Graduate Student Emory University Atlanta, Georgia, United States
Nicholas Harbin (Emory University)| Daniel Lustberg (Emory University)| David Weinshenker (Emory University)| John Hepler (Emory University)
Regulators of G-protein signaling (RGS) proteins are critical for proper regulation of receptor-mediated signaling in the central nervous system and elsewhere. One such RGS protein, RGS14, is highly expressed in pyramidal cells of area CA2 of the hippocampus and interacts with multiple signaling pathways to suppress calcium influx, neuronal excitability, and synaptic plasticity. In contrast to neurons of neighboring CA1 and CA3, CA2 pyramidal neurons are highly resistant to excitotoxic injury (e.g. seizure activity), although the mechanisms governing this resilience are unknown. Because RGS14 blocks calcium influx and downstream signaling in neuronal spines, RGS14 could be crucial for protection of CA2 from excitotoxic injury. We therefore hypothesize that RGS14 may regulate hippocampal response to excitotoxic injury caused by prolonged seizure activity (i.e. status epilepticus).
Using kainic acid (KA) and flurothyl to induce seizures in wild-type (WT) and RGS14 knockout (RGS14 KO) mice, we measured and compared tissue and behavioral responses to each chemoconvulsant between the two genotypes. Additionally, we evaluated RGS14 expression and seizure-induced pathology in the days following KA-induced status epilepticus in WT and RGS14 KO mice. Using a modified Racine scale to monitor seizure progression, we observed no differences in behavioral seizure intensity or mortality caused by either kainic acid or flurothyl. Compared to saline, we found a striking and significant upregulation of RGS14 five and seven days after KA treatment in area CA1 of WT mice, as measured by immunohistochemistry. Using microtubule associated protein 2 (MAP2) as a proxy for neuronal integrity, we observed a significant loss of MAP2 expression in area CA1 of KA-treated RGS14 KO mice but not WT mice at the same time points. Evaluating microgliosis and astrogliosis using ionized calcium binding adaptor molecule (IBA1) and glial fibrillary acidic protein (GFAP) expression as markers, respectively, we found that the abundance of both proteins were upregulated following KA-induced seizures in WT mice but were unchanged in RGS14 KO mice. Taken together, these results suggest that RGS14 plays an essential role in regulating pathological response to seizure injury in the hippocampus without altering seizure threshold.