Retinal Degeneration In Rd10 Mice Research Articles

Nutraceutical supplementation in inherited retinal dystrophies

*Correspondence: rrodrigo@cipf.es; Tel: (+34 96 328 96 80)Retinitis pigmentosa (RP) is the most common inherited retinal dystrophy causing progressive vision loss. Ocular redox status is altered in RP suggesting oxidative stress could contribute to their progression. In addition, it is accompanied by chronic and sustained inflammation, including M1 microglia activation. In our group we evaluated, both the effect of a mixture of nutraceuticals with antioxidant properties (NUT) and the effect of an essential fatty acid (EFA) supplement containing specialized pro‐resolving mediators (SPMs) on retinal degeneration in rd10 mice, a model of RP.Both compounds were orally administered to mice from postnatal day (P)9 to P18. At P18, the electrical activity of the retina was examined by electroretinography (ERG) and innate behaviour in response to light were measured. Retinal degeneration was studied via histology including the TUNEL assay and microglia immunolabelling. Microglia polarization (M1/M2) was assessed by flow cytometry, qPCR and histology. Redox status was analysed by measuring antioxidant enzymes and markers of oxidative damage.Interestingly, the NUT and EFA supplements ameliorated retinal dysfunction and degeneration by improving ERG recording and sensitivity to light, and reducing photoreceptor cell loss.The supplement reduced inflammation and microglia activation attenuating M1 markers as well as inducing a shift to the M2 phenotype in rd10 mouse retinas. These supplements also reduced oxidative stress markers of lipid peroxidation and carbonylation. These findings could open up new therapeutic opportunities with oral supplementation.

An SPM-Enriched Marine Oil Supplement Shifted Microglia Polarization toward M2, Ameliorating Retinal Degeneration in rd10 Mice.

Retinitis pigmentosa (RP) is the most common inherited retinal dystrophy causing progressive vision loss. It is accompanied by chronic and sustained inflammation, including M1 microglia activation. This study evaluated the effect of an essential fatty acid (EFA) supplement containing specialized pro-resolving mediators (SPMs), on retinal degeneration and microglia activation in rd10 mice, a model of RP, as well as on LPS-stimulated BV2 cells. The EFA supplement was orally administered to mice from postnatal day (P)9 to P18. At P18, the electrical activity of the retina was examined by electroretinography (ERG) and innate behavior in response to light were measured. Retinal degeneration was studied via histology including the TUNEL assay and microglia immunolabeling. Microglia polarization (M1/M2) was assessed by flow cytometry, qPCR, ELISA and histology. Redox status was analyzed by measuring antioxidant enzymes and markers of oxidative damage. Interestingly, the EFA supplement ameliorated retinal dysfunction and degeneration by improving ERG recording and sensitivity to light, and reducing photoreceptor cell loss. The EFA supplement reduced inflammation and microglia activation attenuating M1 markers as well as inducing a shift to the M2 phenotype in rd10 mouse retinas and LPS-stimulated BV2 cells. It also reduced oxidative stress markers of lipid peroxidation and carbonylation. These findings could open up new therapeutic opportunities based on resolving inflammation with oral supplementation with SPMs such as the EFA supplement.

Mesenchymal stem cell-derived extracellular vesicles protect retina in a mouse model of retinitis pigmentosa by anti-inflammation through miR-146a-Nr4a3 axis

BackgroundRetinitis pigmentosa is a rod-cone degenerative disease that induces irreversible vision loss. This study probed the protective capacity of mesenchymal stem cell-derived small EVs (MSC-EVs) on the retinas of rd10 mice and the underlying mechanism.MethodsMSC-EVs were injected into the vitreous of rd10 mice at postnatal day 14 and P21; morphology and function were examined at P28. The mechanism of action was explored by using co-culture of photoreceptor cell line 661 W and microglia cell line BV2.ResultsTreatment with MSC-EVs increased the survival of photoreceptors and preserved their structure. Visual function, as reflected by optomotor and electroretinogram responses, was significantly enhanced in MSC-EVs-treated rd10 mice. Mechanistically, staining for Iba1, GFAP, F4/80, CD68 and CD206 showed that MSC-EVs suppressed the activation of microglial, Müller glial and macrophages. Furthermore, western blotting showed that the treatment inhibited the NF-κB pathway. RNA-seq and qPCR showed that MSC-EVs upregulated anti-inflammatory cytokines while downregulating pro-inflammatory cytokines. MSC-EVs application in vitro decreased the number of TUNEL-positive 661 W cells co-cultured with LPS-stimulated BV2, with similar impact on the cytokine expression as in vivo study. Genetic screening predicted miR-146a to be the downstream target of MSC-EVs, which was detected in MSC-EVs and upregulated in co-cultured 661 W cells and BV2 cells after MSC-EVs treatment. Upregulation of miR-146a by using its mimic decreased the expression of the transcription factor Nr4a3, and its downregulation inhibition promoted Nr4a3 expression in both 661 W and BV2 cells. Nr4a3 was further identified as the target gene of miR-146a by dual-luciferase assay. Furthermore, overexpressing miR-146a significantly decreased the expression of LPS-induced pro-inflammatory cytokines in BV2 cells.ConclusionsMSC-EVs delays retinal degeneration in rd10 mice mainly by its anti-inflammatory effect via the miR-146a-Nr4a3axis. Hence, MSC-EVs may be used in the treatment of neurodegenerative diseases.

High‐fat consumption alters the gut microbiome in retinitis pigmentosa mice and accelerates retinal degeneration

AbstractPurposeIntestinal dysbiosis has been linked with the pathogenesis of several degenerative diseases. Moreover, the consumption of high‐fat diets (HFD) can drove to significant changes in the gut microbiome. Our purpose was to investigate changes in gut microbiome and retinal degeneration associated with the ingestion of HFD in a mice model of retinitis pigmentosa (RP).MethodsC57BL/6J mice and rd10 mice were fed either with normal chow (5.5% fat kcal) or with a HFD (61.6% fat kcal) for two weeks since P19. Retinal function was analyzed by electroretinography and optomotor test. Immunohistochemistry was employed to evaluate the structure and integrity of the retinal tissue. 16S rRNA gene sequencing was made to evaluate the gut microbiome.ResultsWe found a higher retinal degeneration in rd10 mice as compared to C57BL/6J mice, both fed with normal chow. Rd10 mice exhibited significantly reduced retinal responsiveness, as well as diminished visual acuity. This loss of retina function went with a decrease in the number of photoreceptor rows, and the remaining photoreceptors showed morphologic anomalies. The photoreceptor degeneration was accompanied by an inflammatory response of the retina, characterized by the proliferation of microglial cells and reactive gliosis of Müller cells. Likewise, the gut microbiome analysis revealed differences in alpha and beta diversity at the genera, species, and amplicon sequence variants levels. HFD generated a significant dysbiosis in the gut microbiome increasing potentially pro‐inflammatory bacteria as Bilophila sp., Alistipes sp. and Mucispirillum schaedleri, and drived the exacerbation of the retinal degeneration.ConclusionsIn retinitis pigmentosa, retinal dysfunction and degeneration are related to significant changes in the gut microbiome, which can be altered by diet, conducing to a worsening of the disease.SupportMINECOFEDER‐BFU2015‐67139‐R, FEDER‐PID2019‐106230RB‐I00, RETICS‐FEDER RD16/0008/0016, IDIFEDER/2017/064.

Wolfberry-derived zeaxanthin dipalmitate delays retinal degeneration in a mouse model of retinitis pigmentosa through modulating STAT3, CCL2 and MAPK pathways.

Retinitis pigmentosa (RP) is a group of inherited photoreceptor degeneration diseases that causes blindness without effective treatment. The pathogenesis of retinal degeneration involves mainly oxidative stress and inflammatory responses. Zeaxanthin dipalmitate (ZD), a wolfberry-derived carotenoid, has anti-inflammatory and anti-oxidative stress effects. Here we investigated whether these properties of ZD can delay the retinal degeneration in rd10 mice, a model of RP, and explored its underlying mechanism. One shot of ZD or control vehicle was intravitreally injected into rd10 mice on postnatal day 16 (P16). Retinal function and structure of rd10 mice were assessed at P25, when rods degenerate substantially, using a visual behavior test, multi-electrode-array recordings and immunostaining. Retinal pathogenic gene expression and regulation of signaling pathways by ZD were explored using transcriptome sequencing and western blotting. Our results showed that ZD treatment improved the visual behavior of rd10 mice and delayed the degeneration of retinal photoreceptors. It also improved the light responses of photoreceptors, bipolar cells and retinal ganglion cells. The expression of genes that are involved in inflammation, apoptosis and oxidative stress were up-regulated in rd10 mice, and were reduced by ZD. ZD further reduced the activation of two key factors, signal transducer and activator of transcription 3 and chemokine (C-C motif) ligand 2, down-regulated the expression of the inflammatory factor GFAP, and inhibited extracellular signal regulated protein kinases and P38, but not the JNK pathways. In conclusion, ZD delays the degeneration of the rd10 retina both morphologically and functionally. Its anti-inflammatory function is mediated primarily through the signal transducer and activator of transcription 3, chemokine (C-C motif) ligand 2 and MAPK pathways. Thus, ZD may serve as a potential clinical candidate to treat RP.

Nutraceutical Supplementation Ameliorates Visual Function, Retinal Degeneration, and Redox Status in rd10 Mice.

Retinitis pigmentosa (RP) is a group of inherited retinal dystrophies characterized by progressive degeneration of photoreceptor cells. Ocular redox status is altered in RP suggesting oxidative stress could contribute to their progression. In this study, we investigated the effect of a mixture of nutraceuticals with antioxidant properties (NUT) on retinal degeneration in rd10 mice, a model of RP. NUT was orally administered to rd10 mice from postnatal day (PD) 9 to PD18. At PD18 retinal function and morphology were examined by electroretinography (ERG) and histology including TUNEL assay, immunolabeling of microglia, Müller cells, and poly ADP ribose polymers. Retinal redox status was determined by measuring the activity of antioxidant enzymes and some oxidative stress markers. Gene expression of the cytokines IL-6, TNFα, and IL-1β was assessed by real-time PCR. NUT treatment delayed the loss of photoreceptors in rd10 mice partially preserving their electrical responses to light stimuli. Moreover, it ameliorated redox status and reduced inflammation including microglia activation, upregulation of cytokines, reactive gliosis, and PARP overactivation. NUT ameliorated retinal functionality and morphology at early stages of RP in rd10 mice. This formulation could be useful as a neuroprotective approach for patients with RP in the future.

Intravitreal administration of adalimumab delays retinal degeneration in rd10 mice.

Retinitis pigmentosa (RP) is a group of inherited retinal dystrophies characterized by the progressive and irreversible loss of vision. We previously found that intraperitoneal administration of Adalimumab, a monoclonal anti-TNFα antibody, slowed down retinal degeneration in the murine model of RP, the rd10 mice. The aims of this study were to improve its neuroprotective effect and to deepen understanding of the molecular mechanisms involved in this effect. We analyzed (i) the in vitro effect of Adalimumab on the TNFα-mediated cell death in retinal cells; (ii) the effect of a single intravitreal injection of Adalimumab on retinal degeneration in rd10 mice at postnatal day (P) 23. In vitro studies showed that TNFα induced caspase and poly ADP ribose polymerase (PARP) activation, downregulation of (kinase receptor-interacting protein 1) RIPK1 and upregulation of RIPK3 in retinal cells. Adalimumab reduced cell death probably through the inhibition of caspase 3 activation. In vivo studies suggested that PARP and NLRP3 inflammasome are mainly activated and to a lesser extent caspase-dependent mechanisms in rd10 retinas at P23. Necroptosis seems to be inhibited by the downregulation of RIPK1. Adalimumab prevented from retinal degeneration without affecting caspase -dependent mechanisms but decreasing PARP activation, microglia activation as well as NLRP3 inflammasome.

The Resveratrol Prodrug JC19 Delays Retinal Degeneration in rd10 Mice.

It has been reported that resveratrol (RES) has a therapeutic effect in different neurodegenerative and ocular diseases. However, RES is rapidly eliminated from the organism, and high doses need to be administered resulting in potential toxic side effects. We hypothesized that a RES prodrug such as 3,4'-diglucosyl resveratrol (JC19) would reduce RES metabolism to produce a neuroprotective effect. Here, we have examined the protective effect of JC19 in an experimental mouse model of autosomal recessive RP. Rd10 mice at postnatal day 13 (P13) were subretinally injected with vehicle and two different doses of JC19. Electroretinogram (ERG) and histological evaluation were performed 15days after injections. The amplitude of a- and b-waves was quantified in ERG recordings, and the number of photoreceptor nuclei in the outer nuclear layer was counted. In addition, the mouse retinas were immunostained with anti-rhodopsin antibodies. JC19 treatment delayed the loss of rod photoreceptor in rd10 mice, maintaining the expression of rhodopsin and preserving their electrical responses to light stimuli. The exact mechanism by which RES delays retinal degeneration in rd10 mice remains to be elucidated, but Sirtuin 1 activation could be one of the key molecular pathways involved in its neuroprotective effect.

(3R)-5,6,7-trihydroxy-3-isopropyl-3-methylisochroman-1-one ameliorates retinal degeneration in Pde6brd10 mice

As a severe photoreceptor-degenerative disease, retinitis pigmentosa (RP) is currently incurable and eventually leads to partial or complete blindness. (3R)-5,6,7-trihydroxy-3-isopropyl-3-methylisochroman-1-one (TIM) is a novel antioxidant isolated from the plant of Alpinia katsumadai Hayata, with protective effects on photoreceptor cells against lipoteichoic acid-induced damage through inhibiting oxidative stress. The present study was to further demonstrate whether TIM could ameliorate retinal degeneration of Pde6brd10 (rd10) mice, a mouse model of RP. rd10 mice were treated with TIM by intraperitoneal injection daily from postnatal Day 10 (P10) to P26. Retinal function was tested by electroretinography. Histology was evaluated by toluidine blue staining and TUNEL assay. Oxidative stress markers were measured by ELISA. Immunohistochemistry, real-time PCR, and western blotting were applied to explore the protective mechanism. Results showed TIM significantly improved the retinal function and decreased photoreceptor cell apoptosis in rd10 mice through reducing oxidative stress. For the first time, this study demonstrated the protective effects of TIM against retinal degeneration in rd10 mice, providing scientific rationale to use TIM treating the RP.

Neuroprotective effects of methyl 3,4 dihydroxybenzoate in a mouse model of retinitis pigmentosa

Retinitis pigmentosa is a photoreceptor-degenerative disease that is currently untreatable and eventually causes blindness. Methyl 3,4 dihydroxybenzoate (MDHB) is a small molecule that exerts neuroprotective effects in vitro. The present study tests whether MDHB protects the retina of rd10 mice, a model of retinitis pigmentosa. MDHB or an equal volume of vehicle was intraperitoneally injected in rd10 mice daily from postnatal day 12 (P12) to P26. Retinal morphology was evaluated by immunostaining, and retinal function by electroretinogram (ERG) and by visual behavior. TUNEL, Iba1, GFAP staining and western blotting were applied to explore the neuroprotective mechanism of MDHB in retina. MDHB treatment significantly promoted photoreceptor survival and preserved cone morphology compared to the untreated animals. The visual behavior and ERG responses were also greatly enhanced in MDHB-treated rd10 mice. Mechanistically, following MDHB treatment, the number of TUNEL-positive cells was decreased in rd10 retina, and the expression of brain-derived neurotrophic factor (BDNF) protein and phosphorylated tropomyosin-related kinase B (TrkB) receptor were increased. Furthermore, blocking TrkB using the antagonist ANA-12 prevented the protective effect of MDHB on photoreceptor survival and structure. MDHB treatment also inhibited microglial activation and Muller cell gliosis in rd10 retina. In conclusion, MDHB treatment delays retinal degeneration in rd10 mice and preserves retinal structure and functions. These effects are likely mediated by the BDNF-TrkB pathway. Due to its neurotrophic effects and ability to reduce reactive gliosis, MDHB may be useful to treat degenerative diseases in retina and brain.

Unilateral intravitreal dexamethazone implant for bilateral retinitis pigmentosa-related macular edema

Dear Editor, I would like to congratulate Srour et al. for their case series about the treatment of macular edema (ME) secondary to retinitis pigmentosa by intravitreal dexamethasone implant (Ozurdex) (DEX implant) [1]. Retinal pigmentosa (RP) is a group of inherited retinal degenerative diseases caused by several gene abnormalities. The first lesion is peripheral, and the central vision of RP patients is relatively preserved. However, when ME occurs in these patients, central vision is often impaired. The ME could be caused by circulating antiretinal antibodies; this suggests that an autoimmune process may be implicated in the formation ofME in RP [2]. Sustained chronic inflammatory reaction may contribute to the pathogenesis of retinal degeneration in rd10 mice, suggesting there is ocular inflammatory reaction in patients with RP [3]. In this case, a treatment by corticosteroids could be efficient. Indeed, Srour et al. report the efficacy of intravitreal dexamethasone implant for macular edema secondary to retinitis pigmentosa on three patients [1]. Only one had bilateral ME and was treated in each eye. For these three patients treated by DEX implant for ME with RP, the decrease of retina thickness was important, but there was recurrence for two patients. Recently, Saatchi reported the treatment of a bilateral ME by an intravitreal dexamethasone implant in each eye too [4]. We would like to report our original experience [5]. A 22-year old man diagnosed of RP was referred to our department because he had bilateral ME and needed to have good vision to be successful in school (Fig. 2a). Carbonic anhydrase inhibitors (acetazolamide, 500mg daily) and brinzolamide (one drop in each eye twice a day) were not effective. We decided to inject intravitreal Ozurdex (0.7 dexamethasone implant). It was administered without complications on the right eye according to standard procedure (Fig. 1). Spectralis SD-OCT revealed reduction of the ME for both eyes, even in the first week (Fig. 2a and b). On the first month follow-up, best-corrected visual acuity (BCVA) had improved from 20/40 to 20/30 for the right eye and from 20/40 to 20/20 for the left eye, while the retina thickness had decreased from 538 μm to 294 μm for the right eye and from 428 μm to 319 μm for the left eye (Fig. 2c). No cataract progression was observed during the study period. In the case of bilateral ME, Dex implant could provide anatomic and functional patient improvements for both eyes in a unilateral injection. It could be interesting for diseases with bilateral ME. We advise waiting for the efficacy of a first

Electrophysiological and Histologic Evaluation of the Time Course of Retinal Degeneration in therd10Mouse Model of Retinitis Pigmentosa

Among several animal models of retinitis pigmentosa (RP), the more recently developed rd10 mouse with later onset and slower rate of retinal degeneration than rd1 mouse is a more suitable model for testing therapeutic modalities. We therefore investigated the time course of retinal degeneration in rd10 mice before adopting this model in our interventional studies. Electroretinogram (ERG) recordings were carried out in postnatal weeks (PW) 3~5 rd10 (n=23) and wild-type (wt) mice (n=26). We compared the amplitude and implicit time of the b-wave of ERG records from wt and rd10 mice. Our results showed that b-wave amplitudes in rd10 mice were significantly lower and the implicit time of b-waves in rd10 mice were also significantly slower than that in wt mice (20~160 µV vs. 350~480 µV; 55~75 ms vs. 100~150 ms: p<0.001) through PW3 to PW5. The most drastic changes in ERG amplitudes and latencies were observed during PW3 to PW4. In multichannel recording of rd10 retina in PW2 to PW4.5, we found no significant difference in mean spike frequency, but the frequency of power spectral peak of local field potential at PW3 and PW3.5 is significantly different among other age groups (p<0.05). Histologic examination of rd10 retinae showed significant decrease in thickness of the outer nuclear layer at PW3. TUNEL positive cells were most frequently observed at PW3. From these data, we confirm that in the rd10 mouse, the most precipitous retinal degeneration occurs between PW3~PW4 and that photoreceptor degeneration is complete by PW5.

Laboratory Evidence of Sustained Chronic Inflammatory Reaction in Retinitis Pigmentosa

To study the nature of retinal inflammatory response in rd10 mice, an animal model of retinitis pigmentosa (RP), and to investigate the effect of an antioxidant on retinal inflammation and photoreceptor apoptosis. Experimental study. This study included 42 untreated rd10 mice, 30 N-acetylcysteine (NAC)-treated rd10 mice, and 20 C57BL/6 mice as controls. Real-time polymerase chain reaction (PCR) was performed to evaluate the expression levels of inflammatory factors (proinflammatory cytokines and chemokines) in rd10 mouse retinas. Rd10 mice were treated with an antioxidant NAC, and its effect on retinal inflammation and photoreceptor apoptosis were examined by immunohistochemistry. Real-time PCR and immunohistochemistry. We demonstrated sequential events involving increased expression of proinflammatory cytokines and chemokines, activation of microglia, and photoreceptor apoptosis during retinal degeneration of rd10 mice. Furthermore, antioxidant treatment with NAC prevented the photoreceptor cell death along with suppression of inflammatory factors and microglial activation. Sustained chronic inflammatory reaction may contribute to the pathogenesis of retinal degeneration in rd10 mice, suggesting interventions for ocular inflammatory reaction using antioxidants as a potential treatment for patients with RP. The authors have no proprietary or commercial interest in any of the materials discussed in this article.

Low-Dose-Rate, Low-Dose Irradiation Delays Neurodegeneration in a Model of Retinitis Pigmentosa

The existence of radiation hormesis is controversial. Several stimulatory effects of low-dose (LD) radiation have been reported to date; however, the effects on neural tissue or neurodegeneration remain unknown. Here, we show that LD radiation has a neuroprotective effect in mouse models of retinitis pigmentosa, a hereditary, progressive neurodegenerative disease that leads to blindness. Various LD radiation doses were administered to the eyes in a retinal degeneration mouse model, and their pathological and physiological effects were analyzed. LD gamma radiation in a low-dose-rate (LDR) condition rescues photoreceptor cell apoptosis both morphologically and functionally. The greatest effect was observed in a condition using 650 mGy irradiation and a 26 mGy/minute dose rate. Multiple rounds of irradiation strengthened this neuroprotective effect. A characteristic up-regulation (563%) of antioxidative gene peroxiredoxin-2 (Prdx2) in the LDR-LD-irradiated retina was observed compared to the sham-treated control retina. Silencing the Prdx2 using small-interfering RNA administration reduced the LDR-LD rescue effect on the photoreceptors. Our results demonstrate for the first time that LDR-LD irradiation has a biological effect in neural cells of living animals. The results support that radiation exhibits hormesis, and this effect may be applied as a novel therapeutic concept for retinitis pigmentosa and for other progressive neurodegenerative diseases regardless of the mechanism of degeneration involved.

Ironing out neurodegeneration: Iron chelation for neuroprotection

Iron is one of the substances for which the adage “Too much of a good thing is not better” holds true. Iron's ability to readily shift its redox state facilitates cellular respiration but can also catalyze the production of harmful hydroxyl radical when iron's level or location is inappropriate. In this issue of Free Radical Biology & Medicine, the paper by Obolensky et al. highlights the neuroprotective potential of iron chelation, even when iron dysregulation is not the primary cause of the degeneration. Their carefully executed study shows that retinal degeneration in rd10 mice can be ameliorated by treatment with the iron chelator zinc–deferoxamine (Zn-DFO). Rd10 mice have a mutation in the rod photoreceptor phosphodiesterase, required for phototransduction, resulting in a nearly complete loss of both rod and cone photoreceptors by about 6 weeks of age. Mice given Zn-DFO by ip injection beginning at postnatal day 4 have relatively preserved retinal structure and function at several ages, as well as diminished oxidative stress. The number of rods and cones is higher in the treated mice. Electroretinography reveals improved rod and cone function with the Zn-DFO treatment. Both immunostaining and biochemical assays reveal diminished oxidative stress in the Zn-DFO-treated mice. This study builds upon several previous publications showing neuroprotection by iron chelation. DFO protects the rat retina from photo-oxidative stress [1] and from ischemia–reperfusion injury [2]. The oral iron chelator deferiprone protects iron-overloaded retinas of ceruloplasmin/hephaestin knockout mice against oxidative stress and retinal degeneration. It also ameliorates a movement disorder and early mortality associated with brain iron accumulation in these mice [3]. Intraperitoneal injection of the endogenous iron-chelating protein transferrin alsomarkedly protects the rd10 retina from degeneration [4]. Iron chelation can also protect the brain. The chelator salicylaldehyde isonicotinoyl hydrazine protects the rodent spinal cord against trauma [5]. Both elevated levels of the endogenous iron-storage protein ferritin and administration of the metal chelator clioquinol protect the mouse brain against the neurotoxin MPTP, which induces a Parkinson-like neurodegeneration [6]. The mechanism of neuroprotection by these iron chelators is probably prevention of iron-catalyzed oxidative stress, as several of the above studies correlate diminished oxidative stress with chelator administration. Iron excess, or mislocalization, has been associated with age-related neurodegeneration such as age-related macular degeneration [7], Alzheimer disease [8], and Parkinson disease [9], so it is primed to exacerbate ongoing degeneration in these conditions. It can also be released from red blood cells after hemorrhage, or from dying neighbors in ongoing neurodegeneration. Iron dysregulation caused by ongoing neurodegeneration could also accelerate disease. For example, retinas of rd10 mice have altered levels of iron, ferritin, and transferrin [10]. Iron may be mishandled during neurodegeneration because its regulation is also influenced by inflammation and hypoxia, potentially leading to toxic iron stores. Inappropriate iron handling can clearly lead to brain and retina degeneration, as in the hereditary diseases aceruloplasminemia [11], Friedreich ataxia [12], and pantothenate kinase-associated neurodegeneration [13]. Mice with iron-regulatory protein knockout or low ferritin levels also experience neurodegeneration [14]. The above studies support the use of iron chelators in clinical trials for neurodegeneration such as in Alzheimer disease [15] and Friedreich ataxia [16]. Route of administration and toxicity are important considerations. Some chelators can readily cross the blood–brain and blood–retinal barriers. Iron deficiency must be avoided, but it is likely that this could be achieved by careful monitoring and by choosing chelators that can bind or redistribute loosely bound, potentially toxic iron in the central nervous system without stripping iron from iron requiring proteins.

Effect of Para-Aminobenzoic Acid on the Course of Retinal Degeneration in the rd10 Mouse

Recent evidence suggests that oxidative injury plays a significant role in the pathogenesis of retinal degenerative diseases. Para-aminobenzoic acid (PABA) is a cyclic amino acid, which may act to decrease lipid peroxidation and oxidative injury. Our aim was to evaluate the efficacy of PABA in attenuating oxidative injury and rate of retinal degeneration in the rd10 mouse. PABA (50 mg/kg) was administered intraperitoneally six times per week in 28 rd10 mice from postnatal day 3. Twenty-four littermate control mice were similarly injected with saline. At 3, 4.5, and 6 weeks of age, electrophysiological (full field electroretinogram-ERG), quantitative histological, and immunohistochemical techniques were used to assess the course and extent of retinal degeneration. Degree of lipid peroxidation was determined by the measurement of thiobarbituric acid reactive species (TBARS) and retinal carbonyl content was quantified using the 2,4-dinitrophenylhydrazine method. Dark adapted mixed rod-cone ERG responses at 3 weeks of age were higher in the PABA-treated group as compared to saline control (P < 0.05). By 4.5 weeks, this protective effect was largely abolished and by 6 weeks ERG was unrecordable in both groups. However, at both 3 and 4.5 weeks of age, light-adapted cone ERG amplitudes were better preserved in PABA-treated animals. At 4.5 weeks, thickness of the outer nuclear layer was 28.6% higher in the peripheral retina of PABA-treated mice as compared to controls (P < 0.05). Quantitative immunohistochemistry revealed 2.4-fold higher red/green cone opsin content in the retinas of PABA-treated mice (P < 0.005). At both 3 and 4.5 weeks, levels of TBARS and protein carbonyls were 49%-69% lower in PABA-treated retinas (P < 0.05-0.0005), suggesting less oxidative injury. PABA treatment may protect retinal function and attenuate the course of retinal degeneration in rd10 mice. Biochemical parameters indicate a lower degree of oxidative injury in PABA-treated retinas. PABA may potentially serve as an addition to antioxidative treatment for retinal and macular degenerations.

Sirt1 Involvement in rd10 Mouse Retinal Degeneration

Sirtuin1 (Sirt1) is an NAD(+)-dependent deacetylase involved in development, cell survival, stress resistance, energy metabolism, and aging. It is expressed in the mammalian central nervous system (CNS) and is activated during processes associated with neuroprotection. The retinal degeneration 10 (rd10) mouse model of retinitis pigmentosa (RP) was used to investigate the possible role of Sirt1 in this type of retinal degeneration. Eyes from control and rd10 mice were used. Sirt1 mRNA was detected by in situ hybridization, and its abundance was estimated by semiquantitative RT-PCR. The presence of Sirt1 protein was investigated by immunohistofluorescence and Western blot analysis. The apoptosis of photoreceptor cells was analyzed by terminal dUTP transferase nick-end labeling (TUNEL). Immunolabeling for Sirt1, apoptosis-inducing factor (Aif), and caspase-12 (Casp-12) was performed on retinal tissue sections. Sirt1 mRNA and immunoreactivity were observed in normal adult mouse eyes. In the control retina, Sirt1 was immunolocalized mostly to the nucleus. In rd10 mice with retinal degeneration, changes in Sirt1 immunolabeling were observed only in the retinal outer nuclear layer (ONL). The pathologic pattern of Sirt1 immunoreactivity correlated with the start of retinal degeneration in rd10 mice. The results suggest a link between Sirt1 production and retinal degeneration in rd10 mice. The anti-apoptotic, neuroprotective role of Sirt1 in the mouse retina is based on the involvement of Sirt1 in double DNA strand-break repair mechanisms and in maintaining energy homeostasis in photoreceptor cells. The results suggest that the neuroprotective properties of Sirt1 may gradually weaken in rd10 mouse photoreceptor cells.

Alteration in Iron Metabolism during Retinal Degeneration in rd10 Mouse

Altered iron metabolism was implicated in retinal and macular degeneration. This study was designed to further elucidate iron homeostasis during the course of retinal degeneration in mice. Retinal mRNA and protein expression of transferrin, transferrin receptor, and ceruloplasmin were evaluated during retinal degeneration in rd10 mice and chemokine receptor 2 (ccr2)-deficient mice. Retinal ferritin protein levels, ferritin-bound iron, and total iron were evaluated in rd10 mice. Transferrin and ceruloplasmin mRNA levels increased between 2- and 12-fold during the course of retinal degeneration in rd10 mice compared with same-age controls (P < 0.01), whereas transferrin receptor mRNA levels increased only at the late stages of degeneration in rd10 mice (2.7-fold; P = 0.005). Transferrin mRNA also increased in retinas of aged ccr2-deficient mice (1.5-fold; P = 0.05). Transferrin and ceruloplasmin protein levels corroborated with mRNA levels changes in rd10 mice albeit at a lower magnitude. Retinal ferritin protein levels increased between 1.5-fold and 2-fold (P < 0.03) in rd10 mice, and ferritin-bound iron levels increased 1.6-fold in 3-week-old rd10 mice (P = 0.03). Three-week-old rd10 mice also had a 1.4-fold increase in total retinal iron level (P = 0.05). Combined with previous reports, these data suggest that retinal degenerations are associated with altered iron homeostasis regardless of the primary insult. Given the potential of iron to generate oxidative injury, its role as a therapeutic target in retinal and macular degenerations should be evaluated.

AAV-Mediated Gene Therapy for Retinal Degeneration in therd10Mouse Containing a Recessive PDEβ Mutation

To test AAV-mediated gene therapy in the rd10 mouse, a natural model of recessive RP caused by mutation of the beta-subunit of rod photoreceptor cGMP phosphodiesterase. One eye of a cohort of rd10 mice kept in a dark environment was subretinally injected at postnatal day (P) 14 with 1 microL AAV5-smCBA-PDEbeta. The contralateral eye was not injected. The animals were then maintained for 2 weeks in the dark before they were moved to a normal 12-hour light/12-hour dark cycling light environment for visually guided behavioral training. Three weeks after injection, treated rd10 mice were examined by scotopic and photopic electroretinography and then killed for biochemical and morphologic examination. Substantial scotopic ERG signals were maintained in treated rd10 eyes, whereas untreated eyes in the same animals showed minimal signals. Treated eyes showed photopic ERG b-wave amplitudes similar to those of the normal eyes; in untreated partner eyes, only half the normal amplitudes remained. Strong PDEbeta expression was observed in photoreceptor outer segments only in treated eyes. Light microscopy showed a substantial preservation of the outer nuclear layer in most parts of the treated retina only. Electron microscopy showed good outer segment preservation only in treated eyes. A visually guided water maze behavioral test under dim light showed significantly improved performance in one eye-treated rd10 mice compared with untreated mice. These data demonstrate that P14 administration of AAV5-smCBA-PDEbeta can prevent retinal degeneration in rd10 mice, as reflected by significant structural, biochemical, electrophysiological, and behavioral preservation/restoration. These results serve as a baseline for studying long-term retinal rescue in rd10 mice.

Activation of Bone Marrow-Derived Microglia Promotes Photoreceptor Survival in Inherited Retinal Degeneration

The role of microglia in neurodegeneration is controversial, although microglial activation in the retina has been shown to provide an early response against infection, injury, ischemia, and degeneration. Here we show that endogenous bone marrow (BM)-derived microglia play a protective role in vascular and neural degeneration in the retinitis pigmentosa model of inherited retinal degeneration. BM-derived cells were recruited to the degenerating retina where they differentiated into microglia and subsequently localized to the degenerating vessels and neurons. Inhibition of stromal-derived factor-1 in the retina reduced the number of BM-derived microglia and accelerated the rate of neurovascular degeneration. Systemic depletion of myeloid progenitors also accelerated the degenerative process. Conversely, activation of BM-derived myeloid progenitors by systemic administration of both granulocyte colony-stimulating factor and erythropoietin resulted in the deceleration of retinal degeneration and the promotion of cone cell survival. These data indicate that BM-derived microglia may play a protective role in retinitis pigmentosa. Functional activation of BM-derived myeloid progenitors by cytokine therapy may provide a novel strategy for the treatment of inherited retinal degeneration and other neurodegenerative diseases, regardless of the underlying genetic defect.