Mécanismes de dérégulation de la réponse à l'hypoxie dans la sclérose latérale amyotrophique

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder of upper and lower motorneurons, leading to death in 3 to 5 years. Respiratory insufficiency and hypoxemia are closely linked during the clinical course of ALS. Chronic respiratory insufficiency and hypoxemia generally occur late in the disease course but rapid episodes of intermittent hypoxemia followed by reoxygenation can occur early and insidiously. Two pathways are involved in the response to hypoxemia: (i) hypoxia inducible factor-1 (HIF-1) and VEGF/HIF-2 and an erythropoietin (EPO) mediated pathway, in response to prolonged hypoxemia; and (ii) nuclear factor κ-B (NFκ-B) during acute hypoxemia followed by reoxygenation episodes, inducing inflammatory mediators: interleukin-6 (IL-6), TNF-α, cyclo oxygenase-2 (COX-2) and prostaglandin E-2 (PGE-2). Our aim was to specify the role of the different functional pathways of response to hypoxemia in sporadic ALS patients, compared with neurological controls and according to the level of hypoxemia. We report the results of several studies of hypoxemic and/or inflammatory mediators in the cerebrospinal fluid (CSF) from ALS patients, according to their respiratory status, showing a selective defect of HIF-1 mediated angiogenic factors (VEGF and angiogenin [ANG]) during chronic hypoxia in sporadic ALS patients, compared to hypoxemic neurological controls; contrasting with an early activation of the NFκ-B pathway since the isolated desaturation stage (IL-6, TNF-α, PGE-2, angiopoietin-2) in the same cohort of sporadic ALS patients. All these results are consistent with a selective impairment of the HIF-1 pathway during chronic hypoxemia in ALS patients. Inflammatory mediators were strongly elevated, since the early stage of the disease until chronic hypoxemia, suggesting a compensatory mechanism.