MEK inhibitors block BDNF-dependent and -independent expression of GABA A receptor subunit mRNAs in cultured mouse cerebellar granule neurons

Abstract

Brain-derived neurotrophic factor (BDNF) can regulate the maturation of developing cerebellar granule neurons. Within 1–2 days of culture, BDNF induces the expression of granule neuron terminal differentiation markers, particularly GABA A receptor α6 subunit (GABA Aα6) mRNA. Other trophic factors including insulin-like growth factor, the neurotrophin NT-3, pituitary adenylate cyclase-activating polypeptide (PACAP), and fetal bovine serum failed to induce this early expression. The expression of other GABA A receptor subunits, including α1 and γ2, was also enhanced by exposure of developing granule neurons to BDNF. This BDNF-dependent expression of GABA A receptor subunit mRNAs could be effectively blocked by treatment with the mitogen-activated protein kinase kinase (MEK) inhibitors, PD98059 or U0126. In the absence of BDNF, GABA Aα6 expression occurs but not until 3–4 days of culture. This BDNF-independent expression of GABA Aα6 was also inhibited by PD98059. Further studies showed that the BDNF-dependent expression GABA Aα6 could also be reduced by LY294002, an inhibitor of the phosphatidylinositol 3-kinase, or depolarizing concentrations of KCl. These results thus suggest that both BDNF-dependent and -independent expressions of GABA A receptor subunits require the activation of MEK and the mitogen-activated protein kinase (MAPK) pathway. However, it is also likely that other signaling pathways modulate this maturation process.