Autophagic degeneration of motor neurons in a model of slow glutamate excitotoxicity in vitro

There is increasing evidence that so-called autophagic cell death participates in cell degeneration in certain pathological conditions. Autophagy might be involved in some neurodegenerative processes, including lateral amyotrophic sclerosis (SLA). The exact mechanism leading to progressive motor neuron (MN) loss remains unclear, but glutamate-mediated mechanism is thought to be responsible. Previous ultrastructural studies by the authors performed on a model of SLA in vitro, based on chronic glutamate excitotoxicity, revealed a subset of morphological features characteristic to different modes of neuronal death, including autophagic degeneration. The contribution of this pathway of MNs death is evaluated in organotypic cultures of rat lumbar spinal cord chronically exposed to specific glutamate uptake blockers: DL-threo-beta-hydroxyaspartate (THA) and L-transpyrrolidine-2,4-dicarboxylate (PDC). The study documents the various steps of authophagy in slowly evolving process of MN neurodegeneration. The cells undergoing autophagy usually exhibited sequestration of some parts of cytoplasm with normal and/or degenerated organelles, whereas other parts of cytoplasm as well as neuronal nucleus remained unchanged. The advanced autophagic changes were often associated with other modes of MN death, especially with apoptosis. Numerous MNs revealed apoptotic nuclear features with typical peripheral margination of nuclear chromatin, accompanied by severe autophagic or autophagic-necrotic degeneration of the cytoplasm. These results support the opinion of unclear distinction between different modes of cell death and indicate the involvement of autophagey in MNs neurodegeneration in vitro.