Involvement of adenylate cyclase and tyrosine kinase signaling pathways in response of crayfish stretch receptor neuron and satellite glia cell to photodynamic treatment

Protection of the Crayfish Mechanoreceptor Neuron and Glial Cells from Photooxidative Injury by Modulators of Diverse Signal Transduction Pathways

Oxidative stress is the reason of diverse neuropathological processes. Photodynamic therapy (PDT), an effective inducer of oxidative stress, is used for cancer treatment, including brain tumors. We studied the role of various signaling pathways in photodynamic injury and protection of single neurons and satellite glial cells in the isolated crayfish mechanoreceptor. It was photosensitized with alumophthalocyanine Photosens in the presence of inhibitors or activators of various signaling proteins. PDT eliminated neuronal activity and killed neurons and glial cells. Inhibitory analysis showed the involvement of protein kinases Akt, glycogen synthase kinase-3β (GSK-3β), mammalian target of rapamycin (mTOR), mitogen-activated protein kinase kinases 1 and 2 (MEK1/2), calmodulin, calmodulin-dependent kinase II (CaMKII), adenylate cyclase, and nuclear factor NF-κB in PDT-induced necrosis of neurons. Nitric oxide (NO) and glial cell-derived neurotrophic factor (GDNF) reduced neuronal necrosis. In glial cells, protein kinases Akt, calmodulin, and CaMKII; protein kinases C and G, adenylate cyclase, and p38; and nuclear transcription factor NF-κB also mediated PDT-induced necrosis. In contrast, NO and neurotrophic factors nerve growth factor (NGF) and GDNF demonstrated anti-necrotic activity. Phospholipase Cγ, protein kinase C, GSK-3β, mTOR, NF-κB, mitochondrial permeability transition pores, and NO synthase mediated PDT-induced apoptosis of glial cells, whereas protein kinase A, tyrosine phosphatases, and neurotrophic factors NGF, GDNF, and neurturin were involved in protecting glial cells from photoinduced apoptosis. Signaling pathways that control cell survival and death differed in neurons and glia. Inhibitors or activators of some signaling pathways may be used as potential protectors of neurons and glia from photooxidative stress and following death.

Epigenetic regulation of death of crayfish glial cells but not neurons induced by photodynamic impact

Epigenetic processes are involved in regulation of cell functions and survival, but their role in responses of neurons and glial cells to oxidative injury is insufficiently explored. Here, we studied the role of DNA methylation and histone deacetylation in reactions of neurons and surrounding glial cells to photodynamic treatment that induces oxidative stress and cell death. Isolated crayfish stretch receptor consisting of a single mechanoreceptor neuron surrounded by glial cells was photosensitized with aluminum phthalocyanine Photosens that induced neuron inactivation, necrosis of the neuron and glia, and glial apoptosis. Inhibitors of DNA methylation 5-azacytidine and 5-aza-2'-deoxycytidine (decitabine) reduced the level of PDT-induced necrosis of glial cells but not neurons by 1.3 and 2.0 times, respectively, and did not significantly influence apoptosis of glial cells. Histone deacetylase inhibitors valproic acid and trichostatin A inhibited PDT-induced both necrosis and apoptosis of satellite glial cells but not neurons by 1.6-2.7 times. Thus, in the crayfish stretch receptor DNA methylation and histone deacetylation are involved in epigenetic control of glial but not neuronal necrosis. Histone deacetylation also participates in glial apoptosis.

On the role of phosphatidylinositol 3-kinase, protein kinase b/Akt, and glycogen synthase kinase-3β in photodynamic injury of crayfish neurons and glial cells

Photodynamic treatment that causes intense oxidative stress and cell death is currently used in neurooncology. However, along with tumor cells, it may damage healthy neurons and glia. To study the involvement of signaling processes in photodynamic injury or protection of neurons and glia, we used crayfish mechanoreceptor consisting of a single neuron surrounded by glial cells. It was photosensitized with alumophthalocyanine Photosens. Application of specific inhibitors showed that phosphatidylinositol 3-kinase did not participate in photoinduced death of neurons and glia. Akt was involved in photoinduced necrosis but not in apoptosis of neurons and glia. Glycogen synthase kinase-3β participated in photoinduced apoptosis of glial cells and in necrosis of neurons. Therefore, phosphatidylinositol 3-kinase/protein kinase Akt/glycogen synthase kinase-3β pathway was not involved as a whole in photodynamic injury of crayfish neurons and glia but its components, Akt and glycogen synthase kinase-3β, independently and cell specifically regulated death of neurons and glial cells. According to these data, necrosis in this system was a controlled but not a non-regulated cell death mode. The obtained results may be used for the search of pharmacological agents selectively modulating death and survival of normal neurons and glial cells during photodynamic therapy of brain tumors.

Elevated activity of the crayfish stretch receptor neuron increases resistance of surrounding glial cells to apoptosis induced by photodynamic treatment

Neuroglial interaction is very important for functioning and survival of nerve and glial cells. In the present work, we studied the influence of the intense neuronal activity on survival of the isolated crayfish stretch receptor neuron and surrounding glial cells subjected to photodynamic treatment, which induces intense oxidative stress. In the experimental group, neurons were stimulated by multiple extensions of the receptor muscle for 1h so that the firing rate did not fall below 10-15 Hz, whereas in the control group, the receptor muscles were relaxed and neurons were silent. After stimulation, the preparations were photosensitized with alumophthalocyanine Photosens and irradiated by 670 nm laser diode. The isolated stretch receptors were stained with propidium iodide and Hoechst 33342, which reveal the nuclei of the necrotic and the apoptotic cells, respectively. The level of apoptosis of photosensitized glial cells was significantly lower in the experimental group compared to the resting control. Necrosis of neurons and glial cells was not significantly influenced. Therefore, elevated neuronal activity increased the resistance of the surrounding glial cells to photoinduced apoptosis. This could be attributed to the depletion of the energetic resources, which are transferred from glia into the neuron to support its firing, or to the neurotrophic neuron-to-glia signaling.

Ultrastructure of neuroglial contacts in crayfish stretch receptor

In order to explore neuroglial relationships in a simple nervous system, we have studied the ultrastructure of the crayfish stretch receptor, which consists of only two mechanoreceptor neurons enwrapped by glial cells. The glial envelope comprises 10-30 glial layers separated by collagen sheets. The intercellular space between the neuronal and glial membranes is generally less than 10-15 nm in width. This facilitates diffusion between neurons and glia but restricts neuron communication with the environment. Microtubule bundles passing from the dendrites to the axon through the neuron body limit vesicular transport between the perikaryon and the neuronal membrane. Numerous invaginations into the neuron cytoplasm strengthen glia binding to the neuron and shorten the diffusion pathway between them. Double-membrane vesicles containing fragments of glial, but not neuronal cytoplasm, represent the captured tips of invaginations. Specific triads, viz., "flat submembrane cisterns - vesicles - mitochondria", are presumably involved in the formation of the invaginations and double-membrane vesicles and in neuroglial exchange. The tubular lattice in the glial cytoplasm might transfer ions and metabolites between the glial layers. The integrity of the neuronal and glial membranes is impaired in some places. However, free neuroglial passage might be prevented or limited by the dense diffuse material accumulated in these regions. Thus, neuroglial exchange with cellular components might be mediated by transmembrane diffusion, especially in the invaginations and submembrane cisterns, by the formation of double-walled vesicles in which large glial masses are captured and by transfer through tubular lattices.

Protection of crayfish glial cells but not neurons from photodynamic injury by nerve growth factor

Photodynamic treatment that causes intense oxidative stress and cell death is currently used in neurooncology. However, along with tumor cells, it may damage healthy neurons and glia. In order to study photodynamic effect on normal nerve and glial cells, we used crayfish stretch receptor, a simple system consisting of only two identified sensory neurons surrounded by glial cells. Photodynamic treatment induced firing abolition and necrosis of neurons as well as necrosis and apoptosis of glial cells. Nerve growth factor but not brain-derived neurotrophic factor or epidermal growth factor protected glial cells but not neurons from photoinduced necrosis and apoptosis. Inhibitors of tyrosine kinases or protein kinase JNK eliminated anti-apoptotic effect of nerve growth factor in photosensitized glial cells but not neurons. Therefore, these signaling proteins were involved in the anti-apoptotic activity of nerve growth factor. These data indicate the possible presence of receptors capable of recognizing murine nerve growth factor in crayfish glial cells. Thus, intercellular signaling mediated by nerve-growth-factor-like neurotrophin, receptor tyrosine kinase, and JNK may be involved in crayfish glia protection from apoptosis induced by photodynamic treatment.

Neuron and gliocyte death induced by photodynamic treatment: signal processes and neuron-glial interactions

The mechanisms of photodynamic (PD) damage to neurons and gliocytes are discussed. The spike reactions of neurons are described, with stimulation at high concentrations of photosensitizer and inhibition at low concentrations, accompanying necrosis. Glial cells developed both necrosis and apoptosis. Local laser inactivation of neurons increased light-induced apoptosis of gliocytes, i.e., neurons maintained gliocyte survival. Inter-and intracellular signaling plays an important role in the photolesioning of these cells. Studies using inhibitors and activators of signal proteins demonstrated the involvement of the Ca(2+)-dependent, adenylate cyclase, and tyrosine kinase pathways in the responses of neurons and gliocytes to PD treatment. Pharmacological modulation may alter the selectivity of PD neuron and gliocyte damage and the efficacy of PD treatment.

Involvement of Ca2+- and cyclic adenosine monophosphate-mediated signaling pathways in photodynamic injury of isolated crayfish neuron and satellite glial cells

To investigate the mechanisms of oxidative injury of neurons and glia, we studied the photodynamic effect on isolated stretch receptor that consists of only two sensory neurons enwrapped by satellite glial cells. Photodynamic therapy (PDT), a potent inducer of oxidative stress, is a prospective method for destruction of brain tumors. PDT induced functional inactivation and necrosis of neurons, necrosis, apoptosis, and proliferation of glial cells. The roles of calmodulin, calmodulin-dependent kinase II, phospholipase C, protein kinases A and C, and phosphodiesterase in these processes were studied by using their inhibitors: fluphenazine, KN-93, D-609, H89, staurosporine, and papaverine, respectively. PDT-induced firing abolishment was enhanced by H89 or papaverine, whereas staurosporine acted oppositely. Fluphenazine or KN-93 reduced necrosis of neurons and glial cells. H89 enhanced necrosis of neurons, whereas staurosporine enhanced necrosis of glial cells. Inhibition of protein kinases A and C enhanced PDT-induced glial apoptosis. Photodynamic gliosis was prevented by KN-93 or staurosporine. These data indicate possible involvement of calmodulin and calmodulin-dependent kinase II in photoinduced necrosis of neurons and glia. Protein kinase C could protect glial cells from necrosis and apoptosis and participate in photoinduced gliosis and loss of neuronal activity. Protein kinase A maintained neuronal firing and protected neurons from photoinduced necrosis and glial cells from apoptosis. Phosphodiesterase reduced necrosis of photosensitized neurons and glia. Thus, Ca(2+)- and cAMP-mediated signaling pathways were involved in photooxidative injury of neurons and glia. Their pharmacological modulation may differently change the efficacy of photodynamic injury of neurons and glial cells.

Crayfish mechanoreceptor neuron prevents photoinduced apoptosis of satellite glial cells

Interactions between neurons and glia play a key role in the development, functioning and survival of the nervous system. However, the influence of neurons on glial cells has received less attention than the role of glia in supporting neural functions. We here investigated the role of isolated crayfish stretch receptor neuron in the death of satellite glial cells under photodynamic impact. After staining with aluminum phthalocyanine photosens, the neuronal cell body was locally irradiated with a focused beam of He-Ne (633 nm, 200 W/cm2) or semiconductor laser (650 nm, 50 W/cm2). This rapidly abolished neuronal activity. The whole preparation was then subjected to total laser irradiation with lower intensity (633 nm, 0.3 W/cm2), which induced death of glial cells. Double staining of the preparation with propidium iodide and Hoechst 33342 in the following 6-7h allowed the visualization of necrotic, apoptotic and alive cells. Previous neuron inactivation with the focused laser beam was found to increase photodynamically-induced apoptosis but not necrosis of satellite glial cells enwrapping the axon. Therefore, the intact neuronal cell body protected satellite glial cells against photoinduced apoptosis. Altogether the data indicate that mechanoreceptor neurons release some signaling molecules involved in the prevention of glial apoptosis. This may provide integrity of the stretch receptor organ and its resistance to injurious factors.

PDT-induced death of sensory neurons and glial cells in the isolated crayfish stretch receptor after proteolytic treatment

To study the involvement of neuroglial interactions in photodynamic damage of crayfish stretch receptor, which consists of only two neurons surrounded by satellite glial cells (SGCs), we attempted to proteolytically uncouple neurons and glia and then compare the responses of these cells to photosensitization when intercellular communications were intact or impaired. After incubation of isolated stretch receptors with pronase or collagenase they were photosensitized with Photosens, a mixture of sulfonated alumophthalocyanines AlPcS(n) (n = 2, 3, and 4; mean n = 3.1). In the next 6 hr the preparations were double fluorochromed with propidium iodide and Hoechst-33342 to visualize necrotic and apoptotic cells. Proteolytic treatment shortened bioelectric neuron response and precipitated its functional inactivation; however, it did not significantly impair neuron morphology and did not induce its necrosis either in the darkness or under photosensitization. Photodynamic treatment induced necrosis of neurons and SGC and apoptosis of glial cells. Pronase but not collagenase increased percent of necrotic and apoptotic SGCs in the darkness and thus reduced the number of glial cells around the neuron; however, both pronase and collagenase prevented photodynamically induced apoptosis of glial cells. The involvement of neuron-to-glia signaling interactions in this phenomenon is suggested.