Profound neuronal dysfunction in the entorhinal cortex contributes to early loss of short-term memory in Alzheimer’s disease1–3. Here we show broad neuroprotective effects of entorhinal brain-derived neurotrophic factor (BDNF) administration in several animal models of Alzheimer’s disease, with extension of therapeutic benefits into the degenerating hippocampus. In amyloid-transgenic mice, BDNF gene delivery, when administered after disease onset, reverses synapse loss, partially normalizes aberrant gene expression, improves cell signaling and restores learning and memory. These outcomes occur independently of effects on amyloid plaque load. In aged rats, BDNF infusion reverses cognitive decline, improves age-related perturbations in gene expression and restores cell signaling. In adult rats and primates, BDNF prevents lesion-induced death of entorhinal cortical neurons. In aged primates, BDNF reverses neuronal atrophy and ameliorates age-related cognitive impairment. Collectively, these findings indicate that BDNF exerts substantial protective effects on crucial neuronal circuitry involved in Alzheimer’s disease, acting through amyloid-independent mechanisms. BDNF therapeutic delivery merits exploration as a potential therapy for Alzheimer’s disease.

BackgroundMisfolding and pathological aggregation of neuronal proteins has been proposed to play a critical role in the pathogenesis of neurodegenerative disorders. Alzheimer's disease (AD) and Parkinson's disease (PD) are frequent neurodegenerative diseases of the aging population. While progressive accumulation of amyloid β protein (Aβ) oligomers has been identified as one of the central toxic events in AD, accumulation of α-synuclein (α-syn) resulting in the formation of oligomers and protofibrils has been linked to PD and Lewy body Disease (LBD). We have recently shown that Aβ promotes α-syn aggregation and toxic conversion in vivo, suggesting that abnormal interactions between misfolded proteins might contribute to disease pathogenesis. However the molecular characteristics and consequences of these interactions are not completely clear.Methodology/Principal FindingsIn order to understand the molecular mechanisms involved in potential Aβ/α-syn interactions, immunoblot, molecular modeling, and in vitro studies with α-syn and Aβ were performed. We showed in vivo in the brains of patients with AD/PD and in transgenic mice, Aβ and α-synuclein co-immunoprecipitate and form complexes. Molecular modeling and simulations showed that Aβ binds α-syn monomers, homodimers, and trimers, forming hybrid ring-like pentamers. Interactions occurred between the N-terminus of Aβ and the N-terminus and C-terminus of α-syn. Interacting α-syn and Aβ dimers that dock on the membrane incorporated additional α-syn molecules, leading to the formation of more stable pentamers and hexamers that adopt a ring-like structure. Consistent with the simulations, under in vitro cell-free conditions, Aβ interacted with α-syn, forming hybrid pore-like oligomers. Moreover, cells expressing α-syn and treated with Aβ displayed increased current amplitudes and calcium influx consistent with the formation of cation channels.Conclusion/SignificanceThese results support the contention that Aβ directly interacts with α-syn and stabilized the formation of hybrid nanopores that alter neuronal activity and might contribute to the mechanisms of neurodegeneration in AD and PD. The broader implications of such hybrid interactions might be important to the pathogenesis of other disorders of protein misfolding.

Amyloid β-peptide (Aβ) is postulated to play a central role in the pathogenesis of Alzheimer's disease. We recently proposed a pathway of Aβ-induced toxicity that is APP dependent and involves the facilitation of APP complex formation by Aβ. The APP-dependent component requires cleavage of APP at position 664 in the cytoplasmic domain, presumably by caspases or caspase-like proteases, with release of a potentially cytotoxic C31 peptide. In this study we show that Aβ interacted directly and specifically with membrane-bound APP to facilitate APP homo-oligomerization. Using chimeric APP molecules, this interaction was shown to take place between Aβ and its homologous sequence on APP. Consistent with this finding, we demonstrated that Aβ also facilitated the oligomerization of β-secretase cleaved APP C-terminal fragment (C99). We found that the YENPTY domain in the APP cytoplasmic tail and contained within C31 is critical for this cell death pathway. Deletion or alanine-scanning mutagenesis through this domain significantly attenuated cell death apparently without affecting either APP dimerization or cleavage at position 664. This indicated that sequences within C31 are required after its release from APP. As the YENPTY domain has been shown to interact with a number of cytosolic adaptor molecules, it is possible that the interaction of APP, especially dimeric forms of APP, with these molecules contribute to cell death. Keywords C31; YENPTY region; APP homo-oligomerizationThe accumulation and deposition of amyloid β-protein (Aβ) within senile plaques in brain is one of the histopathological hallmarks of Alzheimer's disease (AD). Aβ is derived by sequential proteolysis from the amyloid precursor protein (APP). Substantial data suggest that Aβ plays a critical role in initiating the cascade of events that results in AD (reviewed in ref 1). In addition to senile plaques and neurofibrillary tangles, synapse loss and neuronal death are consistently observed, and these latter changes have been hypothesized to be due to the increased levels of Aβ in brain (2). Although the traditional view suggests that Aβ assembled into insoluble and fibrillar forms is cytotoxic, increasing evidence indicates that soluble prefibrillar oligomeric Aβ species are equally, if not more, detrimental to neuronal function in vitro and in vivo (2-6). Many varied mechanisms have been proposed for Aβ-induced toxicity, but no consensus has emerged to account for its deleterious effects (7).APP is a type I membrane protein whose function has not been clearly defined. It belongs to a gene family that includes its mammalian paralogs APLP1 and APLP2 (amyloid precursor- NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript like proteins 1, 2) (8-10). APLP1 and APLP2 are also type I membrane proteins and share sequence similarity with APP in the N and C termini, but do not contain the Aβ domain.APP may function as a cell surface receptor and mediate the transduction of extracellular signals into the cell, although a definitive ...

In Alzheimer's disease increasing evidence attributes synaptic and cognitive deficits to soluble oligomers of amyloid β protein (Aβ), even prior to the accumulation of amyloid plaques, neurofibrillary tangles, and neuronal cell death. Here we show that within 1-2 hours picomolar concentrations of cell-derived, soluble Aβ induce specific alterations in pre-and postsynaptic morphology and connectivity in cultured hippocampal neurons. Clusters of presynaptic vesicle markers decreased in size and number at glutamatergic but not GABAergic terminals. Dendritic spines also decreased in number and became dysmorphic, as spine heads collapsed and/or extended long protrusions. Simultaneous time-lapse imaging of axon-dendrite pairs revealed that shrinking spines sometimes became disconnected from their presynaptic varicosity. Concomitantly, miniature synaptic potentials decreased in amplitude and frequency. Spine changes were prevented by blockers of nAChRs and NMDARs. Washout of Aβ within the first day reversed these spine changes. Further, spine changes reversed spontaneously by two days, because neurons acutely developed resistance to continuous Aβ exposure. Thus, rapid Aβ-induced synapse destabilization may underlie transient behavioral impairments in animal models, and early cognitive deficits in Alzheimer's patients.

Prion protein (PrP)Sc , the only known component of the prion, is present mostly in the brains of animals and humans affected with prion diseases. We now show that a protease-resistant PrP isoform can also be detected in the urine of hamsters, cattle, and humans suffering from transmissible spongiform encephalopathies. Most important, this PrP isoform (UPrP Sc ) was also found in the urine of hamsters inoculated with prions long before the appearance of clinical signs. Interestingly, intracerebrally inoculation of hamsters with UPrP Sc did not cause clinical signs of prion disease even after 270 days, suggesting it differs in its pathogenic properties from brain PrP Sc . We propose that the detection of UPrP Sc can be used to diagnose humans and animals incubating prion diseases, as well as to increase our understanding on the metabolism of PrP Sc in vivo.