Therapeutic Development in Charcot Marie Tooth Type 1 Disease

Charcot-Marie-Tooth disease: from historical landmarks in Brazil to current care perspectives

Hereditary motor and sensory neuropathy, also known as Charcot-Marie-Tooth disease (CMT), traditionally refers to a group of genetic disorders in which neuropathy is the main or sole feature. Its prevalence varies according to different populations studied, with an estimate between 1:2,500 to 1:10,000. Since the identification of PMP22 gene duplication on chromosome 17 by Vance et al., in 1989, more than 100 genes have been related to this group of disorders, and we have seen advances in the care of patients, with identification of associated conditions and better supportive treatments, including clinical and surgical interventions. Also, with discoveries in the field of genetics, including RNA interference and gene editing techniques, new treatment perspectives begin to emerge. In the present work, we report the most import landmarks regarding CMT research in Brazil and provide a comprehensive review on topics such as frequency of different genes associated with CMT in our population, prevalence of pain, impact on pregnancy, respiratory features, and development of new therapies.

Proteostasis plays an important role in demyelinating Charcot Marie Tooth disease

Type 1 Charcot-Marie-Tooth disease (CMT1) is the most common demyelinating peripheral neuropathy. Patients suffer from progressive muscle weakness and sensory problems. The underlying disease mechanisms of CMT1 are still unclear and no therapy is currently available, hence patients completely rely on supportive care. Balancing protein levels is a complex multistep process fundamental to maintain cells in their healthy state and a disrupted proteostasis is a hallmark of several neurodegenerative diseases. When protein misfolding occurs, protein quality control systems are activated such as chaperones, the lysosomal-autophagy system and proteasomal degradation to ensure proper degradation. However, in pathological circumstances, these mechanisms are overloaded and thereby become inefficient to clear the load of misfolded proteins. Recent evidence strongly indicates that a disbalance in proteostasis plays an important role in several forms of CMT1. In this review, we present an overview of the protein quality control systems, their role in CMT1, and potential treatment strategies to restore proteostasis.

The transcription factor Stat-1 is essential for Schwann cell differentiation, myelination and myelin sheath regeneration

BACKGROUND

Myelin sheath is a crucial accessory to the functional nerve-fiber unit, its disruption or loss can lead to axonal degeneration and subsequent neurodegenerative diseases (NDs). Notwithstanding of substantial progress in possible molecular mechanisms underlying myelination, there is no therapeutics that prevent demyelination in NDs. Therefore, it is crucial to seek for potential intervention targets. Here, we focused on the transcriptional factor, signal transducer and activator of transcription 1 (Stat1), to explore its effects on myelination and its potential as a drug target.

METHODS

By analyzing the transcriptome data obtained from Schwann cells (SCs) at different stages of myelination, it was found that Stat1 might be involved in myelination. To test this, we used the following experiments: (1) In vivo, the effect of Stat1 on remyelination was observed in an in vivo myelination mode with Stat1 knockdown in sciatic nerves or specific knockdown in SCs. (2) In vitro, the RNA interference combined with cell proliferation assay, scratch assay, SC aggregate sphere migration assay, and a SC differentiation model, were used to assess the effects of Stat1 on SC proliferation, migration and differentiation. Chromatin immunoprecipitation sequencing (ChIP-Seq), RNA-Seq, ChIP-qPCR and luciferase activity reporter assay were performed to investigate the possible mechanisms of Stat1 regulating myelination.

RESULTS

Stat1 is important for myelination. Stat1 knockdown in nerve or in SCs reduces the axonal remyelination in the injured sciatic nerve of rats. Deletion of Stat1 in SCs blocks SC differentiation thereby inhibiting the myelination program. Stat1 interacts with the promoter of Rab11-family interacting protein 1 (Rab11fip1) to initiate SC differentiation.

CONCLUSION

Our findings demonstrate that Stat1 regulates SC differentiation to control myelinogenic programs and repair, uncover a novel function of Stat1, providing a candidate molecule for clinical intervention in demyelinating diseases.

Clinical genetics of Charcot-Marie-Tooth disease

Recent research in the field of inherited peripheral neuropathies (IPNs) such as Charcot-Marie-Tooth (CMT) disease has helped identify the causative genes provided better understanding of the pathogenesis, and unraveled potential novel therapeutic targets. Several reports have described the epidemiology, clinical characteristics, molecular pathogenesis, and novel causative genes for CMT/IPNs in Japan. Based on the functions of the causative genes identified so far, the following molecular and cellular mechanisms are believed to be involved in the causation of CMTs/IPNs: myelin assembly, cytoskeletal structure, myelin-specific transcription factor, nuclear related, endosomal sorting and cell signaling, proteasome and protein aggregation, mitochondria-related, motor proteins and axonal transport, tRNA synthetases and RNA metabolism, and ion channel-related mechanisms. In this article, we review the epidemiology, genetic diagnosis, and clinicogenetic characteristics of CMT in Japan. In addition, we discuss the newly identified novel causative genes for CMT/IPNs in Japan, namely MME and COA7. Identification of the new causes of CMT will facilitate in-depth characterization of the underlying molecular mechanisms of CMT, leading to the establishment of therapeutic approaches such as drug development and gene therapy.

The Antiepileptic Valproic Acid Ameliorates Charcot-Marie-Tooth 2W (CMT2W) Disease-Associated HARS1 Mutation-Induced Inhibition of Neuronal Cell Morphological Differentiation Through c-Jun N-terminal Kinase

Hereditary peripheral neuropathies called Charcot-Marie-Tooth (CMT) disease affect the sensory nerves as well as motor neurons. CMT diseases are composed of a heterogeneous group of diseases. They are characterized by symptoms such as muscle weakness and wasting. Type 2 CMT (CMT2) disease is a neuropathy with blunted or disrupted neuronal morphological differentiation phenotypes including process formation of peripheral neuronal axons. In the early stages of CMT2, demyelination that occurs in Schwann cells (glial cells) is rarely observed. CMT2W is an autosomal-dominant disease and is responsible for the gene encoding histidyl-tRNA synthetase 1 (HARS1), which is a family molecule of cytoplasmic aminoacyl-tRNA synthetases and functions by ligating histidine to its cognate tRNA. Despite increasing knowledge of the relationship of mutations on responsible genes with diseases, it still remains unclear how each mutation affects neuronal differentiation. Here we show that in neuronal N1E-115 cells, a severe Asp364-to-Tyr (D364Y) mutation of HARS1 leads to formation of small aggregates of HARS1 proteins; in contrast, wild type proteins are distributed throughout cell bodies. Expression of D364Y mutant proteins inhibited process formation whereas expression of wild type proteins possessed the normal differentiation ability to grow processes. Pretreatment with the antiepileptic valproic acid recovered inhibition of process formation by D364Y mutant proteins through the c-Jun N-terminal kinase signaling pathway. Taken together, these results indicate that the D364Y mutation of HARS1 causes HARS1 proteins to form small aggregates, inhibiting process growth, and that these effects are recovered by valproic acid. This could be a potential therapeutic drug for CMT2W at the cellular levels.

Farnesol Ameliorates Demyelinating Phenotype in a Cellular and Animal Model of Charcot-Marie-Tooth Disease Type 1A

Charcot-Marie-Tooth disease (CMT) is a genetically heterogeneous disease affecting the peripheral nervous system that is caused by either the demyelination of Schwann cells or degeneration of the peripheral axon. Currently, there are no treatment options to improve the degeneration of peripheral nerves in CMT patients. In this research, we assessed the potency of farnesol for improving the demyelinating phenotype using an animal model of CMT type 1A. In vitro treatment with farnesol facilitated myelin gene expression and ameliorated the myelination defect caused by PMP22 overexpression, the major causative gene in CMT. In vivo administration of farnesol enhanced the peripheral neuropathic phenotype, as shown by rotarod performance in a mouse model of CMT1A. Electrophysiologically, farnesol-administered CMT1A mice exhibited increased motor nerve conduction velocity and compound muscle action potential compared with control mice. The number and diameter of myelinated axons were also increased by farnesol treatment. The expression level of myelin protein zero (MPZ) was increased, while that of the demyelination marker, neural cell adhesion molecule (NCAM), was reduced by farnesol administration. These data imply that farnesol is efficacious in ameliorating the demyelinating phenotype of CMT, and further elucidation of the underlying mechanisms of farnesol’s effect on myelination might provide a potent therapeutic strategy for the demyelinating type of CMT.

Troponin Variants as Markers of Skeletal Muscle Health and Diseases

Ca2 +-regulated contractility is a key determinant of the quality of muscles. The sarcomeric myofilament proteins are essential players in the contraction of striated muscles. The troponin complex in the actin thin filaments plays a central role in the Ca2+-regulation of muscle contraction and relaxation. Among the three subunits of troponin, the Ca2+-binding subunit troponin C (TnC) is a member of the calmodulin super family whereas troponin I (TnI, the inhibitory subunit) and troponin T (TnT, the tropomyosin-binding and thin filament anchoring subunit) are striated muscle-specific regulatory proteins. Muscle type-specific isoforms of troponin subunits are expressed in fast and slow twitch fibers and are regulated during development and aging, and in adaptation to exercise or disuse. TnT also evolved with various alternative splice forms as an added capacity of muscle functional diversity. Mutations of troponin subunits cause myopathies. Owing to their physiological and pathological importance, troponin variants can be used as specific markers to define muscle quality. In this focused review, we will explore the use of troponin variants as markers for the fiber contents, developmental and differentiation states, contractile functions, and physiological or pathophysiological adaptations of skeletal muscle. As protein structure defines function, profile of troponin variants illustrates how changes at the myofilament level confer functional qualities at the fiber level. Moreover, understanding of the role of troponin modifications and mutants in determining muscle contractility in age-related decline of muscle function and in myopathies informs an approach to improve human health.