Investigation of the Pathophysiology of Spinocerebellar Degeneration

Spinocerebellar degeneration is a neurodegenerative disorder identified as a single entity or as part of another condition. It can occur in an inherited or non-inherited form, which are often clinically identical. In spinocerebellar ataxia and other neurodegenerative disorders such as Alzheimer‘s disease a key feature is the laying down of pathological protein as deposits in the brain. Using cell models and analysis of brain tissue, the disease processes and pathways that lead to these diseases can be elucidated. This may in turn allow the development of techniques to inhibit or reverse the disease process.

This project aims to identify and characterise the genetic cause of a familial form of spinocerebellar ataxia. When the gene is found, it will be only the second gene to be found in families whose main problem is pure cerebellar ataxia. Given the clinical and pathological features of this type of ataxia it may represent an important previously unrecognised pathogenic mechanism. This gene will be characterised in many other ataxia families and in individuals with no family history. The function of the gene will be investigated in cell culture models and donated human brain tissue to identify how this gene causes disease.

The aim of this research is to identify and characterise the processes that lead to spinocerebellar degeneration using clinical, genetic, neuropathological and cell biology approaches that are well established in the host and collaborating laboratories. Ataxia is a common neurological disorder presenting either as an isolated condition or part of another neurological disorder. In ataxia, like many other neurodegenerative disorders, disease protein is deposited in the brain and this process has been proposed to be responsible for the pathogenesis. However, there is increasing evidence that these protein aggregates may in fact protect neurons.

A combination of genetic fine mapping and candidate gene sequencing will be employed to identify the disease gene in a family with a type of spinocerebellar ataxia (SCA11) showing genetic linkage to the genomic region 15q14-15. There is no anticipation in this family and a large repeat expansion has been excluded. Haplotype analysis will also be carried out in other SCA families with a similar phenotype. When identified, the SCA11 gene will be characterised in terms of its structure and pathological tissue expression by Northern and Western blotting analyses with the human SCA11 cDNA and with raised antibodies recognising the SCA11 protein respectively. Subsequently, other SCA families and sporadic cases with this common phenotype will be screened for the SCA11 molecular defect. The functional effects of the SCA11 defect will be analysed in transient and stable neuronal cell lines expressing the SCA11 molecular defect. The expressed proteins will then be investigated using a variety of antibodies recognising molecular routes and pathways implicated in the pathological process of other SCA subtypes.

Together with the cell biology studies, immunohistochemistry using the developed SCA11 antibodies and other primary antibodies will be performed in affected SCA11 brains and compared with other neurodegenerative diseases. Functional studies of the disease protein associated with SCA11 will be carried out using a yeast genetic two-hybrid screen with the aim of identifying interacting proteins and molecular pathways involved in disease. Proteomic studies will then be used to further characterise protein complexes and investigate their role in SCA11 pathogenesis.

This approach will identify, characterise and determine the function of the SCA11 gene and its encoded protein. Like SCA6, SCA11 may prove to be part of a novel mechanism of spinocerebellar degeneration. Deciphering the disease processes and protein interactions in spinocerebellar degeneration and other neurodegenerative diseases should ultimately lead to the development of therapeutic strategies.