calpain and Spinocerebellar-Ataxias

Spinocerebellar ataxia type 17 (SCA17) is a neurodegenerative disease caused by a polyglutamine-encoding trinucleotide repeat expansion in the gene of transcription factor TATA box-binding protein (TBP). While its underlying pathomechanism is elusive, polyglutamine-expanded TBP fragments of unknown origin mediate the mutant protein's toxicity. Calcium-dependent calpain proteases are protagonists in neurodegenerative disorders. Here, we demonstrate that calpains cleave TBP, and emerging C-terminal fragments mislocalize to the cytoplasm. SCA17 cell and rat models exhibited calpain overactivation, leading to excessive fragmentation and depletion of neuronal proteins in vivo. Transcriptome analysis of SCA17 cells revealed synaptogenesis and calcium signaling perturbations, indicating the potential cause of elevated calpain activity. Pharmacological or genetic calpain inhibition reduced TBP cleavage and aggregation, consequently improving cell viability. Our work underlines the general significance of calpains and their activating pathways in neurodegenerative disorders and presents these proteases as novel players in the molecular pathogenesis of SCA17.

Topics: Animals; Calpain; Neurons; Rats; Spinocerebellar Ataxias; Trinucleotide Repeat Expansion

Spastic ataxias are rare neurogenetic disorders involving spinocerebellar and pyramidal tracts. Many genes are involved. Among them, CAPN1, when mutated, is responsible for a complex inherited form of spastic paraplegia (SPG76). We report the largest published series of 21 novel patients with nine new CAPN1 disease-causing variants and their clinical characteristics from two European university hospitals (Paris and Stockholm). After a formal clinical examination, causative variants were identified by next-generation sequencing and confirmed by Sanger sequencing. CAPN1 variants are a rare cause (~ 1.4%) of young-adult-onset spastic ataxia; however, together with all published cases, they allowed us to better describe the clinical and genetic spectra of this form. Truncating variants are the most frequent, and missense variants lead to earlier age at onset in favor of an additional deleterious effect. Cerebellar ataxia with cerebellar atrophy, dysarthria and lower limb weakness are often associated with spasticity. We also suggest that cognitive impairment and depression should be assessed specifically in the follow-up of SPG76 cases.

Topics: Adult; Age of Onset; Calpain; Cerebellar Ataxia; Child; Female; Genetic Association Studies; Humans; Intellectual Disability; Male; Muscle Spasticity; Mutation; Optic Atrophy; Pedigree; Phenotype; Spastic Paraplegia, Hereditary; Spinocerebellar Ataxias; Young Adult

Recessive mutations in the CAPN1 gene have recently been identified in spastic paraplegia 76 (SPG76), a complex hereditary spastic paraplegia (HSP) that is combined with cerebellar ataxia, resulting in an ataxia-spasticity disease spectrum. This study aims to assess the influence of CAPN1 variants on the occurrence of SPG76 and identify factors potentially contributing to phenotypic heterogeneity.. We screened a cohort of 240 unrelated HSP families for variants in CAPN1 using high-throughput sequencing analysis. We described in detail the clinical and genetic features of the SPG76 patients in our cohort and summarized all reported cases.. Our study supports the clinically heterogeneous inter- and intra-family variability of SPG76 patients, and demonstrates that gender and calpain-1 linker structure may contribute to clinical heterogeneity in SPG76 cases.

Topics: Ataxia; Calpain; Cerebellar Ataxia; Female; Humans; Intellectual Disability; Male; Muscle Spasticity; Mutation; Optic Atrophy; Paraplegia; Pedigree; Phenotype; Spastic Paraplegia, Hereditary; Spinocerebellar Ataxias

To characterize the phenotype of CAPN1 (SPG76) mutations in patients diagnosed with hereditary spastic paraplegia (HSP).. The CAPN1 gene, located on chromosome 11q13.1, is a protein-coding gene involved in neuronal plasticity, migration, microtubular regulation and cerebellar development. Several families with CAPN1 mutations have recently been reported to present with autosomal recessive (AR) HSP and/or ataxia.. Patients with HSP were identified through neurological and genetic clinics with detailed phenotyping. Whole exome sequencing revealed novel pathogenic CAPN1 mutations in four patients from 3 families.. Affected families were of Turkish, Japanese, and Punjabi descent and all were consanguineous. Onset of spastic paraplegia in the four patients was between 20 and 37 years. Two also had mild ataxia. Three different novel, homozygous mutations in CAPN1 were found: c.2118+1G > T, c.397C > T, c.843+1G > C. The patient with the earliest onset also manifested profound muscle weakness, likely related to a second homozygous mutation in DYSF (dysferlinopathy).. The phenotype of AR CAPN1 mutations appears to be spastic paraplegia with or without ataxia; onset is most commonly in adulthood. Eye movement abnormalities, skeletal defects, peripheral neuropathy and amyotrophy can sometimes be seen. Occasionally, patients can present with ataxia, illustrating the genotypic and phenotypic overlap between HSP and spastic ataxia. With the advent of exome sequencing, mutations in more than one gene can be identified, which may contribute to the phenotypic variation, even within a family.

Topics: Adult; Calpain; Female; Humans; Intellectual Disability; Male; Muscle Spasticity; Mutation; Optic Atrophy; Paraparesis, Spastic; Phenotype; Spinocerebellar Ataxias

Spino-cerebellar ataxia type 7 (SCA7) is a polyglutamine (polyQ) disorder characterized by neurodegeneration of the brain, cerebellum, and retina caused by a polyglutamine expansion in ataxin7. The presence of an expanded polyQ tract in a mutant protein is known to induce protein aggregation, cellular stress, toxicity, and finally cell death. However, the consequences of the presence of mutant ataxin7 in the retina and the mechanisms underlying photoreceptor degeneration remain poorly understood. In this study, we show that in a retinal SCA7 mouse model, polyQ ataxin7 induces stress within the retina and activates Muller cells. Moreover, unfolded protein response and autophagy are activated in SCA7 photoreceptors. We have also shown that the photoreceptor death does not involve a caspase-dependent apoptosis but instead involves apoptosis inducing factor (AIF) and Leukocyte Elastase Inhibitor (LEI/L-DNase II). When these two cell death effectors are downregulated by their siRNA, a significant reduction in photoreceptor death is observed. These results highlight the consequences of polyQ protein expression in the retina and the role of caspase-independent pathways involved in photoreceptor cell death.

Topics: Animals; Apoptosis Inducing Factor; Ataxin-7; Calpain; Caspases; Cathepsins; Cell Death; Disease Models, Animal; Endodeoxyribonucleases; HEK293 Cells; Humans; Mice, Inbred C57BL; Mice, Transgenic; Peptides; Photoreceptor Cells; Retinal Degeneration; Signal Transduction; Spinocerebellar Ataxias; Stress, Physiological

Increasing availability of next-generation sequencing technologies has revealed several limitations of diagnosis-driven traditional clinicogenetic disease classifications, particularly among patients with an atypical or mixed phenotype. Hereditary spastic paraplegia (HSP) and spinocerebellar ataxia (SCA) are two such disease entities with an often overlapping presentation, in which next generation exome sequencing has played a key role in identification of genes causing disease along a continuum of ataxia and spasticity. We describe a patient who presented with features of both ataxia and spasticity, in whom initial diagnostic testing was inconclusive. Ultimately next generation exome sequencing identified homozygosity for a pathogenic variant in exon 13 of the

Topics: Adult; Calpain; Family Health; Female; Humans; Magnetic Resonance Imaging; Mutation; Phenotype; Spastic Paraplegia, Hereditary; Spinocerebellar Ataxias

A CAPN1 missense mutation in Parson Russell Terrier dogs is associated with spinocerebellar ataxia. We now report that homozygous or heterozygous CAPN1-null mutations in humans result in cerebellar ataxia and limb spasticity in four independent pedigrees. Calpain-1 knockout (KO) mice also exhibit a mild form of ataxia due to abnormal cerebellar development, including enhanced neuronal apoptosis, decreased number of cerebellar granule cells, and altered synaptic transmission. Enhanced apoptosis is due to absence of calpain-1-mediated cleavage of PH domain and leucine-rich repeat protein phosphatase 1 (PHLPP1), which results in inhibition of the Akt pro-survival pathway in developing granule cells. Injection of neonatal mice with the indirect Akt activator, bisperoxovanadium, or crossing calpain-1 KO mice with PHLPP1 KO mice prevented increased postnatal cerebellar granule cell apoptosis and restored granule cell density and motor coordination in adult mice. Thus, mutations in CAPN1 are an additional cause of ataxia in mammals, including humans.

Topics: Aging; Amino Acid Sequence; Animals; Animals, Newborn; Apoptosis; Calpain; Cell Count; Cerebellar Ataxia; Cerebellum; Enzyme Activation; Female; Humans; Intellectual Disability; Male; Mice, Knockout; Motor Activity; Muscle Spasticity; Mutation; Nuclear Proteins; Optic Atrophy; Phosphoprotein Phosphatases; Phosphorylation; Proto-Oncogene Proteins c-akt; Purkinje Cells; Spinocerebellar Ataxias; Synaptic Transmission

Spinocerebellar ataxia (SCA) in the Parson Russell Terrier (PRT) dog breed is a disease of progressive incoordination of gait and loss of balance. Clinical signs usually become notable between 6 and 12 months of age with affected dogs presenting with symmetric spinocerebellar ataxia particularly evident in the pelvic limbs. The degree of truncal ataxia, pelvic limb hypermetria and impaired balance is progressive, particularly during the initial months of disease. A certain degree of stabilisation as well as intermittent worsening may occur. At the later stages of the disease ambulation often becomes difficult, with owners often electing to euthanise affected dogs on welfare grounds. Using a GWAS approach and target-enriched massively-parallel sequencing, a strongly associated non-synonymous SNP in the CAPN1 gene, encoding the calcium dependent cysteine protease calpain1 (mu-calpain), was identified. The SNP is a missense mutation causing a cysteine to tyrosine substitution at residue 115 of the CAPN1 protein. Cysteine 115 is a highly conserved residue and forms a key part of a catalytic triad of amino acids that are crucial to the enzymatic activity of cysteine proteases. The CAPN1 gene shows high levels of expression in the brain and nervous system and roles for the protein in both neuronal necrosis and maintenance have been suggested. Given the functional implications and high level of conservation observed across species, the CAPN1 variant represents a provocative candidate for the cause of SCA in the PRT and a novel potential cause of ataxia in humans.

Topics: Alleles; Amino Acid Sequence; Animals; Base Sequence; Calpain; Chromosomes, Mammalian; Dog Diseases; Dogs; Gait; Genetic Linkage; Heterozygote; High-Throughput Nucleotide Sequencing; Homozygote; Humans; Male; Molecular Sequence Data; Mutation, Missense; Polymorphism, Single Nucleotide; Spinocerebellar Ataxias