Activation of cyclic GMP-dependent protein kinase blocks alcohol-mediated cell death and calcium disruption in cerebellar granule neurons

Protective Effects of Some Grapevine Polyphenols against Naturally Occurring Neuronal Death

The interest in the biological properties of grapevine polyphenols (PPs) in neuroprotection is continuously growing in the hope of finding translational applications. However, there are several concerns about the specificity of action of these molecules that appear to act non-specifically on the permeability of cellular membranes. Naturally occurring neuronal death (NOND) during cerebellar maturation is a well characterized postnatal event that is very useful to investigate the death and rescue of neurons. We here aimed to establish a baseline comparative study of the potential to counteract NOND of certain grapevine PPs of interest for the oenology. To do so, we tested ex vivo the neuroprotective activity of peonidin- and malvidin-3-O-glucosides, resveratrol, polydatin, quercetin-3-O-glucoside, (+)-taxifolin, and (+)-catechin. The addition of these molecules (50 μM) to organotypic cultures of mouse cerebellum explanted at postnatal day 7, when NOND reaches a physiological peak, resulted in statistically significant (two-tailed Mann-Whitney test-p < 0.001) reductions of the density of dead cells (propidium iodide+ cells/mm2) except for malvidin-3-O-glucoside. The stilbenes were less effective in reducing cell death (to 51-60%) in comparison to flavanols, (+)-taxifolin and quercetin 3-O-glucoside (to 69-72%). Thus, molecules with a -OH group in ortho position (taxifolin, quercetin 3-O-glucoside, (+)-catechin, and peonidin 3-O-glucoside) have a higher capability to limit death of cerebellar neurons. As NOND is apoptotic, we speculate that PPs act by inhibiting executioner caspase 3.

Nitric oxide prevents H2O2-induced apoptosis in SK-N-MC human neuroblastoma cells

Nitric oxide (NO) is a cellular signaling molecule in many physiological and pathological processes including neuroprotector. Here we examined the antiapoptotic effect of NO in SK-N-MC cells. H2O2 treatment (10-200 μM) induced cell death in a dose-dependent manner and pretreatment of cells with 100 μM S-nitroso-N-acetylpenicillamine (SNAP), an NO donor, attenuated the occurrence of H2O2-induced cell death. DAPI staining showed H2O2-induced nuclear fragmentation and NO treatment suppressed it. NO inhibited the proteolytic activation of caspase-3 and mitochondrial cytochrome c release. Treatment of soluble guanylyl cyclase inhibitor ODQ decreased the protective effect of SNAP on H2O2-treated cells and increased caspase 3-like enzyme activity and activation, cytochrome c release, PARP cleavage, and DNA fragmentation, indicating that cGMP is a key mediator in NO-mediated antiapoptosis. The cGMP analog 8-Br-cGMP blocked H2O2-induced apoptotic cell death; reduction of caspase-3 enzyme, cytochrome c release, and caspase-8 and -9. These preventive effects of SNAP and 8-Br-cGMP were suppressed by PKG inhibitor KT5823. Levels of PKGI, PKGII, and p-VASP proteins were increased by SNAP and 8-Br-cGMP and suppressed by KT5823 treatment. These results indicate that PKG is a downstream signal mediator in the suppression of apoptosis by NO and cGMP. Akt activation was inhibited the PI3K inhibitors LY294002 and Wortmannin, resulting in the inhibition of cell viability and increase of cytochrome c release. SNAP induced phosphorylation of Akt and Bad and then increased the interactions between 14-3-3β and p-Bad. These data suggest that the NO suppresses H2O2-induced SK-N-MC cell apoptosis by suppressing apoptosis signal mediating the interaction between 14-3-3β and Bad phosphorylation via PKG/PI3K/Akt.

Real-Time Imaging Reveals Augmentation of Glutamate-Induced Ca2+ Transients by the NO-cGMP Pathway in Cerebellar Granule Neurons

Dysfunctions of NO-cGMP signaling have been implicated in various neurological disorders. We have studied the potential crosstalk of cGMP and Ca²⁺ signaling in cerebellar granule neurons (CGNs) by simultaneous real-time imaging of these second messengers in living cells. The NO donor DEA/NO evoked cGMP signals in the granule cell layer of acute cerebellar slices from transgenic mice expressing a cGMP sensor protein. cGMP and Ca²⁺ dynamics were visualized in individual CGNs in primary cultures prepared from 7-day-old cGMP sensor mice. DEA/NO increased the intracellular cGMP concentration and augmented glutamate-induced Ca²⁺ transients. These effects of DEA/NO were absent in CGNs isolated from knockout mice lacking NO-sensitive guanylyl cyclase. Furthermore, application of the cGMP analogues 8-Br-cGMP and 8-pCPT-cGMP, which activate cGMP effector proteins such as cyclic nucleotide-gated cation channels and cGMP-dependent protein kinases (cGKs), also potentiated glutamate-induced Ca²⁺ transients. Western blot analysis failed to detect cGK type I or II in our primary CGNs. The addition of phosphodiesterase (PDE) inhibitors during cGMP imaging showed that CGNs degrade cGMP mainly via Zaprinast-sensitive PDEs, most likely PDE5 and/or PDE10, but not via PDE1, 2, or 3. In sum, these data delineate a cGK-independent NO-cGMP signaling cascade that increases glutamate-induced Ca²⁺ signaling in CGNs. This cGMP–Ca²⁺ crosstalk likely affects neurotransmitter-stimulated functions of CGNs.