Resilience to audiogenic seizures is associated with p-ERK1/2 dephosphorylation in the subiculum of Fmr1 knockout mice

Abstract

Young, but not adult, fragile X mental retardation gene (Fmr1) knockout (KO) mice display audiogenic seizures (AGS) that can be prevented by inhibiting extracellular signal-regulated kinases 1/2 (ERK1/2) phosphorylation. In order to identify the cerebral regions involved in these phenomena, we characterized the response to AGS in Fmr1 KO mice and wild type (WT) controls at postnatal day (P) 45 and P90. To characterize the diverse response to AGS in various cerebral regions, we evaluated the activity markers FosB/ΔFosB and phosphorylated ERK1/2 (p-ERK1/2). Wild running (100% of tested mice) followed by clonic/tonic seizures (30%) were observed in P45 Fmr1 KO mice, but not in WT mice. In P90 Fmr1 KO mice, wild running was only present in 25% of tested animals. Basal FosB/ΔFosB immunoreactivity was higher (P < 0.01 vs. WT) in the CA1 and subiculum of P45 Fmr1 KO mice. Following the AGS test, FosB/ΔFosB expression consistently increased in most of the analyzed regions in both groups at P45, but not at P90. Interestingly, FosB/ΔFosB immunoreactivity was significantly higher in P45 Fmr1 KO mice in the medial geniculate body (P < 0.05 vs. WT) and CA3 (P < 0.01). Neurons presenting with immunopositivity to p-ERK1/2 were more abundant in the subiculum of Fmr1 KO mice in control condition (P < 0.05 vs. WT, in both age groups). In this region, p-ERK1/2-immunopositive cells significantly decreased (–75%, P < 0.01) in P90 Fmr1 KO mice exposed to the AGS test, but no changes were found in P45 mice or in other brain regions. In both age groups of WT mice, p-ERK1/2-immunopositive cells increased in the subiculum after exposure to the acoustic test. Our findings illustrate that FosB/ΔFosB markers are overexpressed in the medial geniculate body and CA3 in Fmr1 KO mice experiencing AGS, and that p-ERK1/2 is markedly decreased in the subiculum of Fmr1 KO mice resistant to AGS induction. These findings suggest that resilience to AGS is associated with dephosphorylation of p-ERK1/2 in the subiculum of mature Fmr1 KO mice.

Progressive Seizure Aggravation in the Repeated 6-Hz Corneal Stimulation Model Is Accompanied by Marked Increase in Hippocampal p-ERK1/2 Immunoreactivity in Neurons

“…These markers have been found to be widely expressed in the hippocampus of animals exposed to seizures induced by kainate (Kim et al, 1994; Crespo-Biel et al, 2007), pilocarpine (Garrido et al, 1998; Berkeley et al, 2002; Houser et al, 2008), bicuculline (Gass et al, 1993; Ben et al, 2014), and dopamine D 1 receptor agonists (Bozzi et al, 2011; Gangarossa et al, 2011, 2014; Bozzi and Borrelli, 2013). We also found p-ERK1/2 to be induced by audiogenic seizures in mice affected by fragile X syndrome (Curia et al, 2013) and, interestingly, changes in p-ERK1/2 have been associated to a different sensitivity to proconvulsant stimuli (Glazova et al, 2015). In order to characterize p-ERK1/2 expression in the repeated 6-Hz corneal stimulation model, we designed an experiment in which p-ERK1/2 was characterized in the hippocampus of mice exposed to one or three sequential seizures.…”

“…A mouse brain atlas-C57BL/6J horizontal 1 was used to assess brain sections. The number of immunoreactive cells per mm 2 was quantified using the image analysis software KS300 (Carl Zeiss Vision GmbH), as previously detailed (Biagini et al, 2005; Curia et al, 2013; Giordano et al, 2015). The border of all analyzed regions was manually traced and the sampled areas, expressed in mm 2 , were automatically determined.…”

“…In particular, we evaluated the expression of FosB/ΔFosB antigens, which are known to be markedly induced either in seizure models (Chen et al, 1995; Mohapel et al, 2001), or in models of epilepsy (Morris et al, 2000; Biagini et al, 2005; Curia et al, 2013). Additionally, FosB/ΔFosB isoforms were directly involved in epileptogenesis since their deletion was associated with adult-onset spontaneous epilepsy (Yutsudo et al, 2013).…”

mTOR and MAPK: from localized translation control to epilepsy

“…In this respect, activation of the metabotropic glutamate receptor 5 (mGluR5) results in excessive protein production in fmr1 knockdown mice [20]. Interestingly, young FXS rats are susceptible to audiogenic seizures [62]. One hypothesis states that elevated protein levels at synapses leads to seizures [27, 63].…”

“…Furthermore, a direct link has been suggested from mGluR5 activation to mTOR and MAPK pathways in modulating FMRP-mediated expression control [66]. Importantly, the fragile X syndrome phenotype can be reversed by blocking ERK activity suggesting an interplay between FMRP and the ERK pathway [20, 62]. Since FXS-patient also suffer from seizures, those results indicate also a possible link to epilepsy.…”