3-nitrotyrosine and Demyelinating-Diseases

Axonal degeneration contributes to permanent neurological disability in inherited and acquired diseases of myelin. Mitochondrial dysfunction has been proposed as a major contributor to this axonal degeneration. It remains to be determined, however, if myelination, demyelination, or remyelination alter the size and distribution of axonal mitochondrial stationary sites or the rates of axonal mitochondrial transport. Using live myelinated rat dorsal root ganglion (DRG) cultures, we investigated whether myelination and lysolecithin-induced demyelination affect axonal mitochondria. Myelination increased the size of axonal stationary mitochondrial sites by 2.3-fold. After demyelination, the size of axonal stationary mitochondrial sites was increased by an additional 2.2-fold and the transport velocity of motile mitochondria was increased by 47%. These measures returned to the levels of myelinated axons after remyelination. Demyelination induced activating transcription factor 3 (ATF3) in DRG neurons. Knockdown of neuronal ATF3 by short hairpin RNA abolished the demyelination-induced increase in axonal mitochondrial transport and increased nitrotyrosine immunoreactivity in axonal mitochondria, suggesting that neuronal ATF3 expression and increased mitochondrial transport protect demyelinated axons from oxidative damage. In response to insufficient ATP production, demyelinated axons increase the size of stationary mitochondrial sites and thereby balance ATP production with the increased energy needs of nerve conduction.

Topics: Activating Transcription Factor 3; Animals; Axonal Transport; Axons; Demyelinating Diseases; Ganglia, Spinal; Gene Knockdown Techniques; Immunohistochemistry; In Vitro Techniques; Lysophosphatidylcholines; Microscopy, Electron; Mitochondria; Myelin Sheath; Oxidative Stress; Rats; Rats, Sprague-Dawley; Schwann Cells; Tyrosine

Nitric oxide (NO) and peroxynitrite (ONOO(-)) are potential mediators of the injury and cytotoxicity occurring over time to oligodendrocytes in multiple sclerosis (MS) lesions. Our in vitro results indicate that human adult CNS-derived oligodendrocytes are relatively resistant to NO-mediated damage. In contrast, human oligodendrocytes are highly susceptible to peroxynitrite-mediated injury. In situ, we found that inducible nitric oxide synthase (iNOS) was expressed in astrocytes and macrophages in all active demyelinating and remyelinating MS lesions examined, yet no correlation was found between numbers of glial cells expressing iNOS and the extent of oligodendrocyte cell death. Nitrotyrosine groups, indicative of the presence of peroxynitrite in vivo, could be detected on astrocytes, macrophages, and oligodendrocytes in MS lesions. High numbers of nitrotyrosine-positive oligodendrocytes were found in one MS case that featured extensive oligodendrocyte cell death. Our results indicate that NO alone is unlikely to induce oligodendrocyte injury, whereas its more potent byproduct peroxynitrite is a potential mediator of injury to oligodendrocytes in MS.

Topics: Astrocytes; Cell Death; Cells, Cultured; Demyelinating Diseases; Humans; Macrophages; Multiple Sclerosis; Myelin Sheath; Nitric Oxide; Nitric Oxide Donors; Nitric Oxide Synthase Type II; Oligodendroglia; Peroxynitrous Acid; Tyrosine

Demyelination is often associated with acute inflammatory events involving the recruitment-activation of microglia/macrophage, astrocytes, and leukocytes. The ultimate role of inflammatory products in demyelinating disease and in the survival of oligodendrocytes, the myelin forming cells, is unresolved. The current study examines the role of inducible NO synthase (iNOS)-derived NO in a neurotoxicant-induced model of demyelination. NO levels were greatly elevated in the midline corpus callosum during demyelination in genetically intact C57BL/6 mice, and this NO was due solely to the induction of iNOS, as the correlates of NO were not found in mice lacking iNOS. C57BL/6 mice lacking iNOS exhibited more demyelination, but did not display an increased overall cellularity in the corpus callosum, attributable to an unimpeded microglia/macrophage presence. An enhanced course of pathology was noted in mice lacking iNOS. This was associated with a greater depletion of mature oligodendrocytes, most likely due to apoptosis of oligodendrocytes. Microglia and astrocytes did not undergo apoptosis during treatment. Our results suggest a moderately protective role for NO during acute inflammation-association demyelination.

Topics: Animals; Apoptosis; Cell Movement; Corpus Callosum; Cuprizone; Demyelinating Diseases; Inflammation; Macrophages; Mice; Mice, Inbred C57BL; Mice, Knockout; Microglia; Microscopy, Fluorescence; Neuroprotective Agents; Nitric Oxide; Nitric Oxide Synthase; Nitric Oxide Synthase Type II; Oligodendroglia; Tyrosine