The tyrosine phosphatase inhibitor orthovanadate mimics NGF-induced neuroprotective signaling in rat hippocampal neurons

A Study of Vanadate Group Substitution into Nanosized Hydroxyapatite Doped with Eu3+ Ions as a Potential Tissue Replacement Material

In this study, nanosized vanadate-substituted hydroxyapatites doped with 1 mol% and 2 mol% Eu3+ ions were obtained via the precipitation method. To evaluate the structure and morphology of the obtained compounds, the XRPD (X-ray powder diffraction) technique, Rietveld refinement, SEM-EDS (scanning electron microscopy-energy-dispersive spectrometry) and TEM (transmission electron microscopy) techniques as well as FTIR (Fourier transform infrared) spectroscopy were performed. Moreover, the chemical formula was confirmed using the ICP-OES (Inductively coupled plasma optical emission spectroscopy spectroscopy). The calculated average grain size for powders was in the range of 25 to 90 nm. The luminescence properties of vanadium-substituted hydroxyapatite were evaluated by recording emission spectra and excitation spectra as well as luminescence kinetics. The crucial step of this research was the evaluation of the biocompatibility of the synthesized nanomaterials. Therefore, the obtained compounds were tested toward sheep red blood cells and normal human dermal fibroblast to confirm the nontoxicity and biocompatibility of new nanosized Eu3+ ion-doped vanadate-hydroxyapatite. Moreover, the final step of the research allowed us to determine the time dependent ion release to the simulated body fluid environment. The study confirmed cytocompatibility of vanadium hydroxyapatite doped with Eu3+ ions.

Cytokine expressions of spinal cord injury treated by neurotropin and nafamostat mesylate

Background

Spinal cord injury (SCI) leads to severe physical disability and sensory dysfunction. Neurotropin (NTP) has been used clinically to alleviate neuropathic pain, while nafamostat mesylate (NM) used clinical on pancreatitis patients through inhibiting synthetic serine protease. Our previous studies showed that NTP and NM were able to repair SCI. However, the underlying mechanism has not been fully explored after treatment with these 2 different drugs.

Methods

The drugs NTP and NM were administered on a contusion SCI Wistar rat model. Cytokine array analysis was performed to describe the changes of 67 proteins after acute SCI. Hierarchical clustering and volcano plot analysis were conducted to clarify protein change profiles. The differently expressed proteins related to biological processes were analyzed by functional protein association networks, Gene Ontology and pathway analysis. Flow cytometric analysis was detected to reflect the activation of immune system after drug intervention, while withdrawal threshold and BBB score were detected to evaluated the mechanical allodynia and functional recovery after SCI.

Results

HGF, β-NGF, and activin were the 3 most upregulated proteins, while the receptor for RAGE, IL-1α, and TNF-α were the 3 most downregulated proteins after NTP treatment. Adiponectin, decorin and CTACK were the 3 most upregulated proteins, while RAGE, IL-1α, and IL-1β were the 3 most downregulated proteins in the NM group. Number of lymphocytes was decreased while BBB score was increased both in NTP and NM group. But only NTP could improve mechanical pain threshold after SCI.

Conclusions

The PI3K-Akt, Jak-STAT signaling pathway and apoptosis might participate in SCI restoration by NTP, while the MAPK and NOD-like receptor signaling pathway may participated in repairing SCI with NM. We concluded that NTP regulated the microenvironment via a neuroprotective effect and inhibition of inflammation to repair SCI, while NM healed SCI through an anti-inflammatory effect. Both NTP and NM could down-regulate the activation of immune system and improve the functional recovery while only NTP could improve the pathological neuralgia after SCI. Elucidating the molecular mechanisms of these 2 clinical drugs indicates that they their expected to be effective clinical treatment for SCI.

Fluorescent Kinase Probes Enabling Identification and Dynamic Imaging of HER2(+) Cells

The human epidermal growth factor receptor, EGFR/ERBB/HER, family of receptor tyrosine kinases is central to many signaling pathways and a validated chemotherapy target in multiple cancers. While EGFR/ERBB-targeted therapies, including monoclonal antibodies, e.g., trastuzumab, and small molecule kinase inhibitors, such as lapatinib, have been developed, rapid identification and classification of cancer cells is key to identifying the best treatment regime. We report ERBB2 (also HER2) targeting kinase probes that exhibit a "turn-on" emission response upon binding. These live cell compatible probes differentiate ERBB2(+) cells from low-level, ERBB2(-) cells by targeting the intracellular ATP-binding pocket of ERBB2 with therapeutic inhibitor-like specificity. Beyond kinase expression levels, probe signal is linked to the phosphotyrosine-correlated activation state of the ERBB2 population. Additionally, the rapid signaling capability of the probes can report changes in activation state in live cells providing a unique type of complementary information to immunohistochemical assays of receptor kinase populations.

Developmental co-expression and functional redundancy of tyrosine phosphatases with neurotrophin receptors in developing sensory neurons

Receptor-type protein tyrosine phosphatases (RPTPs) have been implicated as direct or indirect regulators of neurotrophin receptors (TRKs). It remains less clear if and how such RPTPs might regulate TRK proteins in vivo during development. Here we present a comparative expression profile of RPTP genes and Trk genes during early stages of murine, dorsal root ganglion maturation. We find little if any specific, temporal mRNA co-regulation between individual RPTP and Ntrk genes between E12.5 and E14.5. Moreover, a double fluorescent in-situ hybridization and immunofluorescence study of seven Rptp genes with Ntrks revealed widespread co-expression of RPTPs in individual neurons, but no tight correlation with Trk expression profiles. No Rptp is expressed in 100% of Ntrk1-expressing neurons, whereas at least 6 RPTPs are expressed in 100% of Ntrk2- and Ntrk3-expressing neurons. An exception is Ptpro, which showed very selective expression. Short hairpin RNA suppression of Ptprf, Ptprs or Ptpro in primary, E13.5 DRG neurons did not alter TRK signalling. We therefore propose that TRK signalling may not be simply dependent on rate-limiting regulation by individual RPTP subtypes during sensory neuron development. Instead, TRK signalling has the potential to be buffered by concurrent inputs from several RPTPs in individual neurons.

A loss-of-function screen for phosphatases that regulate neurite outgrowth identifies PTPN12 as a negative regulator of TrkB tyrosine phosphorylation

Alterations in function of the neurotrophin BDNF are associated with neurodegeneration, cognitive decline, and psychiatric disorders. BDNF promotes axonal outgrowth and branching, regulates dendritic tree morphology and is important for axonal regeneration after injury, responses that largely result from activation of its tyrosine kinase receptor TrkB. Although intracellular neurotrophin (NT) signaling presumably reflects the combined action of kinases and phosphatases, little is known about the contributions of the latter to TrkB regulation. The issue is complicated by the fact that phosphatases belong to multiple independently evolved families, which are rarely studied together. We undertook a loss-of-function RNA-interference-based screen of virtually all known (254) human phosphatases to understand their function in BDNF/TrkB-mediated neurite outgrowth in differentiated SH-SY5Y cells. This approach identified phosphatases from diverse families, which either positively or negatively modulate BDNF-TrkB-mediated neurite outgrowth, and most of which have little or no previously established function related to NT signaling. “Classical” protein tyrosine phosphatases (PTPs) accounted for 13% of the candidate regulatory phosphatases. The top classical PTP identified as a negative regulator of BDNF-TrkB-mediated neurite outgrowth was PTPN12 (also called PTP-PEST). Validation and follow-up studies showed that endogenous PTPN12 antagonizes tyrosine phosphorylation of TrkB itself, and the downstream activation of ERK1/2. We also found PTPN12 to negatively regulate phosphorylation of p130cas and FAK, proteins with previously described functions related to cell motility and growth cone behavior. Our data provide the first comprehensive survey of phosphatase function in NT signaling and neurite outgrowth. They reveal the complexity of phosphatase control, with several evolutionarily unrelated phosphatase families cooperating to affect this biological response, and hence the relevance of considering all phosphatase families when mining for potentially druggable targets.

Effects of Hsp90 inhibitors, geldanamycin and its analog, on ceramide metabolism and cytotoxicity in PC12 cells

The inhibitors of heat shock protein-90 (Hsp90), geldanamycin (GA) and 17-(allylamino)-17-desmethoxygeldanamycin, show various cellular effects including destabilization of Hsp90 clients and expression of other chaperones, etc. and modulate cytotoxicity depending on cell types and stimuli. In this study, we investigated the effects of Hsp90 inhibitors on survival of PC12 cells with and without cytotoxic stimuli including orthovanadate, Na(3)VO(4). Treatment with Hsp90 inhibitors at 2 µM for 16 hr did not cause cell detachment and leakage of lactate dehydrogenase, and at concentrations greater than 5 µM resulted in cytotoxicity. The inhibitors at 2 µM enhanced the cytotoxicity of 1 mM Na(3)VO(4), and did not protect PC12 cells at any concentrations against Na(3)VO(4). Next, the effects of Hsp90 inhibitors on the intracellular metabolism of ceramide and arachidonic acid (AA) were examined, since these processes also regulate cytotoxicity. In cells treated with 4-nitrobenzo-2-oxa-1,3-diazole (NBD)-labeled C6-ceramide, Hsp90 inhibitors reduced the formation of NBD-glucosylceramide and Na(3)VO(4)-induced formation of NBD-caproic acid, a counterpart of sphingosine, without affecting other metabolites including NBD-sphingomyelin. GA treatment did not change the amounts of AA released in PC12 cells with and without Na(3)VO(4). In HeLa cells, however, GA treatment decreased the release of AA via cytosolic phospholipase A(2)α's activation probably because of dysfunctional Hsp90 clients. Our results suggest the possible involvement of ceramide metabolism, not AA release, in GA-induced cytotoxicity in PC12 cells.

The basal level of intracellular calcium gates the activation of phosphoinositide 3-kinase-Akt signaling by brain-derived neurotrophic factor in cortical neurons

Brain-derived neurotrophic factor (BDNF) mediates survival and neuroplasticity through the activation of phosphoinositide 3-kinase-Akt pathway. Although previous studies suggested the roles of mitogen-activated protein kinase, phospholipase C-gamma-mediated intracellular calcium ([Ca2+]i) increase, and extracellular calcium influx in regulating Akt activation, the cellular mechanisms are largely unknown. We demonstrated that sub-nanomolar BDNF significantly induced Akt activation in developing cortical neurons. The TrkB-dependent Akt phosphorylation at S473 and T308 required only phosphoinositide 3-kinase, but not phospholipase C and mitogen-activated protein kinase activity. Blocking NMDA receptors, L-type voltage-gated calcium channels, and chelating extracellular calcium by EGTA failed to block BDNF-induced Akt phosphorylation. In contrast, chelating [Ca2+]i by 1,2-bis(o-aminophenoxy)ethane-N,N,N ',N '-tetraacetic acid-acetoxymethyl ester (BAPTA-AM) abolished Akt phosphorylation. Interestingly, sub-nanomolar BDNF did not stimulate [Ca2+]i increase under our culture conditions. Together with that NMDA- and membrane depolarization-induced [Ca2+]i increase did not activate Akt, we conclude that the basal level of [Ca2+]i gates BDNF function. Furthermore, inhibiting calmodulin by W13 suppressed Akt phosphorylation. On the other hand, inhibition of protein phosphatase 1 by okadaic acid and tautomycin rescued Akt phosphorylation in BAPTA-AM and W13-treated neurons. We further demonstrated that the phosphorylation of phosphoinositide-dependent kinase-1 did not correlate with Akt phosphorylation at T308. Our results suggested novel roles of basal [Ca2+]i, rather than activity-induced calcium elevation, in BDNF-Akt signaling.

Vanadate prevents glucocorticoid-induced apoptosis of osteoblasts in vitro and osteocytes in vivo

Skeletal mass is maintained by a balance between formation and resorption, cell proliferation and apoptosis. In vitro, glucocorticoids (GCs) decrease extracellular signal-regulated kinases (ERK) activation by mitogens, thus inhibiting osteoblast proliferation. Both ERK activity and proliferation are restored by co-treatment with the protein tyrosine phosphatase inhibitor, vanadate. Since ERK signalling may also be anti-apoptotic, we explored the effects of vanadate on GC-induced apoptosis in vitro and in vivo. Apoptosis in MBA-15.4 pre-osteoblasts increased from 6 h and remained up to eightfold higher through 6 days of 10(- 6) M dexamethasone (Dex) treatment. Co-incubation with 10(- 7) M vanadate markedly reduced apoptosis at all time points. Vanadate also prevented GC-induced poly-ADP-ribose polymerase cleavage. We assessed the transcriptional profiles of seven anti-apoptotic proteins (Bcl-2, Bcl-X(L), inhibitors of apoptosis protein-1 (IAP-1), IAP-2, X-linked IAP (XIAP), Fas-associated death-domain-like IL-1beta-converting enzyme-inhibitory protein (FLIP(Long)) and FLIP(Short)) in osteoblasts subjected to various stimuli using real-time quantitative PCR. Although these anti-apoptotic genes responded to different mitogenic conditions, Dex failed to repress their expression, and in fact significantly up-regulated Bcl-X(L), IAP-2 and XIAP. Dex may therefore induce apoptosis by up-regulating pro-apoptotic gene expression. We have previously demonstrated that rats treated with GC develop low formation osteoporosis (bone histomorphometry and DEXA) and skeletal fragility (breaking strength) that were largely prevented by co-treatment with vanadate. We report here that vertebrae from rats treated with 3.5 mg/kg per day methylprednisolone for 9 weeks showed increased incidence of terminal deoxynucleotidyl transferase-mediated biotin-dUTP nick end-labelling-positive apoptotic osteocytes, which was reduced by vanadate co-treatment. We conclude that vanadate prevents GC-induced apoptosis of pre-osteoblasts in vitro and osteocytes in vivo, and this may contribute to its bone-sparing effects in vivo.

Stat5 constitutive activation rescues defects in spinal muscular atrophy

Proximal spinal muscular atrophy (SMA) is a motor neuron degeneration disorder for which there is currently no effective treatment. Here, we report three compounds (sodium vanadate, trichostatin A and aclarubicin) that effectively enhance SMN2 expression by inducing Stat5 activation in SMA-like mouse embryonic fibroblasts and human SMN2-transfected NSC34 cells. We found that Stat5 activation enhanced SMN2 promoter activity with increase in both full-length and deletion exon 7 SMN transcripts in SMN2-NSC34 cells. Knockdown of Stat5 expression disrupted the effects of sodium vanadate on SMN2 activation but did not influence SMN2 splicing, suggesting that Stat5 signaling is involved in SMN2 transcriptional regulation. In addition, constitutive activation of Stat5 mutant (Stat5A1*6) profoundly increased the number of nuclear gems in SMA-patient lymphocytes and reduced SMA-like motor neuron axon outgrowth defects. These results demonstrate that Stat5 signaling could be a possible pharmacological target for treating SMA.

LAR protein tyrosine phosphatase receptor associates with TrkB and modulates neurotrophic signaling pathways

The identities of receptor protein tyrosine phosphatases (PTPs) that associate with Trk protein tyrosine kinase (PTK) receptors and modulate neurotrophic signaling are unknown. The leukocyte common antigen-related (LAR) receptor PTP is present in neurons expressing TrkB, and like TrkB is associated with caveolae and regulates survival and neurite outgrowth. We tested the hypothesis that LAR associates with TrkB and regulates neurotrophic signaling in embryonic hippocampal neurons. Coimmunoprecipitation and coimmunostaining demonstrated LAR interaction with TrkB that is increased by BDNF exposure. BDNF neurotrophic activity was reduced in LAR-/- and LAR siRNA-treated LAR+/+ neurons and was augmented in LAR-transfected neurons. In LAR-/- neurons, BDNF-induced activation of TrkB, Shc, AKT, ERK, and CREB was significantly decreased; while in LAR-transfected neurons, BDNF-induced CREB activation was augmented. Similarly, LAR+/+ neurons treated with LAR siRNA demonstrated decreased activation of Trk and AKT. LAR is known to activate the Src PTK by dephosphorylation of its negative regulatory domain and Src transactivates Trk. In LAR-/- neurons, or neurons treated with LAR siRNA, phosphorylation of the Src regulatory domain was increased (indicating Src inactivation), consistent with a role for Src in mediating LAR's ability to up-regulate neurotrophic signaling. Interactions between LAR, TrkB, and Src were further confirmed by the findings that Src coimmunoprecipitated with LAR, that the Src inhibitor PP2 blocked the ability of LAR to augment TrkB signaling, and that siRNA-induced depletion of Src decreased LAR interaction with TrkB. These studies demonstrate that receptor PTPs can associate with Trk complexes and promote neurotrophic signaling and point to receptor PTP-based strategies as a novel approach for modulating neurotrophin function.

Ghrelin and cortistatin in lung cancer: expression of peptides and related receptors in human primary tumors and in vitro effect on the H345 small cell carcinoma cell line

Ghrelin, a natural GH secretagogue (GHS) acylated peptide, and cortistatin (CST), a natural SRIF-like peptide, interfere with neoplastic growth in different cancers. We tested forty-one lung carcinomas and the H345 small cell lung carcinoma (SCLC) cell line by RT-PCR to investigate the presence of ghrelin and CST and related receptors, including type 1a GHS receptor (GHS-R1a), all SRIF-receptor subtypes (sst 1-5) and MRGX2. Moreover, the presence of ghrelin and CST peptides was studied in both tumors and H345 cells. Ghrelin and CST mRNA were present in the majority of tested tumors, but ghrelin and CST proteins were revealed only in tumors with a neuroendocrine phenotype. All the receptors mRNA had a heterogeneous expression without correlation between ghrelin (or CST) and their receptor distribution. All the transcripts, but not GHS-R1a, were expressed in H345 cells. However, ghrelin and desacyl ghrelin induced in vitro a dose-dependent inhibition on the H345 cell proliferation and increased apoptosis. Conversely, neither CST nor SRIF affected H345 cell growth, despite the presence of their specific receptors. The anti-proliferative and the pro-apoptotic effects of ghrelin were consistent with binding experiments on H345 cell, where either acylated or des-acylated ghrelin recognized a common binding site. In conclusion, the present study indicates that: a) ghrelin and CST mRNAs are expressed in lung cancers, although some neuroendocrine tumors contain detectable amounts of the peptides; b) GHSR-1a mRNA is present exclusively in neuroendocrine tumors, whereas MRGX2 mRNA (but not peptide) is expressed in all histological types; c) both ghrelin forms inhibit H345 cell proliferation, both directly and enhancing apoptosis, despite the absence of GHS-R1a, whereas CST and its receptors do not interfere with cell growth.

Glutamate Activates Protein Kinase B (PKB/Akt) through AMPA Receptors in Cultured Bergmann Glia Cells

Glutamate is involved in gene expression regulation in neurons and glial cells through the activation of a diverse array of signaling cascades. In Bergmann glia, Ca2+ -permeable alpha-hydroxy-5-methyl-4-isoazole-propionic acid (AMPA) receptors become tyrosine phosphorylated after ligand binding and by these means form multiprotein signaling complexes. Of the various proteins that associate to these receptors, the phosphatidylinositol 3-kinase (PI-3K) deserves special attention since D3-phosphorylated phosphoinositides are docking molecules for signaling proteins with a pleckstrin homology domain. In order to characterize the role of PI-3K in AMPA receptors signaling, in the present report we analyze the involvement of the serine/threonine protein kinase B in this process. Our results demonstrate an augmentation in protein kinase B phosphorylation and activity after glutamate exposure. Interestingly, the effect is independent of Ca2+ influx, but sensitive to Src blockers. Our present findings broaden our current knowledge of glial glutamate receptors signaling and their involvement glutamatergic neurotransmission.

Multiplex Analysis of Intracellular Signaling Pathways in Lymphoid Cells by Microbead Suspension Arrays

Phosphorylation analysis of signaling proteins is key for examining intracellular signaling pathways. Conventional biochemical approaches, e.g. immunoprecipitation, Western blot, and ELISA, have played a major role in elucidation of individual signaling events. However, these methods are laborious, time-consuming, and difficult to adapt for high throughput analysis. A multiplex approach to measure phosphorylation state of multiple signaling proteins simultaneously would significantly enhance the efficiency and scope of signaling pathway analysis for mechanistic studies and clinical application. This report describes a novel multiplex microbead suspension array approach to examine phosphoproteomic profiles in lymphoid cells. In the Jurkat T-cell leukemia line, the multiplex assay enabled targeted investigation of phosphorylation kinetics of signal transduction from receptor proximal events (tyrosine phosphoproteins CD3, Lck, Zap-70, and linker for T-cell activation) to cytosolic events (serine/threonine phosphoproteins Erk and Akt) to transcription factors (serine/threonine phosphorylated Rsk, cyclic AMP-response element-binding protein, and STAT3). To broaden the application of the multiplex analysis, signaling pathways were also studied in B-cell lymphoid tumor lines that included chronic lymphocytic leukemia lines. In these cell lines, multiplex suspension array enabled phosphoproteomic analysis of signaling cascade mediated by Syk, a homolog of Zap-70. Results obtained by multiplex analysis were confirmed by immunoprecipitation and Western blot methods. The examples of T-cell and B-cell signaling pathway analyses in this report demonstrate the utility of the multiplex suspension arrays to investigate phosphorylation dynamics and kinetics of several signaling proteins simultaneously in signal transduction pathways.

Cytoskeletal Transport in the Aging Brain: Focus on the Cholinergic System

There is now compelling evidence for the aging-related breakdown of cytoskeletal support in neurons. Similarly affected are the principal components of the intracellular microtubule system, the transport units involved in active shuttle of organelles and molecules in an antero- and retrograde manner, and the proteins stabilizing the cytoskeleton and providing trophic support. Here, we review the basic organization of the cytoskeleton, and describe its elements and their interactions. We then critically assess the role of these cytoskeletal proteins in physiological aging and aging-related malfunction. Our focus is on the microtubule-associated protein tau, for which comprehensive investigations suggest a critical role in neurodegenerative diseases, for instance tauopathies. These diseases frequently lead to cognitive decline and are often paralleled by reductions in cholinergic neurotransmission. We propose this reduction to be due to destabilization of the cytoskeleton and protein transport mechanisms in these neurons. Therefore, maintenance of the neuronal cytoskeleton during aging may prevent or delay neurodegeneration as well as cognitive decline during physiological aging.

Insulin modulates hippocampal activity-dependent synaptic plasticity in a N-methyl-d-aspartate receptor and phosphatidyl-inositol-3-kinase-dependent manner

Insulin and its receptor are both present in the central nervous system and are implicated in neuronal survival and hippocampal synaptic plasticity. Here we show that insulin activates phosphatidylinositol 3-kinase (PI3K) and protein kinase B (PKB), and results in an induction of long-term depression (LTD) in hippocampal CA1 neurones. Evaluation of the frequency-response curve of synaptic plasticity revealed that insulin induced LTD at 0.033 Hz and LTP at 10 Hz, whereas in the absence of insulin, 1 Hz induced LTD and 100 Hz induced LTP. LTD induction in the presence of insulin required low frequency synaptic stimulation (0.033 Hz) and blockade of GABAergic transmission. The LTD or LTP induced in the presence of insulin was N-methyl-d-aspartate (NMDA) receptor specific as it could be inhibited by alpha-amino-5-phosphonopentanoic acid (APV), a specific NMDA receptor antagonist. LTD induction was also facilitated by lowering the extracellular Mg(2+) concentration, indicating an involvement of NMDA receptors. Inhibition of PI3K signalling or discontinuing synaptic stimulation also prevented this LTD. These results show that insulin modulates activity-dependent synaptic plasticity, which requires activation of NMDA receptors and the PI3K pathway. The results obtained provide a mechanistic link between insulin and synaptic plasticity, and explain how insulin functions as a neuromodulator.

Nitric oxide synthesis is required for exercise-induced increases in hippocampal BDNF and phosphatidylinositol 3' kinase expression

Previous studies have shown that running exercise, either alone or in combination with antidepressant treatment, results in increased hippocampal BDNF levels. Nitric oxide (NO) is an important signaling molecule that has neuronal survival-promoting properties and has been shown to play an important role in plasticity associated with activating interventions. Herein, we administered the NO synthase (NOS) inhibitor, N-nitro-L-arginine methyl ester (L-NAME), in conjunction with the monoamine oxidase inhibitor (MAOI) antidepressant, tranylcypromine, and voluntary wheel-running exercise to determine whether the enhancement in full-length BDNF mRNA occurring with these interventions is dependent upon NO synthesis. Our results demonstrate that both chronic exercise and chronic exercise-plus-tranylcypromine lead to enhanced hippocampal BDNF mRNA and protein expression. NOS inhibition prevents this effect of chronic exercise, but only partly prevents the effects of the exercise/antidepressant combination. Thus, the robust enhancement in BDNF mRNA occurring with exercise appears to be NO synthesis-dependent, but the intervention including antidepressant may enhance BDNF expression through alternative intracellular mechanisms. In addition, because exercise and antidepressants have both been shown to activate survival-promoting genes, we evaluated the levels of hippocampal phosphatidylinositol 3' kinase (PI-3K), an important signaling molecule within a principal neuronal survival-promoting intracellular pathway. Like BDNF mRNA and protein, exercise increases the expression of PI-3K, whereas concomitant NOS inhibition prevents this increase in PI-3K immunoreactivity above control levels. Our results are discussed in light of possible overlapping, but distinct intracellular pathways activated by exercise and antidepressant treatment to bring about enhancements in BDNF expression and other survival-promoting effects. These findings further demonstrate the potential therapeutic potential of chronic exercise to supplement pharmacotherapeutic treatment of mood disorders.

Nerve Growth Factor-Independent Neuronal Survival: A Role for NO Donors: Fig. 1

Because of the limited therapeutic applications of nerve growth factor (NGF), there has been increasing focus on the development of pharmacological tools to bypass the requirement of NGF for the activation of the TrkA tyrosine kinase receptor neuronal survival pathway. In this issue of Molecular Pharmacology, the work by Culmsee et al. (p. 1006) shows that NGF-independent activation of TrkA by protein tyrosine phosphatase (PTP) inhibitors is only achieved when accompanied by release of nitric oxide (NO). This work identifies the integration of the NO/cGMP/protein kinase G (PKG) and NGF/TrkA pathways to induce activation of Akt and ERK1/2 and mediate neuronal survival in the absence of NGF. In addition, it underscores the potential therapeutic effects of ethyl-3,4-dephostatin (DPN), a stable analog of the naturally occurring PTP inhibitor dephostatin, which serves as a NO donor and protects neurons from apoptosis. This Perspective comparatively reviews two major signal transduction pathways that mediate NGF-independent neuronal survival by activating the TrkA pathway: the NO/cGMP/PKG and adenosine/G-protein-coupled receptor (GPCR) pathways.

Nitric oxide donors induce neurotrophin-like survival signaling and protect neurons against apoptosis

Our previous results showed that inhibition of protein tyrosine phosphatases (PTP) by orthovanadate is an appropriate strategy to mimic nerve growth factor (NGF) effects in neurons, including enhanced phosphorylation of TrkA, stimulation of downstream survival signaling pathways, and protection against apoptotic stress. In this study, we wanted to trigger such NGF-like survival signaling in primary hippocampal neurons with the more specific PTP inhibitors ethyl-3,4-dephostatin (DPN), 4-O-methyl-ethyl-3,4-dephostatin (Me-DPN), and methoxime-3,4-dephostatin. It was striking that only the nitric oxide (NO)-releasing dephostatin analogs DPN and Me-DPN, but not the nitrosamine-free methoxime derivative (which did not release NO), enhanced TrkA phosphorylation and protected the neurons against staurosporine (STS)-induced apoptosis. The established NO donor S-nitroso-N-acetylpenicillamine (SNAP) also enhanced TrkA phosphorylation and prevented apoptosis similarly to DPN and Me-DPN. Analysis of the major signaling pathways downstream of TrkA revealed that both SNAP and DPN enhanced phosphorylation of Akt and the mitogen-activated kinases (MAPK) Erk1/2. Blocking of these signaling pathways by the PI3-K inhibitor wortmannin or the MAPK kinase inhibitor U0126 [1,4-diamino-2,3-dicyano-1,4-bis(2-aminophynyltio)butadiene] equally abolished the neuroprotective effect of the NO donors. It was striking that inhibition of the soluble guanylyl cyclase (sGC) by 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) or protein kinase G (PKG) inhibition by (9S,10R,12R)-2,3,9,10,11,12-hexahydro-10-methoxy-2,9-dimethyl-1-oxo-9,12-epoxy-1H-diindolo-[1,2,3-fg:3',2',1'-kl]pyrrolo[3,4-i][1,6]benzodiazocine-10-carboxylic acid methyl ester (KT5823) also blocked the neuroprotective effect of the NO donors, and ODQ clearly attenuated SNAP-induced phosphorylation of TrkA, Akt, and MAPK. In conclusion, NO release by the dephostatin derivatives and subsequent stimulation of sGC and PKG is essential for their neuroprotective effects. In primary neurons, such NO-activated survival signaling involves NGF-like effects, including enhanced phosphorylation of TrkA and activation of PI3-K/Akt and MAPK pathways.