MicroRNA-34a from GABAergic neurons of the Dorsal Raphe Nuclei contributes to its peripheral plasma level

Aims: The identification of peripheral biomarkers of brain dysfunctions is essential to aid diagnosis and facilitate patient stratification. MicroRNAs are excellent candidate molecules to this purpose, as they can be expressed in the brain with regional and functional specificity, and they are highly stable in blood serum, unlike other RNA transcripts. Mir-34a is expressed with high specificity in a subpopulation of GABAergic neurons within the mouse Dorsal Raphe Nuclei (DRN), where it regulates GABAergic transmission in response to aversive stimuli. However, a direct connection between the brain and blood expression has never been demonstrated. Methods: We employed a genetic strategy to obtain a selectively deletion of miR-34a on GABAergic neurons, by crossing Gad2::Cre with miR-34aloxp/loxp mice. Instead to reach region-specific blockade of miR-34a, we injected a specific antagomiR-34a in DRN. Then, we analyzed the expression of miR-34a in plasma, organs, and different brain regions by qPCR. Results: We observed that genetic deletion of miR-34a in GABAergic neurons leads reduction of miR-34a expression in plasma and in the DRN, while no changes were observed in the others brain structure or organs. A similar reduction in the plasma was found when miR-34a was reduced selectively in the DRN by a specific antagomir-34a. Conclusion: Overall, our results suggest that miR-34a is released in the blood plasma from GABAergic neurons of the DRN and that homeostatic alterations of miR-34a in the brain could be observed in periphery.