MRI biomarkers of disease evolution and efficacy of stem cell therapy in the SOD1(G93A) experimental model of Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is fatal neurodegenerative disorder affecting upper motor neurons in the motor cortex as well as lower motor neurons in the brain stem and spinal cord. In ALS, the absence of a disease marker has a negative consequence: the delay from onset of the disease to diagnosis can vary between 13 and 18 months precluding early initiation of neuroprotective treatments. The capability of Magnetic Resonance Imaging (MRI) in diagnosis of ALS has been recently addressed. The accessible, non-invasive and radiation-free characteristics of MRI make this technique highly practical as a biomarker tool. MRI has been used in ALS patients, but not during the pre-clinical phase, a stage currently inaccessible for human study in what is largely a sporadic disease. The discovery of SOD1 mutations linked with familial ALS has made it possible to develop aetiological models for ALS. Thanks to the SOD1(G93A) animal model, neuroimaging modalities can be used to identify potential biomarkers. This PhD project is divided in two experimental sections.The first section aimed to identify and validate MRI biomarkers in SOD1(G93A) animal model along the disease progression and to monitor the efficacy of stem cells-based therapy. Recent studies have suggested that the disease could initiate in skeletal muscle, rather than in the motor neurons. For this reason, our MRI protocol focused on brain and hind limb and SOD1(G93A) mice were scanned at time point corresponding to disease evolution (preclinical stage, onset and terminal stage). T2-weighted images, T2 map and the subsequent analysis with Voxel Based Morphometry technique, showed brainstem lesions in mice starting from the onset of the disease. In hind limb of SOD1(G93A) we found reduced muscular volume, alteration in Diffusion Tensor Imaging parameters (FA, MD and RD) and in muscle/fat signal intensity ratio. Testing the efficacy of innovative therapy, through the evolution of the previously defined biomarkers, we confirmed the efficacy of stem cells therapy in slowing down the clinical course in the SOD1(G93A) animal model.However, recent studies reported that most biological effects of stem cells are probably mediated by soluble factors released in nanovescicles (exosomes) which influence the surrounding cells. To better understand the action mechanisms and the molecular/cellular target of exosomes, we need elucidation of where exosomes explicate their therapeutic effect. In particular, MRI can be used as a noninvasive method for tracking exosomes in vivo and it can provide information about where exosomes exert their neuroprotective action. In the second section we propose a new approach to label exosomes with iron oxide nanoparticles that allows their detection by MRI preserving their morphology and physiological characteristic. In particular, we showed that by labeling stem cells with ultra-small superparamagnetic iron oxide nanoparticles before nanovesicles extraction, the isolated exosomes retain nanoparticles and can be visualized by MRI both in in vitro and in vivo condition.