Down‐regulation of gephyrin and GABA_A receptor subunits during epileptogenesis in the CA1 region of hippocampus

Abstract

Purpose Epileptogenesis is the process by which a brain becomes hyperexcitable and capable of generating recurrent spontaneous seizures. In humans, it has been hypothesized that following a brain insult there are a number of molecular and cellular changes that underlie the development of spontaneous seizures. Studies in animal models have shown that an injured brain may develop epileptiform activity before appearance of epileptic seizures and that the pathophysiology accompanying spontaneous seizures is associated with a dysfunction of GABAergic neurotransmission. Here, we analyzed the effects of status epilepticus on the expression of GABAA receptors and scaffolding proteins involved in the regulation of GABAA receptor trafficking and anchoring. Methods Western blot analysis was used to determine the levels of proteins involved in GABAAR trafficking and anchoring in adult rats subjected to pilocarpine-induced SE and controls. Cell surface biotinylation using a cell membrane impermeable reagent was used to assay for changes in the expression of receptors at the plasma membrane. Finally, immunoprecipitation experiments were used to evaluate the composition of GABAA receptors. We examined for a correlation between total GABAAR subunit expression, plasma membrane expression and receptor composition. Key Findings Analysis of tissue samples from the CA1 region of hippocampus show that SE promotes a loss of GABAA receptor subunits and of the scaffolding proteins associated with them. We also found a decrease in the levels of receptors located at the plasma membrane and alterations in GABAA receptor composition. Significance The changes in protein expression of GABAA receptors and scaffolding proteins detected in these studies provide a potential mechanism to explain the deficits in GABAergic neurotransmission observed during the epileptogenic period. Our current observations represent an additional step towards the elucidation of the molecular mechanisms underlying GABAAR dysfunction during epileptogenesis.

Gephyrin Cleavage in In Vitro Brain Ischemia Decreases GABAA Receptor Clustering and Contributes to Neuronal Death

“…These truncated forms of gephyrin contribute to the disassembly of the postsynaptic gephyrin clusters, with a consequent loss of the neuroprotective activity mediated by synaptic GABA A R. Therefore, inhibition of gephyrin cleavage might be a therapeutic target to preserve synaptic inhibition in brain ischemia. Given the recent evidence showing a downregulation of gephyrin during epileptogenesis in the CA1 region of the hippocampus [52], which is associated with the accumulation of gephyrin protein fragments [53,54], strategies aiming at preventing calpainmediated gephyrin cleavage may also be effective in epilepsy.…”

Diffusion dynamics of synaptic molecules during inhibitory postsynaptic plasticity

“…For instance, the upregulation of GABA A Rs and gephyrin proteins contributes to iLTP expression, while their downregulation has been observed during status epilepticus in the CA1 region of the hippocampus (Peng et al, 2004; González et al, 2013; Petrini et al, 2014). Moreover, it has been reported that fear conditioning regulates the gene expression of gephyrin in the amygdala (Ressler et al, 2002; Chhatwal et al, 2005).…”

Drug Resistance and Resistance Mechanisms in Epilepsy

“…AEİ'ler ile enflama- [76] Altta yatan mekanizma transkripsiyonel faktörlere bağlı görünmekle birlikte metabolik fonksiyonların yetersizliği de dikkat çeki-cidir. Mitokondriyal fonksiyonun yetersizliği ve ATP kullanı-labilirliğinin azalması reaktif oksijen substratlarını (ROS) artırdığından, hedef moleküllerde hızlı değişikliklerle birlikte enerji tüketimi ve ROS aracılı hasar ile uzun dönemde de bu metabolik fonksiyon yetersizliğinin etkileri gözlenmektedir.…”

“…Bu değişikliklere α4, β2/3 ve γ2 alt ünitelerinin kaybı ve hücre yüzeyindeki reseptörlerin durumunda bir azalmanın eşlik ettiği gösterilmiştir. [76] GABAerjik nörotransmisyondaki eksiklik, GABA-A reseptörleri, reseptör hareketini ve reseptörün membrana yapışarak fonksiyon görmesini sağlayan yapı taşı proteinlerindeki (gefrin, GABARAP [GABA reseptör aracılı protein], GRIP [proteinle etkileşen glutamat reseptör] ve NSF [N-etilmaleimide duyarlı faktör]) ekspresyonel sikliklerinde Alzheimer hastalığı, Parkinson hastalığı veya enflamatuvar bağırsak hastalıklarına yatkınlık oluşur. Uzun süreli farmakolojik inhibisyonu bazı risklerle ilişkili olabilir.…”