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TACE-induced cleavage of NgR and p75^NTR in dorsal root ganglion cultures disinhibits outgrowth and promotes branching of neurites in the presence of inhibitory CNS myelin

Molecular Neuroscience Group, Division of Medical Sciences, University of Birmingham, Birmingham, UK

¹Correspondence: Molecular Neuroscience Group, Division of Medical Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK. E-mail: a.logan{at}bham.ac.uk

ABSTRACT

After binding, central nervous system (CNS) myelin-derived axon growth inhibitory ligands, the Nogo-66 receptor (NgR), complexes with LINGO-1 and either the low-affinity neurotrophin receptor (p75^NTR) or TROY to initiate growth cone collapse via a Rho-A inhibitory signaling pathway and/or Ca²⁺-dependent activation of epidermal growth factor receptor (EGFR) through an unknown signaling pathway. We have shown that axon growth through CNS myelin is disinhibited after neurotrophic factor administration by 1) initiating intramembranous proteolysis (RIP) of p75^NTR, leading to cleavage of the extracellular (p75_ECD) and intracellular domains (p75_ICD) by - and -secretase, respectively, thereby paralyzing inhibitory signaling; 2) shedding of soluble NgR_ECD, which acts as a competitive antagonist to NgR for binding of inhibitory ligands; and 3) antagonizing NgR/p75^NTR clustering by competitive p75_ECD/NgR interaction. Here, we report that TNF-alpha converting enzyme (TACE) (a disintegrin and metalloproteinase 17, ADAM17) induces disinhibition of FGF2-stimulated neurite outgrowth of dorsal root ganglion neurons (DRGN) cultured in the presence of a predetermined concentration of inhibitory CNS myelin-derived ligands. After addition of TACE (which has -secretase activity) to mitotically arrested adult rat mixed DRG cultures, we demonstrate 1) NgR_ECD shedding; 2) release of p75_ECD and p75_ICD by RIP of p75^NTR; 3) blockade of Rho-A activation; 4) reduced EGFR phosphorylation; and 5) increased FGF2-stimulated DRGN neurite outgrowth and branching in the presence of CNS myelin-derived inhibitory ligands. Thus, TACE-induced cleavage of NgR and RIP of p75^NTR abrogates axon growth inhibitory signaling, thereby disinhibiting CNS axon/neurite growth.—Ahmed, Z., Mazibrada, G., Seabright, R. J., Dent, R. G., Berry, M., Logan, A. TACE-induced cleavage of NgR and p75^NTR in dorsal root ganglion cultures disinhibits neurite outgrowth and promotes branching of neurites in the presence of inhibitory CNS myelin.

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