Preventive exercise attenuates IL-2-driven mood disorders in multiple sclerosis

Background: Elevated levels of specific proinflammatory molecules in the cerebrospinal fluid (CSF) have been associated with disability progression, enhanced neurodegeneration and higher incidence of mood disorders in people with multiple sclerosis (MS). Studies in animal models of MS suggest that preventive exercise may play an immunomodulatory activity, with beneficial effects on both motor deficits and behavioral alterations. Here we explored the impact of lifestyle physical activity on clinical presentation and associated central inflammation in a large group of newly diagnosed patients with MS. Furthermore, we addressed the causal link between exercise-mediated immunomodulation and mood symptoms in the animal setting. Methods: A cross-sectional study was conducted on 235 relapsing-remitting MS patients at the time of the diagnosis. Patients were divided into 3 groups ("sedentary", "lifestyle physical activity" and "exercise") according to the level of physical activity in the six months preceding the evaluation. Patients underwent clinical, neuropsychological and psychiatric evaluation, magnetic resonance imaging and lumbar puncture for diagnostic purposes. The CSF levels of proinflammatory and anti-inflammatory cytokines were analyzed and compared with a group of 80 individuals with non-inflammatory and non-degenerative diseases. Behavioral and electrophysiological studies were carried out in control mice receiving intracerebral injection of IL-2 or vehicle. Behavior was also assessed in mice with experimental autoimmune encephalomyelitis (EAE), animal model of MS, reared in standard (sedentary group) or running wheel-equipped (exercise group) cages. Results: In exercising MS patients, depression and anxiety were reduced compared to sedentary patients. The CSF levels of the interleukin-2 and 6 (IL-2, IL-6) were increased in MS patients compared with control individuals. In MS subjects exercise was associated with normalized CSF levels of IL-2. In EAE mice exercise started before disease onset reduced both behavioral alterations and striatal IL-2 expression. Notably, a causal role of IL-2 in mood disorders was shown. IL-2 administration in control healthy mice induced anxious- and depressive-like behaviors and impaired type-1 cannabinoid (CB1) receptor-mediated neurotransmission at GABAergic synapses, mimicking EAE-induced synaptic dysfunction. Conclusions: Our results indicate an immunomodulatory effect of exercise in MS patients, associated with reduced CSF expression of IL-2, which might result in reduced mood disorders. These data suggest that exercise in the early stages may act as a disease-modifying therapy in MS although further longitudinal studies are needed to clarify this issue.