Synergistically acting agonists and antagonists of G protein–coupled receptors prevent photoreceptor cell degeneration
Ontology highlight
ABSTRACT: Photoreceptor degeneration is the central event leading to visual impairment or blindness in most retinal diseases. However, the discovery of safe and effective therapeutic strategies conferring photoreceptor protection remains challenging. A systems pharmacology approach, synergistically targeting distinct cellular pathways could provide an effective strategy for evaluating, preventing or treating retinal dystrophies. Here this concept was investigated using a mouse model of light-induced retinal degeneration. We show that a combination of FDA-approved drugs acting on different G protein-coupled receptors in a synergistic manner could protect retinas against light-induced degeneration when each drug in the combination treatment was administered at a sub-therapeutic dose. Furthermore, transcriptome analyses demonstrated that such combined treatments also preserved patterns of retinal gene expression more characteristic of the normal retina than did single therapies at higher doses. The current study thus supports a new systems pharmacology approach that may extend to other complex neurodegenerative disorders in addition to retinal diseases.
Project description:Photoreceptor cell degeneration is a major cause of blindness and a considerable health burden during aging but effective therapeutic or preventive strategies have not so far become commercially available. Here we show in mouse models that signaling through the tyrosine kinase receptor KIT protects photoreceptor cells against both light-induced and inherited retinal degeneration. Upon light damage, photoreceptor cells upregulate Kit ligand (KITL) and activate KIT signaling, which in turn induces nuclear accumulation of the transcription factor NRF2 and stimulates the expression of the antioxidant gene Hmox1. Conversely, a viable Kit mutation promotes light-induced photoreceptor damage, which is reversed by experimental expression of Hmox1. Furthermore, overexpression of KITL from a viral AAV8 vector prevents photoreceptor cell death and partially restores retinal function after light damage or in genetic models of human retinitis pigmentosa. Hence, application of KITL may provide a novel therapeutic avenue for prevention or treatment of retinal degeneration
Project description:Mutation of rod photoreceptor-enriched transcription factors is a major cause of inherited blindness. We identified the orphan nuclear hormone receptor ERRβ as selectively expressed in rod photoreceptors. Overexpression of ERRβ induces expression of rod-specific genes in retinas of both wildtype and in Nrl-/- mice, which lack rod photoreceptors. Mutation of ERRβ results in dysfunction and degeneration of rods, while inverse agonists of ERRβ trigger rapid rod degeneration, which is rescued by constitutively active mutants of ERRβ. ERRβ coordinates expression of multiple genes that are rate-limiting regulators of ATP generation and consumption in photoreceptors. Furthermore, enhancing ERRβ activity rescues photoreceptor defects that result from loss of the photoreceptor-specific transcription factor Crx. Our findings demonstrate that ERRβ is a critical regulator of rod photoreceptor function and survival, and suggest that ERRβ agonists may be useful in the treatment of certain retinal dystrophies. Affymetrix MOE430 microarrays were used to analyze the expression patterns of P21 mouse retinal tissues. The results were compared across the variable of Genotype, specifically ERRβ knockout versus wildtype.
Project description:Primary and secondary cone photoreceptor cell death in retinal degenerative diseases, including age-related macular degeneration and retinitis pigmentosa, leads to severe vision impairment and blindness. Regardless of the fact that protection of cone photoreceptor cells under stress conditions, such as retinal degenerative diseases, is crucial for maintaining vision, the underlying molecular mechanisms are unclear. Here, we investigated the function of the deubiquitinase Otud7b/Cezanne in the retina. We identified that Otud7b is predominantly expressed in photoreceptor cells in the mouse retina. While the ablation of Otud7b did not cause a significant defect in development and maturation of the mouse retina, Otud7b‒/‒ mice subjected to light-induced damage, which is one of the dry age-related macular degeneration models, exhibited increased cone photoreceptor degeneration. In addition, Otud7b deficiency in Mak‒/‒ mice, a retinitis pigmentosa mouse model, resulted in further cone photoreceptor degeneration. Moreover, neuronal cells deficient in Otud7b were susceptible to serum starvation, resulting in cell death. We found that NF-κB activity is increased in the Otud7b‒/‒ retinas exposed to light by RNA-sequencing analysis. Luciferase reporter assay also demonstrated increased NF-κB activation in Otud7b-deficient neuronal cells under stress. The neuronal cell death resulting from Otud7b deficiency was suppressed through the inhibition of NF-κB. Furthermore, we observed that inhibition of NF-κB attenuated cone photoreceptor degeneration in the light-exposed Otud7b‒/‒ retina. Together, the current study suggests that Otud7b deubiquitinase protects cone photoreceptor cells under stress conditions by modulating the NF-κB activity.
Project description:Due to the high energy demands and characteristic morphology, retinal photoreceptor cells require the specialized lipid metabolism for survival and functions. In this study, we focus on the roles of saturated fatty acids and their metabolism in these processes. Frame-shift mutation of lysophosphatidylcholine acyltransferase 1 (Lpcat1), which introduces saturated fatty acid into lysophosphatidylcholine to produce disaturated phosphatidylcholine (PC), has been reported as a causative for spontaneous retinal degeneration in mice (rd11 mice). However, the molecular basis of retinal degeneration caused by Lpcat1 mutation remains unclear. Here, we report that Lpcat1 deficiency induces light-independent and photoreceptor-specific apoptosis in mice. Lipidomic analyses of retina and isolated photoreceptor outer segment (OS) suggested that loss of Lpcat1 affects not only disaturated PC production, but also the proper cellular fatty acid flux presumably through altering saturated fatty acyl-CoA availabilities. Furthermore, we demonstrated that Lpcat1 deletion increased mitochondrial reactive oxygen species (ROS) levels in photoreceptor cells, but not in other retinal cells, without affecting the OS structure and trafficking of OS localized proteins. These results suggested that LPCAT1-dependent production of disaturated PC is critical for metabolic adaptation during photoreceptor maturation. Our findings highlight the therapeutic potential of saturated fatty acid metabolism in photoreceptor cell degeneration-related retinal diseases.
Project description:Mutation of rod photoreceptor-enriched transcription factors is a major cause of inherited blindness. We identified the orphan nuclear hormone receptor ERRβ as selectively expressed in rod photoreceptors. Overexpression of ERRβ induces expression of rod-specific genes in retinas of both wildtype and in Nrl-/- mice, which lack rod photoreceptors. Mutation of ERRβ results in dysfunction and degeneration of rods, while inverse agonists of ERRβ trigger rapid rod degeneration, which is rescued by constitutively active mutants of ERRβ. ERRβ coordinates expression of multiple genes that are rate-limiting regulators of ATP generation and consumption in photoreceptors. Furthermore, enhancing ERRβ activity rescues photoreceptor defects that result from loss of the photoreceptor-specific transcription factor Crx. Our findings demonstrate that ERRβ is a critical regulator of rod photoreceptor function and survival, and suggest that ERRβ agonists may be useful in the treatment of certain retinal dystrophies.
Project description:Due to the high energy demands and characteristic morphology, retinal photoreceptor cells require a specialized lipid metabolism for survival and function. This study focused on the roles of saturated fatty acids and their metabolism. A frameshift mutation of lysophosphatidylcholine acyltransferase 1 (Lpcat1), introducing saturated fatty acids into lysophosphatidylcholine to produce disaturated phosphatidylcholine (PC), has been reported to cause spontaneous retinal degeneration in mice (rd11 mice). In this study, we performed a detailed characterization of Lpcat1 in the retina and found that Lpcat1 deficiency induces light-independent and photoreceptor-specific apoptosis in mice. Lipidomic analyses of the retina and isolated photoreceptor outer segment (OS) suggested that loss of Lpcat1 affects disaturated PC production and the proper cellular fatty acid flux, presumably by altering saturated fatty acyl-CoA availabilities. Furthermore, we demonstrated that Lpcat1 deletion increased mitochondrial reactive oxygen species (ROS) levels in photoreceptor cells, but not in other retinal cells without affecting the OS structure and trafficking of OS-localized proteins. These results suggest that the LPCAT1-dependent production of disaturated PC is critical for metabolic adaptation during photoreceptor maturation. Our findings highlight the therapeutic potential of saturated fatty acid metabolism in photoreceptor cell degeneration-related retinal diseases.
Project description:Photoreceptor cell death is a major cause of incurable vision loss in retinal degeneration, with little to no treatment options available. To identify drug candidates to maintain photoreceptor survival, we performed an unbiased high-throughput screening of over 6,000 bioactive small molecules using retinal organoids differentiated from induced pluripotent stem cells of rd16 mice, which phenocopy Leber congenital amaurosis (LCA) 10 caused by CEP290 mutations. Five positive hits including the lead compound Reserpine were further validated by the improvement of photoreceptor maintenance and survival in organoid cultures and in vivo retina. Subsequent investigation revealed misregulation of autophagy in degenerative retina, which is associated with compromised primary cilium biogenesis. Reserpine largely restored the balance between autophagy and the ubiquitin-proteasome system, and improved primary cilium assembly in vitro and in vivo. This study identified effective drug candidates for treatment of retinal degeneration and highlights the impact of proteostasis in photoreceptor cell death.
Project description:ST2 heterodimerizes with IL-1RAcp to form the receptor for IL-33, which is primarily associated with allergic inflammation by inducing Th2 responses. Recently, however, IL-33 was found to be expressed in the central nervous system and in retinal Muller cells which imply functions, as yet undescribed, beyond Th2 mediated inflammation. Muller cells support the health of the retina and photoreceptors and are also involved in inflammation in retinal degeneration. It is not known how IL-33/ST2 functions in this capacity. We recently found that ST2 ko mice are protected from CLE-induced photoreceptor loss, implying a detrimental effect of IL33/ST2 in CLE. We wish to perform microarray analysis using WT and ST2 KO mice in CLE model to better understand the mechanism by which IL-33/ST2 regulates retinal degeneration. CLE (Constant Light Exposure) is a model of retinal damage/degeneration in mice. Mice are exposed to bright light 24 hours a day for a period of time which damages retina photoreceptors. This damage is assessed by histology, optical coherence tomography (OCT), which measures retina thickness in vivo. In this experiment, the WT and ST2 KO mice (5 mice per genotype per time point) will be exposed to 1200-lux constant light for 0, 3, 10 days. The retinal RNA will be isolated and analyzed for differential gene expression by microarray.
Project description:While dysfunction and/or death of light-detecting photoreceptor cells underlies most inherited retinal dystrophies, knowledge of the species-specific details of human rod and cone photoreceptor cell development remains limited. Here, we generate retinal organoids using induced pluripotent stem cells (iPSC) derived from a patient with genetic photoreceptor disease, an isogenic control, and an unrelated control. Organoids were sampled using single-cell RNA sequencing across the developmental window encompassing photoreceptor specification, emergence, and maturation; up to 260 days of in vitro differentiation. Using single-cell transcriptomics data, we reconstruct the rod photoreceptor developmental lineage and identify a branchpoint in development unique to the disease state that gives rise to a divergent rod photoreceptor cell population. We show that the rod-specific transcription factor NR2E3 is required for the proper expression of genes involved in phototransduction, including expression of the light-sensitive protein rhodopsin, which is absent in divergent rods. NR2E3-null rods additionally misexpress several cone-specific phototransduction genes at both the transcript and protein level. Using joint multimodal single-cell sequencing on late-stage retinal organoids, we further identify the specific putative regulatory sites where rod-specific factors act to steer rod and cone photoreceptor cell development. Importantly, these findings are strikingly different than that observed in rodent models of disease. Together, these data provide a roadmap of human photoreceptor development and leverage patient iPSCs to define the specific roles of rod transcription factors in photoreceptor cell emergence and maturation.
Project description:Retinal degeneration is the leading cause of irreversible blindness. Retinitis pigmentosa (RP) is a genetically heterogenous group of diseases. In the United States, approximately one in 4000 individuals is affected. RP begins with the loss of night vision due to the loss of rod photoreceptor cells. The disease progresses slowly with the loss of peripheral vision, and eventually leads to complete debilitating and irreversible blindness. The first mutation associated with human RP was identified in the gene encoding rhodopsin, the G-protein coupled receptor of rod photoreceptor cells. Mutations within the rhodopsin gene account for significant portion of RP cases. Specifically, mutations of the proline at residue 347 in rhodopsin have been linked to human RP. We are fortunate to have access to the P347S rhodopsin mutant mice. These mice represent an excellent transgenic mouse model of retinal degeneration. The P347S rhodopsin mutation is one of the best studied mutations, yet the mechanism by which the mutation causes degeneration is still unknown. One study has demonstrated that galectin-1 plays a role in degeneration of neuronal processes (1) and another study has shown that expression level of galectin-3 is elevated in retinas of patients with age-related macular degeneration. These studies in conjunction with the availibility of the P347S mutant mice have provided impetus to examine the pathogenesis of retinal degeneration in the context of the possible role of glycans and glycan-binding proteins. The time course of photoreceptor degeneration in the P347S mouse model has been carefully studied. In these mice, degeneration is barely detectable at 1 month of age, yet biochemical evidence suggests that the rod photoreceptor cells have already begun to die. At 4 months of age, approximately half of the rod photoreceptor cells have degenerated. To distinguish involvement of glycogens at the various stages of retinal degeneration, we have collected retinas of wild type and the mutant mice at four time points (1, 2, 3, and 4 months of age). This will allow us to identify the genes that target early, mid- and late stages of the retinal degeneration process. Thus we request the analysis of total 24 samples as specified below: Age Group (months) Mice No of samples at each time point 1 Wild type 3 2 Wild type 3 3 Wild type 3 4 Wild type 3 1 P347S 3 2 P347S 3 3 P347S 3 4 P347S 3 Total 24.