A role for the p75 neurotrophin receptor in axonal degeneration and apoptosis induced by oxidative stress

Abstract

The p75 neurotrophin receptor (p75NTR) mediates the death of specific populations of neurons during the development of the nervous system or after cellular injury. The receptor has also been implicated as a contributor to neurodegeneration caused by numerous pathological conditions. Because many of these conditions are associated with increases in reactive oxygen species, we investigated whether p75NTR has a role in neurodegeneration in response to oxidative stress. Here we demonstrate that p75NTR signaling is activated by 4-hydroxynonenal (HNE), a lipid peroxidation product generated naturally during oxidative stress. Exposure of sympathetic neurons to HNE resulted in neurite degeneration and apoptosis. However, these effects were reduced markedly in neurons from p75NTR-/- mice. The neurodegenerative effects of HNE were not associated with production of neurotrophins and were unaffected by pretreatment with a receptor-blocking antibody, suggesting that oxidative stress activates p75NTR via a ligand-independent mechanism. Previous studies have established that proteolysis of p75NTR by the metalloprotease TNFα-converting enzyme and γ-secretase is necessary for p75NTR-mediated apoptotic signaling. Exposure of sympathetic neurons to HNE resulted in metalloprotease- and γ-secretase-dependent cleavage of p75NTR. Pharmacological blockade of p75NTR proteolysis protected sympathetic neurons from HNE-induced neurite degeneration and apoptosis, suggesting that cleavage of p75NTR is necessary for oxidant-induced neurodegeneration. In vivo, p75NTR-/- mice exhibited resistance to axonal degeneration associated with oxidative injury following administration of the neurotoxin 6-hydroxydopamine. Together, these data suggest a novel mechanism linking oxidative stress to ligand-independent cleavage of p75NTR, resulting in axonal fragmentation and neuronal death. © 2014 by The American Society for Biochemistry and Molecular Biology, Inc.