Purkinje cell dysfunction and delayed death in plasma membrane calcium ATPase 2-heterozygous mice

Purkinje cell (PC) dysfunction or death has been implicated in a number of disorders including ataxia, autism and multiple sclerosis. Plasma membrane calcium ATPase 2 (PMCA2), an important calcium (Ca²⁺) extrusion pump that interacts with synaptic signaling complexes, is most abundantly expressed in PCs compared to other neurons. Using the PMCA2 heterozygous mouse as a model, we investigated whether a reduction in PMCA2 levels affects PC function. We focused on Ca²⁺ signaling and the expression of glutamate receptors which play a key role in PC function including synaptic plasticity. We found that the amplitude of depolarization and 2-amino-3-(5-methyl-3-oxo-1,2-oxazol-4-yl)propanoic acid receptor (AMPAR)-mediated Ca²⁺ transients are significantly higher in cultured PMCA2^+/- PCs than in PMCA2^+/+ PCs. This is due to increased Ca²⁺ influx, since P/Q type voltage-gated Ca²⁺ channel (VGCC) expression was more pronounced in PCs and cerebella of PMCA2^+/- mice and VGCC blockade prevented the elevation in amplitude. Neuronal nitric oxide synthase (nNOS) activity was higher in PMCA2^+/- cerebella and inhibition of nNOS or the soluble guanylate cyclase (sGC)-cyclic guanosine monophosphate (cGMP) pathway, which mediates nitric oxide (NO) signaling, reduced the amplitude of Ca²⁺ transients in PMCA2^+/- PCs, in vitro. In addition, there was an age-dependent decrease in metabotropic glutamate receptor 1 (mGluR1) and AMPA receptor subunit GluR2/3 transcript and protein levels at 8weeks of age. These changes were followed by PC loss in the 20-week-old PMCA2^+/- mice. Our studies highlight the importance of PMCA2 in Ca²⁺ signaling, glutamate receptor expression and survival of Purkinje cells.