Search results

Glycogen synthase kinase-3 (GSK-3) is ubiquitously expressed throughout the brain and involved in vital molecular pathways such as cell survival and synaptic reorganization and has emerged as a potential drug target for brain diseases. A causal role for GSK-3, in particular the brain-enriched GSK-3ß isoform, has been demonstrated in neurodegenerative diseases such as Alzheimer's and Huntington's, and in psychiatric diseases. Recent studies have also linked GSK-3 dysregulation to neuropathological outcomes in epilepsy. To date, however, there has been no genetic evidence for the involvement of GSK-3 in seizure-induced pathology. Status epilepticus (prolonged, damaging seizure) was induced via a microinjection of kainic acid into the amygdala of mice. Studies were conducted using two transgenic mouse lines: a neuron-specific GSK-3ß overexpression and a neuron-specific dominant-negative GSK-3ß (GSK-3ß-DN) expression in order to determine the effects of increased or decreased GSK-3ß activity, respectively, on seizures and attendant pathological changes in the hippocampus. GSK-3 inhibitors were also employed to support the genetic approach. Status epilepticus resulted in a spatiotemporal regulation of GSK-3 expression and activity in the hippocampus, with decreased GSK-3 activity evident in non-damaged hippocampal areas. Consistent with this, overexpression of GSK-3ß exacerbated status epilepticus-induced neurodegeneration in mice. Surprisingly, decreasing GSK-3 activity, either via overexpression of GSK-3ß-DN or through the use of specific GSK-3 inhibitors, also exacerbated hippocampal damage and increased seizure severity during status epilepticus. In conclusion, our results demonstrate that the brain has limited tolerance for modulation of GSK-3 activity in the setting of epileptic brain injury. These findings caution against targeting GSK-3 as a treatment strategy for epilepsy or other neurologic disorders where neuronal hyperexcitability is an underlying pathomechanism. ; Marie Curie International Mobility Fellowship, the Health Research Board (PD/2009/31 to T.E. and HRA_POR/2011/41 to D.C.H.); Science Foundation Ireland (13/SIRG/2098 and 17/CDA/4708 to T.E. and 16/RC/3948 to D.C.H.) and co-funded under the European Regional Development Fund and by FutureNeuro industry partners;); from the H2020 Marie Skłowdowksa-Curie Actions Individual Fellowship (753527 to E.B.); from the European Union's Horizon 2020 research and innovation programme under the Marie Sklowdowska-Cuire grant agreement (No. 766124 to T.E.); grants from Ministerio de Economía Industria y Competitividad of Spain SAF2009-08233 and SAF2015-65371-R to J.J.L., SAF2016-78603-R to M.M. and BFU2016-77885-P to F.H.; grant PI2015-2/06-3 from CIBERNED-ISCIII to J.J.L.; and institutional grants to CBMSO from Fundación Ramón Areces and Fundación Banco de Santander ; Peer Reviewed

14 p.-5 fig. ; Glycogen synthase kinase-3 (GSK-3) is ubiquitously expressed throughout the brain and involved in vital molecular pathways such as cell survival and synaptic reorganization and has emerged as a potential drug target for brain diseases. A causal role for GSK-3, in particular the brain-enriched GSK-3β isoform, has been demonstrated in neurodegenerative diseases such as Alzheimer's and Huntington's, and in psychiatric diseases. Recent studies have also linked GSK-3 dysregulation to neuropathological outcomes in epilepsy. To date, however, there has been no genetic evidence for the involvement of GSK-3 in seizure-induced pathology. Status epilepticus (prolonged, damaging seizure) was induced via a microinjection of kainic acid into the amygdala of mice. Studies were conducted using two transgenic mouse lines: a neuron-specific GSK-3β overexpression and a neuron-specific dominant-negative GSK-3β (GSK-3β-DN) expression in order to determine the effects of increased or decreased GSK-3β activity, respectively, on seizures and attendant pathological changes in the hippocampus. GSK-3 inhibitors were also employed to support the genetic approach. Status epilepticus resulted in a spatiotemporal regulation of GSK-3 expression and activity in the hippocampus, with decreased GSK-3 activity evident in non-damaged hippocampal areas. Consistent with this, overexpression of GSK-3β exacerbated status epilepticus-induced neurodegeneration in mice. Surprisingly, decreasing GSK-3 activity, either via overexpression of GSK-3β-DN or through the use of specific GSK-3 inhibitors, also exacerbated hippocampal damage and increased seizure severity during status epilepticus. In conclusion, our results demonstrate that the brain has limited tolerance for modulation of GSK-3 activity in the setting of epileptic brain injury. These findings caution against targeting GSK-3 as a treatment strategy for epilepsy or other neurologic disorders where neuronal hyperexcitability is an underlying pathomechanism. ; This work was supported by funding from the Sixth Framework Programme (MIRG-CT-2004-014567, to D.C.H.) a IRCSET-Marie Curie International Mobility Fellowship, the Health Research Board (PD/2009/31 to T.E. and HRA_POR/ 2011/41 to D.C.H.); Science Foundation Ireland (13/SIRG/2098 and 17/CDA/ 4708 to T.E. and 16/RC/3948 to D.C.H.) and co-funded under the European Regional Development Fund and by FutureNeuro industry partners;); from the H2020 Marie Skłowdowksa-Curie Actions Individual Fellowship (753527 to E.B.); from the European Union's Horizon 2020 research and innovation programme under the Marie Sklowdowska-Cuire grant agreement (No. 766124 to T.E.); grants from Ministerio de Economía Industria y Competitividad of Spain SAF2009-08233 and SAF2015-65371-R to J.J.L., SAF2016-78603-R to M.M. and BFU2016-77885-P to F.H.; grant PI2015-2/06-3 from CIBERNED-ISCIII to J.J.L.; and institutional grants to CBMSO from Fundación Ramón Areces and Fundación Banco de Santander. ; Peer reviewed

Prolonged seizures (status epilepticus, SE) may drive hippocampal dysfunction and epileptogenesis, at least partly, through an elevation in neurogenesis, dysregulation of migration and aberrant dendritic arborization of newly-formed neurons. MicroRNA-22 was recently found to protect against the development of epileptic foci, but the mechanisms remain incompletely understood. Here, we investigated the contribution of microRNA-22 to SE-induced aberrant adult neurogenesis. SE was induced by intraamygdala microinjection of kainic acid (KA) to model unilateral hippocampal neuropathology in mice. MicroRNA-22 expression was suppressed using specific oligonucleotide inhibitors (antagomir-22) and newly-formed neurons were visualized using the thymidine analog iodo-deoxyuridine (IdU) and a green fluorescent protein (GFP)-expressing retrovirus to visualize the dendritic tree and synaptic spines. Using this approach, we quantified differences in the rate of neurogenesis and migration, the structure of the apical dendritic tree and density and morphology of dendritic spines in newly-formed neurons.SE resulted in an increased rate of hippocampal neurogenesis, including within the undamaged contralateral dentate gyrus (DG). Newly-formed neurons underwent aberrant migration, both within the granule cell layer and into ectopic sites. Inhibition of microRNA-22 exacerbated these changes. The dendritic diameter and the density and average volume of dendritic spines were unaffected by SE, but these parameters were all elevated in mice in which microRNA-22 was suppressed. MicroRNA-22 inhibition also reduced the length and complexity of the dendritic tree, independently of SE. These data indicate that microRNA-22 is an important regulator of morphogenesis of newly-formed neurons in adults and plays a role in supressing aberrant neurogenesis associated with SE ; This work was supported by funding from Science Foundation Ireland (13/SIRG/2098, 17/CDA/4708 and 16/TIDA/4059 to TE, 13/SIRG/2114 to EJ-M, 17/TIDA/5002 to CR, 13/IA/1891 and 16/RC/3948 to DH and co-funded under the European Regional Development Fund and by FutureNeuro Industry partners) from the Health Research Board (HRA-POR-2015-1243 to TE), from the European Union Seventh Framework Programme (FP7/2007–2013) under grant agreement n◦ 602130 (to DH), from the H2020 Marie Skłowdowksa-Curie Actions Individual Fellowship (753527 to EB), from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement (No 766124 to TE), S2013/ICE-2958 from Comunidad de Madrid to MM-P, from Fundación ''La Caixa'' to JM-R and from Areces Foundation C-XVIII and the Minister of Science and Universities of Spain BFU2014-53654-P to MM-P