This work was supported by grant IND2018/BMD-9751 (Programa de Doctorados Industriales, Comunidad de Madrid, Spain), SAF2016-77575-R (Spanish Ministerio de Economía, Industria y Competitividad-MINECO), and the contract for technological support ApTLR2019-PC-MS-001 (AptaTargets, S.L., Spain) to FdC. BF-G is currently hired by Aptatargets S.L., PG-M is hired under PEJ-2020-AI/BMD-18541 de la Comunidad de Madrid, Spain (associated with the youth guarantee fund to FdC), SN had a predoctoral contract from the UCLM and was hired under SAF2012-40023, SAF2016- 77575-R, RD12-0032/0012 and RD16-0015/0019 (Spanish Ministerio de Economía, Industria y Competitividad-MINECO) and IND2018/BMD-9751, YL has been contracted under ReTics and SAF (to FdC). We thank David Segarra and Mª Eugenia Zarabozo (AptaTargets S.L.) for their constant technological support, Laude Garmendia for her indispensable constant help at the animal facility (Instituto Cajal-CSIC), including the extra effort during Covid-19 pandemics, Profs María Ángeles Moro (Centro Nacional de Investigaciones Cardiovasculares Carlos III, Madrid and Universidad Complutense de Madrid, Spain) and Ignacio Lizasoaín (Universidad Complutense de Madrid, Spain) for lending us the TLR4 knockout mice, and the former GNDe member Dr. Carolina MeleroJerez (currently working at JazzPharma, Spain) for the initial training of BF-G on EAE animal model and different techniques at the laboratory. Human samples were supplied by the UK Multiple Sclerosis Tissue Bank, funded by the Multiple Sclerosis Society of Great Britain and Northern Ireland (registered charity 207495).

ApTOLL is an aptamer specifically designed to antagonize toll-like receptor 4 (TLR4), which is involved in the innate immunity that promotes inflammatory responses in several diseases, including multiple sclerosis (MS). MS is a chronic, immune, demyelinating and neurodegenerative disease of the central nervous system that represents the second most important cause of neurological disability in young adults. The drugs currently available to treat this disease are immunomodulators and, to date, there are no therapeutic remyelinating drugs available to manage MS. In this study, we show that TLR4 is located in post-mortem cortical lesions of MS patients and as a result, we evaluated the effect of its inhibition by ApTOLL in two different animal models of MS, that of experimental autoimmune encephalomyelitis (EAE) and the cuprizone model. ApTOLL administration ameliorated the clinical symptomatology of the affected mice, which was associated with better preservation and restoration of myelin and oligodendrocytes in the demyelinated lesions of these animals. This revealed not only an immunomodulatory but also a remyelinating effect of the treatment with ApTOLL which was corroborated on purified cultures of rodent and adult human oligodendrocyte precursor cells (OPCs). In summary, the molecular nature of ApTOLL and its mechanism of action strongly supports its further study and use in novel strategies to treat MS and eventually, other demyelinating diseases.

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