MicroRNA-92 modulates K(+) Cl(-) co-transporter KCC2 expression in cerebellar granule neurons.

MicroRNAs have been associated to fine-tuning spatial and temporal control of gene expression during neuronal development. The neuronal Cl()) extruding, K(+)Cl()) co-transporter 2 (KCC2) is known to play an important role in neuronal Cl()) homeostasis and in determining the physiological response to activation of anion selective GABA receptors. Here we show that microRNA-92 is developmentally down-regulated during maturation of rat cerebellar granule neurons (CGNs) in vitro. Computational predictions suggest several high-ranking targets for microRNA-92 including the KCC2 gene. Consistently, the KCC2 protein levels were up-regulated in mature CGN in vitro and a functional association between microRNA-92 and KCC2 3¢ untranslated region was established using luciferase assays. The generation of an inward directed Cl()) electrochemical gradient, necessary for the hyperpolarizing effect of GABA, requires robust KCC2 expression in several neuronal types. Here we show that lentiviral-mediated microRNA-92 over-expression reduced KCC2 protein levels and positively shifted reversal potential of GABA induced Cl()) currents in CGNs. In addition KCC2 reexpression reversed microRNA-92 electrophysiological phenotype. Consistently microRNA-92 inhibition induced both an increase of the level of KCC2 and a negative shift in GABA reversal potential. These findings introduce a new player in the developmental change of GABA from depolarization to hyperpolarization.