Purkinje cell COX deficiency and mtDNA depletion in an animal model of spinocerebellar ataxia type 1

• Published in: Journal of neuroscience research 2018-09, Vol.96 (9), p.1576-1585
• Main Authors: Ripolone, Michela, Lucchini, Valeria, Ronchi, Dario, Fagiolari, Gigliola, Bordoni, Andreina, Fortunato, Francesco, Mondello, Stefania, Bonato, Sara, Meregalli, Mirella, Torrente, Yvan, Corti, Stefania, Comi, Giacomo P., Moggio, Maurizio, Sciacco, Monica
• Format: Article
• Language: English
• Subjects: Ataxia; Ataxin; Atrophy; Cell death; Cerebellum; Cytochrome; Cytochromes; Degeneration; Deoxyribonucleic acid; Depletion; DNA; DNA repeat expansion; Gait; laser microdissector; Metabolism; Mice; mitochondria; Mitochondrial DNA; mitochondrial DNA depletion; Mouse devices; oxidative damage; Oxidative metabolism; Phenotypes; Polyglutamine; Polymerase chain reaction; Proteins; Purkinje cell; Purkinje cells; Spinocerebellar ataxia; spinocerebellar ataxia type 1; Transgenic mice; Trinucleotide repeat diseases; Trinucleotide repeats
• ISSN: 0360-4012; 1097-4547
• DOI: 10.1002/jnr.24263

Spinocerebellar ataxias (SCAs) are a genetically heterogeneous group of cerebellar degenerative disorders, characterized by progressive gait unsteadiness, hand incoordination, and dysarthria. Ataxia type 1 (SCA1) is caused by the expansion of a CAG trinucleotide repeat in the SCA1 gene resulting in the atypical extension of a polyglutamine (polyQ) tract within the ataxin‐1 protein. Our main objective was to investigate the mitochondrial oxidative metabolism in the cerebellum of transgenic SCA1 mice. SCA1 transgenic mice develop clinical features in the early life stages (around 5 weeks of age) presenting pathological cerebellar signs with concomitant progressive Purkinje neuron atrophy and relatively little cell loss; this evidence suggests that the SCA1 phenotype is not the result of cell death per se, but a possible effect of cellular dysfunction that occurs before neuronal demise. We studied the mitochondrial oxidative metabolism in cerebellar cells from both homozygous and heterozygous transgenic SCA1 mice, aged 2 and 6 months. Histochemical examination showed a cytochrome‐c‐oxidase (COX) deficiency in the Purkinje cells (PCs) of both heterozygous and homozygous mice, the oxidative defect being more prominent in older mice, in which the percentage of COX‐deficient PC was up to 30%. Using a laser‐microdissector, we evaluated the mitochondrial DNA (mtDNA) content on selectively isolated COX‐competent and COX‐deficient PC by quantitative Polymerase Chain Reaction and we found mtDNA depletion in those with oxidative dysfunction. In conclusion, the selective oxidative metabolism defect observed in neuronal PC expressing mutant ataxin occurs as early as 8 weeks of age thus representing an early step in the PC degeneration process in SCA1 disease. This work uses an animal model to try to understand the pathogenesis of a progressive human disease (Spinocerebellar Ataxia 1, SCA1). In particular, we investigate the mitochondrial oxidative metabolism in the cerebellum of transgenic SCA1 mice focusing our studies on the progressive dysfunction of Purkinje cells (PC). Histochemical examination showed a cytochrome‐c‐oxidase (COX) deficiency in PC of TG‐mice, the oxidative defect being more prominent in older mice, in which the percentage of COX‐deficient PC was up to 30%. Using a laser‐microdissector, we evaluated the mitochondrial DNA content on selectively isolated COX‐competent and COX‐deficient PC by quantitative PCR and we found mtDNA depletion in those with ox