PKCepsilon upregulates voltage-dependent calcium channels in cultured astrocytes

Abstract

Astrocytes express voltage-gated calcium channels (VGCCs) that are upregulated in the context of the reactive astrogliosis occurring in several CNS pathologies. Moreover, the ability of selective calcium channel blockers to inhibit reactive astrogliosis has been revealed in a variety of experimental models. However, the functions and regulation of VGCC in astrocytes are still poorly understood. Interestingly, protein kinase C epsilon (PKCepsilon), one of the known regulators of VGCC in several cell types, induces in astrocytes a stellated morphology similar to that associated to gliosis. Thereby, here we explored the possible regulation of VGCC by adenovirally expressed PKCepsilon in astrocytes. We found that PKCepsilon potently increases the mRNA levels of two different calcium channel alpha(1) subunits, Ca(V)1.2 (L-type channel) and Ca(V)2.1 (P/Q-type channel). The mRNA upregulation was followed by a robust increase in the corresponding peptides. Moreover, the new calcium channels formed as a consequence of PKCepsilon activation are functional, since overexpression of constitutively-active PKCepsilon increased significantly the calcium current density in astrocytes. PKCepsilon raised currents carried by both L- and P/Q-type channels. However, the effect on the P/Q-type channel was more prominent since an increase of the relative contribution of this channel to the whole cell calcium current was observed. Finally, we found that PKCepsilon-induced stellation was significantly reduced by the specific L-type channel blocker nifedipine, indicating that calcium influx through VGCC mediates the change in astrocyte morphology induced by PKCepsilon. Therefore, here we describe a novel regulatory pathway involving VGCC that participates in PKCepsilon-dependent astrocyte activation.