The role of gephyrin translation in inhibitory synaptic plasticity

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PROJECT SUMMARY Synaptic plasticity, the activity-dependent alteration in the strength of neuronal connections, forms the molecular basis of learning, memory, and cognition. Both excitatory and inhibitory connections undergo bidirectional synaptic plasticity to tune neuronal excitability, sculpt neural circuits, and coordinate the balance of excitation and inhibition (E/I balance). GABAergic synaptic plasticity is crucial for maintaining E/I balance, and its dysfunction is implicated in pathologies such as epilepsy, schizophrenia, and autism spectrum disorders. However, inhibitory synaptic plasticity and its molecular underpinnings are critically understudied. A crucial regulator of inhibitory synaptic plasticity is gephyrin, a synaptic scaffolding protein essential for GABAA receptor clustering and inhibitory synaptic transmission. In one form of inhibitory synaptic plasticity, inhibitory long-term potentiation (iLTP), gephyrin clustering increases rapidly at dendritic inhibitory synapses to strengthen GABAergic synapses exclusively in dendrites by 20 min post-stimulation. Early mechanisms of iLTP are independent of translation, but much less is known about iLTP persistence and how translation of key proteins maintains iLTP. Answering these questions will provide insights into mechanisms of synaptic plasticity and how changes in GABAergic synaptic strength shape neural circuits long-term. In this proposal, I will address this knowledge gap by focusing on the role of gephyrin translation for maintaining iLTP and more specifically where it occurs and how it is regulated to enact precise and persistent potentiation of inhibitory synaptic connections. I hypothesize that local gephyrin translation supports iLTP exclusively in the dendrites and that translational regulation of gephyrin influences gephyrin synaptic clustering and inhibitory synaptic strength. I will utilize fluorescent in situ labeling of mRNA and visualization of actively translating proteins to determine localization and translation of gephyrin transcripts in dendrites following iLTP (Aim 1). miR153 is a short, non-coding transcript identified as a key regulator of gephyrin translation and implicated in learning, memory, and cognition. By modulating its expression levels in neurons and employing a combination of immunocytochemistry and electrophysiology, I will determine the impact of miR153 function on gephyrin clustering and inhibitory synaptic strength during iLTP (Aim 2). Together, this approach will elucidate how the localization and regulation of gephyrin translation impact specific and lasting changes to inhibitory synaptic strength during iLTP and ultimately reveal the mechanisms driving inhibitory synaptic plasticity to maintain E/I balance for proper neural function.