Beatrice Terni

Mitochondrial ATP-Synthase in the Entorhinal Cortex Is a Target of Oxidative Stress at Stages I/II of Alzheimer's Disease Pathology

Oxidative stress has been implicated in the pathogenesis of several neurodegenerative diseases including Alzheimers disease (AD). Several proteins have been identified as targets of oxidative damage in AD dementia (usually stages V/VI of Braak) and in subjects with mild cognitive impairment associated with middle stages of AD pathology (stage IV of Braak). In this study, we investigate whether brain proteins are locally modified by oxidative stress at the first stages of AD‐related pathology when morphological lesions are restricted to the entorhinal and transentorhinal cortices of neurofibrillary pathology (stages I/II of Braak). Using a proteomic approach, we show that the α subunit of the mitochondrial adenosine triphosphate (ATP)‐synthase is distinctly lipoxidized in the entorhinal cortex at Braak stages I/II compared with age‐matched controls. In addition, ATP‐synthase activity is significantly lower in Braak stages I/II than age‐matched control, while electron transport chain, expressed by the mitochondrial complex I activity, remains not affected. This is the first study showing oxidative damage in the first stage, and clinically silent period, of AD‐related pathology characterized by entorhinal and transentorhinal tauopathy.

Frontotemporal Dementia with Tau Pathology

Tau is a microtubule-associated protein involved in microtubule assembly and stabilization. Filamentous deposits made of tau constitute a major defining characteristic of several neurodegenerative diseases known as tauopathies including Alzheimer’s disease. The involvement of tau in neurodegeneration has been clarified by the identification of genetic mutations in the tau gene in cases with familial frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17). Although the mechanism through which tau mutations lead to neuronal death is still unresolved, it is clear that tau mutations lead to formation of tau filaments that have a different morphology, contain different types of tau isoforms and produce distinct tau deposits. The range of tau pathology identified in FTDP-17 recapitulates the tau pathology present in sporadic tauopathies and indicates that tau dysfunction plays a major role also in these diseases.

Mutant ubiquitin and p62 immunoreactivity in cases of combined multiple system atrophy and Alzheimer's disease.

Recent studies have shown the co-existence of α-synuclein and phosphorylated tau (pTau) in several neurodegenerative diseases. Here, we report two autopsy cases of combined multiple system atrophy (MSA) and Alzheimer’s disease (AD). In both cases, abundant α-synuclein-positive glial and neuronal cytoplasmic inclusions were found in the brainstem, amygdala and hippocampal formation. pTau-positive neurofibrillary tangles (NFTs) were widely distributed in case 1 (Braak stage VI) and moderate in case 2 (Braak stage III). Although α-synuclein and pTau pathology co-occurred in the hippocampus and entorhinal cortex, only a few neurons showed co-existence of these two proteins. Immunoreactivity for p62, a ubiquitin proteasome system related protein, was found in the majority of NFTs, but in only a small proportion of neuronal α-synuclein inclusions. In addition, UBB+1, a mutant form of ubiquitin and a marker for proteasomal dysfunction, was present in the majority of NFTs, whereas co-existence of α-synuclein and UBB+1 was found in only a few neurons. These findings indicate that α-synuclein and phosphorylated tau co-occur in certain brain regions in cases of combined MSA and AD and that the proteasomal pathways differ between α-synuclein- and pTau-bearing neurons.

SPARC triggers a cell-autonomous program of synapse elimination

Significance Neuronal circuits require eliminating the excess of synaptic connectivity to acquire complete functionality. Here we show that secreted protein acidic and rich in cysteine (SPARC), a molecule secreted exclusively by glia, is a trigger for synapse elimination. Acting through a region located in its C-terminal domain, SPARC activates synapse disassembly and formation of retracted axon terminals in cholinergic neurons in vitro. The onset of this cell-autonomous program in the tails of living tadpoles drives a loss of motor innervation, causing transient paralysis. We propose that along with their well-established role in ending the process of synapse elimination by engulfing retracted terminals, glia can also act as a trigger through the release of specific molecules, such as SPARC. Elimination of the excess synaptic contacts established in the early stages of neuronal development is required to refine the function of neuronal circuits. Here we investigate whether secreted protein acidic and rich in cysteine (SPARC), a molecule produced by glial cells, is involved in synapse removal. SPARC production peaks when innervation of the rat superior cervical ganglion and the tail of Xenopus tropicalis tadpoles are remodeled. The formation of new cholinergic synapses in autaptic single-cell microcultures is inhibited by SPARC. The effect resides in the C-terminal domain, which is also responsible for triggering a concentration- and time-dependent disassembly of stable cholinergic synapses. The loss of synaptic contacts is associated with the formation of retracted axon terminals containing multivesicular bodies and secondary lysosomes. The biological relevance of in vitro results was supported by injecting the tail of Xenopus tropicalis tadpoles with peptide 4.2, a 20-aa sequence derived from SPARC that mimics full-length protein effects. Swimming was severely impaired at ∼5 h after peptide application, caused by the massive elimination of neuromuscular junctions and pruning of axonal branches. Effects revert by 6 d after injection, as motor innervation reforms. In conclusion, SPARC triggers a cell-autonomous program of synapse elimination in cholinergic neurons that likely occurs when protein production peaks during normal development.

Role of neuron-glia interactions in developmental synapse elimination

During the embryonic development of the nervous system there is a massive formation of synapses. However, the exuberant connectivity present after birth must be pruned during postnatal growth to optimize the function of neuronal circuits. Whilst glial cells play a fundamental role in the formation of early synaptic contacts, their contribution to developmental modifications of established synapses is not well understood. The present review aims to highlight the various roles of glia in the developmental refinement of embryonic synaptic connectivity. We summarize recent evidences linking secretory abilities of glial cells to the disassembly of synaptic contacts that are complementary of a well-established phagocytic role. Considering a theoretical framework, it is discussed how release of glial molecules could be relevant to the developmental refinement of synaptic connectivity. Finally, we propose a three-stage model of synapse elimination in which neurons and glia are functionally associated to timely eliminate synapses.

Acute effect of pore-forming Clostridium perfringens ε-toxin on compound action potentials of optic nerve of mouse

Visual Abstract ε-Toxin is a pore forming toxin produced by Clostridium perfringens types B and D. It is synthesized as a less active prototoxin form that becomes fully active upon proteolytic activation. The toxin produces highly lethal enterotoxaemia in ruminants, has the ability to cross the blood–brain barrier (BBB) and specifically binds to myelinated fibers. We discovered that the toxin induced a release of ATP from isolated mice optic nerves, which are composed of myelinated fibers that are extended from the central nervous system. We also investigated the effect of the toxin on compound action potentials (CAPs) in isolated mice optic nerves. When nerves were stimulated at 100 Hz during 200 ms, the decrease of the amplitude and the area of the CAPs was attenuated in the presence of ε-toxin. The computational modelling of myelinated fibers of mouse optic nerve revealed that the experimental results can be mimicked by an increase of the conductance of myelin and agrees with the pore forming activity of the toxin which binds to myelin and could drill it by making pores. The intimate ultrastructure of myelin was not modified during the periods of time investigated. In summary, the acute action of the toxin produces a subtle functional impact on the propagation of the nerve action potential in myelinated fibers of the central nervous system with an eventual desynchronization of the information. These results may agree with the hypothesis that the toxin could be an environmental trigger of multiple sclerosis (MS).

Tight temporal coupling between synaptic rewiring of olfactory glomeruli and the emergence of odor-guided behavior in Xenopus tadpoles

Olfactory sensory neurons (OSNs) are chemoreceptors that establish excitatory synapses within glomeruli of the olfactory bulb. OSNs undergo continuous turnover throughout life, causing the constant replacement of their synaptic contacts. Using Xenopus tadpoles as an experimental system to investigate rewiring of glomerular connectivity, we show that novel OSN synapses can transfer information immediately after formation, mediating olfactory‐guided behavior. Tadpoles recover the ability to detect amino acids 4 days after bilateral olfactory nerve transection. Restoration of olfactory‐guided behavior depends on the efficient reinsertion of OSNs to the olfactory bulb. Presynaptic terminals of incipient synaptic contacts generate calcium transients in response to odors, triggering long lasting depolarization of olfactory glomeruli. The functionality of reconnected terminals relies on well‐defined readily releasable and cytoplasmic vesicle pools. The continuous growth of non‐compartmentalized axonal processes provides a vesicle reservoir to nascent release sites, which contrasts to the gradual development of cytoplasmic vesicle pools in conventional excitatory synapses. The immediate availability of fully functional synapses upon formation supports an age‐independent contribution of OSNs to the generation of odor maps.

Abnormal Expression and Distribution of MMP2 at Initial Stages of Alzheimer's Disease-Related Pathology.

Previous studies have shown that metalloproteinases (MMPs) participate in the clearance of amyloid-β (Aβ) in Alzheimers disease (AD); MMP2 and MMP3 cleave soluble Aβ, and both MMP9 and MT1-MMP are able to degrade soluble and fibrillar forms of Aβ. The present study shows increased expression levels of active MMP2 in the entorhinal cortex at early stages of AD-related pathology (Braak and Braak stages I/II-0 and III/IV-A) as revealed by western blotting and gelatin zymography. Confocal microscopy discloses co-localization of MMP2 and phospho-tau in neurofibrillary tangles and dystrophic neurites. MMP2 has the capacity to cleave recombinant tau in vitro in a dose-dependent manner, consistent with a physiological function of MMP2 in normal tau proteolysis. However, MMP2 does not cleave hyperphosphorylated and dephosphorylated tau from enriched paired helical filament fractions. These observations raise the possibility that accumulation of MMP2 in neurofibrillary tangles and concomitant loss of proteolytic capacity on tau protein is a response geared to eliminating production of toxic truncated tau species in AD brains.

P3-193: Genotype-phenotype relationship is lacking in families with PS1-Met146Leu founder mutation

and other pathologies in clinically demented and non-demented individuals, although its exact contributions to etiology and clinical expression remain unclear. The NACC neuropathology data are gathered from 30 Alzheimer’s Disease Centers funded by the National Institute on Aging. Objective(s): To describe the occurrence of LB pathology at postmortem study by clinical diagnoses for demented and non-demented NACC database subjects who died between 1999 and 2005. Methods: We used NACC data from individuals with a clinical dementia diagnosis or who were clinically non-demented, who had died between 1999 and 2005, and who received neuropathological examination including assessment of LB pathology (N 3660). Before the late 1990s, LB pathology was likely incompletely assessed until the use of ubiquitin and -synuclein stains became widely available. However, a NACC survey indicated that 90% and 80% of ADCs were using -synuclein or ubiquitin immunohistochemistry, respectively, after 1999. LB pathology was categorized as (1) brainstem predominant; (2) transitional/limbic; (3) diffuse neocortical; (4) unspecified type; or (5) no LB. Cases recorded as “not assessed”, unknown or missing were excluded. Results: LB pathology was recorded in 29%, 32%, and 30% of clinically diagnosed Probable AD, Possible AD and Non-AD dementias, respectively. Across those same diagnostic categories, “diffuse neocortical” LB pathology was the most frequent type, occurring in 11%, 17% and 16%, respectively. LB pathology occurred proportionally more with increasing Braak stage: Braak 0; 18%, I-II: 24%; III-IV: 33%; V-VI; 28%. [p(trend) 0.01]. Among persons with a clinical diagnosis of DLB (with or without probable AD) (n 268), 41% had diffuse neocortical LB and 31% had no LB pathology. Conversely, among individuals without clinically diagnosed DLB (n 3392), 8.6% had diffuse neocortical LB, while 76% had no LB pathology. Conclusions: The large numbers of subjects included in the NACC database allow patterns of LB pathology to be observed. LB pathology appears commonly in both clinically diagnosed AD and non-AD dementias (including clinically unrecognized DLB cases); within LB pathology categories, diffuse neocortical type predominates. LB pathology and Braak stage were significantly associated; possibly resulting from an association between tau protein and alpha-synuclein.