RARE DISEASE
X-linked Charcot-Marie-Tooth disease type 6
X-linked Charcot-Marie-Tooth disease type 6
X-linked Charcot-Marie-Tooth disease type 6
Synonyms: CMT6X, CMTX6
Synonyms: CMT6X, CMTX6
Synonyms: CMT6X, CMTX6
Drug discovery
66
papers
On emerging therapies
Overview
X-linked Charcot-Marie-Tooth disease type 6 (CMTX6) is a rare axonal peripheral sensorimotor neuropathy caused by PDK3 gene mutations on Xp22.11. It presents with childhood/adolescent-onset progressive distal muscle weakness (primarily lower limbs), panmodal sensory loss, bilateral pes cavus, and steppage gait. Females typically exhibit mild/asymptomatic phenotypes (hand tremors, minor muscle atrophy), while males experience moderate-severe symptoms. Diagnosis combines nerve conduction studies (axonal pattern) and genetic testing [1][9][15][17].
Population
Rare subtype (<1/1,000,000 prevalence), reported in 5 families globally (Australia, Brazil, Korea, Germany)
X-linked dominant inheritance: males significantly more affected than female carriers
Symptoms manifest in 2nd decade, progressing to proximal muscle involvement in severe cases [1][6][15][17]
Burden
High disability: 67% require walking aids by 3rd decade; chronic neuropathic pain affects 30-40%
Progressive functional decline impacts education/employment, with 25% reporting reduced quality of life
Limited treatment accessibility due to diagnostic delays (average 7.2 years from symptom onset) [9][12][15][17]
Categories: rare developmental anomalies during embryogenesis, rare genetic diseases, rare neurological diseases, rare otorhinolaryngological diseases
Research Papers
66 drug discovery papers about X-linked Charcot-Marie-Tooth disease type 6, with 2 first-in-class emerging drug candidates forecasted to outperform the average preclinical success rate. Recent publications:
66 drug discovery papers about X-linked Charcot-Marie-Tooth disease type 6, with 2 first-in-class emerging drug candidates forecasted to outperform the average preclinical success rate. Recent publications:
categories:
Small molecules
gene therapies
2023-12-21 | X-linked Charcot Marie Tooth mutations alter CO2 sensitivity of connexin32 hemichannels
Connexin32 (Cx32) is expressed in myelinating Schwann cells. It forms both reflexive gap junctions, to facilitate transfer of molecules from the outer to the inner myelin layers and hemichannels at the paranode to permit action potential-evoked release of ATP into the extracellular space. Loss of function mutations in Cx32 cause X-linked Charcot Marie Tooth disease (CMTX), a slowly developing peripheral neuropathy. The mechanistic links between Cx32 mutations and CMTX are not well understood. As Cx32 hemichannels can be opened by increases in PCO 2 , we have examined whether CMTX mutations alter this CO 2 sensitivity. By using Ca 2+ imaging, dye loading and genetically encoded ATP sensors to measure ATP release, we have found 5 CMTX mutations that abolish the CO 2 sensitivity of Cx32 hemichannels (A88D, 111–116 Del, C179Y, E102G, V139M). Others cause a partial loss (L56F, R220Stop, and R15W). Some CMTX mutations have no apparent effect on CO 2 sensitivity (R15Q, L9F, G12S, V13L, V84I, W133R). The mutation R15W alters multiple additional aspects of hemichannel function including Ca 2+ and ATP permeability. The mutations that abolish CO 2 sensitivity are transdominant and abolish CO 2 sensitivity of co-expressed Cx32 WT . We have shown that Schwannoma RT4 D6P2T cells can release ATP in response to elevated PCO 2 via the opening of Cx32. This is consistent with the hypothesis that the CO 2 sensitivity of Cx32 may be important for maintenance of healthy myelin. Our data, showing a transdominant effect of certain CMTX mutations on CO 2 sensitivity, may need to be taken into account in any future gene therapies for this condition.
2021-03-10 | AAV9-mediated Schwann cell-targeted gene therapy rescues a model of demyelinating neuropathy
Mutations in the GJB1 gene, encoding the gap junction (GJ) protein connexin32 (Cx32), cause X-linked Charcot-Marie-Tooth disease (CMT1X), an inherited demyelinating neuropathy. We developed a gene therapy approach for CMT1X using an AAV9 vector to deliver the GJB1/Cx32 gene under the myelin protein zero (Mpz) promoter for targeted expression in Schwann cells. Lumbar intrathecal injection of the AAV9-Mpz.GJB1 resulted in widespread biodistribution in the peripheral nervous system including lumbar roots, sciatic and femoral nerves, as well as in Cx32 expression in the paranodal non-compact myelin areas of myelinated fibers. A pre-, as well as post-onset treatment trial in Gjb1-null mice, demonstrated improved motor performance and sciatic nerve conduction velocities along with improved myelination and reduced inflammation in peripheral nerve tissues. Blood biomarker levels were also significantly ameliorated in treated mice. This study provides evidence that a clinically translatable AAV9-mediated gene therapy approach targeting Schwann cells could potentially treat CMT1X.
2021-02-04 | AAV1.NT-3 gene therapy for X-linked Charcot–Marie–Tooth neuropathy type 1
Abstract X-linked Charcot-Marie-Tooth neuropathy (CMTX) is caused by mutations in the gene encoding Gap Junction Protein Beta-1 (GJB1)/Connexin32 (Cx32) in Schwann cells. Neurotrophin-3 (NT-3) is an important autocrine factor supporting Schwann cell survival and differentiation and stimulating axon regeneration and myelination. Improvements in these parameters have been shown previously in a CMT1 model, Trembler J mouse, with NT-3 gene transfer therapy. For this study, scAAV1.tMCK.NT-3 was delivered to the gastrocnemius muscle of 3-month-old Cx32 knockout (KO) mice. Measurable levels of NT-3 were found in the serum at 6-month post gene delivery. The outcome measures included functional, electrophysiological and histological assessments. At 9-months of age, NT-3 treated mice showed no functional decline with normalized compound muscle action potential amplitudes. Myelin thickness and nerve conduction velocity significantly improved compared with untreated cohort. A normalization toward age-matched wildtype histopathological parameters included increased number of Schmidt-Lanterman incisures, and muscle fiber diameter. Collectively, these findings suggest a translational application to CMTX1.
2019-08-06 | Gene replacement therapy after neuropathy onset provides therapeutic benefit in a model of CMT1X
Abstract X-linked Charcot-Marie-Tooth disease (CMT1X), one of the commonest forms of inherited demyelinating neuropathy, results from GJB1 gene mutations causing loss of function of the gap junction protein connexin32 (Cx32). The aim of this study was to examine whether delayed gene replacement therapy after the onset of peripheral neuropathy can provide a therapeutic benefit in the Gjb1-null/Cx32 knockout model of CMT1X. After delivery of the LV-Mpz.GJB1 lentiviral vector by a single lumbar intrathecal injection into 6-month-old Gjb1-null mice, we confirmed expression of Cx32 in lumbar roots and sciatic nerves correctly localized at the paranodal myelin areas. Gjb1-null mice treated with LV-Mpz.GJB1 compared with LV-Mpz.Egfp (mock) vector at the age of 6 months showed improved motor performance at 8 and 10 months. Furthermore, treated mice showed increased sciatic nerve conduction velocities, improvement of myelination and reduced inflammation in lumbar roots and peripheral nerves at 10 months of age, along with enhanced quadriceps muscle innervation. Plasma neurofilament light (NEFL) levels, a clinically relevant biomarker, were also ameliorated in fully treated mice. Intrathecal gene delivery after the onset of peripheral neuropathy offers a significant therapeutic benefit in this disease model, providing a proof of principle for treating patients with CMT1X at different ages.
2018-07-13 | Intrathecal Delivery of Viral Vectors for Gene Therapy
Gene delivery to the peripheral nervous system for therapeutic applications remains technically challenging but could eventually have a significant impact on the development of innovative treatments not only for inherited but also for acquired peripheral neuropathies. Here we describe the method for lumbar intrathecal injection of viral vectors in experimental mice. This gene delivery route provides widespread and stable over time Schwann cell-targeted or ubiquitous gene expression in the peripheral nervous system.
small molecules
2026-01-01 | A high-content phenotypic screen identifies luteolin as a repurposed drug to reduce pyruvate dehydrogenase phosphorylation and enhance energy production in CMTX6 cell models
Gonzalo Perez-Siles, Masahiro Nishide, Melina Ellis, Richard M Wynn, Gauri Shishodia, Steve Vucic, Marina L Kennerson; A high-content phenotypic screen ide
2024-03-14 | Gp78 regulates PMP22 and causes ER stress and autophagy in EV71-VP1-overexpressing mouse Schwann cells
Background: During Enterovirus type 71 (EV71) infection, the structural viral protein 1 (VP1) activates endoplasmic reticulum (ER) stress associated with peripheral myelin protein 22 (PMP22) accumulation and induces autophagy.However, the specific mechanism behind this process remains elusive.Methods: In this research, we used the VP1-overexpressing mouse Schwann cells (SCs) models co-transfected with a PMP22 silencing or Autocrine motility factor receptor (AMFR/gp78) overexpressing vector to explore the regulation of gp78 on PMP22 and its relationship with autophagy and apoptosis.Results: The activity of gp78 could be influenced by EV71-VP1, leading to a decrease in the ubiquitination and degradation of PMP22, resulting in PMP22 accumulation in ER.In VP1overexpressing mouse SCs, all three ER stress sensors, including pancreatic endoplasmic reticulum kinase (PERK), activating transcription factor 6 (ATF6) and inositol-requiring enzyme 1 (IRE1) and the related downstream signals (C/EBP-homologous protein (CHOP) and Caspase 12) were activated, as well as the ER-resident chaperone Glucoseregulated protein 78 (GRP78).In addition, VP1 upregulated the autophagy marker Microtubule-associated protein 1 light chain 3 beta (LC3B), while PMP22 silencing or gp78 overexpression reversed the phenomenon.Meanwhile, PMP22 silencing or gp78 overexpression increased proliferation of EV71-VP1-transfected mouse SCs.Conclusion:Gp78 could regulate PMP22 accumulation through ubiquitination degradation and cause ER stress and autophagy in EV71-VP1-overexpressing mouse SCs.Therefore, the gp78/PMP22/ER stress axis might emerge as a promising therapeutic target for myelin and neuronal damage induced by EV71 infection.
2023-07-21 | Amlexanox: Readthrough Induction and Nonsense-Mediated mRNA Decay Inhibition in a Charcot–Marie–Tooth Model of hiPSCs-Derived Neuronal Cells Harboring a Nonsense Mutation in GDAP1 Gene
Nonsense mutations are involved in multiple peripheral neuropathies. These mutations induce the presence of a premature termination codon (PTC) at the mRNA level. As a result, a dysfunctional or truncated protein is synthesized, or even absent linked to nonsense-mediated mRNA degradation (NMD) system activation. Readthrough molecules or NMD inhibitors could be innovative therapies in these hereditary neuropathies, particularly molecules harboring the dual activity as amlexanox. Charcot–Marie–Tooth (CMT) is the most common inherited pathology of the peripheral nervous system, affecting 1 in 2500 people worldwide. Nonsense mutations in the GDAP1 gene have been associated with a severe form of CMT, prompting us to investigate the effect of readthrough and NMD inhibitor molecules. Although not clearly defined, GDAP1 could be involved in mitochondrial functions, such as mitophagy. We focused on the homozygous c.581C>G (p.Ser194*) mutation inducing CMT2H using patient human induced pluripotent stem cell (hiPSC)-derived neuronal cells. Treatment during 20 h with 100 µM of amlexanox on this cell model stabilized GDAP1 mRNAs carrying UGA-PTC and induced a restoration of the mitochondrial morphology. These results highlight the potential of readthrough molecules associated to NMD inhibitors for the treatment of genetic alterations in CMT, opening the way for future investigations and a potential therapy.
2023-07-01 | Rapid degeneration of iPSC-derived motor neurons lacking Gdap1 engages a mitochondrial-sustained innate immune response
Charcot-Marie-Tooth disease is a chronic hereditary motor and sensory polyneuropathy targeting Schwann cells and/or motor neurons. Its multifactorial and polygenic origin portrays a complex clinical phenotype of the disease with a wide range of genetic inheritance patterns. The disease-associated gene GDAP1 encodes for a mitochondrial outer membrane protein. Mouse and insect models with mutations in Gdap1 have reproduced several traits of the human disease. However, the precise function in the cell types affected by the disease remains unknown. Here, we use induced-pluripotent stem cells derived from a Gdap1 knockout mouse model to better understand the molecular and cellular phenotypes of the disease caused by the loss-of-function of this gene. Gdap1-null motor neurons display a fragile cell phenotype prone to early degeneration showing (1) altered mitochondrial morphology, with an increase in the fragmentation of these organelles, (2) activation of autophagy and mitophagy, (3) abnormal metabolism, characterized by a downregulation of Hexokinase 2 and ATP5b proteins, (4) increased reactive oxygen species and elevated mitochondrial membrane potential, and (5) increased innate immune response and p38 MAP kinase activation. Our data reveals the existence of an underlying Redox-inflammatory axis fueled by altered mitochondrial metabolism in the absence of Gdap1. As this biochemical axis encompasses a wide variety of druggable targets, our results may have implications for developing therapies using combinatorial pharmacological approaches and improving therefore human welfare. A Redox-immune axis underlying motor neuron degeneration caused by the absence of Gdap1. Our results show that Gdap1-/- motor neurons have a fragile cellular phenotype that is prone to degeneration. Gdap1-/- iPSCs differentiated into motor neurons showed an altered metabolic state: decreased glycolysis and increased OXPHOS. These alterations may lead to hyperpolarization of mitochondria and increased ROS levels. Excessive amounts of ROS might be the cause of increased mitophagy, p38 activation and inflammation as a cellular response to oxidative stress. The p38 MAPK pathway and the immune response may, in turn, have feedback mechanisms, leading to the induction of apoptosis and senescence, respectively. CAC, citric acid cycle; ETC, electronic transport chain; Glc, glucose; Lac, lactate; Pyr, pyruvate.
2023-03-23 | Intermolecular And Dynamic Investigation of The Mechanism of Action of Reldesemtiv on Fast Skeletal Muscle Troponin Complex Toward the Treatment of Impaired Muscle Function
Muscle weakness as a secondary feature of attenuated neuronal input often leads to disability and sometimes death in patients with neurogenic neuromuscular diseases. These impaired muscle function has been observed in several diseases including amyotrophic lateral sclerosis, Charcot-Marie-Tooth, spinal muscular atrophy and Myasthenia gravis. This has spurred the search for small molecules which could activate fast skeletal muscle troponin complex as a means to increase muscle strength. Discovered small molecules have however been punctuated by off-target and side effects leading to the development of the second-generation small molecule, Reldesemtiv. In this study, we investigated the impact of Reldesemtiv binding to the fast skeletal troponin complex and the molecular determinants that condition the therapeutic prowess of Redesemtiv through computational techniques. It was revealed that Reldesemtiv binding possibly potentiates troponin C compacting characterized by reduced exposure to solvent molecules which could favor the slow release of calcium ions and the resultant sensitization of the subunit to calcium. These conformational changes were underscored by conventional and carbon hydrogen bonds, pi-alkyl, pi-sulfur and halogen interactions between Reldesemtiv the binding site residues. Arg113 (-3.96 kcal/mol), Met116 (-2.23 kcal/mol), Val114 (-1.28 kcal/mol) and Met121 (-0.63 kcal/mol) of the switch region of the inhibitory subunit were among the residues that contributed the most to the total free binding energy of Reldesemtiv highlighting their importance. These findings present useful insights which could lay the foundation for the development of fast skeletal muscle small molecule activators with high specificity and potency.
proteins
2023-06-01 | Cytokine-Induced Neurogenesis in Charcot-Marie-Tooth neuropathy with Connexin 32 Gene Mutation
Charcot-Marie-Tooth (CMT) neuropathy is one of the most common neuromuscular disorders.Despite the identification of more than 100 causative genes, there are few therapeutic options.We present the case of a 66-year-old man carrying a CMT mutation in the connexin 32 gene with the APOE genotype ε4/ε3 that had exhibited symptoms of slowly progressive muscle weakness and atrophy in the hands and feet and recently developed memory impairment.The muscle weakness, motor dysfunction, and memory impairment symptoms were significantly improved by cytokine-induced neurogenesis combined with physical wave therapy using an arbitrary waveform generator (AWG).Here, we discuss the possible mechanistic basis of how this new treatment ameliorates the symptoms of CMT and propose a novel clinical treatment strategy for CMT.
2017-10-25 | Cx32 hemichannel opening by cytosolic Ca2+ is inhibited by the R220X mutation that causes Charcot-Marie-Tooth disease
Mutations of the GJB1 gene encoding connexin 32 (Cx32) cause the X-linked form of Charcot–Marie–Tooth disease (CMTX1), a demyelinating peripheral neuropathy for which there is no cure. A growing body of evidence indicates that ATP release through Cx32 hemichannels in Schwann cells could be critical for nerve myelination, but it is unknown if CMTX1 mutations alter the cytosolic Ca2+-dependent gating mechanism that controls Cx32 hemichannel opening and ATP release. The current study uncovered that loss of the C-terminus in Cx32 (R220X mutation), which causes a severe CMTX1 phenotype, inhibits hemichannel opening during a canonical IP3-mediated increase in cytosolic Ca2+ in HeLa cells. Interestingly, the gating function of R220X hemichannels was completely restored by both the intracellular and extracellular application of a peptide that mimics the Cx32 cytoplasmic loop. All-atom molecular dynamics simulations suggest that loss of the C-terminus in the mutant hemichannel triggers abnormal fluctuations of the cytoplasmic loop which are prevented by binding to the mimetic peptide. Experiments that stimulated R220X hemichannel opening by cell depolarization displayed reduced voltage sensitivity with respect to wild-type hemichannels which was explained by loss of subconductance states at the single channel level. Finally, experiments of intercellular diffusion mediated by wild-type or R220X gap junction channels revealed similar unitary permeabilities to ions, signalling molecules (cAMP) or larger solutes (Lucifer yellow). Taken together, our findings support the hypothesis that paracrine signalling alteration due to Cx32 hemichannel dysfunction underlies CMTX1 pathogenesis and suggest a candidate molecule for novel studies investigating a therapeutic approach.
gene therapies
2023-12-21 | X-linked Charcot Marie Tooth mutations alter CO2 sensitivity of connexin32 hemichannels
Connexin32 (Cx32) is expressed in myelinating Schwann cells. It forms both reflexive gap junctions, to facilitate transfer of molecules from the outer to the inner myelin layers and hemichannels at the paranode to permit action potential-evoked release of ATP into the extracellular space. Loss of function mutations in Cx32 cause X-linked Charcot Marie Tooth disease (CMTX), a slowly developing peripheral neuropathy. The mechanistic links between Cx32 mutations and CMTX are not well understood. As Cx32 hemichannels can be opened by increases in PCO 2 , we have examined whether CMTX mutations alter this CO 2 sensitivity. By using Ca 2+ imaging, dye loading and genetically encoded ATP sensors to measure ATP release, we have found 5 CMTX mutations that abolish the CO 2 sensitivity of Cx32 hemichannels (A88D, 111–116 Del, C179Y, E102G, V139M). Others cause a partial loss (L56F, R220Stop, and R15W). Some CMTX mutations have no apparent effect on CO 2 sensitivity (R15Q, L9F, G12S, V13L, V84I, W133R). The mutation R15W alters multiple additional aspects of hemichannel function including Ca 2+ and ATP permeability. The mutations that abolish CO 2 sensitivity are transdominant and abolish CO 2 sensitivity of co-expressed Cx32 WT . We have shown that Schwannoma RT4 D6P2T cells can release ATP in response to elevated PCO 2 via the opening of Cx32. This is consistent with the hypothesis that the CO 2 sensitivity of Cx32 may be important for maintenance of healthy myelin. Our data, showing a transdominant effect of certain CMTX mutations on CO 2 sensitivity, may need to be taken into account in any future gene therapies for this condition.
2021-03-10 | AAV9-mediated Schwann cell-targeted gene therapy rescues a model of demyelinating neuropathy
Mutations in the GJB1 gene, encoding the gap junction (GJ) protein connexin32 (Cx32), cause X-linked Charcot-Marie-Tooth disease (CMT1X), an inherited demyelinating neuropathy. We developed a gene therapy approach for CMT1X using an AAV9 vector to deliver the GJB1/Cx32 gene under the myelin protein zero (Mpz) promoter for targeted expression in Schwann cells. Lumbar intrathecal injection of the AAV9-Mpz.GJB1 resulted in widespread biodistribution in the peripheral nervous system including lumbar roots, sciatic and femoral nerves, as well as in Cx32 expression in the paranodal non-compact myelin areas of myelinated fibers. A pre-, as well as post-onset treatment trial in Gjb1-null mice, demonstrated improved motor performance and sciatic nerve conduction velocities along with improved myelination and reduced inflammation in peripheral nerve tissues. Blood biomarker levels were also significantly ameliorated in treated mice. This study provides evidence that a clinically translatable AAV9-mediated gene therapy approach targeting Schwann cells could potentially treat CMT1X.
2021-02-04 | AAV1.NT-3 gene therapy for X-linked Charcot–Marie–Tooth neuropathy type 1
Abstract X-linked Charcot-Marie-Tooth neuropathy (CMTX) is caused by mutations in the gene encoding Gap Junction Protein Beta-1 (GJB1)/Connexin32 (Cx32) in Schwann cells. Neurotrophin-3 (NT-3) is an important autocrine factor supporting Schwann cell survival and differentiation and stimulating axon regeneration and myelination. Improvements in these parameters have been shown previously in a CMT1 model, Trembler J mouse, with NT-3 gene transfer therapy. For this study, scAAV1.tMCK.NT-3 was delivered to the gastrocnemius muscle of 3-month-old Cx32 knockout (KO) mice. Measurable levels of NT-3 were found in the serum at 6-month post gene delivery. The outcome measures included functional, electrophysiological and histological assessments. At 9-months of age, NT-3 treated mice showed no functional decline with normalized compound muscle action potential amplitudes. Myelin thickness and nerve conduction velocity significantly improved compared with untreated cohort. A normalization toward age-matched wildtype histopathological parameters included increased number of Schmidt-Lanterman incisures, and muscle fiber diameter. Collectively, these findings suggest a translational application to CMTX1.
2019-08-06 | Gene replacement therapy after neuropathy onset provides therapeutic benefit in a model of CMT1X
Abstract X-linked Charcot-Marie-Tooth disease (CMT1X), one of the commonest forms of inherited demyelinating neuropathy, results from GJB1 gene mutations causing loss of function of the gap junction protein connexin32 (Cx32). The aim of this study was to examine whether delayed gene replacement therapy after the onset of peripheral neuropathy can provide a therapeutic benefit in the Gjb1-null/Cx32 knockout model of CMT1X. After delivery of the LV-Mpz.GJB1 lentiviral vector by a single lumbar intrathecal injection into 6-month-old Gjb1-null mice, we confirmed expression of Cx32 in lumbar roots and sciatic nerves correctly localized at the paranodal myelin areas. Gjb1-null mice treated with LV-Mpz.GJB1 compared with LV-Mpz.Egfp (mock) vector at the age of 6 months showed improved motor performance at 8 and 10 months. Furthermore, treated mice showed increased sciatic nerve conduction velocities, improvement of myelination and reduced inflammation in lumbar roots and peripheral nerves at 10 months of age, along with enhanced quadriceps muscle innervation. Plasma neurofilament light (NEFL) levels, a clinically relevant biomarker, were also ameliorated in fully treated mice. Intrathecal gene delivery after the onset of peripheral neuropathy offers a significant therapeutic benefit in this disease model, providing a proof of principle for treating patients with CMT1X at different ages.
2018-07-13 | Intrathecal Delivery of Viral Vectors for Gene Therapy
Gene delivery to the peripheral nervous system for therapeutic applications remains technically challenging but could eventually have a significant impact on the development of innovative treatments not only for inherited but also for acquired peripheral neuropathies. Here we describe the method for lumbar intrathecal injection of viral vectors in experimental mice. This gene delivery route provides widespread and stable over time Schwann cell-targeted or ubiquitous gene expression in the peripheral nervous system.
small molecules
2026-01-01 | A high-content phenotypic screen identifies luteolin as a repurposed drug to reduce pyruvate dehydrogenase phosphorylation and enhance energy production in CMTX6 cell models
Gonzalo Perez-Siles, Masahiro Nishide, Melina Ellis, Richard M Wynn, Gauri Shishodia, Steve Vucic, Marina L Kennerson; A high-content phenotypic screen ide
2024-03-14 | Gp78 regulates PMP22 and causes ER stress and autophagy in EV71-VP1-overexpressing mouse Schwann cells
Background: During Enterovirus type 71 (EV71) infection, the structural viral protein 1 (VP1) activates endoplasmic reticulum (ER) stress associated with peripheral myelin protein 22 (PMP22) accumulation and induces autophagy.However, the specific mechanism behind this process remains elusive.Methods: In this research, we used the VP1-overexpressing mouse Schwann cells (SCs) models co-transfected with a PMP22 silencing or Autocrine motility factor receptor (AMFR/gp78) overexpressing vector to explore the regulation of gp78 on PMP22 and its relationship with autophagy and apoptosis.Results: The activity of gp78 could be influenced by EV71-VP1, leading to a decrease in the ubiquitination and degradation of PMP22, resulting in PMP22 accumulation in ER.In VP1overexpressing mouse SCs, all three ER stress sensors, including pancreatic endoplasmic reticulum kinase (PERK), activating transcription factor 6 (ATF6) and inositol-requiring enzyme 1 (IRE1) and the related downstream signals (C/EBP-homologous protein (CHOP) and Caspase 12) were activated, as well as the ER-resident chaperone Glucoseregulated protein 78 (GRP78).In addition, VP1 upregulated the autophagy marker Microtubule-associated protein 1 light chain 3 beta (LC3B), while PMP22 silencing or gp78 overexpression reversed the phenomenon.Meanwhile, PMP22 silencing or gp78 overexpression increased proliferation of EV71-VP1-transfected mouse SCs.Conclusion:Gp78 could regulate PMP22 accumulation through ubiquitination degradation and cause ER stress and autophagy in EV71-VP1-overexpressing mouse SCs.Therefore, the gp78/PMP22/ER stress axis might emerge as a promising therapeutic target for myelin and neuronal damage induced by EV71 infection.
2023-07-21 | Amlexanox: Readthrough Induction and Nonsense-Mediated mRNA Decay Inhibition in a Charcot–Marie–Tooth Model of hiPSCs-Derived Neuronal Cells Harboring a Nonsense Mutation in GDAP1 Gene
Nonsense mutations are involved in multiple peripheral neuropathies. These mutations induce the presence of a premature termination codon (PTC) at the mRNA level. As a result, a dysfunctional or truncated protein is synthesized, or even absent linked to nonsense-mediated mRNA degradation (NMD) system activation. Readthrough molecules or NMD inhibitors could be innovative therapies in these hereditary neuropathies, particularly molecules harboring the dual activity as amlexanox. Charcot–Marie–Tooth (CMT) is the most common inherited pathology of the peripheral nervous system, affecting 1 in 2500 people worldwide. Nonsense mutations in the GDAP1 gene have been associated with a severe form of CMT, prompting us to investigate the effect of readthrough and NMD inhibitor molecules. Although not clearly defined, GDAP1 could be involved in mitochondrial functions, such as mitophagy. We focused on the homozygous c.581C>G (p.Ser194*) mutation inducing CMT2H using patient human induced pluripotent stem cell (hiPSC)-derived neuronal cells. Treatment during 20 h with 100 µM of amlexanox on this cell model stabilized GDAP1 mRNAs carrying UGA-PTC and induced a restoration of the mitochondrial morphology. These results highlight the potential of readthrough molecules associated to NMD inhibitors for the treatment of genetic alterations in CMT, opening the way for future investigations and a potential therapy.
2023-07-01 | Rapid degeneration of iPSC-derived motor neurons lacking Gdap1 engages a mitochondrial-sustained innate immune response
Charcot-Marie-Tooth disease is a chronic hereditary motor and sensory polyneuropathy targeting Schwann cells and/or motor neurons. Its multifactorial and polygenic origin portrays a complex clinical phenotype of the disease with a wide range of genetic inheritance patterns. The disease-associated gene GDAP1 encodes for a mitochondrial outer membrane protein. Mouse and insect models with mutations in Gdap1 have reproduced several traits of the human disease. However, the precise function in the cell types affected by the disease remains unknown. Here, we use induced-pluripotent stem cells derived from a Gdap1 knockout mouse model to better understand the molecular and cellular phenotypes of the disease caused by the loss-of-function of this gene. Gdap1-null motor neurons display a fragile cell phenotype prone to early degeneration showing (1) altered mitochondrial morphology, with an increase in the fragmentation of these organelles, (2) activation of autophagy and mitophagy, (3) abnormal metabolism, characterized by a downregulation of Hexokinase 2 and ATP5b proteins, (4) increased reactive oxygen species and elevated mitochondrial membrane potential, and (5) increased innate immune response and p38 MAP kinase activation. Our data reveals the existence of an underlying Redox-inflammatory axis fueled by altered mitochondrial metabolism in the absence of Gdap1. As this biochemical axis encompasses a wide variety of druggable targets, our results may have implications for developing therapies using combinatorial pharmacological approaches and improving therefore human welfare. A Redox-immune axis underlying motor neuron degeneration caused by the absence of Gdap1. Our results show that Gdap1-/- motor neurons have a fragile cellular phenotype that is prone to degeneration. Gdap1-/- iPSCs differentiated into motor neurons showed an altered metabolic state: decreased glycolysis and increased OXPHOS. These alterations may lead to hyperpolarization of mitochondria and increased ROS levels. Excessive amounts of ROS might be the cause of increased mitophagy, p38 activation and inflammation as a cellular response to oxidative stress. The p38 MAPK pathway and the immune response may, in turn, have feedback mechanisms, leading to the induction of apoptosis and senescence, respectively. CAC, citric acid cycle; ETC, electronic transport chain; Glc, glucose; Lac, lactate; Pyr, pyruvate.
2023-03-23 | Intermolecular And Dynamic Investigation of The Mechanism of Action of Reldesemtiv on Fast Skeletal Muscle Troponin Complex Toward the Treatment of Impaired Muscle Function
Muscle weakness as a secondary feature of attenuated neuronal input often leads to disability and sometimes death in patients with neurogenic neuromuscular diseases. These impaired muscle function has been observed in several diseases including amyotrophic lateral sclerosis, Charcot-Marie-Tooth, spinal muscular atrophy and Myasthenia gravis. This has spurred the search for small molecules which could activate fast skeletal muscle troponin complex as a means to increase muscle strength. Discovered small molecules have however been punctuated by off-target and side effects leading to the development of the second-generation small molecule, Reldesemtiv. In this study, we investigated the impact of Reldesemtiv binding to the fast skeletal troponin complex and the molecular determinants that condition the therapeutic prowess of Redesemtiv through computational techniques. It was revealed that Reldesemtiv binding possibly potentiates troponin C compacting characterized by reduced exposure to solvent molecules which could favor the slow release of calcium ions and the resultant sensitization of the subunit to calcium. These conformational changes were underscored by conventional and carbon hydrogen bonds, pi-alkyl, pi-sulfur and halogen interactions between Reldesemtiv the binding site residues. Arg113 (-3.96 kcal/mol), Met116 (-2.23 kcal/mol), Val114 (-1.28 kcal/mol) and Met121 (-0.63 kcal/mol) of the switch region of the inhibitory subunit were among the residues that contributed the most to the total free binding energy of Reldesemtiv highlighting their importance. These findings present useful insights which could lay the foundation for the development of fast skeletal muscle small molecule activators with high specificity and potency.
proteins
2023-06-01 | Cytokine-Induced Neurogenesis in Charcot-Marie-Tooth neuropathy with Connexin 32 Gene Mutation
Charcot-Marie-Tooth (CMT) neuropathy is one of the most common neuromuscular disorders.Despite the identification of more than 100 causative genes, there are few therapeutic options.We present the case of a 66-year-old man carrying a CMT mutation in the connexin 32 gene with the APOE genotype ε4/ε3 that had exhibited symptoms of slowly progressive muscle weakness and atrophy in the hands and feet and recently developed memory impairment.The muscle weakness, motor dysfunction, and memory impairment symptoms were significantly improved by cytokine-induced neurogenesis combined with physical wave therapy using an arbitrary waveform generator (AWG).Here, we discuss the possible mechanistic basis of how this new treatment ameliorates the symptoms of CMT and propose a novel clinical treatment strategy for CMT.
2017-10-25 | Cx32 hemichannel opening by cytosolic Ca2+ is inhibited by the R220X mutation that causes Charcot-Marie-Tooth disease
Mutations of the GJB1 gene encoding connexin 32 (Cx32) cause the X-linked form of Charcot–Marie–Tooth disease (CMTX1), a demyelinating peripheral neuropathy for which there is no cure. A growing body of evidence indicates that ATP release through Cx32 hemichannels in Schwann cells could be critical for nerve myelination, but it is unknown if CMTX1 mutations alter the cytosolic Ca2+-dependent gating mechanism that controls Cx32 hemichannel opening and ATP release. The current study uncovered that loss of the C-terminus in Cx32 (R220X mutation), which causes a severe CMTX1 phenotype, inhibits hemichannel opening during a canonical IP3-mediated increase in cytosolic Ca2+ in HeLa cells. Interestingly, the gating function of R220X hemichannels was completely restored by both the intracellular and extracellular application of a peptide that mimics the Cx32 cytoplasmic loop. All-atom molecular dynamics simulations suggest that loss of the C-terminus in the mutant hemichannel triggers abnormal fluctuations of the cytoplasmic loop which are prevented by binding to the mimetic peptide. Experiments that stimulated R220X hemichannel opening by cell depolarization displayed reduced voltage sensitivity with respect to wild-type hemichannels which was explained by loss of subconductance states at the single channel level. Finally, experiments of intercellular diffusion mediated by wild-type or R220X gap junction channels revealed similar unitary permeabilities to ions, signalling molecules (cAMP) or larger solutes (Lucifer yellow). Taken together, our findings support the hypothesis that paracrine signalling alteration due to Cx32 hemichannel dysfunction underlies CMTX1 pathogenesis and suggest a candidate molecule for novel studies investigating a therapeutic approach.
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