Mouse brain expression patterns of Spg7, Afg3l1, and Afg3l2 transcripts, encoding for the mitochondrial m-AAA protease

Multifaceted Roles of AFG3L2, a Mitochondrial ATPase in Relation to Neurological Disorders

AFG3L2 is a zinc metalloprotease and an ATPase localized in an inner mitochondrial membrane involved in mitochondrial quality control of several nuclear- and mitochondrial-encoded proteins. Mutations in AFG3L2 lead to diseases like slow progressive ataxia, which is a neurological disorder. This review delineates the cellular functions of AFG3L2 and its dysfunction that leads to major clinical outcomes, which include spinocerebellar ataxia type 28, spastic ataxia type 5, and optic atrophy type 12. It summarizes all relevant AFG3L2 mutations associated with the clinical outcomes to understand the detailed mechanisms attributable to its structure-related multifaceted roles in proteostasis and quality control. We face early diagnostic challenges of ataxia and optic neuropathy due to asymptomatic parents and variable clinical manifestations due to heterozygosity/homozygosity of AFG3L2 mutations. This review intends to promote AFG3L2 as a putative prognostic or diagnostic marker.

Mitochondrial Parkinsonism: A Practical Guide to Genes and Clinical Diagnosis

BACKGROUND

Primary mitochondrial diseases (PMDs) are the most common inborn errors of energy metabolism, with a combined prevalence of 1 in 4300. They can result from mutations in either nuclear DNA (nDNA) or mitochondrial DNA (mtDNA). These disorders are multisystemic and mainly affect high energy-demanding tissues, such as muscle and the central nervous system (CNS). Among many clinical features of CNS involvement, parkinsonism is one of the most common movement disorders in PMDs.

METHODS

This review provides a pragmatic educational overview of the most recent advances in the field of mitochondrial parkinsonism, from pathophysiology and genetic etiologies to phenotype and diagnosis.

RESULTS

mtDNA maintenance and mitochondrial dynamics alterations represent the principal mechanisms underlying mitochondrial parkinsonism. It can be present in isolation, alongside other movement disorders or, more commonly, as part of a multisystemic phenotype. Mutations in several nuclear-encoded genes (ie, POLG, TWNK, SPG7, and OPA1) and, more rarely, mtDNA mutations, are responsible for mitochondrial parkinsonism. Progressive external opthalmoplegia and optic atrophy may guide genetic etiology identification.

CONCLUSION

A comprehensive deep-phenotyping approach is needed to reach a diagnosis of mitochondrial parkinsonism, which lacks distinctive clinical features and exemplifies the intricate genotype-phenotype interplay of PMDs.

Parkinsonism in complex neurogenetic disorders: lessons from hereditary dementias, adult-onset ataxias and spastic paraplegias

Parkinsonism is a syndrome characterized by bradykinesia in combination with either rest tremor, rigidity, or both. These features are the cardinal manifestations of Parkinson's disease, the most common cause of parkinsonism, and atypical parkinsonian disorders. However, parkinsonism can be a manifestation of complex neurological and neurodegenerative genetically determined disorders, which have a vast and heterogeneous motor and non-motor phenotypic features. Hereditary dementias, adult-onset ataxias and spastic paraplegias represent only few of this vast group of neurogenetic diseases. This review will provide an overview of parkinsonism's clinical features within adult-onset neurogenetic diseases which a neurologist could face with. Understanding parkinsonism and its characteristics in the context of the aforementioned neurological conditions may provide insights into pathophysiological mechanisms and have important clinical implications, including diagnostic and therapeutic aspects.

Analysis of dog breed diversity using a composite selection index

During breed development, domestic dogs have undergone genetic bottlenecks and sustained selective pressures, as a result distinctive genomic diversity occurs to varying degrees within and between breed groups. This diversity can be identified using standard methods or combinations of these methods. This study explored the application of a combined selection index, composite selection signals (CSS), derived from multiple methods to an existing genotype dataset from three breed groups developed in distinct regions of Asia: Qinghai-Tibet plateau dogs (adapted to living at altitude), Xi dogs (with superior running ability) and Mountain hounds (used for hunting ability). The CSS analysis confirmed top ranked genomic regions on CFA10 and CFA21 in Qinghai-Tibet plateau dogs, CFA1 in Xi dogs and CFA5 in Mountain hounds. CSS analysis identified additional significant genomic regions in each group, defined by a total of 1,397, 1,475 and 1,675 significant SNPs in the Qinghai-Tibetan Plateau dogs, Xi dogs and Mountain hounds, respectively. Chitinase 3 Like 1 (CHI3L1) and Leucine Rich Repeat Containing G Protein-Coupled Receptor 6 (LGR6) genes were located in the top ranked region on CFA7 (0.02-1 Mb) in the Qinghai-Tibetan Plateau dogs. Both genes have been associated with hypoxia responses or altitude adaptation in humans. For the Xi dogs, the top ranked region on CFA25 contained the Transient Receptor Potential Cation Channel Subfamily C Member 4 (TRPC4) gene. This calcium channel is important for optimal muscle performance during exercise. The outstanding signals in the Mountain dogs were on CFA5 with 213 significant SNPs that spanned genes involved in cardiac development, sight and generation of biochemical energy. These findings support the use of the combined index approach for identifying novel regions of genome diversity in dogs. As with other methods, the results do not prove causal links between these regions and phenotypes, but they may assist in focusing future studies that seek to identify functional pathways that contribute to breed diversity.

Molecular and functional heterogeneity in dorsal and ventral oligodendrocyte progenitor cells of the mouse forebrain in response to DNA damage

In the developing mouse forebrain, temporally distinct waves of oligodendrocyte progenitor cells (OPCs) arise from different germinal zones and eventually populate either dorsal or ventral regions, where they present as transcriptionally and functionally equivalent cells. Despite that, developmental heterogeneity influences adult OPC responses upon demyelination. Here we show that accumulation of DNA damage due to ablation of citron-kinase or cisplatin treatment cell-autonomously disrupts OPC fate, resulting in cell death and senescence in the dorsal and ventral subsets, respectively. Such alternative fates are associated with distinct developmental origins of OPCs, and with a different activation of NRF2-mediated anti-oxidant responses. These data indicate that, upon injury, dorsal and ventral OPC subsets show functional and molecular diversity that can make them differentially vulnerable to pathological conditions associated with DNA damage.

Positive DAT-SCAN in SPG7: a case report mimicking possible MSA-C

Background

Spastic Paraplegia type 7 (SPG7) is one of the most common autosomal recessive Hereditary Spastic Paraplegias (HSP); Spastic Paraplegias (SPGs) can present as hereditary ataxias. However, ataxia is frequently the symptom of presentation of many other hereditary/sporadic disorders, such as Multiple system atrophy type C (MSA-C), an α-synuclein sporadic neurodegenerative disorder, in which cerebellar ataxia is one of the main clinical features. Dopamine Transporter imaging (DAT-SCAN), associated with clinical features, can be a helpful tool in order to distinguish MSA-C from other causes of ataxia.

Case-presentation

We present the case of a 70-year-old man with gait difficulties over a period of 3 years and frequent backward/lateral falls. He also reported urinary urge incontinence, but no symptoms that are compatible with orthostatic hypotension. On neurological examination he showed ataxic gait, spasticity in the left lower limb and trunk and limb ataxia, especially on the left side. Mild hypokinesia was found in all 4 limbs, especially in the left foot. MRI revealed atrophy of the cerebellar hemispheres and vermis. DAT-SCAN imaging revealed bilateral nigro-striatal degeneration, which was compatible with a diagnosis of possible MSA-C. Considering the atypical disease course (the patient walked without any support after 3 years), we carried out a genetic investigation for Ataxia, and a mutation in SPG7 was found.

Conclusions

DAT-SCAN imaging, evaluated together with the clinical findings, can be useful for differentiating MSA from other possible causes of adult-onset Ataxia. Indeed, patients with MSA-C generally show a decreased uptake of dopamine transporters in DAT-SCAN imaging. Ours is the first case reported in the literature of a patient with SPG7 mutation with nigrostriatal degeneration and a clinical presentation of a possible MSA-C. Performing genetic investigations in patients with an atypical disease course is important to avoid MSA-mimicries.

Identifying the correct diagnosis is important not only for prognostic reasons, but also for possible future genetic therapies.

Elovl5 Expression in the Central Nervous System of the Adult Mouse

ELOVL5 (Elongase of Very-Long Fatty Acid 5) gene encodes for an enzyme that elongates long chain fatty acids, with a marked preference for polyunsaturated molecules. In particular, it plays an essential role in the elongation of omega-3 and omega-6 fatty acids, precursors for long-chain polyunsaturated fatty acids (PUFAs). Mutations of ELOVL5 cause the spino-cerebellar ataxia type 38 (SCA38), a rare autosomal neurological disease characterized by gait abnormality, dysarthria, dysphagia, hyposmia and peripheral neuropathy, conditions well represented by a mouse model with a targeted deletion of this gene (Elovl5^–/– mice). However, the expression pattern of this enzyme in neuronal and glial cells of the central nervous system (CNS) is still uninvestigated. This work is aimed at filling this gap of knowledge by taking advantage of an Elovl5-reporter mouse line and immunofluorescence analyses on adult mouse CNS sections and glial cell primary cultures. Notably, Elovl5 appears expressed in a region- and cell type-specific manner. Abundant Elovl5-positive cells were found in the cerebellum, brainstem, and primary and accessory olfactory regions, where mitral cells show the most prominent expression. Hippocampal pyramidal cells of CA2/CA3 where also moderately labeled, while in the rest of the telencephalon Elovl5 expression was high in regions related to motor control. Analysis of primary glial cell cultures revealed Elovl5 expression in oligodendroglial cells at various maturation steps and in microglia, while astrocytes showed a heterogeneous in vivo expression of Elovl5. The elucidation of Elovl5 CNS distribution provides relevant information to understand the physiological functions of this enzyme and its PUFA products, whose unbalance is known to be involved in many pathological conditions.

c-Jun N-terminal kinase 1 (JNK1) modulates oligodendrocyte progenitor cell architecture, proliferation and myelination

During Central Nervous System ontogenesis, myelinating oligodendrocytes (OLs) arise from highly ramified and proliferative precursors called oligodendrocyte progenitor cells (OPCs). OPC architecture, proliferation and oligodendro-/myelino-genesis are finely regulated by the interplay of cell-intrinsic and extrinsic factors. A variety of extrinsic cues converge on the extracellular signal-regulated kinase/mitogen activated protein kinase (ERK/MAPK) pathway. Here we found that the germinal ablation of the MAPK c-Jun N-Terminal Kinase isoform 1 (JNK1) results in a significant reduction of myelin in the cerebral cortex and corpus callosum at both postnatal and adult stages. Myelin alterations are accompanied by higher OPC density and proliferation during the first weeks of life, consistent with a transient alteration of mechanisms regulating OPC self-renewal and differentiation. JNK1 KO OPCs also show smaller occupancy territories and a less complex branching architecture in vivo. Notably, these latter phenotypes are recapitulated in pure cultures of JNK1 KO OPCs and of WT OPCs treated with the JNK inhibitor D-JNKI-1. Moreover, JNK1 KO and WT D-JNKI-1 treated OLs, while not showing overt alterations of differentiation in vitro, display a reduced surface compared to controls. Our results unveil a novel player in the complex regulation of OPC biology, on the one hand showing that JNK1 ablation cell-autonomously determines alterations of OPC proliferation and branching architecture and, on the other hand, suggesting that JNK1 signaling in OLs participates in myelination in vivo.

Evidence for Non-Mendelian Inheritance in Spastic Paraplegia 7

BACKGROUND

Although the typical inheritance of spastic paraplegia 7 is recessive, several reports have suggested that SPG7 variants may also cause autosomal dominant hereditary spastic paraplegia (HSP).

OBJECTIVES

We aimed to conduct an exome-wide genetic analysis on a large Canadian cohort of HSP patients and controls to examine the association of SPG7 and HSP.

METHODS

We analyzed 585 HSP patients from 372 families and 1175 controls, including 580 unrelated individuals. Whole-exome sequencing was performed on 400 HSP patients (291 index cases) and all 1175 controls.

RESULTS

The frequency of heterozygous pathogenic/likely pathogenic SPG7 variants (4.8%) among unrelated HSP patients was higher than among unrelated controls (1.7%; OR 2.88, 95% CI 1.24-6.66, P = 0.009). The heterozygous SPG7 p.(Ala510Val) variant was found in 3.7% of index patients versus 0.85% in unrelated controls (OR 4.42, 95% CI 1.49-13.07, P = 0.005). Similar results were obtained after including only genetically-undiagnosed patients. We identified four heterozygous SPG7 variant carriers with an additional pathogenic variant in known HSP genes, compared to zero in controls (OR 19.58, 95% CI 1.05-365.13, P = 0.0031), indicating potential digenic inheritance. We further identified four families with heterozygous variants in SPG7 and SPG7-interacting genes (CACNA1A, AFG3L2, and MORC2). Of these, there is especially compelling evidence for epistasis between SPG7 and AFG3L2. The p.(Ile705Thr) variant in AFG3L2 is located at the interface between hexamer subunits, in a hotspot of mutations associated with spinocerebellar ataxia type 28 that affect its proteolytic function.

CONCLUSIONS

Our results provide evidence for complex inheritance in SPG7-associated HSP, which may include recessive and possibly dominant and digenic/epistasis forms of inheritance. © 2021 International Parkinson and Movement Disorder Society.

OMA1-An integral membrane protease?

OMA1 is a mitochondrial protease. Among its substrates are DELE1, a signaling peptide, which can elicit the integrated stress response, as well as the membrane-shaping dynamin-related GTPase OPA1, which can drive mitochondrial outer membrane permeabilization. OMA1 is dormant under physiological conditions but rapidly activated upon mitochondrial stress, such as loss of membrane potential or excessive reactive oxygen species. Accordingly, OMA1 was found to be activated in a number of disease conditions, including cancer and neurodegeneration. OMA1 has a predicted transmembrane domain and is believed to be tethered to the mitochondrial inner membrane. Yet, its structure has not been resolved and its context-dependent regulation remains obscure. Here, I review the literature with focus on OMA1's biochemistry. I provide a good homology model of OMA1's active site with a root-mean-square deviation of 0.9 Å and a DALI Z-score of 19.8. And I build a case for OMA1 actually being an integral membrane protease based on OMA1's role in the generation of small signaling peptides, its functional overlap with PARL, and OMA1's homology with ZMPSTE24. The refined understanding of this important enzyme can help with the design of tool compounds and development of chemical probes in the future.

KRIT1 loss-mediated upregulation of NOX1 in stromal cells promotes paracrine pro-angiogenic responses

Cerebral cavernous malformation (CCM) is a cerebrovascular disorder of proven genetic origin characterized by abnormally dilated and leaky capillaries occurring mainly in the central nervous system, with a prevalence of 0.3-0.5% in the general population. Genetic studies have identified causative mutations in three genes, CCM1/KRIT1, CCM2 and CCM3, which are involved in the maintenance of vascular homeostasis. However, distinct studies in animal models have clearly shown that CCM gene mutations alone are not sufficient to cause CCM disease, but require additional contributing factors, including stochastic events of increased oxidative stress and inflammation. Consistently, previous studies have shown that up-regulation of NADPH oxidase-mediated production of reactive oxygen species (ROS) in KRIT1 deficient endothelium contributes to the loss of microvessel barrier function. In this study, we demonstrate that KRIT1 loss-of-function in stromal cells, such as fibroblasts, causes the up-regulation of NADPH oxidase isoform 1 (NOX1) and the activation of inflammatory pathways, which in turn promote an enhanced production of proangiogenic factors, including vascular endothelial growth factor (VEGF) and prostaglandin E2 (PGE2). Furthermore and importantly, we show that conditioned media from KRIT1 null fibroblasts induce proliferation, migration, matrix metalloproteinase 2 (MMP2) activation and VE-cadherin redistribution in wild type human endothelial cells. Taken together, our results demonstrate that KRIT1 loss-of-function in stromal cells affects the surrounding microenvironment through a NOX1-mediated induction and release of angiogenic factors that are able to promote paracrine proangiogenic responses in human endothelial cells, thus pointing to a novel role for endothelial cell-nonautonomous effects of KRIT1 mutations in CCM pathogenesis, and opening new perspectives for disease prevention and treatment.

Upregulation of Peroxiredoxin 3 Protects Afg3l2-KO Cortical Neurons In Vitro from Oxidative Stress: A Paradigm for Neuronal Cell Survival under Neurodegenerative Conditions

Several neurodegenerative disorders exhibit selective vulnerability, with subsets of neurons more affected than others, possibly because of the high expression of an altered gene or the presence of particular features that make them more susceptible to insults. On the other hand, resilient neurons may display the ability to develop antioxidant defenses, particularly in diseases of mitochondrial origin, where oxidative stress might contribute to the neurodegenerative process. In this work, we investigated the oxidative stress response of embryonic fibroblasts and cortical neurons obtained from Afg3l2-KO mice. AFG3L2 encodes a subunit of a protease complex that is expressed in mitochondria and acts as both quality control and regulatory enzyme affecting respiration and mitochondrial dynamics. When cells were subjected to an acute oxidative stress protocol, the survival of AFG3L2-KO MEFs was not significantly influenced and was comparable to that of WT; however, the basal level of the antioxidant molecule glutathione was higher. Indeed, glutathione depletion strongly affected the viability of KO, but not of WT MEF, thereby indicating that oxidative stress is more elevated in KO MEF even though well controlled by glutathione. On the other hand, when cortical KO neurons were put in culture, they immediately appeared more vulnerable than WT to the acute oxidative stress condition, but after few days in vitro, the situation was reversed with KO neurons being more resistant than WT to acute stress. This compensatory, protective competence was not due to the upregulation of glutathione, rather of two mitochondrial antioxidant proteins: superoxide dismutase 2 and, at an even higher level, peroxiredoxin 3. This body of evidence sheds light on the capability of neurons to activate neuroprotective pathways and points the attention to peroxiredoxin 3, an antioxidant enzyme that might be critical for neuronal survival also in other disorders affecting mitochondria.

Loss of paraplegin drives spasticity rather than ataxia in a cohort of 241 patients with SPG7

OBJECTIVE

We took advantage of a large multinational recruitment to delineate genotype-phenotype correlations in a large, trans-European multicenter cohort of patients with spastic paraplegia gene 7 (SPG7).

METHODS

We analyzed clinical and genetic data from 241 patients with SPG7, integrating neurologic follow-up data. One case was examined neuropathologically.

RESULTS

Patients with SPG7 had a mean age of 35.5 ± 14.3 years (n = 233) at onset and presented with spasticity (n = 89), ataxia (n = 74), or both (n = 45). At the first visit, patients with a longer disease duration (>20 years, n = 62) showed more cerebellar dysarthria (p < 0.05), deep sensory loss (p < 0.01), muscle wasting (p < 0.01), ophthalmoplegia (p < 0.05), and sphincter dysfunction (p < 0.05) than those with a shorter duration (<10 years, n = 93). Progression, measured by Scale for the Assessment and Rating of Ataxia evaluations, showed a mean annual increase of 1.0 ± 1.4 points in a subgroup of 30 patients. Patients homozygous for loss of function (LOF) variants (n = 65) presented significantly more often with pyramidal signs (p < 0.05), diminished visual acuity due to optic atrophy (p < 0.0001), and deep sensory loss (p < 0.0001) than those with at least 1 missense variant (n = 176). Patients with at least 1 Ala510Val variant (58%) were older (age 37.6 ± 13.7 vs 32.8 ± 14.6 years, p < 0.05) and showed ataxia at onset (p < 0.05). Neuropathologic examination revealed reduction of the pyramidal tract in the medulla oblongata and moderate loss of Purkinje cells and substantia nigra neurons.

CONCLUSIONS

This is the largest SPG7 cohort study to date and shows a spasticity-predominant phenotype of LOF variants and more frequent cerebellar ataxia and later onset in patients carrying at least 1 Ala510Val variant.

Identification of novel compound heterozygous SPG7 mutations-related hereditary spastic paraplegia in a Chinese family: a case report

Background

Autosomal recessive hereditary spastic paraplegias (ARHSPs) are a group of clinically and genetically heterogeneous neurodegenerative diseases with progressive spasticity and weakness in the lower limbs. Mutations in the Spastic Paraplegia gene 7 (SPG7) account for about 5–21% of ARHSP cases. However, in Asians, few reports about the mutations exist. In this study, we firstly report a novel finding from a Chinese family with compound heterozygous SPG7 mutations, in which three siblings were affected with a complicated form of ARHSP.

Case presentation

A 56-year-old man presented with progressive stiffness, weakness and ataxia in the lower limbs. Two sisters of him had similar symptoms and dysarthria. Brain magnetic resonance imaging (MRI) revealed cerebellar atrophy in each of the patients. Genetic analysis, which exerted a targeted next generation sequencing (NGS) panel covering 917 comprehensive ataxia genes to the proband, followed by Sanger sequencing of candidate genes in other eight family members, was used to find the etiology of the disease. Ultimately, we identified compound heterozygous SPG7 mutations with two mutations: (c.1150_1150-1insCTAC and c.2062C > T, p.Arg688Trp) and one single nucleotide polymorphism (c.2063G > A, p.Arg688Gln).

Conclusions

The four bases insertion mutation (4bIM) was predicted to cause frameshift mutation or affect the splicing, and the last two variants were led to a stop codon mutation (p.Arg688Ter). As located in highly conserved positions and encoded paraplegin, the mutations were speculated to result in a truncated or defective protein and would be pathogenic factors of the disease. This paper proves to be the first case report of SPG7 mutation in ARHSP reported in Chinese population. Our findings widen the spectrum of SPG7 mutations of ARHSP and indicate that the SPG7 mutation is an important cause of adult-onset undiagnosed ataxia.

Electronic supplementary material

The online version of this article (10.1186/s12883-018-1199-9) contains supplementary material, which is available to authorized users.

Mice harbouring a SCA28 patient mutation in AFG3L2 develop late-onset ataxia associated with enhanced mitochondrial proteotoxicity

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.

SPG7 and Impaired Emotional Communication

The goal of this report is to describe the genetic mutations of a patient with cerebellar degeneration who had ataxia and impaired emotional communication that led to damage of family relationships. We extracted genomic DNA from peripheral blood lymphocytes and performed whole exome sequencing (WES) in this patient and his unaffected parents and siblings. Found mutations were confirmed by Sanger sequencing in each individual. We found compound heterozygous mutations in the paraplegin (SPG7) gene. One mutated allele has been previously described as a disease-causing missense mutation for spastic paraplegia type 7 (SPG7) (c.1529C > T, p.Ala510Val). The second mutated allele involved a single nucleotide deletion which results in a frameshift in the coding sequence (c.2271delG, p.Met757fs*65). The second allele is similar to, but unique from, other described, SPG7-linked truncation mutations. The abnormal emotional communication in this patient broadens the phenotypic boundary of SPG7.

Recessive AFG3L2 Mutation Causes Progressive Microcephaly, Early Onset Seizures, Spasticity, and Basal Ganglia Involvement

BACKGROUND

Mutations in AFG3L2, a gene encoding a subunit of the mitochondrion m-AAA protease, cause spinocerebellar ataxia type 28 and recessive spastic ataxia type 5. Neuroimaging shows cerebellar atrophy.

METHODS

Retrospective review of the patient charts including their clinical evaluation and molecular genetic, neurodiagnostic, and neuroradiological investigations.

RESULTS

We describe five members of a large consanguineous family with a severe mitochondrial disease phenotype in the form of regression of the developmental milestones in the first year of life, refractory epilepsy, progressive microcephaly, increased blood lactate, basal ganglia involvement, and premature death. Exome sequencing showed homozygous mutation of the AFG3L2 gene in all individuals: c.1714G>A (p.Ala572Thr).

CONCLUSIONS

Our findings add to the phenotypic, neuroradiological, genetic, and biochemical spectrum of AFG3L2 mutations.

A Newly Identified Missense Mutation in FARS2 Causes Autosomal-Recessive Spastic Paraplegia

Hereditary spastic paraplegia (HSP) is a clinically and genetically heterogeneous group of neurodegenerative disorders characterized by spasticity of the lower limbs due to pyramidal tract dysfunction. Here, we report that a missense homozygous mutation c.424G>T (p.D142Y) in the FARS2 gene, which encodes a mitochondrial phenylalanyl tRNA synthetase (mtPheRS), causes HSP in a Chinese consanguineous family by using combination of homozygous mapping and whole-exome sequencing. Immunohistochemical experiments were performed showing that the FARS2 protein was highly expressed in the Purkinje cells of rat cerebellum. The aminoacylation activity of mtPheRS was severely disrupted by the p.D142Y substitution in vitro not only in the first aminoacylation step but also in the last transfer step. Taken together, our results indicate that a missense mutation in FARS2 contributes to HSP, which has the clinical significance of the regulation of tRNA synthetases in human neurodegenerative diseases.

Selection of internal reference genes for normalization of quantitative reverse transcription polymerase chain reaction (qRT-PCR) analysis in the canine brain and other organs

Quantitative reverse transcription polymerase chain reaction (qRT-PCR) is a specific and sensitive technique for quantifying gene expression. To analyze qRT-PCR data accurately, suitable reference genes that show consistent expression patterns across different tissues and experimental conditions should be selected. The objective of this study was to obtain the most stable reference genes in dogs, using samples from 13 different brain tissues and 10 other organs. 16 well-known candidate reference genes were analyzed by the geNorm, NormFinder, and BestKeeper programs. Brain tissues were derived from several different anatomical regions, including the forebrain, cerebrum, diencephalon, hindbrain, and metencephalon, and grouped accordingly. Combination of the three different analyses clearly indicated that the ideal reference genes are ribosomal protien S5 (RPS5) in whole brain, RPL8 and RPS5 in whole body tissues, RPS5 and RPS19 in the forebrain and cerebrum, RPL32 and RPS19 in the diencephalon, GAPDH and RPS19 in the hindbrain, and MRPS7 and RPL13A in the metencephalon. These genes were identified as ideal for the normalization of qRT-PCR results in the respective tissues. These findings indicate more suitable and stable reference genes for future studies of canine gene expression.

Genome-wide expression profiling and functional characterization of SCA28 lymphoblastoid cell lines reveal impairment in cell growth and activation of apoptotic pathways

Background

SCA28 is an autosomal dominant ataxia associated with AFG3L2 gene mutations. We performed a whole genome expression profiling using lymphoblastoid cell lines (LCLs) from four SCA28 patients and six unrelated healthy controls matched for sex and age.

Methods

Gene expression was evaluated with the Affymetrix GeneChip Human Genome U133A 2.0 Arrays and data were validated by real-time PCR.

Results

We found 66 genes whose expression was statistically different in SCA28 LCLs, 35 of which were up-regulated and 31 down-regulated. The differentially expressed genes were clustered in five functional categories: (1) regulation of cell proliferation; (2) regulation of programmed cell death; (3) response to oxidative stress; (4) cell adhesion, and (5) chemical homeostasis. To validate these data, we performed functional experiments that proved an impaired SCA28 LCLs growth compared to controls (p < 0.005), an increased number of cells in the G0/G1 phase (p < 0.001), and an increased mortality because of apoptosis (p < 0.05). We also showed that respiratory chain activity and reactive oxygen species levels was not altered, although lipid peroxidation in SCA28 LCLs was increased in basal conditions (p < 0.05). We did not detect mitochondrial DNA large deletions. An increase of TFAM, a crucial protein for mtDNA maintenance, and of DRP1, a key regulator of mitochondrial dynamic mechanism, suggested an alteration of fission/fusion pathways.

Conclusions

Whole genome expression profiling, performed on SCA28 LCLs, allowed us to identify five altered functional categories that characterize the SCA28 LCLs phenotype, the first reported in human cells to our knowledge.

Autosomal dominant cerebellar ataxias

Cerebellar ataxias with autosomal dominant transmission (ADCA) are far rarer than sporadic cases of cerebellar ataxia. The identification of genes involved in dominant forms has confirmed the genetic heterogeneity of these conditions and of the underlying mechanisms and pathways. To date, at least 28 genetic loci and, among them, 20 genes have been identified. In many instances, the phenotype is not restricted to cerebellar dysfunction but includes more complex multisystemic neurological deficits. Seven ADCA (SCA1, 2, 3, 6, 7, 17, and dentatorubro-pallido-luysian atrophy) are caused by repeat expansions in the corresponding proteins; phenotype-genotype correlations have shown that repeat size influences the progression of the disease, its severity and clinical differences among patients, including the phenomenon of anticipation between generations. All other ADCA are caused either by non-coding repeat expansions, conventional mutations or large rearrangements in genes with different functions. This review will focus on the genetic features of ADCA and on the clinical differences among the different forms.

Loss of the tuberous sclerosis complex protein tuberin causes Purkinje cell degeneration

Tuberous sclerosis complex (TSC) is a neurogenetic disorder that often causes brain abnormalities leading to epilepsy, developmental delay, and autism. TSC is caused by inactivating mutations in either of the genes encoding the proteins hamartin (TSC1) and tuberin (TSC2). These proteins form a heterodimer that inhibits the mammalian target of rapamycin complex 1 (mTORC1) pathway, controlling translation and cell growth. Loss of either protein results in dysregulated mTORC1 activation, an important aspect of TSC pathogenesis. About thirty percent of TSC patients have cerebellar pathology that is poorly understood. To investigate the effects of TSC on the cerebellum, we created a mouse model in which the Tsc2 gene was selectively deleted from Purkinje cells starting at postnatal day 6 (P6). The loss of Tsc2 caused a progressive increase in Purkinje cell size and subsequent death from apoptosis. Purkinje cell loss was predominantly cell type specific and associated with motor deficits. Immunohistochemical analysis showed that both endoplasmic reticulum (ER) and oxidative stress were increased in Tsc2-null Purkinje cells. The cell death and ER stress phenotypes were rescued by treatment with the mTORC1 inhibitor rapamycin. To assess whether the murine Purkinje cell loss has a correlate to the human TSC, we analyzed postmortem cerebellum samples from TSC patients and detected Purkinje cell loss in half of the samples. Our results establish a critical role for the TSC complex in Purkinje cell survival by regulating ER and oxidative stress and reveal a novel aspect of TSC neuropathology.