OBJECTIVE: Traumatic brain injury is a major risk factor for acquired epilepsies, and understanding the mechanisms underlying the early pathophysiology could yield viable therapeutic targets. Growing evidence indicates a role for inflammatory signaling in modifying neuronal excitability and promoting epileptogenesis. Here we examined the effect of innate immune receptor Toll-like receptor 4 (TLR4) on excitability of the hippocampal dentate gyrus and epileptogenesis after brain injury. METHODS: Slice and in vivo electrophysiology and Western blots were conducted in rats subject to fluid percussion brain injury or sham injury. RESULTS: The studies identify that TLR4 signaling in neurons augments dentate granule cell calcium-permeable α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor (CP-AMPAR) currents after brain injury. Blocking TLR4 signaling in vivo shortly after brain injury reduced dentate network excitability and seizure susceptibility. When blocking of TLR4 signaling after injury was delayed, however, this treatment failed to reduce postinjury seizure susceptibility. Furthermore, TLR4 signal blocking was less efficacious in limiting seizure susceptibility when AMPAR currents, downstream targets of TLR4 signaling, were transiently enhanced. Paradoxically, blocking TLR4 signaling augmented both network excitability and seizure susceptibility in uninjured controls. Despite the differential effect on seizure susceptibility, TLR4 antagonism suppressed cellular inflammatory responses after injury without impacting sham controls. INTERPRETATION: These findings demonstrate that independently of glia, the immune receptor TLR4 directly regulates post-traumatic neuronal excitability. Moreover, the TLR4-dependent early increase in dentate excitability is causally associated with epileptogenesis. Identification and selective targeting of the mechanisms underlying the aberrant TLR4-mediated increase in CP-AMPAR signaling after injury may prevent epileptogenesis after brain trauma. ANN NEUROL 2020;87:497-515.
OBJECTIVE:Traumatic brain injury is a major risk factor for acquired epilepsies, and understanding the mechanisms underlying the early pathophysiology could yield viable therapeutic targets. Growing evidence indicates a role for inflammatory signaling in modifying neuronal excitability and promoting epileptogenesis. Here we examined the effect of innate immune receptor Toll-like receptor 4 (TLR4) on excitability of the hippocampal dentate gyrus and epileptogenesis after brain injury. METHODS: Slice and in vivo electrophysiology and Western blots were conducted in rats subject to fluid percussion brain injury or sham injury. RESULTS: The studies identify that TLR4 signaling in neurons augments dentate granule cell calcium-permeable α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor (CP-AMPAR) currents after brain injury. Blocking TLR4 signaling in vivo shortly after brain injury reduced dentate network excitability and seizure susceptibility. When blocking of TLR4 signaling after injury was delayed, however, this treatment failed to reduce postinjury seizure susceptibility. Furthermore, TLR4 signal blocking was less efficacious in limiting seizure susceptibility when AMPAR currents, downstream targets of TLR4 signaling, were transiently enhanced. Paradoxically, blocking TLR4 signaling augmented both network excitability and seizure susceptibility in uninjured controls. Despite the differential effect on seizure susceptibility, TLR4 antagonism suppressed cellular inflammatory responses after injury without impacting sham controls. INTERPRETATION: These findings demonstrate that independently of glia, the immune receptor TLR4 directly regulates post-traumatic neuronal excitability. Moreover, the TLR4-dependent early increase in dentate excitability is causally associated with epileptogenesis. Identification and selective targeting of the mechanisms underlying the aberrant TLR4-mediated increase in CP-AMPAR signaling after injury may prevent epileptogenesis after brain trauma. ANN NEUROL 2020;87:497-515.
Authors: Pablo M Casillas-Espinosa; Pedro Andrade; Cesar Santana-Gomez; Tomi Paananen; Gregory Smith; Idrish Ali; Robert Ciszek; Xavier Ekolle Ndode-Ekane; Rhys D Brady; Jussi Tohka; Matthew R Hudson; Piero Perucca; Emma L Braine; Riikka Immonen; Noora Puhakka; Sandy R Shultz; Nigel C Jones; Richard J Staba; Asla Pitkänen; Terence J O'Brien Journal: Epilepsy Res Date: 2019-04-27 Impact factor: 3.045
Authors: Pavel Klein; Raymond Dingledine; Eleonora Aronica; Christophe Bernard; Ingmar Blümcke; Detlev Boison; Martin J Brodie; Amy R Brooks-Kayal; Jerome Engel; Patrick A Forcelli; Lawrence J Hirsch; Rafal M Kaminski; Henrik Klitgaard; Katja Kobow; Daniel H Lowenstein; Phillip L Pearl; Asla Pitkänen; Noora Puhakka; Michael A Rogawski; Dieter Schmidt; Matti Sillanpää; Robert S Sloviter; Christian Steinhäuser; Annamaria Vezzani; Matthew C Walker; Wolfgang Löscher Journal: Epilepsia Date: 2017-12-15 Impact factor: 5.864
Authors: Carol Eisenberg; Deepak Subramanian; Milad Afrasiabi; Patryk Ziobro; Jack DeLucia; Pamela R Hirschberg; Michael W Shiflett; Vijayalakshmi Santhakumar; Tracy S Tran Journal: Transl Psychiatry Date: 2021-10-18 Impact factor: 6.222