PMCA4 (ATP2B4) mutation in familial spastic paraplegia causes delay in intracellular calcium extrusion.
BACKGROUND
Familial spastic paraplegia (FSP) is a heterogeneous group of disorders characterized primarily by progressive lower limb spasticity and weakness. More than 50 disease loci have been described with different modes of inheritance. Recently, we described a novel missense mutation (c.803G>A, p.R268Q) in the plasma membrane calcium ATPase (PMCA4, or ATP2B4) gene in a Chinese family with autosomal dominant FSP. Further to this finding, here we describe the functional effect of this mutation.


METHODS
As PMCA4 removes cytosolic calcium, we measured transient changes and the time-dependent decay of cytosolic calcium level as visualized by using fura-2 fluorescent dye with confocal microscopy in human SH-SY5Y neuroblastoma cells overexpressing either wild-type or R268Q mutant PMCA4.


RESULTS
Overexpressing both wild-type and R268Q PMCA4 significantly reduced maximum calcium surge after KCl-induced depolarization as compared with vector control cells. However, cells overexpressing mutant PMCA4 protein demonstrated significantly higher level of calcium surge when compared with wild-type. Furthermore, the steady-state cytosolic calcium concentration in these mutant cells remained markedly higher than the wild-type after SERCA inhibition by thapsigargin.


CONCLUSION
Our result showed that p.R268Q mutation in PMCA4 resulted in functional changes in calcium homeostasis in human neuronal cells. This suggests that calcium dysregulation may be associated with the pathogenesis of FSP.
['Ho|Philip Wing-Lok|PW|', 'Pang|Shirley Yin-Yu|SY|', 'Li|Miaoxin|M|', 'Tse|Zero Ho-Man|ZH|', 'Kung|Michelle Hiu-Wai|MH|', 'Sham|Pak-Chung|PC|', 'Ho|Shu-Leong|SL|']
D044466:Asians D015153:Blotting, Western D002118:Calcium D005456:Fluorescent Dyes D016257:Fura-2 D006801:Humans D018613:Microscopy, Confocal D020125:Mutation, Missense D053499:Plasma Membrane Calcium-Transporting ATPases D060888:Real-Time Polymerase Chain Reaction D015419:Spastic Paraplegia, Hereditary
ATP2B4 Familial spastic paraplegia PMCA calcium transient neurodegeneration