Strength of ERK1/2 MAPK Activation Determines Its Effect on Myelin and Axonal Integrity in the Adult CNS.
Myelin growth is a tightly regulated process driven by multiple signals. ERK1/2-MAPK signaling is an important regulator of myelin thickness. Because, in demyelinating diseases, the myelin formed during remyelination fails to achieve normal thickness, increasing ERK1/2 activity in oligodendrocytes is of obvious therapeutic potential for promoting efficient remyelination. However, other studies have suggested that increased levels of ERK1/2 activity could, in fact, have detrimental effects on myelinating cells. Because the strength, duration, or timing of ERK1/2 activation may alter the biological outcomes of cellular responses markedly, here, we investigated the effect of modulating ERK1/2 activity in myelinating cells using transgenic mouse lines in which ERK1/2 activation was upregulated conditionally in a graded manner. We found enhanced myelin gene expression and myelin growth in the adult CNS at both moderate and hyperactivated levels of ERK1/2 when upregulation commenced during developmental myelination or was induced later during adulthood in quiescent preexisting oligodendrocytes, after active myelination is largely terminated. However, a late onset of demyelination and axonal degeneration occurred at hyperelevated, but not moderately elevated, levels regardless of the timing of the upregulation. Similarly, myelin and axonal pathology occurred with elevated ERK1/2 activity in Schwann cells. We conclude that a fine tuning of ERK1/2 signaling strength is critically important for normal oligodendrocyte and Schwann cell function and that disturbance of this balance has negative consequences for myelin and axonal integrity in the long term. Therefore, therapeutic modulation of ERK1/2 activity in demyelinating disease or peripheral neuropathies must be approached with caution.



ERK1/2-MAPK activation in oligodendrocytes and Schwann cells is an important signal for promoting myelin growth during developmental myelination. Here, we show that, when ERK1/2 are activated in mature quiescent oligodendrocytes during adulthood, new myelin growth is reinitiated even after active myelination is terminated, which has implications for understanding the mechanism underlying plasticity of myelin in adult life. Paradoxically, simply increasing the "strength" of ERK1/2 activation changed the biological outcome from beneficial to detrimental, adversely affecting myelin and axonal integrity in both the CNS and PNS. Therefore, this study highlights the complexity of ERK1/2-MAPK signaling in the context of oligodendrocyte and Schwann cell function in the adult animal and emphasizes the need to approach potential therapeutic modulation of ERK1/2 activity with caution.
Department of Neuroscience, University of Connecticut Medical School, Farmington, Connecticut 06030, and.
Akihiro
A
Ishii
Department of Neuroscience, University of Connecticut Medical School, Farmington, Connecticut 06030, and.
Miki
M
Furusho
Department of Anatomy and Neurobiology, Virginia Commonwealth University, Richmond, Virginia 23298.
Jeffrey L
0000-0002-6235-570X
JL
Dupree
Department of Neuroscience, University of Connecticut Medical School, Farmington, Connecticut 06030, and bansal@neuron.uchc.edu.
Rashmi
R
Bansal
D063309:2',3'-Cyclic Nucleotide 3'-Phosphodiesterase / Q000235:genetics / Q000378:metabolism; D000367:Age Factors; D000818:Animals; D000831:Animals, Newborn; D001369:Axons / Q000378:metabolism* / Q000648:ultrastructure; D002490:Central Nervous System / Q000378:metabolism*; D005260:Female; D005786:Gene Expression Regulation / Q000235:genetics*; D020935:MAP Kinase Signaling System / Q000502:physiology*; D008297:Male; D051379:Mice; D008822:Mice, Transgenic; D020929:Mitogen-Activated Protein Kinase Kinases / Q000235:genetics / Q000378:metabolism*; D009043:Motor Activity / Q000235:genetics; D000068079:Motor Disorders / Q000235:genetics / Q000473:pathology; D053580:Muscle Strength / Q000235:genetics; D018991:Myelin Proteolipid Protein / Q000235:genetics / Q000378:metabolism; D009186:Myelin Sheath / Q000378:metabolism* / Q000648:ultrastructure; D009836:Oligodendroglia / Q000378:metabolism; D022661:RNA, Untranslated / Q000235:genetics / Q000378:metabolism; D058570:TOR Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism
C110853:Gt(ROSA)26Sor non-coding RNA, mouse; D018991:Myelin Proteolipid Protein; C047516:Plp1 protein, mouse; D022661:RNA, Untranslated; C546843:mTOR protein, mouse; D058570:TOR Serine-Threonine Kinases; D020929:Mitogen-Activated Protein Kinase Kinases; D063309:2',3'-Cyclic Nucleotide 3'-Phosphodiesterase; C571338:Cnp protein, mouse
Schwann cells; myelin; oligodendrocyte