Nitric oxide induces pathological synapse loss by a protein kinase G-, Rho kinase-dependent mechanism preceded by myosin light chain phosphorylation.
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.
Sunico
Carmen R
CR
Area de Fisiología, Facultad de Medicina, Universidad de Cádiz, 11003 Cádiz, Spain.
González-Forero
David
D
Domínguez
Germán
G
García-Verdugo
José Manuel
JM
Moreno-López
Bernardo
B
D000704:Analysis of Variance; D000818:Animals; D000831:Animals, Newborn; D001933:Brain Stem / Q000166:cytology; D017869:Cyclic GMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000235:genetics; D004791:Enzyme Inhibitors / Q000494:pharmacology; D049452:Green Fluorescent Proteins / Q000235:genetics; D006801:Humans; D020437:Hypoglossal Nerve Diseases / Q000473:pathology; D066298:In Vitro Techniques; D008297:Male; D016253:Microscopy, Immunoelectron / Q000379:methods; D009046:Motor Neurons / Q000187:drug effects / Q000473:pathology* / Q000648:ultrastructure; D018994:Myosin Light Chains / Q000378:metabolism*; D009569:Nitric Oxide / Q000494:pharmacology; D052248:Nitric Oxide Synthase Type I / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology; D009687:Nuclear Proteins / Q000235:genetics; D018408:Patch-Clamp Techniques; D010766:Phosphorylation / Q000187:drug effects / Q000502:physiology; D017729:Presynaptic Terminals / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D051381:Rats; D017208:Rats, Wistar; D013569:Synapses / Q000187:drug effects / Q000473:pathology* / Q000648:ultrastructure; D055366:Synaptic Potentials / Q000187:drug effects / Q000235:genetics; D016708:Synaptophysin / Q000378:metabolism; D014162:Transfection; D050599:Vesicular Glutamate Transport Protein 2 / Q000378:metabolism; D050495:Vesicular Inhibitory Amino Acid Transport Proteins / Q000378:metabolism; D054460:rho-Associated Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000070584:Tripartite Motif Proteins
D017869:Cyclic GMP-Dependent Protein Kinases; D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; D049452:Green Fluorescent Proteins; D018994:Myosin Light Chains; D009569:Nitric Oxide; D052248:Nitric Oxide Synthase Type I; D009687:Nuclear Proteins; D016708:Synaptophysin; D050599:Vesicular Glutamate Transport Protein 2; D050495:Vesicular Inhibitory Amino Acid Transport Proteins; D054460:rho-Associated Kinases; C118623:Slc32a1 protein, rat; C489295:Trim27 protein, rat; D000070584:Tripartite Motif Proteins; C485184:enhanced green fluorescent protein