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Abstract Spinocerebellar ataxia 28 is an autosomal dominant neurodegenerative disorder caused by missense mutations affecting the proteolytic domain of AFG3L2, a major component of the mitochondrial m -AAA protease. However, little is known of the underlying pathogenetic mechanisms or how to treat patients with SCA28. Currently available Afg3l2 mutant mice harbour deletions that lead to severe, early-onset neurological phenotypes that do not faithfully reproduce the late-onset and slowly progressing SCA28 phenotype. Here we describe production and detailed analysis of a new knock-in murine model harbouring an Afg3l2 allele carrying the p.Met665Arg patient-derived mutation. Heterozygous mutant mice developed normally but adult mice showed signs of cerebellar ataxia detectable by beam test. Although cerebellar pathology was negative, electrophysiological analysis showed a trend towards increased spontaneous firing in Purkinje cells from heterozygous mutants with respect to wild-type controls. As homozygous mutants died perinatally with evidence of cardiac atrophy, for each genotype we generated mouse embryonic fibroblasts (MEFs) to investigate mitochondrial function. MEFs from mutant mice showed altered mitochondrial bioenergetics, with decreased basal oxygen consumption rate, ATP synthesis and mitochondrial membrane potential. Mitochondrial network formation and morphology was altered, with greatly reduced expression of fusogenic Opa1 isoforms. Mitochondrial alterations were also detected in cerebella of 18-month-old heterozygous mutants and may be a hallmark of disease. Pharmacological inhibition of de novo mitochondrial protein translation with chloramphenicol caused reversal of mitochondrial morphology in homozygous mutant MEFs, supporting the relevance of mitochondrial proteotoxicity for SCA28 pathogenesis and therapy development. Graphical abstract Unlabelled Image Highlights • We generated a knock-in mouse model of SCA28 harbouring a p.Met665Arg -Afg3l2 allele. • Homozygous mutants died perinatally with evidence of cardiac atrophy. • Heterozygous mice developed normally but presented late-onset cerebellar ataxia. • MEFs showed altered mitochondrial bioenergetics and dynamics. • Proteotoxicity is suggested to be responsible for SCA28 pathogenesis. [ABSTRACT FROM AUTHOR]

Transition metals are cofactors for a wide range of vital enzymes and are directly or indirectly involved in the response against reactive oxygen species (ROS), which can damage cellular components. Their altered homeostasis has been studied in neurodegenerative disorders such as Alzheimer's disease (AD), Parkinson's disease (PD) and amyotrophic lateral sclerosis (ALS), but no data are available on rarer conditions. We aimed at studying the role of essential trace elements in ataxia telangiectasia (A-T), a rare form of pediatric autosomal recessive cerebellar ataxia with altered antioxidant response. We found an increased level of copper (Cu, p = 0.0002) and a reduced level of zinc (Zn, p = 0.0002) in the blood of patients (n. 16) compared to controls, using inductively coupled plasma mass spectrometry (ICP-MS). Other trace elements involved in the oxidative stress response, such as manganese (Mn) and selenium (Se), were unaltered. Cu/Zn-dependent superoxide dismutase (SOD1) was shown to have a 30% reduction in gene expression and 40% reduction in enzyme activity upon analysis of lymphoblastoid cell lines of patients (Student's t -test, p = 0.0075). We also found a 30% reduction of Mn-SOD (SOD2; Student's t -test, p = 0.02), probably due to a feedback regulatory loop between the two enzymes. The expression of antioxidant enzymes, such as erythrocyte glutathione peroxidase ( GPX1 ), and SOD2 was unaltered, whereas catalase ( CAT ) was increased in A-T cells, both at the mRNA level and in terms of enzyme activity (~ 25%). Enhanced CAT expression can be attributed to the high ROS status, which induces CAT transcription. These results suggest that alterations in essential trace elements and their related enzymes may play a role in the pathogenesis of A-T, although we cannot conclude if altered homeostasis is a direct effect of A-T mutated genes ( ATM ). Altered homeostasis of trace elements may be more prevalent in neurodegenerative diseases than previously thought, and it may represent both a biomarker and a generic therapeutic target for different disorders with the common theme of altered antioxidant enzyme responses associated with an unbalance of metals. [ABSTRACT FROM AUTHOR]