Unraveling the molecular mechanism underlying ALS-linked astrocyte toxicity for motor neurons

Mutations in superoxide dismutase-1 (SOD1) cause a familial form of amyotrophic lateral sclerosis (ALS), a fatal paralytic disorder. Transgenic mutant SOD1 rodents capture the hallmarks of this disease, which is characterized by a progressive loss of motor neurons. Studies in chimeric and conditional transgenic mutant SOD1 mice indicate that non-neuronal cells, such as astrocytes, play an important role in motor neuron degeneration. Consistent with this non-cell autonomous scenario are the demonstrations that wild-type primary and embryonic stem cell-derived motor neurons selectively degenerate when cultured in the presence of either mutant SOD1-expressing astrocytes or medium conditioned with such mutant astrocytes. The work in this thesis rests on the use of an unbiased genomic strategy that combines RNA-Seq and "reverse gene engineering" algorithms in an attempt to decipher the molecular underpinnings of motor neuron degeneration caused by mutant astrocytes. To allow such analyses, first, mutant SOD1-induced toxicity on purified embryonic stem cell-derived motor neurons was validated and characterized. This was followed by the validation of signaling pathways identified by bioinformatics in purified embryonic stem cell-derived motor neurons, using both pharmacological and genetic techniques, leading to the discovery that nuclear factor kappa B (NF-κB) is instrumental in the demise of motor neurons exposed to mutant astrocytes in vitro. These findings demonstrate the usefulness of this novel genomic approach to study neurodegeneration and to point to NF-κB as a potential valuable therapeutic target for ALS.