In Vitro Studies on AMPA Receptor-Mediated Motor Neuron Death: Relevance for Amyotrophic Lateral Sclerosis

De Paola, Massimiliano (2009). In Vitro Studies on AMPA Receptor-Mediated Motor Neuron Death: Relevance for Amyotrophic Lateral Sclerosis. PhD thesis The Open University.

DOI: https://doi.org/10.21954/ou.ro.0000f26a

Abstract

Amyotrophic Lateral Sclerosis (ALS) is a neurological disease mainly characterized by progressive motor neuron degeneration and muscle atrophy that lead to premature death. It is not yet fully understood in terms of etiology and, as a consequence, it is still orphan of cures. This project was aimed at studying some of the main reliable causal events leading to motor neuron degeneration in ALS, i.e. AMPA receptor (AMPAR)-dependent excitotoxicity, neuroinflammation and intracellular protein aggregation.

1) We investigated the intracellular mechanisms that are induced in motor neurons by AMPAR-mediated excitotoxicity, demonstrating that different death pathways were activated depending on the intensity of the initial stimulus to the receptor. Low AMPAR agonist concentrations induce, indeed, the typical intracellular events of the apoptotic pathway, while higher concentrations trigger to non-apoptotic motor neuron death.

2) We analysed the intracellular effect of mediators of the inflammatory signalling, i.e. TNF-α and IL-8, and their interaction with the AMPAR-dependent excitotoxic pathway. We demonstrated that IL-8-induced motor neuron death is specifically mediated by the CXCR2 chemokine receptor. TNF-α exerts both neurotoxicity and neuroprotection against AMPAR-mediated cell death. The presence of mature and active glial population is determinant in mediating TNF-α effect.

3) We studied the effect of intracellular α-synuclein accumulation in motor neurons, revealing a dual concentration-dependent effect since micromolar protein concentrations are neurotoxic, while nanomolar concentrations induce neuroprotective effect against oxidative stress.

In light of such results, we tested the effectiveness of potentially neuroprotective drugs which could interfere with the intracellular death mechanisms of motor neurons. We found that Erythropoietin (EPO) and different non-erythropoietic EPO derivatives (CEPO, ASIALOEPO and HBP) have specific neuroprotective properties against the apoptotic AMPAR-dependent death pathway. Reparixin, an orally active chemokine receptor (CXCR1/2) inhibitor was successfully tested against the IL-8-dependent motor neuron death.

All together these results add further useful information to define the complex ALS etiology and provide interesting pharmacological approaches which could be relevant for the treatment of the pathology.