Key points• The cerebellum plays crucial roles in controlling sensorimotor functions, and patients with spinocerebellar ataxia type 13 exhibit cerebellar atrophy and cerebellar symptoms.• The disease is an autosomal dominant disorder caused by missense mutations in the voltage-gated K + channel Kv3.3, which is expressed intensely in the cerebellar Purkinje cells, the sole output neurons from the cerebellar cortex.• Here, we examined how these mutations cause the cerebellar disease by lentiviral expression of the mutant Kv3.3 in mouse cultured Purkinje cells.• Expression of the mutant Kv3.3 suppressed outward currents, broadened action potentials and elevated basal intracellular calcium concentration in Purkinje cells. Moreover, the mutant-expressing Purkinje cells showed impaired dendrites and extensive cell death, both of which were significantly rescued by blockade of P/Q-type Ca 2+ channels.• These results suggest that Purkinje cells in the patients also exhibit similar abnormalities, which may account for the pathology of the disease.
AbstractThe cerebellum plays crucial roles in controlling sensorimotor functions. The neural output from the cerebellar cortex is transmitted solely by Purkinje cells (PCs), whose impairment causes cerebellar ataxia. Spinocerebellar ataxia type 13 (SCA13) is an autosomal dominant disease, and SCA13 patients exhibit cerebellar atrophy and cerebellar symptoms. Recent studies have shown that missense mutations in the voltage-gated K + channel Kv3.3 are responsible for SCA13. In the rodent brain, Kv3.3 mRNAs are expressed most strongly in PCs, suggesting that the mutations severely affect PCs in SCA13 patients. Nevertheless, how these mutations affect the function of Kv3.3 in PCs and, consequently, the morphology and neuronal excitability of PCs remains unclear. To address these questions, we used lentiviral vectors to express mutant mouse Kv3.3 (mKv3.3) channels harbouring an R424H missense mutation, which corresponds to the R423H mutation in the Kv3.3 channels of SCA13 patients, in mouse cerebellar cultures. The R424H mutant-expressing PCs showed decreased outward current density, broadened action potentials and elevated basal [Ca 2+ ] i compared with PCs expressing wild-type mKv3.3 subunits or those expressing green fluorescent protein alone. Moreover, expression of R424H mutant subunits induced impaired dendrite development and cell death selectively in PCs, both of which were rescued by blocking P/Q-type Ca 2+ channels in the culture conditions. We therefore concluded that expression of R424H mutant subunits in PCs markedly affects the function of endogenous Kv3 channels, neuronal excitability and, eventually, basal [Ca 2+ ] i , leading to cell death. These
