Nitric Oxide Donors Induce Neurotrophin-Like Survival Signaling and Protect Neurons against Apoptosis

Abstract

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: 3Ј,2Ј,1Ј-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 SNAPinduced 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.Nitric oxide is an endogenous regulator of different cellular functions, including vascular tone (Gruetter et al., 1979;Furchgott and Zawadzki, 1980), neurotransmission (Vincent, 1994;Garthwaite and Boulton, 1995), inflammation (Nathan and Shiloh, 2000), and cellular signaling cascades (Dawson et al., 1992). In neurons, NO has been found to be a Janus-faced molecule that can mediate survival signaling (Troy et al., 2000;Contestabile and Ciani, 2004) but may on the other hand contribute to neuronal death and brain damage in neurological diseases [e.g., stroke (Zhang et al., 1996), Alzheimer's disease , amyotrophic lateral sclerosis (Urushitani and Shimohama, 2001), or Parkinson's disease (Liberatore et al., 1999)]. In the brain, NO can be Article, publication date, and citation information can be found at http://molpharm.aspetjournals.org.

The antitumor properties of a nontoxic, nitric oxide–modified version of saquinavir are independent of Akt

“…In agreement with this hypothesis, the neuroprotective role of NO has been shown to depend, at least partially, on its ability to promote Akt phosphorylation (39). In addition, Saq has been shown, in a manner dependent on its ability to down-regulate the PI3K/Akt pathway, to dramatically affect the propagation of signals triggered by insulin receptor binding, and thereby to trigger insulin resistance in treated cells (11).…”

Kavalactones Protect Neural Cells against Amyloid β Peptide-Induced Neurotoxicity via Extracellular Signal-Regulated Kinase 1/2-Dependent Nuclear Factor Erythroid 2-Related Factor 2 Activation

“…In contrast, there are suggestions that ERK1/2 activation may also be associated with neuronal cell death in various neurodegeneration models, especially if occurring coincidentally with oxidative stress (Zhu et al, 2004). However, activation of ERK1/2 in situations devoid of prevailing oxidative stress, as may be the case with kavalactones, could be neuroprotective (see below; Culmsee et al, 2005).…”

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

“…In this system, through TrkA receptor phosphorylation, adenosine is capable of activating the PI3-kinase/Akt cascade, resulting in a survival response in PC-12 and hippocampal cells in the absence of NGF. The results of Culmsee et al (2005) identify the NO/cGMP pathway as another signal transduction pathway that is integrated with NGF/TrkA signaling to modulate activation of PI3 Kinase/Akt pathway and subsequent neuronal survival. Both NO and adenosine can phosphorylate TrkA and exert neuroprotective effects in the absence of NGF.…”

“…In this issue of Molecular Pharmacology, the article by Culmsee et al (2005) reveals phosphorylation of TrkA as a novel point of cross-talk between the NGF and NO neuronal survival pathways. Culmsee et al (2005) shed light on the molecular mechanism used by NO donors to rescue neurons from apoptosis.…”

“…Culmsee et al (2005) shed light on the molecular mechanism used by NO donors to rescue neurons from apoptosis. These investigators previously identified that inhibition of PTPs by orthovanadate stimulates the NGF/TrkA signaling pathway (Gerling et al, 2004 The NGF/TrkA signaling pathway converges with painrelated ion channels to regulate NGF-mediated heat sensitivity of sensory neurons (Chuang et al, 2001) and with G-protein-coupled receptors (GPCR) to regulate neuronal survival (Lee and Chao, 2001).…”