Saturday, February 18, 2017
Exhibit Hall (Hynes Convention Center)
Kimberly Cruz, Trinity Washington University, Washington, DC
In Multiple Sclerosis, damage to the myelin sheath and oligodendrocyte loss results in debilitating neurological symptoms. Oligodendrocytes are myelin-producing cells in the CNS white matter, whose membranes ensheath neuronal axons for rapid neurotransmission. Strategies for oligodendrocyte replacement will improve myelin repair in disease. The transcription factor Sox-17 has been shown to promote differentiation of oligodendrocyte progenitor cells (OPCs) into myelinating oligodendrocytes. Transgenic mice overexpressing Sox-17 in oligodendrocytes show enhanced regeneration of cells and protection from damage in white matter lesions. However, the signaling mechanism by which it promotes differentiation and white matter repair is unknown. Wnt/b-Catenin signaling inhibits differentiation of OPCs, which is supported by reports that demyelinating lesions show abnormally high b-Catenin levels. Sox-17 has been shown to inhibit the Wnt/b-Catenin pathway as well as increase white matter levels of Hedgehog mediator Gli2. Oligodendrocyte progenitor cells isolated from Sox-17-overexpressing transgenic mice show increased Hedgehog co-receptor clustering on cell membranes in response to agonist stimulation, suggesting Gli2 activation. We hypothesize that Sox-17 promotes OPC differentiation through Gli2 to antagonize b-Catenin signaling. To test this hypothesis, we performed mouse genotyping and analyzed experimental white matter lesions in Sox-17 transgenic mice. Lysophosphatidylcholine (Lyso), a detergent which disrupts myelin sheaths, was surgically injected into the white matter region of the brain to generate a demyelinated lesion and induce spontaneous repair. Using immunohistochemistry, we observed that Lyso injection results in increased cells expressing activated b-Catenin in unaltered wild type mice, whereas b-Catenin was activated by Lyso in significantly fewer cells in Sox-17 transgenic mice. To investigate possible antagonistic interactions between the transcription factors Gli2 and b-Catenin, we prepared plasmids and conducted transcription reporter assays in human oligodendroglioma cells. Using the b-Catenin responsive reporter Topflash, and a GLI-responsive reporter GliBSLuc, these transfections showed that, while b-Catenin activated Topflash, it had no effect on GliBSLuc. Gli2 however had differential effects. Gli2deltaN (active Gli2) functioned as an activator on GliBSLuc, but as a repressor on Topflash. In contrast, Gli2FL (Full length, inactivated Gli2) neither suppressed nor activated Gli or Topflash. This indicates that Gli2 activation is necessary for its repression of b-Catenin. We conclude that the presence of Sox-17 increases Gli2 activation, resulting in lower activation levels of b-Catenin signaling. This contributes to enhanced regeneration of oligodendrocytes, thus producing a protective effect in disease.