p75NTR in the spleen: age-dependent changes, effect of NGF and 4-methylcatechol treatment, and structural changes in p75NTR-deficient mice

Nerve Growth Factor Receptor (NGFR/p75NTR) of the Small-Spotted Catshark (Scyliorhinus canicula): Evolutionary Conservation and Brain Function

The p75NTR receptor, a member of the tumor necrosis factor (TNF) receptor superfamily, can participate in signaling pathways either by forming heteromeric complexes with other receptors, such as the Trk family (tropomyosin receptor kinases), or by functioning independently. p75NTR was investigated prevalently in the brain and retina of mammals, whereas almost nothing is known about its conservation among species. Here, we reconstructed the phylogenetic arb of p75NTR and described for the first time the p75NTR expression in the brain of the basal vertebrate Chondrichthyan Scyliorhinus canicula (S. canicula), uncovering the existing parallelism between ancient vertebrates and mammals. p75NTR functional conservation among vertebrates was further investigated by cloning the S. canicula nerve growth factor (NGF) and performing the canonical posterior commissure (PC)-12 differentiation assay, which results in standard neurite-like production. We then investigated the S. canicula p75NTR, which proves to be capable of complementing a specific clone of PC-12 lacking p75NTR (PC-12 p75NTR-/-). All together, our results highlighted the expression and functional conservation of p75NTR among vertebrates during the evolution.

NGFR regulates stromal cell activation in germinal centers

Nerve growth factor receptor (NGFR) is expressed by follicular dendritic cells (FDCs). However, the role of NGFR in the humoral response is not well defined. Here, we study the effect of Ngfr loss on lymph node organization and function, demonstrating that Ngfr depletion leads to spontaneous germinal center (GC) formation and an expansion of the GC B cell compartment. In accordance with this effect, stromal cells are altered in Ngfr-/- mice with a higher frequency of FDCs, characterized by CD21/35, MAdCAM-1, and VCAM-1 overexpression. GCs are located ectopically in Ngfr-/- mice, with lost polarization together with impaired high-affinity antibody production and an increase in circulating autoantibodies. We observe higher levels of autoantibodies in Bcl2 Tg/Ngfr-/- mice, concomitant with a higher incidence of autoimmunity and lower overall survival. Our work shows that NGFR is involved in maintaining GC structure and function, participating in GC activation, antibody production, and immune tolerance.

Transient receptor potential vanilloid subtype 1 depletion mediates mechanical allodynia through cellular signal alterations in small-fiber neuropathy

Transient receptor potential vanilloid subtype 1 (TRPV1) is a polymodal nociceptor that monitors noxious thermal sensations. Few studies have addressed the role of TRPV1 in mechanical allodynia in small-fiber neuropathy (SFN) caused by sensory nerve damage. Accordingly, this article reviews the putative mechanisms of TRPV1 depletion that mediates mechanical allodynia in SFN. The intraepidermal nerve fibers (IENFs) degeneration and sensory neuronal injury are the primary characteristics of SFN. Intraepidermal nerve fibers are mainly C-polymodal nociceptors and Aδ-fibers, which mediated allodynic pain after neuronal sensitization. TRPV1 depletion by highly potent neurotoxins induces the upregulation of activating transcription factor 3 and IENFs degeneration which mimics SFN. TRPV1 is predominately expressed by the peptidergic than nonpeptidergic nociceptors, and these neurochemical discrepancies provided the basis of the distinct pathways of thermal analgesia and mechanical allodynia. The depletion of peptidergic nociceptors and their IENFs cause thermal analgesia and sensitized nonpeptidergic nociceptors respond to mechanical allodynia. These distinct pathways of noxious stimuli suggested determined by the neurochemical-dependent neurotrophin cognate receptors such as TrkA and Ret receptors. The neurogenic inflammation after TRPV1 depletion also sensitized Ret receptors which results in mechanical allodynia. The activation of spinal TRPV1(+) neurons may contribute to mechanical allodynia. Also, an imbalance in adenosinergic analgesic signaling in sensory neurons such as the downregulation of prostatic acid phosphatase and adenosine A1 receptors, which colocalized with TRPV1 as a membrane microdomain also correlated with the development of mechanical allodynia. Collectively, TRPV1 depletion-induced mechanical allodynia involves a complicated cascade of cellular signaling alterations.

Alteration of testicular regulatory and functional molecules following long-time exposure to 900 MHz RFW emitted from BTS

The aim of this investigation was to evaluate changes in testosterone and some of the functional and regulatory molecules of testis such as P450scc, steroidogenic acute regulatory protein (StAR), tumour necrosis factor-α (TNF-α), interleukin-1α (IL-1α), interleukin-1β (IL-1β) and nerve growth factor (NGF) following exposure to 900 MHz radio frequency (RF). Thirty adult male Sprague Dawley rats (190 ± 20 g BW) were randomly classified in three equal groups, control (sham, without any exposure), short-time exposure (2 hr) (STE) and long-time exposure (4 hr) (LTE). The exposure was performed for 30 consecutive days. The testosterone level in both exposed groups was significantly less than control (p < .05). Level of TNF-α in both exposed groups was significantly greater than control (p < .05). IL-1α and NGF levels in LTE were significantly higher than the STE and control groups (p < .05). Level of IL-1β in LTE was significantly higher than control (p < .05). Expression of both P450scc and StAR mRNA was significantly down-regulated in both exposed groups compared to control (p < .05). Our results showed that RFW can affect testis and reproductive function through changes in factors, which are important during steroidogenesis, and also through changes in inflammatory factors, which regulate Leydig cell functions.

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.

Neurotrophic and antioxidant effects of silymarin comparable to 4-methylcatechol in protection against gentamicin-induced ototoxicity in guinea pigs

BACKGROUND

Despite that gentamicin is a very effective aminoglycoside, its potential ototoxicity which is of irreversible nature makes a challenge and limitation for its use. This study was designed to investigate possible neurotrophic and antioxidant effects of silymarin comparable to 4-methylcatechol in protection against gentamicin-induced ototoxicity.

METHODS AND RESULTS

Twenty pigmented guinea pigs were divided into four equal groups, where group I served as normal control group. The other groups received gentamicin (120 mg/kg/day, ip) for 19 days where group II given vehicle of 1% CMC, group III and group IV were pre-treated 2h before gentamicin by 4-methylcatechol (10 μg/kg, ip) and silymarin (100mg/kg, oral gavage), respectively. The main findings indicated that silymarin exhibited restoration of nerve growth factor (NGF) levels and increased tropomyosin-related kinase receptors-A (Trk-A) m-RNA expression in cochlear tissue and preservation of hair cells of organ of Corti by scanning electron microscopy (SEM) with significant decrease in auditory brainstem response (ABR) threshold compared to 4-methylcatechol. Only silymarin caused significant amelioration in oxidative stress state by reducing malondialdehyde (MDA) levels and increasing catalase activity.

CONCLUSIONS

Silymarin exerts superiority over 4-methylcatechol when recommended as protective agent against gentamicin ototoxicity based on its efficient neurotrophic and antioxidant activities.

Development of Adenoviral Delivery Systems to Target Hepatic Stellate Cells In Vivo

Hepatic stellate cells (HSCs) are known as initiator cells that induce liver fibrosis upon intoxication or other noxes. Deactivation of this ongoing remodeling process of liver parenchyma into fibrotic tissue induced by HSCs is an interesting goal to be achieved by targeted genetic modification of HSCs. The most widely applied approach in gene therapy is the utilization of specifically targeted vectors based on Adenovirus (Ad) serotype 5. To narrow down the otherwise ubiquitous tropism of parental Ad, two modifications are required: a) ablating the native tropism and b) redirecting the vector particles towards a specific entity solely present on the cells of interest. Therefore, we designed a peptide of the nerve growth factor (NGF_p) with specific affinity for the p75 neurotrophin receptor (p75NTR) present on HSCs. Coupling of this NGF_p to vector particles was done either via chemical conjugation using bifunctional polyethylene glycol (PEG) or, alternatively, by molecular bridging with a fusion protein specific for viral fiber knob and p75NTR. Both Ad vectors transmit the gene for the green fluorescent protein (GFP). GFP expression was monitored in vitro on primary murine HSCs as well as after systemic administration in mice with healthy and fibrotic livers using intravital fluorescence microscopy. Coupling of NGF_p to Ad via S11 and/or PEGylation resulted in markedly reduced liver tropism and an enhanced adenoviral-mediated gene transfer to HSCs. Transduction efficiency of both specific Ads was uniformly higher in fibrotic livers, whereas Ad.GFP-S11-NGF_p transduce activated HSCs better than Ad.GFP-PEG-NGF_p. These experiments contribute to the development of a targeted gene transfer system to specifically deliver antifibrotic compounds into activated HSCs by systemically applied adenoviral vector modified with NGF_p.

Expression of nerve growth factor and its receptor in distracted tibial nerve after limb lengthening

Despite many experimental and clinical studies conducted on distraction osteogenesis (DO) in the past decade, changes in the surrounding tissues that occur after the procedure remains poorly understood. To study the biochemical changes of recovery in nerve tissues upon DO-induced nerve injury, we prepared a rabbit model of tibia lengthening to observe the expression pattern of nerve growth factor (NGF) and low-affinity NGF receptor (p75NGFR) in the distracted tibial nerve. The distracted tibial nerve was harvested at various time points during the consolidation period of new bone formation and immunohistochemical staining was performed to detect the expression of NGF and p75NGFR. The expression levels of NGF and p75NGFR were found to be different at various times after DO. The changes in expression of these two cellular factors show similar tendencies with significantly elevated expression in Schwann cells at 7 and 14 days after distraction, but low or undetectable levels of expression at 0, 28, and 56 days. These results suggest that NGF and p75NGFR may play important roles in the adaptive process of the distracted nerve. NGF and p75NGFR are autocrine growth factors present in the distracted nerve during the early consolidation period. NGF interacts with p75NGFR to promote damage repair and reconstruction of nerves. Together, this study furthers the understanding of the relative mechanisms of nerve repair, as well as provides a further basis for the clinical application of neurotrophins.

Effects of 4-methylcatechol on skin reinnervation: promotion of cutaneous nerve regeneration after crush injury

We assessed the effects of treatment with 4-methylcatechol (4MC), a known inducer of nerve growth factor, on peripheral nerve regeneration by analyzing cutaneous and muscular reinnervation in mice after sciatic nerve crush injury. At 3 months postinjury, the skin innervation index was significantly higher in the 4MC group than the control group (p=0.0002); there was also increased unmyelinated fiber density (p=0.0042) and unmyelinated fibers/Remak bundle (p = 0.001) in sural nerves, indicating unmyelinated nerve fiber regeneration. These changes were accompanied by increases of transcripts for nerve growth factor (p = 0.0026) and glial cell line-derived neurotrophic factor (p=0.03) in the 4MC group. In contrast, muscle innervation indices were similar in both groups and were higher than the skin innervation index (p < 0.0001). The regeneration of myelinated nerve fibers, as assessed by fiber density, diameter and g ratio analyses in sural nerves, and amplitudes of muscle action potential in sciatic nerves, was similar in both groups. Taken together, these data suggest that 4MC specifically promoted the regeneration of unmyelinated nerve fibers and reinnervation of the skin by increasing the expression of nerve growth factor and glial cell line-derived neurotrophic factor.

Enhancement of cutaneous nerve regeneration by 4-methylcatechol in resiniferatoxin-induced neuropathy

To generate an experimental neuropathy model in which small-diameter sensory nerves are specifically affected and to test a potential treatment, adult mice were given a single injection (50 microg/kg, i.p.) of the capsaicin analog resiniferatoxin (RTX). On Day 7 after RTX treatment, there was a 53% reduction in unmyelinated nerve density in the medial plantar nerve (p = 0.0067) and a 66% reduction in epidermal nerve density of hind paw skin (p = 0.0004) compared with vehicle-treated controls. Substance P-immunoreactive dorsal root ganglion neurons were also markedly depleted (p = 0.0001). These effects were associated with the functional deficit of prolonged withdrawal latencies to heat stimuli (p = 0.0007) on a hot plate test. The potential therapeutic effects of 4-methylcatechol (4MC) on this neuropathy were then tested by daily injections of 4MC (10 microg/kg, i.p.) from Days 7 to 35 after neuropathy induction. On Day 35, 4MC-treated mice had an increase in unmyelinated (p = 0.014) and epidermal nerve (p = 0.0013) densities and a reduction in thermal withdrawal latency (p = 0.0091) compared with RTX-only controls. These results indicate that 4MC promoted regeneration of unmyelinated nerves in experimental RTX-induced neuropathy and enhanced function.

Effects of increased nerve growth factor plasma levels on the expression of TrkA and p75 in rat testicles

In addition to their well-known roles within the nervous system, the neurotrophins and their receptors regulate some functions in the reproductive system. In this study we used combined morphological and immunohistochemical techniques to investigate the presence and cellular localization in the rat testicle of the two receptors of nerve growth factor (NGF), i.e. TrkA and p75(NTR). Furthermore, to evaluate whether increased plasma levels of NGF affect the ageing process, 4-methylcathechol (4-MC), an inductor of NGF synthesis, was administered. Both TrkA and p75(NTR) were expressed in rat testicles, but the pattern and intensity of immunoreaction were marginally different between them. In adult rats TrkA was expressed in spermatozoa and spermatids, and p75 was expressed in spermatogonia. In newborn rats TrkA immunoreactivity was found in the Leydig cells, whereas p75 was detected in a cellular layer that surrounds the seminiferous tubules. In adult treated animals the immunoreaction for TrkA and p75(NTR) was also localized in the spermatocytes, whereas in newborn treated rats no changes in the pattern of immunoreaction was observed. The present findings suggest a role of the NGF/TrkA/p75 system in the physiology of reproduction, but the practical relevance of this remains to be established.

Expression of the neurotrophin receptor TrkB in the mouse liver

Neurotrophins acting through Trk signal-transducing receptors play essential roles in the nervous system, and probably in some non-neuronal tissues. In the present study, we used RT-PCR, Western-blot and immunohistochemistry to investigate the occurrence and cellular localization of TrkB in the mouse liver, from newborns to 6 months. Furthermore, the structure of the liver in mice carrying a mutation in the trkB gene, resulting in a non-functional protein, was studied. The analysis of the DNA sequence showed that hepatic trkB gene is identical to the cerebral one, and TrkB mRNA and TrkB full-length protein (145 kDa) were detected at all the ages sampled. Immunohistochemistry revealed age-dependent changes in the pattern of TrkB expression. From 0 to 15 days, the TrkB was detected in morphologically and immunohistochemically identified monocyte-macrophage-dendric cells scattered throughout the organ, while in animals 3- and 6-months-old it was restricted to nerve fibres. Interestingly, there was a parallelism between TrkB expression by monocyte-macrophage-dendric cells and the presence of hepatic erythroblastic islands. In agreement with a possible role of TrkB on hepatic haematopoiesis, the liver of 15 days old TrkB (-/-) mice still contained erythroblastic islands, whereas they were absent in the wild-type littermates. Another striking finding was the absence of nerve profiles in the TrkB (-/-) animals. All together, present results support the role of TrkB in the murine liver in maintaining the innervation of the organ, and more importantly throughout an unknown mechanism in controlling the hepatic haematopoietic function.

Expression of TrkB in the murine kidney

Neurotrophins acting through Trk signal-transducing receptors play essential roles in the nervous system, and probably in some nonneuronal tissues. In the present study we used Western-blot and immunohistochemistry to investigate the occurrence and cellular localization of TrkB in the mouse kidney. Furthermore, the structure and ultrastructure of the kidney in mice carrying a mutation in the trkB gene were analyzed. TrkB in the kidney was identical to the cerebral one (145 kDa). Since the antibody used recognize a sequence within the tyrosine-kinase domain of TrkB, the renal TrkB receptor identified here must be regarded as able to mediate biological effects of their ligands. TrkB immunoreactivity was restricted to the juxtaglomerular apparatus, including differentiated vascular cells and extaglomerular mesangial cells. In these cells, TrkB colocalized with renin. The structural analysis revealed no major changes in the kidney structure of TrkB-deficient mice, with the exception of a significant reduction of the glomerular area. Nevertheless, in these animals there was an apparent increase in the number of extraglomerular mesangial cells (which retain the ability to synthesize renin) and absence of the macula densa. Taken together, these results strongly suggest a role of TrkB and their ligands in the control of the normal development and maintenance of the juxtaglomerular apparatus.

Vertebrate thymus and the neurotrophin system

An immunomodulary role has been proposed for growth factors included in the family of neurotrophins. This is supported by the presence of both neurotrophins and neurotrophin receptors in the immune organs and some immunocompetent cells, the in vitro and in vivo effects of the neurotrophins on the immune cells, and the structural changes of lymphoid organs in mice deficient in neurotrophins and their receptors. The current data strongly indicate that neurotrophins regulate the biology of thymic stromal cells and T cells, including survival, and are involved in the thymic organogenesis. This review compiles the available data about the occurrence and distribution of neurotrophins and their signaling receptors (Trk proteins and p75(NTR)) in the vertebrate thymus and the possible contribution of these molecules to the thymic microenvironment and, therefore, to the T cells differentiation.

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.