Cellular prion protein is implicated in the regulation of local Ca2+ movements in cerebellar granule neurons

The cellular prion protein (PrPC) is a cell-surface glycoprotein mainly expressed in the CNS. The structural conversion of PrPC generates the prion, the infectious agent causing transmissible spongiform encephalopathies, which are rare and fatal diseases affecting animals and humans. Despite decades of intensive research, the mechanism of prion-associated neurodegeneration and the physiologic role of PrPC are still obscure. Recent evidence, however, supports the hypothesis that PrPC may be involved in the control of Ca2+ homeostasis. Given the universal significance of Ca2+ as an intracellular messenger for both the life and death of cells, this possibility may help explain the complex, often controversial, dataset accumulated on PrPC physiology, and the events leading to prion-associated neuronal demise. In this study, we have compared local Ca2+ movements in cerebellar granule neurons (CGN) derived from wild-type (WT), or PrP-knockout (KO), mice, by means of the Ca2+-sensitive photo-probe, aequorin, genetically targeted to specific intracellular domains and delivered to CGN by lentiviral vectors. The use of an aequorin that localizes to the cytosolic domains proximal to the plasma membrane has allowed us to demonstrate that there was a dramatic increase of store-operated Ca2+ entry in PrP-KO CGN compared to WT neurons. Notably, this phenotype was rescued upon restoring PrPC expression. The Ca2+-phenotype of PrP-KO neurons can in part be explained by the lower expression of two major Ca2+-extruding proteins, namely the plasma membrane and the sarco-endoplasmic reticulum Ca2+-ATPases. The lower sarco-endoplasmic reticulum Ca2+-ATPase content may also contribute to explain why PrP-KO CGN accumulated less Ca2+ in the endoplasmic reticulum than the WT counterpart.