Amygdalar expression of the microRNA miR‐101a and its target Ezh2 contribute to rodent anxiety‐like behaviour

A greater understanding of neural mechanisms contributing to anxiety is needed in order to develop better therapeutic interventions. This study interrogates a novel molecular mechanism that shapes anxiety‐like behaviour, demonstrating that the microRNA miR‐101a‐3p and its target, enhancer of zeste homolog 2 (Ezh2) in the amygdala, contribute to rodent anxiety‐like behaviour. We utilized rats that were selectively bred for differences in emotionality and stress reactivity, showing that high‐novelty‐responding (HR) rats, which display low trait anxiety, have lower miR‐101a‐3p levels in the amygdala compared to low‐novelty‐responding (LR) rats that characteristically display high trait anxiety. To determine whether there is a causal relationship between amygdalar miR‐101a‐3p and anxiety behaviour, we used a viral approach to overexpress miR‐101a‐3p in the amygdala of HR rats and test whether it would increase their typically low levels of anxiety‐like behaviour. We found that increasing miR‐101a‐3p in the amygdala increased HRs' anxiety‐like behaviour in the open‐field test and elevated plus maze. Viral‐mediated miR‐101a‐3p overexpression also reduced expression of the histone methyltransferase Ezh2, which mediates gene silencing via trimethylation of histone 3 at lysine 27 (H3K27me3). Knockdown of Ezh2 with short‐interfering RNA (siRNA) also increased HRs' anxiety‐like behaviour, but to a lesser degree than miR‐101a‐3p overexpression. Overall, our data demonstrate that increasing miR‐101a‐3p expression in the amygdala increases anxiety‐like behaviour and that this effect is at least partially mediated via repression of Ezh2. This work adds to the growing body of evidence implicating miRNAs and epigenetic regulation as molecular mediators of anxiety behaviour. We examined the role of microRNAs (miRNA) in regulating anxiety behaviour. Rats selectively bred to display low levels of trait anxiety have relatively low levels of microRNA miR‐101a‐3p in the amygdala as well as increased expression of its gene target Ezh2, which is responsible for trimethylation of histone 3 at lysine 27 (H3K27me3). Overexpressing miR‐101a‐3p in the amygdala leads these rats to show higher levels of anxiety behaviour while siRNA knockdown of Ezh2 increased their anxiety behaviour.