specificity, attaching to presumed excitatory pyramidal neurons but not GABAergic neurons. Fractionation of ADDLs bound to forebrain synaptosomes showed association with postsynaptic density complexes containing NMDA receptors, consistent with observed attachment of ADDLs to dendritic spines. During binding to hippocampal neurons, ADDLs promoted a rapid decrease in membrane expression of memory-related receptors (NMDA and EphB2). Continued exposure resulted in abnormal spine morphology, with induction of long thin spines reminiscent of the morphology found in mental retardation, deafferentation, and prionoses. Ultimately, ADDLs caused a significant decrease in spine density. Synaptic deterioration, which was accompanied by decreased levels of the spine cytoskeletal protein drebrin, was blocked by the Alzheimer9s therapeutic drug Namenda. The observed disruption of dendritic spines links ADDLs to a major facet of AD pathology, providing strong evidence that ADDLs in AD brain cause neuropil damage believed to underlie dementia.

https://www.jneurosci.org/content/jneuro/27/4/796.full.pdf

Aβ Oligomer-Induced Aberrations in Synapse Composition, Shape, and Density Provide a Molecular Basis for Loss of Connectivity in Alzheimer's Disease

The cognitive hallmark of early Alzheimer's disease (AD) is an extraordinary inability to form new memories. For many years, this dementia was attributed to nerve-cell death induced by deposits of fibrillar amyloid β (Aβ). A newer hypothesis has emerged, however, in which early memory loss is considered a synapse failure caused by soluble Aβ oligomers. Such oligomers rapidly block long-term potentiation, a classic experimental paradigm for synaptic plasticity, and they are strikingly elevated in AD brain tissue and transgenic-mouse AD models. The current work characterizes the manner in which Aβ oligomers attack neurons. Antibodies raised against synthetic oligomers applied to AD brain sections were found to give diffuse stain around neuronal cell bodies, suggestive of a dendritic pattern, whereas soluble brain extracts showed robust AD-dependent reactivity in dot immunoblots. Antigens in unfractionated AD extracts attached with specificity to cultured rat hippocampal neurons, binding within dendritic arbors at discrete puncta. Crude fractionation showed ligand size to be between 10 and 100 kDa. Synthetic Aβ oligomers of the same size gave identical punctate binding, which was highly selective for particular neurons. Image analysis by confocal double-label immunofluorescence established that >90% of the punctate oligomer binding sites colocalized with the synaptic marker PSD-95 (postsynaptic density protein 95). Synaptic binding was accompanied by ectopic induction of Arc, a synaptic immediate-early gene, the overexpression of which has been linked to dysfunctional learning. Results suggest the hypothesis that targeting and functional disruption of particular synapses by Aβ oligomers may provide a molecular basis for the specific loss of memory function in early AD.

https://www.jneurosci.org/content/jneuro/24/45/10191.full.pdf

Synaptic Targeting by Alzheimer's-Related Amyloid β Oligomers

Disclosed and claimed herein are compositions comprising ADDL receptors, related compositions, and related methods. ADDL receptors are typically, but perhaps not exclusively, localized at the post-synaptic density (PSD) of neuronal cells. Related compositions include, but are not limited to, compounds that affect, positively or negatively, ADDL binding to neuronal cells, either via one or more receptors localized at the post-synaptic density (PSD) or otherwise. Related methods include, but are not limited to, procedures to screen for compounds that affect, either positively or negatively, ADDL binding to neuronal cells, either via one or more receptors localized at the post-synaptic density (PSD) or otherwise. Other related methods include, but are not limited to, prevention and treatment of ADDL-related diseases, such as Alzheimer's disease, mild cognitive impairment, Down's syndrome, and the like, using compositions that inhibit, block, or otherwise interfere with ADDL binding to one or more receptors localized at the post-synaptic density of neuronal cells.

Compositions Comprising Addl Receptors, Related Compositions, and Related Methods

P3-319 Synaptic targeting by Alzheimer's related abeta oligomers

L'invention concerne des compositions contenant des recepteurs d'ADDL, ainsi que des compositions et des methodes associees. Les recepteurs d'ADDL sont generalement, mais pas exclusivement, localises au niveau de la densite postsynaptique (PSD) des cellules neuronales. Les compositions associees contiennent, entre autres, des composes qui modifient, positivement ou negativement, la liaison des ADDL aux cellules neuronales, soit par l'intermediaire d'au moins un recepteur localise au niveau de la densite postsynaptique (PSD) soit autrement. Les methodes associees comprennent, entre autres, des procedures de criblage de composes qui modifient, soit positivement soit negativement, la liaison des ADDL aux cellules neuronales, soit par l'intermediaire d'au moins un recepteur localise au niveau de la densite postsynaptique (PSD) soit autrement. D'autres methodes associees comprennent, entre autres, la prevention et le traitement de maladies liees aux ADDL, telles que la maladie d'Alzheimer, la deficience cognitive legere, le syndrome de Down et analogues, au moyen de compositions inhibant, bloquant ou entravant d'une autre maniere la liaison des ADDL a au moins un recepteur localise au niveau de la densite postsynaptique des cellules neuronales.

Maria C. Buniel

Papers

Aβ Oligomer-Induced Aberrations in Synapse Composition, Shape, and Density Provide a Molecular Basis for Loss of Connectivity in Alzheimer's Disease

Synaptic Targeting by Alzheimer's-Related Amyloid β Oligomers

Compositions Comprising Addl Receptors, Related Compositions, and Related Methods

P3-319 Synaptic targeting by Alzheimer's related abeta oligomers

Compositions contenant des recepteurs d'addl, compositions et methodes associees