Contributions
Abstract: P776
Type: Poster Sessions
Abstract Category: Pathology and pathogenesis of MS - Neurodegeneration
It is increasingly apparent that multiple sclerosis has a strong neurodegenerative component, now recognised to be the main structural correlate of disability progression. This occurs both as a primary event as well as secondary to neuroinflammatory damage, and might be driven by an impairment of neuronal calcium homeostasis. To address this hypothesis, an animal model of optic neuritis, a common manifestation of multiple sclerosis, was used. This involves immunisation of Brown Norway rats with myelin oligodendrocyte glycoprotein resulting in optic nerve demyelination, but preceded by the onset of retinal ganglion cell (RGC) degeneration. Using magnesium-enhanced magnetic resonance imaging, we have previously demonstrated calcium accumulation to occur within the retina during the onset of neurodegeneration.
Therefore, we addressed calcium homeostasis in RGCs using calcium imaging on both retinal slices (to assess ganglion cell layer cells within an acute and intact environment) and acutely isolated RGCs (to determine RGC specificity) to elucidate possible disturbances in calcium regulatory pathways. Cells/slices were obtained from different disease stages (healthy - naïve, controls; induction phase - following onset of RGC degeneration but prior to optic nerve demyelination; and clinical phase - after optic nerve demyelination).
Following challenge with glutamate to induce calcium influx, extracellular calcium was removed (by EGTA chelation) and the resultant reduction in intracellular calcium indicative of calcium clearance mechanisms was measured. The rate and magnitude of calcium clearance was significantly reduced in both retinal slices and isolated RGCs taken during the clinical phase of the disease compared to cells/slices from healthy rats or from the induction phase. To control for differences in glutamate receptor activity during disease progression, the experiment was repeated but using the calcium ionophore 4-bromo A-23187 to obtain a stable and comparable intracellular calcium concentration prior to removal of extracellular calcium, with similar results. Recent findings regarding the contribution of the two major calcium exporter families, plasma membrane calcium ATPases and the sodium calcium exchangers, will be reported.
In conclusion, we report that a significant impairment of calcium clearance in RGCs occurs during progression of autoimmune optic neuritis which might contribute to ongoing retinal neurodegeneration.
Disclosure: The authors have nothing to disclose. This study was supported by the German Research Foundation (FOR2289).
Abstract: P776
Type: Poster Sessions
Abstract Category: Pathology and pathogenesis of MS - Neurodegeneration
It is increasingly apparent that multiple sclerosis has a strong neurodegenerative component, now recognised to be the main structural correlate of disability progression. This occurs both as a primary event as well as secondary to neuroinflammatory damage, and might be driven by an impairment of neuronal calcium homeostasis. To address this hypothesis, an animal model of optic neuritis, a common manifestation of multiple sclerosis, was used. This involves immunisation of Brown Norway rats with myelin oligodendrocyte glycoprotein resulting in optic nerve demyelination, but preceded by the onset of retinal ganglion cell (RGC) degeneration. Using magnesium-enhanced magnetic resonance imaging, we have previously demonstrated calcium accumulation to occur within the retina during the onset of neurodegeneration.
Therefore, we addressed calcium homeostasis in RGCs using calcium imaging on both retinal slices (to assess ganglion cell layer cells within an acute and intact environment) and acutely isolated RGCs (to determine RGC specificity) to elucidate possible disturbances in calcium regulatory pathways. Cells/slices were obtained from different disease stages (healthy - naïve, controls; induction phase - following onset of RGC degeneration but prior to optic nerve demyelination; and clinical phase - after optic nerve demyelination).
Following challenge with glutamate to induce calcium influx, extracellular calcium was removed (by EGTA chelation) and the resultant reduction in intracellular calcium indicative of calcium clearance mechanisms was measured. The rate and magnitude of calcium clearance was significantly reduced in both retinal slices and isolated RGCs taken during the clinical phase of the disease compared to cells/slices from healthy rats or from the induction phase. To control for differences in glutamate receptor activity during disease progression, the experiment was repeated but using the calcium ionophore 4-bromo A-23187 to obtain a stable and comparable intracellular calcium concentration prior to removal of extracellular calcium, with similar results. Recent findings regarding the contribution of the two major calcium exporter families, plasma membrane calcium ATPases and the sodium calcium exchangers, will be reported.
In conclusion, we report that a significant impairment of calcium clearance in RGCs occurs during progression of autoimmune optic neuritis which might contribute to ongoing retinal neurodegeneration.
Disclosure: The authors have nothing to disclose. This study was supported by the German Research Foundation (FOR2289).