title: Mechanisms involved in spinal cord central synapse loss in a mouse model of spinal muscular atrophy.
abstract: Motoneuron (MN) cell death is the histopathologic hallmark of spinal muscular atrophy (SMA), although MN loss seems to be a late event. Conversely, disruption of afferent synapses on MNs has been shown to occur early in SMA. Using a mouse model of severe SMA (SMNΔ7), we examined the mechanisms involved in impairment of central synapses. We found that MNs underwent progressive degeneration in the course of SMA, with MN loss still occurring at late stages. Loss of afferent inputs to SMA MNs was detected at embryonic stages, long before MN death. Reactive microgliosis and astrogliosis were present in the spinal cord of diseased animals after the onset of MN loss. Ultrastructural observations indicate that dendrites and microglia phagocytose adjacent degenerating presynaptic terminals. Neuronal nitric oxide synthase was upregulated in SMNΔ7 MNs, and there was an increase in phosphorylated myosin light chain expression in synaptic afferents on MNs; these observations implicate nitric oxide in MN deafferentation and suggest that the RhoA/ROCK pathway is activated. Together, our observations suggest that the earliest change occurring in SMNΔ7 mice is the loss of excitatory glutamatergic synaptic inputs to MNs; reduced excitability may enhance their vulnerability to degeneration and death.
authors.affiliation: From the Unitat de Neurobiologia Cel·lular, Departament de Medicina Experimental, Facultat de Medicina, Universitat de Lleida and Institut de Recerca Biomèdica de Lleida, Lleida, Catalonia (OT, FJC, JEE, JC); and Grup de Neurobiologia Cel·lular, Institut Universitari d'Investigacions en Ciències de la Salut and Departament de Biologia, Universitat de les Illes Balears, Palma de Mallorca (VC-M, AC-R, GO, JL), Spain.
authors.forename: Olga
authors.initials: O
authors.lastname: Tarabal
authors.forename: Víctor
authors.initials: V
authors.lastname: Caraballo-Miralles
authors.forename: Andrea
authors.initials: A
authors.lastname: Cardona-Rossinyol
authors.forename: Francisco J
authors.initials: FJ
authors.lastname: Correa
authors.forename: Gabriel
authors.initials: G
authors.lastname: Olmos
authors.forename: Jerònia
authors.initials: J
authors.lastname: Lladó
authors.forename: Josep E
authors.initials: JE
authors.lastname: Esquerda
authors.forename: Jordi
authors.initials: J
authors.lastname: Calderó
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D002135:Calcium-Binding Proteins / Q000378:metabolism; D002452:Cell Count; D004195:Disease Models, Animal; D005091:Exons / Q000235:genetics; D017353:Gene Deletion; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D008840:Microfilament Proteins / Q000378:metabolism; D009046:Motor Neurons / Q000378:metabolism / Q000473:pathology* / Q000648:ultrastructure; D009134:Muscular Atrophy, Spinal / Q000150:complications / Q000235:genetics / Q000473:pathology*; D009410:Nerve Degeneration / Q000209:etiology / Q000235:genetics / Q000473:pathology; D009419:Nerve Tissue Proteins / Q000378:metabolism; D013116:Spinal Cord / Q000473:pathology*; D055540:Survival of Motor Neuron 2 Protein / Q000235:genetics; D013569:Synapses / Q000000981:diagnostic imaging / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D014463:Ultrasonography; D015854:Up-Regulation / Q000235:genetics; D050495:Vesicular Inhibitory Amino Acid Transport Proteins / Q000378:metabolism
chemical_list: C491049:Aif1 protein, mouse; D002135:Calcium-Binding Proteins; D008840:Microfilament Proteins; D009419:Nerve Tissue Proteins; C526477:SMN2 protein, human; D055540:Survival of Motor Neuron 2 Protein; D050495:Vesicular Inhibitory Amino Acid Transport Proteins; C492244:Viaat protein, mouse