TrkC Expression Research Articles

Changes of motor function, Nt-3 and Trkc expression in rats at 14 day post-spinal cord injury and the effect of different electroacupuncture

Changes of motor function, Nt-3 and Trkc expression in rats at 14 day post-spinal cord injury and the effect of different electroacupuncture

Prognostic value of tropomyosin-related kinases A, B, and C in gastric cancer.

Tropomyosin-related kinase (Trk) receptors play critical roles in tumor development and are considered attractive targets for cancer therapy. We investigated correlations of the expression of TrkA, TrkB, and TrkC with clinicopathological features and outcomes in gastric cancer. Tumor samples were obtained from 221 patients with gastric cancer who underwent gastrectomy between 2003 and 2007. The expression of TrkA, TrkB, and TrkC was analyzed using immunohistochemical staining. The relationship of their expression to clinicopathological factors and outcomes was assessed. High expression of TrkA, TrkB, or TrkC was significantly associated with histopathology (p=0.022, p<0.001, and p<0.001). High expression of TrkA was significantly correlated with variables related to tumor progression, including lymph node metastasis (p=0.024) and distant metastasis or recurrence (p<0.001). Distant metastasis or recurrence was found in a significantly higher proportion of patients with high expression of TrkC than in those with low expression (p=0.036). High expression of TrkA was significantly associated with poorer relapse-free survival (RFS) in univariate analysis (p=0.001). High expression of TrkA or TrkC was significantly associated with poorer disease-specific survival (DSS) in univariate analysis (p<0.001 and p=0.008). In multivariate analysis, TrkA was an independent predictor of RFS [hazard ratio (HR), 2.294; 95% confidence interval (CI), 1.309-4.032; p=0.004] and DSS (HR, 2.146; 95% CI, 1.195-3.861; p=0.011). Expression of TrkB was not associated with RFS or DSS in univariate analysis. Our results demonstrated that TrkA expression was associated with tumor progression and poor survival, and was an independent predictor of poor outcomes in gastric cancer patients.

Neurotrophic Factor Receptors trkB and trkC in Experimental Model of Lesion in Rat Brain Structures in Schizophrenia.

The maldevelopmental model of schizophrenia postulates pathological alterations in embryonal neurogenesis as the etiopathogenetic basis of schizophrenic psychoses. The neurotrophic factor hypothesis explains these neuropathological abnormalities as the result of alterations of the neurotrophin system caused by different mechanisms such as a genetic, infectious and traumatic factors. The tyrosine-kinase containing receptors trkB and trkC mediate growth-promoting effects of neurotrophins and respond to changes in neurotrophic factors availability. The aim of the present study was to establish the expression pattern of trkB and trkC in rat brain structures by a developmental model of schizophrenia. On cryostat coronal brain sections of control and lesioned rats (after infusion of ibotenic acid solution bilaterally into the hippocampal formation), immunoreactions for trkB and trkC were performed. We found diminished expression of trkB and trkC in the hippocampal formation of lesioned animals compared to the controls. Quantitative measurements of immunohistochemical reactions intensity and statistical analysis confi rmed the reduced immunoreactivity for antigens under study (trkB and trkC) in the positive hippocampal neurons of 56-day-old lesioned rats compared to the control animals. The observed downregulation of neurotrophic factor receptors expression may compromise the function and plasticity of hippocampal formation in schizophrenic brains.

Establishment of a cellular model to study TrkC-dependent neuritogenesis.

The rat PC12 cell line has become a widely used research tool for many aspects of neurobiology. Nerve growth factor (NGF)-responsive PC12 cells were engineered to drive expression of doxycycline (Dox)-induced gene of interest in the Tet-On expression system that resulted in obtaining PC12-Tet-On cells. TrkA and TrkC are neurotrophin receptors derived from the tropomyosin-related kinase (Trk) family of receptor tyrosine kinases. TrkA receptor binds and is activated mainly by NGF, while TrkC receptor binds and is activated by neurotrophin 3 (NT3). The purpose of this research was to design and describe PC12-based neuronal cell model to study TrkC-triggered versus TrkA-triggered neurite outgrowth. The second-generation tetracycline-responsive promoter (P tight) was used in order to provide low basal expression in the absence of Dox and high-level Dox-induced expression of TrkC. The main advantage of presented model system is dependence of TrkC level on Dox concentration. It also allows to compare activation of intracellular signaling proteins and neurite outgrowth following activation of TrkA and TrkC receptors by NGF and NT3, respectively, in the context of the same quality and quantity of intracellular adaptor proteins, Ras proteins, protein kinases and phosphatases, and phospholipase Cγ1, as a difference in the activation of intracellular signaling network by these two distinct although related receptor tyrosine kinases is expected. The results of our studies suggest that despite slightly weaker activation of ERK1/2 mitogen-activated protein kinases, NT3-triggered TrkC seems to provide apparently stronger than NGF-triggered TrkA signal for neurite elongation in differentiating PC12 cells.

Neurotrophin receptors expression in mesial temporal lobe epilepsy with and without psychiatric comorbidities and their relation with seizure type and surgical outcome.

Epilepsy and psychiatric comorbidities are frequently associated, but their common biological substrate is unknown. We have previously reported altered structural elements and neurotrophins (NTs) expression in mesial temporal lobe epilepsy (MTLE) patients with psychiatric comorbidities. NTs receptors can regulate neurotransmission and promote neuroplasticity, being important candidates in the regulation and manifestation of psychopatological states and seizure-related events. MTLE hippocampi of subjects without psychiatric history, MTLE + major depression, MTLE + interictal psychosis derived from epilepsy surgery, and control necropsies were investigated for p75NTR, TrkB, TrkA, and TrkC immunohistochemistry. Increased expression of p75NTR, decreased TrkA, unaltered TrkC, and complex alterations involving TrkB expression were seen in MTLE groups. Increased TrkB expression in patients without complete seizure remission and in those with secondarily generalized seizures was seen. Decreased p75NTR expression associated with interictal psychosis, and increased TrkB in those with psychosis or major depression was also reported, although their p75NTR/TrkB ratios were lower than in MTLE without psychiatric comorbidities. Our results provide evidence of alterations in expression of NTs receptors in the epileptogenic hippocampus that are differentially modulated in presence of psychiatric comorbidities. As already explored in animal models, even in chronic human MTLE increased TrkB expression, among other NT receptors alterations, may play a major role in seizure type, frequency and surgery outcome.

Electro-acupuncture promotes the survival and differentiation of transplanted bone marrow mesenchymal stem cells pre-induced with neurotrophin-3 and retinoic acid in gelatin sponge scaffold after rat spinal cord transection.

In the past decades, mesenchymal stem cells (MSCs) as a promising cell candidate have received the most attention in the treatment of spinal cord injury (SCI). However, due to the low survival rate and low neural differentiation rate, the grafted MSCs do not perform well as one would have expected. In the present study, we tested a combinational therapy to improve on this situation. MSCs were loaded into three-dimensional gelatin sponge (GS) scaffold. After 7days of induction with neurotrophin-3 (NT-3) and retinoic acid (RA) in vitro, we observed a significant increase in TrkC mRNA transcription by Real-time PCR and this was confirmed by in situ hybridization. The expression of TrkC was also confirmed by Western blot and immunohistochemistry. Differentiation potential of MSCs in vitro into neuron-like cells or oligodendrocyte-like cells was further demonstrated by using immunofluorescence staining. The pre-induced MSCs seeding in GS scaffolds were then grafted into the transected rat spinal cord. One day after grafting, Governor Vessel electro-acupuncture (GV-EA) treatment was applied to rats in the NR-MSCs + EA group. At 30days after GV-EA treatment, it found that the grafted MSCs have better survival rate and neuron-like cell differentiation compared with those without GV-EA treatment. The sustained TrkC expression in the grafted MSCs as well as increased NT-3 content in the injury/graft site by GV-EA suggests that NT-3/TrkC signaling pathway may be involved in the promoting effect. This study demonstrates that GV-EA and pre-induction with NT-3 and RA together may promote the survival and differentiation of grafted MSCs in GS scaffold in rat SCI.

TrkC expression predicts good clinical outcome in the invasive ductal carcinoma of the breast independent of NT-3 expression

Little is known on the action of TrkC for the clinical prognosis and progression of breast cancer according to the availability of its ligand NT-3. We sought to investigate the prognostic relevance of NT-3-TrkC axis in breast cancer and estimate its role during the process of breast cancer progression. TrkC and NT-3 expression were evaluated in 236 invasive ductal carcinoma (IDC), 60 pure ductal carcinoma in situ and 30 normal breast tissues by immunohistochemistry. Spearman’s rank correlation test, Kaplan-Meier method and Cox proportional hazards model were used for statistical analysis. TrkC expression was negatively associated with lymph node metastasis and tumor proliferation (p < 0.05). Patients with lower TrkC expressing tumors had a higher risk of recurrence (odds ratio, 0.401; 95% confidence interval, 0.207-0.778; p = 0.007). The layered analysis indicated that patients with high TrkC expression tumors had a favorable disease free survival whether NT-3 and TrkC were co-expressed or solitarily expressed in the tumor (p = 0.000). NT-3 expression was inversely correlated with the progression of breast cancer (r = — 0.341, p = 0.000). TrkC expression reduces tumor relapse independent of NT-3 availability in IDC. Elevated NT-3 expression contributes to the progression of breast cancer. Little is known on the action of TrkC for the clinical prognosis and progression of breast cancer according to the availability of its ligand NT-3. We sought to investigate the prognostic relevance of NT-3-TrkC axis in breast cancer and estimate its role during the process of breast cancer progression. TrkC and NT-3 expression were evaluated in 236 invasive ductal carcinoma (IDC), 60 pure ductal carcinoma in situ and 30 normal breast tissues by immunohistochemistry. Spearman’s rank correlation test, Kaplan-Meier method and Cox proportional hazards model were used for statistical analysis. TrkC expression was negatively associated with lymph node metastasis and tumor proliferation (p < 0.05). Patients with lower TrkC expressing tumors had a higher risk of recurrence (odds ratio, 0.401; 95% confidence interval, 0.207-0.778; p = 0.007). The layered analysis indicated that patients with high TrkC expression tumors had a favorable disease free survival whether NT-3 and TrkC were co-expressed or solitarily expressed in the tumor (p = 0.000). NT-3 expression was inversely correlated with the progression of breast cancer (r = — 0.341, p = 0.000). TrkC expression reduces tumor relapse independent of NT-3 availability in IDC. Elevated NT-3 expression contributes to the progression of breast cancer.

Immunohistochemical expression of Ki67, EGFR and TRKC and their correlation with prognostic factors in medulloblastoma

Introduction: Medulloblastoma is a malignant embryonal tumor of the cerebellum with poor prognosis. The treatment is based only on clinical criteria, such as risk group that only considers age, extent of tumor resection, recurrence, and metastasis. Objective: To evaluate a possible relationship between the immunoexpression of biomarkers (Ki67, receptor neutrophin-3 [TRKC], epidermal growth factor receptor [EGFR], B-cell lymphoma 2 [Bcl-2], and cyclin-D1), and the classical clinical prognostic factors of medulloblastoma. Material and method: thirty-five samples of pediatric medulloblastoma free of neoadjuvant chemotherapy were separated and reviewed for their histopathological classification; two areas representative of tumor were used in the construction of tissue microarrays. The following clinical data from 29 patients were used for comparison with the biomarkers expression: patient's age, presence or absence of complete tumor resection, staging patient's risk group, presence or absence of metastases, presence or absence of postoperative chemotherapy, and presence or absence of recurrence. Clinical follow-up of the study ranged from two to thirteen years, and cases with fatal outcome were also analyzed. Results: Patients with upper age showed higher expression of TRKC (p = 0.033). There was inversely proportional and statistically significant correlation between TRKC and Ki67 (p = 0.027). There was no statistical significance in the analysis of EGFR, Bcl2, and cyclin-D1. Conclusion: The immunoexpression of TRKC might be considered a biomarker related to tumors with better prognosis in patients with medulloblastoma, contributing to better risk groups' stratification.

Neurotrophin receptors expression in mesial temporal lobe epilepsy with and without psychiatric comorbidities and their relation with seizure type and surgical outcome

Epilepsy and psychiatric comorbidities are frequently associated, but their common biological substrate is unknown. We have previously reported altered structural elements and neurotrophins (NTs) expression in mesial temporal lobe epilepsy (MTLE) patients with psychiatric comorbidities. NTs receptors can regulate neurotransmission and promote neuroplasticity, being important candidates in the regulation and manifestation of psychopatological states and seizure-related events. MTLE hippocampi of subjects without psychiatric history, MTLE + major depression, MTLE + interictal psychosis derived from epilepsy surgery, and control necropsies were investigated for p75NTR, TrkB, TrkA, and TrkC immunohistochemistry. Increased expression of p75NTR, decreased TrkA, unaltered TrkC, and complex alterations involving TrkB expression were seen in MTLE groups. Increased TrkB expression in patients without complete seizure remission and in those with secondarily generalized seizures was seen. Decreased p75NTR expression associated with interictal psychosis, and increased TrkB in those with psychosis or major depression was also reported, although their p75NTR/TrkB ratios were lower than in MTLE without psychiatric comorbidities. Our results provide evidence of alterations in expression of NTs receptors in the epileptogenic hippocampus that are differentially modulated in presence of psychiatric comorbidities. As already explored in animal models, even in chronic human MTLE increased TrkB expression, among other NT receptors alterations, may play a major role in seizure type, frequency and surgery outcome.

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.

Expression of TrkC receptors in the developing brain of the Monodelphis opossum and its effect on the development of cortical cells.

In this study, we investigated the distribution, localization and several various functions of TrkC receptors during development of the Monodelphis opossum brain. Western blotting analysis showed that two different forms of the TrkC receptor, the full-length receptor and one of its truncated forms, are abundantly expressed in the opossum brain. The expression of TrkC receptors was barely detected in the brain of newborn opossums. At postnatal day (P) 3, the expression of full-length TrkC remained at low levels, while moderate expression of the TrkC truncated form was detected. The expression levels of both forms of this protein gradually increased throughout development, peaking at P35. We found that in different neocortical areas located both at the rostral and caudal regions of the cortex, up to 98% of BrdU-labeled cells forming cortical layers (II-VI) had prominently expressed TrkC. To assess which developmental processes of cortical cells are regulated by TrkC receptors, three different shRNAs were constructed. The shRNAs were individually tested in transfected cortical progenitor cells grown on culture plates for 2 days. The effects of the shRNA-TrkC constructs were similar: blockade of TrkC receptors decreased the number of Ki67-positive and apoptotic cells, and it did not change the number of TUJ-positive neurons in vitro. Thus, the lack of TrkC receptors in cultured progenitor cells provided insight on the potential role of these receptors in the regulation of proliferation and cell survival but not in the differentiation of cortical cells.

Dok5 is involved in the signaling pathway of neurotrophin-3 against TrkC-induced apoptosis

TrkC is a dependence receptor and many reports have shown that neurotrophin-3 promotes cell survival by inhibiting TrkC-induced apoptosis in many cell lines. However, the identity of the adaptor protein involved in the NT-3/TrkC signaling pathway regulating cell death and survival remains unclear. The downstream of tyrosine kinase/docking protein (Dok) adaptor protein 5 is one substrate of the TrkC receptor. Because NT-3 and its receptor, TrkC, are strongly expressed by sensory neurons, we measured the expression of Dok5 and TrkC in the developing mouse spinal cord and dorsal root ganglia (DRG). We found that the number of cells positive for both Dok5 and TrkC decreases with DRG development. Immunoprecipitation and immunofluorescence staining showed that Dok5 interacted with TrkC and partially colocalized with TrkC in DRG neurons. In HEK293T cells, TrkC triggered apoptosis, but NT-3 prevented TrkC-induced apoptosis. Interestingly, siRNA knockdown of Dok5 expression partially prevented the protection of NT-3 against TrkC-induced apoptosis by regulating the activity of caspase-3. Taken together, we concluded that Dok5 is necessary for NT-3 signaling to block TrkC-induced apoptosis.

Neuroprotective effect of insulin-like growth factor-1: Effects on tyrosine kinase receptor (Trk) expression in dorsal root ganglion neurons with glutamate-induced excitotoxicity in vitro

Insulin-like growth factor-1 (IGF-1) may play an important role in regulating the expression of distinct tyrosine kinase receptor (Trk) in primary sensory dorsal root ganglion (DRG) neurons. Glutamate (Glu) is the main excitatory neurotransmitter and induces neuronal excitotoxicity for primary sensory neurons. It is not known whether IGF-1 influences expression of TrkA, TrkB, and TrkC in DRG neurons with excitotoxicity induced by Glu. In the present study, primary cultured DRG neurons with Glu-induced excitotoxicity were used to determine the effects of IGF-1 on TrkA, TrkB, and TrkC expression. The results showed that IGF-1 increased the expression of TrkA and TrkB and their mRNAs, but not TrkC and its mRNA, in primary cultured DRG neurons with excitotoxicity induced by Glu. Interestingly, neither the extracellular signal-regulated protein kinase (ERK1/2) inhibitor PD98059 nor the phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002 blocked the effect of IGF-1, but both inhibitors together were effective. IGF-1 may play an important role in regulating different Trk receptor expression in DRG neurons through ERK1/2 and PI3K/Akt signaling pathways. The contribution of distinct Trk receptors might be one of the mechanisms that IGF-1 rescues dying neurons from Glu excitotoxic injury. These data imply that IGF-1 signaling might be a potential target on modifying distinct Trk receptor-mediated biological effects of primary sensory neurons with excitotoxicity.

NeuroD regulates neuronal migration.

NeuroD is required for the survival of many subtypes of developing neurons in the vertebrate central nervous system. Because NeuroD-deficient neurons in the hippocampus, cerebellum, and inner ear die prematurely in the early stage of neurogenesis, the role of NeuroD during the later stages of neurogenesis of these cell subtypes is not well understood. In addition, the mechanism of NeuroDdeficient neuronal death has not been investigated. It was hypothesized that NeuroD-dependent neuronal death occurs through a Bax-dependent apoptotic pathway. Based on this hypothesis, this study attempted to rescue neuronal cell death by deleting the Bax gene in NeuroD null mice to investigate the role of NeuroD in surviving neurons. The NeuroD and Bax double null mice displayed a decrease in the number of apoptotic cells in the hippocampus and the cerebellum and the rescue of vestibulocochlear ganglion (VCG) neurons that failed to migrate and innervate. In addition, at E13.5, the NeuroD(-/-)Bax(-/-) VCG neurons failed to express TrkB and TrkC, which are known to be essential for the survival of those neurons. These data suggest that neuronal death in NeuroD null mice is mediated by Bax-dependent apoptosis and that NeuroD is required for the migration of VCG neurons. Finally, these data show that TrkB and TrkC expression in E13.5 VCG neurons requires NeuroD and that TrkB and TrkC expression may be necessary for the normal migration and innervations of those neurons.

Abstract 3036: The dependence receptor TrkC is a putative colon cancer tumor suppressor.

Abstract Backgrounds &amp; Aims: The TrkC neurotrophin receptor belongs to the functional dependence receptors family, members of which share the ability to induce apoptosis in the absence of their ligands. Such a trait has been hypothesized to confer tumor-suppressor activity. Indeed, cells that express these receptors are thought to be dependent on ligand availability for their survival, a mechanism that inhibits uncontrolled tumor cell proliferation and migration. TrkC is yet a relatively classic tyrosine kinase receptor and therefore generally rather considered as a proto-oncogene. We investigated here whether, because of its dependence receptor activity, TrkC is a putative tumor suppressor in colorectal malignancies. Methods: The level of TrkC was analyzed in a panel of 45 primary sporadic colorectal carcinomas. Loss of heterozygosity and epigenetic alterations in the TrkC promoter were also analyzed. The level of TrkC was also analyzed in a panel of colorectal cancer cell lines. The TrkC tumor suppressive activity was investigated by expressing TrkC and related TrkC variants in colorectal cancer cell lines and by measuring apoptosis, anchorage-independent growth, migration and tumor growth in a chicken model. Results: We show here that TrkC expression is down-regulated in a large fraction of human colorectal cancers, mainly through promoter methylation. Moreover, we show that TrkC silencing by promoter methylation is a selective advantage for colorectal cell lines to limit tumor cell death. Consequently, we show that reestablished TrkC expression in colorectal cancer cell lines is associated with tumor cell death and inhibition of in vitro characteristics of cell transformation and in vivo tumor growth. Conclusions: The loss of TrkC expression observed in human colorectal cancer is a selective advantage for tumor cell survival. Thus, TrkC appears to be a putative new colon cancer tumor suppressor. Citation Format: Anne-Laure Genevois, Gabriel Ichim, Marie-May Coissieux, Marie-Pierre Lambert, Florian Lepinasse, Zdenko Herceg, Jean-Yves Scoazec, Servane Tauszig-Delamasure, Patrick Mehlen. The dependence receptor TrkC is a putative colon cancer tumor suppressor. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3036. doi:10.1158/1538-7445.AM2013-3036

Oligodendroglial Expression of TrkB Independently Regulates Myelination and Progenitor Cell Proliferation

The neurotrophin brain-derived neurotrophic factor (BDNF) has been implicated in regulating CNS myelination. BDNF mutant mice exhibit a hypomyelinating phenotype, and BDNF exerts distinct effects upon oligodendroglial proliferation, differentiation, and myelination in vitro. To investigate the precise influence that BDNF exerts in regulating CNS myelination in vivo, we have generated conditional knock-out mice in which TrkB has been deleted specifically in oligodendrocytes. Deletion of TrkB disrupted normal oligodendrocyte myelination, resulting in a significant reduction in myelin protein expression and myelination of CNS white matter tracts during development. Importantly, conditional knock-out mice exhibited normal numbers of mature oligodendrocytes and normal numbers of myelinated axons; however, myelin thickness was significantly reduced during development. These data indicate that while TrkB expression in oligodendrocytes plays no role in the initial contact with axons, it exerts an important influence in subsequent stages to promote myelin ensheathment. The conditional knock-out mice also exhibited an increased density of oligodendrocyte progenitor cells (OPCs) in CNS white matter tracts. Concordant with these results, in vitro analyses using OPCs subjected to TrkB knockdown also revealed increased OPC proliferation. Our data suggested this effect was dependent upon TrkC and p75 expression. Thus, our data demonstrate that TrkB expression in oligodendroglia exerts a direct effect on oligodendrocytes to promote myelination and an indirect effect upon the OPC population, modifying their proliferative potential.

The integration of NSC-derived and host neural networks after rat spinal cord transection

Rebuilding structures that can bridge the injury gap and enable signal connection remains a challenging issue in spinal cord injury. We sought to determine if genetically enhanced expression of TrkC in neural stem cells (NSCs) and neurotrophin-3 in Schwann cells (SCs) co-cultured in a gelatin sponge scaffold could constitute a neural network, and whether it could act as a relay to rebuilt signal connection after spinal cord transection. Indeed, many NSCs in the scaffold assumed neuronal features including formation of synapses. By whole-cell patch clamp, the synapses associated with NSC-derived neurons were excitable. Grafting of the scaffold with differentiating NSCs + SCs into rats with a segment of the spinal cord removed had resulted in a significant functional recovery of the paralyzed hind-limbs. Remarkably, the NSC-derived neurons formed new synaptic contacts suggesting that the scaffold can form a relay for conduction of signals through the injury gap of spinal cord.

Dependence receptor TrkC is a putative colon cancer tumor suppressor

The TrkC neurotrophin receptor belongs to the functional dependence receptor family, members of which share the ability to induce apoptosis in the absence of their ligands. Such a trait has been hypothesized to confer tumor-suppressor activity. Indeed, cells that express these receptors are thought to be dependent on ligand availability for their survival, a mechanism that inhibits uncontrolled tumor cell proliferation and migration. TrkC is a classic tyrosine kinase receptor and therefore generally considered to be a proto-oncogene. We show here that TrkC expression is down-regulated in a large fraction of human colorectal cancers, mainly through promoter methylation. Moreover, we show that TrkC silencing by promoter methylation is a selective advantage for colorectal cell lines to limit tumor cell death. Furthermore, reestablished TrkC expression in colorectal cancer cell lines is associated with tumor cell death and inhibition of in vitro characteristics of cell transformation, as well as in vivo tumor growth. Finally, we provide evidence that a mutation of TrkC detected in a sporadic cancer is a loss-of-proapoptotic function mutation. Together, these data support the conclusion that TrkC is a colorectal cancer tumor suppressor.

Tropomyosin receptor kinases B and C are tumor progressive and metastatic marker in colorectal carcinoma

Members of the tropomyosin receptor kinase (Trk) family have a high affinity for neurotrophins and regulate neuronal survival. The role of Trks in cancer is still controversial. The expression and role of TrkB and TrkC were examined in colorectal cancer (CRC). Immunohistochemical analysis of TrkB and TrkC was performed in 133 patients with CRC. Using human CRC cell lines, expression of vascular endothelial growth factor (VEGF) and transforming growth factor β, cell growth, invasion, and apoptosis were examined by knockdown methods. Immunohistochemistry showed positive results of TrkB and TrkC (23.3% and 12.8%, respectively). TrkB expression was associated with local progression (P = .0284), clinical stage (P = .0026), nodal metastasis (P = .0068), and peritoneal metastasis (P = .0026). TrkC expression was only related to liver metastasis (P = .0001). Coexpression of TrkB or TrkC and their ligands was found in 80.6% and 82.4% of cases, respectively. In vitro analysis using human CRC cells showed that TrkB positively regulated gene expression of VEGF-A (P < .05) and VEGF-C (P < .05), whereas TrkC suppressed transforming growth factor β expression (P < .05). TrkB and TrkC induced cell growth (P < .05) and invasion (P < .05), respectively. Both TrkB and TrkC showed antiapoptotic effect (P < .05). These results suggest that TrkB and TrkC have a tumor progressive function and may be a useful diagnostic and therapeutic target in CRC.

Neuregulin-1β regulates tyrosine kinase receptor expression in cultured dorsal root ganglion neurons with excitotoxicity induced by glutamate

Neuregulin-1 (NRG-1) signaling regulates neuronal development, migration, myelination, and synaptic maintenance. Three members of tyrosine kinase receptor (Trk) family, TrkA, TrkB, and TrkC, have been identified in DRG neurons. Whether NRG-1β and its signaling pathways influence the expression of these Trk receptors in DRG neurons is still unclear. In the present study, primary cultured DRG neurons were used to determine the effects of NRG-1β on TrkA, TrkB, and TrkC expression in DRG neurons with excitotoxicity induced by glutamate (Glu). The involvement of phosphatidylinositol 3-kinase (PI3K)/Akt and the effects of extracellular signal-regulated protein kinase (ERK1/2) signaling pathways on NRG-1β were also determined. DRG neurons were cultured for 48h and then exposed to Glu, Glu plus NRG-1β, LY294002 plus Glu plus NRG-1β, PD98059 plus Glu plus NRG-1β, and PD98059 plus LY294002 plus Glu plus NRG-1β for an additional 24h. The DRG neurons were continuously exposed to culture media as a control. After that, all cultures were processed for detection of mRNA levels of TrkA, TrkB, and TrkC using real time-PCR analysis. Protein levels of TrkA, TrkB, and TrkC were detected using a Western blot assay. The expression of TrkA, TrkB, and TrkC in situ was determined by a fluorescent labeling technique. The levels of phosphorylated Akt (pAkt), phosphorylated ERK1/2 (pERK1/2), total protein levels of Akt and ERK1/2 were detected using a Western blot assay. The results indicated that in primary cultured DRG neurons with excitotoxicity induced by Glu, NRG-1β increased the expression of TrkA and TrkB their mRNAs, but not TrkC and its mRNA. Inhibitors (LY294002, PD98059) either alone or in combination blocked the effects of NRG-1β. NRG-1β may play an important role in regulating the expression of different Trk receptors in DRG neurons through the PI3K/Akt and ERK1/2 signaling pathways.