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Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. How may light of different wave lengths directly affect mitochondrial function?
  5. Effect of light on Apoptosis inducing factor (AIF)
  6. Influence of light on mitochondrial electron transport system
  7. Light action on Dexras1
  8. Conclusions
  9. Author biographies
  10. Acknowledgments
  11. References

Visible light (360–760 nm) entering the eye impinges on the many ganglion cell mitochondria in the non-myelinated part of their axons. The same light also disrupts isolated mitochondrial function in vitro and kills cells in culture with the blue light component being particularly lethal whereas red light has little effect. Significantly, a defined light insult only affects the survival of fibroblasts in vitro that contain functional mitochondria supporting the view that mitochondrial photosensitizers are influenced by light. Moreover, a blue light insult to cells in culture causes a change in mitochondrial structure and membrane potential and results in a release of cytochrome c. Blue light also causes an alteration in mitochondria located components of the OXPHOS (oxidative phosphorylation system). Complexes III and IV as well as complex V are significantly upregulated whereas complexes I and II are slightly but significantly up- and downregulated, respectively. Also, blue light causes Dexras1 and reactive oxygen species to be upregulated and for mitochondrial located apoptosis-inducing factor to be activated. A blue light detrimental insult to cells in culture does not involve the activation of caspases but is known to be attenuated by necrostatin-1, typical of a death mechanism named necroptosis.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. How may light of different wave lengths directly affect mitochondrial function?
  5. Effect of light on Apoptosis inducing factor (AIF)
  6. Influence of light on mitochondrial electron transport system
  7. Light action on Dexras1
  8. Conclusions
  9. Author biographies
  10. Acknowledgments
  11. References

Although the eye is exposed to daily fluxes of solar radiation, the amount of non-ionizing radiation actually reaching the retina is between 390 and 760 nm of the so-called “visible component” of the electromagnetic spectrum (1). Experimental studies have clearly shown that excessive light (390–760 nm) has a negative effect on the survival of photoreceptors and the retinal pigment epithelial (RPE) cells (2–4) and, as a consequence, excessive light has been suggested to enhance the progression and severity of human age-related macular degeneration and perhaps some forms of retinitis pigmentosa (5–7). The prime reason for deducing that photoreceptors/RPE cells are affected by excessive light (390–760 nm) in experimental animals is because these cell types express appropriate photosensitizers that are able to absorb and be affected by light (1,4) and also because their damage can be recognized by observation of flash electroretinograms and by simple examination of histological retinal sections (2,3). As a consequence, any possible detrimental influences of light on inner retinal cells have been largely ignored despite the fact that the inner retina, unlike the outer retina, is not protected from light (particularly in the blue light range) by the macular carotenoids, zeaxanthin and lutein, located chiefly in the outer plexiform layer (8).

Light-induced injury to the photoreceptors/RPE is accompanied by local edema in the subretinal space and outer retina (9,10) and this understandably leads to secondary changes associated with other retinal cell types. Indeed, Müller cells obtained from retinas that had been subjected to blue light insults in vivo show a decrease in potassium conductance and potassium and aquaporin proteins as well as an upregulation of glial fibrillary acidic protein (11). Ganglion cell loss is known to be associated with phototoxic-induced photoreceptor loss (12,13) but it remains unclear whether this is solely a consequence of secondary events associated with photoreceptor loss or because of a direct action of light on ganglion cell mitochondria.

Our recent studies have been based on the proposition that of all the neuron types in the inner retina, ganglion cells are the most likely to be affected directly by light and this can have negative consequences in certain situations (14,15). This is because retinal ganglion cell axons are unmyelinated within the ocular globe and have varicosities that are rich in mitochondria (16,17). In the myelinated regions of the ganglion, cell axons outside the globe mitochondria are very much fewer in number except in the nodes of Ranvier where energy is required for the continuous propagation of action potentials (Fig. 1). Light entering the retina will therefore directly impinge on the ganglion cell intra-axonal mitochondria lacking myelin before penetrating to the deeper retinal cells to eventually activate photoreceptor rhodopsin. We have therefore formulated the working hypothesis that light is absorbed by ganglion cell mitochondrial photosensitizers on entering the eye but this is tolerated when ganglion cells are in a homeostatic state. However, when the homeostatic state of ganglion cells is compromised as might occur in glaucoma, diabetic retinopathy or because of a genetic defect (Leber’s Heriditary Optic Neuropathy), then this might not be the case (15,18).

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Figure 1.  This is a schematic view of a retinal ganglion cell where the axon in the optic nerve is myelinated and where clusters of mitochondria are located in regions of the Nodes of Ranvier. In contrast, many mitochondria are associated with the unmyelinated part of the ganglion cell axons within the globe.

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How may light of different wave lengths directly affect mitochondrial function?

  1. Top of page
  2. Abstract
  3. Introduction
  4. How may light of different wave lengths directly affect mitochondrial function?
  5. Effect of light on Apoptosis inducing factor (AIF)
  6. Influence of light on mitochondrial electron transport system
  7. Light action on Dexras1
  8. Conclusions
  9. Author biographies
  10. Acknowledgments
  11. References

The idea that light might affect mitochondrial function by acting directly on mitochondrial photosensitizers was first mooted by the great German biochemist Otto Warburg in his Nobel speech of 1932. He suggested that there must be an interaction between light and enzymes responsible for consuming oxygen in cellular respiration. Warburg suggested that the rate of cellular respiration would depend on the absorption spectrum of an individual respiratory pigment and noted that the spectrum of such a pigment is located to mitochondria that have properties similar to hemoglobin and chlorophyll. Warburg even suggested that hemoglobin and chlorophyll evolved from respiratory pigments. We now know that cellular respiration takes place in mitochondria and that some of their components are able to absorb light at different wavelengths unequally.

Various mitochondrial components have the capacity to absorb specific wavelengths of light differentially. These include complex IV or cytochrome c oxidase (19,20), cytochrome P450 (21) and various forms of flavin proteins that include complex I, complex II and apoptosis-inducing factor (AIF) (22–24).

A number of studies have shown that short-wave length blue light is particularly damaging to retinal tissues (3,4,25). Blue light is one of the components of light that is used routinely in various ophthalmologic instruments and therefore might contribute to the development of macular edema after surgery. Blue light also plays a part in solar retinitis and is implicated strongly in the pathogenesis of age-related macular degeneration (7,26).

Our studies, as shown in Fig. 2, also show that blue light is particularly detrimental to the survival of a transformed cell line (RGC-5 cells). RGC-5 cells express certain retinal cell markers (27,28) and resemble retinal ganglion cells by having functional mitochondria. In these studies, RGC-5 cells were exposed to blue, visible and red light of specific intensities for defined periods of time where it was clearly demonstrated that red light with a significantly greater intensity than blue light had little effect on the survival of cells whereas this was not the case for blue light. In addition, the negative influence of visible light can be blunted by substances such as trolox and EGCG (29). Moreover, we found that an insult of sodium azide to RGC-5 cells in culture was partially attenuated by red light and exacerbated by blue light (30). Our findings with red light are in accordance with studies carried out by Eells and collaborators who have demonstrated that cells in culture when exposed to red light are more resistant to a toxic insult than those that are not (31).

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Figure 2.  Results of a viability assay (Resarzurin-Reduction procedure) to show the effects of blue (465–470 nm, 400 lux), visible (400–800 nm, 1000 lux) and red (625–635 nm, 1000 lux) light (for 24 or 48 h) on the survival of cells (RGC-5 cells) in culture. It can be seen that red light had little influence whereas visible and particularly blue light significantly reduced cell survival. Results are mean values ± SEMs for six different cultures, each analyzed in quadruplet or more. Significant differences (***< 0.0001; **< 0.01; *< 0.05) were determined by two-way ANOVA analysis followed by a Bonferroni test.

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Karu et al. proposed that the initial site of action of light in cells is cytochrome c oxidase (complex IV of the mitochondrial respiratory chain) where the mixed-valence copper components of cytochrome c oxidase, CuA and CuB, act as photoacceptors. Moreover, at least two cellular actions have been suggested to occur following light interaction with cytochrome c oxidase, one being the dissociation of nitric oxide from cytochrome c oxidase and the other being an alteration in ATP synthesis that has a negative or positive overall action on the cell depending on the intensity and duration of light on cytochrome c oxidase (28,32–34). In addition, cytochrome c oxidase appears to absorb light preferentially in the red (approximately 700–800 nm) rather than in the blue (approximately 400–500 nm) spectrum (20,32,33). However, cytochromes clearly have the capacity to absorb blue light (35), even though it has been proposed that blue light is sensed more by flavin than cytochrome chromophores (36). It would appear therefore that the negative effect of blue light on cells in culture might be initiated by an action on both flavin and cytochrome mitochondrial photosensitizers.

Evidence for the direct interaction of light with mitochondria

In our very initial studies, we exposed freshly isolated mitochondria from the liver to light (400–760 nm) of wavelengths that impinge on the retina (18). In these studies, intact isolated mitochondria or mitochondria disrupted by sonication were maintained in the dark or exposed to light at two different intensities (800 or 4000 lux) for 12 h. Thereafter, the mitochondrial dehydrogenase (WST-1 assay) and redox potential (MTT assay) of the samples were assessed. WST-1 is a tetrazolium dye containing an electron coupling agent that is cleaved by mitochondrial dehydrogenase enzyme to a formazan dye with an absorbance at 490 nm. MTT is reduced to an insoluble, blue formazan product because of the acceptance of electrons from cellular-reducing equivalents such as NADH, NADPH or succinate, thus providing an assay for the redox state of the sample. The results show that light decreases mitochondrial dehydrogenase and the redox state of the mitochondria when compared with the dark state (Fig. 3). Moreover, when mitochondrial function was disrupted by sonication, light had no effect on mitochondrial dehydrogenase or redox state. These studies strongly suggest that light (400–760 nm) can decrease the metabolic state of mitochondria by a direct action on certain components.

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Figure 3.  In these studies, equivalent amounts of freshly isolated mitochondria from rat liver in physiological medium were maintained in dark or exposed to visible light (800 or 4000 lux) for 12 h. In some instances, mitochondria were first sonicated to damage their integrity before being kept in the dark. Samples were subsequently analyzed for their redox potential (by MTT assay) and mitochondrial dehydrogenase content (by WST-1 assay). It can be seen that sonication and light exposure affect mitochondrial functions when compared with mitochondria kept in the dark. Results are mean values where = 6. Significant differences (***< 0.01, *< 0.05) were determined by a Bonferroni posttest analysis. Source: Osborne et al. (18).

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More persuasive evidence for light (400–760 nm) having a direct action on mitochondria was subsequently demonstrated in cultures of fibroblasts (29). In these studies, fibroblasts were exposed to ethidium bromide for 50 days so impairing mitochondrial DNA and affecting their respiratory chain activity. These fibroblasts with impaired mitochondria were unaffected by a specific light insult. In contrast, the same light insult caused a generation of ROS and cell death to fibroblasts with functional mitochondria. These findings on the use of fibroblasts also provided evidence that light (400–760 nm) was not affecting constituents within the culture medium to indirectly affect cell survival as described elsewhere (37,38).

Additional evidence to support the view that mitochondria of RGC-5 cells are affected by a light insult can be demonstrated by staining of their mitochondria with a cell-permeant MitoTracker probe (Fig. 4) or for cytochrome c, a protein loosely attached to the inner mitochondrial membrane (Fig. 5) or for JC-1 dye that is used to detect a change in the characteristics of the mitochondrial electrochemical potential that results in cell death (Fig. 6). Mitochondria in RGC-5 cells maintained in the dark appeared elongated in structure but, after light exposure (48 h in visible light), they appeared more dot-like in morphology (Fig. 4). Moreover, light results in cytochrome c being located not only in the mitochondria but also in the cytoplasm (Fig. 5).

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Figure 4.  RGC-5 cells mitochondria revealed by the use of a MitoTracker dye. RGC-5 cells maintained in dark conditions (Fig. 4A) showed a typical elongated morphology (arrows) whereas exposure to blue light (400 lux for 24 h, Fig. 4B) resulted in them appearing dot-like (arrows) in morphology.

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Figure 5.  The localization of cytochrome c (green, A and D) and MitoTracker (red, B and E) in RGC-5 cells maintained in the dark (A, B, C) or after a blue light insult (400 lux for 24 h) (D, E, F). Cytochrome c is located to mitochondria and colocalizes with MitoTracker in the dark maintained cells (A, B, C). A light insult clearly shows that some cytochrome c is now located outside MitoTracker-stained mitochondria and present in the cytosol (D, E, F).

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Figure 6.  This figure shows that a blue light insult (400 lux for 24 h) to RGC-5 cells causes a change in mitochondrial inner membrane electrochemical potential by use of JC-1 dye. The dye JC-1 is known to undergo a reversible change in fluorescence emission from green to red as the mitochondrial membrane potential increases. This is clearly seen to be the case when RGC-5 cells are exposed to blue light (B) as compared with being maintained in the dark (A).

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Effect of light on Apoptosis inducing factor (AIF)

  1. Top of page
  2. Abstract
  3. Introduction
  4. How may light of different wave lengths directly affect mitochondrial function?
  5. Effect of light on Apoptosis inducing factor (AIF)
  6. Influence of light on mitochondrial electron transport system
  7. Light action on Dexras1
  8. Conclusions
  9. Author biographies
  10. Acknowledgments
  11. References

The mature form of AIF comprises three structural domains: a NADH-binding, FAD-binding and a C-terminal domain (39–41). Like other flavoproteins, the oxydoreductase part of AIF (composed by the NADH- and FAD-binding domains) adopts a typical Rossman fold conferring an electron transfer activity of the protein. FAD-bound AIF can be reduced by NAD(P)H without the accumulation of a semiquinone intermediate. Furthermore, reduced AIF can catalyze a NADH-dependent reduction of small molecules, such as cytochrome c (42,43). Although we are unaware of any studies that have investigated the manner by which light of different wavelengths might directly act on FAD-bound AIF in situ, it seems plausible to suggest that blue light in particular might be able to affect the structure in a way that eventually results in cell death. According to Losi and Gärtner (44) blue light is particularly sensed by flavin chromophores. Significantly, our studies showed that when RGC-5 cells are exposed to visible light, AIF located to mitochondrial membranes is activated and a major cleaved product of 57 kDa is produced in a time-dependent way to be released into the cytoplasm (29). Recent studies comparing the influence of blue, red and visible light on RGC-5 cell AIF show that blue light of lower intensity (465–470 nm, 400 lux) is more effective than visible light (400–600 nm, 1000 lux) over a period of 48 h in causing a cleavage of AIF whereas red light (625–635 nm, 1000 lux) had no significant influence (Fig. 7). Moreover, immunohistochemistry shows that, in RGC-5 cells exposed to blue or visible light, AIF-immunoreactivity is located in some cells to the nucleus whereas this is never the case for cultures maintained in the dark where AIF-immunoreactivity is located to mitochondria (Fig. 7). These data therefore strongly support the idea that light-induced cell death causes mitochondrial AIF to be activated with a cleaved product entering nuclei to participate in DNA damage. We predict that light might have a direct effect on mitochondrial membrane AIF but cannot at this stage rule out the possibility that the influence is indirect, caused perhaps by elevated ROS or the activation of other proteins such as PARP-1 (29). There are published reports that suggest that AIF can be affected by the activation of nuclear-located PARP-1 (45).

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Figure 7.  In these studies, RGC-5 cells were exposed to light of different wavelengths as described in Fig. 2. In the left panels, extracts of identical amounts of proteins subjected to electrophoresis and Western blotting using antibodies that recognize actin or apoptosis-inducing factor (AIF) proteins. The AIF antibody recognizes a single protein of 67 kDa in RGC-5 cells maintained in the dark or exposed to red light. However, exposure of cells to visible or blue light results in the generation of a second AIF-immunoreactive band with a molecular weight of 57 kDa. In these studies, parts of the same gel were “stained” for actin (molecular weight 45 kDa). A comparison of the relative amounts of actin in relation to the AIF 57 kDa protein shows that blue light in particularly causes AIF to be cleaved to form an additional species. Results are mean values ± SEMs where = 3 and significant (*< 0.05) values were determined by a Student’s paired t-test. Immunohistochemistry data shown in the panels on the right provide evidence that AIF immunoreactivity (A1 and B1) located to mitochondria in the dark (A1 and A2) appears also to be present in the nuclei of RGC-5 cells (B1 and B2) after a blue light insult. Green AIF immunoreactivity (A1 and B1) and red MitoTracker (A2 and B2) colocalize in RGC-5 cells maintained in the dark but this is not the case when cells are exposed to blue light where AIF immunoreactivity (arrows) is also located to the nuclei of RGC-5 cells.

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Influence of light on mitochondrial electron transport system

  1. Top of page
  2. Abstract
  3. Introduction
  4. How may light of different wave lengths directly affect mitochondrial function?
  5. Effect of light on Apoptosis inducing factor (AIF)
  6. Influence of light on mitochondrial electron transport system
  7. Light action on Dexras1
  8. Conclusions
  9. Author biographies
  10. Acknowledgments
  11. References

Our working hypothesis for light being potentially detrimental to retinal ganglion cells in certain situations stems from the idea that light has the potential to interact and affect any of a number of putative photosensitizers associated with the oxidative phosphorylation (OXPHOS) complexes (14,18). OXPHOS produces almost all the necessary ATP required for neuron function to remain optimum and consists of five multisubunit enzyme complexes: complex I is the NADH:ubiquinone oxidoreductase, complex II or succinate reductase, complex III or ubiquinone:cytochrome c oxidoreductase, complex IV or cytochrome c oxidase and complex V the H+ATPsynthase. Electrons enter the respiratory chain at either complex I or II and travel via redox centers in complexes I, III and IV where protons are extruded into the intermembrane space. The proton current is ultimately harnessed by complex V to allow for the phosphorylation of ADP to ATP.

It is known that OXPHOS dysfunction consequent to mtDNA or nuclearDNA mutations results in reduced generation of ATP, an increase in reactive oxygen species production and subsequently oxidative stress (46–48). However, it might be of significance that a clear depression of ATP synthesis is seen only in isolated (nonsynaptic) brain mitochondria after the inhibition of complex I, III or IV by 60–70% (49). This raises the intriguing possibility that the initial consequence of limited inhibition of mitochondrial electron transport may be oxidative stress rather than ATP depletion as might occur should light directly affect the OXPHOS complexes.

Using an antibody that localizes all the OXPHOS complexes showed no unequivocal alterations in the localization of OXPHOS immunoreactivity in RGC-5 cells exposed to blue light (465–470 nm, 400 lux for 24 h) or cells maintained in dark (Fig. 8) but Western blot studies using this antibody clearly revealed that light causes an upregulation of complexes III, IV and V. However, when using antibodies to localize the individual OXPHOS complexes, it was concluded that all were affected by blue light (Figs. 9 and 10). Blue light causes a small but statistically significant increase in complex I when using an antibody that detected subunit NDUFV1 but not by the use of an antibody that detected subunit NDUFB8. In contrast, complex II is decreased slightly in a significant way. A more robust increase in complexes III and IV occurs following a blue light insult. These findings reveal that blue light has an influence on mitochondrial OXPHOS function but do not answer the question as to whether this is because of a direct or indirect action on all or defined complexes.

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Figure 8.  Western blot (A) and immunocytochemistry (B) of OXPHOS proteins using the antibody MitoProfile Total OXPHOS Antibody Cocktail (MitoSciences). It can be seen that the antibody recognizes five OXPHOS proteins in RGC-5 cell extracts with molecular weights that correspond with complexes I–V and that blue light (400 lux, 24 h) increases significantly the amount of complexes III–V. Results are mean values ± SEMs where = 4 and significant (*< 0.05) values were determined by a Student’s paired t-test (A). Immunocytochemistry (panels on the left) shows OXPHOS immunoreactivity (green) located to mitochondria in an ordered way in the dark (B1) but more disorganized in appearance after a blue light insult (B2). DAPI was used to stain the nuclei blue.

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Figure 9.  (A–D) This figure shows how individual mitochondrial complexes in RGC-5 cells are affected following a blue light (400 lux, 24 h) insult using Western blot analysis. Figure (A) shows results for NADH ubiquinone oxidoreductase (complex I, CI) where antibodies that either recognizes complex I subunit NDUFB8 (MitoSciences) or NDUFV1 (Santa Cruz Biotechnology) were used. It can be seen that blue light caused a small but significant increase in complex I when using an antibody for the NDUFV1 subunit. Figure (B) shows results for succinate dehydrogenase complex protein (complex II, CII) using an antibody for Complex II subunit 30 KDa (MitoSciences). It can be seen that blue light caused a downregulation of complex II. Figure (C) shows results for ubiquinol cytochrome c oxidoreductase complex protein (complex III, CIII) using an antibody for Complex III subunit Core 2 (MitoSciences) where complex III is upregulated by blue light. Figure (D) shows results for cytochrome c oxidoreductase complex protein (complex IV, CIV) using an antibody for Complex IV subunit I (MitoSciences) where complex IV is also upregulated. Results are mean values ± SEMs where = 4 and significant (*< 0.05) values were determined by a Student’s paired t-test.

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Figure 10.  Localization of complex II (A), complex III (B), complex IV (C) (green fluorescence) immunoreactivities in RGC-5 cells in the dark (A1,B1,C1) and following a blue light (400 lux, 24 h) insult (A2,B2,C2). In the dark complex II (A1) and IV (C1), immunoreactivities are clearly located to mitochondria in the cytoplasm with no clear complex III immunoreactivity (B1) detected. Following a blue light insult, green immunoreactive complex I (A2) and complex IV (C2) are clearly downregulated but in the case of complex III (B2) it is upregulated. These findings are consistent with Western blot analysis as shown in Fig. 9. Note: Cell nuclei are stained blue using DAPI dye.

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Light action on Dexras1

  1. Top of page
  2. Abstract
  3. Introduction
  4. How may light of different wave lengths directly affect mitochondrial function?
  5. Effect of light on Apoptosis inducing factor (AIF)
  6. Influence of light on mitochondrial electron transport system
  7. Light action on Dexras1
  8. Conclusions
  9. Author biographies
  10. Acknowledgments
  11. References

Sang et al. (50) recently reported that a transient high expression of Dexras1 and retinal ganglion cell death occur following a 2 h exposure of rats to visible light (16 000 lux). The death process involves an activation of caspase-3 and is attenuated by the administration of a nitric oxide synthase inhibitor. These studies can be interpreted to suggest that light action on retinal photoreceptors leads to a cascade of actions on postsynaptic neurons to eventually cause a rise in Dexras1 protein and nitric oxide in ganglion cells. An alternative possibility is that light might have had a direct effect on ganglion cell mitochondria in situ to cause an elevation of Dexras1 and nitric oxide. Our studies on RGC-5 cells in culture support this latter idea where we show that blue light (465–470 nm, 400 lux for 24 hours) causes an upregulation of Dexras1 protein (Fig. 11) and an upregulation of reactive oxygen species (12,13) that probably includes nitric oxide. These combined data are in accordance with the idea that Dexras1 is a novel physiological molecule used to enhance nitric oxide signaling (51). Nitric oxide is generally upregulated in nervous tissues following insults of various types and significantly this goes hand in hand with an elevation of Dexras1 (52,53). It is also of interest to note that Dextras1 is proposed to be involved at integrating photic and nonphotic input into the circadian clock and that this process is partially driven by the release of glutamate/PACAP from intrinsically photosensitive retinal ganglion cells (54,55).

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Figure 11.  Western blot (A) and immunocytochemistry (B) of Dexras protein using the antibody Dexras1/2 (Santa Cruz Biotechnology). Both Western blot and immunocytochemistry (green fluorescence) showed that blue light (400 lux, 24 h) caused an upregulation of Dexras located to the cytoplasm (blue DAPI staining of nuclei) of RGC-5 cells. Results are mean values ± SEMs where = 6 and significant values (*< 0.05) were determined by a Student’s paired t-test.

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Conclusions

  1. Top of page
  2. Abstract
  3. Introduction
  4. How may light of different wave lengths directly affect mitochondrial function?
  5. Effect of light on Apoptosis inducing factor (AIF)
  6. Influence of light on mitochondrial electron transport system
  7. Light action on Dexras1
  8. Conclusions
  9. Author biographies
  10. Acknowledgments
  11. References

Retinal ganglion cells in situ can be induced to die in rats following exposure to excessive amounts of light (12,50,56). Whether this is due to a direct or indirect action of light on ganglion cell mitochondria remains unknown. A small population of retinal ganglion cells containing melanopsin are directly affected by light and appear to have a longer survival time compared with other ganglion cells in various situations (57). One possible explanation for this is that light absorbed by melanopsin reduces any detrimental action on mitochondria? Use of cell cultures in contrast have demonstrated that light as impinging on the retina can indeed have a direct detrimental effect on a cell’s survival by a mechanism that involves an action on their mitochondria. For example, fibroblasts with deficient mitochondria are unaffected by a light insult that causes death of such cells with functional mitochondria. Moreover, light affects isolated mitochondrial function negatively and also RGC-5 cell mitochondria, indicated by the localization of cytochrome c in the cytoplasm and an alteration in mitochondrial morphology. We have also demonstrated that the blue light component of white light is particularly damaging to RGC-5 cells in culture. The damaging effect of light to RGC-5 cells in culture is indicated by changes to a number of parameters that include a generation of ROS (by use of DHE), a differential influence on the various components of OXPHOS, breakdown of DNA-resembling apoptosis (29,30), a stimulation of AIF and the upregulation of Dexras1. The demise of RGC-5 cells in culture because of a light insult does not involve that activation of caspases and is known to be blunted by various substances that include necrostatin-1, an inhibitor of necroptosis (30). Data to date therefore suggest that light entering the eye has the capacity to kill cells by interacting with hitherto unidentified components within mitochondria to cause their death by necroptosis. Necroptosis death is defined as caspase insensitive, necrostatin-1 sensitive and involves the activation of AIF.

Author biographies

  1. Top of page
  2. Abstract
  3. Introduction
  4. How may light of different wave lengths directly affect mitochondrial function?
  5. Effect of light on Apoptosis inducing factor (AIF)
  6. Influence of light on mitochondrial electron transport system
  7. Light action on Dexras1
  8. Conclusions
  9. Author biographies
  10. Acknowledgments
  11. References

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Susana del Olmo-Aguado began her studies at the University of León and then obtained a master’s degree in Visual Sciences in 2008 at the University of Valladolid. In 2009, she moved to the Fundación de Investigación Oftalmológica in Oviedo where she is presently working toward her Ph.D. degree carried out in collaboration with the University of Oviedo.

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Alberto García Manso obtained a Biochemistry degree from the University of Oviedo in 2003. Thereafter he began studying for a Ph.D. degree on the subject of Reverse Genetics, which was completed in 2010. He then joined the Fundación de Investigación Oftalmológica in Oviedo and started carrying out research in ocular neuroprotection.

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Neville N. Osborne studied at London University and obtained Ph.D. and D.Sc. degrees from St. Andrews University in Scotland. After spending 6 years at a Max Planck Institute in Germany, he returned to the UK to take up a position at Oxford University where he had a large research team and taught medical students. Professor Osborne now spends a significant part of his time at the Fundación de Investigación Oftalmológica in Oviedo developing a research department. His main research interest relates to retinal neuronal death in ocular diseases and neuroprotection.

References

  1. Top of page
  2. Abstract
  3. Introduction
  4. How may light of different wave lengths directly affect mitochondrial function?
  5. Effect of light on Apoptosis inducing factor (AIF)
  6. Influence of light on mitochondrial electron transport system
  7. Light action on Dexras1
  8. Conclusions
  9. Author biographies
  10. Acknowledgments
  11. References
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