Dynamics of ultrastructural alterations in photosensitized crayfish glial and neuronal cells: Structures involved in transport processes and neuroglial interactions

Structural alterations in cell organelles induced by photodynamic treatment with chlorin p6 -histamine conjugate in human oral carcinoma cells probed by 3D fluorescence microscopy

We have explored the intracellular cell organelle's structural alterations after photodynamic treatment with chlorin p₆ -histamine conjugate (Cp₆ -his) in human oral cancer cells. Herein, the cells were treated with Cp₆ -his (10 μm) and counterstained with organelle-specific fluorescence probes to find the site of intracellular localization using confocal microscopy. For photodynamic therapy (PDT), the cells were exposed to ~30 kJ/m² red light (660 ± 20 nm) to induce ~90% cytotoxicity. We used the three-dimensional (3D) image reconstruction approach to analyze the photodynamic damage to cell organelles. The result showed that Cp₆ -his localized mainly in the endoplasmic reticulum (ER) and lysosomes but not in mitochondria and Golgi apparatus (GA). The 3D model revealed that in necrotic cells, PDT led to extensive fragmentation of ER and fragmentation and swelling of GA as well. Results suggest that the indirect damage to GA occurred due to loss of connection between ER and GA. Moreover, in damaged cells with no sign of necrosis, the perinuclear ER appeared condensed and surrounded by several small clumps at the peripheral region of the cell, and the GA was observed to form a single condensed structure. Since these structural changes were associated with apoptotic cell death, it is suggested that the necrotic and apoptotic death induced by PDT with Cp₆ -his is determined by the severity of damage to ER and indirect damage to GA. The results suggest that the indirect damage to cell organelle apart from the sites of photosensitizer localization and the severity of damage at the organelle level contribute significantly to the mode of cell death in PDT.

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.

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.

Neuroprotective response after photodynamic therapy: role of vascular endothelial growth factor

Background

Anti-vascular endothelial growth factor (VEGF) drugs and/or photodynamic therapy (PDT) constitute current treatments targeting pathological vascular tissues in tumors and age-related macular degeneration. Concern that PDT might induce VEGF and exacerbate the disease has led us to current practice of using anti-VEGF drugs with PDT simultaneously. However, the underlying molecular mechanisms of these therapies are not well understood.

Methods

We assessed VEGF levels after PDT of normal mouse retinal tissue, using a laser duration that did not cause obvious tissue damage. To determine the role of PDT-induced VEGF and its downstream signaling, we intravitreally injected a VEGF inhibitor, VEGFR1 Fc, or a PI3K/Akt inhibitor, LY294002, immediately after PDT. Then, histological and biochemical changes of the retinal tissue were analyzed by immunohistochemistry and immunoblot analyses, respectively.

Results

At both the mRNA and protein levels, VEGF was upregulated immediately and transiently after PDT. VEGF suppression after PDT resulted in apoptotic destruction of the photoreceptor cell layer in only the irradiated area during PDT. Under these conditions, activation of the anti-apoptotic molecule Akt was suppressed in the irradiated area, and levels of the pro-apoptotic protein BAX were increased. Intravitreal injection of a PI3K/Akt inhibitor immediately after PDT increased BAX levels and photoreceptor cell apoptosis.

Conclusion

Cytotoxic stress caused by PDT, at levels that do not cause overt tissue damage, induces VEGF and activates Akt to rescue the neural tissue, suppressing BAX. Thus, the immediate and transient induction of VEGF after PDT is neuroprotective.