PICALM, a clathrin adaptor protein, plays important roles in clathrin-mediated endocytosis in all cell types. Recently, genome-wide association studies identified single nucleotide polymorphisms in PICALM gene as genetic risk factors for late-onset Alzheimer disease (LOAD). We analysed by western blotting with several anti-PICALM antibodies the pattern of expression of PICALM in human brain extracts. We found that PICALM was abnormally cleaved in AD samples and that the level of the uncleaved 65-75 kDa full-length PICALM species was significantly decreased in AD brains. Cleavage of human PICALM after activation of endogenous calpain or caspase was demonstrated in vitro. Immunohistochemistry revealed that PICALM was associated in situ with neurofibrillary tangles, co-localising with conformationally abnormal and hyperphosphorylated tau in LOAD, familial AD and Down syndrome cases. PHF-tau proteins co-immunoprecipitated with PICALM. PICALM was highly expressed in microglia in LOAD. These observations suggest that PICALM is associated with the development of AD tau pathology. PICALM cleavage could contribute to endocytic dysfunction in AD.

Enlarged early endosomes have been observed in neurons and fibroblasts in Down syndrome (DS). These endosome abnormalities have been implicated in the early development of Alzheimer's disease (AD) pathology in these subjects. Here, we show the presence of enlarged endosomes in blood mononuclear cells and lymphoblastoid cell lines (LCLs) from individuals with DS using immunofluorescence and confocal microscopy. Genotype-phenotype correlations in LCLs carrying partial trisomies 21 revealed that triplication of a 2.56 Mb locus in 21q22.11 is associated with the endosomal abnormalities. This locus contains the gene encoding the phosphoinositide phosphatase synaptojanin 1 (SYNJ1), a key regulator of the signalling phospholipid phosphatidylinositol-4,5-biphosphate that has been shown to regulate clathrin-mediated endocytosis. We found that SYNJ1 transcripts are increased in LCLs from individuals with DS and that overexpression of SYNJ1 in a neuroblastoma cell line as well as in transgenic mice leads to enlarged endosomes. Moreover, the proportion of enlarged endosomes in fibroblasts from an individual with DS was reduced after silencing SYNJ1 expression with RNA interference. In LCLs carrying amyloid precursor protein (APP) microduplications causing autosomal dominant early-onset AD, enlarged endosomes were absent, suggesting that APP overexpression alone is not involved in the modification of early endosomes in this cell type. These findings provide new insights into the contribution of SYNJ1 overexpression to the endosomal changes observed in DS and suggest an attractive new target for rescuing endocytic dysfunction and lipid metabolism in DS and in AD.

The transcription factor Elk-1 plays a key role in cell differentiation, proliferation and apoptosis. This role is thought to arise from its phosphorylation by activated extracellular signal-regulated kinases (ERKs), a critical posttranslational event for the transcriptional activity of the ternary complex composed of Elk-1 and a dimer of serum response factor (SRF) at the serum response element (SRE) regulatory site of transcription. In addition to its nuclear localization, Elk-1 is found in the dendrites and soma of neuronal cells and recent evidence implicate a cytoplasmic proapoptotic function of Elk-1, via its association with the mitochondrial permeability transition pore complex. Thus, the nuclear versus cytoplasmic localization of Elk-1 seems to be crucial for its biological function. In this study we show that the excitatory neurotransmitter, glutamate, induces an ERK-dependent Elk-1 activation and nuclear relocalization. We demonstrate that Elk-1 phosphorylation on Ser383/389 has a dual function and triggers both Elk-1 nuclear translocation and SRE-dependent gene expression. Mutating these sites into inactive residues or using a synthetic penetrating peptide (TAT-DEF-Elk-1), which specifically interferes with the DEF docking domain of Elk-1, prevents Elk-1 nuclear translocation without interfering with ERK nor MSK1 (mitogenand stress-activated protein kinase 1), a CREB kinase downstream from ERK-activation. This results in a differential regulation of glutamate-induced IEG regulation when compared with classical inhibitors of the ERK pathway. Using the TAT-DEF-Elk-1 peptide or the dominant-negative version of Elk-1, we show that Elk-1 phosphorylation controls dendritic elongation, SRF and Actin expression levels as well as cytoskeleton dynamics.

Chromatin remodelling is thought to play a key role in gene regulation that underlies long-term synaptic plasticity and memory formation. The dynamic process of chromatin remodelling requires post-translational modifications of histones, a group of highly basic proteins that are tightly linked to DNA. In the present study, we investigated histone H3 modifications in response to glutamate stimulation leading to c-Fos and c-Jun induction in an in vitro model system of striatal neurons in culture. Intracellular signalling pathways implicated in these modifications were analysed. Histone H3 acetylation was strong in basal conditions and unmodified by glutamate treatment. By contrast, glutamate induced a strong phosphorylation of histone H3 that was inhibited by selective inhibitors of the extracellular signal-regulated kinase (ERK) and p38 mitogen-activated protein kinase (p38 MAPK) pathways, U0126 and SB203580, respectively. Blocking activation of mitogen-and stress-activated kinase 1 (MSK1), a kinase downstream ERK and p38 MAPK, by pharmacological approach or using striatal cells from MSK1 deficient mice, totally abolished H3 phosphorylation, as well as c-Fos and c-Jun induction. Chromatin immunoprecipitation assays confirmed increased levels of phosphorylated H3 at the c-jun promoter. Altogether, our data highlight the crucial role of MSK1 in the nucleosomal response necessary for gene induction in neuronal cells. Keywords: chromatin immunoprecipitation, extracellular signal-regulated kinase and p38mitogen-activated protein kinase, glutamate, histone H3, immediate early gene, mitogen and stress-activated kinase-1, striatal neurons.

Despite its low chemical reactivity, the noble gas xenon possesses a remarkable spectrum of biological effects. In particular, xenon is a strong neuroprotectant in preclinical models of hypoxic-ischemic brain injury. In this study, we wished to determine whether xenon retained its neuroprotective potential in experimental settings that model the progressive loss of midbrain dopamine (DA) neurons in Parkinson's disease. Using rat midbrain cultures, we established that xenon was partially protective for DA neurons through either direct or indirect effects on these neurons. So, when DA neurons were exposed to L-trans-pyrrolidine-2,4-dicarboxylic acid so as to increase ambient glutamate levels and generate slow and sustained excitotoxicity, the effect of xenon on DA neurons was direct. The vitamin E analog Trolox also partially rescued DA neurons in this setting and enhanced neuroprotection by xenon. However, in the situation where DA cell death was spontaneous, the protection of DA neurons by xenon appeared indirect as it occurred through the repression of a mechanism mediated by proliferating glial cells, presumably astrocytes and their precursor cells. Xenon also exerted trophic effects for DA neurons in this paradigm. The effects of xenon were mimicked and improved by the N-methyl-Daspartate glutamate receptor antagonist memantine and xenon itself appeared to work by antagonizing N-methyl-Daspartate receptors. Note that another noble gas argon could not reproduce xenon effects. Overall, present data indicate that xenon can provide protection and trophic support to DA neurons that are vulnerable in Parkinson's disease. This suggests that xenon might have some therapeutic value for this disorder.

Noble gases such as xenon and argon have been reported to provide neuroprotection against acute brain ischemic/anoxic injuries. Herein, we wished to evaluate the protective potential of these two gases under conditions relevant to the pathogenesis of chronic neurodegenerative disorders. For that, we established cultures of neurons typically affected in Alzheimer's disease (AD) pathology, that is, cortical neurons and basal forebrain cholinergic neurons and exposed them to L-trans-pyrrolidine-2,4-dicarboxylic acid (PDC) to generate sustained, low-level excitotoxic stress. Over a period of 4 days, PDC caused a progressive loss of cortical neurons which was prevented substantially when xenon replaced nitrogen in the cell culture atmosphere. Unlike xenon, argon remained inactive. Xenon acted downstream of the inhibitory and stimulatory effects elicited by PDC on glutamate uptake and efflux, respectively. Neuroprotection by xenon was mimicked by two noncompetitive antagonists of NMDA glutamate receptors, memantine and ketamine. Each of them potentiated xenon-mediated neuroprotection when used at concentrations providing suboptimal rescue to cortical neurons but most surprisingly, no rescue at all. The survival-promoting effects of xenon persisted when NMDA was used instead of PDC to trigger neuronal death, indicating that NMDA receptor antagonism was probably accountable for xenon’s effects. An excess of glycine failed to reverse xenon neuroprotection, thus excluding a competitive interaction of xenon with the glycine-binding site of NMDA receptors. Noticeably, antioxidants such as Trolox and N-acetylcysteine reduced PDC-induced neuronal death but xenon itself lacked free radical-scavenging activity. Cholinergic neurons were also rescued efficaciously by xenon in basal forebrain cultures. Unexpectedly, however, xenon stimulated cholinergic traits and promoted the morphological differentiation of cholinergic neurons in these cultures. Memantine reproduced some of these neurotrophic effects, albeit with less efficacy than xenon. In conclusion, we demonstrate for the first time that xenon may have a therapeutic potential in AD.

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International audienceXenon is a monatomic gas that belongs to the family of noble gases. Like other noble gases, it is characterized by a filled valence shell and therefore exhibits low chemical reactivity. Paradoxically, xenon possesses a remarkable spectrum of biological effects that are of potential clinical interest. Xenon is an approved anesthetic drug with analgesic properties. In addition to that xenon is neuroprotective in preclinical models of focal and global brain ischemia, spinal cord ischemia and traumatic brain injury. These neuroprotective effects are generally observed at concentrations of xenon ranging from 35 to 75%. Although the activation of ATP-sensitive potassium channels or of two-pore potassium channels may explain some of the neuroprotective effects of xenon, the noble gas appears to work primarily by limiting the overstimulation of N-methyl-D-aspartate (NMDA) glutamate receptors under excitotoxic stress conditions. More specifically, xenon has been reported to compete with glycine, a co-agonist for NMDA receptor activation. Excitotoxic stress mediated through NMDA receptors is most generally associated to acute central nervous system insults such as ischemia and traumatic brain injury, but chronic, low-level overexcitation of these receptors is also a possible contributor to neuronal death in a number of chronic neurodegenerative conditions, including amyotrophic lateral sclerosis, Parkinson's disease and Alzheimer's disease (AD). The implication of excitotoxic stress in AD-mediated neurodegeneration is specifically supported by studies reporting the benefits of treatments with NMDA receptor antagonists in preclinical models of the disease. Of interest, one of these antagonists memantine has also a small beneficial effect on cognitive impairment in AD patients