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Myelin-associated glycoprotein modulates expression and phosphorylation of neuronal cytoskeletal elements and their
Suzanne M Dashiell1, Sandra L Tanner, Harish C Pant
1Laboratory of Molecular and Cellular Neurobiology, National Institute of Neurological Disorders and Stroke, NIH, Bethesda, Maryland 20892, USA.
Abstract:
Decreased phosphorylation of neurofilaments in mice lacking myelin-associated glycoprotein (MAG) was shown to be associated with decreased activities of extracellular-signal regulated kinases (ERK1/2) and cyclin-dependent kinase-5 (cdk5). These in vivo changes could be caused directly by the absence of a MAG-mediated signaling pathway or secondary to a general disruption of the Schwann cell-axon junction that prevents signaling by other molecules. Therefore, in vitro experimental paradigms of MAG interaction with neurons were used to determine if MAG directly influences expression and phosphorylation of cytoskeletal proteins and their associated kinases. COS-7 cells stably transfected with MAG or with empty vector were co-cultured with primary dorsal root ganglion (DRG) neurons. Total amounts of the middle molecular weight neurofilament subunit (NF-M), microtubule-associated protein 1B (MAP1B), MAP2, and tau were up-regulated significantly in DRG neurons in the presence of MAG. There was also increased expression of phosphorylated high molecular weight neurofilament subunit (NF-H), NF-M, and MAP1B. Additionally, in similar in vitro paradigms, total and phosphorylated NF-M were increased significantly in PC12 neurons co-cultured with MAG-expressing COS cells or treated with a soluble MAG Fc-chimera. The increased expression of phosphorylated cytoskeletal proteins in the presence of MAG in vitro was associated with increased activities of ERK 1/2 and cdk5. We propose that interaction of MAG with an axonal receptor(s) induces a signal transduction cascade that regulates expression of cytoskeletal proteins and their phosphorylation by these proline-directed protein kinases.
Insights
Myelin-associated glycoprotein (MAG) directly promotes neurofilament expression and phosphorylation in neurons. This interaction involves signaling pathways regulating cytoskeletal proteins and kinase activity, crucial for neuronal health.
Area of Science:
- Neuroscience
- Cell Biology
- Molecular Biology
Background:
- Myelin-associated glycoprotein (MAG) deficiency in mice correlates with reduced neurofilament phosphorylation and kinase activity (ERK1/2, cdk5).
- This reduction may stem from direct MAG signaling absence or secondary disruption of the Schwann cell-axon junction.
Purpose of the Study:
- To investigate whether MAG directly influences the expression and phosphorylation of cytoskeletal proteins and associated kinases in neurons using in vitro models.
Main Methods:
- Co-culture of primary dorsal root ganglion (DRG) neurons with MAG-expressing COS-7 cells.
- Co-culture of PC12 neurons with MAG-expressing COS cells or treatment with soluble MAG Fc-chimera.
- Analysis of cytoskeletal protein expression and phosphorylation levels, and kinase activities.
Main Results:
- MAG significantly increased the expression of neurofilament-M (NF-M), MAP1B, MAP2, and tau in DRG neurons.
- MAG also enhanced the phosphorylation of NF-H, NF-M, and MAP1B.
- Increased expression and phosphorylation of NF-M were observed in PC12 neurons treated with MAG, correlating with elevated ERK1/2 and cdk5 activities.
Conclusions:
- MAG directly interacts with axonal receptors to initiate a signal transduction cascade.
- This cascade regulates the expression and phosphorylation of cytoskeletal proteins via proline-directed protein kinases like ERK1/2 and cdk5.
- MAG plays a direct role in maintaining neuronal cytoskeletal integrity through specific signaling pathways.