Mutations in GDAP1 Influence Structure and Function of the Trans-Golgi Network.

Charcot-Marie-Tooth disease (CMT) is a heritable neurodegenerative disease that displays great genetic heterogeneity. The genes and mutations that underlie this heterogeneity have been extensively characterized by molecular genetics. However, the molecular pathogenesis of the vast majority of CMT subtypes remains terra incognita. Any attempts to perform experimental therapy for CMT disease are limited by a lack of understanding of the pathogenesis at a molecular level. In this study, we aim to identify the molecular pathways that are disturbed by mutations in the gene encoding GDAP1 using both yeast and human cell, based models of CMT-GDAP1 disease. We found that some mutations in GDAP1 led to a reduced expression of the GDAP1 protein and resulted in a selective disruption of the Golgi apparatus. These structural alterations are accompanied by functional disturbances within the Golgi. We screened over 1500 drugs that are available on the market using our yeast-based CMT-GDAP1 model. Drugs were identified that had both positive and negative effects on cell phenotypes. To the best of our knowledge, this study is the first report of the Golgi apparatus playing a role in the pathology of CMT disorders. The drugs we identified, using our yeast-based CMT-GDAP1 model, may be further used in translational research.

A Yeast-Based Model for Hereditary Motor and Sensory Neuropathies: A Simple System for Complex, Heterogeneous Diseases.

Charcot-Marie-Tooth (CMT) disease encompasses a group of rare disorders that are characterized by similar clinical manifestations and a high genetic heterogeneity. Such excessive diversity presents many problems. Firstly, it makes a proper genetic diagnosis much more difficult and, even when using the most advanced tools, does not guarantee that the cause of the disease will be revealed. Secondly, the molecular mechanisms underlying the observed symptoms are extremely diverse and are probably different for most of the disease subtypes. Finally, there is no possibility of finding one efficient cure for all, or even the majority of CMT diseases. Every subtype of CMT needs an individual approach backed up by its own research field. Thus, it is little surprise that our knowledge of CMT disease as a whole is selective and therapeutic approaches are limited. There is an urgent need to develop new CMT models to fill the gaps. In this review, we discuss the advantages and disadvantages of yeast as a model system in which to study CMT diseases. We show how this single-cell organism may be used to discriminate between pathogenic variants, to uncover the mechanism of pathogenesis, and to discover new therapies for CMT disease.

[Therapeutic perspective in hereditary polyneuropathies]. / Perspektywy terapii w polineuropatiach genetycznie uwarunkowanych.

Hereditary motor and sensory neuropathies (HMSN) also called as Charcot-Marie-Tooth disorders (CMT) are extremely heterogeneous group of disorders of peripheral nervous system. Over 80 genes have been reported in different types of CMT. In all CMT affected patients the main symptoms are slowly progressive wasting of the distal muscles of the lower and upper limbs. To date no efficient therapeutic approach basing upon molecular pathology of CMT has been proposed. This review presents the current state of knowledge concerning clinical, molecular pathogenesis and experimental therapy aspects in CMT disorders. Additionally the possibilities resulting from the use of the yeast model to the identification of new therapeutic substances as well as of neurotoxins are also discussed.

Models for IGHMBP2-associated diseases: an overview and a roadmap for the future.

Models are practical tools with which to establish the basic aspects of a diseases. They allow systematic research into the significance of mutations, of cellular and molecular pathomechanisms, of therapeutic options and of functions of diseases associated proteins. Thus, disease models are an integral part of the study of enigmatic proteins such as immunoglobulin mu-binding protein 2 (IGHMBP2). IGHMBP2 has been well defined as a helicase, however there is little known about its role in cellular processes. Notably, it is unclear why changes in such an abundant protein lead to specific neuronal disorders including spinal muscular atrophy with respiratory distress type 1 (SMARD1) and Charcot-Marie-Tooth type 2S (CMT2S). SMARD1 is caused by a loss of motor neurons in the spinal cord that results in muscle atrophy and is accompanied by rapid respiratory failure. In contrast, CMT2S manifests as a severe neuropathy, but typically without critical breathing problems. Here, we present the clinical manifestation of IGHMBP2 mutations, function of protein and models that may be used for the study of IGHMBP2-associated disorders. We highlight the strengths and weaknesses of specific models and discuss the orthologs of IGHMBP2 that are found in different systems with regard to their similarity to human IGHMBP2.

Pathogenic Effect of GDAP1 Gene Mutations in a Yeast Model.

The question of whether a newly identified sequence variant is truly a causative mutation is a central problem of modern clinical genetics. In the current era of massive sequencing, there is an urgent need to develop new tools for assessing the pathogenic effect of new sequence variants. In Charcot-Marie-Tooth disorders (CMT) with their extreme genetic heterogeneity and relatively homogenous clinical presentation, addressing the pathogenic effect of rare sequence variants within 80 CMT genes is extremely challenging. The presence of multiple rare sequence variants within a single CMT-affected patient makes selection for the strongest one, the truly causative mutation, a challenging issue. In the present study we propose a new yeast-based model to evaluate the pathogenic effect of rare sequence variants found within the one of the CMT-associated genes, GDAP1. In our approach, the wild-type and pathogenic variants of human GDAP1 gene were expressed in yeast. Then, a growth rate and mitochondrial morphology and function of GDAP1-expressing strains were studied. Also, the mutant GDAP1 proteins localization and functionality were assessed in yeast. We have shown, that GDAP1 was not only stably expressed but also functional in yeast cell, as it influenced morphology and function of mitochondria and altered the growth of a mutant yeast strain. What is more, the various GDAP1 pathogenic sequence variants caused the specific for them effect in the tests we performed. Thus, the proposed model is suitable for validating the pathogenic effect of known GDAP1 mutations and may be used for testing of unknown sequence variants found in CMT patients.

A role for the GDAP1 gene in the molecular pathogenesis of Charcot­Marie­Tooth disease.

In 2002 a series of mutations in the GDAP1 gene were reported in patients suffering from Charcot­Marie­Tooth disease manifesting as early-onset, progressive distal­muscle wasting and weakness. The molecular etiology of Charcot­Marie­Tooth ­GDAP1 disease has been elucidated but its pathogenesis remains unclear, especially given the seemingly contradictory function of the GDAP1 protein. Expression of GDAP1 is observed almost exclusively in neuronal cells, however, the GDAP1 protein is present in mitochondria, where it plays a role in fission, a ubiquitous process occurring in all cells. While GDAP1 contains two glutathione S­transferase (GST) domains, its GST activity is in fact very limited. Additionally, despite GDAP1 affecting mitochondrial functionality, and hence being of great importance to cellular function, the GDAP1­associated Charcot-Marie-Tooth disease is mainly characterized by axonal degeneration. Finally, mutations in the GDAP1 gene may be inherited in a recessive or dominant manner. Given the way such varied observations are hard to reconcile with one another, the investigation of GDAP1 is at one and the same time a difficult but also challenging endeavour. The purpose of this review is to summarize the current knowledge on the GDAP1 protein and its function in the cell. A further part is the characterization of GDAP1­associated Charcot-Marie-Tooth disease, its symptoms and course, as well as an outlining of the possible mechanisms underpinning the disorder.