Implication of peripheral macrophages in amyotrophic lateral sclerosis

Les cellules microgliales/macrophages périphériques participent à la dégénérescence des motoneurones au cours de la SLA. Cependant, l’implication et le site d’action des macrophages périphériques entourant l’axone du motoneurone n’étaient pas connus. Bien que ces deux populations partagent des caractéristiques communes, elles ont des origines développementales différentes, et évoluent dans des environnements différents ce qui pourrait induire une implication différente dans la SLA. Le but de cette étude était donc de caractériser l’implication des macrophages périphériques au cours de la SLA. Nous avons dans un premier temps confirmé l’activation des macrophages au cours de la maladie dans deux modèles murins de SLA (exprimant la SOD1 mutée) présentant une évolution différente de la maladie, et nous avons pour la première fois montré la présence de macrophages autour des axones des motoneurones dans la racine ventrale de la moelle épinière d’un patient atteint de SLA. Nous avons montré que l’infiltration des macrophages dans la moelle épinière était minimale et semblait dépendre de l’évolution de la maladie. Notre étude transcriptomique a montré que la microglie et les macrophages périphériques avaient des profils inflammatoires complexes et très différents. Enfin le remplacement des macrophages mutés, à la périphérie par des macrophages plus trophiques ou moins toxiques a permis d’améliorer différents signes pathologiques associés à la maladie et de ralentir sa phase symptomatique. Ainsi, nous avons montré qu’il est possible d’utiliser les macrophages périphériques pour moduler la progression de la maladie, et qu’ils constituent donc une cible à potentiel thérapeutique.Microglial cells and peripheral macrophages participate to motor neuron degeneration in ALS. However, the precise role of the peripheral macrophages surrounding motor neuron axons had not been discriminated from the role of CNS microglia. Although microglia and peripheral macrophages share common characteristics both populations have different developmental origins and are located in different cellular environments, which could lead to specific implications in the disease. In this study, we aimed to characterize the implication and the site of action of peripheral macrophages in ALS. We first confirmed the activation of peripheral macrophages in the sciatic nerve of two different mouse lines (expressing mutant SOD1) with different disease progression. We also showed for the first time the presence of macrophages surrounding motor neuron axons in the ventral root of a human ALS case. We showed that infiltration of macrophages in the spinal cord was minimal during the disease and was dependent on disease progression. Our transcriptional analyses showed major differences between microglia and peripheral macrophages even though both populations displayed a complex inflammatory profile. Finally, replacement of mutated macrophages by cells more neurotrophic or less neurotoxic led to an improvement of several pathophysiological markers and delayed symptomatic stage of the disease in ALS mice. In conclusion, we provide new evidence suggesting an active role of peripheral macrophages in ALS, supporting future therapeutic strategies by targeting peripheral macrophages

New insights on the disease contribution of neuroinflammation in ALS

International audiencePurpose of review: Amyotrophic lateral sclerosis (ALS) is a degenerative motor neuron disease with a strong neuroinflammatory component. This review summarizes how the connection between neurodegeneration and the immune system is strengthened by new discoveries from ALS genetics and the analysis of subpopulations of immune cells in ALS.Recent findings: Recent genes identified in ALS encode for proteins with direct immune roles, which when mutated lead to deregulation of immune functions, potentially influencing the disease. Although neuroinflammation in the central nervous system (CNS) of ALS patients has been well documented, new evidence suggests also direct malfunctions of immune cells in the CNS and at the periphery. Although CD4+ T-regulatory lymphocytes are protective in ALS, their number and function are altered over the disease course. CD8+ T cells are detrimental for motor neurons in the CNS but show some protective roles at the periphery. Similarly, the presence of mast cells in muscles of ALS models and patients and impairments of monocyte functions reveal potential new players in ALS disease progression.Summary: Although motor neuron degeneration is considered the prime event in ALS, dysfunctions in immune processes can impact the disease, highlighting that targeting specific immune components is a strategy for developing biomarkers and ultimately new drugs

Deletion of the inflammatory S100-A9/MRP14 protein does not influence survival in hSOD1 G93A ALS mice

International audienceNeuroinflammation is a hallmark of Amyotrophic Lateral Sclerosis (ALS) in hSOD1 G93A mouse models where microglial cells contribute to the progressive motor neuron degenerative process. S100-A8 and S100-A9 (also known as MRP8 and MRP14, respectively) are cytoplasmic proteins expressed by inflammatory myeloid cells, including microglia and macrophages. Mainly acting as a heterodimer, S100-A8/A9, when secreted, can activate Tolllike Receptor 4 on immune cells, leading to deleterious proinflammatory cytokine production. Deletion of S100a9 in Alzheimer's disease mouse models showed a positive outcome, reducing pathology. We now assessed its role in ALS. Unexpectedly, our results show that deleting S100a9 in hSOD1 G93A ALS mice had no impact on mouse survival, but rather accelerated symptoms with no impact on microglial activation and motor neuron survival, suggesting that blocking S100-A9 would not be a valuable strategy for ALS

Modifying macrophages at the periphery has the capacity to change microglial reactivity and to extend ALS survival

International audienceMicroglia and peripheral macrophages have both been implicated in amyotrophic lateral sclerosis (ALS), although their respective roles have yet to be determined. We now show that macrophages along peripheral motor neuron axons in mouse models and patients with ALS react to neurodegeneration. In ALS mice, peripheral myeloid cell infiltration into the spinal cord was limited and depended on disease duration. Targeted gene modulation of the reactive oxygen species pathway in peripheral myeloid cells of ALS mice, using cell replacement, reduced both peripheral macrophage and microglial activation, delayed symptoms and increased survival. Transcriptomics revealed that sciatic nerve macrophages and microglia reacted differently to neurodegeneration, with abrupt temporal changes in macrophages and progressive, unidirectional activation in microglia. Modifying peripheral macrophages suppressed proinflammatory microglial responses, with a shift toward neuronal support. Thus, modifying macrophages at the periphery has the capacity to influence disease progression and may be of therapeutic value for ALS

Impact of a frequent nearsplice SOD1 variant in Amyotrophic Lateral Sclerosis: optimizing SOD1 genetic screening for gene therapy opportunities

International audienceObjective Mutations in superoxide dismutase 1 gene ( SOD1) , encoding copper/zinc superoxide dismutase protein, are the second most frequent high penetrant genetic cause for amyotrophic lateral sclerosis (ALS) motor neuron disease in populations of European descent. More than 200 missense variants are reported along the SOD1 protein. To limit the production of these aberrant and deleterious SOD1 species, antisense oligonucleotide approaches have recently emerged and showed promising effects in clinical trials. To offer the possibility to any patient with SOD1-ALS to benefit of such a gene therapy, it is necessary to ascertain whether any variant of unknown significance (VUS), detected for example in SOD1 non-coding sequences, is pathogenic. Methods We analysed SOD1 mutation distribution after SOD1 sequencing in a large cohort of 470 French familial ALS (fALS) index cases. Results We identified a total of 27 SOD1 variants in 38 families including two SOD1 variants located in nearsplice or intronic regions of the gene. The pathogenicity of the c.358–10T>G nearsplice SOD1 variant was corroborated based on its high frequency (as the second most frequent SOD1 variant) in French fALS, the segregation analysis confirmed in eight affected members of a large pedigree, the typical SOD1-related phenotype observed (with lower limb onset and prominent lower motor neuron involvement), and findings on postmortem tissues showing SOD1 misaccumulation. Conclusions Our results highlighted nearsplice/intronic mutations in SOD1 are responsible for a significant portion of French fALS and suggested the systematic analysis of the SOD1 mRNA sequence could become the method of choice for SOD1 screening, not to miss these specific cases