Navigating the future of retinitis pigmentosa treatments: A comprehensive analysis of therapeutic approaches in rd10 mice.

Retinitis pigmentosa (RP) is a degenerative disease, caused by genetic mutations that lead to a loss in photoreceptors. For research on RP, rd10 mice, which carry mutations in the phosphodiesterase (PDE) gene, exhibit degenerative patterns comparable to those of patients with RP, making them an ideal model for investigating potential treatments. Although numerous studies have reported the potential of biochemical drugs, gene correction, and stem cell transplantation in decelerating rd10 retinal degeneration, a comprehensive review of these studies has yet to be conducted. Therefore, here, a comparative analysis of rd10 mouse treatment research over the past decade was performed. Our findings suggest that biochemical drugs capable of inhibiting the inflammatory response may be promising therapeutics. Additionally, significant progress has been made in the field of gene therapy; nevertheless, challenges such as strict delivery requirements, bystander editing, and off-target effects still need to be resolved. Nevertheless, secretory function is the only unequivocal protective effect of stem cell transplantation. In summary, this review presents a comprehensive analysis and synthesis of the treatment approaches employing rd10 mice as experimental subjects, describing a clear pathway for future RP treatment research and identifies potential clinical interventions.

Cyclooxygenase-1 mediates neuroinflammation and neurotoxicity in a mouse model of retinitis pigmentosa.

BACKGROUND: Retinitis pigmentosa (RP) is a group of inherited eye disorders with progressive degeneration of photoreceptors in the retina, ultimately leading to partial or complete blindness. The mechanisms underlying photoreceptor degeneration are not yet completely understood. Neuroinflammation is reported to play a pathological role in RP. However, the mechanisms that trigger neuroinflammation remain largely unknown. To address this question, we investigated the role of cyclooxygenase-1 (COX-1), a key enzyme in the conversion of arachidonic acid to proinflammatory prostaglandins, in the rd10 mouse model of RP. METHODS: We backcrossed COX-1 knockout mice (COX-1-/-) onto the rd10 mouse model of RP and investigated the impact of COX-1 deletion on neuroinflammation in the resulting COX-1-/-/rd10 mouse line, using a combination of immunocytochemistry, flow cytometry, qPCR, ELISA, and a series of simple visual tests. RESULTS: We found that genetic ablation or pharmacological inhibition of COX-1 alleviated neuroinflammation and subsequently preserved retinal photoreceptor and function and visual performance in rd10 mice. Moreover, we observed that the pharmacological inhibition of the prostaglandin E2 (PGE2) EP2 receptors largely replicated the beneficial effects of COX-1 deletion, suggesting that EP2 receptor was a critical downstream effector of COX-1-mediated neurotoxicity in rd10 mice. CONCLUSION: Our data suggest that the COX-1/PGE2/EP2 signaling pathway was partly responsible for significantly increased neuroinflammation and disease progression in rd10 mice, and that EP2 receptor could be targeted therapeutically to block the pathological activity of COX-1 without inducing any potential side effects in treating RP patients.

(Z)-7,4'-Dimethoxy-6-hydroxy-aurone-4-O-ß-glucopyranoside mitigates retinal degeneration in Rd10 mouse model through inhibiting oxidative stress and inflammatory responses.

Purpose: As an inherited retinal dystrophy characterised by progressive degeneration of photoreceptor cells, retinitis pigmentosa (RP) leads to partial or total blindness eventually. Possible causes of the photoreceptor cell death are oxidative stress and inflammatory responses. (Z)-7,4'-Dimethoxy-6-hydroxy-aurone-4-O-ß-glucopyranoside (DHAG) is a novel compound with potent antioxidant properties. The aim of this study was to investigate whether DHAG could mitigate photoreceptor cell degeneration in an established mouse model of RP.Materials and method: Rd10 mice were treated with DHAG daily by gavage from postnatal day 12 (P12) to P33. Retinal morphology was evaluated by haematoxylin and eosin staining. Apoptosis-positive cells were detected by terminal deoxynucleotidyl transferase dUTP nick end labelling (TUNEL) assay. Oxidative stress markers and inflammatory factors were measured by enzyme-linked immunosorbent assay (ELISA). Real-time polymerase chain reaction, immunostaining and western blot were applied to measure the gene and protein change to explore the underlying mechanisms.Results: Results showed that DHAG significantly preserved the retinal morphology, reducing photoreceptor cell apoptosis, decreasing oxidative stress and inhibiting inflammatory responses in Rd10 mice. The mechanism might be related to inhibit the activation of P38 pathway.Conclusions: This study showed the beneficial effects of DHAG, a compound possessing antioxidant properties, and provided scientific rationale to develop DHAG as a potential agent to treat RP.

3,5-Dimethoxy-4-hydroxy myricanol ameliorates photoreceptor cell degeneration in Pde6brd10 mouse model.

INTRODUCTION: Retinitis pigmentosa (RP) caused by the photoreceptor cell degeneration is currently incurable and leads to partial or complete blindness eventually. 3,5-dimethoxy-4-hydroxy myricanol (DM) is a novel compound isolated from the leaves of Micromelum integerrimum, with proliferative activities on NIH3T3 cells. This study was to investigate whether DM could mitigate retinal degeneration of rd10 mice, a well-characterized mouse model of RP. MATERIALS AND METHOD: Rd10 mice were treated with DM daily by intraperitoneal injection from postnatal day 12 (P12) to P26. Electroretinography (ERG) reflects the mass response of photoreceptor cells and was used to test the outer retinal function after DM treatment. Haematoxylin and Eosin staining was used to show the retinal morphology and evaluate the rod photoreceptor cell loss. TUNEL assay was used to detect the apoptosis-positive cells. Inflammatory factors were measured by ELISA to show the inflammatory response. Real-time PCR and western blot were applied to measure the gene and protein change to explore the underlying mechanisms. RESULTS: Results showed that DM significantly improved the retinal function by increasing the ERG amplitude, preserving the retinal morphology, reducing photoreceptor cell apoptosis, decreasing inflammatory response, and inhibiting endoplasmic reticulum stress in rd10 mice. CONCLUSION: This is the first time when the protective effects of DM against photoreceptor cell degeneration of rd10 mice have been demonstrated, providing scientific rationale to develop DM as a potential agent to treat RP.

(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.

Photoreceptor protection via blockade of BET epigenetic readers in a murine model of inherited retinal degeneration.

BACKGROUND: The bromodomain and extraterminal domain (BET) family proteins (BET2, BET3, and BET4) "read" (bind) histone acetylation marks via two distinct bromodomains (Brom1 and Brom2) facilitating transcriptional activation. These epigenetic "readers" play crucial roles in pathogenic processes such as inflammation. The role of BETs in influencing the degenerative process in the retina is however unknown. METHODS: We employed the rd10 mouse model (Pde6b rd10 mutation) of retinitis pigmentosa (RP) to examine the involvement of BET proteins in retinal neurodegeneration. RESULTS: Inhibition of BET activity by intravitreal delivery of JQ1, a BET-specific inhibitor binding both Brom1 and Brom2, ameliorated photoreceptor degeneration and improved electroretinographic function. Rescue effects of JQ1 were related to the suppression of retinal microglial activation in vivo, as determined by decreased immunostaining of activation markers (IBA1, CD68, TSPO) and messenger RNA (mRNA) levels of inflammatory cytokines in microglia purified from rd10 retinas. JQ1 pre-treatment also suppressed microglial activation in vitro, decreasing microglial proliferation, migration, and mRNA expression of inflammatory cytokines (TNFα, MCP-1, IL-1ß, IL-6, and RANTES). Expression of BET2, but not BET3 and BET4, was significantly elevated during photoreceptor degeneration at postnatal day (PN)24 in retinas of rd10 mice relative to age-matched wild-type controls. siRNA knockdown of BET2 but not BET4, and the inhibitor of Brom2 (RVX208) but not of Brom1 (Olinone), decreased microglial activation. CONCLUSIONS: These findings indicate that BET inhibition rescues photoreceptor degeneration likely via the suppression of microglial activation and implicates BET interference as a potential therapeutic strategy for the treatment of degenerative retinal diseases.

(2R, 3S)-Pinobanksin-3-cinnamate ameliorates photoreceptor degeneration in Pde6rd10 mice.

As an inherited disorder caused by initial death of rod photoreceptors, retinitis pigmentosa is currently untreatable and usually leads to partial or complete blindness. (2R, 3S)-Pinobanksin-3-cinnamate (PC) is a new flavonone isolated from the seed of Alpinia galanga Willd, and has been reported to exert neuroprotective effects by upregulating endogenous antioxidant enzymes. In this study, the anti-oxidative and neuroprotective activity of PC against photoreceptor apoptosis in rd10 mouse model of retinitis pigmentosa was explored. PC showed to produce significant improvement in histology and function in rd10 mice through reducing oxidative stress. For the first time, the protective effects of PC were demonstrated against retina degeneration in rd10 mice and our study provides scientific rationale on using PC as the supplementary treatment to the outer retina diseases, including retinitis pigmentosa, in which oxidative stress is thought to contribute to disease progression.

Suppression of microglial activation is neuroprotective in a mouse model of human retinitis pigmentosa.

Retinitis pigmentosa (RP) is a photoreceptor-degenerative disease caused by various mutations and is characterized by death of rod photoreceptor cell followed by gradual death of cone photoreceptors. The molecular mechanisms that lead to rod and cone death are not yet fully understood. Neuroinflammation contributes to the progression of many chronic neurodegenerative disorders. However, it remains to be determined how microglia contribute to photoreceptor disruption in RP. In this study, we explored the role of microglia as a contributor to photoreceptor degeneration in the rd10 mouse model of RP. First, we demonstrated that microglia activation was an early alteration in RP retinas. Inhibition of microglia activation by minocycline reduced photoreceptor apoptosis and significantly improved retinal structure and function and visual behavior in rd10 mice. Second, we identified that minocycline exerted its neuroprotective effects through both anti-inflammatory and anti-apoptotic mechanisms. Third, we found that Cx3cr1 deficiency dysregulated microglia activation and subsequently resulted in increased photoreceptor vulnerability in rd10 mice, suggesting that the Cx3cl1/Cx3cr1 signaling pathway might protect against microglia neurotoxicity. We concluded that suppression of neuroinflammatory responses could be a potential treatment strategy aimed at improving photoreceptor survival in human RP.

Piceid Octanoate Protects Retinal Cells against Oxidative Damage by Regulating the Sirtuin 1/Poly-ADP-Ribose Polymerase 1 Axis In Vitro and in rd10 Mice.

Retinitis pigmentosa is a common cause of inherited blindness in adults, which in many cases is associated with an increase in the formation of reactive oxygen species (ROS) that induces DNA damage, triggering Poly-ADP-Ribose Polymerase 1 (PARP1) activation and leading to parthanatos-mediated cell death. Previous studies have shown that resveratrol (RSV) is a promising molecule that can mitigate PARP1 overactivity, but its low bioavailability is a limitation for medical use. This study examined the impact of a synthesized new acylated RSV prodrug, piceid octanoate (PIC-OCT), in the 661W cell line against H2O2 oxidative stress and in rd10 mice. PIC-OCT possesses a better ADME profile than RSV. In response to H2O2, 661W cells pretreated with PIC-OCT preserved cell viability in more than 38% of cells by significantly promoting SIRT1 nuclear translocation, preserving NAD+/NADH ratio, and suppressing intracellular ROS formation. These effects result from expressing antioxidant genes, maintaining mitochondrial function, reducing PARP1 nuclear expression, and preventing AIF nuclear translocation. In rd10 mice, PIC-OCT inhibited PAR-polymer formation, increased SIRT1 expression, significantly reduced TUNEL-positive cells in the retinal outer nuclear layer, preserved ERGs, and enhanced light chamber activity (all p values < 0.05). Our findings corroborate that PIC-OCT protects photoreceptors by modulating the SIRT1/PARP1 axis in models of retinal degeneration.

Electrophysiological and Histologic Evaluation of the Time Course of Retinal Degeneration in the rd10 Mouse 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.

Correlated Activity in the Degenerate Retina Inhibits Focal Response to Electrical Stimulation.

Retinal prostheses have shown some clinical success in patients with retinitis pigmentosa and age-related macular degeneration. However, even after the implantation of a retinal prosthesis, the patient's visual acuity is at best less than 20/420. Reduced visual acuity may be explained by a decrease in the signal-to-noise ratio due to the spontaneous hyperactivity of retinal ganglion cells (RGCs) found in degenerate retinas. Unfortunately, abnormal retinal rewiring, commonly observed in degenerate retinas, has rarely been considered for the development of retinal prostheses. The purpose of this study was to investigate the aberrant retinal network response to electrical stimulation in terms of the spatial distribution of the electrically evoked RGC population. An 8 × 8 multielectrode array was used to measure the spiking activity of the RGC population. RGC spikes were recorded in wild-type [C57BL/6J; P56 (postnatal day 56)], rd1 (P56), rd10 (P14 and P56) mice, and macaque [wild-type and drug-induced retinal degeneration (RD) model] retinas. First, we performed a spike correlation analysis between RGCs to determine RGC connectivity. No correlation was observed between RGCs in the control group, including wild-type mice, rd10 P14 mice, and wild-type macaque retinas. In contrast, for the RD group, including rd1, rd10 P56, and RD macaque retinas, RGCs, up to approximately 400-600 µm apart, were significantly correlated. Moreover, to investigate the RGC population response to electrical stimulation, the number of electrically evoked RGC spikes was measured as a function of the distance between the stimulation and recording electrodes. With an increase in the interelectrode distance, the number of electrically evoked RGC spikes decreased exponentially in the control group. In contrast, electrically evoked RGC spikes were observed throughout the retina in the RD group, regardless of the inter-electrode distance. Taken together, in the degenerate retina, a more strongly coupled retinal network resulted in the widespread distribution of electrically evoked RGC spikes. This finding could explain the low-resolution vision in prosthesis-implanted patients.

The protective, rescue and therapeutic potential of multi-target iron-chelators for retinitis pigmentosa.

Retinitis pigmentosa (RP) is a group of inherited diseases in which mutations result in the initial loss of night vision, followed by complete blindness. There is currently no effective therapeutic option for RP patients. Given the extremely heterogeneous nature of RP, any causative gene-specific therapy would be practical in a small fraction of patients with RP. Non-gene-specific therapeutics that is applicable to the majority of RP patients regardless of causative mutations may have an enormous impact on RP treatment. Several theories including apoptosis, oxidative stress and neuroinflammation have been proposed as possible underlying mechanisms for photoreceptor death in RP. We have designed and synthesized a series of iron-chelating compounds that possess diverse pharmacological properties and can act in a non-gene-specific manner on multiple pathological features ascribed to Alzheimer's disease, Parkinson's disease and RP. In this review, we discuss the multiple effects of several brain-permeable multi target iron-chelating compounds on photoreceptor degeneration in a mouse model of human RP. Specifically, we focus on the anti-apototic, neuroprotective and neurorescue effects of the compound VK28, M30 and VAR10303 on the histologic and functional preservation of photoreceptors in a mouse model of RP. We consider such drugs as potential therapeutic agents for RP patients.

Protective effect of sulforaphane against retinal degeneration in the Pde6rd10 mouse model of retinitis pigmentosa.

PURPOSE: Retinitis pigmentosa (RP) is a group of inherited diseases characterized by the death of rod photoreceptors, followed by the death of cone photoreceptors, progressively leading to partial or complete blindness. Currently no specific treatment is available for RP patients. Sulforaphane (SFN) has been confirmed to be an effective antioxidant in the treatment of many diseases. In this study, we tested the therapeutic effects of SFN against photoreceptor degeneration in Pde6brd10 mice. METHODS: rd10 mice and C57/BL6 wild-type (WT) mice were treated with SFN and saline, respectively, from P6 to P20. Electroretinography (ERG), terminal deoxynucleotidyl transferase dUTP nick end labeling and western blot were tested, respectively, at P21 for the analysis of retinal function, retinal cell apoptosis or death and the protein express of GRP78/BiP (TUNEL) as a marker of endoplasmic reticulum (ER) stress. RESULTS: Compared with the saline group, the SFN-treated group showed significantly higher ERG a-wave and b-wave amplitudes, less photoreceptor death, and the downregulation of GRP78/BiP. CONCLUSIONS: Our data showed that SFN ameliorated the retinal degeneration of rd10 mice, which is possibly related to the downregulation of GRP78 expression.

Spontaneous Oscillatory Rhythms in the Degenerating Mouse Retina Modulate Retinal Ganglion Cell Responses to Electrical Stimulation.

Characterization of the electrical activity of the retina in the animal models of retinal degeneration has been carried out in part to understand the progression of retinal degenerative diseases like age-related macular degeneration (AMD) and retinitis pigmentosa (RP), but also to determine optimum stimulus paradigms for use with retinal prosthetic devices. The models most studied in this regard have been the two lines of mice deficient in the ß-subunit of phosphodiesterase (rd1 and rd10 mice), where the degenerating retinas exhibit characteristic spontaneous hyperactivity and oscillatory local field potentials (LFPs). Additionally, there is a robust ~10 Hz rhythmic burst of retinal ganglion cell (RGC) spikes on the trough of the oscillatory LFP. In rd1 mice, the rhythmic burst of RGC spikes is always phase-locked with the oscillatory LFP and this phase-locking property is preserved regardless of postnatal ages. However, in rd10 mice, the frequency of the oscillatory rhythm changes according to postnatal age, suggesting that this rhythm might be a marker of the stage of degeneration. Furthermore when a biphasic current stimulus is applied to rd10 mice degenerate retina, distinct RGC response patterns that correlate with the stage of degeneration emerge. This review also considers the significance of these response properties.

Spontaneous Oscillatory Rhythm in Retinal Activities of Two Retinal Degeneration (rd1 and rd10) Mice.

Previously, we reported that besides retinal ganglion cell (RGC) spike, there is ~ 10 Hz oscillatory rhythmic activity in local field potential (LFP) in retinal degeneration model, rd1 mice. The more recently identified rd10 mice have a later onset and slower rate of photoreceptor degeneration than the rd1 mice, providing more therapeutic potential. In this study, before adapting rd10 mice as a new animal model for our electrical stimulation study, we investigated electrical characteristics of rd10 mice. From the raw waveform of recording using 8×8 microelectrode array (MEA) from in vitro-whole mount retina, RGC spikes and LFP were isolated by using different filter setting. Fourier transform was performed for detection of frequency of bursting RGC spikes and oscillatory field potential (OFP). In rd1 mice, ~10 Hz rhythmic burst of spontaneous RGC spikes is always phase-locked with the OFP and this phase-locking property is preserved regardless of postnatal ages. However, in rd10 mice, there is a strong phase-locking tendency between the spectral peak of bursting RGC spikes (~5 Hz) and the first peak of OFP (~5 Hz) across different age groups. But this phase-locking property is not robust as in rd1 retina, but maintains for a few seconds. Since rd1 and rd10 retina show phase-locking property at different frequency (~10 Hz vs. ~5 Hz), we expect different response patterns to electrical stimulus between rd1 and rd10 retina. Therefore, to extract optimal stimulation parameters in rd10 retina, first we might define selection criteria for responding rd10 ganglion cells to electrical stimulus.