A Combination of G Protein-Coupled Receptor Modulators Protects Photoreceptors from Degeneration

Retinal proteome profiling of inherited retinal degeneration across three different mouse models suggests common drug targets in retinitis pigmentosa

Inherited retinal degenerations (IRDs) are a leading cause of blindness among the population of young people in the developed world. Approximately half of IRDs initially manifest as gradual loss of night vision and visual fields, characteristic of retinitis pigmentosa (RP). Due to challenges in genetic testing, and the large heterogeneity of mutations underlying RP, targeted gene therapies are an impractical largescale solution in the foreseeable future. For this reason, identifying key pathophysiological pathways in IRDs that could be targets for mutation-agnostic and disease-modifying therapies (DMTs) is warranted. In this study, we investigated the retinal proteome of three distinct IRD mouse models, in comparison to sex- and age-matched wild-type mice. Specifically, we used the Pde6βRd10 (rd10) and RhoP23H/WT (P23H) mouse models of autosomal recessive and autosomal dominant RP, respectively, as well as the Rpe65-/- mouse model of Leber´s congenital amaurosis type 2 (LCA2). The mice were housed at two distinct institutions and analyzed using LC-MS in three separate facilities/instruments following data-dependent and data-independent acquisition modes. This cross-institutional and multi-methodological approach signifies the reliability and reproducibility of the results. The largescale profiling of the retinal proteome, coupled with in vivo electroretinography recordings, provided us with a reliable basis for comparing the disease phenotypes and severity. Despite evident inflammation, cellular stress, and downscaled phototransduction observed consistently across all three models, the underlying pathologies of RP and LCA2 displayed many differences, sharing only four general KEGG pathways. The opposite is true for the two RP models in which we identify remarkable convergence in proteomic phenotype even though the mechanism of primary rod death in rd10 and P23H mice is different. Our data highlights the cAMP and cGMP second-messenger signaling pathways as potential targets for therapeutic intervention. The proteomic data is curated and made publicly available, facilitating the discovery of universal therapeutic targets for RP.

A combination treatment based on drug repurposing demonstrates mutation-agnostic efficacy in pre-clinical retinopathy models

Inherited retinopathies are devastating diseases that in most cases lack treatment options. Disease-modifying therapies that mitigate pathophysiology regardless of the underlying genetic lesion are desirable due to the diversity of mutations found in such diseases. We tested a systems pharmacology-based strategy that suppresses intracellular cAMP and Ca2+ activity via G protein-coupled receptor (GPCR) modulation using tamsulosin, metoprolol, and bromocriptine coadministration. The treatment improves cone photoreceptor function and slows degeneration in Pde6βrd10 and RhoP23H/WT retinitis pigmentosa mice. Cone degeneration is modestly mitigated after a 7-month-long drug infusion in PDE6A-/- dogs. The treatment also improves rod pathway function in an Rpe65-/- mouse model of Leber congenital amaurosis but does not protect from cone degeneration. RNA-sequencing analyses indicate improved metabolic function in drug-treated Rpe65-/- and rd10 mice. Our data show that catecholaminergic GPCR drug combinations that modify second messenger levels via multiple receptor actions provide a potential disease-modifying therapy against retinal degeneration.

Distinct mouse models of Stargardt disease display differences in pharmacological targeting of ceramides and inflammatory responses

Mutations in many visual cycle enzymes in photoreceptors and retinal pigment epithelium (RPE) cells can lead to the chronic accumulation of toxic retinoid byproducts, which poison photoreceptors and the underlying RPE if left unchecked. Without a functional ATP-binding cassette, sub-family A, member 4 (ABCA4), there is an elevation of all-trans-retinal and prolonged buildup of all-trans-retinal adducts, resulting in a retinal degenerative disease known as Stargardt-1 disease. Even in this monogenic disorder, there is significant heterogeneity in the time to onset of symptoms among patients. Using a combination of molecular techniques, we studied Abca4 knockout (simulating human noncoding disease variants) and Abca4 knock-in mice (simulating human misfolded, catalytically inactive protein variants), which serve as models for Stargardt-1 disease. We compared the two strains to ascertain whether they exhibit differential responses to agents that affect cytokine signaling and/or ceramide metabolism, as alterations in either of these pathways can exacerbate retinal degenerative phenotypes. We found different degrees of responsiveness to maraviroc, a known immunomodulatory CCR5 antagonist, and to the ceramide-lowering agent AdipoRon, an agonist of the ADIPOR1 and ADIPOR2 receptors. The two strains also display different degrees of transcriptional deviation from matched WT controls. Our phenotypic comparison of the two distinct Abca4 mutant-mouse models sheds light on potential therapeutic avenues previously unexplored in the treatment of Stargardt disease and provides a surrogate assay for assessing the effectiveness for genome editing.

CCR2-positive monocytes contribute to the pathogenesis of early diabetic retinopathy in mice

AIMS/HYPOTHESIS

Accumulating evidence suggests that leucocytes play a critical role in diabetes-induced vascular lesions and other abnormalities that characterise the early stages of diabetic retinopathy. However, the role of monocytes has yet to be fully investigated; therefore, we used Ccr2^-/- mice to study the role of CCR2⁺ inflammatory monocytes in the pathogenesis of diabetes-induced degeneration of retinal capillaries.

METHODS

Experimental diabetes was induced in wild-type and Ccr2^-/- mice using streptozotocin. After 2 months, superoxide levels, expression of inflammatory genes, leucostasis, leucocyte- and monocyte-mediated cytotoxicity against retinal endothelial cell death, retinal thickness and visual function were evaluated. Retinal capillary degeneration was determined after 8 months of diabetes. Flow cytometry of peripheral blood for differential expression of CCR2 in monocytes was assessed.

RESULTS

In nondiabetic mice, CCR2 was highly expressed on monocytes, and Ccr2^-/- mice lack CCR2⁺ monocytes in the peripheral blood. Diabetes-induced retinal superoxide, expression of proinflammatory genes Inos and Icam1, leucostasis and leucocyte-mediated cytotoxicity against retinal endothelial cells were inhibited in diabetic Ccr2-deficient mice and in chimeric mice lacking Ccr2 only from myeloid cells. In order to focus on monocytes, these cells were immuno-isolated after 2 months of diabetes, and they significantly increased monocyte-mediated endothelial cell cytotoxicity ex vivo. Monocytes from Ccr2-deficient mice caused significantly less endothelial cell death. The diabetes-induced retinal capillary degeneration was inhibited in Ccr2^-/- mice and in chimeric mice lacking Ccr2 only from myeloid cells.

CONCLUSIONS/INTERPRETATION

CCR2⁺ inflammatory monocytes contribute to the pathogenesis of early lesions of diabetic retinopathy.

The Selective α1 Antagonist Tamsulosin Alters ECM Distributions and Cellular Metabolic Functions of ARPE 19 Cells in a Concentration-Dependent Manner

The purpose of the present study was to examine the effect of the selective α1 antagonist tamsulosin (TAM) on human retinal pigment epithelium cells, ARPE 19. Two-dimension (2D) and three-dimension (3D) cultured ARPE 19 cells were used in the following characterizations: (1) ultrastructure by scanning electron microscopy (SEM) (2D); (2) barrier functions by transepithelial electrical resistance (TEER) measurements, and FITC-dextran permeability (2D); (3) real time cellular metabolisms by Seahorse Bioanalyzer (2D); (4) physical properties, size and stiffness measurements (3D); and (5) expression of extracellular matrix (ECM) proteins, including collagen1 (COL1), COL4, COL6 and fibronectin (FN) by qPCR and immunohistochemistry (2D and 3D). TAM induced significant effects including: (1) alteration of the localization of the ECM deposits; (2) increase and decrease of the TEER values and FITC-dextran permeability, respectively; (3) energy shift from glycolysis into mitochondrial oxidative phosphorylation (OXPHOS); (4) large and stiffened 3D spheroids; and (5) down-regulations of the mRNA expressions and immune labeling of most ECM proteins in a concentration-dependent manner. However, in some ECM proteins, COL1 and COL6, their immunolabeling intensities were increased at the lowest concentration (1 μM) of TAM. Such a discrepancy between the gene expressions and immunolabeling of ECM proteins may support alterations of ECM localizations as observed by SEM. The findings reported herein indicate that the selective α1 antagonist, TAM, significantly influenced ECM production and distribution as well as cellular metabolism levels in a concentration-dependent manner.

The GPCR Antagonistic Drug CM-20 Stimulates Mitochondrial Activity in Human RPE Cells

Background:

Mitochondrial dysfunction in retinal pigment epithelium (RPE) is a pathogenic factor in age-related macular degeneration (AMD). Improvement of mitochondrial function may ameliorate RPE bioenergetics status, which may in turn nourish the retinal photoreceptors against degenerative loss.

Objective:

The purpose of this study is to examine the G-protein coupled receptor (GPCR) antagonistic drug CM-20 in modulating mitochondrial function in RPE cells.

Methods:

Human-derived ARPE-19 cell line was differentiated to improve RPE morphology. Dose response of CM-20 was performed to examine mitochondrial membrane potential (MMP). Secondary validation with multiplexed live-cell mitochondrial imaging was performed. Protection of CM-20 to mitochondria against oxidative stress was detected under co-treatment with hydrogen peroxide.

Results:

Treatment with CM-20 elicited a dose-dependent increase of MMP. Multiplexed live-cell mitochondrial imaging showed consistent increase of MMP at an optimal concentration of CM-20 (12.5 µM). MMP was significantly reduced under hydrogen peroxide-induced oxidative stress and treatment with CM-20 showed rescue effects to MMP.

Conclusion:

CM-20 increases mitochondrial function and protects mitochondria under oxidative stress. As both GPCRs and mitochondria are potential drug targets, retinal neuroprotective testing of CM-20 is warranted in animal models of retinal degeneration.

VCP/p97 inhibitor CB-5083 modulates muscle pathology in a mouse model of VCP inclusion body myopathy

BACKGROUND

Pathogenic gain of function variants in Valosin-containing protein (VCP) cause a unique disease characterized by inclusion body myopathy with early-onset Paget disease of bone and frontotemporal dementia (also known as Multisystem proteinopathy (MSP)). Previous studies in drosophila models of VCP disease indicate treatment with VCP inhibitors mitigates disease pathology. Earlier-generation VCP inhibitors display off-target effects and relatively low therapeutic potency. New generation of VCP inhibitors needs to be evaluated in a mouse model of VCP disease. In this study, we tested the safety and efficacy of a novel and potent VCP inhibitor, CB-5083 using VCP patient-derived myoblast cells and an animal model of VCP disease.

METHODS

First, we analyzed the effect of CB-5083 in patient-derived myoblasts on the typical disease autophagy and TDP-43 profile by Western blot. Next, we determined the maximum tolerated dosage of CB-5083 in mice and treated the 2-month-old VCPR155H/R155H mice for 5 months with 15 mg/kg CB-5083. We analyzed motor function monthly by Rotarod; and we assessed the end-point blood toxicology, and the muscle and brain pathology, including autophagy and TDP-43 profile, using Western blot and immunohistochemistry. We also treated 12-month-old VCPR155H/+ mice for 6 months and performed similar analysis. Finally, we assessed the potential side effects of CB-5083 on retinal function, using electroretinography in chronically treated VCPR155H/155H mice.

RESULTS

In vitro analyses using patient-derived myoblasts confirmed that CB-5083 can modulate expression of the proteins in the autophagy pathways. We found that chronic CB-5083 treatment is well tolerated in the homozygous mice harboring patient-specific VCP variant, R155H, and can ameliorate the muscle pathology characteristic of the disease. VCP-associated pathology biomarkers, such as elevated TDP-43 and p62 levels, were significantly reduced. Finally, to address the potential adverse effect of CB-5083 on visual function observed in a previous oncology clinical trial, we analyzed retinal function in mice treated with moderate doses of CB-5083 for 5 months and documented the absence of permanent ocular toxicity.

CONCLUSIONS

Altogether, these findings suggest that long-term use of CB-5083 by moderate doses is safe and can improve VCP disease-associated muscle pathology. Our results provide translationally relevant evidence that VCP inhibitors could be beneficial in the treatment of VCP disease.

Regulation of Adrenergic, Serotonin, and Dopamine Receptors to Inhibit Diabetic Retinopathy: Monotherapies versus Combination Therapies

We compared monotherapies and combinations of therapies that regulate G-protein-coupled receptors (GPCRs) with respect to their abilities to inhibit early stages of diabetic retinopathy (DR) in streptozotocin-diabetic mice. Metoprolol (MTP; 0.04-1.0 mg/kg b.wt./day), bromocriptine (BRM; 0.01-0.1 mg/kg b.wt./day), doxazosin (DOX; 0.01-1.0 mg/kg b.wt./day), or tamsulosin (TAM; 0.05-0.25 mg/kg b.wt./day) were injected individually daily for 2 months in dose-response studies to assess their effects on the diabetes-induced increases in retinal superoxide and leukocyte-mediated cytotoxicity against vascular endothelial cells, both of which abnormalities have been implicated in the development of DR. Each of the individual drugs inhibited the diabetes-induced increase in retinal superoxide at the higher concentrations tested, but the inhibition was lost at lower doses. To determine whether combination therapies had superior effects over individual drugs, we intentionally selected for each drug a low dose that had little or no effect on the diabetes-induced retinal superoxide for use separately or in combinations in 8-month studies of retinal function, vascular permeability, and capillary degeneration in diabetes. At the low doses used, combinations of the drugs generally were more effective than individual drugs, but the low-dose MTP alone totally inhibited diabetes-induced reduction in a vision task, BRM or DOX alone totally inhibited the vascular permeability defect, and DOX alone totally inhibited diabetes-induced degeneration of retinal capillaries. Although low-dose MTP, BRM, DOX, or TAM individually had beneficial effects on some endpoints, combination of the therapies better inhibited the spectrum of DR lesions evaluated. SIGNIFICANCE STATEMENT: The pathogenesis of early stages of diabetic retinopathy remains incompletely understood, but multiple different cell types are believed to be involved in the pathogenic process. We have compared the effects of monotherapies to those of combinations of drugs that regulate GPCR signaling pathways with respect to their relative abilities to inhibit the development of early diabetic retinopathy.

Sensory Transduction in Photoreceptors and Olfactory Sensory Neurons: Common Features and Distinct Characteristics

The past decades have seen tremendous progress in our understanding of the function of photoreceptors and olfactory sensory neurons, uncovering the mechanisms that determine their properties and, ultimately, our ability to see and smell. This progress has been driven to a large degree by the powerful combination of physiological experimental tools and genetic manipulations, which has enabled us to identify the main molecular players in the transduction cascades of these sensory neurons, how their properties affect the detection and discrimination of stimuli, and how diseases affect our senses of vision and smell. This review summarizes some of the common and unique features of photoreceptors and olfactory sensory neurons that make these cells so exciting to study.

Photoreceptor Cell Calcium Dysregulation and Calpain Activation Promote Pathogenic Photoreceptor Oxidative Stress and Inflammation in Prodromal Diabetic Retinopathy

This study tested the hypothesis that diabetes promotes a greater than normal cytosolic calcium level in rod cells that activates a Ca2+-sensitive protease, calpain, resulting in oxidative stress and inflammation, two pathogenic factors of early diabetic retinopathy. Nondiabetic and 2-month diabetic C57Bl/6J and calpain1 knockout (Capn1-/-) mice were studied; subgroups were treated with a calpain inhibitor (CI). Ca2+ content was measured in photoreceptors using Fura-2. Retinal calpain expression was studied by quantitative RT-PCR and immunohistochemistry. Superoxide and expression of inflammatory proteins were measured using published methods. Proteomic analysis was conducted on photoreceptors isolated from untreated diabetic mice or treated daily with CI for 2 months. Cytosolic Ca2+ content was increased twofold in photoreceptors of diabetic mice as compared with nondiabetic mice. Capn1 expression increased fivefold in photoreceptor outer segments of diabetic mice. Pharmacologic inhibition or genetic deletion of Capn1 significantly suppressed diabetes-induced oxidative stress and expression of proinflammatory proteins in retina. Proteomics identified a protein (WW domain-containing oxidoreductase [WWOX]) whose expression was significantly increased in photoreceptors from mice diabetic for 2 months and was inhibited with CI. Knockdown of Wwox using specific siRNA in vitro inhibited increase in superoxide caused by the high glucose. These results suggest that reducing Ca2+ accumulation, suppressing calpain activation, and/or reducing Wwox up-regulation are novel targets for treating early diabetic retinopathy.

Stargardt disease and progress in therapeutic strategies

Background: Stargardt disease (STGD1) is an autosomal recessive retinal dystrophy due to mutations in ABCA4, characterized by subretinal deposition of lipofuscin-like substances and bilateral centrifugal vision loss. Despite the tremendous progress made in the understanding of STGD1, there are no approved treatments to date. This review examines the challenges in the development of an effective STGD1 therapy.Materials and Methods: A literature review was performed through to June 2021 summarizing the spectrum of retinal phenotypes in STGD1, the molecular biology of ABCA4 protein, the in vivo and in vitro models used to investigate the mechanisms of ABCA4 mutations and current clinical trials.Results: STGD1 phenotypic variability remains an challenge for clinical trial design and patient selection. Pre-clinical development of therapeutic options has been limited by the lack of animal models reflecting the diverse phenotypic spectrum of STDG1. Patient-derived cell lines have facilitated the characterization of splice mutations but the clinical presentation is not always predicted by the effect of specific mutations on retinoid metabolism in cellular models. Current therapies primarily aim to delay vision loss whilst strategies to restore vision are less well developed.Conclusions: STGD1 therapy development can be accelerated by a deeper understanding of genotype-phenotype correlations.

Comparison of effects of tamsulosin and silodosin on subfoveal choroidal thickness and pupil size diameters in patients with prostatic hyperplasia

PURPOSE

To compare the effects of selective α-1 adrenoceptor antagonists on subfoveal choroidal thickness (SFCT) and pupil diameter size (PDS).

METHODS

This prospective study included 87 patients diagnosed with benign prostatic hyperplasia who were treated with tamsulosin hydrochloride (n = 41) or silodosin (n = 46). SFCT measurements were obtained using spectral domain optic coherence tomography (SD-OCT), and PDS measurements were obtained under mesopic, photopic and scotopic conditions using a photography-based topography system. SFCT and PDS were evaluated at baseline and 3-, 6- and 12-mo follow-ups.

RESULTS

The initial mean SFCT was 270.53 ± 21.48 µm in tamsulosin group and 271.95 ± 24. 73 in silodosin group (P = 0.078). There was no statistically significant change in SFCT at the 3-mo visit. At the 6-mo follow-up, the mean SFCT was 281.34 ± 22.09 µm in tamsulosin group and 272.5 ± 22.4 µm in silodosin group. At the 12th month, the mean SFCT in tamsulosin group was 290.80 ± 17.27 µm, and it was 270.80 ± 13.14 µm in silodosin group. There was statistically significant difference in at 6th and 12-mo visits (P = 0.014 and P = 0.00). During the follow-up, both drugs induced a similar significant decrease in PDS under all conditions.

CONCLUSIONS

Tamsulosin hydrochloride caused a significant increase in SFCT. In contrast, SFCT did not increase in silodosin group. The decreases in PDS achieved using both drugs were similar. This should be kept in mind when choroidal disease and its response to treatment are followed by CT imaging.

An inducible Cre mouse for studying roles of the RPE in retinal physiology and disease

The retinal pigment epithelium (RPE) provides vital metabolic support for retinal photoreceptor cells and is an important player in numerous retinal diseases. Gene manipulation in mice using the Cre-LoxP system is an invaluable tool for studying the genetic basis of these retinal diseases. However, existing RPE-targeted Cre mouse lines have critical limitations that restrict their reliability for studies of disease pathogenesis and treatment, including mosaic Cre expression, inducer-independent activity, off-target Cre expression, and intrinsic toxicity. Here, we report the generation and characterization of a knockin mouse line in which a P2A-CreER^T2 coding sequence is fused with the native RPE-specific 65 kDa protein (Rpe65) gene for cotranslational expression of CreER^T2. Cre^+/– mice were able to recombine a stringent Cre reporter allele with more than 99% efficiency and absolute RPE specificity upon tamoxifen induction at both postnatal days (PD) 21 and 50. Tamoxifen-independent Cre activity was negligible at PD64. Moreover, tamoxifen-treated Cre^+/– mice displayed no signs of structural or functional retinal pathology up to 4 months of age. Despite weak RPE65 expression from the knockin allele, visual cycle function was normal in Cre^+/– mice. These data indicate that Rpe65^CreERT2 mice are well suited for studies of gene function and pathophysiology in the RPE.

A p97/Valosin-Containing Protein Inhibitor Drug CB-5083 Has a Potent but Reversible Off-Target Effect on Phosphodiesterase-6

CB-5083 is an inhibitor of p97/valosin-containing protein (VCP), for which phase I trials for cancer were terminated because of adverse effects on vision, such as photophobia and dyschromatopsia. Lower dose CB-5083 could combat inclusion body myopathy with early-onset Paget disease and frontotemporal dementia or multisystem proteinopathy caused by gain-of-function mutations in VCP. We hypothesized that the visual impairment in the cancer trial was due to CB-5083's inhibition of phosphodiesterase (PDE)-6, which mediates signal transduction in photoreceptors. To test our hypothesis, we used in vivo and ex vivo electroretinography (ERG) in mice and a PDE6 activity assay of bovine rod outer segment (ROS) extracts. Additionally, histology and optical coherence tomography were used to assess CB-5083's long-term ocular toxicity. A single administration of CB-5083 led to robust ERG signal deterioration, specifically in photoresponse kinetics. Similar recordings with known PDE inhibitors sildenafil, tadalafil, vardenafil, and zaprinast showed that only vardenafil had as strong an effect on the ERG signal in vivo as did CB-5083. In the biochemical assay, CB-5083 inhibited PDE6 activity with a potency higher than sildenafil but lower than that of vardenafil. Ex vivo ERG revealed a PDE6 inhibition constant of 80 nM for CB-5083, which is 7-fold smaller than that for sildenafil. Finally, we showed that the inhibitory effect of CB-5083 on visual function is reversible, and its chronic administration does not cause permanent retinal anomalies in aged VCP-disease model mice. Our results warrant re-evaluation of CB-5083 as a clinical therapeutic agent. We recommend preclinical ERG recordings as a routine drug safety screen. SIGNIFICANCE STATEMENT: This report supports the use of a valosin-containing protein (VCP) inhibitor drug, CB-5083, for the treatment of neuromuscular VCP disease despite CB-5083's initial clinical failure for cancer treatment due to side effects on vision. The data show that CB-5083 displays a dose-dependent but reversible inhibitory action on phosphodiesterase-6, an essential enzyme in retinal photoreceptor function, but no long-term consequences on retinal function or structure.

Homeostatic plasticity in the retina is associated with maintenance of night vision during retinal degenerative disease

Neuronal plasticity of the inner retina has been observed in response to photoreceptor degeneration. Typically, this phenomenon has been considered maladaptive and may preclude vision restoration in the blind. However, several recent studies utilizing triggered photoreceptor ablation have shown adaptive responses in bipolar cells expected to support normal vision. Whether such homeostatic plasticity occurs during progressive photoreceptor degenerative disease to help maintain normal visual behavior is unknown. We addressed this issue in an established mouse model of Retinitis Pigmentosa caused by the P23H mutation in rhodopsin. We show robust modulation of the retinal transcriptomic network, reminiscent of the neurodevelopmental state, and potentiation of rod - rod bipolar cell signaling following rod photoreceptor degeneration. Additionally, we found highly sensitive night vision in P23H mice even when more than half of the rod photoreceptors were lost. These results suggest retinal adaptation leading to persistent visual function during photoreceptor degenerative disease.

Successful induction of diabetes in mice demonstrates no gender difference in development of early diabetic retinopathy

Purpose

Female mice have been found to be resistant to streptozotocin (STZ)-induced diabetes, and pre-clinical research related to diabetic complications commonly omits females. The purpose of this study was to develop a method to induce diabetes in female mice, and to determine if retinas of diabetic female mice develop molecular changes and histopathological abnormalities comparable to those which develop in male diabetic mice.

Methods

To induce diabetes, animals of both sexes received daily intraperitoneal (i.p.) injection of STZ for 5 consecutive days at 55 mg/kg BW (a dose that is known to induce diabetes in male mice) or for females, 75 mg/kg BW of STZ. Retinal abnormalities that have been implicated in the development of the retinopathy (superoxide generation and expression of inflammatory proteins, iNOS and ICAM-1) were evaluated at 2 months of diabetes, and retinal capillary degeneration was evaluated at 8 months of diabetes.

Results

Daily i.p. injection of STZ for 5 consecutive days at a concentration of 55 mg/kg BW was sufficient to induce diabetes in 100% of male mice, but only 33% of female mice. However, females did become hyperglycemic when the dose of STZ administered was increased to 75 mg/kg BW. The resulting STZ-induced hyperglycemia in female and male mice was sustained for at least 8 months. After induction of the diabetes, both sexes responded similarly with respect to the oxidative stress, expression of iNOS, and degeneration of retinal capillaries, but differed in the limited population evaluated with respect to expression of ICAM-1.

Conclusions

The resistance of female mice to STZ-induced diabetes can be overcome by increasing the dose of STZ used. Female mice can, and should, be included in pre-clinical studies of diabetes and its complications.

A Mixture of U.S. Food and Drug Administration-Approved Monoaminergic Drugs Protects the Retina From Light Damage in Diverse Models of Night Blindness

Purpose

The purpose of this study was to test the extent of light damage in different models of night blindness and apply these paradigms in testing the therapeutic efficacy of combination therapy by drugs acting on the G_i, G_s, and G_q protein-coupled receptors.

Methods

Acute bright light exposure was used to test susceptibility to light damage in mice lacking the following crucial phototransduction proteins: rod transducin (GNAT1), cone transducin (GNAT2), visual arrestin 1 (ARR1), and rhodopsin kinase 1 (GRK1). Mice were intraperitoneally injected with either vehicle or drug combination consisting of metoprolol (β₁-receptor antagonist), bromocriptine (dopamine family-2 receptor agonist) and tamsulosin (α₁-receptor antagonist) before bright light exposure. Light damage was primarily assessed with optical coherence tomography and inspection of cone population in retinal whole mounts. Retinal inflammation was assessed in a subset of experiments using autofluorescence imaging by scanning laser ophthalmoscopy and by postmortem inspection of microglia and astrocyte activity.

Results

The Gnat1^−/− mice showed slightly increased susceptibility to rod light damage, whereas the Gnat2^−/− mice were very resistant. The Arr1^−/− and Grk1^−/− mice were sensitive for both rod and cone light damage and showed robust retinal inflammation 7 days after bright light exposure. Pretreatment with metoprolol + bromocriptine + tamsulosin rescued the retina in all genetic backgrounds, starting at doses of 0.2 mg/kg metoprolol, 0.02 mg/kg bromocriptine, and 0.01 mg/kg tamsulosin in the Gnat1^−/− mice. The therapeutic drug doses increased in parallel with light-damage severity.

Conclusions

Our results suggest that congenital stationary night blindness and Oguchi disease patients can be at an elevated risk of the toxic effects of bright light. Furthermore, systems pharmacology drug regimens that stimulate G_i signaling and attenuate G_s and G_q signaling present a promising disease-modifying therapy for photoreceptor degenerative diseases.

Retinal Gene Distribution and Functionality Implicated in Inherited Retinal Degenerations Can Reveal Disease-Relevant Pathways for Pharmacologic Intervention

The advent of genetic therapies for inherited retinal diseases (IRDs) has spurred the need for precise diagnosis and understanding of pathways for therapeutic targeting. The majority of IRDs that are clinically diagnosed, however, lack an identifiable mutation in established disease-causing loci and thus can be investigated with limited rational drug discovery methods. Transcriptome profiling of the retina can reveal the functional state of the tissue, and geographic profiling can uncover the various clinical phenotypic presentations of IRDs and aid in pharmaceutical intervention. In this investigation, we detail the retinal geographic expression of known retinal disease-causing genes in the primate retina and functional targetable pathways in specific IRDs. Understanding the genetic basis as well as the resulting functional consequences will assist in the discovery of future therapeutic interventions and provide novel insights to medicinal chemists. Herein, we report that, despite the genetic heterogeneity of retinal diseases, potential functional pathways can be elucidated for therapeutic targeting and be used for predictive phenotypic and genotypic modeling of novel IRD presentations.

A novel small molecule chaperone of rod opsin and its potential therapy for retinal degeneration

Rhodopsin homeostasis is tightly coupled to rod photoreceptor cell survival and vision. Mutations resulting in the misfolding of rhodopsin can lead to autosomal dominant retinitis pigmentosa (adRP), a progressive retinal degeneration that currently is untreatable. Using a cell-based high-throughput screen (HTS) to identify small molecules that can stabilize the P23H-opsin mutant, which causes most cases of adRP, we identified a novel pharmacological chaperone of rod photoreceptor opsin, YC-001. As a non-retinoid molecule, YC-001 demonstrates micromolar potency and efficacy greater than 9-cis-retinal with lower cytotoxicity. YC-001 binds to bovine rod opsin with an EC50 similar to 9-cis-retinal. The chaperone activity of YC-001 is evidenced by its ability to rescue the transport of multiple rod opsin mutants in mammalian cells. YC-001 is also an inverse agonist that non-competitively antagonizes rod opsin signaling. Significantly, a single dose of YC-001 protects Abca4 -/- Rdh8 -/- mice from bright light-induced retinal degeneration, suggesting its broad therapeutic potential.