Contactin-associated protein-2 antibodies in non-paraneoplastic cerebellar ataxia

Background Relatively few studies have searched for potentially pathogenic antibodies in non-paraneoplastic patients with cerebellar ataxia. Methods and Results We first screened sera from 52 idiopathic ataxia patients for binding of serum IgG antibodies to cerebellar neurons. One strong-binding serum was selected for immunoprecipitation and mass spectrometry, which resulted in the identification of contactin-associated protein 2 (CASPR2) as a major antigen. CASPR2 antibodies were then found by a cell-based assay in 9/88 (10%) ataxia patients, compared to 3/144 (2%) multiple sclerosis or dementia controls (p=0.011). CASPR2 is strongly expressed in the cerebellum, only partly in association with voltage-gated potassium channels. Conclusions Prospective studies are now needed to see whether identification of CASPR2 antibodies has relevance for the diagnosis and treatment of idiopathic cerebellar ataxia

Candidate Screening of the TRPC3 Gene in Cerebellar Ataxia

The hereditary cerebellar ataxias are a diverse group of neurodegenerative disorders primarily characterised by loss of balance and coordination due to dysfunction of the cerebellum and its associated pathways. Although many genetic mutations causing inherited cerebellar ataxia have been identified, a significant percentage of patients remain whose cause is unknown. The transient receptor potential (TRP) family member TRPC3 is a non-selective cation channel linked to key signalling pathways that are affected in cerebellar ataxia. Furthermore, genetic mouse models of TRPC3 dysfunction display cerebellar ataxia, making the TRPC3 gene an excellent candidate for screening ataxic patients with unknown genetic aetiology. Here, we report a genetic screen for TRPC3 mutations in a cohort of 98 patients with genetically undefined late-onset cerebellar ataxia and further ten patients with undefined episodic ataxia. We identified a number of variants but no causative mutations in TRPC3. Our findings suggest that mutations in TRPC3 do not significantly contribute to the cause of late-onset and episodic human cerebellar ataxias

Investigating the effects of a point mutation in the TRPC3 channel – cause of cerebellar ataxia in Moonwalker mice – on the Purkinje cells in mice

The Moonwalker (Mwk) mouse is a mouse model of cerebellar ataxia that harbours a point mutation in the Trpc3 gene. TRPC3 is a non-selective cation channel, most highly expressed in the Purkinje cells of the cerebellum. The gain-of-function mutation in the TRPC3 protein affects the development of Purkinje cell dendrites by reducing their branching, and also leads to abnormal motor coordination and cerebellar ataxia in Mwk mice at the age of 3 weeks. The aim of this thesis was to determine how the mutation in the TRPC3 channel results in the observed pathology.Proper function of the TRPC3 channel relies on its interaction with other proteins, hence we investigated binding partners of TRPC3. The study revealed PI synthase and CaMKIV as novel interaction partners of TRPC3. PI synthase is implicated in the upstream signalling events leading to TRPC3 activation, whereas CaMKIV is activated by Ca2+, possibly due to TRPC3 activation. We have identified alterations in phosphorylation of several key Ca2+ signalling proteins (CaMKII, CaMKIV, CREB and ERK), which indicates that there are changes in Ca2+ homeostasis in Mwk cerebella. Down-regulation of CaMKIV and up-regulation of CREB phosphorylation occurs as early as P21, which indicates that their abnormal activity could contribute to the Mwk phenotype. Microarray analysis comparing wild-type and Mwk Purkinje cells has revealed gene expression changes, which are likely due to abnormal Ca2+ signalling. Genes Ipo5, Opn3 and Sv2c are up-regulated at P11; Car2 and Stk17b are down-regulated at P14; and Cntn3 is up-regulated at P18 in Mwk Purkinje cells. High quality RNA from Purkinje cells was extracted using an optimised laser-capture microdissection method.Work on the Mwk mice points to the importance of TRPC3 activity for the proper development of Purkinje cell dendrites and depicts TRPC3 as a possible target for cerebellar ataxia treatment.</p

Investigating the effects of a point mutation in the TRPC3 channel – cause of cerebellar ataxia in Moonwalker mice – on the Purkinje cells in mice

The Moonwalker (Mwk) mouse is a mouse model of cerebellar ataxia that harbours a point mutation in the Trpc3 gene. TRPC3 is a non-selective cation channel, most highly expressed in the Purkinje cells of the cerebellum. The gain-of-function mutation in the TRPC3 protein affects the development of Purkinje cell dendrites by reducing their branching, and also leads to abnormal motor coordination and cerebellar ataxia in Mwk mice at the age of 3 weeks. The aim of this thesis was to determine how the mutation in the TRPC3 channel results in the observed pathology.Proper function of the TRPC3 channel relies on its interaction with other proteins, hence we investigated binding partners of TRPC3. The study revealed PI synthase and CaMKIV as novel interaction partners of TRPC3. PI synthase is implicated in the upstream signalling events leading to TRPC3 activation, whereas CaMKIV is activated by Ca2+, possibly due to TRPC3 activation. We have identified alterations in phosphorylation of several key Ca2+ signalling proteins (CaMKII, CaMKIV, CREB and ERK), which indicates that there are changes in Ca2+ homeostasis in Mwk cerebella. Down-regulation of CaMKIV and up-regulation of CREB phosphorylation occurs as early as P21, which indicates that their abnormal activity could contribute to the Mwk phenotype. Microarray analysis comparing wild-type and Mwk Purkinje cells has revealed gene expression changes, which are likely due to abnormal Ca2+ signalling. Genes Ipo5, Opn3 and Sv2c are up-regulated at P11; Car2 and Stk17b are down-regulated at P14; and Cntn3 is up-regulated at P18 in Mwk Purkinje cells. High quality RNA from Purkinje cells was extracted using an optimised laser-capture microdissection method.Work on the Mwk mice points to the importance of TRPC3 activity for the proper development of Purkinje cell dendrites and depicts TRPC3 as a possible target for cerebellar ataxia treatment.This thesis is not currently available via ORA