My group’s research focuses on physiological mechanisms underlying Purkinje cell dysfunction and degeneration, particularly in the context of dominantly inherited spinocerebellar ataxias (SCAs), a group of neurological disorders characterized by loss of balance and motor coordination. Using knockout technology we have created a new in vivo model of ataxia, which in conjunction with cell culture methods is being studied to unravel what biological pathways and cell populations underlie progressive ataxia.
Causal genetic mutations have been identified for sixteen subtypes of SCA and recently mutations in the gene SPTBN2, which encodes β-III spectrin, were identified as the genetic cause of SCA5 (Ikeda et al., 2006). We know from my previous work that β-III spectrin interacts with and increases EAAT4 cell surface expression, the glutamate transporter predominantly expressed in cerebellar Purkinje cells (Jackson et al., 2001). Sodium-dependent glutamate transporters remove glutamate from the synaptic cleft and neurotoxic levels of glutamate arise from the malfunction or aberrant expression of these proteins.
To further investigate the role of β-III spectrin in normal cerebellar development and SCA5 disease pathogenesis we have knocked-out the expression of β-III spectrin, creating an in vivo β-III spectrin deficient model. This has revealed that loss of β-III spectrin function leads to a splayed gait, progressive motor incoordination, tremor, and cerebellar degeneration, all characteristic features of cerebellar ataxia (Perkins et al., 2010). Analysis of this disease model has allowed us to identify sodium channel dysfunction and glutamate transporter loss, both neuronal (EAAT4) and astroglial (GLAST), as factors in disease pathogenesis.
Our current research directions focus on 1) elucidating what changes occur in the absence of wild type β-III spectrin or in the presence of β-III spectrin with mutations associated with SCA5; 2) identifying whether astrocytes play a role in Purkinje cell degeneration; 3) determining whether the disease phenotype can be rescued; 4) understanding the role β-III spectrin plays in normal Purkinje cell development and; 5) identifying other proteins that interact with β-III spectrin, thus highlighting other potential cellular pathways that could underlie neurodegeneration. A variety of techniques including genetic crosses, electrophysiology, cellular imaging, cell culture studies and yeast two-hybrid screens are being employed in the lab to achieve the research aims.
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Lise S, Clarkson Y, Perkins E et al. Recessive mutations in SPTBN2 implicate Beta-III spectrin in both cognitive and motor development. PLoS Genet (2012) Dec;8(12): e1003074
Gao Y, Perkins EM, Clarkson YL, Tobia S, Lyndon AR, Jackson M, Rothstein JD (2011) Beta-III spectrin is critical for development of Purkinje cell dendritic tree and spine morphogenesis. J Neuroscience 31, 16581-90
Clarkson YL, Gillespie T, Perkins EM, Lyndon AR and Jackson M (2010) Beta-III spectrin mutation L253P associated with spinocerebellar ataxia type 5 interferes with binding to Arp1 and protein trafficking from Golgi. Hum. Mol. Genet. 19: 3634-364
Perkins EM, Clarkson YL, Sabatier N et al (2010) Loss of Beta-III spectrin leads to Purkinje cell dysfunction recapitulating the behaviour and neuropathology of spinocerebellar ataxia type 5 in humans. J. Neurosci. 30: 4857-4867
Longhurst DM, Watanabe M, Rothstein JD and Jackson M (2006) Interaction of PDZRhoGEF with microtubule-associated protein 1 light chains: Link between microtubules, actin cytoskeleton and neuronal polarity. J. Biol. Chem. 281: 12030-12040
Jackson M, Song W, Liu M-Y, Jin L, Dykes-Hoberg M, Lin, C-LG, Bowers WJ, Federoff HJ, Sternweis PC and Rothstein JD (2001). Modulation of the neuronal glutamate transporter EAAT4 by two interacting proteins. Nature 410:89-93
This article was published on Aug 5, 2013