Versican V2 and the central inhibitory domain of Nogo-A inhibit neurite growth via p75NTR/NgR-independent pathways that converge at RhoA.
Myelin is a major obstacle for regenerating nerve fibers of the adult mammalian central nervous system (CNS). Several proteins including Nogo-A, myelin-associated glycoprotein (MAG), oligodendrocyte myelin glycoprotein (OMgp) and the chondroitin-sulfate proteoglycan (CSPG) Versican V2 have been identified as inhibitory components present in CNS myelin. MAG, OMgp as well as the Nogo specific domain Nogo-66 exert their inhibitory activity by binding to a neuronal receptor complex containing the Nogo-66 receptor NgR and the neurotrophin receptor p75(NTR). While this suggests a converging role of the p75(NTR)/NgR receptor complex for myelin-derived neurite growth inhibitors, we show here that NgR/p75(NTR) is not required for mediating the inhibitory activity of the two myelin components NiG, unlike Nogo-66 a distinct domain of Nogo-A, and Versican V2. Primary neurons derived from a complete null mutant of p75(NTR) are still sensitive to NiG and Versican V2. In line with this result, neurite growth of p75(NTR) deficient neurons is still significantly blocked on total bovine CNS myelin. Furthermore, modulation of RhoA and Rac1 in p75(NTR)-/- neurons persists with NiG and Versican V2. Finally, we demonstrate that neither NiG nor Versican V2 interact with the p75(NTR)/NgR receptor complex and provide evidence that the binding sites of NiG and Nogo-66 are physically distinct from each other on neural tissue. These results indicate not only the existence of neuronal receptors for myelin inhibitors independent from the p75(NTR)/NgR receptor complex but also establish Rho GTPases as a common point of signal convergence of diverse myelin-induced regeneration inhibitory pathways.
Institute of Medical Chemistry and Biochemistry, Medical University of Innsbruck, A-6020 Innsbruck, Austria.
Rüdiger
R
Schweigreiter
Adrian R
AR
Walmsley
Barbara
B
Niederöst
Dieter R
DR
Zimmermann
Thomas
T
Oertle
Elisabeth
E
Casademunt
Stefan
S
Frentzel
Georg
G
Dechant
Anis
A
Mir
Christine E
CE
Bandtlow
D000818:Animals; D016466:CHO Cells; D002417:Cattle; D049109:Cell Proliferation; D002540:Cerebral Cortex / Q000378:metabolism / Q000502:physiology; D011508:Chondroitin Sulfate Proteoglycans / Q000235:genetics / Q000502:physiology*; D006224:Cricetinae; D006131:Growth Inhibitors / Q000502:physiology*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009185:Myelin Proteins / Q000235:genetics / Q000502:physiology*; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000502:physiology*; D016501:Neurites / Q000502:physiology*; D000070798:Nogo Proteins; D011485:Protein Binding / Q000502:physiology; D051381:Rats; D020800:Receptor, Nerve Growth Factor; D017475:Receptors, Nerve Growth Factor / Q000235:genetics / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology*; D053675:Versicans; D020742:rhoA GTP-Binding Protein / Q000235:genetics / Q000502:physiology*
D011508:Chondroitin Sulfate Proteoglycans; D006131:Growth Inhibitors; D009185:Myelin Proteins; D009419:Nerve Tissue Proteins; D000070798:Nogo Proteins; D020800:Receptor, Nerve Growth Factor; D017475:Receptors, Nerve Growth Factor; C000603201:Rtn4 protein, mouse; C000603197:Rtn4 protein, rat; C508323:Vcan protein, mouse; C508324:Vcan protein, rat; D053675:Versicans; D020742:rhoA GTP-Binding Protein