Charbel Moussa

The Role of α‐Synuclein in Both Neuroprotection and Neurodegeneration

Abstract: Although α‐synuclein is a central player in the pathophysiology of the dopaminergic neurodegeneration that occurs in Parkinsons disease (PD), emerging results suggest that the fundamental property of the wild‐type form of this protein may be one of neuroprotection, as it can inhibit apoptosis in response to various pro‐apoptotic stimuli. Such properties may be lost by its familial PD‐linked mutations upon alterations in its expression levels or clearance (overexpression of the gene, reduced protein degradation) or following exposure to certain neurotoxins. Moreover, converging observations suggest that a primary function for α‐synuclein in dopaminergic neurons may be the regulation of dopamine content and tone at the synapse. In this paper, we review how, indeed, α‐synuclein regulates both the synthesis of dopamine, its storage into vesicles, its release in the synapse, and its re‐uptake into the dopaminergic neurons. We also show how disruption of these events, and of the neuroprotective effects of α‐synuclein, can initiate the observed neurotoxicity of α‐synuclein in dopaminergic neurons and the genesis of the degenerative processes associated with PD.

Abnormal migration of human wild-type α-synuclein upon gel electrophoresis

Abstract α-Synuclein aggregates have been linked to the pathogenesis of Parkinsons disease (PD), with Lewy bodies (LBs) and Lewy neurites (LNs) constituting the pathological hallmarks in the brains of patients with PD and dementia with LBs. LBs are formed by the conversion of soluble monomers of α-synuclein into insoluble aggregates. Here we report an abnormal electrophoretic mobility, at a higher molecular weight (MW) than the expected theoretical MW, of both recombinant histidine-tagged human α-synuclein, human α-synuclein expressed in SH-SY5Y human neuroblastoma cells or Ltk− fibroblasts, and rat brain α-synuclein, on SDS–PAGE polyacrylamide, but not on Nu-PAGE gradient peptide, gels, suggesting possible α-synuclein data misinterpretations associated with gel electrophoresis. These studies raise important considerations about the type of protein gel electrophoresis system suitable to study the alterations of α-synuclein associated with neurodegeneration, PD and other synucleinopathies.

Resveratrol for Alzheimer's disease

The amyloid hypothesis suggests that the progressive accumulation and deposition of central nervous system (CNS) amyloid with aging is the proximate cause of Alzheimers disease (AD). Thus, targeting molecular mechanisms of aging may be a viable treatment approach. Caloric restriction prevents diseases of aging, including AD, in animal models, perhaps by activation of sirtuins. The sirtuins (e.g., mammalian SIRT1) are deacetylases that link energy balance (NAD+/NADH) to regulation of gene transcription. Resveratrol is a potent activator of SIRT1, and thus may mimic caloric restriction to prevent diseases of aging. We conducted a randomized, double‐blind, placebo‐controlled, phase II trial of resveratrol for individuals with mild‐to‐moderate AD. Resveratrol (1) is detectable in cerebrospinal fluid (at low nanomolar levels), (2) is safe and well tolerated, (3) alters AD biomarker trajectories, (4) preserves blood–brain barrier integrity, and (5) modulates the CNS immune response. Further studies are needed to determine the safety and efficacy of resveratrol and the validity of this approach in the treatment and prevention of AD and other diseases of aging.

Mitochondrial Dysfunction in Skeletal Muscle of Amyloid Precursor Protein-overexpressing Mice

Background: Intracellular accumulation of β-amyloid is a key step in pathogenesis of the inclusion body myositis (IBM). Results: Intramyofiber accumulation of β-amyloid in MCK-βAPP mice leads to structural and functional mitochondrial abnormalities. Conclusion: Mitochondrial abnormalities precede IBM-related histological and motor deficits in MCK-βAPP mice. Significance: The diminished mitochondrial function may play a key role during the β-amyloid mediated pathogenesis in IBM. Inclusion body myositis, the most common muscle disorder in the elderly, is partly characterized by abnormal expression of amyloid precursor protein (APP) and intracellular accumulation of its proteolytic fragments collectively known as β-amyloid. The present study examined the effects of β-amyloid accumulation on mitochondrial structure and function of skeletal muscle from transgenic mice (MCK-βAPP) engineered to accumulate intramyofiber β-amyloid. Electron microscopic analysis revealed that a large fraction of myofibers from 2–3-month-old MCK-βAPP mice contained numerous, heterogeneous alterations in mitochondria, and other cellular organelles. [1H-decoupled]13C NMR spectroscopy showed a substantial reduction in TCA cycle activity and indicated a switch from aerobic to anaerobic glucose metabolism in the MCK-βAPP muscle. Isolated muscle fibers from the MCK-βAPP mice also exhibited a reduction in cytoplasmic pH, an increased rate of ROS production, and a partially depolarized plasmalemma. Treatment of MCK-βAPP muscle cells with Ru360, a mitochondrial Ca2+ uniporter antagonist, reversed alterations in the plasmalemmal membrane potential (Vm) and pH. Consistent with altered redox state of the cells, treatment of MCK-βAPP muscle cells with glutathione reversed the effects of β-amyloid accumulation on Ca2+ transient amplitudes. We conclude that structural and functional alterations in mitochondria precede the reported appearance of histopathological and clinical features in the MCK-βAPP mice and may represent key early events in the pathogenesis of inclusion body myositis.

Dopamine D1 receptor-mediated toxicity in human SK-N-MC neuroblastoma cells

Striatal degeneration occurs through unknown mechanisms in certain neurodegenerative disorders characterized by increased and sustained synaptic levels of dopamine. In the present studies, we examined the effects of treatment of SK-N-MC neuroblastoma cells with dopamine to understand the participation of dopamine D(1) receptor in postsynaptic cytotoxicity. Treatment of SK-N-MC cells either with dopamine or the D(1) receptor agonist SKF R-38393 resulted in a significant increase in the production of reactive oxygen species (by approximately 2.75-fold) and cell death ( approximately 50%), while antagonism of the D(1) receptor with SCH 23390 significantly reversed (to approximately 75% of control level) these effects. Accumulation of cAMP in dopamine treated cells (t(1/2)=1.5h) preceded changes in ionic gradient (t(1/2)=6.5h), as measured by intracellular potassium concentration and leakage of cytochrome c into the cytosol (t(1/2)=13 h), suggesting a possible staging of toxic events as a result of activation of D(1) receptor by dopamine. Examination of cellular metabolic properties with (13)C NMR spectroscopy showed an inhibitory effect on tricarboxylic acid cycle metabolism via D(1)-mediated receptors after treatment with dopamine, suggesting a direct role for D(1) receptor in dopamine-induced postsynaptic cell death. The present studies provide novel insight into a possible patho-physiological staging of cytotoxic events that are mediated by activation of D(1) receptor.

NAAG Peptidase Inhibitors Act via mGluR3: Animal Models of Memory, Alzheimer’s, and Ethanol Intoxication

Glutamate carboxypeptidase II (GCPII) inactivates the peptide neurotransmitter N-acetylaspartylglutamate (NAAG) following synaptic release. Inhibitors of GCPII increase extracellular NAAG levels and are efficacious in animal models of clinical disorders via NAAG activation of a group II metabotropic glutamate receptor. mGluR2 and mGluR3 knock-out (ko) mice were used to test the hypothesis that mGluR3 mediates the activity of GCPII inhibitors ZJ43 and 2-PMPA in animal models of memory and memory loss. Short- (1.5xa0h) and long- (24xa0h) term novel object recognition tests were used to assess memory. Treatment with ZJ43 or 2-PMPA prior to acquisition trials increased long-term memory in mGluR2, but not mGluR3, ko mice. Nine month-old triple transgenic Alzheimer’s disease model mice exhibited impaired short-term novel object recognition memory that was rescued by treatment with a NAAG peptidase inhibitor. NAAG peptidase inhibitors and the group II mGluR agonist, LY354740, reversed the short-term memory deficit induced by acute ethanol administration in wild type mice. 2-PMPA also moderated the effect of ethanol on short-term memory in mGluR2 ko mice but failed to do so in mGluR3 ko mice. LY354740 and ZJ43 blocked ethanol-induced motor activation. Both GCPII inhibitors and LY354740 also significantly moderated the loss of motor coordination induced by 2.1xa0g/kg ethanol treatment. These data support the conclusion that inhibitors of glutamate carboxypeptidase II are efficacious in object recognition models of normal memory and memory deficits via an mGluR3 mediated process, actions that could have widespread clinical applications.

Parkin mediates beclin-dependent autophagic clearance of defective mitochondria and ubiquitinated Abeta in alzheimer's DISEASE models

tase modulators induce ratio changes opposite to ratio changes induced by FAD mutations. Conclusions: We conclude that gamma-secretase inhibitors, under the conditions tested, can induce FAD-like ratio changes in non-transgenic models, reflected by increased levels of longer versus shorter Abeta peptides. Gamma-secretase modulators lead to increased production of shorter peptides with concomitant decrease of longer more toxic peptides. More research is needed to fully understand the pharmacodynamic profile of GSM and GSI cpds in vivo and the underlying mechanism of action. The results caution for the use of GSIs as disease modifying agents.

RESVERATROL ACTIVATES THE CNS SIRTUIN1/MATRIX METTALOPROTEINASE-9 PATHWAY AND REGULATES NEUROINFLAMMATION IN ALZHEIMER’S DISEASE

Study Activities of Daily Living; ADCS-ADL) scores. Threemonthly assessment included magnetic resonance imaging (MRI) as a disease modifying outcome. Other secondary outcomes included ADCS-CGIC and MMSE. Results:A total of 891 patients were randomized, of whom 62% were female. Approved AD treatments were being taken in 85%. The mean age was 70.6 (SD 9.0) years and baseline MMSE score was 18.7 (SD 3.4). Dementia was of moderate severity (MMSE score 14-19) in 61%. The study efficacy and safety outcomes will be reported. Conclusions:The outcomes of this phase 3 trial will highlight the potential therapeutic value of tau aggregation inhibitor therapy in AD. A second phase 3 trial of LMTM for AD will be completed and reported later in 2016.