Biology subjects

Megarbane, A.

Publications and source records attributed to Megarbane, A..

5 recordsLinked to original sources

bioRxiv2025

Bi-allelic mutations in KCTD11 cause a new form of autosomal recessive intermediate Charcot-Marie-Tooth disease

Charcot-Marie-Tooth disease (CMT) is the most common inherited neuromuscular disorder, characterized by progressive, length-dependent degeneration of peripheral nerves, resulting in distal muscle atrophy and weakness, foot and hand deformities, and sensory deficits. The disease is clinically and genetically heterogeneous, with over 125 disease-causing genes identified to date. Here, genetic studies in ten patients from 5 unrelated families of diverse ethnic background, led to the identification of KCTD11 as a novel CMT gene, responsible for a new autosomal recessive intermediate CMT subtype, RI-CMTE. The variants identified are loss of function. KCTD11 encodes KCTD11/REN, a protein of yet unknown function in the Peripheral Nervous System, known to regulate HDAC1, {beta}-catenin, and mTORC1, key regulators of myelination and neuronal differentiation in the PNS. To explore KCTD11s role in the PNS, we used a constitutive Kctd11-/- mouse model and the derived in vitro myelin model of sensory neuron and Schwann cell co-culture (DRGN/SC), to mimic the loss-of-function induced by patient mutations. We first demonstrate that the loss of KCTD11 is due to enhanced degradation of the mutated protein via autophagy. Both in vitro and in vivo, we demonstrate abnormal myelination in vivo and altered myelination dynamics in vitro. These defects were associated with dysregulation of the expression of key transcription factors in Schwann cells, such as Egr2 and Sox10, along with other myelin-related genes, as revealed by mRNA-sequencing data. Regarding pathophysiological mechanisms, we identified dysregulation of HDAC1 expression, as well as alterations in the Wnt/{beta}-catenin, Sonic Hedgehog and Hippo/YAP signaling pathways. The deregulation of these pathways seem to converge to altered autophagy and altered balance between proliferation, differentiation and apoptosis, at least in Schwann cells. These mechanisms remain to be explored in axons from PNS neurons. Altogether, our results identify KCTD11 as a novel gene defective in autosomal recessive intermediate RI-CMTE and highlight the key role of KCTD11 in maintaining myelin homeostasis through regulation of HDAC1 and phosphorylated {beta}-catenin levels, thereby preventing late-onset myelin abnormalities and degradation.

genetics↗

bioRxiv2024

Altered NRG1/ErbB4 signaling and cholesterol metabolism dysregulation are key pathomechanisms in VRK1-related motor neuropathies and motor neuron diseases

Hereditary Motor and Sensory Neuropathy (HMSN), or Charcot-Marie-Tooth disease (CMT), are the most common group of Inherited peripheral neuropathies (IPN), characterized by a strong clinical and genetic heterogeneity. Among them, distal Hereditary Motor Neuropathy (dHMN), also known as neuronopathy, is a subgroup, where only motor nerves are affected. This subgroup is also genetically heterogeneous, with 25 genes described to date, of which VRK1, that we have recently described as responsible for dHMN, associated to upper motor neuron signs. There are now more than thirty mutations in VRK1, which cause a range of neurological diseases affecting motor neurons (mainly lower, but also upper) or their axons in the peripheral nervous system, that we design as VRK1-related motor neuron diseases. In two previous studies, we have demonstrated that dHMN due to VRK1 mutations lead to reduced levels of VRK1 in the nucleus, and that this depletion alters the dynamics of coilin, a phosphorylation target of VRK1. hiPSC-derived Motor Neurons (hiPSC-MN) from these patients, display Cajal Bodies (CBs) disassembly and defects in neurite outgrowth and branching, altered Action Potential (AP) waveform and decreased Axonal Initial Segment (AIS) length. In this study, we have further studied the link between the loss of VRK1 function and the defects observed in hiPSC-MNs, by realizing bulk mRNA-Seq sequencing in this in vitro model of the disease. Our results evidenced altered NRG1/ERBB4 signaling, leading to cholesterol metabolism dysregulation and deregulation of genes encoding the glutamate receptors AMPAR and NMDAR, which role in the Axonal Initial Segment and abnormal AP initiation in hiPSC-MNs remains to be investigated.

genetics↗

bioRxiv2023

Epigenetic Age Acceleration in Surviving versus Deceased COVID-19 Patients with Acute Respiratory Distress Syndrome following Hospitalization

Aging has been reported as a major risk factor for severe symptoms and higher mortality rates in COVID-19 patients. Molecular hallmarks such as epigenetic alterations and telomere attenuation reflect the biological process of aging. Epigenetic clocks have been shown to be valuable tools for measuring biological age in a variety of tissues and samples. As such, these epigenetic clocks can determine accelerated biological aging and time-to-mortality across various tissues. Previous reports have shown accelerated biological aging and telomere attrition acceleration following SARS-CoV-2 infection. However, the effect of accelerated epigenetic aging on outcome (death/recovery) in COVID-19 patients with Acute Respiratory Distress Syndrome (ARDS) has not been well investigated. In this study, we measured DNA methylation age and telomere attrition in 87 severe COVID-19 cases with ARDS under mechanical ventilation. Furthermore, we compared dynamic changes in epigenetic aging across multiples time-points until recovery or death. Epigenetic age was measured using the Horvath, Hannum, DNAm skin and blood, GrimAge, and PhenoAge clocks, whereas telomere length was calculated using the surrogate marker DNAmTL. Our analysis revealed significant accelerated epigenetic aging but no telomere attrition acceleration in severe COVID-19 cases. In addition, we observed epigenetic age deceleration at inclusion vs end of follow-up in recovered but not in deceased COVID-19 cases using certain clocks. When comparing dynamic changes in epigenetic age acceleration (EAA), we detected higher EAA using both the Horvath and PhenoAge clocks in deceased vs recovered patients. The DNAmTL measurements revealed telomere attrition acceleration in deceased COVID19 patients between inclusion and end of follow-up as well as a significant change in dynamic telomere attrition acceleration when comparing patients who recovered vs those who died. In conclusion, EAA and telomere attrition acceleration was associated with treatment outcome in hospitalized COVID-19 Patients with ARDS. A better understanding of the long-term effects of EAA in COVID19 patients and how they might contribute to Long COVID symptoms in recovered individuals is urgently needed.

genetics↗

bioRxiv2022

Imbalance of Neuregulin1-ErbB2/3 signaling underlies altered myelin homeostasis in models of Charcot-Marie-Tooth disease type 4H

Charcot Marie Tooth disease (CMT) is one of the most common inherited neurological disorders, affecting either axons from the motor and/or sensory neurons or Schwann cells (SC) of the peripheral nervous system, and caused by more than 100 genes. We previously identified mutations in FGD4, as responsible for CMT4H, an autosomal recessive demyelinating form of CMT. FGD4 encodes FRABIN a GDP/GTP nucleotide exchange factor (GEF), particularly for the small GTPase cdc42. Remarkably, nerves from patients with CMT4H display excessive redundant myelin called outfoldings that arise from focal hypermyelination, suggesting that FRABIN could play a role in the control of PNS myelination. To gain insights into the role of FGD4/FRABIN in SC myelination, we generated a knock-out mouse model, with conditional ablation of fgd4 in SC. We showed that the specific deletion of FRABIN in SCs leads to aberrant myelination in vitro, in dorsal root ganglion (DRG)/SCs cocultures as well in vivo, in distal sciatic nerves. We observed that those myelination defects are related to an upregulation of some interactors of the NRG1 type III/ErbB2/3 signaling pathway, which is known to ensure a proper level of myelination in the PNS. Based on a yeast two-hybrid screen, we identified SNX3 as a new partner of FRABIN, which is involved in the regulation of endocytic trafficking. Interestingly, we showed that loss of FRABIN impairs endocytic trafficking which may contribute to the defective NRG1 type III/ErbB2/3 signaling and myelination. Finally, we showed that the reestablishment of proper levels of the NRG1 type III/ErbB2/3 pathway using Niacin treatment reduces myelin outfoldings in nerves of CMT4H mice. Overall, our work reveals a new role of FRABIN in the regulation of NRG1 type III/ErbB2/3 NRG1signaling and myelination and opens future therapeutic strategies based on the modulation of NRG1 type III/ErbB2/3 NRG1to reduce CMT4H pathology and more generally others demyelinating CMT.

neuroscience↗

bioRxiv2021

Altered action potential waveform and shorter axonal initial segment in hiPSC-derived motor neurons with mutations in VRK1

We recently described new pathogenic variants in VRK1, in patients affected with distal Hereditary Motor Neuropathy associated with upper motor neurons signs. Specifically, we provided evidences that hiPSC-derived Motor Neurons (hiPSC-MN) from these patients display Cajal bodies (CBs) disassembly and defects in neurite outgrowth and branching. We here focused on the Axonal Initial Segment (AIS) and the related firing properties of hiPSC-MNs from these patients. We found that the patients Action Potential (AP) was smaller in amplitude, larger in duration, and displayed a more depolarized threshold while the firing patterns were not altered. These alterations were accompanied by a decrease in the AIS length measured in patients hiPSC-MNs. These data indicate that mutations in VRK1 impact the AP waveform and the AIS organization in MNs and may ultimately lead to the related motor neuron disease. HighlightsO_LIhiPSC-MNs are functional and sustain firing patterns, typical of spinal MNs C_LIO_LIhiPSC-MNs from patients with VRK1 mutations have altered Action Potential C_LIO_LIAxonal Initial Segment is shorter in hiPSC-MNs from patients with mutated VRK1 C_LIO_LIhiPSC-MNs are a useful platform to study Motor Inherited Peripheral Neuropathies C_LI eTOC BlurbIn human spinal Motor Neurons derived from induced Pluripotent Stem Cells from patients with VRK1 -related distal Hereditary Motor Neuropathy, Bos, Rihan et al. show that the mutations in VRK1 affect the electrical properties of these neurons: they display defects in the initiation of the Action Potential due to a shortening of the Axonal Initial Segment.

neuroscience↗