Multimodal MRI to monitor disease and treatment in a chronic-progressive EAE mouse model of multiple sclerosis

Abstract

Background: Multiple sclerosis (MS) is a chronic autoimmune disease of the central nervous system (CNS) that affects both white matter (WM) and grey matter (GM). Although currently available therapies are useful to mitigate relapsing-remitting MS disease (RR-MS), none of these have been useful to suppress secondary-progressive MS (SP-MS). Magnetic resonance imaging (MRI) is used widely for clinical diagnosis of MS. In particular, gadolinium (Gd) post contrast T1-weighted imaging has been considered the gold standard for MS lesion identification. However, with increased concern about Gd-induced toxicity, non-Gd based MRI modalities are attracting attention. Aims: The major aim of this project was to utilise in vivo multi-modal MRI at 9.4 Tesla to characterise pathological changes in spinal cord in a chronic-progressive experimental autoimmune encephalomyelitis (EAE) mouse model of MS. In vivo magnetic resonance spectroscopy (MRS), high-resolution diffusion tensor imaging (DTI) and high-resolution proton density (PD) imaging techniques were applied to elucidate and compare biomarkers of disease status. MRI results were validated using immunohistochemistry (IHC) indicating demyelination and microglia and astrocyte activation. The biomarkers were then examined to characterise EAE disease in transgenic mice lacking the complement C5 receptors (C5aR1KO and C5L2KO) to provide further understanding of the influence of the complement system in MS and demonstrate its potential as a therapeutic target. Finally, the project aimed to investigate the therapeutic efficacy of a drug (MCC950) that has been found to target inflammasome (MCC950) mitigating EAE disease. Methods: Multi-modal MRI was performed in vivo at the lumbar spinal cord of C57BL/6 mice using a cryoprobe RF coil. Chronic-progressive EAE was induced with oligodendrocyte glycoprotein emulsified in complete Freund’s adjuvant. This was followed by an intraperitoneal injection of pertussis toxin to disrupt the blood brain barrier and facilitate development of EAE. MR scans were performed at 21 days ±3 post immunisation. Animal cohorts included five main groups: (i) wild type (WT) groups that compromise of control WT-naïve and WT-EAE mice, (ii) two genetically modified groups, lacking C5aR1 (C5aR1KO-EAE) and C5L2 (C5L2KO-EAE), induced with EAE, and (iii) mice induced with EAE and subsequently treated with MCC950. Results: MRS revealed that compared to control WT-naïve: (i) N-acetylaspartate was significantly lower in WT-EAE whereas choline, Taurine and glycine were significantly higher. (ii) DTI showed significant reduction in FA and AD in WT-EAE and significant increase in RD in WM. (iii) In GM, FA was significantly higher in WT-EAE. (iv) High-resolution PD imaging (segmented using spinal cord toolbox) successfully detected atrophy in GM and hypertrophy (swelling) in WM in WT-EAE mice. (v) IHC staining detected demyelination, microglia and astrocyte activation in WT-EAE,detected by disappearance of FluoroMyelin signal, and high signal in Iba-1 and GFAP staining respectively. Mice lacking C5 receptors (C5aR1KO-EAE and C5L2KO-EAE) showed a reduced EAE score, which was reflected by MRI and MRS parameters, as well as the IHC findings. Changes in metabolite concentrations and DTI parameters indicate that the ablation of C5L2, to a greater extent than the ablation of C5aR1, made these mice less susceptible to EAE induced neuronal damage compared to wild-type mice. Mice treated with MCC950 showed highly similar parameter values to control WT-naïve in terms of all MR measurements. Significance of findings: We found that MRS and DTI were sensitive to EAE pathology, and they were highly correlated with EAE score. These observations provide the basis for a set of MR biomarkers for monitoring the status of EAE pathology in vivo in this important animal model of MS. Application of this approach demonstrated that multi-modal MRI is valuable tool that can provide non-invasive measures of neurodegenerative disease and facilitate the development of potential therapeutic candidates.