Nicola J. Corbett

Inactivation of the microRNA-183/96/182 cluster results in syndromic retinal degeneration

The microRNA-183/96/182 cluster is highly expressed in the retina and other sensory organs. To uncover its in vivo functions in the retina, we generated a knockout mouse model, designated “miR-183CGT/GT,” using a gene-trap embryonic stem cell clone. We provide evidence that inactivation of the cluster results in early-onset and progressive synaptic defects of the photoreceptors, leading to abnormalities of scotopic and photopic electroretinograms with decreased b-wave amplitude as the primary defect and progressive retinal degeneration. In addition, inactivation of the miR-183/96/182 cluster resulted in global changes in retinal gene expression, with enrichment of genes important for synaptogenesis, synaptic transmission, photoreceptor morphogenesis, and phototransduction, suggesting that the miR-183/96/182 cluster plays important roles in postnatal functional differentiation and synaptic connectivity of photoreceptors.

Identification of TMEM230 mutations in familial Parkinson's disease

Parkinsons disease is the second most common neurodegenerative disorder without effective treatment. It is generally sporadic with unknown etiology. However, genetic studies of rare familial forms have led to the identification of mutations in several genes, which are linked to typical Parkinsons disease or parkinsonian disorders. The pathogenesis of Parkinsons disease remains largely elusive. Here we report a locus for autosomal dominant, clinically typical and Lewy body–confirmed Parkinsons disease on the short arm of chromosome 20 (20pter-p12) and identify TMEM230 as the disease-causing gene. We show that TMEM230 encodes a transmembrane protein of secretory/recycling vesicles, including synaptic vesicles in neurons. Disease-linked TMEM230 mutants impair synaptic vesicle trafficking. Our data provide genetic evidence that a mutant transmembrane protein of synaptic vesicles in neurons is etiologically linked to Parkinsons disease, with implications for understanding the pathogenic mechanism of Parkinsons disease and for developing rational therapies.

Dendritic spine and synapse morphological alterations induced by a neural cell adhesion molecule mimetic.

The neural cell adhesion molecule (NCAM) is a glycoprotein expressed on the surface of neurons and glial cells. It plays a key role in morphogenesis of the nervous system, regeneration of damaged neural tissue and synaptic plasticity. The extracellular domain of NCAM engages in homophilic interactions (NCAM binding to NCAM) and in heterophilic interactions between NCAM and other proteins such as the fibroblast growth factor (FGF) receptor. It promotes synaptogenesis and activity-dependent remodelling of synapses but less is known of its influence on synaptic and dendritic morphology. Recently, quantitative electron microscopy and 3-dimensional reconstruction (3-D) of ultrathin serial sections has been used to examine the morphology of synapses and dendritic spines in the hippocampus of rats treated with a neural cell adhesion molecule-derived fibroblast growth factor receptor agonist, FGL-peptide (an NCAM mimetic). These data show clearly that the FGL peptide has marked influences on both spine and synaptic form.

Amyloid-Beta Induced CA1 Pyramidal Cell Loss in Young Adult Rats Is Alleviated by Systemic Treatment with FGL, a Neural Cell Adhesion Molecule-Derived Mimetic Peptide

Increased levels of neurotoxic amyloid-beta in the brain are a prominent feature of Alzheimer’s disease. FG-Loop (FGL), a neural cell adhesion molecule-derived peptide that corresponds to its second fibronectin type III module, has been shown to provide neuroprotection against a range of cellular insults. In the present study impairments in social recognition memory were seen 24 days after a 5 mg/15 µl amyloid-beta(25–35) injection into the right lateral ventricle of the young adult rat brain. This impairment was prevented if the animal was given a systemic treatment of FGL. Unbiased stereology was used to investigate the ability of FGL to alleviate the deleterious effects on CA1 pyramidal cells of the amyloid-beta(25–35) injection. NeuN, a neuronal marker (for nuclear staining) was used to identify pyramidal cells, and immunocytochemistry was also used to identify inactive glycogen synthase kinase 3beta (GSK3β) and to determine the effects of amyloid-beta(25–35) and FGL on the activation state of GSK3β, since active GSK3β has been shown to cause a range of AD pathologies. The cognitive deficits were not due to hippocampal atrophy as volume estimations of the entire hippocampus and its regions showed no significant loss, but amyloid-beta caused a 40% loss of pyramidal cells in the dorsal CA1 which was alleviated partially by FGL. However, FGL treatment without amyloid-beta was also found to cause a 40% decrease in CA1 pyramidal cells. The action of FGL may be due to inactivation of GSK3β, as an increased proportion of CA1 pyramidal neurons contained inactive GSK3β after FGL treatment. These data suggest that FGL, although potentially disruptive in non-pathological conditions, can be neuroprotective in disease-like conditions.

Dendritic Spine and Synapse Morphological Alterations Induced by a Neural Cell Adhesion Molecule Mimetic

The neural cell adhesion molecule (NCAM) is a glycoprotein expressed on the surface of neurons and glial cells. It plays a key role in morphogenesis of the nervous system, regeneration of damaged neural tissue and synaptic plasticity. The extracellular domain of NCAM engages in homophilic interactions (NCAM binding to NCAM) and in heterophilic interactions between NCAM and other proteins such as the fibroblast growth factor (FGF) receptor. It promotes synaptogenesis and activity-dependent remodelling of synapses but less is know of its influence on synaptic and dendritic morphology. Recently, quantitative electron microscopy and 3-dimensional reconstruction (3-D) of ultrathin serial sections has been used to examine the morphology of synapses and dendritic spines in the hippocampus of rats treated with a neural cell adhesion molecule-derived fibroblast growth factor receptor agonist, FGL-peptide (an NCAM mimetic). These data show clearly that the FGL peptide has marked influences on both spine and synaptic form.

Store depletion-induced h-channel plasticity rescues a channelopathy linked to Alzheimer’s disease

HIGHLIGHTSAccommodation at perithreshold currents is exacerbated with age in CA1 neurons of ADTg mice.HCN1 is sequestered perisomatically in aged ADTg mice.HCN1 is sequestered as a multimolecular complex with TRIP8b in aged ADTg mice.Ex vivo and in vivo SDh plasticity rescue HCN channel function/mislocalization. ABSTRACT Voltage‐gated ion channels are critical for neuronal integration. Some of these channels, however, are misregulated in several neurological disorders, causing both gain‐ and loss‐of‐function channelopathies in neurons. Using several transgenic mouse models of Alzheimer’s disease (AD), we find that sub‐threshold voltage signals strongly influenced by hyperpolarization‐activated, cyclic nucleotide‐gated (HCN) channels progressively deteriorate over chronological aging in hippocampal CA1 pyramidal neurons. The degraded signaling via HCN channels in the transgenic mice is accompanied by an age‐related global loss of their non‐uniform dendritic expression. Both the aberrant signaling via HCN channels and their mislocalization could be restored using a variety of pharmacological agents that target the endoplasmic reticulum (ER). Our rescue of the HCN channelopathy helps provide molecular details into the favorable outcomes of ER‐targeting drugs on the pathogenesis and synaptic/cognitive deficits in AD mouse models, and implies that they might have beneficial effects on neurological disorders linked to HCN channelopathies.

Tau proteolysis in the pathogenesis of tauopathies: neurotoxic fragments and novel biomarkers

With predictions showing that 131.5 million people worldwide will be living with dementia by 2050, an understanding of the molecular mechanisms underpinning disease is crucial in the hunt for novel therapeutics and for biomarkers to detect disease early and/or monitor disease progression. The metabolism of the microtubule-associated protein tau is altered in different dementias, the so-called tauopathies. Tau detaches from microtubules, aggregates into oligomers and neurofibrillary tangles, which can be secreted from neurons, and spreads through the brain during disease progression. Post-translational modifications exacerbate the production of both oligomeric and soluble forms of tau, with proteolysis by a range of different proteases being a crucial driver. However, the impact of tau proteolysis on disease progression has been overlooked until recently. Studies have highlighted that proteolytic fragments of tau can drive neurodegeneration in a fragment-dependent manner as a result of aggregation and/or transcellular propagation. Proteolytic fragments of tau have been found in the cerebrospinal fluid and plasma of patients with different tauopathies, providing an opportunity to develop these fragments as novel disease progression biomarkers. A range of therapeutic strategies have been proposed to halt the toxicity associated with proteolysis, including reducing protease expression and/or activity, selectively inhibiting protease-substrate interactions, and blocking the action of the resulting fragments. This review highlights the importance of tau proteolysis in the pathogenesis of tauopathies, identifies putative sites during tau fragment-mediated neurodegeneration that could be targeted therapeutically, and discusses the potential use of proteolytic fragments of tau as biomarkers for different tauopathies.

SOLUBLE AMYLOID PRECURSOR PROTEIN α (SAPPα) PROMOTES SYNAPTOGENESIS IN HUMAN-INDUCED PLURIPOTENT STEM CELL-DERIVED NEURONS

oxidase (MAO), membrane bound ATPases, intracellular calcium levels and lipid peroxidation in presence of neuropeptides. Results: The results obtained in the present work revealed that increased activities of antioxidant enzymes, membrane bound ATPases and decrease in level of calcium levels, MAO actiivty and lipid peroxidation in presence of NKB and combined NKB and Ab in vivo estradiol (E2) treated aging rat brain. NKB treatment reversed the beneficial in preventing some of the age related changes in the brain. An in vitro incubation of E2 treated synaptosomes with Ab showed toxic effects on all the parameters, while NKB showed stimulating effects and the combined NKB and Ab showed a partial effects as compared to Ab (25-35) and NKB alone. Conclusions: Present study elucidates an antioxidant, neuromodulatory and neuroprotective role of tachykinin peptide NKB against the beta amyloid induced toxicity in E2 treated female rats. NKB treatment reversed the beneficial in preventing some of the age related changes in the brain.

AMYLOID-β DEGRADATION IN INDUCED PLURIPOTENT STEM CELL (IPSC)-DERIVED NEURONS

C-terminal end of Ng. The present work was aimed at identifying enzymes generating this cleavage pattern. Methods:Two quenched fluorogenic peptides based on sequences of the main cleavage regions were used to test enzymes known to be upregulated in AD as well as probe fractionated mouse brain extracts for Ng-cleaving activity. The Ng fragments from in vitro cleavage were determined by MALDI-TOF MS and LC-ESI-MS. Results:We identified calpain I as cleaving Ng in its central region, at the C-terminal end of amino acids 37, 42 and 65. Fragments starting at amino acid 43 and smaller were among the dominant fragments seen by IPMS in CSF.We also identified the intracellular enzyme prolyl endopeptidase as being able to generate fragments lacking the very Cterminal three amino acids, which are also seen in CSF. While shorter Ng fragments were readily cleaved in vitro by prolyl endopeptidase, the efficiency of cleavage on larger Ng fragments was much lower. Conclusions: Calpain I and prolyl endopeptidase were identified as candidate enzymes involved in the formation of endogenous Ng peptides found in CSF, cleaving in the central region near the IQ domain and after Ng75. Whereas full length Ng is able to bind to calmodulin in the absence of Ca ions, most of the calpain fragments of Ng in CSF are lacking the IQ domain and are thus unable to do so. While the action of prolyl endopeptidase can explain the appearance of fragments lacking the last three C-terminal amino acids, the functional significance of that activity is still unclear. However, calpainand prolyl endopeptidase-specific fragments of Ng may give clues to increased activities of these enzymes during progression of AD.