SELECTIVE NEURONAL VULNERABILITY IN SPORADIC ALS

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The neurodegenerative diseases including amyotrophic lateral sclerosis (ALS) are devastating idiopathic clinical disorders that result in selective neuronal injury and death. Our general hypothesis is that increased intracellular calcium, produced by active calcium influx across the plasmalemma or release of calcium from intracellular stores, and/or limited calcium buffering capacity, is critically important in neurodegenerative cell injury. Factors dictating selective vulnerability in these diseases may include alterations in any of these processes, likely coupled with selective sensitivity to altered calcium homeostasis. Our own studies of sporadic neurodegenerative disease have documented the presence of antibodies to voltage-gated calcium channels (VGCCs) in sporadic but not familial ALS. ALS IgG produce different electrophysiologically assayed effects on different VGCC types, inhibiting calcium current when added to skeletal muscle L- type VGCCs, while enhancing calcium current, increasing intracellular calcium, and causing cell death when added to neuronal VGCCs in motor neuron cell lines. The motor neuron cell line (VSC 4.1), developed in our laboratory by fusion or murine N18TG2 neuroblastoma line and dissociated embryonic rat ventral spinal cord, expresses biochemical and morphological motor neuron markers as well as neuronal VGCCs when differentiated in the presence of cAMP and aphidocolin. After ALS IgG addition in vitro, there is a marked enhancement of calcium current in differentiated cells (not noted with disease control IgG). Using calcium imaging techniques, ALS IgG also induces a marked, prolonged increase in intracellular calcium, which is followed by VSC 4.1 cell death after twenty-four to seventy-two hours. This cell system will allow us to define ALS IgG-dependent mechanisms permitting prolonged increases in intracellular calcium. We plan to define the relationship in detail between the increased intracellular calcium and the subsequent cell death. Furthermore, since VSC 4.1 cells demonstrate decreased immunohistochemically recognized calbindin D28K and parvalbumin levels during differentiation (concomitant with onset of vulnerability to ALS IgG), a detailed evaluation will be undertaken of the potential role of these calcium binding proteins in selective vulnerability. These studies should aid in understanding the roles played by increased intracellular calcium and altered calcium buffering on selective neuronal vulnerability in sporadic ALS.