Retinoic acid regulates RARα-mediated control of translation in dendritic RNA granules during homeostatic synaptic plasticity

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Abstract
Homeostatic plasticity is thought to play an important role in maintaining the stability of neuronal circuits. During one form of homeostatic plasticity, referred to as synaptic scaling, activity blockade leads to a compensatory increase in synaptic transmission by stimulating in dendrites the local translation and synaptic insertion of the AMPA receptor subunit GluR1. We have previously shown that all-trans retinoic acid (RA) mediates activity blockade-induced synaptic scaling by activating dendritic GluR1 synthesis and that this process requires RARα, a member of the nuclear RA receptor family. This result raised the question of where RARα is localized in dendrites and whether its localization is regulated by RA and/or activity blockade. Here, we show that activity blockade or RA treatment in neurons enhances the concentration of RARα in the dendritic RNA granules and activates local GluR1 synthesis in these RNA granules. Importantly, the same RNA granules that contain RARα also exhibit an accumulation of GluR1 protein but with a much slower time course than that of RARα, suggesting that the former regulates the latter. Taken together, our results provide a direct link between dendritically localized RARα and local GluR1 synthesis in RNA granules during RA-mediated synaptic signaling in homeostatic synaptic plasticity.