Mutation of plasma membrane Ca2+ ATPase isoform 3 in a family with X-linked congenital cerebellar ataxia impairs Ca2+ homeostasis

CA(2+) in neurons is vital to processes such as neurotransmission, neurotoxicity, synaptic development, and gene expression. Disruption of CA(2+) homeostasis occurs in brain aging and in neurodegenerative disorders. Membrane transporters, among them the Calmodulin (CaM)-activated plasma membrane CA(2+) ATPases (PMCAs) that extrude CA(2+) from the cell, play a key role in neuronal CA(2+) homeostasis. Using X-exome Sequencing we have identified a missense mutation (G1107D) in the CaM-binding domain of isoform 3 of the PMCAs in a family with X-linked congenital cerebellar ataxia. PMCA3 is highly expressed in the cerebellum, particularly in the presynaptic terminals of parallel fibers-Purkinje neurons. To study the effects of the mutation on CA(2+) extrusion by the pump, model cells (HeLa) were cotransfected with expression plasmids encoding its mutant or wild-type (wt) variants and with the CA(2+)-sensing probe aequorin. The mutation reduced the ability of the PMCA3 pump to control the cellular homeostasis of CA(2+). It significantly slowed the return to baseline of the CA(2+) transient induced by an inositol-trisphosphate (InsP(3))-linked plasma membrane agonist. It also compromised the ability of the pump to oppose the influx of CA(2+) through the plasma membrane capacitative channels.