Elevated FKBP5 expression associates with epilepsy-related molecular changes and promotes neuronal hyperexcitability

OBJECTIVE Epilepsy is one of the neurological disorders, characterized by recurrent, spontaneous seizures arising from neuronal hyperexcitability and hypersynchrony in the brain. The mechanisms of epilepsy are intricate and remain elusive. FKBP5 has emerged as a significant protein implicated in neurological disorders such as Alzheimer's disease (AD) and Parkinson's disease (PD). This study aims to investigate the role of FKBP5 in a kainic acid (KA)-induced intrahippocampal epilepsy model and assessed how FKBP5 gain-of-function and FKBP51 inhibition influence neurotransmitter dynamics and neuronal excitability. METHODS We examined the expression of FKBP5 in the hippocampus of the kainic acid (KA)-induced epilepsy model. To explore the impact of FKBP5 on neuronal activity, we overexpressed FKBP5 in primary cortical neurons and astrocytes, assessing extracellular glutamate levels in neuron-astrocytes co-cultures with or without the FKBP51-selective inhibitor SAFit2 (250 nM). Intrinsic excitability, voltage-gated Na+ currents, and network activity were evaluated using whole-cell patch-clamp recordings and high-density microelectrode arrays (HD-MEAs). RESULTS We observed an elevated level of FKBP5 in the hippocampus of a kainic acid (KA)-induced chronic epilepsy mouse model, whereas cortical FKBP5 did not show clear changes across the examined post-insult time points.. Moreover, FKBP5 overexpression induced a remarkable increase in the extracellular glutamate level in co-cultured primary cortical neurons and astrocytes. Intriguingly, FKBP5 overexpression modifies the electrophysiological properties of primary neurons, resulting in increased intrinsic excitability and enhanced Na+ currents. Additionally, the network activity exhibits hyperexcitability with FKBP5 overexpression. Notably, SAFit2 treatment was also associated with elevated extracellular glutamate in the co-culture system, while intracellular FKBP5 and EAAT2 protein levels showed no significant group differences in the current dataset. CONCLUSION These findings suggested that FKBP5 played a significant role in regulating neuronal excitability and extracellular glutamate homeostasis. However, due to discrete sampling and the lack of continuous seizure monitoring, the present in vivo data do not establish a definitive causal contribution of FKBP5 to epileptogenesis, warranting future studies integrating longitudinal EEG and cell-type-specific manipulations.