Repair strategies for traumatic spinal cord injury, with special emphasis on novel biomaterial-based approachesSylvia Soares*, Ysander von Boxberg*, Fatiha Nothias

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Impact of different chitosan hydrogel formulations on macrophage polarization in vitro

International audienceInflammation is a normal event following a lesion, and is usually resolved after a certain time together with the reconstitution of the damaged tissue. In case of a central nervous system lesion, however, in particular a traumatic spinal cord injury (SCI), inflammation is somehow "uncontrolled", and will generally spread from the site of the initial impact towards originally unaffected tissue, creating important secondary damage. Today, development of novel therapeutic strategies for SCI should thus include a better control of the inflammatory reaction. We have recently shown that a fragmented physical hydrogel suspension (FPHS) of chitosan (4% DA, 2.5% Cp), implanted into a rat spinal cord hemisection, is a very efficient bio-scaffold material, allowing already by itself for massive axon regrowth through the lesion site, neovascularization, neural tissue reconstitution and reduction of cystic cavitation, long-term survival of (re-)myelinating Schwann cells, sand last not least, enhanced functional recovery [1]. This appears to be linked, at least in part, to a reduction -in comparison to a non-treated lesion- in classically activated, inflammatory ("M1") macrophages, and a prolonged presence of anti-inflammatory ("M2") macrophages that normally disappear from the lesion site after only about one week.To address the question whether the observed effect on macrophage polarization was due to the chitosan itself, or rather secondary to, for example, the invasion of diverse cell types attaching to the biomaterial serving as matrix replacement, the reduced astrocytic reaction, or better oxygen supply thanks to efficient revascularization, we introduced an in vitro assay in which different formulations of chitosan are used as substrate for culturing pre-polarized macrophages of the M1 and M2 subtypes. We show that indeed, chitosan directly influences the level of expression of typical M1 and M2 macrophage "marker molecules", dependent on the degree of acetylation (DA), and to a lesser extent also the concentration of chitosan within the hydrogel. The effect is only observed if macrophages are in direct contact with the hydrogel particles. This assay may thus be used to fine-tune the formulation of chitosan hydrogel intended for SCI treatment, and also serve as a rapid and easy means to test a newly generated biomaterial for its impact on macrophage polarization

Hydrogels physiques de chitosane pour la réparation des tissus de lamoelle épinière.

International audienceUne lésion traumatique du système nerveux central adulte (cerveau et moelle épinière) est généralementsuivie d ?une très faible repousse axonale à travers le site de la lésion, contrairementau système nerveux périphérique. Néanmoins, la recherche sur les lésions de la moelle épinière(SCI) a récemment fait un grand bond en avant dans l ?élucidation des processus dégénératifs,inflammatoires et protecteurs déclenchés par les lésions de la moelle, et des mécanismes limitantla repousse des fibres lésées dans le SNC adulte.Dans ce travail [1], nous avons développé des formulations de biomatériaux à base de chitosane,offrant de nouvelles voies pour induire une régénération tissulaire et une recouvrancefonctionnelle, sur un modèle de rat. Notre stratégie est basée sur l ?optimisation de formulationd ?hydrogel physique de chitosane à l ?état fragmenté, offrant ainsi une structure ouverte etrésorbable aux macrophages dont la polarisation permet une reconstruction tissulaire avec unenéovascularisation, un pontage axonal de la lésion, et in fine un gain du score BBB quantifiantla fonction locomotrice

Expression of MAP1B protein and its phosphorylated form MAP1B-P in the CNS of a continuously growing fish, the rainbow trout

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The expression level of alpha-synuclein in different neuronal populations is the primary determinant of its prion-like seeding

International audienceAlpha-synuclein (aSyn)-rich aggregates propagate in neuronal networks and compromise cellular homeostasis leading to synucleinopathies such as Parkinson's disease. Aggregated aSyn spread follows a conserved spatio-temporal pattern that is not solely dependent on connectivity. Hence, the differential tropism of aSyn-rich aggregates to distinct brain regions, or their ability to amplify within those regions, must contribute to this process. To better understand what underlies aSyn-rich aggregates distribution within the brain, we generated primary neuronal cultures from various brain regions of wild-type mice and mice expressing a reduced level of aSyn, and exposed them to fibrillar aSyn. We then assessed exogenous fibrillar aSyn uptake, endogenous aSyn seeding, and endogenous aSyn physiological expression levels. Despite a similar uptake of exogenous fibrils by neuronal cells from distinct brain regions, the seeded aggregation of endogenous aSyn differed greatly from one neuronal population to another. The different susceptibility of neuronal populations was linked to their aSyn expression level. Our data establish that endogenous aSyn expression level plays a key role in fibrillar aSyn prion-like seeding, supporting that endogenous aSyn expression level participates in selective regional brain vulnerability

Repair strategy for traumatic spinal cord injury; an advance in bioengineering-based preclinical approaches

International audienceRecovery from traumatic spinal cord injury (SCI) usually fails due to a cascade of cellular and molecular events that compromise neural tissue reconstitution by giving rise to glial scarring and cavity formation. We designed a scaffold material for SCI treatment containing only chitosan and water as fragmented physical hydrogel suspension (Chitosan-FPHS), with defined degree of acetylation (DA), polymer concentration, and mean fragment size. As a proof of concept, we previously demonstrated (Chedly et al., 2017) that implantation of Chitosan-FPHS alone into rat spinal cord immediately after a bilateral dorsal hemisection promoted reconstitution of spinal tissue and vasculature. Fibrous glial scarring was diminished, allowing the border between lesion site and intact tissue to become permissive for regrowth of numerous axons into, and for some even beyond the lesion site. This structural remodeling was associated with significant, long-lasting gain in locomotor function recovery. We are now investigating our strategy in a rat model of contusion injury, which is even more severe than the bilateral dorsal hemisection used in the initial study, and above all a much more common type of SCI in humans. Our data show that also after a contusion injury Chitosan-FPHS, now implanted 24 hours post-injury, is highly effective in that it improves functional locomotor recovery and tissue restoration. A major contribution of the biomaterial to tissue repair appears to be its modulation of the inflammatory response, favoring inflammation resolution through macrophage polarization towards the anti-inflammatory M2 phenotype. Thus, our tissue engineering approach seems very promising, as it promotes a highly dynamic tissue restorative process by favoring cell survival and axon growth, and by modulating the immune response. Our perspective for a follow-up of the present study is to determine the suitable time window for the biomaterial implantation to test the relevance of the strategy in a chronic lesion model

Macrophage polarization in vitro and in vivo modified by contact with fragmented chitosan hydrogel Running title: Chitosan hydrogel and inflammation

International audienceWe have previously shown that implantation of a fragmented chitosan hydrogel suspension (chitosan-FPHS) into a traumatic spinal cord lesion in adult rats led to significant axon regrowth and functional recovery, which was associated to a modulation of inflammation. Using an in vitro culture system, we show here that polarization of bone marrow-derived macrophages is indeed modified by direct contact with chitosan-FPHS. Reducing the degree of acetylation (DA), and raising the concentration of chitosan (Cp, from 1.5% to 3%), favors macrophage polarization towards anti-inflammatory subtypes. These latter also migrate and adhere efficiently on low, but not high DA chitosan-FPHS, both in vitro and in vivo, while inflammatory macrophages rarely invade a chitosan-FPHS implant in vivo, no matter the DA. Our in vitro model setup should prove a valuable tool for screening diverse biomaterial formulations and combinations thereof for their inflammatory potential prior to implantation in vivo

Regenerative biomaterial matrices for traumatic spinal cord repair

International audienceThe ongoing search for novel, efficient therapeutic strategies for treatment of spinal cord injury (SCI) should greatly profit from the recent progress in the production of innovative biomaterials that when implanted into the lesion site, will function both as extracellular matrix substitute, and as bioactive support structure.Accordingly and as first step, we developed a therapeutic strategy based on the use of chitosan polymer, that exhibits ideal characteristics for tissue engineering. Biological evaluation of diverse formulations (varying in physical and chemicals features) allowed determining the formulations best suited to integrate into spinal cord tissue. Our experimental paradigm is a thoracic dorsal hemisection in adult female rat, with or without implantation of polymer directly after the lesion. Indeed, implantation of the selected chitosan hydrogel formulation induces (i) strong reduction of the astrocytic reaction, (ii) functional vascularization within the implant, (iii) modulated inflammatory response (iv), and most remarkably, growth of a very high number of axons through the implant, evidence for the material per se being extremely favorable for axon regrowth. Finally, these structural remodeling is associated with an improvement of the partial locomotor recovery. Because it effectively induces neural tissue repair, the chitosan biomaterial may be a promising new approach to treat SCI