Expression Of TrkA Receptors Research Articles

Cytotoxic effects of nerve growth factor and its combinations with chemotherapeutic drugs on anaplastoc astrocytoma, glioblastoma and medubloblastoma cells <i>in vitro</i>

BACKGROUND: Currently, the effectiveness of the treatment of malignant tumors using surgical resection, radiotherapy and chemotherapy is insufficient. Therefore, new research is needed to find alternative molecules with antitumor effects. It is known that nerve growth factor (NGF) inhibits invasion, migration, and angiogenesis of tumor cells. Studying the effects of NGF on brain tumors, as well as its combinations with chemotherapy drugs used in medicine, may contribute to the development of new treatment regimens for malignant neoplasms in the central nervous system. AIM: The purpose of this study is an exploration the molecular and cellular mechanisms of anticancer effects of individual and combined preparations of NGF and chemotherapeutic drugs on brain tumor cells (gliomas C6, U251, anaplastic astrocytoma, glioblastoma and medulloblastoma). MATERIALS AND METHODS: The study was performed on rat glioma C6, human U251 glioma cell lines, as well as on primary cells of anaplastic astrocytoma (n = 9), glioblastoma (n = 9) and medulloblastoma (n = 38) patients. The cytotoxicity of chemotherapeutic drugs, NGF and their combinations against tumor cells was assessed using the MTT assay. The expression of TrkA and p75 receptors on anaplastic astrocytoma, glioblastoma and medulloblastoma cells was assessed by immunofluorescence analysis using anti-TrkA and anti-p75 monoclonal antibodies. RESULTS: Nerve growth factor exhibits in vitro cytotoxic activity that exceeds the activity of chemotherapy drugs towards rat glioma C6, human U251, anaplastic astrocytoma (AA), glioblastoma (GBM) and medulloblastoma cells. The cytotoxic activity of NGF in combination with chemotherapy drugs is significantly higher than the activity of the individual NGF drug against medulloblastoma cells, while against anaplastic astrocytoma cells it is comparable to the indicators of the isolated action of NGF, and lower for glioblastoma cells. The effectiveness of the cytotoxic effect of the combinations NGF + cisplatin and NGF + temozolomide (TMZ) on AA and GBM cells correlates with both the expression of TrkA, p75 receptors, and their coexpression, indicating that expression indicators can be considered as markers of tumor cell sensitivity to NGF. CONCLUSIONS: The data obtained allow us to consider NGF as a potential anticancer drug for the treatment of brain tumors. Thus, NGF can act as a potential anticancer drug for the development of new therapeutic regimens for brain tumors.

The effects of painless nerve growth factor on human microglia polarization.

Previous studies in the rat suggest that microglial cells represent a potential druggable target for nerve growth factor (NGF) in the brain. The painless human Nerve Growth Factor (hNGFp) is a recombinant mutated form of human nerve growth factor (hNGF) that shows identical neurotrophic and neuroprotective properties of wild-type NGF but displays at least 10-fold lower algogenic activity. From the pharmacological point of view, hNGFp is a biased tropomyosin receptor kinase A (TrkA) agonist and displays a significantly lower affinity for the p75 neurotrophin receptor (p75NTR). This study aimed to evaluate the expression of TrkA and p75NTR NGF receptors in two different human microglia cell lines, and to investigate the effects of hNGFp and wild-type NGF (NGF) on L-arginine metabolism, taken as a marker of microglia polarization. Both NGF receptors are expressed in human microglia cell lines and are effective in transducing signals triggered by NGF and hNGFp. The latter and, to a lesser extent, NGF inhibit cytokine-stimulated inducible nitric oxide synthase (iNOS) expression and nitric oxide (NO) production in these cells. Conversely NGF but not hNGFp stimulates arginase-mediated urea production.

BDE-47 induced PC-12 cell differentiation via TrkA downstream pathways and caused the loss of hippocampal neurons in BALB/c mice

As the most abundant congener of polybrominated diphenyl ethers (PBDEs) detected in environment and human biotic samples, 2, 2′, 4, 4′-tetrabromodiphenyl ether (BDE-47) has been found to accumulate in brain and induce neurotoxicity, however, the detailed mechanism has not been clearly elucidated. To investigate the neurotoxicity of BDE-47, undifferentiated PC-12 cells were exposed to different doses of BDE-47, and BDE-47 dissolved in corn oil was orally administered to mice for 8 consecutive weeks. Our data showed that BDE-47 obviously changed cell morphology, altered cell viability, promoted cell apoptosis, and induced reactive oxygen species (ROS) production. BDE-47 promoted the differentiation of PC-12 cells by enhancing the expression of TrkA receptor and the phosphorylation levels of ERK and Akt. Moreover, BDE-47-induced differentiation of PC-12 cells was suppressed by inhibitors of corresponding pathways (MAPK/ERK and PI3K/Akt). H&E staining of brain showed neurons in DG and CA1 areas of hippocampus decreased after BDE-47 exposure. Transcriptome sequencing of brain tissue suggested that multiple signaling pathways related to neuron death and nerve function were significantly regulated. In conclusion, these results provided new evidence for revealing the neurotoxicity of BDE-47, and offered important experimental basis for environmental controlling and post-exposure health risk assessment of BDE-47.

Effect of Aloe vera on the Expression of Nerve Factors, p75 and TrkA Receptors in the Hippocampus of Diabetic Rats

Effect of Aloe vera on the Expression of Nerve Factors, p75 and TrkA Receptors in the Hippocampus of Diabetic Rats

Related expression of TRKA and P75 receptors and the changing copy number of MYC-oncogenes determine the sensitivity of brain tumor cells to the treatment of the nerve growth factor in combination with cisplatin and temozolomide.

Objectives Oncological diseases are an urgent medical and social problem. The chemotherapy induces not only the death of the tumor cells but also contributes to the development of their multidrug resistance and death of the healthy cells and tissues. In this regard, the search for the new pharmacological substances with anticancer activity against drug-resistant tumors is of utmost importance. In the present study we primarily investigated the correlation between the expression of TrkA and p75 receptors with the nerve growth factor (NGF) and cisplatin or temozolomide sensitivity of anaplastic astrocytoma (AA), glioblastoma (GB) and medulloblastoma (MB) cell cultures. We then evaluated the changing of copy numbers of MYCC and MYCN and its correlation with cytotoxicity index (CI) in MBcells under NGF exposition. Methods The primary cell cultures were obtained from the tumor biopsy samples of the patients with AA (n=5), GB (n=7) or MB (n=25) prior to radiotherapy and chemotherapy. The cytotoxicity effect of NGF and its combinations with cisplatin or temozolomide, the relative expression of TrkA and p75 receptors, its correlations with CI in AA, GB and MB primary cell cultures were studied by trypan blue cytotoxicity assay and immunofluorescence staining respectively. The effect of NGF on MYCC and MYCN copy numbers in MBcell cultures was studied by fluorescence in situ hybridization. Results We found that the expression of TrkA and p75 receptors (p=0.03) and its ratio (p=0.0004) depends on the sensitivity of AA and GBcells to treatment with NGF and its combinations with cisplatin or temozolomide. NGF reduces (p<0.05) the quantity of MBcells with six or eight copies of MYCN and three or eight copies of MYCC. Besides, NGF increases (p<0.05) the quantity of MBcells containing two copies of both oncogenes. The negative correlation (r=-0.65, p<0.0001) is established between MYCC average copy numbers and CI of NGF in MBcells. Conclusions The relative expression of NGF receptors (TrkA/p75) and its correlation with CI of NGF and its combinations in AA and GBcells point to the mechanism involving a cell death signaling pathway. NGF downregulates (p<0.05) some increased copy numbers of MYCC and MYCN in the human MBcell cultures, and upregulates normal two copies of both oncogenes (p<0.05).

Related expression of TRKA and P75 receptors and the changing copy number of MYC-oncogenes determine the sensitivity of brain tumor cells to the treatment of the nerve growth factor in combination with cisplatin and temozolomide.

Oncological diseases are an urgent medical and social problem. The chemotherapy induces not only the death of the tumor cells but also contributes to the development of their multidrug resistance and death of the healthy cells and tissues. In this regard, the search for the new pharmacological substances with anticancer activity against drug-resistant tumors is of utmost importance. In the present study we primarily investigated the correlation between the expression of TrkA and p75 receptors with the nerve growth factor (NGF) and cisplatin or temozolomide sensitivity of anaplastic astrocytoma (AA), glioblastoma (GB) and medulloblastoma (MB) cell cultures. We then evaluated the changing of copy numbers of MYCC and MYCN and its correlation with cytotoxicity index (CI) in MBcells under NGF exposition. The primary cell cultures were obtained from the tumor biopsy samples of the patients with AA (n=5), GB (n=7) or MB (n=25) prior to radiotherapy and chemotherapy. The cytotoxicity effect of NGF and its combinations with cisplatin or temozolomide, the relative expression of TrkA and p75 receptors, its correlations with CI in AA, GB and MB primary cell cultures were studied by trypan blue cytotoxicity assay and immunofluorescence staining respectively. The effect of NGF on MYCC and MYCN copy numbers in MBcell cultures was studied by fluorescence in situ hybridization. We found that the expression of TrkA and p75 receptors (p=0.03) and its ratio (p=0.0004) depends on the sensitivity of AA and GBcells to treatment with NGF and its combinations with cisplatin or temozolomide. NGF reduces (p<0.05) the quantity of MBcells with six or eight copies of MYCN and three or eight copies of MYCC. Besides, NGF increases (p<0.05) the quantity of MBcells containing two copies of both oncogenes. The negative correlation (r=-0.65, p<0.0001) is established between MYCC average copy numbers and CI of NGF in MBcells. The relative expression of NGF receptors (TrkA/p75) and its correlation with CI of NGF and its combinations in AA and GBcells point to the mechanism involving a cell death signaling pathway. NGF downregulates (p<0.05) some increased copy numbers of MYCC and MYCN in the human MBcell cultures, and upregulates normal two copies of both oncogenes (p<0.05).

Cyclic tensile stimulation enrichment of Schwann cell-laden auxetic hydrogel scaffolds towards peripheral nerve tissue engineering

The nervous system in the body is a complex network of nerves and cells that regulates several functions. Neural regeneration is a complex process that involves matrix secretion and remodeling, in which growth factors play a huge role in regulating such processes. Recent studies demonstrated the structures and topography of scaffolds are expected to provide a spectrum of unique biomimetic 3D microenvironments to regulate cell behavior. In this study, we fabricated auxetic scaffolds using fish gelatin methacrylamide and evaluated the effects of cyclic tensile stimulation effects on the neural differentiation capabilities of human Schwann cells. The auxetic hydrogels were found to withstand up to 20% tensile strain without tears, and the hydrogels had lost only about 10% weight after immersed for 14 days. The tensile forces were able to enhance cell viability and proliferation as compared to a static culture. In addition, the secretion of neural regeneration-related proteins was enhanced in the tensile stimulation group. The cell-laden auxetic scaffold with tensile stimulation caused improvement in the nerve growth factor and TRKA receptor expression. This is the first study to combine tensile stimulation with NGF. The initial results showed the positive potential of such conditions being applied in clinical applications.

A new porous cationic metal–organic framework: selective sorption of organic dyes and treatment on neural stem cells during spinal cord injury treatment

A novel metal–organic framework containing Co(II) of {(Me2NH2)4[Co12(OH)4(abtc)6 (H2O)12]·14H2O}n (1) has been synthesized via Co(NO3)2·6H2O to react with the 3,3′,5,5′-azobenzenetetracarboxylic acid (H4abtc) ligand under solvothermal conditions. Furthermore, methylene blue (MB) can easily replace free cations; after half a day, more than 90% of the MB (10−5 M) is absorbed selectively, and it makes the title compound become a good medium for the separation and adsorption of the dye. In biological section, the enhancement activity of the compound on the nerve growth factor for the spinal cord injury treatment was evaluated. The relative gene expression of trkA receptor was measured with reverse transcription polymerase chain reaction. In addition to this, the activation of PI3K/Akt signaling pathway in neural stem cells after treated by compound was evaluated with western blot. The results of potential binding models were predicted by molecular docking, and the binding poses provided possible binding mechanisms of the functional groups of the complex to the TRKA protein.

Disease activity-dependent expression of nerve growth factor TRKA and P75 receptors on elevated dendritic cells and peripheral leucocytes in patients with systemic lupus erythematosus.

The nervous system modulates rheumatic diseases in neurogenic inflammation (NI). Nerve growth factor (NGF) plays a pivotal role in NI and chronic nociceptive pain. However, the role of NGF in autoimmune inflammatory diseases is not well understood. The aim of this study was to analyse NGF high- (TrkA) and low-affinity (p75) receptors on all major leucocyte subsets of patients with systemic lupus erythematosus (SLE) as a potential indicator of NI. A total of 13 patients were analysed by fluorescence-activated cell sorting and compared to 13 healthy control (HC) subjects. Patients were also stratified for high or low disease activity (CRP, ESR, SLEDAI, ANA, anti-dsDNA and C3/C4). Statistics included the Kruskal-Wallis test and Mann-Whitney U-test. When comparing patients and HC, TrkA was not differentially expressed. In contrast, p75 was increased on CD16+ and CD56+ leucocytes in patients. CD11c+ dendritic cells (DC) were in total increased in SLE. DCs were also significantly elevated in active patients. Furthermore, we found an intermediate CD11b+ population strongly expressing TrkA in patients and HC. We demonstrate for the first time differential NGF receptor expression in SLE. The increased CD11c+ DCs might indicate additional activation in SLE.

Potential Effects of Indole-3-Lactic Acid, a Metabolite of Human Bifidobacteria, on NGF-induced Neurite Outgrowth in PC12 Cells.

Gut microbiota-derived tryptophan metabolites such as indole derivatives are an integral part of host metabolome that could mediate gut–brain communication and contribute to host homeostasis. We previously reported that infant-type Human-Residential Bifidobacteria (HRB) produced higher levels of indole-3-lactic acid (ILA), suggesting the former might play a specific role in microbiota–host crosstalk by producing ILA in human infants. Nonetheless, the biological meaning of bifidobacteria-derived ILA in infant health development remains obscure. Here, we sought to explore the potential role of ILA in neuronal differentiation. We examined the neurite outgrowth and acetylcholinesterase (AchE) activity of PC12 cells following exposure to ILA and NGF induction. We found that ILA substantially enhanced NGF-induced neurite outgrowth of PC12 cells in a dose-dependent manner, and had the most prominent effect at 100 nM. Significant increases in the expression of TrkA receptor, ERK1/2 and CREB were observed in ILA-treated PC12 cells, suggesting ILA potentiated NGF-induced neurite outgrowth through the Ras/ERK pathway. Additionally, ILA was found to act as the aryl hydrocarbon receptor (AhR) agonist and evoked NGF-induced neurite outgrowth in an AhR-mediated manner. These new findings provide clues into the potential involvement of ILA as the mediator in bifidobacterial host–microbiota crosstalk and neuronal developmental processes.

Mouse Nerve Growth Factor Facilitates the Growth of Interspinal Schwannoma Cells by Activating NGF Receptors.

ObjectiveNerve growth factor (NGF) is a member of the neurotrophic factor family and plays a vital role in the physiological processes of organisms, especially in the nervous system. Many recent studies have reported that NGF is also involved in the regulation of tumourigenesis by either promoting or suppressing tumor growth, which depends on the location and type of tumor. However, little is known regarding the effect of NGF on interspinal schwannoma (IS). In the present study, we aimed to explored whether mouse nerve growth factor (mNGF), which is widely used in the clinic, can influence the growth of interspinal schwannoma cells (ISCs) isolated from IS in vitro. MethodsISCs were isolated, cultured and identified by S-100 with immunofluorescence analysis. S-100-positive cells were divided into five groups, and separately cultured with various concentrations of mNGF (0 [phosphate buffered saline, PBS], 40, 80, 160, and 320 ng/mL) for 24 hours. Western blot and quantantive real time polymerase chain reaction (PCR) were applied to detect tyrosine kinase A (TrkA) receptor and p75 neurotrophin receptor (p75NTR) in each group. Crystal violet staining was selected to assess the effect of mNGF (160 ng/mL) on ISCs growth. ResultsISCs growth was enhanced by mNGF in a dose-dependent manner. The result of crystal violet staining revealed that it was significantly strengthened the cells growth kinetics when cultured with 160 ng/mL mNGF compared to PBS group. Western blot and quantantive real time PCR discovered that TrkA receptor and mRNA expression were both up-regualated under the condition of mNGF, expecially in 160 ng/mL, while the exoression of p75NTR demonstrated no difference among groups. ConclusionFrom these data, we conclude that exogenous mNGF can facilitate ISC growth by activating both TrkA receptor and p75NTR. In addition, patients who are suffering from IS should not be administered mNGF in the clinic.

Blocking colony stimulating factor 1 receptor (CSF-1R) and tropomyosin receptor kinase A (TrkA) improves the antitumor efficacy of immune checkpoint blockade

Abstract Established tumors can escape immune responses by secreting the cytokine colony stimulating factor 1 (CSF-1), stimulating the proliferation and recruitment of immunosuppressive myeloid cells to the tumor microenvironment by binding to colony stimulating factor-1 receptor (CSF-1R). Additionally, the neurotrophin nerve growth factor (NGF) is a ligand for tropomyosin receptor kinase A (TrkA), which is over-expressed on multiple tumor types. Signaling through TrkA via the Akt and MAPK pathways regulates survival, proliferation and invasion of tumor cells. This invasion can occur around nerves, and perineural invasion (PNI) has emerged as a critical pathological feature of multiple malignancies, resulting in poor prognosis. PLX7486 is a novel orally bioavailable small molecule Trk and CSF-1R dual-inhibitor that is now being studied in Phase I clinical trials. We hypothesized that PLX7486 would synergize with immune checkpoint blockade to result in a greater antitumor effect, by targeting Trk signaling directly on cancer cells and by inhibiting the recruitment of immunosuppressive myeloid cells through CSF-1R, thus enabling an improved antitumor T cell response. We confirmed the expression of TrkA receptor on multiple murine cancer cell lines in vitro and exposed them to PLX7486, showing a direct cytotoxic effect with an IC50 of 5–8μM on most of the cell lines and an inhibition of AKT pathway signaling in MC38 cells. PLX7486 also had a direct cytotoxic effect on bone marrow-derived macrophages and the murine macrophage cell line RAW264.7 with an IC50 &amp;lt;1μM, while it had no effect on activated T cells in vitro. Combining PLX7486 and anti-CTLA-4 or anti-PD-1 in vivo in MC38 and B16F10 tumor models resulted in increased antitumor effects.

THE RATIO OF TrkA AND p75 RECEPTORS ON THE CELL NEUROEPITHELIAL TUMORS – A NEW TARGET EFFECT OF NERVE GROWTH FACTOR WITH CISPLATIN AND TEMOZOLOMIDE AND THE COMBINATIONS

Objective. To study the change of expression of TrkA, p75 receptors and their ratio on the human anaplastic astrocytoma, glioblastoma and medulloblastoma cells cultures exposed to nerve growth factor (NGF) and its combination with cisplatin or temozolomide, to establish participation of expression of the receptors in sensitivity tumor cells to NGF and its combinations with chemotherapeutical drugs. Materials and methods . In primary cell cultures of anaplastic astrocytoma, glioblastoma and medulloblastoma were studied: 1) cytotoxicity effects of nerve growth factor and its combination with cisplatin or temozolomide; 2) the expression of TrkA, p75 receptors and the its ratio by immunofluorescence; 3) correlation between expression of TrkA, p75 receptors, the its ratio and index of cytotoxicity of reagents. Results. It is found that the expression of the receptors and the relationship depends on the tumor type and reagents’ mechanism of action. Expression of TrkA and p75 receptors and their ratio correlated with sensitivity of anaplastic astrocytoma and glioblastoma cells to NGF and its combination with cisplatin or temozolomide. Conclusion. Relative expression of TrkA/p75 receptor, and its coefficient of correlation with index of cytotoxicity point to a mechanism (signaling pathway), on which there is cell death.

The expression of the TrkA and TrkB high-affinity neurotrophin receptors in the rat hippocampus after intracerebroventricular administration of Aβ(25–35)

We studied the changes in the expression of high-affinity TrkA and TrkB receptors of the nerve-growth factor and brain-derived neurotrophic factor in the rat hippocampus at different time points after the administration of Aβ(25–35) into the lateral cerebral ventricles. Studies on TrkA and TrkB expression were performed using immunohistochemistry and the method of the real-time polymerase chain reaction. We found that intracerebroventricular administration of Aβ(25–35) to rats resulted in long-term alterations in the system of neurotrophic signaling in the hippocampus. Expression of the TrkA receptor increased 28 days after treatment, whereas expression of the TrkB receptor increased 12 days and then decreased by 28 days after the treatment. Thus, alterations in neurotrophin signaling may be involved in the mechanisms that are responsible for Aβ(25–35)-induced impairment of hippocampal functions in rats.

Receptor tyrosine kinase KIT may regulate expression of genes involved in spontaneous regression of neuroblastoma

Hallmark of neuroblastoma is an ability of this malignant tumor to undergo spontaneous regression or differentiation into benign tumor during any stage of the disease, but it is little known about mechanisms of these phenomena. We studied effect of receptor tyrosine kinase receptor KIT on expression of genes, which may be involved in tumor spontaneous regression. Downregulation of KIT expression by RNA interference in SH-SY5Y cells causes suppression of neurotrophin receptor NGFR expression that may promote the loss of sensibility of cells to nerve growth factors, also it causes upregulation of TrkA receptor expression which can stimulate cell differentiation or apoptosis in NGF dependent manner. Furthermore there is an upregulation of genes which stimulate malignant cell detection by immune system, such as genes of major histocompatibility complex HLA class I HLA-B and HLA-C, and interferon-γ receptors IFNGR1 and IFNGR2 genes. Thus KIT can mediate neuroblastoma cell sensibility to neurotrophins and immune system components--two factors directly contributing to spontaneous regression of neuroblastoma.

Elevated TrkA receptor expression is associated with all-trans retinoic acid-induced neuroblastoma differentiation.

Neuroblastoma is the most common and one of the deadliest among pediatric tumors; however, a subset of infants with neuroblastoma display spontaneous regression. The mechanism of spontaneous regression remains to be elucidated. TrkA plays an essential role in the differentiation and functionality of neurons; abundant TrkA expression is associated with favorable prognosis of neuroblastoma. All-trans retinoic acid (ATRA), a first-line drug for acute promyelocytic leukemia (APL) treatment, has been shown to induce differentiation and inhibit cell growth. Neuroblastoma tissues in our hospital inpatient were collected, primary cell culture was performed, and the cells were separated and purified to be cell line. Trypan blue exclusion was used to count the numbers of cells alive, morphological changes were observed under the phase-contrast microscope. RT-PCR was used to determine the expression level of TrkA. In this study, a human neuroblastoma cell line was successfully established; in addition, we demonstrated that ATRA induces growth arrest and promotes the differentiation of neuroblastoma cells. In addition, ATRA was shown to significantly increase the levels of TrkA mRNA expression. Therefore, we concluded that the elevated expression of the TrkA receptor is associated with ATRA-induced growth arrest and differentiation o neuroblastoma cells. The results of this study provide a theoretical basis for the clinical application of differentiation-inducing ATRA for neuroblastoma therapy.

Selective conversion of fibroblasts into peripheral sensory neurons.

Humans and mice detect pain, itch, temperature, pressure, stretch and limb position via signaling from peripheral sensory neurons. These neurons are divided into three functional classes (nociceptors/pruritoceptors, mechanoreceptors and proprioceptors) that are distinguished by their selective expression of TrkA, TrkB or TrkC receptors, respectively. We found that transiently coexpressing Brn3a with either Ngn1 or Ngn2 selectively reprogrammed human and mouse fibroblasts to acquire key properties of these three classes of sensory neurons. These induced sensory neurons (iSNs) were electrically active, exhibited distinct sensory neuron morphologies and matched the characteristic gene expression patterns of endogenous sensory neurons, including selective expression of Trk receptors. In addition, we found that calcium-imaging assays could identify subsets of iSNs that selectively responded to diverse ligands known to activate itch- and pain-sensing neurons. These results offer a simple and rapid means for producing genetically diverse human sensory neurons suitable for drug screening and mechanistic studies.

Neonatal Bee Venom Exposure Induces Sensory Modality-Specific Enhancement of Nociceptive Response in Adult Rats

Previous studies have shown that inflammatory pain at the neonatal stage can produce long-term structural and functional changes in nociceptive pathways, resulting in altered pain perception in adulthood. However, the exact pattern of altered nociceptive response and associated neurochemical changes in the spinal cord in this process is unclear. In this study, we used an experimental paradigm in which each rat first received intraplantar bee venom (BV) or saline injection on postnatal day 1, 4, 7, 14, 21, or 28. This was followed 2 months later by a second intraplantar bee venom injection in the same rats to examine the difference in nociceptive responses. We found that neonatal inflammatory pain induced by the first BV injection significantly reduced baseline paw withdrawal mechanical threshold, but not baseline paw withdrawal thermal latency, when rats were examined 2 months from the first BV injection. Neonatal inflammatory pain also exacerbated mechanical, but not thermal, hyperalgesia in response to the second BV injection in these same rats. Rats exposed to neonatal inflammation also showed up-regulation of spinal NGF, TrkA receptor, BDNF, TrkB receptor, IL-1β, and COX-2 expression following the second BV injection, especially with prior BV exposure on postnatal day 21 or 28. These results indicate that neonatal inflammation produces sensory modality-specific changes in nociceptive behavior and alters neurochemistry in the spinal cord of adult rats. These results also suggest that a prior history of inflammatory pain during the developmental period might have an impact on clinical pain in highly susceptible adult patients.

Insulin-like growth factor-1 prevents dorsal root ganglion neuronal tyrosine kinase receptor expression alterations induced by dideoxycytidine in vitro.

Dideoxycytidine (zalcitabine, ddC) produces neurotoxic effects. It is particularly important to understand the toxic effects of ddC on different subpopulations of dorsal root ganglion (DRG) neurons which express distinct tyrosine kinase receptor (Trk) and to find therapeutic factors for prevention and therapy for ddC-induced peripheral sensory neuropathy. Insulin-like growth factor-1 (IGF-1) has been shown to have neurotrophic effects on DRG sensory neurons. However, little is known about the effects of ddC on distinct Trk (TrkA, TrkB, and TrkC) expression in DRG neurons and the neuroprotective effects of IGF-1 on ddC-induced neurotoxicity. Here, we have tested the extent to which the expression of TrkA, TrkB, and TrkC receptors in primary cultured DRG neurons is affected by ddC in the presence or absence of IGF-1. In this experiment, we found that exposure of 5, 25, and 50μmol/L ddC caused a dose-dependent decrease of the mRNA, protein, and the proportion of TrkA-, TrkB-, and TrkC-expressing neurons. IGF-1 (20nmol/L) could partially reverse the decrease of TrkA and TrkB, but not TrkC, expression with ddC exposure. The phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002 (10μmol/L) blocked the effects of IGF-1. These results suggested that the subpopulations of DRG neurons which express distinct TrkA, TrkB, and TrkC receptors were affected by ddC exposure. IGF-1 might relieve the ddC-induced toxicity of TrkA- and TrkB-, but not TrkC-expressing DRG neurons. These data offer new clues for a better understanding of the association of ddC with distinct Trk receptor expression and provide new evidence of the potential therapeutic role of IGF-1 on ddC-induced neurotoxicity.

Nerve growth factor acts through the TrkA receptor to protect sensory neurons from the damaging effects of the HIV-1 viral protein, Vpr

Distal sensory polyneuropathy (DSP) with associated neuropathic pain is the most common neurological disorder affecting patients with human immunodeficiency virus/acquired immunodeficiency syndrome (HIV/AIDS). Viral protein R (Vpr) is a neurotoxic protein encoded by HIV-1 and secreted by infected macrophages. Vpr reduces neuronal viability, increases cytosolic calcium and membrane excitability of cultured dorsal root ganglion (DRG) sensory neurons, and is associated with mechanical allodynia in vivo. A clinical trial with HIV/AIDS patients demonstrated that nerve growth factor (NGF) reduced the severity of DSP-associated neuropathic pain, a problem linked to damage to small diameter, potentially NGF-responsive fibers. Herein, the actions of NGF were investigated in our Vpr model of DSP and we demonstrated that NGF significantly protected sensory neurons from the effects of Vpr. Footpads of immunodeficient Vpr transgenic (vpr/RAG1−/−) mice displayed allodynia (p<0.05), diminished epidermalinnervation (p<0.01) and reduced NGF mRNA expression (p<0.001) compared to immunodeficient (wildtype/RAG1−/−) littermate control mice. Compartmented cultures confirmed recombinant Vpr exposure to the DRG neuronal perikarya decreased distal neurite extension (p<0.01), whereas NGF exposure at these distal axons protected the DRG neurons from the Vpr-induced effect on their cell bodies. NGF prevented Vpr-induced attenuation of the phosphorylated glycogen synthase-3 axon extension pathway and tropomyosin-related kinase A (TrkA) receptor expression in DRG neurons (p<0.05) and it directly counteracted the cytosolic calcium burst caused by Vpr exposure to DRG neurons (p<0.01). TrkA receptor agonist indicated that NGFacted through the TrkA receptor to block the Vpr-mediated decrease in axon outgrowth in neonatal and adult rat and fetal human DRG neurons (p<0.05). Similarly, inhibiting the lower affinity NGF receptor, p75, blocked Vpr’s effect on DRG neurons. Overall, NGF/TrkA signaling or p75 receptor inhibition protects somatic sensory neurons exposed to Vpr, thus laying the groundwork for potential therapeutic options for HIV/AIDS patients suffering from DSP.