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The Journal of Neuroscience, July 9, 2008, 28(28):7174-7183; doi:10.1523/JNEUROSCI.0150-08.2008

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Cellular/Molecular
Constitutively Active Akt Induces Enhanced Myelination in the CNS

Ana I. Flores,^1 * S. Priyadarshini Narayanan,^1 * Emily N. Morse,¹ H. Elizabeth Shick,¹ Xinghua Yin,¹ Grahame Kidd,¹ Robin L. Avila,² Daniel A. Kirschner,² and Wendy B. Macklin¹

¹Department of Neurosciences, Cleveland Clinic, Cleveland, Ohio 44195, and ²Department of Biology, Boston College, Chestnut Hill, Massachusetts 02467

Correspondence should be addressed to Wendy B. Macklin, Department of Neurosciences, NC30, Cleveland Clinic, 9500 Euclid Avenue, Cleveland, OH 44195. Email: mackliw{at}ccf.org

The serine/threonine kinase Akt regulates multiple cellular functions. The current studies identify a new role for Akt in CNS myelination. In earlier studies on cultured oligodendrocytes, we showed that neuregulin signals through phosphatidylinositol-3'-OH kinase and Akt to enhance survival of oligodendrocytes. However, when transgenic animals were generated that overexpressed constitutively active Akt in oligodendrocytes and their progenitor cells, no enhanced survival of oligodendrocytes or progenitors was found. No alteration in the proliferation or death of progenitors was noted. In contrast, the major impact of Akt overexpression in oligodendrocytes was enhanced myelination. Most interestingly, oligodendrocytes in these mice continued actively myelinating throughout life. Thus, expression of constitutively active Akt in oligodendrocytes and their progenitor cells generated no more oligodendrocytes, but dramatically more myelin. The increased myelination continued as these mice aged, resulting in enlarged optic nerves and white matter areas. In older animals with enlarged white matter areas, the density of oligodendrocytes was reduced, but because of the increased area, the total number of oligodendrocytes remained comparable with wild-type controls. Interestingly, in these animals, overexpression of Akt in Schwann cells did not impact myelination. Thus, in vivo, constitutively active Akt enhances CNS myelination but not PNS myelination and has no impact developmentally on oligodendrocyte number. Understanding the unique aspects of Akt signal transduction in oligodendrocytes that lead to myelination rather than uncontrolled proliferation of oligodendrocyte progenitor cells may have important implications for understanding remyelination in the adult nervous system.

Key words: Akt; phosphatidylinositol-3'-OH kinase; oligodendrocyte; myelin; Schwann cell; transgenic

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Received Feb. 12, 2007; revised March 31, 2008; accepted May 5, 2008.

Correspondence should be addressed to Wendy B. Macklin, Department of Neurosciences, NC30, Cleveland Clinic, 9500 Euclid Avenue, Cleveland, OH 44195. Email: mackliw{at}ccf.org

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