Functional role of RIM3 in the regulation of neuronal network excitability

Abstract

Neuronal networks are highly intricate systems, where synapses play a crucial role in intercellular communication and neuronal plasticity. While the large isoforms of the Rab3 interacting molecule (RIM) family, particularly RIM1 and RIM2, are well characterized in presynaptic function, the smaller isoform, RIM3, remains poorly understood. This study provides the first functional characterization of a newly generated RIM3 knockout (KO) mouse line, investigating its role in synaptic function, plasticity, spontaneous network activity, and the regulation of excitability in neuronal networks. Using transcriptomics and proteomics approaches, we show that RIM3 deletion induces significant alterations at the mRNA level without affecting the proteome. These changes suggest that RIM3 participates in synapse-related processes, including neurotransmitter release and synaptic plasticity, and may influence activity-dependent gene transcription via transcriptional modulation rather than direct protein changes. <br /> Network-level activity was assessed using multielectrode arrays (MEAs), revealing that culture density significantly impacts neuronal synchronization and maturation. Notably, RIM3 deletion led to contrasting effects on network activity across different culture densities: reduced activity in high-density networks and increased synchronicity in low-density networks. These results suggest that RIM3 plays a dual role in regulating excitability, promoting activity in highly synchronized networks and constraining it in less synchronized ones. Furthermore, loss of RIM3 in glutamatergic neurons increased firing rates, while its deletion in GABAergic neurons disrupted network synchronization. These findings indicate that RIM3 may act as a negative regulator of excitability in both neuronal subtypes at low densities. Homeostatic plasticity, on the other hand, was not affected by the deletion of RIM3. <br /> In conclusion, this study provides novel insights into the neuronal functions of RIM3, highlighting its role in modulating network excitability. These findings lay the groundwork for future research on RIM3’s involvement in neurological disorders such as epilepsy and schizophrenia.