Similarities between spinocerebellar ataxia type 7 (SCA7) cell models and human brain: proteins recruited in inclusions and activation of caspase-3

Abstract

Spinocerebellar ataxia type 7 (SCA7) is an autosomal dominant polyglutamine disorder presenting with progressive cerebellar ataxia and blindness. The molecular mechanisms underlying the selective neuronal death typical of SCA7 are unknown. We have established SCA7 cell culture models in HEK293 and SH-SY5Y cells, in order to analyse the effects of overexpression of the mutant ataxin-7 protein. The cells readily formed anti-ataxin-7 positive, fibrillar inclusions and small, nuclear electron dense structures. We have compared the inclusions in cells expressing mutant ataxin-7 and in human SCA7 brain tissue. There were consistent signs of ongoing abnormal protein folding, including the recruitment of heat-shock proteins and proteasome subunits. Occasionally, sequestered transcription factors were found. Activated caspase-3 was recruited into the inclusions in both the cell models and human SCA7 brain and its expression was upregulated in cortical neurones, suggesting that it may play a role in the disease process. Finally, on the ultrastructural level, there were signs of autophagy and nuclear indentations, indicative of a major stress response in cells expressing mutant ataxin-7.

Inhibition of Autophagy via p53-Mediated Disruption of ULK1 in a SCA7 Polyglutamine Disease Model

“…This hypothesis is supported by the observation of p53 in SCA7 inclusions (Zander et al, 2001), and co-aggregation of p53 with ATXN7 and FIP200 in our model. However, ATXN7 could also indirectly alter p53 function by activating signaling pathways resulting in post-translational modification of p53.…”

“…The p53 protein has been reported to be sequestered into inclusions in several polyQ diseases, including SCA7 (Zander et al, 2001). We therefore considered that sequestration of the p53-FIP200 complex into ATXN7 aggregates could be involved in the destabilization of ULK1 and the autophagy inhibition.…”

A Conditional Pan-NeuronalDrosophilaModel of Spinocerebellar Ataxia 7 with a Reversible Adult Phenotype Suitable for Identifying Modifier Genes

“…Previously described truncated versions of the SCA7 cDNA (amino acids 1-232) (Zander et al, 2001), wild type (SCA7T-10Q) and expanded (SCA7T-100Q), with an added nuclear localization signal derived from Sv40 (simian virus 40), were subcloned in pUAST (Brand and Perrimon, 1993), during which two CAG triplets were added because of instability of the sequence. All constructs were sequenced, and the size of the expressed proteins was confirmed by Western blot.…”

“…We showed previously that the transgenes encoding truncated forms (amino acids 1-232) of wild-type (SCA7T-10Q) and mutant (SCA7T-100Q) ATXN7 are expressed at higher levels, and the resulting proteins aggregate faster than full-length ATXN7 in human cells in culture (Zander et al, 2001). We have now used these transgenes to generate SCA7 Drosophila.…”

“…PolyQ diseases are postulated to result from a pathogenic gain of function mediated by the polyQ expansion, but the role of NIIs in the pathogenesis of the disease remains unclear: toxic Scherzinger et al, , 1999Skinner et al, 1997;Becher et al, 1998;Gusella and MacDonald, 2000), nontoxic (Holmberg et al, 1998;Klement et al, 1998;Saudou et al, 1998;Sathasivam et al, 1999), or protective (Saudou et al, 1998). Cell stress markers have been found in NIIs in cell culture (Zander et al, 2001;Latouche et al, 2006) and mouse models of SCA7 (Yvert et al, , 2001La Spada et al, 2001;Yoo et al, 2003), but the polyQ expansion in ATXN7 may impair the activity of TFTC/STAGA complexes independently of aggregate formation (McMahon et al, 2005;Palhan et al, 2005;Strom et al, 2005).…”