p75NTR Immunoreactivity Research Articles

Co‐expression of trkA and p75 neurotrophin receptor in extracranial olfactory neuroblastoma cells

Olfactory neuroblastoma (ON, esthesioneuroblastoma) is a high-grade malignant tumour of neuronal origin. Little is known about the neurobiological behaviour of this tumour. Ten cases of ON and five cases of nasopharyngeal carcinoma were examined for expression of trkA and p75 neurotrophin receptor (p75NTR) using immunohistochemistry and double labelling fluorescence. We found that all ON tissues from 10 cases expressed both trkA and p75NTR at different levels. Double staining revealed that almost all trkA-immunoreactive ON cells also contained p75NTR immunoreactivity. By contrast, no trkA or p75NTR immunoreactivity was detected in nasopharyngeal carcinoma cells from five patients. These results suggest that nerve growth factor may play a role in the generation of ON and staining of trkA and p75NTR may assist in the diagnosis of ON.

Amyloid β Binds Trimers as Well as Monomers of the 75-kDa Neurotrophin Receptor and Activates Receptor Signaling

p75(NTR), a nerve growth factor co-receptor that has been implicated in apoptosis of neurons, is structurally related to Fas and the receptors for tumor necrosis factor-alpha that display ligand independent assembly into trimers. Using embryonic day 17 fetal rat cortical neurons and p75(NTR)-expressing NIH-3T3 cells, we now show that p75(NTR) exists as a trimer as well as a monomer. Furthermore, we have reported and others have confirmed that amyloid beta binds p75(NTR), and that this binding leads to apoptotic cell death. We now report that amyloid beta binds to trimers of p75(NTR) as well as to p75(NTR) monomers but not to the p140(trkA), the nerve growth factor co-receptor that mediates neuronal survival. Furthermore, amyloid beta activates p75(NTR), strongly inducing the transcription of c-Jun mRNA and stimulating the stress-activated c-Jun NH(2)-terminal kinase, as measured by phosphorylation of its substrate (glutathione S-transferase-c-Jun-(1-79)). Our data suggest that p75(NTR) may be present as a preformed trimer that binds amyloid beta to induce receptor activation, and support the hypothesis that p75(NTR) activation by amyloid beta is causally related to Alzheimer's disease.

Nerve Growth Factor Modulates the Activation Status and Fast Axonal Transport of ERK 1/2 in Adult Nociceptive Neurones

Mature dorsal root ganglion cells respond to neurotrophins, and the intracellular signalling pathways activated by neurotrophins have been characterized in vitro. We have now used immunocytochemistry and Western blots to examine the expression and activation of extracellular signal-regulated protein kinase-1/2 (ERK) in rat dorsal root ganglion cells in vivo, using antisera to total (tERK) and phosphorylated (pERK) forms. This has revealed a number of novel findings. tERK immunoreactivity is present in most dorsal root ganglion cells but is expressed most strongly in small (nociceptive) cells and, surprisingly, is absent in a population of large cells that expressed trkB or trkC but mainly lack p75NTR immunoreactivity. In contrast pERK is prominent in a few trkA cells and in satellite glial cells, and is further increased by NGF treatment. tERK and pERK both undergo fast anterograde and retrograde axonal transport, indicated by accumulation at a sciatic nerve ligature, and NGF reduces the level of retrograde pERK transport.

Photic regulation of circadian rhythms and the expression of p75 neurotrophin receptor immunoreactivity in the suprachiasmatic nucleus in rats

Neurotrophic factors have been implicated in the mechanism underlying photic regulation of circadian rhythms in mammals. In rats, the most abundant neurotrophin receptor found in the suprachiasmatic nucleus (SCN), the circadian clock, is the low affinity p75 neurotrophin receptor (p75NTR). This receptor is expressed by retinal afferents of the SCN, but nothing is known about its role in photic regulation of circadian rhythms. We show here that neonatal treatment with the retinal neurotoxin, monosodium glutamate (MSG), which has no effect on photic entrainment of circadian rhythms, nearly completely abolished p75NTR immunoreactivity in the SCN in rats. These findings suggest that p75NTR from retinal sources do not play an essential role in the mechanism mediating photic entrainment of circadian rhythms in rats.

Upregulation of the p75 low-affinity neurotrophin receptor by phagocytically active perivascular active cells in the rat neural lobe.

Expression of the p75 low-affinity neurotrophin receptor (p75NTR) was investigated immunocytochemically at the light and ultrastructural level during the axonal degeneration that follows partial denervation of the rat neural lobe (NL) and following systemic administration of lipopolysaccharide (LPS). A significant increase in the intensity and extent of p75NTR immunoreactivity in the NL of partially denervated animals compared with age-matched, sham-operated controls was observed at 5-10 days postdenervation, with immunoreactivity returning to control values by 35 days. Dual-label confocal comparison of p75NTR localization with that of the C3bi complement receptor, a microglial marker, and S100, an astrocyte-specific Ca2+-binding protein, revealed no colocalization. Immunoelectron-microscopic examination demonstrated that the p75NTR immunoreactivity is present in a subpopulation of cells located within the extensive perivascular space of the NL. No examples of p75NTR-immunoreactive pituicytes or endothelia were observed at the light or ultrastructural level. Dense p75NTR immunoreactivity was frequently observed surrounding endocytotic omega profiles of plasmalemma engulfing extracellular debris as well as lining vacuoles within the cytoplasm of perivascular cells. The association of p75NTR with phagocytosis was confirmed by confocal microscopy, showing the presence of p75NTR in all cells expressing the ED-1 antigen, which is restricted to the lysosomal membrane of phagocytes (Damoiseaux et al. 1994). Likewise, a marked increase in p75NTR and ED-1 immunoreactivity was observed in the NL following systemic administration of LPS. These results suggest a strong correlation between modulation of p75NTR immunoreactivity and conditions that induce high levels of phagocytic activity by perivascular cells in the NL of the rat. Implications for understanding the mechanisms by which phagocytes may support compensatory responses to neuronal injury are discussed.

Enteric neural crest‐derived cells: Origin, identification, migration, and differentiation

Enteric neural crest‐derived cells: Origin, identification, migration, and differentiation

Dexamethasone Induces TrkA and p75NTR Immunoreactivity in the Cerebral Cortex and Hippocampus

Nerve growth factor (NGF) plays a crucial role in synaptic plasticity during brain development and adulthood by activating a dual receptor system composed of TrkA and p75 (p75NTR) receptors. Exogenous NGF modulates the expression of both receptors. Little is known about the ability of endogenous NGF to regulate the expression of these receptors in basal forebrain cholinergic terminals. The ability of glucocorticoids to increase NGF expression in the hippocampus prompted us to investigate whether the synthetic glucocorticoid dexamethasone (DEX) increases TrkA and p75NTR expression in NGF-target cholinergic neurons in developing rats. We first examined the effect of DEX on NGF mRNA by in situ hybridization. DEX given systemically (0.5 mg/kg, sc) for 1 week to 7-day-old rats elicited an increase in NGF mRNA levels in the dentate gyrus of the hippocampus and superficial layers II and III of the cerebral cortex. Immunohistochemical analysis of p75NTR and TrkA levels revealed a dramatic increase in p75NTR immunoreactivity (IR) in both basal forebrain and hippocampus and TrkA IR in the hippocampus. Interestingly, in DEX-treated rats more axonal terminals were immunopositive for p75NTR in the hippocampus and cortex, suggesting an increase in p75NTR IR in cell bodies as well as in terminals. Our data indicate that the endogenously produced NGF elicits biological changes similar to those of the exogenously delivered NGF. We suggest that glucocorticoids might regulate and coordinate cholinergic neuronal maturation by increasing the biosynthesis of NGF.

P75NTR immunoreactivity in the rat dentate gyrus is mostly within presynaptic profiles but is also found in some astrocytic and postsynaptic profiles.

To localize neurotrophin binding sites within the rat dentate gyrus, the distribution of low-affinity p75 neurotrophin receptor (p75NTR) immunoreactivity (IR) was examined by using antiserum raised against the cytoplasmic domain of the receptor. Semiquantitative electron microscopic examination of p75NTR-labeled sections showed that most p75NTR-labeled profiles were axons and axon terminals (72% from a total of 3,975); p75NTR-IR was observed throughout the extent of these structures and was not limited to the plasmalemmal surface. Axons and axon terminals containing p75NTR-IR were distributed in approximately equal proportions across the hilus, infragranular zone, and the inner, middle, and outer molecular layers; significantly fewer p75NTR-labeled profiles were observed in the granule cell layer. Axon terminals containing p75NTR-IR, which made synapses (296 of 552), formed equal proportions of symmetric and asymmetric synapses, primarily with the shafts and spines of dendrites. The remainder of the p75NTR-labeled terminals apposed unlabeled somata and dendrites without forming synapses in the single sections analyzed. In addition, p75NTR-IR was contained within some astrocytes (17.5% of 3,975) and dendritic shafts (3%) and spines (5%). Within dendritic spines, p75NTR-IR was most often associated with the plasmalemmal surface near postsynaptic densities; in dendritic shafts, p75NTR labeling was associated with microfilaments distant from the plasmalemma. Most p75NTR-labeled dendritic profiles were located in the molecular layer, and some originated from granule cells. Moreover, in some granule cell somata (<1% of 3,975), p75NTR-IR was associated with endosomes. The primary localization of p75NTR-IR to presynaptic structures in the dentate gyrus, presumably arising from medial septal/diagonal band neurons, agrees with previous reports. However, p75NTR-IR within some astrocytes, somata, and dendritic structures suggests that this receptor may also be involved in controlling local neurotrophin levels and possibly modulating the viability of local hippocampal cell populations.

Glucocorticoid regulation of motoneuronal parameters in rats with spinal cord injury.

1. Glucocorticoids exert beneficial effects after acute CNS injury in humans and experimental animals. To elucidate potential mechanisms of glucocorticoid action in the lesioned spinal cord, we have studied if treatment with dexamethasone (DEX) modulated the neurotrophin binding receptor p75 (p75NTR) and choline acetyltransferase (ChAT), a marker of neuronal functional viability. 2. Rats with a sham operation or with spinal cord transection at the thoracic level received vehicle or DEX several times postlesion and were sacrificed 48 hr after surgery. The lumbar region caudal to the lesion was processed for p75NTR and ChAT immunoreactivity (IR) using quantitative densitometric analysis. 3. We observed that p75NTR-IR was absent from ventral horn motoneurons of sham-operated rats, in contrast to strong staining of neuronal perikaryon in TRX rats. Administration of DEX to TRX rats had no effect on the number of neuronal cell bodies expressing p75NTR-IR but significantly increased the number and length of immunostained neuronal processes. 4. Furthermore, spinal cord transection reduced ChAT immunostaining of motoneurons by 50%, whereas DEX treatment reverted this pattern to cells with a strong immunoreaction intensity in perikaryon and cell processes. 5. It is hypothesized that increased expression of p75NTR in cell processes and of ChAT in motoneurons may be part of a mechanism by which glucocorticoids afford neuroprotection, in addition to their known antiinflammatory effects.

Dexamethasone Induces Hypertrophy of Developing Medial Septum Cholinergic Neurons: Potential Role of Nerve Growth Factor

Glucocorticoid hormones influence neuronal plasticity during development; however little is known about the mechanisms of this trophic activity. Because glucocorticoids increase nerve growth factor (NGF) synthesis in selected brain areas and NGF plays a role in the development of basal forebrain cholinergic neurons, we tested the hypothesis that glucocorticoids may foster maturation of the cholinergic phenotype during postnatal development via the induction of NGF biosynthesis. The synthetic glucocorticoid dexamethasone (DEX) was injected systemically (0.5 mg/kg, s.c.) once a day for 1 week in 7-d-old (P7) rats. DEX elicited an increase in NGF mRNA and protein levels in the cerebral cortex and hippocampus as well as specific NGF responses, such as TrkA tyrosine phosphorylation in the septum, choline acetyltransferase (ChAT) and p75 neurotrophin receptor (p75NTR) immunoreactivity, and a relative number of cholinergic neurons in the medial septum. To examine whether the effect of DEX is age-related, we treated 1- and 14-d-old rats with DEX for 1 week. DEX increased NGF expression in rats treated from P1 to P8 but not in those treated from P14 to P21. The age-related increased expression of NGF correlated with the induction of ChAT immunoreactivity in the medial septum. Moreover, in the spinal cord, neither NGF nor ChAT levels were increased by DEX, suggesting that the glucocorticoid-mediated changes seen in the basal forebrain are associated with specific NGF responses. Our data suggest that by increasing NGF levels, glucocorticoids may play a role in the maturation of postnatal cholinergic neurons.

Reversal of the low-affinity neurotrophin receptor stromal-epithelial expression pattern between benign and malignant human prostate

Reduced expression of the low-affinity p75 neurotrophin receptor (p75 NTR) occurs in prostate epithelial cells during malignant transformation. Recent studies indicating that the p75 NTR can transduce signals that induce apoptosis suggest that diminished p75 NTR in transformed prostate cells may contribute to immortalization. Mutations in the transmembrane domain of the p75 NTR gene have been associated with decreased p75 NTR protein expression and may block the ability of the p75 NTR to induce apoptosis. Therefore, we used Western blot to analyze prostate cancer (PC) cell lines for p75 NTR protein expression and gene single strand conformation polymorphism (SSCP) analysis and direct DNA sequencing to analyze mutations in the transmembrane domain of the p75 NTR. p75 NTR Protein was present in all cell lines, and mutations in the p75 NTR gene were not detected in cDNA derived from any cell line. To define the expression pattern of p75 NTR in PCs in vivo, we used immunohistochemical techniques to examine tissue specimens from 20 benign, 19 malignant primary, and 14 metastatic prostate specimens. In benign prostate tissues, expression of p75 NTR was universally detected in basal cells but not in secretory epithelial or stromal cells. In both primary and metastatic PC tissues, p75 NTR immunoreactivity could not be detected in malignant prostate epithelial cells. However, in contrast to the benign prostate, p75 NTR protein was expressed in stromal cells surrounding malignant epithelial cells. Stromal p75 NTR expression was present in 84% (16 of 19) primary and in 86% (12 of 14) metastatic specimens. These data show that in the benign prostate p75 NTR protein is expressed by basal cells and not stromal cells whereas in malignant prostate p75 NTR protein is expressed by stromal cells but not prostatic carcinoma cells. Reversal of the p75 NTR stromal-epithelial pattern of expression between benign and malignant prostate suggests that p75 NTR may contribute to the development and maintenance of prostate cancer.

Expression of nerve growth factor receptors in cutaneous inflammation.

Evidence indicates that the neurotrophin nerve growth factor (NGF) is a mediator of cutaneous inflammatory responses. Cellular responses to NGF are facilitated by two receptors called trk A and p75 neurotrophin receptor (p75NTR). In the current study we have investigated the expression of these receptors in lesional and non-lesional skin from patients with plaque psoriasis and in normal skin exposed to three times the minimal erythema dose of ultraviolet (UV) B radiation. Trk A immunostaining was confined to the basal keratinocytes in normal skin. There was a significant reduction in trk A immunostaining in both non-lesional and lesional psoriatic skin compared with control skin. In UVB-irradiated normal skin, there was a significant reduction in trk A immunostaining at 4 h after irradiation, which was still evident at 48 h. In normal skin, p75NTR immunopositive fine nerve fibres were present throughout the dermis and occasionally seen in the epidermis. Thick nerve fibres were evident in the deep dermis and in the middle region of the dermis. p75NTR immunopositive basal keratinocytes were occasionally seen. There was a statistically significant loss of p75NTR immunopositive fine nerve fibres in the epidermis of lesional psoriatic skin and a statistically significant loss of p75NTR immunopositive fine nerve fibres in the dermis in both non-lesional and lesional psoriatic skin. p75NTR immunopositive thick nerve fibres were reduced in lesional psoriatic skin compared with normal skin. UVB irradiation of normal skin led to a statistically significant decrease in the p75NTR immunopositive fine nerve fibres in the epidermis at 48 h after irradiation. There was no significant reduction in the dermal p75NTR immunoreactivity. These results demonstrated that expression of both NGF receptors is decreased following an acute inflammatory stimulus and also in association with a chronic inflammatory dermatosis.

192 IgG-saporin abolishes p75 neurotrophin receptor immunoreactivity in rat SCN.

The rat suprachiasmatic (SCN) contains a dense plexus of low-affinity p75 neurotrophin receptor (p75NTR)-immunoreactivity. In some SCN neurons, p75NTR is co-localized with vasoactive intestinal peptide (VIP). The present study examines the effect of third ventricle administration of 192 IgG-saporin immunotoxin on p75NTR and VIP immunoreactivity in the rat SCN. The 192 IgG-saporin immunotoxin abolished p75NTR immunoreactivity in the SCN. VIP immunoreactivity in the SCN of saporin-lesioned animals was not significantly different from that of control animals. Immunolesions of the p75NTR-ir cell population in the SCN may prove useful in clarifying the role of p75NTR in circadian timing.

Delayed loss of p75 neurotrophin receptor-immunoreactivity in the rat suprachiasmatic nucleus and intergeniculate leaflet after binocular enucleation

The rat suprachiasmatic nucleus (SCN) contains a dense plexus of low-affinity p75 neurotrophin receptor (p75NTR)-immunoreactivity. Scattered patches of p75NTR immunoreactivity are present in the intergeniculate leaflet (IGL). Both SCN and IGL receive a direct retinal input. After binocular enucleation, there is a delayed loss of p75NTR-immunoreactivity in the SCN and IGL beginning at, respectively, 4 and 8 weeks post-enucleation, with complete loss occurring in both nuclei by week 12. This delayed loss may be due to an up-regulation of growth factor secretion by local cells in response to retinal axon degeneration.