Low Light Exposure Research Articles

A unifying multiple sclerosis etiology linking virus infection, sunlight, and vitamin D, through viral interleukin-10

Multiple sclerosis (MS) is a neurodegenerative disease of uncertain etiology. In MS, neurodegeneration is thought to be secondary to autoimmune-mediated damage. However, no cohesive explanation yet exists as to how environmental factors interact to induce a neurodegenerative autoimmune response. Insufficient sunlight exposure and chronic viral infections have been proposed as unrelated environmental risk factors for MS. We suggest that these risk factors may act synergistically to enable the pathogenic autoimmune response. Low ultraviolet light (UVL) exposure depletes vitamin D3 stores, and low vitamin D3 levels correlate strongly with high MS risk. The central nervous system converts vitamin D3 into 1,25-dihydroxyvitamin D3 (1,25-(OH)2 D3), a biologically active hormone with anti-inflammatory and neuro-protective functions that depend on IL-10-producing regulatory lymphocytes. Herpesvirus infection also correlates with MS risk. Some herpesviruses like Epstein-Barr virus produce an IL-10-like cytokine termed vIL-10. We hypothesize that vIL-10 may induce a dysfunction of IL-10-producing regulatory lymphocytes, thereby undermining the protective functions of sunlight, vitamin D3, and 1,25-(OH)2 D3. The vIL-10 could elicit a host immune response capable of neutralizing or depleting IL-10, or the vIL-10 could compete with IL-10 but fail to perform an essential IL-10 function. In either case, the lack of sunlight exposure and the herpes virus infection might synergize to induce a defect in IL-10-producing regulatory lymphocyte function that undermines self-tolerance mechanisms and enables a pathogenic autoimmune response to neural proteins.

Functional Comparisons of Visual Arrestins in Rod Photoreceptors of Transgenic Mice

To examine the biochemical characteristics of rod and cone arrestin with respect to their ability to quench the activity of light-activated rhodopsin in transgenic mice. The mouse rod opsin promoter was used to drive expression of mouse cone arrestin in rod photoreceptor cells of rod arrestin knockout (arr1-/-) mice. Suction electrode recordings from single rods were performed to investigate cone arrestin's ability to quench the catalytic activity of light-activated rhodopsin. In addition, the ability of cone arrestin to prevent light-induced retinal damage caused by prolonged activation of the phototransduction cascade was assessed. Two independent lines of transgenic mice were obtained that expressed cone arrestin in rod photoreceptors, and each was bred into the arr1-/- background. Flash responses measured by suction electrode recordings showed that cone arrestin reduced signaling from photolyzed rhodopsin but was unable to quench its activity completely. Consistent with this observation, expression of mouse cone arrestin conferred dose-dependent protection against photoreceptor cell death caused by low light exposure to arr1-/- retinas, but did not appear to be as effective as rod arrestin. Cone arrestin can partially substitute for rod arrestin in arr1-/- rods, offering a degree of protection from light-induced damage and increasing the extent of rhodopsin deactivation in response to flashes of light. Although earlier work has shown that rod arrestin can bind and deactivate cone pigments efficiently, the results suggest that cone arrestin binds light-activated, phosphorylated rhodopsin less efficiently than does rod arrestin in vivo. These results suggest that the structural requirements for high-affinity binding are fundamentally distinct for rod and cone arrestins.

Spiro-oxazine photochromic fiber optical switch

A photochromic all-optical switch in telecommunication-grade fiber is fabricated by filling a fiber Bragg grating Fabry-Pérot resonator with a spiro-oxazine solution. The narrow linewidth of the resonator allows for a high sensitivity of the resonance wavelengths to the index change. The switch is controlled by low intensity UV light exposure, and operation at infrared telecommunication wavelengths is demonstrated. The switching speed on the order of minutes has been achieved.

THE SPREAD OF DAMAGE IN CULTURED GASTRIC AND COLONIC EPITHELIAL CELLS AFTER PHOTO‐DAMAGE

The gastrointestinal epithelium can be hurt by chemical or toxin damage, bacterial invasion or other insults. After two-photon absorption to damage specific gastric cells in vivo, we find that damage spreads to adjacent cells prior to repair. The aim of this study was to ask if damage spreads in tissue culture models of gastric (AGS) or intestinal (HT29) epithelial cells. Cell monolayers on glass coverslips were mounted and superfused on a Zeiss LSM510 two-photon microscope stage. Cells were imaged over time by transmitted light and two-photon auto-fluorescence of NADH (730nm EX, 435-485nm EM). Photo-damage, to ~ 240μm2 (3–5 cells) target areas, was caused by repeated scanning at high laser power. Membrane blebbing and the drop in NADH auto-fluorescence measured cell damage. Graded levels of damage were seen after 0.4, 0.3 or 0.2 W laser powers at time zero. In photodamaged HT29 cells, blebbing was observed at ~ 0.2, 5 ± 1 or 11 ± 2 min, resp. In AGS cells, blebbing occurred at ~ 0.2, 0.2 and 4 ± 2 min, resp. Five min after 0.4 or 0.2 W light exposure, NADH fluorescence in HT29 cells decreased 26 ± 3% or 11 ± 2%. In AGS cells, the decrease was 38 ± 5% or 6 ± 3%, resp. By both measures, AGS cells were more sensitive to high vs. low light exposure than HT29. Laser power also caused graded damage spread to adjacent (non-photodamaged) cells and to areas >5 cells distant, suggesting that release of toxic products and/or cell-cell communication spread damage.

A biocompatible micro cell culture chamber (μCCC) for the culturing and on-line monitoring of eukaryote cells

We have previously shown that a polymeric (PMMA) chip with medium perfusion and integrated heat regulation provides sufficiently precise heat regulation, pH-control and medium exchange to support cell growth for weeks. However, it was unclear how closely the cells cultured in the chip resembled cells cultured in the culture flask. In the current study, gene expression profiles of cells cultured in the chip were compared with gene expression profiles of cells cultured in culture flasks. The results showed that there were only two genes that were differently expressed in cells grown in the cell culture chip compared to cell culture flasks. The cell culture chip could without further modification support cell growth of two other cell lines. Light coming from the microscope lamp during optical recordings of the cells was the only external factor identified, that could have a negative effect on cell survival. Low grade light exposure was however compatible with optical recordings as well as cell viability. These results strongly indicate that a cell culture chip could be constructed that allowed for on-line optical recording of cellular events without affecting the cell culturing condition compared to cell cultured in culture flasks incubated in a dark and CO2 conditioned incubator.

Transducin Activation State Controls Its Light-dependent Translocation in Rod Photoreceptors

Light-dependent redistribution of transducin between the rod outer segments (OS) and other photoreceptor compartments including the inner segments (IS) and synaptic terminals (ST) is recognized as a critical contributing factor to light and dark adaptation. The mechanisms of light-induced transducin translocation to the IS/ST and its return to the OS during dark adaptation are not well understood. We have probed these mechanisms by examining light-dependent localizations of the transducin-alpha subunit (Gtalpha)in mice lacking the photoreceptor GAP-protein RGS9, or expressing the GTPase-deficient mutant GtalphaQ200L. An illumination threshold for the Gtalpha movement out of the OS is lower in the RGS9 knockout mice, indicating that the fast inactivation of transducin in the wild-type mice limits its translocation to the IS/ST. Transgenic GtalphaQ200L mice have significantly diminished levels of proteins involved in cGMP metabolism in rods, most notably the PDE6 catalytic subunits, and severely reduced sensitivity to light. Similarly to the native Gtalpha, the GtalphaQ200L mutant is localized to the IS/ST compartment in light-adapted transgenic mice. However, the return of GtalphaQ200L to the OS during dark adaptation is markedly slower than normal. Thus, the light-dependent translocations of transducin are controlled by the GTP-hydrolysis on Gtalpha, and apparently, do not require Gtalpha interaction with RGS9 and PDE6.

The relationship between fatigue and light exposure during chemotherapy.

Fatigue is one of the most common and distressing complaints among cancer patients, not only during radiation and chemotherapy, but also for months to years after the completion of treatment. Fatigue interferes with patients' daily lives, reduces their quality of life, and is often a significant reason why patients discontinue treatment. We hypothesized that some of the fatigue may be related to disrupted circadian rhythms and low light exposure. The main objective of this study therefore was to investigate the association between fatigue and light exposure among patients with breast cancer. As part of a larger, ongoing prospective study on fatigue, sleep, and circadian rhythms in patients with breast cancer, an analysis of 63 women newly diagnosed with stage I-IIIA breast cancer and scheduled to receive four cycles of adjuvant or neoadjuvant anthracycline-based chemotherapy was conducted. Data were collected before and during weeks 1, 2, and 3 of cycle 1 and cycle 4. Fatigue was assessed using the Short Form of Multidimensional Fatigue Symptom Inventory. Light exposure was recorded with a wrist actigraph. There were significant correlations between fatigue levels and light exposure (r=-0.28 to -0.45) within both cycle 1 and cycle 4, such that higher levels of fatigue were associated with less light exposure. There were also significant correlations between changes in light exposure and changes in fatigue within the first 2 weeks of each cycle (r=-0.28 to -0.52). Increased fatigue was significantly correlated with decreased light exposure among patients with breast cancer. Although the cause and effect of exacerbated fatigue and decreased light exposure cannot be confirmed by the current study, and lower light exposure may just in part be due to the fatigued patients spending less time outdoors in bright light, two hypotheses are proposed about the mechanisms by which light may alleviate the fatigue of patients with breast cancer. These results suggest the need for prospective intervention studies of light therapy for breast-cancer-related fatigue.

Rubisco activase chaperone activity is regulated by a post-translational mechanism in maize leaves.

Rubisco activase (RCA) is a molecular chaperone present in maize as 43 kDa and 41 kDa polypeptides. They are encoded by two different genes comprising an identical ORF that corresponds to the 43 kDa RCA polypeptide, and their transcripts do not show putative splicing sites. To determine the origin of the 41 kDa polypeptide, leaf poly A(+) mRNA was in vitro translated. Results demonstrated de novo synthesis only for the 43 kDa RCA. Antibodies developed against peptides from either the carboxy- or the amino-terminal end of 43 kDa RCA showed by western blot that the 43 kDa polypeptide amino-terminal region is missing in the 41 kDa polypeptide, whereas both RCA polypeptides shared the carboxy-end region. Regulation of RCA polypeptide ratios was determined in plant leaves at different developmental stages and under stressing environmental conditions. Increased levels of 43/41 kDa RCA ratio were found in leaves under low light exposure, whereas this ratio declined under water stress. Measurements of chaperone activity either on each RCA polypeptide alone or in a mixture showed the functional relevance of different 43/41 kDa RCA polypeptide ratios. Greater chaperone activity was found for the 41 kDa than for the 43 kDa polypeptide. Taken together, these results indicate that 41 kDa RCA polypeptide formation is regulated by limited proteolysis of the 43 kDa RCA at its amino-terminal region. This pathway is sensitive to developmental and environmental signals, and seems to play a relevant function during plant stress.

Facilitation of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate receptor transmission in the suprachiasmatic nucleus by aniracetam enhances photic responses of the biological clock in rodents.

This study was designed to test whether the alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) receptor-facilitating drug, aniracetam, could potentiate photic responses of the biological clock in the suprachiasmatic nucleus (SCN) of rodents. Using the whole-cell patch technique, we first demonstrated that AMPA currents elicited by either local AMPA application or optic chiasm stimulation were augmented by aniracetam in the neurons of the SCN. The AMPA application-elicited increase of intracellular Ca2+ concentration in SCN slices was also enhanced by aniracetam treatment. The systemic injection of aniracetam dose-dependently (10-100 mg/kg) potentiated the phase delay in behavioral rhythm induced by brief light exposure of low intensity (3 lux) but not high intensity (10 or 60 lux) during early subjective night. Under the blockade of NMDA receptors by (+) MK801, aniracetam failed to potentiate a light (3 lux)-induced phase delay in behavioral rhythm. Aniracetam increased the photic induction of c-Fos protein in the SCN that was elicited by low intensity light exposure (3 lux). These results suggest that AMPA receptor-mediated responses facilitated by aniracetam can explain enhanced photic responses of the biological clock in the SCN of rodents.

Photosynthetic performance of Vigna radiata L. leaves developed at different temperature and irradiance levels

The photosynthetic performance of mungbean ( Vigna radiata L.) leaves developed at (1) 30/25 °C+700 PFD (LT+HI), (2) 40/25 °C+700 PFD (HT+HI), and (3) 40/25 °C+200 PFD (HT+LI) was evaluated. Photosynthetic CO 2 assimilation rate ( P n) and different Chl a fluorescence parameters of those leaves were measured at different temperatures and photon flux density (PFD). P n of the LT+HI-developed leaves continued to increase till 2000 PFD while the P n was lower in the leaves developed at high temperature. HT+HI-developed leaves showed higher P n than that developed at the same temperature but with low light (HT+LI). Rapid light curves revealed that leaves developed at high light had better photosynthetic efficiency at fast changing light environment than those developed at low light irrespective of their growth temperatures. LT+HI-plants had the highest photochemical quenching ( q P) as well as non-photochemical quenching ( q N) compared to the plants developed at high temperature (HT+HL and HT+LI). Heat acclimation in the presence of high light appreciably protected the activity of photosynthetic apparatus from heat shock-damage. This was disclosed with the higher photosynthetic efficiency of HT+HI-grown plants after heat shock treatment up to 55 °C than the plants developed at the same temperature but with low light. Leaves developed at HT+LI showed severe photoinhibition of photosynthesis when exposed to strong light for 9 h and did not recover appreciably from the damage compared to those developed at high light (LT+HI and HT+HI). From the various Chl a fluorescence parameters that we determined it would appear that high light exposure protects efficiently the photochemical activity of leaf against its inactivation by heat compared to low light exposure.

The Effect of High and Very Low Fluorescent Light Exposure Levels on Age-related Cataract in a Pigmented Mouse Strain

This study examined the effect of fluorescent light on the timing and severity of age-related cataracts in a fully pigmented mouse strain, the (C57BL/6×C3H)F1, that normally develops slowly progressing age-related cataracts only beyond middle age. Two groups of 56 animals each were exposed, respectively, either to a daily range of 66–222 foot candles (FC) or to 1FC of standard fluorescent lighting for a period beginning at 5 weeks of age and ending at 33.5 months (by which time approximately 65% of the colony had died). Contrary to previous reports involving albino rats or mice and a strain of pigmented but cataract-prone transgenic mice, the two groups of animals in this experiment did not differ for cataract development in time of first occurrence, rate of advancement, or degree of severity. It was concluded that genetic predisposition, based on levels of oxidative free radical production vs antioxidant enzyme and repair enzyme protection in the lens, was probably the major factor governing the rate and degree of age-related cataract development in these animals. The effect of relatively intense life-long fluorescent light exposure was so minimal as not to be manifested in this strain of mice under the conditions of this experiment. Remarkably, maintaining the one group of mice in semi-darkness from 5 weeks of age to beyond their mean lifespans did nothing to delay or reduce the incidence or severity of their age-related cataracts.

Influence of light and temperature on the colour and oxidative stability of processed cheese

Pasteurised processed cream cheese stored in sealed glass containers for one year was found to undergo different types of chemical changes depending on storage temperature and light exposure. High temperature storage (37°C) induced browning reactions evident as colour changes developing linearly with time. Browning was less significant at ambient temperature (20°C) and absent at low temperature (5°C) and light exposure (2000 lx) had little if any influence on browning. Light exposure induced formation of lipid peroxides, which were found stable at 5°C, but not at higher temperatures. Riboflavin, a potential photosensitiser, was degraded on light exposure independently of storage temperature. β-Carotene was not degraded whereas α-tocopherol was, especially in samples exposed to light, but less than 20% after one year of storage at any of the storage temperatures. Cholesterol oxidation was only detectable after long-term storage while exposed to light at high temperature.

Viability of dried cells, and survivability and reproduction under water stress, low light, heat, and UV exposure in Chlorella vulgaris

Dried Chlorella vulgaris Beyerinck cells were 100% viable when stored in desiccators over fused CaCl 2 for 2 days either in light or dark, but the viability decreased to1% after 30 days at 20 C in light. Neither dried nor wet cells remained viable after10 days at 0 C in dark. Tolerance of C. vulgaris cells to dry storage might be dueeither to their unicellular nature or to the chemical composition of cell wall containing sporopollenin. Osmotic regulation did not seem to occur, as the alga was salt-sensitive. Autospores or young vegetative cells were more sensitive than autospore mother cells to both physical and physiological water stress, imposed respectively by growing them on media with a high agar content or in salinized liquid media. The rupture of autospore mother cells and release of autospores did not occur even in100 mM NaCl. The vegetative cells remained viable in darkness at 22 1 C for 45days, but the formation of autospore mother cells required light intensities of more than 10 mmol m –2 s –1 . The vegetative cells were sensitive to heat or UV.

Viability of dried cells, and survivability and reproduction under water stress, low light, heat, and UV exposure in Chlorella vulgaris

Viability of dried cells, and survivability and reproduction under water stress, low light, heat, and UV exposure in Chlorella vulgaris

Insulin action on GLUT4 traffic visualized in single 3T3-l1 adipocytes by using ultra-fast microscopy.

A novel imaging technology, high-speed microscopy, has been used to visualize the process of GLUT4 translocation in response to insulin in single 3T3-L1 adipocytes. A key advantage of this technology is that it requires extremely low light exposure times, allowing the quasi-continuous capture of information over 20-30 min without photobleaching or photodamage. The half-time for the accumulation of GLUT4-eGFP (enhanced green fluorescent protein) at the plasma membrane in a single cell was found to be of 5-7 min at 37 degrees C. This half-time is substantially longer than that of exocytic vesicle fusion in neuroendocrine cells, suggesting that additional regulatory mechanisms are involved in the stimulation of GLUT4 translocation by insulin. Analysis of four-dimensional images (3-D over time) revealed that, in response to insulin, GLUT4-eGFP-enriched vesicles rapidly travel from the juxtanuclear region to the plasma membrane. In nontransfected adipocytes, impairment of microtubule and actin filament function inhibited insulin-stimulated glucose transport by 70 and 50%, respectively. When both filament systems were impaired insulin-stimulated glucose transport was completely inhibited. Taken together, the data suggest that the regulation of long-range motility of GLUT4-containing vesicles through the interaction with microtubule- and actin-based cytoskeletal networks plays an important role in the overall effect of insulin on GLUT4 translocation.

Reduced excretion of a melatonin metabolite in workers exposed to 60 Hz magnetic fields.

The effects of occupational 60 Hz magnetic field and ambient light exposures on the pineal hormone, melatonin, were studied in 142 male electric utility workers in Colorado, 1995-1996. Melatonin was assessed by radioimmunoassay of its metabolite, 6-hydroxymelatonin sulfate (6-OHMS), in post-work shift urine samples. Personal magnetic field and light exposures were measured over 3 consecutive days using EMDEX C meters adapted with light sensors. Two independent components of magnetic field exposure, intensity (geometric time weighted average) and temporal stability (standardized rate of change metric or RCMS), were analyzed for their effects on creatinine-adjusted 6-OHMS concentrations (6-OHMS/cr) after adjustment for age, month, and light exposure. Geometric mean magnetic field exposures were not associated with 6-OHMS/cr excretion. Men in the highest quartile of temporally stable magnetic field exposure had lower 6-OHMS/cr concentrations on the second and third days compared with those in the lowest quartile. Light exposure modified the magnetic field effect. A progressive decrease in mean 6-OHMS/cr concentrations in response to temporally stable magnetic fields was observed in subjects with low workplace light exposures (predominantly office workers), whereas those with high ambient light exposure showed negligible magnetic field effects. Melatonin suppression may be useful for understanding human biologic responses to magnetic field exposures.

POTENTIAL FOR IMPROVEMENT OF MANGO SKIN COLOUR DURING STORAGE

External fruit colour is a major determinant of consumer appeal in mango. Mangoes are generally harvested at the hard, green preclimacteric stage, with ripening occurring after harvest. The optimum ripening temperature for cv. Kensington Pride, the main Australian mango cultivar, is 18-24°C. These conditions generally allow parallel skin yellowing and flesh softening. Prolonged mango storage (e.g. at 13°C) or ripening at 30°C desynchronises these two ripening processes, so that fruit generally soften but retain some of the green skin colour. In addition, some mango cultivars develop a red blush prior to harvest but this is often limited by reduced fruit exposure to light due to shading during growth, subtropical seasonal haze and too high temperatures. Therefore, there is a need for a postharvest method to improve mango skin colour. To test the potential for postharvest illumination to improve mango skin colour at ripe fruits of cvs. Kensington Pride and Tommy Atkins at commercial maturity were exposed soon after harvest to cool-white fluorescent illumination at 13°C and 20°C (temperatures recommended for mango storage and ripening in Australia, respectively). Two levels of photon fluency rate (135 μmol/m 2 .s and 175 μmol/m 2 .s) were tested. In both cultivars the response to illumination was greater at 20°C than at 13°C. Both levels of illumination provided similar improvements in skin colour at ripe. Illumination of 'Kensington Pride' for 5 and 48 hrs at both low and high light intensity, resulted in significantly more yellow and red colour on the skin at ripe. Low intensity light exposure for 1 hr was not effective. Twenty four hours illumination of 'Tommy Atkins' fruit with low intensity illumination increased both the yellow and red colour of the skin at ripe.

Influence of sunlight on DNA damage in mussels exposed to polycyclic aromatic hydrocarbons

DNA single-strand break levels were compared in mussels deployed in San Diego Bay. Mussels were deployed at two locations, a reference site and at a location known to have high concentrations of PAHs. Two vertically oriented lines of mussels were deployed at each location for a period of 32 days. Mussels were attached to the lines at depths of 0.3, 1 and 3 m. One line was fully exposed to ambient sunlight, the other was shaded from sunlight to examine the role of PAH light activation on the expression of DNA damage in hemocytes and whole organism growth. Damage and growth measurements were made on days 0, 5, 14, and 32. Temperatures at the stations varied only by ≈0.5 °C. Hydrocarbon levels at the high PAH station were on average six times higher than the reference station. Slower growth and higher DNA damage was observed in cells from light exposed mussels at the PAH contaminated site. These effects decreased with depth. High levels of DNA damage could be induced with low intensity ultraviolet light exposure of cells from depurated or shaded mussels exposed to PAHs. DNA damage in mussels from the high impact site could be reduced to baseline levels after 24 h depuration in the dark. These results confirm previous findings showing increased DNA damage in PAH and sunlight exposed mussels, and demonstrate the significant impact of photoactivation on the health of these organisms.

Regulation of Photosynthetic Induction State by the Magnitude and Duration of Low Light Exposure.

This study was undertaken to examine the dependence of the regulatory enzymes of photosynthetic induction on photon flux density (PFD) exposure in soybean (Glycine max L.). The induction state varies as a function of both the magnitude and duration of the PFD levels experienced prior to an increase in PFD. The photosynthetic induction state results from the combined activity of separate processes that each in turn depend on prior PFD environment in different ways. Direct measurement of enzyme activities coupled with determination of in situ metabolite pool sizes indicated that the fast-induction component was associated with the activation state of stromal fructose-1,6-bisphosphatase (FBPase, EC 3.1.3.11) and showed rapid deactivation in the dark and at low PFD. The fast-induction component was activated at low PFD levels, around 70 [mu]mol photons m-2 s-1. Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco, EC 2.7.1.19) deactivated very slowly in the dark and required higher PFD for activation. Both enzymes saturated at lower PFD than did photosynthesis, around 400 [mu]mol photons m-2 s-1. Ribulose-5-phosphate kinase (EC 2.7.1.19) appeared never to be limiting to photosynthesis, and saturated at much lower PFD than either FBPase or Rubisco. Determination of photosynthetic metabolite pool sizes from leaves at different positions within a soybean canopy showed a limitation to carbon uptake at the stromal FBPase and possibly the sedoheptulose-1,7-bisphosphatase (EC 3.1.3.37) in shade leaves upon initial illumination at saturating PFD levels.

The phycocyanin to chlorophyll α ratio and other cell components as indicators of nutrient limitation in two planktonic cyanobacteria subjected to low-light exposures

The phycocyanin to chlorophyll α ratio and other cell components as indicators of nutrient limitation in two planktonic cyanobacteria subjected to low-light exposures