Achieving an improved understanding of Schwann cell (SC) proliferation and myelination is important for maximizing the clinical promise of these cells in the repair of nervous system injury and disease. Extensive work has shown that neuregulins and cyclic adenosine mono-phosphate (cAMP) are major regulators of both SC proliferation and myelination, but the signaling pathways by which their actions are manifest have received ittle attention. In four Specific Aims, we will test a central hypothesis that cAMP exerts its effects on SC function by regulating intracellular signaling initiated by growth factors, including neuregulin and insulin.
Aim 1. The ERK and PI3K pathways, activated by heregulin, are required for SC proliferation and cAMP regulates the kinetics of both pathways at unknown sites upstream of MEK and Akt, respectively. The target(s) of cAMP mediating the heregulin-dependent ERK and Akt activation in rat and human SCs will be identified. Specifically, the role of Rap1 and B-Raf in cAMP regulation of MEK and Akt will be determined.
Aim 2. cAMP, in the presence of insulin, induces the expression of myelination-associated genes (MGs) in cultured SCs . Newer work suggests that neuregulin is also involved. The regulation of the expression of mRNA and protein for Krox-20, a master regulator of MG expression and myelination, by cAMP, neuregulin and insulin will be studied. Further, the role of the ERK, PI3K, PKA and EPAC pathways in these events, and the linkage between signaling and the activation of the Krox-20 promoter will be determined.
Aim 3. The elevation of cAMP mimics axonal signals in the regulation of SC proliferation and myelination. To test if axonal contact increases cAMP levels in SC, fluorescent cAMP sensors or reporters will be used to determine changes in the level of cAMP after contact axons. These changes will be correlated with changes in the patterns of activation of ERK and Akt and with SC proliferation. Specific inhibitors of adenylyl cyclase, PKA, ERK and Akt will be used to define the path of cAMP-mediated signaling by axons. To study the role of cAMP in myelin formation, the change in cAMP levels following the addition of ascorbate, which precisely triggers myelination, will be monitored, and correlated to Krox-20 induction and MBP expression. Antagonist of PKA, ERK and Akt will be used to determine their roles in myelin formation.
Aim 4. Studies in this laboratory (Pearse et al., Nat Med 10:610-6, 2004) have shown that cAMP dramatically increases myelination after SC transplantation. Elevated cAMP could exert its action on neurons in the host spinal cord or on the transplanted SC or both. To determine if cAMP-activated pathways in SCs are involved, cAMP levels and the response of intracellular targets of cAMP, will be monitored in the transplanted cells, and correlated to the arrival of regenerating axons and the onset of myelination. The completion of these experiments will improve our understanding of how cAMP regulates normal SC proliferation and myelination, specifically, and signaling from receptor tyrosine kinases in general.

Agency
National Institute of Health (NIH)
Institute
National Institute of Neurological Disorders and Stroke (NINDS)
Type
Research Project (R01)
Project #
5R01NS009923-39
Application #
7761725
Study Section
Neurogenesis and Cell Fate Study Section (NCF)
Program Officer
Kleitman, Naomi
Project Start
1976-05-01
Project End
2012-02-28
Budget Start
2010-03-01
Budget End
2012-02-28
Support Year
39
Fiscal Year
2010
Total Cost
$330,924
Indirect Cost
Name
University of Miami School of Medicine
Department
Neurosurgery
Type
Schools of Medicine
DUNS #
052780918
City
Coral Gables
State
FL
Country
United States
Zip Code
33146
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Bacallao, Ketty; Monje, Paula V (2015) Requirement of cAMP signaling for Schwann cell differentiation restricts the onset of myelination. PLoS One 10:e0116948
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Flora, Govinder; Joseph, Gravil; Patel, Samik et al. (2013) Combining neurotrophin-transduced schwann cells and rolipram to promote functional recovery from subacute spinal cord injury. Cell Transplant 22:2203-17
Bacallao, Ketty; Monje, Paula V (2013) Opposing roles of PKA and EPAC in the cAMP-dependent regulation of schwann cell proliferation and differentiation [corrected]. PLoS One 8:e82354
Hill, Caitlin E; Brodak, Danika M; Bartlett Bunge, Mary (2012) Dissociated predegenerated peripheral nerve transplants for spinal cord injury repair: a comprehensive assessment of their effects on regeneration and functional recovery compared to Schwann cell transplants. J Neurotrauma 29:2226-43
Williams, Ryan R; Pearse, Damien D; Tresco, Patrick A et al. (2012) The assessment of adeno-associated vectors as potential intrinsic treatments for brainstem axon regeneration. J Gene Med 14:20-34
Gamez Sazo, Rodolfo E; Maenaka, Katsumi; Gu, Weiyong et al. (2012) Fabrication of growth factor- and extracellular matrix-loaded, gelatin-based scaffolds and their biocompatibility with Schwann cells and dorsal root ganglia. Biomaterials 33:8529-39

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