Also, RPE phagocytosis of thetips o

Also, RPE phagocytosis of the
tips of shed ROS, and the expression of retinal c-fos and c-jun, are light entrained (LaVail,
1976b; Goldman et al., 1980; Yoshida et al., 1993; Imaki et al., 1995). In the ONL, c-fos is
normally elevated at night, while its expression in the inner retina, particularly in ganglion
cells, is transiently enhanced at light onset (Yoshida et al., 1993). In rats, RPE-65 mRNA levels
are also highest at the beginning of the day, but RPE-65 protein levels do not correlate with
circadian dependent light damage susceptibility (Beatrice et al., 2003). Other evidence
indicates that melanopsin, a protein located within a subset of ganglion cells, serves as a retinal
circadian irradiance detector (Provencio et al., 2000; Hattar et al., 2002; Berson et al., 2002).
Potential circadian phase resetting cryptochromes are also found in the inner retinal layers
(Yagita et al., 2001). Although melanopsin and cryptochromes are both photoreceptive
proteins, and even though both may trigger light-induced signals in the retina, the inner nuclear
layer (INL) is not usually damaged by visible light. This might be related to inefficient light
absorption by these photoreceptive proteins, or to high GSH levels in the INL which serves to
block oxidative damage (Winkler 2008).
Despite the relative resistance of the inner retina to light damage, rod photoreceptors are
vulnerable to light damage at night while being well protected during the day. In an attempt to
understand how changes in retinal gene expression and circadian light damage susceptibility
might be related, we performed gene array analysis and confirmed some results by real time
PCR. Figure 6 contains rt-PCR mRNA expression profiles for several retinal transcription
factors and protein markers of oxidative stress. Rat retinas were collected at 9 am and 5 pm
and compared with those obtained at 1 am, the time point of maximum light damage
susceptibility (Organisciak et al., 2000). In totally dark adapted rats, the expression of retinal
c-fos, c-jun, fra-1, GFAP, HO-1 and macrophage chemoattractant protein-1 (MCP-1) increased
1–4 fold between 1 am and 9 am (Figure 6A). Other rats were treated with intense light for 8
hours, starting at 1 am, to determine the time course of light-induced changes in transcription
factors (Figure 6B). Light exposure led to increases in mRNA expression for several
transcription factors, and most exceeded the increases found in retinas from dark adapted rats.
When rats were given the antioxidant DMTU before light treatment, c-fos and fra-1 mRNA
levels decreased 7–10 fold, suggesting that their expression was originally triggered by lightinduced
oxidative stress. At the same time, the expression of c-jun, NFkB and Atf3, an
endoplasmic reticulum factor, were largely unaffected by light.
As shown by the mRNA expression patterns for protein markers of oxidative stress, the timing
of light treatment also affects their synthesis (Figure 6C). For rats treated with 8 hours of light
starting at 1 am, the increases in retinal GFAP and MCP-1 expression were significantly greater
than for other rats treated with light starting at 9 am or 5 pm. The large increase in expression
for MCP-1 between 1 am and 9 am, suggests that a strong signal for macrophage invasion was
generated by retinal damage. Antioxidant pretreatment resulted in a dramatic reduction in
mRNA levels for MCP-1 and for the Muller cell stress protein GFAP, indicating that their expression was driven by oxidative stress. For HO-1, the light-induced increase in expression
was about 10 fold for exposures starting at 1 am and 9 am. These increases were greater than
for rats treated with light at 5 pm, the time point when light damage is minimal (Organisciak
et al., 2000). This indicates that the effect of oxidative stress in the retina is far greater for light
exposures beginning at 1 am than for light treatments at other times during the day. Our findings
also confirm some of the changes found in retinal gene array studies using bright light treated
albino mice (Chen et al., 2004; Huang et al., 2005) and further suggest that time of day can
affect the outcomes of both gene array and PCR measurements.
The synthesis of corticosterone, the rodent equivalent of human cortisol, also occurs on a 24
hour circadian cycle, and an increase in its synthesis is part of the normal stress response. In
rats, circulating corticosterone levels were found to vary with time of day, but they did not
correlate with the circadian profile of retinal light damage (Vaughan et al., 2002). In mice,
Wenzel et al. (2001) found that the stress of overnight fasting induced corticosterone synthesis
and glucocorticoid receptor translocation. Both stress induced corticosterone and
dexamethasone, a synthetic glucocorticoid, protected against light damage and both inhibited
the expression of activator protein-1 (AP-1) (Wenzel et al., 2001b). However, in the T4R
rhodopsin mutant dog, brief light exposure resulted in extensive photoreceptor cell damage
that was not inhibited by corticoids, including dexamethasone, even though AP-1 and c-fos
activation were inhibited (Gu et al., 2009). Heterodimeric complexes of c- jun and c-fos, or
fra-1 (Wenzel et al., 2002), form the transcription factor AP-1 and may promote cell death in
light exposed mice (Hafazi et al., 1997b). In the dog model this did not happen, providing yet
another example of species differences that can involve divergent pathways of light-induced
retinal cell death.
6. The Emerging Picture and Future Directions
The effects of intense or prolonged light exposure on the retina vary by species, region of the
retina, time of day, diet, prior light rearing history and genetic background. From the
perspective of sorting out mechanisms, each variable has proven useful. While the use of
different animal models has provided insights into understanding light damage, the data also
indicate that damage or cell death mechanisms are not easily extrapolated between species.
The notion that “the mouse is not a small rat” was recognized by LaVail in one of the first
comprehensive studies relating strain and species differences with the extent of retinal light
damage (LaVail et al., 1987). We now know that the L450M amino acid variation in RPE-65
correlates with resistance to light damage in many strains of mice (Danciger et al., 2000). The
oxidation of methionine 450 in RPE-65 to methionine sulfoxide is probably beneficial, because
it leads to reduced enzyme levels, slower rhodopsin regeneration, and light damage protection
(Danciger et al., 2000; Wenzel et al., 2001a). Although the regeneration of rhodopsin correlates
with light damage susceptibility in some mice, RPE-65 activity is not the rate limiting step in
regenerating rhodopsin in the rat (Iseli et al., 2002). Photobleaching of rhodopsin - and quite
possibly the initial rate of bleaching- is a key factor for light damage in rats. The same may
hold for exceedingly light sensitive dogs and mice with glycosylation defects in the amino
terminal region of rhodopsin (Gu et al., 2009; White et al., 2007). Whatever rhodopsin’s exact
role is in light damage, photoreceptors become hyperpolarized by light and remain that way
for the duration of exposure. As pointed out by Sieving et al. (2001), prolonged
hyperpolarization of rod photoreceptors is insufficient to cause retinal light damage, but lightinduced
changes in intracellular ions is still an area amenable to study in animal models.
There is also a need for additional comparative light damage studies in a variety of animal
models. For example, a comparative proteomics analysis subsequent to a standard light insult
of macaque and owl monkey retina might be very informative. The macaque shares its
diurnality with the human, and the owl monkey is only recently evolved from a diurnal ancestor (Dyer et al., 2009), so we might thereby gain insights about possible damage, repair, or cell
death mechanisms shared (or not) by traditional rodent models and humans. Diurnal rodent
studies are more feasible than primate studies and offer a complementary approach to the
existing literature, which has focused on discerning damage pathways in vulnerable nocturnal
rodents so that protective therapies can be designed. Studies of damage-resistant rodents would
provide a useful counterpoint for identifying naturally evolved protective or repair mechanisms
that appear to confer even greater bright light tolerance than is already intrinsic to the foveate
primate. The diurnal ground squirrel model has an additional feature that must be borne in
mind, which is its hibernation physiology. The emerging consensus is that animals that
hibernate exhibit neuroprotection from a variety of insults, but our understanding of
hibernation’s protective mechanisms is too incomplete to say whether they do, or do not,
contribute to light damage resistance. Hibernators spend months in continuous darkness, during
which time the metabolic activity of the predominant cones is profoundly suppressed, whereas
rods seem to retain mitochondrial activity (Figure 7). Dark-rearing potentiates light damage in
many nocturnal rodents, but it is unknown whether hibernation does so in the ground squirrel.
Finally, diurnal rodent retinas provide a means for exploring various environmental and
hereditary sensitizers to light damage, particularly those that may endanger cones. Only
cautious comparisons between species will reduce confusion and advance our understanding
of damage mechanisms.

Hasil (Bahasa Indonesia) 1:

Juga, RPE fagositosis dariTips dari gudang ROS, dan ekspresi c-fos retina dan c-jun, yang entrained cahaya (LaVail,1976b; Goldman et al., 1980; Yoshida et al., 1993; Imaki et al., 1995). Dalam ONL, c-fos adalahbiasanya ditinggikan di malam hari, sementara ekspresi pada retina batin, khususnya di ganglionsel, transiently ditingkatkan pada cahaya awal (Yoshida et al., 1993). Pada tikus, RPE-65 mRNA tingkatjuga tertinggi di awal hari, tetapi tingkat tidak berkorelasi dengan protein RPE-65sirkadian tergantung kerusakan ringan kerentanan (Beatrice et al., 2003). Bukti lainmenunjukkan bahwa melanopsin, protein yang terletak di dalam sebuah subset dari sel-sel saraf, yang berfungsi sebagai retinairradiance sirkadian detektor (Provencio et al., 2000; Hattar et al., 2002; Berson et al., 2002).Potensi sirkadian fase ulang cryptochromes juga ditemukan dalam lapisan retina(Yagita et al., 2001). Meskipun melanopsin dan cryptochromes keduanya photoreceptiveprotein, dan meskipun keduanya dapat memicu sinyal cahaya-diinduksi dalam retina, batin nuklirlapisan (INL) biasanya tidak rusak oleh cahaya tampak. Ini mungkin terkait dengan tidak efisien cahayapenyerapan protein photoreceptive, atau tingkat tinggi GSH di INL yang berfungsi untukblok kerusakan oksidatif (Winkler 2008).Meskipun perlawanan relatif retina batin untuk kerusakan ringan, batang fotoreseptor yangrentan terhadap kerusakan ringan di malam hari sembari dilindungi baik siang hari. Dalam upaya untukmemahami bagaimana perubahan dalam ekspresi gen retina dan sirkadian cahaya kerusakan kerentananmungkin terkait, kami melakukan analisis array gen dan dikonfirmasi beberapa hasil secara real timePCR. Gambar 6 berisi profil ekspresi rt-PCR mRNA transkripsi retina beberapafaktor dan protein spidol stres oksidatif. Tikus retina dikumpulkan di 09: 00 dan 17: 00dan dibandingkan dengan orang-orang yang diperoleh pada 1 am, titik waktu maksimum cahaya kerusakankerentanan (Organisciak et al., 2000). Dalam benar-benar gelap disesuaikan tikus, ekspresi retinac-fos, c-jun, fra-1, GFAP, chemoattractant HO-1 dan makrofag protein-1 (MCP-1) meningkat1 – 4 kali lipat antara 1 dan 9 am (gambar 6A). Tikus lain diperlakukan dengan intens cahaya untuk 8Jam, mulai pukul 1 pagi, untuk menentukan waktu perubahan cahaya-induced transkripsifaktor (angka ayat 6B). Eksposur cahaya yang menyebabkan kenaikan dalam mRNA ekspresi untuk beberapafaktor-faktor transkripsi, dan sebagian besar melebihi yang meningkat yang ditemukan di retina dari tikus disesuaikan gelap.Kapan tikus yang diberikan antioksidan DMTU sebelum perawatan ringan, mRNA c-fos dan fra-1tingkat penurunan 7-10 kali lipat, menyarankan bahwa ekspresi mereka awalnya dipicu oleh lightinducedStres oksidatif. Pada saat yang sama, ekspresi c-jun, NFkB dan Atf3,faktor endoplasma, yang sebagian besar tidak terpengaruh oleh cahaya.Seperti yang ditunjukkan oleh mRNA pola ekspresi untuk protein spidol stres oksidatif, waktuof light treatment also affects their synthesis (Figure 6C). For rats treated with 8 hours of lightstarting at 1 am, the increases in retinal GFAP and MCP-1 expression were significantly greaterthan for other rats treated with light starting at 9 am or 5 pm. The large increase in expressionfor MCP-1 between 1 am and 9 am, suggests that a strong signal for macrophage invasion wasgenerated by retinal damage. Antioxidant pretreatment resulted in a dramatic reduction inmRNA levels for MCP-1 and for the Muller cell stress protein GFAP, indicating that their expression was driven by oxidative stress. For HO-1, the light-induced increase in expressionwas about 10 fold for exposures starting at 1 am and 9 am. These increases were greater thanfor rats treated with light at 5 pm, the time point when light damage is minimal (Organisciaket al., 2000). This indicates that the effect of oxidative stress in the retina is far greater for lightexposures beginning at 1 am than for light treatments at other times during the day. Our findingsalso confirm some of the changes found in retinal gene array studies using bright light treatedalbino mice (Chen et al., 2004; Huang et al., 2005) and further suggest that time of day canaffect the outcomes of both gene array and PCR measurements.The synthesis of corticosterone, the rodent equivalent of human cortisol, also occurs on a 24hour circadian cycle, and an increase in its synthesis is part of the normal stress response. Inrats, circulating corticosterone levels were found to vary with time of day, but they did notcorrelate with the circadian profile of retinal light damage (Vaughan et al., 2002). In mice,Wenzel et al. (2001) found that the stress of overnight fasting induced corticosterone synthesisand glucocorticoid receptor translocation. Both stress induced corticosterone anddexamethasone, a synthetic glucocorticoid, protected against light damage and both inhibitedthe expression of activator protein-1 (AP-1) (Wenzel et al., 2001b). However, in the T4Rrhodopsin mutant dog, brief light exposure resulted in extensive photoreceptor cell damagethat was not inhibited by corticoids, including dexamethasone, even though AP-1 and c-fosactivation were inhibited (Gu et al., 2009). Heterodimeric complexes of c- jun and c-fos, orfra-1 (Wenzel et al., 2002), form the transcription factor AP-1 and may promote cell death inlight exposed mice (Hafazi et al., 1997b). In the dog model this did not happen, providing yetanother example of species differences that can involve divergent pathways of light-inducedretinal cell death.6. The Emerging Picture and Future DirectionsThe effects of intense or prolonged light exposure on the retina vary by species, region of theretina, time of day, diet, prior light rearing history and genetic background. From theperspective of sorting out mechanisms, each variable has proven useful. While the use ofmodel hewan yang berbeda telah memberikan wawasan ke dalam pemahaman kerusakan ringan, data jugamenunjukkan bahwa kerusakan atau sel mekanisme kematian tidak mudah ekstrapolasi antar spesies.Gagasan bahwa "mouse bukanlah tikus kecil" diakui oleh LaVail di salah satu yang pertamakomprehensif studi perbedaan ketegangan dan spesies yang berhubungan dengan tingkat retina cahayakerusakan (LaVail et al., 1987). Kita sekarang tahu bahwa variasi asam amino L450M RPE-65berkorelasi dengan resistensi terhadap kerusakan ringan di banyak strain tikus (Danciger et al., 2000). Theoksidasi metionin 450 di RPE-65 ke sulfoxide metionin mungkin menguntungkan, karenaitu mengarah pada tingkat berkurang enzim, lambat regenerasi rhodopsin, dan perlindungan kerusakan ringan(Danciger et al., 2000; Wenzel et al., 2001a). Meskipun regenerasi rhodopsin berkorelasidengan kerusakan ringan kerentanan pada beberapa tikus, RPE-65 aktivitas bukanlah tingkat membatasi langkah dalamregenerasi rhodopsin di tikus (Iseli et al., 2002). Photobleaching rhodopsin - dan cukupmungkin awal tingkat pemutihan - adalah faktor kunci untuk kerusakan ringan pada tikus. Sama mungkinmenahan untuk anjing sensitif sangat ringan dan tikus dengan cacat glikosilasi aminoTerminal wilayah rhodopsin (Gu et al., 2009; Putih et al., 2007). Rhodopsin apa pun yang tepatperan dalam kerusakan ringan, fotoreseptor menjadi hyperpolarized oleh cahaya dan tetap seperti ituuntuk durasi pemaparan. Seperti ditunjukkan oleh analisa saringan et al. (2001), berkepanjanganhyperpolarization of rod photoreceptors is insufficient to cause retinal light damage, but lightinducedchanges in intracellular ions is still an area amenable to study in animal models.There is also a need for additional comparative light damage studies in a variety of animalmodels. For example, a comparative proteomics analysis subsequent to a standard light insultof macaque and owl monkey retina might be very informative. The macaque shares itsdiurnality with the human, and the owl monkey is only recently evolved from a diurnal ancestor (Dyer et al., 2009), so we might thereby gain insights about possible damage, repair, or celldeath mechanisms shared (or not) by traditional rodent models and humans. Diurnal rodentstudies are more feasible than primate studies and offer a complementary approach to theexisting literature, which has focused on discerning damage pathways in vulnerable nocturnalrodents so that protective therapies can be designed. Studies of damage-resistant rodents wouldprovide a useful counterpoint for identifying naturally evolved protective or repair mechanismsthat appear to confer even greater bright light tolerance than is already intrinsic to the foveateprimate. The diurnal ground squirrel model has an additional feature that must be borne inmind, which is its hibernation physiology. The emerging consensus is that animals thathibernate exhibit neuroprotection from a variety of insults, but our understanding ofmekanisme pelindung hibernasi di tidak terlalu lengkap untuk mengatakan apakah mereka melakukan, atau tidak,berkontribusi terhadap kerusakan ringan perlawanan. Hibernators menghabiskan bulan diselubungi oleh kegelapan, selamasaat aktivitas metabolik kerucut dominan mendalam ditekan, sedangkanbatang tampaknya mempertahankan mitokondria aktivitas (gambar 7). Membesarkan gelap mempotensiasi kerusakan ringan dibanyak tikus nokturnal, tetapi tidak diketahui apakah hibernasi tidak begitu dalam tupai tanah.Akhirnya, retina pengerat diurnal menyediakan sarana untuk menjelajahi berbagai lingkungan danketurunan sensitizers untuk kerusakan ringan, terutama mereka yang dapat membahayakan kerucut. Hanyaberhati-hati perbandingan antara spesies akan mengurangi kebingungan dan memajukan pemahaman kitamekanisme kerusakan.