Transient inhibition of TrkB kinase after status epilepticus prevents development of temporal lobe epilepsy

Abstract

Temporal lobe epilepsy is the most common and often devastating form of human epilepsy. The molecular mechanism underlying the development of temporal lobe epilepsy remains largely unknown. Emerging evidence suggests that activation of the BDNF receptor TrkB promotes epileptogenesis caused by status epilepticus. We investigated a mouse model in which a brief episode of status epilepticus results in chronic recurrent seizures, anxiety-like behavior, and destruction of hippocampal neurons. We used a chemical-genetic approach to selectively inhibit activation of TrkB. We demonstrate that inhibition of TrkB commencing after status epilepticus and continued for 2 weeks prevents recurrent seizures, ameliorates anxiety-like behavior, and limits loss of hippocampal neurons when tested weeks to months later. That transient inhibition commencing after status epilepticus can prevent these long-lasting devastating consequences establishes TrkB signaling as an attractive target for developing preventive treatments of epilepsy in humans.

Figure 1. Transient inhibition of TrkB kinase prevents SRS following SE

(A) Total number of SRS detected during weeks 1–2 post SE during treatment with vehicle or 1NMPP1 in WT or TrkB^F616A mice (heat map in panel C). Occurrence of SRS was significantly reduced by 1NMPP1 treatment in TrkB^F616A (*p<0.05) but not WT mice compared to their vehicle-treated controls. (B) Total number of SRS detected during weeks 5–6 post-SE (heat map in panel D); video-EEG analyses were initiated in these mice approximately 2 weeks after terminating treatment with 1NMPP1. Among the ten 1NMPP1-treated TrkB^F616A mice monitored during 1–2 weeks after SE, eight of them (the left first eight columns on the bottom right panel of Fig 1C) were monitored during weeks 5–6 after SE (Fig 1D). Occurrence of SRS was prevented in these eight 1NMPP1-treated TrkB^F616A mice (***p<0.001), but not in WT mice compared to their vehicle-treated controls. (C) and (D) Number of SRS detected each day during weeks 1–2 (C) and weeks 5–6 (D) after SE are presented as heat maps (one mouse per column). Note that SRS were detected in only two of ten 1NMPP1-treated TrkB^F616A mice during weeks 1–2 (C) and one of eight 1NMPP1-treated TrkB^F616A mice during weeks 5–6 (D). By contrast, all vehicle-treated TrkB^F616A mice (7 of 7) and all WT mice treated with either vehicle (6 of 6) or 1NMPP1 (6 of 6) exhibited SRS during weeks 1–2 (C) and weeks 5–6 (D) post-SE. Statistics were performed using two-way ANOVA with Bonferroni post hoc tests, n=6–10. M: male and F: female. Animal #s correspond to #s in Figures S3 and S4 in supplementary information.

Figure 2. SE-induced anxiety-like behavior is reduced by inhibition of TrkB kinase

(A) Both WT and TrkB^F616A mice undergoing SE and treated with vehicle thereafter exhibited prolonged latency to exit the darkened and enter the lighted compartment compared to PBS controls (WT: **P<0.01; TrkB^F616A: *p<0.05). 1NMPP1 treatment reduced this latency in TrkB^F616A mice (**p<0.01), but not in WT mice. (B) Both WT and TrkB^F616A mice undergoing SE and treated with vehicle thereafter spent less time in lighted compartment compared to PBS controls (WT: **p<0.01; TrkB^F616A: **p<0.01). 1NMPP1 treatment increased the time spent in the lighted compartment in TrkB^F616A mice (***p<0.001), but not in WT mice. Data are presented as mean ± SEM and analyzed using two-way ANOVA with Bonferroni corrections, n=5–9.

Figure 3. SE-induced hippocampal damage is attenuated by inhibition of TrkB kinase

(A) Representative images of immunostaining of NeuN and GFAP in the hippocampal CA3b region ipsilateral to the infusion site in WT and TrkB^F616A mice in respective PBS controls, SE-vehicle treated, and SE-1NMPP1 treated mice, scale bar = 50 µM. Insets: GFAP positive cells exhibited enhanced immunoreactivity and enlarged cell bodies and braches in SE-vehicle or 1NMPP1 treated WT mice and in SE-vehicle treated TrkB^F616A mice, scale bar = 20 µM. (B) Number of NeuN positive cells within ipsilateral CA3b hippocampus was reduced in both WT and TrkB^F616A mice undergoing SE and treated with vehicle thereafter compared to PBS controls (WT: ***p<0.001; TrkB^F616A: ***p<0.001). 1NMPP1 treatment inhibited loss of NeuN positive cells in TrkB^F616A mice (***p<0.001), but not in WT mice. Data are presented as mean ± SEM and analyzed using two-way ANOVA with Bonferroni post hoc tests, n=3–6.