GDF-15 enhances intracellular Ca(2+) by increasing Ca(v)1.3 expression in rat cerebellar granule neurons

GDF-15 (growth/differentiation factor 15) is a novel member of the TGF (transforming growth factor)-β superfamily that has critical roles in the central and peripheral nervous systems. We reported previously that GDF-15 increased delayed rectifier outward K(+) currents and K(v)2.1 α subunit expression through TβRII (TGF-β receptor II) to activate Src kinase and Akt/mTOR (mammalian target of rapamycin) signalling in rat CGNs (cerebellar granule neurons). In the present study, we found that treatment of CGNs with GDF-15 for 24 h increased the intracellular Ca(2+) concentration ([Ca(2+)](i)) in response to membrane depolarization, as determined by Ca(2+) imaging. Whole-cell current recordings indicated that GDF-15 increased the inward Ca(2+) current (I(Ca)) without altering steady-state activation of Ca(2+) channels. Treatment with nifedipine, an inhibitor of L-type Ca(2+) channels, abrogated GDF-15-induced increases in [Ca(2+)](i) and I(Ca). The GDF-15-induced increase in I(Ca) was mediated via up-regulation of the Ca(v)1.3 α subunit, which was attenuated by inhibiting Akt/mTOR and ERK (extracellular-signal-regulated kinase) pathways and by pharmacological inhibition of Src-mediated TβRII phosphorylation. Given that Ca(v)1.3 is not only a channel for Ca(2+) influx, but also a transcriptional regulator, our data confirm that GDF-15 induces protein expression via TβRII and activation of a non-Smad pathway, and provide novel insight into the mechanism of GDF-15 function in neurons.