NGF retards apoptosis in chick embryo bursal cell in vitro

NGF and Its Receptors in the Regulation of Inflammatory Response

There is growing interest in the complex relationship between the nervous and immune systems and how its alteration can affect homeostasis and result in the development of inflammatory diseases. A key mediator in cross-talk between the two systems is nerve growth factor (NGF), which can influence both neuronal cell function and immune cell activity. The up-regulation of NGF described in inflamed tissues of many diseases can regulate innervation and neuronal activity of peripheral neurons, inducing the release of immune-active neuropeptides and neurotransmitters, but can also directly influence innate and adaptive immune responses. Expression of the NGF receptors tropomyosin receptor kinase A (TrkA) and p75 neurotrophin receptor (p75NTR) is dynamically regulated in immune cells, suggesting a varying requirement for NGF depending on their state of differentiation and functional activity. NGF has a variety of effects that can be either pro-inflammatory or anti-inflammatory. This apparent contradiction can be explained by considering NGF as part of an endogenous mechanism that, while activating immune responses, also activates pathways necessary to dampen the inflammatory response and limit tissue damage. Decreases in TrkA expression, such as that recently demonstrated in immune cells of arthritis patients, might prevent the activation by NGF of regulatory feed-back mechanisms, thus contributing to the development and maintenance of chronic inflammation.

Age-related development and histomorphological observation of bursa of Fabricius in yellow quails

He, M., Liang, X., Wang, K., Pu, H., Hu, Y., Ye, G., Li, X. and Liu, L. 2015. Age-related development and histomorphological observation of bursa of Fabricius in yellow quails. Can. J. Anim. Sci. 95: 487–491. The purpose of this study was to observe the age-related development and histomorphological changes in the bursa of Fabricius (BF) in Chinese yellow quails. One hundred and twenty Chinese yellow quails were divided into 12 groups. After dissecting, the weight, length, width and index analysis of the BF were determined, and histomorphological observation was performed using hematoxylin and eosin (HE) staining at different ages. The weight of the BF gradually increased with age from 0 to 5 wk, reached a peak at 5 wk (100.23±6.47), then decreased quickly from 5 to 9 wk (63.21±3.90) and decreased slowly after 9 wk (P<0.05). The length of the BF was greater at 5 wk old than at 0 wk old (11.00±2.45 vs. 5.00±1.15, P<0.05), and there was no significant difference after 5 wk of age (P>0.05). The width of the BF was similar to the length. The organ index was higher at 1 wk of age compared with 5 wk of age (1.25±0.11 vs. 0.71±0.05, P<0.05) and reached its maximum from 0 to 36 wk of age. Histomorphological analysis revealed the different development stages of the BF at different ages. We detected the age-related development of the BF in Chinese yellow quails and observed the histomorphological modifications. This study may help increase our understanding of the quail's immune system and provide a basis for immunization research in Chinese yellow quails.

NGF in Early Embryogenesis, Differentiation, and Pathology in the Nervous and Immune Systems

The physiology of NGF is extremely complex, and although the study of this neurotrophin began more than 60 years ago, it is far from being concluded. NGF, its precursor molecule pro-NGF, and their different receptor systems (i.e., TrkA, p75NTR, and sortilin) have key roles in the development and adult physiology of both the nervous and immune systems. Although the NGF receptor system and the pathways activated are similar for all types of cells sensitive to NGF, the effects exerted during embryonic differentiation and in committed mature cells are strikingly different and sometimes opposite. Bearing in mind the pleiotropic effects of NGF, alterations in its expression and synthesis, as well as variations in the types of receptor available and in their respective levels of expression, may have profound effects and play multiple roles in the development and progression of several diseases. In recent years, the use of NGF or of inhibitors of its receptors has been prospected as a therapeutic tool in a variety of neurological diseases and injuries. In this review, we outline the different roles played by the NGF system in various moments of nervous and immune system differentiation and physiology, from embryonic development to aging. The data collected over the past decades indicate that NGF activities are highly integrated among systems and are necessary for the maintenance of homeostasis. Further, more integrated and multidisciplinary studies should take into consideration these multiple and interactive aspects of NGF physiology in order to design new therapeutic strategies based on the manipulation of NGF and its intracellular pathways.

Nerve growth factor as a signaling molecule for nerve cells and also for the neuroendocrine-immune systems

Nerve growth factor (NGF) is a signaling molecule, originally discovered for its role on differentiation and survival of peripheral sensory and sympathetic neurons. It has also been associated with functional activities of cells of the immune and endocrine systems. NGF biological activity is mediated by two classes of receptors: (i) p75 neurotrophin receptor (p75(NTR)), a 75 kDa glycoprotein, belonging to a superfamily of cytokine receptors including TNF receptors, and (ii) TrkA, a transmembrane tyrosine kinase of 140 kDa. Both TrkA and p75(NTR) are known to play a marked action in neurodegenerative disorders, immune-related deficits, and neuroendocrine (including adipoendocrine) mechanisms. This review focuses on these cellular events and presents a working model which attempts to explain the close interrelationships of the neuro-endocrine-immune triad via a modulatory action of NGF.

Structural and Ultrastructural Localization of NGF and NGF Receptors in the Thymus of Subjects Affected by Myasthenia Gravis

We have previously reported that the thymus of patients affected by myasthenia gravis (MG) is characterized by an elevated level of nerve growth factor (NGF), an endogenous polypeptide which plays a marked role in the cell biology of nervous and immune system. A consistent number of studies has shown altered expression of NGF in diseases associated with inflammatory and/or autoimmune responses. To evaluate the biochemical and molecular mechanisms implicated in NGF action in human myasthenic thymus, it is important to identify the cellular and structural organization of NGF receptors. To address this question, we investigated, both at light and electron microscopic levels, the cellular distribution of immunoreactivity for NGF and its low-affinity receptors, (p75) and its high-affinity receptor (TrkA) in the thymus of patients with MG. The present investigation shows that NGF and NGF receptors are overexpressed in the thymic cells of patients with MG compared to control subjects.

Age-related changes in the avian primary lymphoid organs (thymus and bursa of Fabricius)

The avian primary lymphoid organs, the thymus and the bursa of Fabricius, undergo age-dependent changes leading in some cases to the complete atrophy of the organ. Nevertheless, the timetable of the involutive process as well as the consequences in the structure and functionality of the organs vary largely in the time frame and structural changes among species. On the other hand, and in contrast with the large body of literature reporting the structural and functional changes in mammalian primary lymphoid organs, the age-dependent changes in avian thymus and bursa of Fabricius are scarce, fragmentary, and heterogeneous. This article reviews the current literature on this topic, and focuses primarily on the involution of the bursa of Fabricius.

Neurotrophins and the immune system

The neurotrophins are a family of polypeptide growth factors that are essential for the development and maintenance of the vertebrate nervous system. In recent years, data have emerged indicating that neurotrophins could have a broader role than their name might suggest. In particular, the putative role of NGF and its receptor TrkA in immune system homeostasis has become a much studied topic, whereas information on the other neurotrophins is scarce in this regard. This paper reviews what is known about the expression and possible functions of neurotrophins and their receptors in different immune tissues and cells, as well as recent data obtained from studies of transgenic mice in our laboratory. Results from studies to date support the idea that neurotrophins may regulate some immune functions. They also play an important role in the development of the thymus and in the survival of thymocytes.

CD34-positive cells in human umbilical cord blood express nerve growth factor and its specific receptor TrkA

In this study, we investigated whether hematopoietic stem cells (HSC) and progenitors present in human cord blood can express nerve growth factor (NGF)-specific receptors, TrkA and p75. Our results showed a marked expression of TrkA and NGF in cord blood CD34(+) cells. A gradient of TrkA and NGF expression exists and is highest in cord blood CD34(+) cells, reduced in cord blood mononuclear cells (MNC) and minimal in mononuclear cells isolated from adult peripheral blood. Our findings suggest that NGF may play a role in the differentiation of hematopoietic progenitors and indicate a different requirement for NGF by immune cells, depending on their state of maturity.

Upregulation of TrkA neurotrophin receptor expression in the thymic subcapsular, paraseptal, perivascular, and cortical epithelial cells during thymus regeneration

Neuroimmune networks in the thymic microenvironment are thought to be involved in the regulation of T cell development. Here, we report upon an examination of the expression of the TrkA neurotrophin receptor, the high affinity receptor for nerve growth factor, during regeneration following acute involution induced by cyclophosphamide in the rat thymus. Light and electron microscopic immunocytochemistry demonstrated enhanced expression of the TrkA receptor in the subcapsular, paraseptal, perivascular, and cortical epithelial cells during thymus regeneration. In addition, various morphological alterations, suggestive of a hyperfunctional and dynamic state, of the subcapsular, paraseptal, and perivascular epithelial cells were also observed. The presence of TrkA protein in extracts from the control and regenerating rat thymus was confirmed by western blot. Furthermore, RT-PCR analysis supported these results by demonstrating that thymic extracts contain TrkA mRNA at higher levels during thymus regeneration. Thus, our results suggest that the TrkA receptor located on the thymic subcapsular, paraseptal, perivascular, and cortical epithelial cells could play a role in the development of new T cells to replace T cells damaged during thymus regeneration.

Nerve growth factor: a neurotrophin with activity on cells of the immune system

Numerous studies published in the last two decades provide evidence that nerve growth factor (NGF), a polypeptide originally discovered because of its neurotrophic activity, acts on a variety of cells of the immune system, including mast cells, eosinophils, and B and T lymphocytes. NGF has been shown to increase during inflammatory responses, autoimmune disorders, parasitic infections, and allergic diseases. Moreover, stress, which is characterized also by activation of a variety of immune cells, causes a significant increase in basal plasma NGF levels. Recently published studies reveal that hematopoietic progenitor cells seem to be able to produce and/or respond to NGF. We report these data and discuss the hypothesis of the possible implication of NGF on the functional activities of immune cells.

A protein from Naegleria amoebae causes apoptosis in chick embryo and CHO cells after they become confluent

Exposure for less than an hour to a protein isolated from Naegleria amoebae initiates a process that has no apparent effect on the appearance or growth of chick embryo or CHO cell cultures for 4 to 9 days; after the development of confluency, at some unknown signal, all of the cells undergo an apoptotic death within a 12- to 24-hour period. Abnormalities detected among the last mitotic cells include chromosomal breakage and early reversal in metaphase to telo/interphase daughter nuclei with irregular shapes. Additional events in the dying cultures include the development of a cytoplasmic amoebic-related immunogen, gross DNA fragmentation, cell blebbing, shrinkage, and apoptotic body formation. Culture death included all cells, those present in confluent cultures when the protein was added, and in other cultures, those formed during a more than 30-fold increase in cells as the cultures became confluent. The increase in the number of cells followed by the uniformity and synchrony of their death pattern indicates that the signal to kill has increased and spread throughout the culture; upon an unknown condition related to confluency, events are initiated that lead to the unusual apoptotic death of the culture.

Endogenous activation of apoptosis in bursal lymphocytes: inhibition by phorbol esters and protein synthesis inhibitors

The bursa of Fabricius represents the primary immune organ where immature B cells undergo maturational changes in avian species. Isolation of bursal lymphocytes for analysis in cell culture results in the rapid endogenous activation of apoptosis. After 2 h of incubation, over 45% of the lymphocytes were shown to be undergoing apoptosis and by 6 h 80% were undergoing apoptosis as demonstrated by a terminal deoxynucleotidyltransferase-mediated dUTP-fluorescein isothiocynate nick end-labeling flow-cytometric analysis. These results were corroborated by a propidium iodide-staining flow-cytometric assay and by an agarose gel electrophoresis DNA fragmentation assay that demonstrated internucleosomal DNA cleavage of genomic DNA in apoptotic bursal lymphocytes. Endogenous activation of apoptosis in bursal lymphocytes could be inhibited in a dose-dependent fashion with the phorbol ester, phorbol 12-myristate 13-acetate, but not the phorbol ester antagonist 4 alpha-phorbol 12,13-didecanoate. In addition, apoptosis could be inhibited in a dose-dependent fashion with inhibitors of protein translation, cycloheximide, and puromycin, as well as the transcriptional inhibitor actinomycin D. These results suggest that endogenous activation of bursal lymphocyte apoptosis may be mediated by the protein kinase C signal transduction pathway and activation of this process appears to be dependent upon de novo protein biosynthesis.

Nerve growth factor (NGF) reduces and NGF antibody exacerbates retinal damage induced in rabbit by experimental ocular hypertension

BACKGROUND

It has been shown that intravitreal injection of NGF inhibits ganglion cell degeneration after optic nerve transection and ischemic injury. The aim of our study was to investigate the presence of NGF in aqueous humor and its involvement in retinal damage during ocular hypertension.

METHODS

We used an experimental model of ocular hypertension in rabbit. Before treatment and 4, 10 and 15 days after induction of hypertension, we evaluated histological retinal damage and NGF levels in aqueous humor using an immunoenzymatic assay. Polyclonal anti-NGF antibodies were injected intravitreally into one eye of each rabbit (n = 6), and the animals were killed after 4 days of hypertension. Another group of rabbits (n = 12) was injected retro-ocularly with NGF and killed after 10 or 15 days of treatment for histologic evaluation of the retina.

RESULTS

Our data show that experimental ocular hypertension in adult rabbits induces retinal damage and enhances local NGF levels. The highest NGF value was found after 4 days of intraocular hypertension: high levels persisted, though to a lesser extent, for up to 15 days. Histological examination revealed that the number of retinal ganglion cells (RGC) remained unchanged during the first 4 days but decreased at 10 days. These studies also showed that retro-ocular administration of NGF reduced RGC loss, whereas intraocular injection of NGF antibodies, which inhibited the endogenous NGF, exacerbated the retinal insult.

CONCLUSION

These findings demonstrate a protective effect of NGF on RGC damaged by ocular hypertension and prompt further investigations to evaluate a possible therapeutic use of NGF to retard RGC death in humans.

A hypothalamic neuronal cell line persistently infected with scrapie prions exhibits apoptosis

Neuronal death and vacuolation are characteristics of the CNS degeneration found in prion diseases. Relatively few cultured cell lines have been identified that can be persistently infected with scrapie prions, and none of these cells show cytopathologic changes reminiscent of prion neuropathology. The differentiated neuronal cell line GT1, established from gonadotropin hormone releasing-hormone neurons immortalized by genetically targeted tumorigenesis in transgenic mice (P. L. Mellon, JJ. Windle, P. C. Goldsmith, C. A. Padula, J. L. Roberts, and R. I. Weiner, Neuron 5:1-10, 1990), was examined for its ability to support prion formation. We found that GT1 cells could be persistently infected with mouse RML prions and that conditioned medium from infected cells could transfer prions to uninfected cells. In many but not all experiments, a subpopulation of cells showed reduced viability, morphological signs of neurodegeneration and vacuolation, and features of apoptosis. Subclones of GT1 cells that were stably transfected with the trk4 gene encoding the high-affinity nerve growth factor (NGF) receptor (GT1-trk) could also be persistently infected. NGF increased the viability of the scrapie-infected GT1-trk cells and reduced the morphological and biochemical signs of vacuolation and apoptosis. GT1 cells represent a novel system for studying the molecular mechanisms underlying prion infectivity and subsequent neurodegenerative changes.

The expanding role of nerve growth factor: from neurotrophic activity to immunologic diseases

Numerous studies published in the last 10-15 years have shown that nerve growth factor (NGF), a polypeptide originally discovered in connection with its neurotrophic activity, also acts on cells of the immune system. NGF has been found in various immune organs including the spleen, lymph nodes, and thymus, and cells such as mast cells, eosinophils, and B and T cells. The circulating levels of NGF increase in inflammatory responses, in various autoimmune diseases, in parasitic infections, and in allergic diseases. Stress-related events both in animal models and in man also result in an increase of NGF, suggesting that this molecule is involved in neuroendocrine functions. The rapid release of NGF is part of an alerting signal in response to either psychologically stressful or anxiogenic conditions in response to homeostatic alteration. Thus, the inflammation and stress-induced increase in NGF might alone or in association with other biologic mediators induce the activation of immune cells during immunologic insults. A clearer understanding of the role of NGF in these events may be useful to identify the mechanisms implicated in certain neuroimmune and immune dysfunctions.

Trk-like proteins during the post-hatching growth of the avian bursa of Fabricius

Neurotrophins are growth factors acting on responsive cells through membrane receptors identified as Trk tyrosine kinase proteins (A, B and C). Trks are present in the mammalian lymphoid organs, and indirect evidence suggests that they are also present in the avian bursa of Fabricius. This study was designed to analyze (a) the occurrence and localization of Trk proteins in the bursa of Fabricius; and (b) whether the post-hatching growth of the organ (from hatching to 75 days) involves cells expressing Trk proteins. We used pigeon bursae of Fabricius, and rabbit polyclonal antibodies against specific epitopes of TrkA, TrkB and TrkC. Cytokeratins and vimentin were studied in parallel with label non-lymphoid cells of the bursal follicles. Immunoreactivity (IR) for all assessed antigens was found in specific non-lymphoid cells. From hatching to 15 days, TrkB-like IR was found outside the follicles in cells localized beneath the follicle associated (FAE) and interfollicular (IFE) epithelium. Between 30-75 days TrkB-like IR labelled the medullary secretory dendritic cells (SDC). The density of SDC displaying IR increased up to 60 days. TrkA-like and TrkC-like IR was primarily observed in FAE and IFE, but also in the medullary reticular epithelial cells (REC) up to 15 days. The present results provide evidence of the occurrence, localization and post-hatching changes in Trk proteins in avian bursa of Fabricius. Trks were localized on non-lymphoid cells which participate in providing the adequate microenvironment for B lymphocyte maturation. Furthermore, the cell segregation in the expression of Trks suggests specific roles for their ligands in controlling the function of medullary SDC and REC, hence bursal lymphoid follicle physiology.

Nerve growth factor delays retinal degeneration in C3H mice

BACKGROUND

The aim of the present study was to investigate the biological role of nerve growth factor (NGF) on retinal degeneration in the C3H mouse strain. This strain is characterized by a single gene mutation (rd) which leads to photoreceptor degeneration resembling human retinitis pigmentosa.

METHODS

Neural retinas from 1- to 25 day-old C3H mice were dissected from outer ocular tissues, dissociated in cell suspension, stained with a vital dye and counted in a hemocytometer. For in vivo study, NGF was injected into the intraocular or retro-ocular area, and at the end of the treatment the mice were killed. The eyes were enucleated, fixed and cut by cryostat into 14-microns serial sections. The serial sections were stained with hematoxylin-eosin and the outer nuclear layer (ONL) was measured using a computerized image analysis system.

RESULTS

An intraocular injection of NGF, or repeated retro-ocular injections, induced a significant increase in ONL thickness compared to controls.

CONCLUSION

Our data show that NGF inhibits retinal degeneration in C3H mice. The mechanism(s) underlying the protective action of NGF against retinal cell death remains to be established.