Neuronal cell death in the visual cortex is a prominent feature of the X-linked recessive mitochondrial deafness-dystonia syndrome caused by mutations in the TIMM8a gene

Clinical, neuroimaging and genetic findings in Brazilian patients with neurodegeneration with brain iron accumulation

Neurodegeneration with brain iron accumulation (NBIA) encompasses a clinically and genetically heterogeneous group of rare disorders. Here, we report clinical, neuroimaging and genetic studies in twenty three Brazilian NBIA patients. In thirteen subjects, deleterious variants were detected in known NBIA-causing genes (PANK2, PLA2G6, C9ORF12, WDR45 and FA2H), including previously unreported variants in PANK2 and PLA2G6. Two patients carried rare, likely pathogenic variants in genes not previously associated with NBIA: KMT2A c.11785A > C (p.Ile3929Leu), and TIMM8A c.127T > C (p.Cys43Arg), suggesting an expansion of their associated phenotypes to include NBIA. In eight patients the etiology remains unsolved, suggesting variants undetectable by the adopted methods, or the existence of additional NBIA-causing genes.

Mitochondrial protein dysfunction in pathogenesis of neurological diseases

Mitochondria are essential organelles for neuronal function and cell survival. Besides the well-known bioenergetics, additional mitochondrial roles in calcium signaling, lipid biogenesis, regulation of reactive oxygen species, and apoptosis are pivotal in diverse cellular processes. The mitochondrial proteome encompasses about 1,500 proteins encoded by both the nuclear DNA and the maternally inherited mitochondrial DNA. Mutations in the nuclear or mitochondrial genome, or combinations of both, can result in mitochondrial protein deficiencies and mitochondrial malfunction. Therefore, mitochondrial quality control by proteins involved in various surveillance mechanisms is critical for neuronal integrity and viability. Abnormal proteins involved in mitochondrial bioenergetics, dynamics, mitophagy, import machinery, ion channels, and mitochondrial DNA maintenance have been linked to the pathogenesis of a number of neurological diseases. The goal of this review is to give an overview of these pathways and to summarize the interconnections between mitochondrial protein dysfunction and neurological diseases.

The mitochondrial intermembrane space: the most constricted mitochondrial sub-compartment with the largest variety of protein import pathways

The mitochondrial intermembrane space (IMS) is the most constricted sub-mitochondrial compartment, housing only about 5% of the mitochondrial proteome, and yet is endowed with the largest variability of protein import mechanisms. In this review, we summarize our current knowledge of the major IMS import pathway based on the oxidative protein folding pathway and discuss the stunning variability of other IMS protein import pathways. As IMS-localized proteins only have to cross the outer mitochondrial membrane, they do not require energy sources like ATP hydrolysis in the mitochondrial matrix or the inner membrane electrochemical potential which are critical for import into the matrix or insertion into the inner membrane. We also explore several atypical IMS import pathways that are still not very well understood and are guided by poorly defined or completely unknown targeting peptides. Importantly, many of the IMS proteins are linked to several human diseases, and it is therefore crucial to understand how they reach their normal site of function in the IMS. In the final part of this review, we discuss current understanding of how such IMS protein underpin a large spectrum of human disorders.

Functional analysis of a novel mutation in the TIMM8A gene that causes deafness-dystonia-optic neuronopathy syndrome

Background

The rare, X‐linked neurodegenerative disorder, Mohr–Tranebjaerg syndrome (also called deafness‐dystonia‐optic neuronopathy [DDON] syndrome), is caused by mutations in the TIMM8A gene. DDON syndrome is characterized by dystonia, early‐onset deafness, and various other neurological manifestations. The TIMM8A gene product localizes to the intermembrane space in mitochondria where it functions in the import of nuclear‐encoded proteins into the mitochondrial inner membrane. Frameshifts or premature stops represent the majority of mutations in TIMM8A that cause DDON syndrome. However, missense mutations have also been reported that result in loss of the TIMM8A gene product.

Methods

We report a novel TIMM8A variant in a patient with DDON syndrome that alters the initiation codon and employed functional analyses to determine the significance of the variant and its impact on mitochondrial morphology.

Results

The novel base change in the TIMM8A gene (c.1A>T, p.Met1Leu) results in no detectable protein and a reduction in TIMM8A transcript abundance. We observed a commensurate decrease in the steady‐state level of the Tim13 protein (the binding partner of Tim8a) but no decrease in TIMM13 transcripts. Patient fibroblasts exhibited elongation and/or increased fusion of mitochondria, consistent with prior reports.

Conclusion

This case expands the spectrum of mutations that cause DDON syndrome and demonstrates effects on mitochondrial morphology that are consistent with prior reports.

Function of hTim8a in complex IV assembly in neuronal cells provides insight into pathomechanism underlying Mohr-Tranebjærg syndrome

Human Tim8a and Tim8b are members of an intermembrane space chaperone network, known as the small TIM family. Mutations in TIMM8A cause a neurodegenerative disease, Mohr-Tranebjærg syndrome (MTS), which is characterised by sensorineural hearing loss, dystonia and blindness. Nothing is known about the function of hTim8a in neuronal cells or how mutation of this protein leads to a neurodegenerative disease. We show that hTim8a is required for the assembly of Complex IV in neurons, which is mediated through a transient interaction with Complex IV assembly factors, in particular the copper chaperone COX17. Complex IV assembly defects resulting from loss of hTim8a leads to oxidative stress and changes to key apoptotic regulators, including cytochrome c, which primes cells for death. Alleviation of oxidative stress with Vitamin E treatment rescues cells from apoptotic vulnerability. We hypothesise that enhanced sensitivity of neuronal cells to apoptosis is the underlying mechanism of MTS.

Phenotype prediction of Mohr-Tranebjaerg syndrome (MTS) by genetic analysis and initial auditory neuropathy

Background

Mohr-Tranebjaerg syndrome (MTS) is a rare X-linked recessive neurodegenerative disorder resulting in early-onset hearing impairment, gradual dystonia and optic atrophy. MTS is caused by variations in the nuclear TIMM8A gene, which is involved in mitochondrial transport of metabolites. This study aimed to identify the pathogenic gene variations in three Chinese families associated with predicted MTS with or without X-linked agammaglobulinaemia.

Methods

Otologic examinations, vestibular, neurological, optical and other clinical evaluations were conducted on the family members. Targeted genes capture combining next generation sequencing (NGS) was performed, and then Sanger sequencing was used to confirm the causative variation.

Results

A novel variation, c.232_233insCAAT, in TIMM8A was identified as the pathogenic variation in one Chinese family. This variation co-segregated with the most frequent phenotypic deafness and was absent in the 1000 Genomes Project, ExAC and 1751 ethnicity-matched controls. Clinically, otological examinations illustrated the typical postsynaptic auditory neuropathy for the proband without the symptoms of dystonia or optic atrophy. MRI demonstrated abnormal small cochlear symmetric nerves, while the vestibular function appeared to be less influenced. Furthermore, we found another two TIMM8A variations, the deletion c.133_135delGAG and a copy number variation (CNV) including the TIMM8A gene, in two independent case, when we performed NGS on an auditory neuropathy population.

Conclusion

We identified two novel variations in the TIMM8A gene (c.232_233insCAAT and c.133_135delGAG) and a CNV including the TIMM8A gene in three independent Chinese families with predicted MTS. To our knowledge, this is the first report of TIMM8A variations being identified in a Chinese population. Our results enrich the variation spectrum of TIMM8A and clinical heterogeneity of MTS. Genetic detection and diagnosis is a powerful tool for better understanding and managing syndromic hearing impairments, such as MTS, before they become full-blown.

Electronic supplementary material

The online version of this article (10.1186/s12881-018-0741-3) contains supplementary material, which is available to authorized users.

Underappreciated Roles of the Translocase of the Outer and Inner Mitochondrial Membrane Protein Complexes in Human Disease

Mitochondria are critical for cellular survival, and for their proper functioning, translocation of ∼1500 proteins across the mitochondrial membranes is required. The translocase of the outer (TOMM) and inner mitochondrial membrane (TIMM) complexes are major components of this translocation machinery. Through specific processes, preproteins and other molecules are imported, translocated, and directed to specific mitochondrial compartments for their function. In this study, we review the association of subunits of these complexes with human disease. Pathogenic mutations have been identified in the TIMM8A (DDP) and DNAJC19 (TIMM14) genes and are linked to Mohr-Tranebjærg syndrome and dilated cardiomyopathy syndrome (with and without ataxia), respectively. Polymorphisms in TOMM40 have been associated with Alzheimer's disease, frontotemporal lobar degeneration, Parkinson's disease with dementia, dementia with Lewy bodies, nonpathological cognitive aging, and various cardiovascular-related traits. Furthermore, reduced protein expression levels of several complex subunits have been associated with Parkinson's disease, Meniere's disease, and cardiovascular disorders. However, increased mRNA and protein levels of complex subunits are found in cancers. This review highlights the importance of the mitochondrial import machinery in human disease and stresses the need for further studies. Ultimately, this knowledge may prove to be critical for the development of therapeutic modalities for these conditions.

Neurodegenerative changes detected by neuroimaging in a patient with contiguous X-chromosome deletion syndrome encompassing BTK and TIMM8A genes

Introduction

In this study we describe a patient with gross deletion containing the BTK and TIMM8A genes. Mutations in these genes are responsible for X-linked agammaglobulinemia and Mohr-Tranebjaerg syndrome, respectively. X linked agammaglobulinemia is a rare primary immunodeficiency characterized by low levels of B lymphocytes and recurrent microbial infections, whereas, Mohr-Tranebjaerg syndrome is a progressive neurodegenerative disorder with early onset of sensorineural deafness.

Material and methods

For neuroimaging, the magnetic resonance imaging and magnetic resonance spectroscopy of the brain were performed. Microarray analysis was performed to establish the extent of deletion.

Results

The first clinical symptoms observed in our patient at the age of 6 months were connected with primary humoral immunodeficiency, whereas clinical signs of MTS emerged in the third year of live. Interestingly, the loss of speech ability was not accompanied by hearing failure. Neuroimaging of the brain suggested leukodystrophy. Molecular tests revealed contiguous X-chromosome deletion syndrome encompassing BTK (from exons 6 through 19) and TIMM8A genes. The loss of the patient’s DNA fragment was accurately localized from 100 601 727 to 100 617 576 bp on chromosome’s loci Xq22.1.

Conclusions

We diagnosed XLA-MTS in the first Polish patient on the basis of particular molecular methods. We detected neurodegenerative changes in MRI and MR spectroscopy in this patient. Our results provide further insight into this rare syndrome.

A neurodegenerative perspective on mitochondrial optic neuropathies

Mitochondrial optic neuropathies constitute an important cause of chronic visual morbidity and registrable blindness in both the paediatric and adult population. It is a genetically heterogeneous group of disorders caused by both mitochondrial DNA (mtDNA) mutations and a growing list of nuclear genetic defects that invariably affect a critical component of the mitochondrial machinery. The two classical paradigms are Leber hereditary optic neuropathy (LHON), which is a primary mtDNA disorder, and autosomal dominant optic atrophy (DOA) secondary to pathogenic mutations within the nuclear gene OPA1 that encodes for a mitochondrial inner membrane protein. The defining neuropathological feature is the preferential loss of retinal ganglion cells (RGCs) within the inner retina but, rather strikingly, the smaller calibre RGCs that constitute the papillomacular bundle are particularly vulnerable, whereas melanopsin-containing RGCs are relatively spared. Although the majority of patients with LHON and DOA will present with isolated optic nerve involvement, some individuals will also develop additional neurological complications pointing towards a greater vulnerability of the central nervous system (CNS) in susceptible mutation carriers. These so-called “plus” phenotypes are mechanistically important as they put the loss of RGCs within the broader perspective of neuronal loss and mitochondrial dysfunction, highlighting common pathways that could be modulated to halt progressive neurodegeneration in other related CNS disorders. The management of patients with mitochondrial optic neuropathies still remains largely supportive, but the development of effective disease-modifying treatments is now within tantalising reach helped by major advances in drug discovery and delivery, and targeted genetic manipulation.

TRANSLOCASE OF THE INNER MEMBRANE9 and 10 are essential for maintaining mitochondrial function during early embryo cell and endosperm free nucleus divisions in Arabidopsis

In the life cycle of flowering plants, the sporophytic generation takes up most of the time and plays a dominant role in influencing plant growth and development. The embryo cell and endosperm free nucleus divisions establish the critical initiation phase of early sporophyte development, which forms mature seeds through a series of cell growth and differentiation events. Here, we report on the biological functions of two Arabidopsis (Arabidopsis thaliana) mitochondrial proteins, TRANSLOCASE OF THE INNER MEMBRANE9 (TIM9) and TIM10. We found that dysfunction of either AtTIM9 or AtTIM10 led to an early sporophyte-lethal phenotype; the embryo and endosperm both arrest division when the embryo proper developed to 16 to 32 cells. The abortion of tim9-1 and tim10 embryos at the 16/32-cell stage was caused by the loss of cell viability and the cessation of division in the embryo proper region, and this inactivation was due to the collapse of the mitochondrial structure and activity. Our characterization of tim9-1 and tim10 showed that mitochondrial membrane permeability increased and that cytochrome c was released from mitochondria into the cytoplasm in the 16/32-cell embryo proper, indicating that mitochondrial dysfunction occurred in the early sporophytic cells, and thus caused the initiation of a necrosis-like programmed cell death, which was further proved by the evidence of reactive oxygen species and DNA fragmentation tests. Consequently, we verified that AtTIM9 and AtTIM10 are nonredundantly essential for maintaining the mitochondrial function of early embryo proper cells and endosperm-free nuclei; these proteins play critically important roles during sporophyte initiation and development in Arabidopsis.

The optic nerve: a "mito-window" on mitochondrial neurodegeneration

Retinal ganglion cells (RGCs) project their long axons, composing the optic nerve, to the brain, transmitting the visual information gathered by the retina, ultimately leading to formed vision in the visual cortex. The RGC cellular system, representing the anterior part of the visual pathway, is vulnerable to mitochondrial dysfunction and optic atrophy is a very frequent feature of mitochondrial and neurodegenerative diseases. The start of the molecular era of mitochondrial medicine, the year 1988, was marked by the identification of a maternally inherited form of optic atrophy, Leber's hereditary optic neuropathy, as the first disease due to mitochondrial DNA point mutations. The field of mitochondrial medicine has expanded enormously over the last two decades and many neurodegenerative diseases are now known to have a primary mitochondrial etiology or mitochondrial dysfunction plays a relevant role in their pathogenic mechanism. Recent technical advancements in neuro-ophthalmology, such as optical coherence tomography, prompted a still ongoing systematic re-investigation of retinal and optic nerve involvement in neurodegenerative disorders. In addition to inherited optic neuropathies, such as Leber's hereditary optic neuropathy and dominant optic atrophy, and in addition to the syndromic mitochondrial encephalomyopathies or mitochondrial neurodegenerative disorders such as some spinocerebellar ataxias or familial spastic paraparesis and other disorders, we draw attention to the involvement of the optic nerve in classic age-related neurodegenerative disorders such as Parkinson and Alzheimer disease. We here provide an overview of optic nerve pathology in these different clinical settings, and we review the possible mechanisms involved in the pathogenesis of optic atrophy. This may be a model of general value for the field of neurodegeneration. This article is part of a Special Issue entitled 'Mitochondrial function and dysfunction in neurodegeneration'.

Inherited hearing loss: molecular genetics and diagnostic testing

BACKGROUND

Hearing loss is a clinically and genetically heterogeneous condition with major medical and social consequences. It affects up to 8% of the general population.

OBJECTIVE

This review recapitulates the principles of auditory physiology and the molecular basis of hearing loss, outlines the main types of non-syndromic and syndromic deafness by mode of inheritance, and provides an overview of current clinically available genetic testing.

METHODS

This paper reviews the literature on auditory physiology and on genes, associated with hearing loss, for which genetic testing is presently offered.

RESULTS/CONCLUSION

The advent of molecular diagnostic assays for hereditary hearing loss permits earlier detection of the underlying causes, facilitates appropriate interventions, and is expected to generate the data necessary for more specific genotype-phenotype correlations.

Convergent mechanisms in etiologically-diverse dystonias

INTRODUCTION

Dystonia is a neurological disorder associated with twisting motions and abnormal postures, which compromise normal movements and can be both painful and debilitating. It can affect a single body part (focal), several contiguous regions (segmental), or the entire body (generalized), and can arise as a result of numerous causes, both genetic and acquired. Despite the diversity of causes and manifestations, shared clinical features suggest that common mechanisms of pathogenesis may underlie many dystonias.

AREAS COVERED

Shared themes in etiologically-diverse dystonias exist at several biological levels. At the cellular level, abnormalities in the dopaminergic system, mitochondrial function and calcium regulation are often present. At the anatomical level, the basal ganglia and the cerebellum are frequently implicated. Global CNS dysfunction, specifically aberrant neuronal plasticity, inhibition and sensorimotor integration, are also observed in a number of dystonias. Using clinical data and data from animal models, this article seeks to highlight shared pathways that may be critical in understanding mechanisms and identifying novel therapeutic strategies in dystonia.

EXPERT OPINION

Identifying shared features of pathogenesis can provide insight into the biological processes that underlie etiologically diverse dystonias, and can suggest novel targets for therapeutic intervention that may be effective in a broad group of affected individuals.

Differential regulation of PML-RARα stability by the ubiquitin ligases SIAH1/SIAH2 and TRIAD1

The ubiquitin proteasome system plays an important role in normal and malignant hematopoiesis and relies on the concerted action of three enzyme families. The E2 ubiquitin conjugase UBCH8 (ubiquitin conjugating enzyme [human] 8) cooperates with the E3 ubiquitin ligases SIAH1 and SIAH2 (seven in absentia homolog 1/2) to mediate the proteasomal degradation of oncoproteins. One such protein is the leukemia fusion protein PML-RARα (promyelocytic leukemia-retinoic acid receptorα) that is associated with acute promyelocytic leukemia. A limited number of UBCH8 interaction partners that participate in the UBCH8-dependent depletion of cancer-relevant proteins are known. We report here that TRIAD1 (two RING fingers and DRIL [double RING finger linked] 1), an E3 ubiquitin ligase relevant for the clonogenic growth of myloid progenitors, binds UBCH8 as well as PML-RARα. Moreover, there is concurrent induction of TRIAD1 and UBCH8 upon combinatorial treatment of acute promyelocytic leukemia cells with the pro-apoptotic epigenetic modulator valproic acid and the differentiation inducing agent all-trans retinoic acid. However, in sharp contrast to SIAH1/SIAH2 and UBCH8, TRIAD1 binding to PML-RARα has no effect on its turnover. In summary, our data exclude TRIAD1 as crucial regulator of the leukemic determinant PML-RARα, but highlight the prominence of the UBCH8/SIAH axis in PML-RARα degradation.

Mitochondrial disorders and the eye

The clinical significance of disturbed mitochondrial function in the eye has emerged since mitochondrial DNA (mtDNA) mutation was described in Leber's hereditary optic neuropathy. The spectrum of mitochondrial dysfunction has become apparent through increased understanding of the contribution of nuclear and somatic mtDNA mutations to mitochondrial dynamics and function. Common ophthalmic manifestations of mitochondrial dysfunction include optic atrophy, pigmentary retinopathy, and ophthalmoplegia. The majority of patients with ocular manifestations of mitochondrial disease also have variable central and peripheral nervous system involvement. Mitochondrial dysfunction has recently been associated with age-related retinal disease including macular degeneration and glaucoma. Therefore, therapeutic targets directed at promoting mitochondrial biogenesis and function offer a potential to both preserve retinal function and attenuate neurodegenerative processes.

Mitochondrial optic neuropathies - disease mechanisms and therapeutic strategies

Leber hereditary optic neuropathy (LHON) and autosomal-dominant optic atrophy (DOA) are the two most common inherited optic neuropathies in the general population. Both disorders share striking pathological similarities, marked by the selective loss of retinal ganglion cells (RGCs) and the early involvement of the papillomacular bundle. Three mitochondrial DNA (mtDNA) point mutations; m.3460G>A, m.11778G>A, and m.14484T>C account for over 90% of LHON cases, and in DOA, the majority of affected families harbour mutations in the OPA1 gene, which codes for a mitochondrial inner membrane protein. Optic nerve degeneration in LHON and DOA is therefore due to disturbed mitochondrial function and a predominantly complex I respiratory chain defect has been identified using both in vitro and in vivo biochemical assays. However, the trigger for RGC loss is much more complex than a simple bioenergetic crisis and other important disease mechanisms have emerged relating to mitochondrial network dynamics, mtDNA maintenance, axonal transport, and the involvement of the cytoskeleton in maintaining a differential mitochondrial gradient at sites such as the lamina cribosa. The downstream consequences of these mitochondrial disturbances are likely to be influenced by the local cellular milieu. The vulnerability of RGCs in LHON and DOA could derive not only from tissue-specific, genetically-determined biological factors, but also from an increased susceptibility to exogenous influences such as light exposure, smoking, and pharmacological agents with putative mitochondrial toxic effects. Our concept of inherited mitochondrial optic neuropathies has evolved over the past decade, with the observation that patients with LHON and DOA can manifest a much broader phenotypic spectrum than pure optic nerve involvement. Interestingly, these phenotypes are sometimes clinically indistinguishable from other neurodegenerative disorders such as Charcot-Marie-Tooth disease, hereditary spastic paraplegia, and multiple sclerosis, where mitochondrial dysfunction is also thought to be an important pathophysiological player. A number of vertebrate and invertebrate disease models has recently been established to circumvent the lack of human tissues, and these have already provided considerable insight by allowing direct RGC experimentation. The ultimate goal is to translate these research advances into clinical practice and new treatment strategies are currently being investigated to improve the visual prognosis for patients with mitochondrial optic neuropathies.

The mitochondrial connection in auditory neuropathy

'Auditory neuropathy' (AN), the term used to codify a primary degeneration of the auditory nerve, can be linked directly or indirectly to mitochondrial dysfunction. These observations are based on the expression of AN in known mitochondrial-based neurological diseases (Friedreich's ataxia, Mohr-Tranebjærg syndrome), in conditions where defects in axonal transport, protein trafficking, and fusion processes perturb and/or disrupt mitochondrial dynamics (Charcot-Marie-Tooth disease, autosomal dominant optic atrophy), in a common neonatal condition known to be toxic to mitochondria (hyperbilirubinemia), and where respiratory chain deficiencies produce reductions in oxidative phosphorylation that adversely affect peripheral auditory mechanisms. This body of evidence is solidified by data derived from temporal bone and genetic studies, biochemical, molecular biologic, behavioral, electroacoustic, and electrophysiological investigations.

The mitochondrial proteome and human disease

For nearly three decades, the sequence of the human mitochondrial genome (mtDNA) has provided a molecular framework for understanding maternally inherited diseases. However, the vast majority of human mitochondrial disorders are caused by nuclear genome defects, which is not surprising since the mtDNA encodes only 13 proteins. Advances in genomics, mass spectrometry, and computation have only recently made it possible to systematically identify the complement of over 1,000 proteins that comprise the mammalian mitochondrial proteome. Here, we review recent progress in characterizing the mitochondrial proteome and highlight insights into its complexity, tissue heterogeneity, evolutionary origins, and biochemical versatility. We then discuss how this proteome is being used to discover the genetic basis of respiratory chain disorders as well as to expand our definition of mitochondrial disease. Finally, we explore future prospects and challenges for using the mitochondrial proteome as a foundation for systems analysis of the organelle.

Otopathology in Mohr-Tranebjaerg syndrome

BACKGROUND

Mohr-Tranebjaerg syndrome (MTS) is an X-linked, recessive, syndromic sensorineural hearing loss (HL) characterized by onset of deafness in childhood followed later in adult life by progressive neural degeneration affecting the brain and optic nerves. MTS is caused by mutations in the DDP/TIMM8A gene, which encodes for a 97 amino acid polypeptide; this polypeptide is a translocase of the inner mitochondrial membrane.

OBJECTIVES

To describe the otologic presentation and temporal bone histopathology in four affected individuals with MTS.

MATERIAL AND METHODS

All four subjects belonged to a large, multigenerational Norwegian family and were known to carry a frame shift mutation in the TIMM8A gene. Temporal bones were removed at autopsy and studied by light microscopy. Cytocochleograms were constructed for hair cells, stria vascularis, and cochlear neuronal cells. Vestibular neurons were also counted.

RESULTS

All four subjects developed progressive HL in early childhood, becoming profoundly deaf by the age of 10 years. All four developed language, and at least one subject used amplification in early life. Audiometric evaluation in two subjects showed 80- to 100-dB HL by the age of 10 years. The subjects died between the ages of 49 and 67. The otopathology was strikingly similar in that all bones examined showed near-total loss of cochlear neuronal cells and severe loss of vestibular neurons. When compared with age-matched controls, there was 90% to 95% loss of cochlear neurons and 75% to 85% loss of vestibular neurons.

CONCLUSIONS

We infer that the HL in MTS is likely to be the result of a postnatal and progressive degeneration of cochlear neurons and that MTS constitutes a true auditory neuropathy. Our findings have implications for clinical diagnosis of patients with MTS and management of the HL.

Differential cerebral cortex transcriptomes of baboon neonates consuming moderate and high docosahexaenoic acid formulas

BACKGROUND

Docosahexaenoic acid (DHA, 22:6n-3) and arachidonic acid (ARA, 20:4n-6) are the major long chain polyunsaturated fatty acids (LCPUFA) of the central nervous system (CNS). These nutrients are present in most infant formulas at modest levels, intended to support visual and neural development. There are no investigations in primates of the biological consequences of dietary DHA at levels above those present in formulas but within normal breastmilk levels.

METHODS AND FINDINGS

Twelve baboons were divided into three formula groups: Control, with no DHA-ARA; "L", LCPUFA, with 0.33%DHA-0.67%ARA; "L3", LCPUFA, with 1.00%DHA-0.67%ARA. All the samples are from the precentral gyrus of cerebral cortex brain regions. At 12 weeks of age, changes in gene expression were detected in 1,108 of 54,000 probe sets (2.05%), with most showing <2-fold change. Gene ontology analysis assigns them to diverse biological functions, notably lipid metabolism and transport, G-protein and signal transduction, development, visual perception, cytoskeleton, peptidases, stress response, transcription regulation, and 400 transcripts having no defined function. PLA2G6, a phospholipase recently associated with infantile neuroaxonal dystrophy, was downregulated in both LCPUFA groups. ELOVL5, a PUFA elongase, was the only LCPUFA biosynthetic enzyme that was differentially expressed. Mitochondrial fatty acid carrier, CPT2, was among several genes associated with mitochondrial fatty acid oxidation to be downregulated by high DHA, while the mitochondrial proton carrier, UCP2, was upregulated. TIMM8A, also known as deafness/dystonia peptide 1, was among several differentially expressed neural development genes. LUM and TIMP3, associated with corneal structure and age-related macular degeneration, respectively, were among visual perception genes influenced by LCPUFA. TIA1, a silencer of COX2 gene translation, is upregulated by high DHA. Ingenuity pathway analysis identified a highly significant nervous system network, with epidermal growth factor receptor (EGFR) as the outstanding interaction partner.

CONCLUSIONS

These data indicate that LCPUFA concentrations within the normal range of human breastmilk induce global changes in gene expression across a wide array of processes, in addition to changes in visual and neural function normally associated with formula LCPUFA.

Blepharospasm and limb dystonia caused by Mohr-Tranebjaerg syndrome with a novel splice-site mutation in the deafness/dystonia peptide gene

Mohr-Tranebjaerg syndrome (MTS) is an X-linked disorder characterized by childhood-onset progressive deafness, dystonia, spasticity, mental deterioration, and blindness. It is due to mutations in the deafness/dystonia peptide (DDP1) gene. We describe a sporadic 42-year-old man with MTS presenting with postlingual deafness, adult-onset progressive dystonia with marked arm tremor, mild spasticity of the legs, and visual disturbance due to a novel mutation (g to a transition at the invariant gt of the 5' splice donor site of exon 1) in the DDP1 gene. This case, and a review of previously reported cases, highlights a variety of potential diagnostic pitfalls in this condition.

Novel roles for metallothionein-I + II (MT-I + II) in defense responses, neurogenesis, and tissue restoration after traumatic brain injury: Insights from global gene expression profiling in wild-type and MT-I + II knockout mice

Traumatic injury to the brain is one of the leading causes of injury-related death or disability, especially among young people. Inflammatory processes and oxidative stress likely underlie much of the damage elicited by injury, but the full repertoire of responses involved is not well known. A genomic approach, such as the use of microarrays, provides much insight in this regard, especially if combined with the use of gene-targeted animals. We report here the results of one of these studies comparing wild-type and metallothionein-I + II knockout mice subjected to a cryolesion of the somatosensorial cortex and killed at 0, 1, 4, 8, and 16 days postlesion (dpl) using Affymetrix genechips/oligonucleotide arrays interrogating approximately 10,000 different murine genes (MG_U74Av2). Hierarchical clustering analysis of these genes readily shows an orderly pattern of gene responses at specific times consistent with the processes involved in the initial tissue injury and later regeneration of the parenchyma, as well as a prominent effect of MT-I + II deficiency. The results thoroughly confirmed the importance of the antioxidant proteins MT-I + II in the response of the brain to injury and opened new avenues that were confirmed by immunohistochemistry. Data in KO, MT-I-overexpressing, and MT-II-injected mice strongly suggest a role of these proteins in postlesional activation of neural stem cells.

Interaction of the deafness-dystonia protein DDP/TIMM8a with the signal transduction adaptor molecule STAM1

The Mohr-Tranebjaerg-Jensen deafness-dystonia-optic atrophy protein DDP/TIMM8a is translated on cytoplasmic ribosomes but targeted ultimately to the mitochondrial intermembrane space, where it is involved in mitochondrial protein import. STAM1 is a cytoplasmic signal-transducing adaptor molecule implicated in cytokine signaling. We report here a direct interaction between DDP and STAM1, identified by yeast two-hybrid screening and confirmed by co-immunoprecipitation, fusion protein "pull downs," and nuclear redistribution assays. DDP coordinates Zn(2+), and Zn(2+) was found to stimulate the DDP-STAM1 interaction in vitro. Endogenous STAM1 localizes predominantly to early endosomes, and we found no evidence that STAM1 is imported into mitochondria in vitro. Thus, the DDP-STAM1 interaction likely occurs in the cytoplasm or at the mitochondrial outer membrane. The DDP-STAM1 interaction requires a coiled-coil region in STAM1 that overlaps with the immunoreceptor tyrosine-based activation motif (ITAM), a region previously shown to be important for interaction with Jak2/3 and hepatocyte growth factor-regulated tyrosine kinase substrate (Hrs). Thus, DDP binding may alter the interactions of STAM1 with several cytoplasmic proteins involved in cell signaling and endosomal trafficking.