Dystonia-Associated Hippocalcin Mutants Dysregulate Cellular Calcium Influx

Abstract

Dystonia is a neurological movement disorder that provokes muscle spasms and contractions. It is characterized by sustained or intermittent muscle contractions causing abnormal, often repetitive movements and painful postures. Recently, mutations at positions T71N and A190T in the neuronal calcium-binding protein hippocalcin, have been shown to be critical in development of DYT2 dystonia. However, the effect of these mutations on the physiological role of hippocalcin has not yet been elucidated. Using a multidisciplinary approach, we showed that mutations T71N and A190T in hippocalcin did not affect stability, calcium-binding affinity, translocation to cellular membranes (Ca2+/myristoyl switch) and three-dimensional structure of the protein. However, the disease-associated mutations caused a defect in calcium-induced oligomerisation of hippocalcin. In KCl-stimulated SH-SY5Y cells expressing mutated hippocalcin, we observed an increased calcium influx, mostly driven by N-type voltage-gated calcium channels. Our data demonstrate that the dystonia-associated mutations strongly affect hippocalcin cellular functions which suggest a central role for perturbed calcium signalling in DYT2 dystonia. This work has been funded by the Leverhulme Trust RPG-2014-194.