Objective: With a growing base of literature finding widespread hypo-editing in neurodegenerative diseases characterised by synapse loss, we aimed to investigate the role of ADAR2-mediated RNA editing, particularly at the GluA2 Q/R site, in regulating dendritic spine density in hippocampal neurons.

Methods: We used siRNA knockdown (KD) and viral overexpression of ADAR2 and and force-edited GluA2(R) in primary hippocampal neurons. RNA editing efficiency was assessed using RT-qPCR, while dendritic spine density was analysed through fluorescent microscopy and 3D reconstruction.

Results: ADAR2 KD significantly reduced editing at both GluA2 and GluK1 Q/R sites and led to a substantial loss of dendritic spines, with spine numbers correlating strongly with ADAR2 expression. Overexpression of ADAR2 increased GluK1 Q/R site editing and restored GluA2 Q/R editing in ADAR2 KD neurons. Importantly, ADAR2 overexpression increased dendritic spine numbers compared to controls, even in ADAR2 KD cells. Furthermore, GluA2(R) overexpression specifically restored GluA2 Q/R editing following ADAR2 KD without affecting GluK1 editing. Notably, GluA2(R) overexpression increased spine density and rescued spine loss in ADAR2 KD neurons.

Conclusion: Our findings establish a direct link between ADAR2-mediated GluA2 Q/R site editing and dendritic spine maintenance in hippocampal neurons. The rescue of spine density by both ADAR2 and GluA2(R) overexpression suggests that GluA2 Q/R site editing is not only necessary but sufficient for spine regulation. This mechanism provides a potential target for therapeutic interventions in neurodegenerative diseases characterised by RNA-editing deficits and synaptic loss, offering a novel approach to maintaining cognitive function through the preservation of dendritic spines.