Abstract

Abstract GABA B receptors mediate prolonged inhibition in the brain and are important for keeping neuronal excitation and inhibition in a healthy balance. However, under excitotoxic/ischemic conditions, GABA B receptors are downregulated by dysregulated endocytic trafficking and can no longer counteract the severely enhanced excitation, eventually triggering neuronal death. Recently, we developed interfering peptides targeting protein-protein interactions involved in downregulating the receptors. Treatment with these peptides restored GABA B receptor expression after an ischemic insult and thereby inhibited neuronal overexcitation and progressive neuronal death. In this study, we searched for GABA B receptor interactions that specifically occur under ischemic conditions. We found that the E3 ubiquitin ligase MARCH1 is specifically upregulated under ischemic/excitotoxic conditions. Upregulated MARCH1 interacts with GABA B receptors and triggered downregulation of plasma membrane GABA B receptors by inhibiting fast recycling of the receptors. We developed an interfering peptide that inhibits the MARCH1/GABA B receptor interaction. Treatment of cultured neurons subjected to ischemic stress with this peptide restored receptor expression and as a consequence stopped progressive neuronal death. Thus, inhibiting the interaction of GABA B receptors with MARCH1 to restore cell surface receptor expression might be a promising strategy to prevent progressive neuronal death induced by ischemic conditions.