Antoine Ghestem

In vivo recordings of brain activity using organic transistors

In vivo electrophysiological recordings of neuronal circuits are necessary for diagnostic purposes and for brain-machine interfaces. Organic electronic devices constitute a promising candidate because of their mechanical flexibility and biocompatibility. Here we demonstrate the engineering of an organic electrochemical transistor embedded in an ultrathin organic film designed to record electrophysiological signals on the surface of the brain. The device, tested in vivo on epileptiform discharges, displayed superior signal-to-noise ratio due to local amplification compared with surface electrodes. The organic transistor was able to record on the surface low-amplitude brain activities, which were poorly resolved with surface electrodes. This study introduces a new class of biocompatible, highly flexible devices for recording brain activity with superior signal-to-noise ratio that hold great promise for medical applications.

Biochemical Staging of Synucleinopathy and Amyloid Deposition in Dementia With Lewy Bodies

The primary feature of dementia with Lewy bodies (DLB) is the aggregation of alpha-synuclein into characteristic lesions: Lewy bodies (LBs) and Lewy neurites. However, in most of DLB cases, LBs are associated with neurofibrillary tangles and amyloid plaques (both Alzheimer disease [AD]-related lesions). We wanted to determine if this overlap of lesions is statistical, as a result of the late onset of both diseases, or results from a specific physiopathological synergy between synucleinopathy and either tauopathy or amyloid pathology. All patients with DLB from our prospective and multidisciplinary study were analyzed. These cases were compared with cases with pure AD and patients with Parkinson disease and controls. All cases were analyzed thoroughly at the neuropathologic and biochemical levels with a biochemical staging of aggregated &agr;-synuclein, tau, and A&bgr; species. All sporadic cases of DLB were associated with abundant deposits of A&bgr; x-42 that were similar in quality and quantity to those of AD. Amyloid precursor protein (APP) dysfunction is a risk factor for AD as demonstrated by pathogenic mutations and A&bgr; accumulation. The constant and abundant A&bgr; x-42 deposition in sporadic DLB suggests that synucleinopathy is also promoted by APP dysfunction. Therefore, we conclude that APP is a therapeutic target for both AD and DLB.

Progressive decrease of amyloid precursor protein carboxy terminal fragments (APP-CTFs), associated with tau pathology stages, in Alzheimer's disease

Amyloid precursor protein (APP) dysfunction is a key aetiologic agent in Alzheimers disease (AD). The processing of this transmembrane protein generates carboxy terminal fragments (CTFs) upstream of β‐amyloid peptide (Aβ) production. The physiologic significance of APP‐CTFs is still poorly understood, as well as the relationship that could link APP dysfunction and tau pathology in familial and non‐familial AD (non‐FAD). In the present study, we have investigated the quantitative and qualitative changes of APP‐CTFs in different brain areas of non‐demented and demented patients from a prospective and multidisciplinary study. A significant decrease of the five APP‐CTFs was observed, which correlated well with the progression of tau pathology, in most cases with infraclinical AD and AD, either familial or non‐FAD. Furthermore, solubility properties and the ratio between the five bands were also modified, both in the Triton‐soluble and/or ‐insoluble fractions. Together, we show here for the first time a modification directly observed on APP‐CTFs upstream of Aβ products and its relationship with tau pathology, which could reflect the basic aetiological mechanisms of AD.

Phosphorylation of amyloid precursor carboxy-terminal fragments enhances their processing by a gamma-secretase-dependent mechanism

In Alzheimers disease, the complex catabolism of amyloid precursor protein (APP) leads to the production of amyloid-beta (Abeta) peptide, the major component of amyloid deposits. APP is cleaved by beta- and alpha-secretases to generate APP carboxy-terminal fragments (CTFs). Abeta peptide and amyloid intracellular domain are resulting from the cleavage of APP-CTFs by the gamma-secretase. In the present study, we hypothesize that post-translational modification of APP-CTFs could modulate their processing by the gamma-secretase. Inhibition of the gamma-secretase was shown to increase the total amount of APP-CTFs. Moreover, we showed that this increase was more marked among the phosphorylated variants and directly related to the activity of the gamma-secretase, as shown by kinetics analyses. Phosphorylated CTFs were shown to associate to presenilin 1, a major protein of the gamma-secretase complex. The phosphorylation of CTFs at the threonine 668 resulting of the c-Jun N-terminal kinase activation was shown to enhance their degradation by the gamma-secretase. Altogether, our results demonstrated that phosphorylated CTFs can be the substrates of the gamma-secretase and that an increase in the phosphorylation of APP-CTFs facilitates their processing by gamma-secretase.

Adenosine Receptor Antagonists Including Caffeine Alter Fetal Brain Development in Mice

Exposure to adenosine receptor antagonists in utero affects fetal brain development in mice. Adenosine Receptor Antagonists and Fetal Brain Development Neural development is strongly influenced by environmental factors including certain drugs. Little information is available about the effects of adenosine receptor antagonists such as caffeine on neural development. To address this question, Silva et al. added caffeine to the drinking water of female mice throughout pregnancy and lactation. They found that caffeine or an adenosine receptor antagonist that specifically blocks type 2A adenosine receptors delayed the migration of specific populations of neurons during brain maturation, resulting in their delayed insertion into target regions. They then showed that 1-week-old offspring of pregnant mice treated with adenosine receptor antagonists were more susceptible to seizures when exposed to a seizure-inducing agent. They further demonstrated that adult offspring of pregnant mice treated with adenosine receptor antagonists had reduced numbers of certain neuronal types as well as impaired memory on certain types of memory tests. This study raises questions about the effects of adenosine receptor antagonists including caffeine on brain development in humans. Retrospective and longitudinal prospective human studies will be needed to evaluate the consequences of caffeine consumption during pregnancy. Consumption of certain substances during pregnancy can interfere with brain development, leading to deleterious long-term neurological and cognitive impairments in offspring. To test whether modulators of adenosine receptors affect neural development, we exposed mouse dams to a subtype-selective adenosine type 2A receptor (A2AR) antagonist or to caffeine, a naturally occurring adenosine receptor antagonist, during pregnancy and lactation. We observed delayed migration and insertion of γ-aminobutyric acid (GABA) neurons into the hippocampal circuitry during the first postnatal week in offspring of dams treated with the A2AR antagonist or caffeine. This was associated with increased neuronal network excitability and increased susceptibility to seizures in response to a seizure-inducing agent. Adult offspring of mouse dams exposed to A2AR antagonists during pregnancy and lactation displayed loss of hippocampal GABA neurons and some cognitive deficits. These results demonstrate that exposure to A2AR antagonists including caffeine during pregnancy and lactation in rodents may have adverse effects on the neural development of their offspring.

Pin1: a therapeutic target in Alzheimer neurodegeneration.

In Alzheimers disease, the peptidyl prolyl cis/trans isomerase Pin1 binds to phospho-Thr231 on Tau proteins and, hence, is found within degenerating neurons, where it is associated to the large amounts of abnormally phosphorylated Tau proteins. Conversely, Pin1 may restore the tubulin polymerization function of these hyperphosphorylated Tau. In the present work, we investigated, both at the cellular and molecular levels, the role of Pin1 in Alzheimers disease through the study of its interactions with phosphorylated Tau proteins. We also showed that in neuronal cells, Pin1 upregulates the expression of cyclin D1. This, in turn, could facilitate the transition from quiescence to the G1 phase (re-entry in cell cycle) in a neuron and, subsequently, neuronal dedifferentiation and apoptosis. The involvement of Pin1 in the G0/G1 transition in neurons points to its function as a good target for the development of new therapeutic strategies in neurodegenerative disorders.

Changes in interictal spike features precede the onset of temporal lobe epilepsy

One cornerstone event during epileptogenesis is the occurrence of the first spontaneous seizure (SZ1). It is therefore important to identify biomarkers of the network alterations leading to SZ1. In experimental models of temporal lobe epilepsy (TLE), interictal‐like activity (ILA) precedes SZ1 by several days. The goal of this study was to determine whether ILA dynamics bore electrophysiological features signaling the impeding transition to SZ1.

Two-Dimensional Electrophoresis of Tau Mutants Reveals Specific Phosphorylation Pattern Likely Linked to Early Tau Conformational Changes

The role of Tau phosphorylation in neurofibrillary degeneration linked to Alzheimers disease remains to be established. While transgenic mice based on FTDP-17 Tau mutations recapitulate hallmarks of neurofibrillary degeneration, cell models could be helpful for exploratory studies on molecular mechanisms underlying Tau pathology. Here, “human neuronal cell lines” overexpressing Wild Type or mutated Tau were established. Two-dimensional electrophoresis highlights that mutated Tau displayed a specific phosphorylation pattern, which occurs in parallel to the formation of Tau clusters as visualized by electron microscopy. In fact, this pattern is also displayed before Tau pathology onset in a well established mouse model relevant to Tau aggregation in Alzheimers disease. This study suggests first that pathological Tau mutations may change the distribution of phosphate groups. Secondly, it is possible that this molecular event could be one of the first Tau modifications in the neurofibrillary degenerative process, as this phenomenon appears prior to Tau pathology in an in vivo model and is linked to early steps of Tau nucleation in Tau mutants cell lines. Such cell lines consist in suitable and evolving models to investigate additional factors involved in molecular pathways leading to whole Tau aggregation.

Predicting and treating stress-induced vulnerability to epilepsy and depression.

Accumulation of stressful events can render individuals susceptible to develop epilepsy and comorbidities. Whether such vulnerability can be predicted and reversed is not known. Here we show that social defeat, although not producing depression by itself, produced in 50% of rats reduced threshold for status epilepticus (SE), accelerated epileptogenesis, and once epilepsy was induced, depression‐like profile and cognitive deficits. Low serum brain‐derived neurotrophic factor (BDNF) levels measured before SE identified this vulnerable population. Treatment with a BDNF analog before SE prevented the occurrence of comorbidities. Thus, vulnerability to comorbidities after epilepsy onset due to unresolved past stressful events may be predicted and reversed. Ann Neurol 2015;78:128–136

Tau pathology modulates Pin1 post-translational modifications and may be relevant as biomarker

A prerequisite to dephosphorylation at Ser-Pro or Thr-Pro motifs is the isomerization of the imidic peptide bond preceding the proline. The peptidyl-prolyl cis/trans isomerase named Pin1 catalyzes this mechanism. Through isomerization, Pin1 regulates the function of a growing number of targets including the microtubule-associated tau protein and is supposed to be deregulated Alzheimers disease (AD). Using proteomics, we showed that Pin1 is posttranslationally modified on more than 5 residues, comprising phosphorylation, N-acetylation, and oxidation. Although Pin1 expression remained constant, Pin1 posttranslational two-dimensional pattern was modified by tau overexpression in a tau-inducible neuroblastoma cell line, in our THY-Tau22 mouse model of tauopathy as well as in AD. Interestingly, in all of these systems, Pin1 modifications were very similar. In AD brain tissue when compared with control, Pin1 is hyperphosphorylated at serine 16 and found in the most insoluble hyperphosphorylated tau fraction of AD brain tissue. Furthermore, in all tau pathology conditions, acetylation of Pin1 may also contribute to the differences observed. In conclusion, Pin1 displays several posttranslational modifications, which are specific in tauopathies and may be useful as biomarker.