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Toll‐like Receptor 4 Signaling in Neurons Enhances Calcium‐Permeable AMPA Receptor Currents and Drives Post‐Traumatic Epileptogenesis
Author(s) -
Korgaonkar Akshata A.,
Li Ying,
Sekhar Dipika,
Subramanian Deepak,
Guevarra Jenieve,
Swietek Bogumila,
Pallottie Alexandra,
Singh Sukwinder,
Kella Kruthi,
Elkabes Stella,
Santhakumar Vijayalakshmi
Publication year - 2020
Publication title -
annals of neurology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 4.764
H-Index - 296
eISSN - 1531-8249
pISSN - 0364-5134
DOI - 10.1002/ana.25698
Subject(s) - epileptogenesis , ampa receptor , neuroscience , dentate gyrus , traumatic brain injury , tlr4 , hippocampal formation , medicine , glutamate receptor , receptor , biology , psychiatry
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