The method of isolation of the crayfish abdominal stretch receptor maintaining a connection of the sensory neuron to the ventral nerve cord ganglion

E2F1 Expression and Apoptosis Initiation in Crayfish and Rat Peripheral Neurons and Glial Cells after Axonal Injury

Neurotrauma is among the main causes of human disability and mortality. The transcription factor E2F1 is one of the key proteins that determine the fate of cells. The involvement of E2F1 in the regulation of survival and death of peripheral nerve cells after axotomy has not been previously studied. We, for the first time, studied axotomy-induced changes in the expression and localization of E2F1 following axonal injury in rats and crayfish. Immunoblotting and immunofluorescence microscopy were used for the analysis of the expression and intracellular localization of E2F1 and its changes after axotomy. To evaluate whether this transcription factor promotes cell apoptosis, we examined the effect of pharmacological inhibition of E2F activity in axotomized rat models. In this work, axotomy caused increased expression of E2F1 as early as 4 h and even 1 h after axotomy of mechanoreceptor neurons and ganglia of crayfish ventral nerve cord (VNC), as well as rat dorsal root ganglia (DRG). The level of E2F1 expression increased both in the cytoplasm and the nuclei of neurons. Pharmacological inhibition of E2F demonstrated a pronounced neuroprotective activity against axotomized DRGs. E2F1 and downstream targets could be considered promising molecular targets for the development of potential neuroprotective agents.

Calcium in Neuronal and Glial Response to Axotomy

Neurotrauma assumes an instant or delayed disconnection of axons (axotomy), which affects not only neurons, but surrounding glia as well. Not only mechanically injured glia near the site of disconnection, especially transection, is subjected to the damage, but also glia that is remote from the lesion site. Glial cells, which surround the neuronal body, in turn, support neuron survival, so there is a mutual protection between neuron and glia. Calcium signaling is a central mediator of all post-axotomy events, both in neuron and glia, playing a critical role in their survival/regeneration or death/degeneration. The involvement of calcium in post-axotomy survival of the remote, mechanically intact glia is poorly studied. The purpose of this review is to sum up the calcium-involving mechanisms in responses of neurons and glial cells to axotomy to show their importance and to give some suggestions for future research of remote glia in this context.

HDAC1 Expression, Histone Deacetylation, and Protective Role of Sodium Valproate in the Rat Dorsal Root Ganglia After Sciatic Nerve Transection

Nerve injury is an important reason of human disability and death. We studied the role of histone deacetylation in the response of the dorsal root ganglion (DRG) cells to sciatic nerve transection. Sciatic nerve transection in the rat thigh induced overexpression of histone deacetylase 1 (HDAC1) in the ipsilateral DRG at 1-4 h after axotomy. In the DRG neurons, HDAC1 initially upregulated at 1 h but then redistributed from the nuclei to the cytoplasm at 4 h after axotomy. Histone H3 was deacetylated at 24 h after axotomy. Deacetylation of histone H4, accumulation of amyloid precursor protein, a nerve injury marker, and GAP-43, an axon regeneration marker, were observed in the axotomized DRG on day 7. Neuronal injury occurred on day 7 after axotomy along with apoptosis of DRG cells, which were mostly the satellite glial cells remote from the site of sciatic nerve transection. Administration of sodium valproate significantly reduced apoptosis not only in the injured ipsilateral DRG but also in the contralateral ganglion. It also reduced the deacetylation of histones H3 and H4, prevented axotomy-induced accumulation of amyloid precursor protein, which indicated nerve injury, and overexpressed GAP-43, a nerve regeneration marker, in the axotomized DRG. Therefore, HDAC1 was involved in the axotomy-induced injury of DRG neurons and glial cells. HDAC inhibitor sodium valproate demonstrated the neuroprotective activity in the axotomized DRG.

The Expression of E2F1, p53, and Caspase 3 in the Rat Dorsal Root Ganglia After Sciatic Nerve Transection

Neurotrauma is among the main causes of human disability and mortality. Nerve injury impairs not only neurons but also causes death of satellite glial cells remote from the injury site. We studied the dynamics of expression of different proapoptotic proteins (E2F1, p53, caspase 3) in the dorsal root ganglia (DRG) of a rat after sciatic nerve transection. TUNEL staining and immunoblotting were used for analysis of cell apoptosis and axotomy-induced biochemical changes. Apoptosis of glial cells was observed at 24 h after sciatic nerve transection and increased on day 7, when apoptosis of some neurons only started. The earliest proapoptotic event in the injured DRG was overexpression of transcription factor E2F1 at 4 h after sciatic nerve transection. This preceded the induction of p53 and cleavage of caspase 3 at 24-h post-axotomy. The nerve injury marker amyloid precursor protein and the nerve regeneration marker GAP-43 were overexpressed in DRG on day 7 after sciatic nerve transection. We also developed a novel fluorescence method for differential visualization of the rat DRG and nerves by means of double staining with propidium iodide and Hoechst 33342 that impart red and blue-green fluorescence, respectively. The present experiments showed that glial cells remote from the nerve transection site were more vulnerable to axotomy than DRG neurons. E2F1 and p53 may be considered promising molecular targets for development of potential neuroprotective agents.

The effect of axotomy on firing and ultrastructure of the crayfish mechanoreceptor neurons and satellite glial cells

Neurotrauma is among main causes of human disability and death. We studied effects of axotomy on ultrastructure and neuronal activity of a simple model object - an isolated crayfish stretch receptor that consists of single mechanoreceptor neurons (MRN) enwrapped by multilayer glial envelope. After isolation, MRN regularly fired until spontaneous activity cessation. Axotomy did not change significantly MRN spike amplitude and firing rate. However, the duration of neuron activity from MRN isolation to its spontaneous cessation decreased in axotomized MRN relative to intact neuron. [Ca²⁺] in MRN axon and soma increased 3-10 min after axotomy. Ca²⁺ entry through ion channels in the axolemma accelerated axotomy-stimulated firing cessation. MRN incubation with Ca²⁺ionophore ionomycin accelerated MRN inactivation, whereas Ca²⁺-channel blocker Cd²⁺ prolonged firing. Activity duration of either intact, or axotomized MRN did not change in the presence of ryanodine or dantrolene, inhibitors of ryanodin-sensitive Ca²⁺ channels in endoplasmic reticulum. Thapsigargin, inhibitor of endoplasmic reticulum Ca²⁺-ATPase, or its activator ochratoxin were ineffective. Ultrastructural study showed that the defect in the axon transected by thin scissors is sealed by fused axolemma, glial and collagen layers. Only the 30-50 μm long segment completely lost microtubules and contained swelled mitochondria. The microtubular bundle remained undamaged at 300 μm away from the axotomy site. However, mitochondria within the 200-300 μm segment were strongly condensed and lost matrix and cristae. Glial and collagen layers exhibited greater damage. Swelling and edema of glial layers, collagen disorganization and rupture occurred within this segment. Thus, axotomy stronger damages glia/collagen envelope, axonal microtubules and mitochondria.

The Localization of p53 in the Crayfish Mechanoreceptor Neurons and Its Role in Axotomy-Induced Death of Satellite Glial Cells Remote from the Axon Transection Site

Neuron and glia death after axon transection is regulated by various signaling proteins. Protein p53 is a key regulator of diverse cell functions including stress response, DNA repair, proliferation, and apoptosis. We showed that p53 was overexpressed in crayfish ganglia after bilateral axotomy. In the isolated crayfish stretch receptor, a simple natural neuroglial preparation, which consists of a single mechanoreceptor neuron (MRN) enveloped by glial cells, p53 regulated axotomy-induced death of glial cells remote from the axon transection site. In MRN, p53 immunofluorescence was highest in the nucleolus and in the narrow cytoplasmic ring around the nucleus; its levels in the nucleus and cytoplasm were lower. After axotomy, p53 accumulated in the neuronal perikaryon. Its immunofluorescence also increased in the neuronal and glial nuclei. However, p53 immunofluorescence in the most of neuronal nucleoli disappeared. Axotomy-induced apoptosis of remote glial cells increased in the presence of p53 activators WR-1065 and nutlin-3 but reduced by pifithrin-α that inhibits transcriptional activity of p53. Pifithrin-μ that inhibits p53 effect on mitochondria increased axotomy-induced apoptosis of remote glial cells but reduced their necrosis. Therefore, axotomy-induced apoptosis of remote glial cells was associated with p53 effect on transcription processes, whereas glial necrosis was rather associated with transcription-independent p53 effect on mitochondria. Apparently, the fate of remote glial cells in the axotomized crayfish stretch receptor is determined by the balance between different modalities of p53 activity.

Ca2+ mediates axotomy-induced necrosis and apoptosis of satellite glial cells remote from the transection site in the isolated crayfish mechanoreceptor

Severe nerve injury such as axotomy induces neuron degeneration and death of surrounding glial cells. Using a crayfish stretch receptor that consists of a single mechanoreceptor neuron enveloped by satellite glia, we showed that axotomy not only mechanically injures glial cells at the transection location, but also induces necrosis or apoptosis of satellite glial cells remote from the transection site. We studied Ca²⁺role in spontaneous or axotomy-induced death of remote glial cells. Stretch receptors were isolated using the original technique that kept the neuron connected to the ventral cord ganglion (control preparations). Using Ca²⁺-sensitive fluorescence probe fluo-4, we showed Ca²⁺ accumulation in neuronal perikarion and glial envelope. Ca²⁺ gradually accumulated in glial cells after axotomy. In saline with triple Ca²⁺ concentration the axotomy-induced apoptosis of glial cells increased, but spontaneous or axotomy-induced necrosis was unexpectedly reduced. Saline with 1/3[Ca²⁺], oppositely, enhanced glial necrosis. Application of ionomycin, CdCl₂, thapsigargin, and ryanodine showed the involvement of Ca²⁺ influx through ionic channels in the plasma membrane, inhibition of endoplasmic reticulum Ca²⁺-ATPase, and Ca²⁺ release from endoplasmic reticulum through ryanodine receptors in axotomy-induced glial necrosis. Apoptosis of glial cells surrounding axotomized neurons was promoted by ionomycin and thapsigargin. Possibly, other Ca²⁺ sources such as penetration through the plasma membrane contributed to axotomy-induced apoptosis and necrosis of remote glial cells. Thus, modulating different pathways that maintain calcium homeostasis, one can modulate axotomy-induced death of glial cells remote from the transection site.