The p75 neurotrophin receptor (p75(NTR)) regulates a wide range of cellular functions, including programmed cell death, axonal growth and degeneration, cell proliferation, myelination, and synaptic plasticity. The multiplicity of cellular functions governed by the receptor arises from the variety of ligands and co-receptors which associate with p75(NTR) and regulate its signaling. P75(NTR) promotes survival through interactions with Trk receptors, inhibits axonal regeneration via partnerships with Nogo receptor (Nogo-R) and Lingo-1, and promotes apoptosis through association with Sortilin. Signals downstream of these interactions are further modulated through regulated intramembrane proteolysis (RIP) of p75(NTR) and by interactions with numerous cytosolic partners. In this chapter, we discuss the intricate signaling mechanisms of p75(NTR), emphasizing how these signals are differentially regulated to mediate these diverse cellular functions.

Background:The p75 neurotrophin receptor (p75 NTR ) promotes neurodegeneration during development and in response to cellular injury. Results: Reactive oxygen species promoted cleavage of p75 NTR , leading to axonal degeneration and apoptosis. Conclusion: Oxidative stress activates intracellular p75 NTR signaling to induce neurodegeneration. Significance: These results suggest a novel mechanism through which p75 NTR contributes to neurodegeneration associated with cellular injury or pathological conditions.

Neuroblastoma is a pediatric malignancy of the sympathetic ganglia and adrenal glands, hypothesized to originate from progenitors of the developing sympathetic nervous system. Amplification of the MYCN oncogene is a genetic marker of risk in this disease. Understanding the impact of oncogene expression on sympathoadrenal progenitor development may improve our knowledge of neuroblastoma initiation and progression. We isolated sympathoadrenal progenitor cells from the postnatal murine adrenal gland by sphere culture and found them to be multipotent, generating differentiated colonies of neurons, Schwann cells, and myofibroblasts. MYCN overexpression in spheres promoted commitment to the neural lineage, evidenced by an increased frequency of neuron-containing colonies. MYCN promoted proliferation of both sympathoadrenal progenitor spheres and differentiated neurons derived from these spheres, but there was also an increase in apoptosis. The proliferation, apoptosis, and neural lineage commitment induced by MYCN are tumor-like characteristics and thereby support the hypothesis that multipotent adrenal medullary progenitor cells are cells of origin for neuroblastoma. We find, however, that MYCN overexpression is not sufficient for these cells to form tumors in nude mice, suggesting that additional transforming mutations are necessary for tumorigenesis.

No abstract

Neurite degeneration is associated with early stages of neurodegenerative disorders such as Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis. One method that is commonly used to analyze neurite degeneration involves calculation of a Degeneration Index (DI) following utilization of the Analyze Particles tool of ImageJ to detect neurite fragments in micrographs of cultured cells. However, DI analyses are prone to several types of measurement error, can be time consuming to perform, and are limited in application. Here, we describe an improved method for performing DI analyses. Accuracy of measurements was enhanced through modification of selection criteria for detecting neurite fragments, removal of image artifacts and non-neurite materials from images, and optimization of image contrast. Such enhancements were implemented into an ImageJ macro that enables rapid and fully automated DI analysis of multiple images. The macro features operations for automated removal of cell bodies from micrographs, thus expanding the application of DI analyses to use in experiments involving dissociated cultures. We present experimental findings supporting that, compared to the conventional method, the enhanced analysis method yields measurements with increased accuracy and requires significantly less time to perform. Furthermore, we demonstrate the utility of the method to investigate neurite degeneration in a cell culture model of PD by conducting an experiment revealing the effects of c-Jun N-terminal Kinase on neurite degeneration induced by oxidative stress in human mesencephalic cells. This improved analysis method may be used to gain novel insight into factors underlying neurite degeneration and the progression of neurodegenerative disorders. Significance StatementNeurite degeneration is a cellular event associated with the early stages of multiple types of neurodegenerative disorders. Molecular factors that regulate neurite degeneration remain poorly understood, and existing methods for studying neurite degeneration have limited application and efficiency. Here, we identify modifications to a widely used procedure for analyzing neurite degeneration that reduce measurement error. Such methodological enhancements were incorporated into an ImageJ macro, thereby facilitating rapid and completely automated analysis 2 of neurite degeneration using large sets of micrographs. Using a cell culture model of Parkinson's disease, we demonstrate that the macro facilitates more accurate and efficient neurite degeneration measurements while expanding the suitability of the analysis method for experiments involving dissociated cultures.