Characteristics of partially purified nerve growth factor receptor

Specific binding of 125I-hippocampal cholinergic neurostimulating peptide (HCNP) to rat brain membranes: characterization and regional distribution

An undecapeptide-hippocampal cholinergic neurostimulating peptide (HCNP), originally purified from young rat hippocampus, enhances cholinergic phenotype development in the medial septal nucleus in vitro. To survey and characterize the HCNP receptor within the central nervous system, we used iodinated HCNP as a labeled ligand. In preliminary experiments, [125I]HCNP binding was highest in the crude P2 membrane fraction, so all subsequent experiments were performed using this fraction. The binding was saturable and reversible, and unlabeled ligand inhibited it. Scatchard analysis of the concentration-dependent saturation of binding indicated a single population of non-interacting sites with K(d) 4.0+/-0.7 nM and B(max) 10.7+/-3.8 pmol/mg protein. Dissociation experiments revealed a dissociation constant (K(-1)) of 0.07 min(-1). Inhibition experiments using HCNP and its shorter peptide fragments suggested that the active binding site resided close to the peptide's C-terminal sequence. Since [125I]HCNP binding was found in crude P2 membrane fractions from animals at all ages examined, HCNP may also perform important functional roles in the adult brain. Further, the predominant distribution of the receptor in the P2 membrane fraction, and the similarity in distribution patterns between the binding site and HCNP-precursor protein mRNA expression suggest that the peptide exerts its functions in the vicinity of the dendrites of the neurons that produce it.

Low-affinity nerve growth factor receptor (p75) in dermatofibrosarcoma protuberans and other nonneural tumors: a study of 1,150 tumors and fetal and adult normal tissues

Low-affinity nerve growth factor receptor (p75) is a member of the tumor necrosis factor receptor family. It may modulate the binding of nerve growth factor (NGF) to the functional high-affinity receptor tyrosine kinase (trk) A. NGF is thought to be responsible for growth, apoptosis, and function of the nervous system. The presence of this receptor (p75) was determined in a large group of neural and nonneural tumors and fetal and adult tissues. One thousand one hundred fifty tumors were analyzed with monoclonal antibody for p75, along with selected normal fetal and adult tissues. Immunoreactivity for p75 was present in adult pericytes, perivascular fibroblasts, basal cells of several types of epithelia, perineurial cells, and dendritic reticulum cells. Additionally, a wide zone of subepithelial mesenchyme and skeletal muscle were positive in the first-trimester fetus, but were diminished or negative in the adult. Consistently positive nonneural mesenchymal tumors included dermatofibrosarcoma protuberans (DFSP), embryonal and alveolar rhabdomyosarcoma, synovial sarcoma, and spindle cell hemangio(endotheli)oma. Schwann cell tumors, ganglioneuroma, granular cell tumor, and malignant peripheral nerve sheath tumor (MPNST) were also p75 positive. Mesenchymal nonneural tumors that were variably positive (32% to 69%) for p75 included fibrosarcoma variants, solitary fibrous tumor, hemangiopericytoma, spindle cell lipoma, Ewing's sarcoma, mesenchymal chondrosarcoma, and malignant melanoma. Nervous system tumors such as paragangliomas, neuroblastoma, meningioma, and perineurioma and nonneural mesenchymal tumors, including extraskeletal osteosarcoma, benign fibrous histiocytomas, fibromas, alveolar soft part sarcoma, epithelioid sarcoma, smooth muscle and gastrointestinal stromal tumors, and angiosarcomas, were almost always negative for p75. Epithelial tumors that were consistently positive included mixed tumor and adenoid cystic carcinoma, whereas mesothelioma, adenocarcinomas, and most squamous cell carcinomas were negative. p75 is not a specific marker for nerve sheath tumors. It is present in a variety of other mesenchymal tumors including synovial sarcoma and in CD34-positive tumors such as DFSP, spindle cell lipoma, and hemangiopericytoma. The presence of p75 in nonneural tumors such as DFSP and rhabdomyosarcoma mimic its presence in early fetal mesenchyme and skeletal muscle, suggesting oncofetal expression in these tumors. p75 may be useful to distinguish DFSP from benign fibrous histiocytoma.

Detection of increased tissue concentrations of nerve growth factor with an improved extraction procedure

Nerve growth factor (NGF) is a protein essential for the survival and normal function of sympathetic neurons. Two-site immunoassays have been developed over the past decade in several laboratories and used to estimate its endogenous concentrations in a variety of effector tissues. However, levels appear restricted to a narrow range, display only a poor correlation with innervation density, and show obvious inter- and intralaboratory variations, the origins of which are unclear. This led us to examine alternative extraction procedures for NGF before quantification. In particular, we have found treatment of tissue extracts with high and low pH in the presence of detergent results in the detection of higher NGF concentrations in immunoassays using either polyclonal or commercially available monoclonal antibodies. These increases were tissue-specific (sciatic nerve, mesenteric arteries, and thoracic aorta > heart and brain > sympathetic ganglia > abdominal aorta) and as much as 10 times greater than the amounts detected by traditional procedures. The method should also prove useful for the assay of other members of the neurotrophin family when appropriate antibodies become available.

An improved procedure for the immunohistochemical localization of nerve growth factor-like immunoreactivity

Nerve growth factor (NGF) is a survival factor required by a number of neuronal populations including most post-ganglionic sympathetic neurones. NGF has been detected and quantified in many tissues but there is little information regarding its cellular localization. Although it has been argued that histological detection has proven difficult due to the low levels of NGF present, other factors may contribute to prevent its identification. In the present study, we report a method for the histological detection of NGF-like immunoreactivity in the rat superior cervical ganglia (SCG). Adult Wistar-Kyoto rats were perfused briefly with either a high or low pH buffer prior to fixation and routine immunohistochemistry. Polyclonal antibodies to native mouse NGF used in the present study recognized mouse NGF but not recombinant human neurotrophin 3 (rhNT3) or brain-derived neurotrophic factor (rhBDNF) by immunoblot analysis. NGF-like immunoreactivity was localized to most sympathetic neurones. Immunoreactivity was detected in the cytoplasm with dense labelling around nuclei. No stain was seen in sections incubated with normal sheep IgG or from animals perfused with phosphate buffer (pH 7.4) prior to fixation. In addition, axotomy resulted in the disappearance of NGF immunoreactivity which was confirmed by biochemical quantification. Finally, no NGF immunoreactivity was found in neurones of rats treated systemically with NGF antiserum 3 days earlier. Possible mechanisms underlying the improvement of NGF immunohistochemistry by pH manipulation before fixation are discussed.

Axonal transport and MR imaging: prospects for contrast agent development

Axonal transport plays a critical role in the physiology and pathology of neurons, yet there have been virtually no clinical tools for its evaluation in human subjects. A wide variety of molecules that can act as axonal transport facilitators have been discovered and, in many cases, used to deliver labels detectable with histologic methods. Recently a number of investigators have reported preliminary success in developing intraneural contrast agents based on various versions of dextran-coated magnetite that may render magnetic resonance imaging capable of depicting axonal transport. It is not yet clear whether any clinically useful agents will eventually be developed, but there has been considerable progress in identifying design factors for such a pharmaceutical agent.

Spectroscopic and chemical studies of the interaction between nerve growth factor (NGF) and the extracellular domain of the low affinity NGF receptor

Nerve growth factor (NGF) interacts with a cell surface receptor on responsive neurons to initiate a series of cellular events leading to neuronal survival and/or differentiation. The first step in this process is the binding of NGF to a low affinity and/or a high affinity receptor. In the present report, we have studied the conformation and stability of recombinant receptor extracellular domain (RED) from the human low affinity receptor and the structural basis of its interaction with NGF. Circular dichroism (CD) studies indicate that the RED is primarily random coil in nature with little regular secondary structure. Thermal stability studies have shown that this irregular conformation is a specific structure that can undergo a reversible two-state thermal denaturation with a concomitant fluorescent and CD change. During heating at 100 degrees C for 15 min, the structure of RED is sufficiently unfolded for a reducing agent, dithiothreitol, to inactivate the receptor toward NGF binding and cross-linking. The complex formation between the RED and NGF has been examined by differential CD measurements, and we have shown that a small, reproducible change in conformation occurs in RED or NGF upon interaction. These results are interpreted in terms of the initiation of NGF cell surface binding and possible modes of signal transduction.

Effects of gonadal steroids on nerve growth factor receptors in sympathetic and sensory ganglia of neonatal rats

The numbers of neurons in the rat superior cervical sympathetic ganglion (SCG) differ in males and females, with the males having 30% more SCG neurons than females at 60 days of age. This sex difference arises during the early postnatal period, when testosterone administration increases the numbers of neurons and alters the nerve growth factor (NGF) content of the rat SCG. In contrast, there is no gender difference in number of neurons in the L1 dorsal root ganglion. In both males and females, the amount of NGF bound per ganglion increased between postnatal days 5 and 15 (P5 and P15) in both dorsal root ganglia (DRGs) and the SCG. There is also a gender difference in NGF binding: SCGs and DRGs of female rats at both P5 and P15 bind more NGF per ganglion than do those of males. This effect was more marked in DRGs than in the SCG. Treatment of neonatal females with testosterone reduced NGF binding in both SCGs and DRGs to levels comparable to males at P5, and in DRGs at P15. In contrast, treatment of males with testosterone from birth resulted in a 2-3 fold increase of NGF binding in both SCGs and DRGs as compared to controls at P15. At P15, testosterone treatment of females increased NGF binding in the SCG. Males and females had opposing responses to neonatal exposure to estradiol. Treatment with estradiol from birth increased NGF binding in SCGs and DRGs of females, but had no effect on NGF binding of SCGs, and reduced NGF binding in DRGs of males.(ABSTRACT TRUNCATED AT 250 WORDS)