MicroRNAs (miRNA) play an important role in posttranscriptional gene regulation of several physiological and pathological processes. In multiple sclerosis (MS), a chronic inflammatory and degenerative disease of the CNS, and in its mouse model, the experimental autoimmune encephalomyelitis (EAE), miRNA dysregulation has been mainly related to immune system dysfunction and white matter pathology. However, little is known about their role in grey matter pathology. Here, we explored miRNA involvement in the inflammation-driven alterations of synaptic structure and function, collectively known as synaptopathy, a neuropathological process contributing to excitotoxic neurodegeneration in MS/EAE. Particularly, we observed that miR-142-3p is increased in the cerebrospinal fluid (CSF) of patients with active MS and in EAE brains. We propose miR-142-3p as a molecular mediator of the IL-1β-dependent down-regulation of the glial glutamate-aspartate transporter (GLAST), which causes an enhancement of the glutamatergic transmission in the EAE cerebellum. The synaptic abnormalities mediated by IL-1β and the clinical and neuropathological manifestations of EAE disappeared in miR-142 knock-out mice. Furthermore, we observed that in vivo miR-142-3p inhibition, either by a preventive and local treatment or by a therapeutic and systemic strategy, abolished IL-1β- and GLAST-dependent synaptopathy in EAE wild-type mice. Consistently, miR-142-3p was responsible for the glutamatergic synaptic alterations caused by CSF of patients with MS, and CSF levels of miR-142-3p correlated with prospective MS disease progression. Our findings highlight miR-142-3p as key molecular player in IL-1β-mediated synaptic dysfunction possibly leading to excitotoxic damage in both EAE and MS diseases. Inhibition of miR-142-3p could be neuroprotective in MS.
Current studies suggest the role of glutamate excitotoxicity in the development and progression of MS and of its mouse model EAE. The molecular mechanisms linking inflammation and synaptic alterations in MS/EAE are still unknown. Here, we identified miR-142-3p as a determinant molecular actor in inflammation-dependent synaptopathy typical of both MS and EAE. miR-142-3p was up-regulated in the cerebrospinal fluid of MS patients and in EAE brains. Inhibition of miR-142-3p, locally in EAE brain and in a MS chimeric in vitro model, recovered glutamatergic synaptic enhancement typical of EAE/MS. We proved that miR-142-3p promoted the IL-1β-dependent glutamate dysfunction by targeting GLAST, a crucial glial transporter involved in glutamate homeostasis. Finally, we suggest miR-142-3p as a negative prognostic factor in RRMS patients.
↵* co-first authors
This work was supported by the Italian Ministry of Health (Progetto Giovani Ricercatori) to G.M. (No. GR-2011-02347036) and A.M. (No. GR-2011-02351422) and by the European Research Council (ERC-2013, AdG 340172--MUNCODD) and AriSLA full grant 2014 “ARCI” to I.B. We thank Vladimiro Batocchi, Massimo Tolu and Plaisant Allevamenti srl for helpful technical assistance.