Cellular approach for the treatment of amyotrophic lateral sclerosis using adult mesenchymal stem cells

Amyotrophic lateral sclerosis (ALS) is a progressive, lethal, degenerative disorder of the CNS. The hallmark of this disease is the premature and selective death of upper and lower motor neurons (MNs) in the brain and spinal cord, leading to fatal paralysis. Although the archetypal vision of neurotoxicity in neurodegenerative diseases is based on the idea that a specific neuronal population is particularly vulnerable to a cumulative toxic event (protein aggregation, mitochondria dysfunction, compromised axonal transport etc…), experimental evidence illustrate that ALS possibly does not arise strictly from damage within MNs. There is now convincing data supporting a non-cell autonomous mechanism in which neurodegeneration is influenced by the toxicity of non-neuronal cells in the vicinity of neurons such as astrocytes and microglia. Considering the accumulation of data implicating astrocytes in the pathogenesis of ALS (loss of GLT-1, secretion of toxic factor, enhanced inflammation, etc…), approaches aiming at replacing astrocytes at site of lesions constitute promising therapeutic strategies. Rapid progresses in the characterization of adult stem cell biology have generated considerable enthusiasm for the development of therapeutic strategies for CNS insults. Several observations support the hypothesis that stem cells may display a valuable influence on diseased host tissues by exerting a protective “chaperone” effect to neurons after differentiation in glial cells. Hence, we decided to study the neuroprotective potential of adult mesenchymal stem cells (MSCs) in ALS. In contrast to neural stem cells (NSCs) which localization in the central nervous system complicates their isolation, MSCs are easily isolated from the bone marrow. The relevance of using on MSCs in stem cell therapies of neurodegenerative disorders is also justified by their capacity to (trans)differentiate into neural cells. For this purpose, we exposed MSCs to growth factors involved in the astroglial differentiation of NSCs. The differentiation of MSCs was characterized by the acquisition of astrocyte morphology in addition to an increased expression of gene related to NSCs (nestin) and astrocytes (glutamine synthetase). The astroglial differentiation of MSCs is associated with the acquisition of a glial-like specific regulation of the production of GDNF, a potent neurotrophic factor for neurons. Then, we characterized the glutamate uptake in differentiated MSCs, a critical function of astrocytes. Our data demonstrate that the differentiation of MSCs is associated with an increased expression of the high affinity glutamate transporter, GLT-1. Thus, our in vitro results confirm the astrocytic differentiation potential of MSCs and we decided to use then in stem cell therapy of ALS. Indeed, we demonstrated that mechanism of stem cell recruitment is present in the spinal cord during the development of the disease by the secretion of stem cell factor (SCF). We injected MSCs derived from healthy animals into the cerebrospinal fluid of a transgenic rat model of familial ALS (expressing a mutated form of the human superoxide dismutase-1, hSOD1G93A) at disease onset. MSCs were found to infiltrate the nervous parenchyma and migrate substantially into the ventral grey matter by interacting with the SCF. At the site of lesion, MSCs differentiated massively into astrocytes around MNs. The intrathecal delivery of MSCs preserved motor functions and extended the survival of hSOD1G93A rats. Investigation of the lumbar spinal cord 35 days after graft demonstrated that the generation of healthy astrocytes from MSCs decreased motor neuron loss. However, this beneficial effect is not related to a decreased excitotoxicity by the rescue of GLT-1 expression but rather a decreased inflammation around MNs. Together, the data presented in this thesis highlight the protective capacity of adult MSC-derived astrocytes in the treatment of ALS.(SBIM 3) -- UCL, 200