Opera Medica et Physiologica

Synapse

Endogenous Nitric Oxide Synthase Activity Regulates Synaptic Transmitter Release

Introduction

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Abstract

Nitric oxide (NO) signalling contributes to many biological processes involved in activity-dependent fine tuning of neuronal communication. NO is involved in early developmental signalling of the nervous system and is associated with pathological pathways and age-related decline in neuronal function, thus playing a critical role in regulating neuronal function in physiology and disease. Here we assessed the effects of modulating endogenous neuronal nitric oxide synthase (NOS) activity on synaptic function, specifically on neurotransmitter release at the glutamatergic Drosophila neuromuscular junction (NMJ). We found that the absence of NOS activity enhanced synaptic release at the NMJ and conversely, overexpression of NOS diminished transmitter release. The effects of alterations in NO signalling are the consequence of acute signalling at the synapse as we did not observe any developmental changes in NMJ morphology or synaptic parameters, such as expression of the active zone protein, bruchpilot, which could account for changes in release. Ultrastructural analysis did not show any developmental effects in boutons from larvae with reduced NOS activity. Together, our data present evidence for a negative regulation of transmitter release by NO which has implications for physiological synaptic function but also pathological and age-related dysregulation of synaptic signalling. 

 

Analysis of Protein SUMOylation and SUMO Pathway Enzyme Levels in Alzheimer’s Disease and Down’s Syndrome

Introduction

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PDF icon OMP_2017_01_0042.pdf693.98 KB

Abstract

Understanding the molecular and cellular processes that cause dementia is one of the most important challenges in neuroscience. SUMOylation is a post-translational protein modification that has been strongly implicated in neurodegenerative diseases. To investigate SUMOylation in dementia we profiled the expression of key SUMOylation pathway proteins in post mortem brain tissue from Alzheimer’s Disease (AD) and Down’s Syndrome (DS) patients. As expected, both AD and DS tissue displayed massively increased levels of phosphorylated tau compared to age- and sex-matched controls. Surprisingly, there were no changes in the levels of the E1 and E2 enzymes required for protein SUMOylation, or in levels of the deSUMOylating enzyme SENP1.  There was, however, a marked decrease in the SUMO-2/3-specific deSUMOylating enzyme SENP3 in DS. There were also increased levels of SUMO-1 conjugated proteins in DS, but not in AD tissue. While these results do not exclude roles for SUMOylation in AD, they demonstrate clear differences in the profile of SUMOylation and in the expression of deSUMOylating enzymes between AD and DS brain.

Pathophysiology of Ng2-Glia: a ‘Chicken and Egg’ Scenario of Altered Neurotransmission and Disruption of Ng2-Glial Cell Function

Introduction

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PDF icon OMP_2016_01_0022.pdf909.28 KB

Abstract

Classically, the central nervous system (CNS) was considered to contain neurons and three main types of glial cells - astrocytes, oligodendrocytes, and microglia.  Now, it has been clearly established that NG2-glia are a fourth glial cell type that are defined by their expression of the NG2 chondroitin sulfate proteoglycan (Cspg4).  NG2-glia are also known as oligodendrocyte precursor cells (OPCs) and express the alpha receptor for platelet-derived growth factor (Pdgfra) as well as other oligodendrocyte lineage markers. NG2-glia are most numerous during CNS development when they are responsible for massive generation of oligodendrocytes, the myelin-forming cells of the CNS. A significant population of NG2-glia persist in the adult CNS, where they generate oligodendrocytes throughout life. A unique feature of NG2-glia is that they receive synaptic inputs from neurons and are able to respond rapidly to neurotransmission via their specific ion channel and receptor profiles. Moreover, synaptic and neuronal integrity depend on NG2-glia. Notably, concomitant disruption of NG2-glia, myelin and neurotransmission are key features of many neuropathologies, including Multiple Sclerosis and Alzheimer’s disease (AD). The fact that neurotransmission both regulates and is reliant on NG2-glia and myelin raises the ‘chicken and egg’ question of what comes first – disruption of NG2-glia/myelin or synapses/neurons. It is more useful to think of neurons, NG2-glia and oligodendrocytes/myelin as being functionally integrated and interdependent units, whereby disruption of any one can result in a vicious cycle with potentially devastating effects on CNS function.

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