Abstract
The molecular signaling that underpins synapse loss in neuropathological conditions remains unknown. Concomitant upregulation of the neuronal nitric oxide (NO) synthase (nNOS) in neurodegenerative processes places NO at the center of attention. We found that de novo nNOS expression was sufficient to induce synapse loss from motoneurons at adult and neonatal stages. In brainstem slices obtained from neonatal animals, this effect required prolonged activation of the soluble guanylyl cyclase (sGC)/protein kinase G (PKG) pathway and RhoA/Rho kinase (ROCK) signaling. Synapse elimination involved paracrine/retrograde action of NO. Furthermore, before bouton detachment, NO increased synapse myosin light chain phosphorylation (p-MLC), which is known to trigger actomyosin contraction and neurite retraction. NO-induced MLC phosphorylation was dependent on cGMP/PKG-ROCK signaling. In adulthood, motor nerve injury induced NO/cGMP-dependent synaptic stripping, strongly affecting ROCK-expressing synapses, and increased the percentage of p-MLC-expressing inputs before synapse destabilization. We propose that this molecular cascade could trigger synapse loss underlying early cognitive/motor deficits in several neuropathological states.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Analysis of Variance
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Animals
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Animals, Newborn
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Brain Stem / cytology
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Cyclic GMP-Dependent Protein Kinases / antagonists & inhibitors
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Cyclic GMP-Dependent Protein Kinases / metabolism*
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DNA-Binding Proteins / genetics
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Enzyme Inhibitors / pharmacology
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Green Fluorescent Proteins / genetics
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Humans
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Hypoglossal Nerve Diseases / pathology
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In Vitro Techniques
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Male
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Microscopy, Immunoelectron / methods
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Motor Neurons / drug effects
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Motor Neurons / pathology*
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Motor Neurons / ultrastructure
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Myosin Light Chains / metabolism*
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Nitric Oxide / pharmacology
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Nitric Oxide Synthase Type I / genetics
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Nitric Oxide Synthase Type I / metabolism*
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Nitric Oxide Synthase Type I / pharmacology
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Nuclear Proteins / genetics
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Patch-Clamp Techniques
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Phosphorylation / drug effects
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Phosphorylation / physiology
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Presynaptic Terminals / drug effects
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Presynaptic Terminals / metabolism
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Presynaptic Terminals / ultrastructure
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Rats
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Rats, Wistar
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Synapses / drug effects
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Synapses / pathology*
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Synapses / ultrastructure
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Synaptic Potentials / drug effects
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Synaptic Potentials / genetics
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Synaptophysin / metabolism
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Transfection
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Vesicular Glutamate Transport Protein 2 / metabolism
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Vesicular Inhibitory Amino Acid Transport Proteins / metabolism
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rho-Associated Kinases / antagonists & inhibitors
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rho-Associated Kinases / metabolism*
Substances
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DNA-Binding Proteins
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Enzyme Inhibitors
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Myosin Light Chains
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Nuclear Proteins
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Slc32a1 protein, rat
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Synaptophysin
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Trim27 protein, rat
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Vesicular Glutamate Transport Protein 2
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Vesicular Inhibitory Amino Acid Transport Proteins
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enhanced green fluorescent protein
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Green Fluorescent Proteins
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Nitric Oxide
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Nitric Oxide Synthase Type I
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rho-Associated Kinases
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Cyclic GMP-Dependent Protein Kinases