| Abstract No.: | B-B2050 |
| Country: | Canada |
| | |
| Title: | MITOGEN ACTIVATED PROTEIN KINASE P38 ALPHA REGULATES TRANSCRIPTION FACTOR KROX-20 EXPRESSION AND CREB ACTIVATION TO CONTROL SCHWANN CELL DIFFERENTIATION IN PERIPHERAL MYELINATION |
| | |
| Authors/Affiliations: | 1 Shireen Hossain*; 2 David B. Parkinson; 1 Walter E. Mushynski; 1 Guillermina Almazan;
1 McGill University, Montreal, QC, Canada; 2 Peninsula Medical School, Plymouth, United Kingdom
|
| | |
| Content: | Schwann cells (SC) synthesize myelin in the Peripheral Nervous System (PNS). Deficiencies in myelin result in neuropathies such as Charcot-Marie Toothe disease. The molecular mechanisms by which PNS myelination occurs have yet to be fully elucidated. Our laboratory has previously demonstrated a pivotal role for p38 Mitogen Activated Protein Kinase (MAPK) in laminin or ascorbate-induced SC myelination. The expression of several key myelin genes including myelin basic protein (MBP), myelin associated glycoprotein (MAG) and protein zero (P0) are regulated by p38 however, the mechanism by which this takes place, remains obscure.
Objective: To identify transcription factors regulated by p38 MAPK to modulate expression of these myelin genes.
Materials and Methods: Primary cocultures of dorsal root ganglion neurons-Schwann cells (DRGN-SC) were prepared from the spinal cords of embryonic day 15-16 Sprague-Dawley rats, plated on collagen-coated dishes and allowed to grow for 21 days.
Results: Using these myelin-competent DRGN-SC cultures in combination with a specific p38 alpha/beta inhibitor (PD169316), we demonstrate a marked reduction in protein levels of the zinc-finger transcription factor Krox-20 (Egr2). Krox-20 is a master regulator of several myelin genes, including MAG, Protein zero and MBP. These results were confirmed using a siRNA directed against p38 alpha, the predominant isoform expressed in SCs. Protein levels of the cyclin-dependent kinase inhibitor p27Kip1 and MAG (an early marker of myelination) were also reduced by PD169316. Moreover, p38 was found to regulate activation of the transcription factor CREB (cyclic AMP Response Element Binding) protein as PD169316 blocked extracellular matrix-induced phosphorylation. CREB regulates the expression of target genes via the cAMP response elements and can selectively regulate gene expression by interacting with different dimerization partners. Results from ultrastructural studies suggest the arrest of SCs at a promyelinating stage, where they do not proceed further than forming a 1:1 association relation with axons. Neither neuronal morphology nor neurofilament expression appears to be altered under p38 inhibitory conditions. Overexpression of Krox-20 using an adenovirus was insufficient to promote the formation of MBP positive internodes in the presence of the PD169316, despite the expression of MAG.
Conclusion: Thus the MAPK p38 appears to partly regulate myelination of axons by SCs at the level of the transcription factor Krox-20 expression and CREB activation in SCs. Further studies will determine whether this is occurring at the level of gene expression or translation. In addition, we are currently investigating the possible regulation of other transcription factors by p38.
Funded by the Multiple Sclerosis Society of Canada.
|
| | |
| Back |
|
