Elucidation of pathological mechanism caused by human disease mutation in CaMKIIß.

ABSTRACT

Recently, we have identified CaMKIIα and CaMKIIß mutations in patients with neurodevelopmental disorders by whole exome sequencing study. Most CaMKII mutants have increased phosphorylation of Thr286/287, which induces autonomous activity of CaMKII, using cell culture experiments. In this study, we explored the pathological mechanism of motor dysfunction observed exclusively in a patient with Pro213Leu mutation in CaMKIIß using a mouse model of the human disease. The homozygous CaMKIIß Pro213Leu knockin mice showed age-dependent motor dysfunction and growth failure from 2 weeks after birth. In the cerebellum, the mutation did not alter the mRNA transcript level, but the CaMKIIß protein level was dramatically decreased. Furthermore, in contrast to previous result from cell culture, Thr287 phosphorylation of CaMKIIß was also reduced. CaMKIIß Pro213Leu knockin mice showed similar motor dysfunction as CaMKIIß knockout mice, newly providing evidence for a loss of function rather than a gain of function. Our disease model mouse showed similar phenotypes of the patient, except for epileptic seizures. We clearly demonstrated that the pathological mechanism is a reduction of mutant CaMKIIß in the brain, and the physiological aspects of mutation were greatly different between in vivo and cell culture.