Cédric Raoul

Oligodendrocytes play an essential role in axonal metabolic support and myelination, and their dysfunction is associated with amyotrophic lateral sclerosis (ALS). LINGO1 is a major inhibitor of oligodendrocyte differentiation and axonal regeneration, identified as a promising therapeutic targeted for inflammatory demyelinating diseases. Here, we investigated the expression pattern of LINGO1 in the well-established SOD1(G93A) transgenic mouse model of ALS. We show that LINGO1 protein expression is significantly elevated in both grey and white matter of the mutant spinal cord during both the symptomatic and end stages of the disease. LINGO1 is also notably co-expressed with astroglial and neuronal markers. However, neither the levels of LINGO1 transcripts, nor levels of microRNAs predicted to regulate its expression were altered in the mutant spinal cord, suggesting the involvement of alternative regulatory mechanisms. Our analysis of microRNAs revealed in the mutant a significant downregulation of miR-138, a microRNA known to promote myelination. The differential expression of LINGO1 and miR-138 in ALS mice thus may drive deleterious processes during disease progression in adulthood. Moreover, our data show that white-matter pathology arises earlier than initially thought, as evidenced by significant alterations of oligodendrogenesis that manifest as early as postnatal day 5. Study of the molecular determinants of this developmental defect shows increased miR-138 expression, which may promote oligodendrocyte progenitor cell maturation and involve compensatory mechanisms. Overall, our work identifies disrupted expression of LINGO1 and/or miR-138 in brain during early oligodendrogenesis and at symptomatic disease stages. These findings open the way to further investigations that may consider miR-138 as a potential presymptomatic biomarker and LINGO1 as a therapeutic target to promote remyelination in the context of ALS.

Genetic testing in amyotrophic lateral sclerosis (ALS) often reveals variants of uncertain significance (VUS), which are frequently omitted from diagnostic reports or reported with limited clinical interpretation. To address this gap, we developed a rapid functional assessment pipeline in collaboration with FILSLAN, the French ALS care network, combining in vitro and in vivo neurogenetic assays. We illustrate this approach through the reclassification of the SOD1 p.Val120Leu variant, identified in an ALS patient, as pathogenic. Functional studies demonstrated that this variant leads to cytoplasmic aggregation, reduced neurite outgrowth, and abnormal motor behavior in zebrafish. These results support the systematic use of functional assays to clarify the pathogenicity of uncertain variants, thereby improving diagnostic accuracy, preventing misdiagnosis, and enabling timely therapeutic interventions in ALS.

Proteinopathies, such as amyotrophic lateral sclerosis (ALS), are marked by the accumulation of misfolded proteins that disrupt cellular processes. Eukaryotic cells have developed protein quality control systems to eliminate these aberrant proteins, but these systems often fail to differentiate between normal and misfolded proteins. In ALS, pathological inclusions primarily composed of misfolded TDP-43 are a hallmark of the disease. Recently, a novel unconventional secretion process called misfolding-associated protein secretion (MAPS) has been discovered to selectively export misfolded proteins. USP19, an Endoplasmic Reticulum-associated ubiquitin peptidase, plays a crucial role in this process. In this study, we investigated the impact of ER-anchored USP19 on the secretion of misfolded TDP-43. Here we found that USP19 overexpression significantly promotes the secretion of soluble and aggregated misfolded TDP-43, requiring both ER anchoring and ubiquitin peptidase activity. Characterization of the cellular and molecular mechanisms involved in this process highlighted the importance of early autophagosomal and late endosomal/amphisomal compartments, while lysosomes did not play a key role. By using dominant-negative mutants and small interfering RNAs, we identified that USP19-mediated secretion of misfolded TDP-43 is modulated by key factors involved in cellular trafficking and secretion pathways, such as ATG7, the ESCRT-O HGS/HRS, the Rab GTPases RAB11A, RAB8A, and RAB27A, and the v-SNARE VAMP7. We also confirmed the crucial role of the DNAJC5/CSPα cochaperone. Overall, this study provides new insights into how cells manage the secretion of misfolded TDP-43 proteins and potentially opens new avenues for therapeutic interventions in ALS and related disorders.

We investigate the etiology of amyotrophic lateral sclerosis (ALS) in a 35-year-old woman presenting with progressive weakness in her left upper limb. Prior to sequencing, a comprehensive neurological work-up was performed, including neurological examination, electrophysiology, biomarker assessment, and brain and spinal cord MRI. Six months before evaluation, the patient experienced weakness and atrophy in her left hand, accompanied by brisk reflexes and Hoffman sign in the same arm. Electroneuromyography revealed lower motor neuron involvement in three body regions. Neurofilament light chains were elevated in her cerebrospinal fluid. Brain imaging showed asymmetrical T2 hyperintensity of the corticospinal tracts and T2 linear hypointensity of the precentral gyri. Trio genome sequencing identified a likely pathogenic de novo variant in the KIF1A gene (NM_001244008.2): c.574A>G, p.(Ile192Val). Pathogenic variants in KIF1A have been associated with a wide range of neurological manifestations called KIF1A-associated neurological diseases (KAND). This report describes a likely pathogenic de novo variant in KIF1A associated with ALS, expanding the phenotypic spectrum of KAND and our understanding of the pathophysiology of ALS.

Objectives: To investigate the etiology of amyotrophic lateral sclerosis (ALS) in an adult female patient. Methods: We conducted trio genome sequencing on a 35-year-old woman with progressive weakness in her left upper limb, as well as on her parents. Prior to sequencing, we performed a comprehensive neurological work-up on the patient, including neurological exam, electrophysiology, biomarker assessment, and brain and spinal cord MRI. Results : The propositus experienced weakness and atrophy in her left hand 6 months before the evaluation. This was associated with brisk reflexes and Hoffman sign in the same arm. Electroneuromyography revealed lower motor neuron involvement in three body regions. Neurofilament light chains were elevated in her cerebrospinal fluid. Brain imaging showed asymmetrical T2 hyperintensity of the corticospinal tracts and T2 linear hypointensity of the precentral gyri. Genome trio sequencing identified a likely pathogenic de novo variant in the propositus’s KIF1A gene (NM_001244008.2): c.574A>G, p.(Ile192Val). Discussion: Pathogenic variants in the KIF1A gene have been associated with a wide range of neurological manifestations called KIF1A-associated neurological diseases (KAND). The present report describe a likely pathogenic de novo variant in KIF1A associated with ALS, expanding the phenotypic spectrum of KAND and our understanding of the pathophysiology of ALS.

Amyotrophic lateral sclerosis (ALS) and spinal muscular atrophy (SMA) are the most common motoneuron diseases affecting adults and infants, respectively. ALS and SMA are both characterized by the selective degeneration of motoneurons. Although different in their genetic etiology, growing evidence indicates that they share molecular and cellular pathogenic signatures that constitute potential common therapeutic targets. We previously described a motoneuron-specific death pathway elicited by the Fas death receptor, whereby vulnerable ALS motoneurons show an exacerbated sensitivity to Fas activation. However, the mechanisms that drive the loss of SMA motoneurons remains poorly understood. Here, we describe an in vitro model of SMA-associated degeneration using primary motoneurons derived from Smn2B/- SMA mice and show that Fas activation selectively triggers death of the proximal motoneurons. Fas-induced death of SMA motoneurons has the molecular signature of the motoneuron-selective Fas death pathway that requires activation of p38 kinase, caspase-8, -9 and -3 as well as upregulation of collapsin response mediator protein 4 (CRMP4). In addition, Rho-associated Kinase (ROCK) is required for Fas recruitment. Remarkably, we found that exogenous activation of Fas also promotes axonal elongation in both wildtype and SMA motoneurons. Axon outgrowth of motoneurons promoted by Fas requires the activity of ERK, ROCK and caspases. This work defines a dual role of Fas signaling in motoneurons that can elicit distinct responses from cell death to axonal growth.

Amyotrophic lateral sclerosis (ALS) is a fatal and incurable paralytic disorder caused by the progressive death of upper and lower motoneurons. Although numerous strategies have been developed to slow disease progression and improve life quality, to date only a few therapeutic treatments are available with still unsatisfactory therapeutic benefits. The secretome of dental pulp stem cells (DPSCs) contains numerous neurotrophic factors that could promote motoneuron survival. Accordingly, DPSCs confer neuroprotective benefits to the SOD1^G93A mouse model of ALS. However, the mode of action of DPSC secretome on motoneurons remains largely unknown. Here, we used conditioned medium of human DPSCs (DPSCs-CM) and assessed its effect on survival, axonal length, and electrical activity of cultured wildtype and SOD1^G93A motoneurons. To further understand the role of individual factors secreted by DPSCs and to circumvent the secretome variability bias, we focused on GDF15 and HB-EGF whose neuroprotective properties remain elusive in the ALS pathogenic context. DPSCs-CM rescues motoneurons from trophic factor deprivation-induced death, promotes axon outgrowth of wildtype but not SOD1^G93A mutant motoneurons, and has no impact on the spontaneous electrical activity of wildtype or mutant motoneurons. Both GDF15 and HB-EGF protect SOD1^G93A motoneurons against nitric oxide-induced death, but not against death induced by trophic factor deprivation. GDF15 and HB-EGF receptors were found to be expressed in the spinal cord, with a two-fold increase in expression for the GDF15 low-affinity receptor in SOD1^G93A mice. Therefore, the secretome of DPSCs appears as a new potential therapeutic candidate for ALS.

Amyotrophic lateral sclerosis (ALS) is the third most frequent neurodegenerative disease after Alzheimer’s and Parkinson’s disease. ALS is characterized by the selective and progressive loss of motoneurons in the spinal cord, brainstem and cerebral cortex. Clinical manifestations typically occur in midlife and start with focal muscle weakness, followed by the rapid and progressive wasting of muscles and subsequent paralysis. As with other neurodegenerative diseases, the condition typically begins at an initial point and then spreads along neuroanatomical tracts. This feature of disease progression suggests the spreading of prion-like proteins called prionoids in the affected tissues, which is similar to the spread of prion observed in Creutzfeldt-Jakob disease. Intensive research over the last decade has proposed the ALS-causing gene products Cu/Zn superoxide dismutase 1, TAR DNA-binding protein of 43 kDa, and fused in sarcoma as very plausible prionoids contributing to the spread of the pathology. In this review, we will discuss the molecular and cellular mechanisms leading to the propagation of these prionoids in ALS.