KCNQ and KCNE potassium channel subunit expression in bovine retinal pigment epithelium

Splicing variants in MYRF cause partial loss of function in the retinal pigment epithelium

Myelin Regulatory Factor (MYRF) regulates retinal pigment epithelial (RPE) development and variants in the C-terminus are linked to isolated nanophthalmos, while loss-of-function variants cause syndromic disease. To define the molecular mechanism of this discrepancy, in vitro and animal studies were performed on a pathogenic C-terminal variant (p.Gly1126fs30* or dG-MYRF). ARPE-19 cells transduced with dG-MYRF revealed reduced target gene expression compared to WT-MYRF, with reduced steady state levels of C-terminal MYRF cleavage product, but intact cleavage and localization. A homozygous humanized MYRF C-terminal ( Myrf humdG/humdG ) mouse model was embryonic lethal by embryonic day (E) 18.5, while humanized wildtype ( Myrf humWT/humWT ) showed normal expression and survival. Bioinformatic analysis on integrated single cell RNA-seq from humanized E17.5 and knockout Rx-Cre;Myrf fl/fl (E15.5 and P0) mice supported shared differentially expressed genes with decreased effect size in Myrf humdG/humdG eyes. These findings, and the viability differences, support that dG-MYRF is a hypomorphic allele. Further, two novel MYRF splicing variants were identified in families with isolated nanophthalmos, with one confirmed to alter 40% of spliced transcripts, creating a nonfunctional isoform. These cases corroborate that isolated nanophthalmos results from hypomorphic alleles of MYRF, supporting a tissue-specific threshold effect and suggests that the C-terminus has unique roles in the RPE.

Ion channels research in hPSC-RPE cells: bridging benchwork to clinical applications

Ion channels in retinal pigment epithelial (RPE) cells are crucial for retinal health and vision functions. Defects in such channels are intricately associated with the development of various retinopathies that cause blindness. Human pluripotent stem cells (hPSC)-derived RPE cells, including those from human-induced pluripotent stem cells (hiPSC) and human embryonic stem cells (hESC), have been used as in vitro models for investigating pathogenic mechanisms and screening potential therapeutic strategies for retinopathies. Therefore, the cellular status of hPSC-RPE cells, including maturity and physiologic functions, have been widely explored. Particularly, research on ion channels in hPSC-RPE cells can lead to the development of more stable models upon which robust investigations and clinical safety assessments can be performed. Moreover, the use of patient-specific hiPSC-RPE cells has significantly accelerated the clinical translation of gene therapy for retinal channelopathies, such as bestrophinopathies. This review consolidates current research on ion channels in hPSC-RPE cells, specifically Kir7.1, Bestrophin-1, CLC-2, and CaV1.3, providing a foundation for future research.

Discernibility of the Interdigitation Zone (IZ), a Potential Optical Coherence Tomography (OCT) Biomarker for Visual Dysfunction in Aging

PURPOSE

Photoreceptor (PR) outer segments, retinal pigment epithelium apical processes, and inter-PR matrix contribute to the interdigitation zone (IZ) of optical coherence tomography (OCT). We hypothesize that this interface degrades over adulthood, in concert with a delay of rod mediated dark adaptation (RMDA). To explore this idea, we determined IZ discernibility and RMDA in younger and older adults.

METHODS

For this cross-sectional study, eyes of 20 young (20-30 years) and 40 older (≥60 years) participants with normal maculas according to the AREDS 9-step grading system underwent OCT imaging and RMDA testing at 5° superior to the fovea. Custom FIJI plugins enabled analysis for IZ discernibility at 9 eccentricities in 0.5 mm steps on one single horizontal B-scan through the fovea. Locations with discernible IZ met two criteria: visibility on B-scans and a distinct peak on a longitudinal reflectivity profile. The frequency of sites meeting both criteria was compared between both age groups and correlated with rod intercept time (RIT).

RESULTS

The median number of locations with discernible IZ was significantly higher (foveal, 4 vs. 0, p = 0.0099; extra-foveal 6 vs. 0, p < 0.001) in eyes of young (26 ± 3 years) compared to older (73 ± 5 years) participants. For the combined young and older sample, the higher frequency of discernible IZ was correlated with shorter RIT (faster dark adaptation) (rs = -0.56, p < 0.0001). This association was significant within young eyes (rs = -0.54; p = 0.0134) and not within older eyes (rs = -0.29, p = 0.706).

CONCLUSIONS

Results suggest that the interface between outer segments and apical processes degrades in normal aging, potentially contributing to delayed rod-mediated dark adaptation. More research is needed to verify an age-related association between IZ discernibility and rod-mediated dark adaptation. If confirmed in a large sample, IZ discernibility might prove to be a valuable biomarker and predictor for visual function in aging.

OUP accepted manuscript

Human pluripotent stem cell (hPSC)-derived retinal pigment epithelium (RPE) is extensively used in RPE research, disease modeling, and transplantation therapies. For successful outcomes, a thorough evaluation of their physiological authenticity is a necessity. Essential determinants of this are the different ion channels of the RPE, yet studies evaluating this machinery in hPSC-RPE are scarce. We examined the functionality and localization of potassium (K⁺) channels in the human embryonic stem cell (hESC)-derived RPE. We observed a heterogeneous pattern of voltage-gated K⁺ (K_V) and inwardly rectifying K⁺ (Kir) channels. Delayed rectifier currents were recorded from most of the cells, and immunostainings showed the presence of K_V1.3 channel. Sustained M-currents were also present in the hESC-RPE, and based on immunostaining, these currents were carried by KCNQ1-KCNQ5 channel types. Some cells expressed transient A-type currents characteristic of native human fetal RPE (hfRPE) and cultured primary RPE and carried by K_V1.4 and K_V4.2 channels. Of the highly important Kir channels, we found that Kir7.1 is present both at the apical and basolateral membranes of the hESC- and fresh native mouse RPE. Kir currents, however, were recorded only from 14% of the hESC-RPE cells with relatively low amplitudes. Compared to previous studies, our data suggest that in the hESC-RPE, the characteristics of the delayed rectifier and M-currents resemble native adult RPE, while A-type and Kir currents resemble native hfRPE or cultured primary RPE. Overall, the channelome of the RPE is a sensitive indicator of maturity and functionality affecting its therapeutic utility.

The Changes of KCNQ5 Expression and Potassium Microenvironment in the Retina of Myopic Guinea Pigs

KCNQ5 is suggestively associated with myopia, but its specific role in the myopic process has not been studied further. The aim of this study was to investigate the expression of potassium channel gene KCNQ5 and the changes of K+ microenvironment within the retina of form deprivation myopia (FDM) guinea pigs. A total of 60 guinea pigs were randomly divided into the normal control (NC) group, the self-control (SC) group, and the form-deprivation (FD) group for different treatments. Molecular assays and immunohistochemistry (IHC) were conducted to measure the expression and distribution of KCNQ5-related gene and protein in the retina. We determined the K+ concentration in the retina. In addition, the possible effects of form deprivation on potassium ionic currents and the pharmacological sensitivity of KCNQ5 activator Retigabine and inhibitor XE991 to the M-current in RPE cells were investigated using the patch-clamp technique. As a result, FD eyes exhibited more myopic refraction and longer AL. The mRNA and protein levels of KCNQ5 significantly decreased in the FD eyes, but the K+ concentration increased. In addition, the M-type K+ current [IK(M)] density decreased in FD RPE cells, and were activated or inhibited in a concentration-dependent manner due to the addition of Retigabine or XE991. Overall, KCNQ5 was significantly downregulated in the retina of FD guinea pigs, which may be associated with the increasing K+ concentration, decreasing IK(M) density, and elongating ocular axis. It suggested that KCNQ5 may play a role in the process of myopia, and the intervention of potassium channels may contribute to the prevention and control of myopia.

Lipid Landscape of the Human Retina and Supporting Tissues Revealed by High-Resolution Imaging Mass Spectrometry

The human retina provides vision at light levels ranging from starlight to sunlight. Its supporting tissues regulate plasma-delivered lipophilic essentials for vision, including retinoids. The macula is an anatomic specialization for high-acuity and color vision that is also vulnerable to prevalent blinding diseases. The retina's exquisite architecture comprises numerous cell types that are aligned horizontally, yielding structurally distinct cell, synaptic, and vascular layers that are visible in histology and in diagnostic clinical imaging. MALDI imaging mass spectrometry (IMS) is now capable of uniting low micrometer spatial resolution with high levels of chemical specificity. In this study, a multimodal imaging approach fortified with accurate multi-image registration was used to localize lipids in human retina tissue at laminar, cellular, and subcellular levels. Multimodal imaging results indicate differences in distributions and abundances of lipid species across and within single cell types. Of note are distinct localizations of signals within specific layers of the macula. For example, phosphatidylethanolamine and phosphatidylinositol lipids were localized to central RPE cells, whereas specific plasmalogen lipids were localized to cells of the perifoveal RPE and Henle fiber layer. Subcellular compartments of photoreceptors were distinguished by PE(20:0_22:5) in the outer nuclear layer, PE(18:0_22:6) in outer and inner segments, and cardiolipin CL(70:5) in the mitochondria-rich inner segments. Several lipids, differing by a single double bond, have markedly different distributions between the central fovea and the ganglion cell and inner nuclear layers. A lipid atlas, initiated in this study, can serve as a reference database for future examination of diseased tissues.

Long-Term Follow-Up of Peripheral Pigmentary Retinopathy in Asian Patients with Danon Disease

Background: Peripheral pigmentary changes are common amongst women with Danon disease; however, there is currently a lack of longitudinal observational studies of the retinal changes in this condition, and the long-term visual prognosis is not well understood. Methods and Results: In this report, we present long-term follow-up data (12 years of follow-up) regarding peripheral retinopathy in an Asian woman and her mother who were both diagnosed with Danon disease. Both patients showed a novel nonsense mutation of the LAMP2 gene (c.123 of exon 2). During the follow-up period, no evident extension of peripheral pigmented lesions or visual field progression was observed. Conclusions: We report, for the first time, the long-term longitudinal follow-up of Danon disease-related retinopathy in an Asian patient featuring an indolent macular-sparing peripheral lesion.

Kv7 channel inhibition increases hypoxic pulmonary vasoconstriction in endotoxemic mouse lungs

PURPOSE

Hypoxic pulmonary vasoconstriction (HPV) regulates regional pulmonary blood flow in order to match regional ventilation to preserve arterial oxygenation. HPV is impaired in patients with sepsis or acute respiratory distress syndrome (ARDS). Endotoxemic mice show reduced HPV and recent evidence suggests a central role of voltage gated potassium channel 7 (Kv7) in regulating HPV. Therefore, we tested the hypothesis if Kv7 is induced and inhibition of Kv7 increases HPV in endotoxemia.

MATERIALS AND METHODS

Isolated lungs of LPS-pretreated and untreated animals were perfused with and without specific inhibitors of Kv7 (linopirdine (LI) 0, 0.1, 1 and 10 µM) or Kv7.1 (HMR1556 100 nM). Pulmonary artery pressure (PAP) during normoxic (FiO₂ 0.21) as well as hypoxic (FiO₂ 0.01) ventilation were obtained. Expressions of Kv7 composing (KCNQ1-5) as well as auxiliary subunits (KCNE1-5) were measured in mouse lungs with and without endotoxemia.

RESULTS

HPV was impaired in lungs from LPS mice (16 ± 7% vs 105 ± 13% control, p < 0.05). Perfusion of control lungs with 10 µM LI or 100 nM HMR1556 did not affect HPV (LI 105 ± 12% vs 105 ± 13% vehicle, HMR1556 100 ± 6% vs 98 ± 26%, P = NS). In LPS mice perfusion with 10 µM LI (74.2 ± 7% vs. 16 ± 7% vehicle, P < 0.05) or HMR1556 100 nM augmented HPV (74 ± 28% vs. 15 ± 17% vehicle, P < 0.05). KCNQ1, 4 and 5 gene- and protein expressions as well as KCNE1, 2 and 4 gene expressions were unaltered in endotoxemic lungs. KCNE3 gene and protein expressions were increased in lungs of LPS treated mice (3.1 ± 1.3-fold and 1.8 ± 0.3-fold, respectively, P < 0.05 for both).

CONCLUSIONS

Endotoxemia does not alter KCNQ1, 4 and 5 gene and protein expressions but increases pulmonary KCNE3 gene and protein expression. In isolated perfused endotoxemic mouse lungs, perfusion with 10 µM LI or 100 nM HMR1556 augments HPV.

Kaempferol Protects Against Hydrogen Peroxide-Induced Retinal Pigment Epithelium Cell Inflammation and Apoptosis by Activation of SIRT1 and Inhibition of PARP1

Purpose: This study investigated the protective effect of Kaempferol against hydrogen peroxides (H₂O₂)-induced retinal pigment epithelium (RPE) cell oxidative stress, inflammation, and apoptosis and investigated if this protection involves modulation of poly(ADP-ribose) polymerase-1 (PARP1)/silent information regulator 1 (SIRT1) signaling pathway. Methods: ARPE-19 cells were pretreated with increasing doses of Kaempferol (10, 25, 50, 100 μM) for 24 h in Dulbecco's modified Eagle's medium/F-12 medium with or without postincubation with H₂O₂. Control cells remained untreated. Results: Kaempferol, in a dose-dependent manner, significantly increased cell survival and reduced levels of reactive oxygen species, malondialdehyde, single-stranded DNA (ssDNA), and lactate dehydrogenase but increased levels of glutathione (GSH) and manganese-superoxide dismutase (MnSOD) in H₂O₂-treated ARPE-19 cells. It also increased GSH and MnSOD in a dose-dependent manner in control + Kaempferol treated cells. At a dose of 50 μM, the most effective dose, Kaempferol also inhibited protein levels of tumor necrosis factor alpha and interleukin-6, nuclear activity and protein levels of total, acetylated, and cleaved PARP1, and increased nuclear levels and activity of SIRT1 in H₂O₂-treated cells. In parallel, it increased total nuclear levels of Nrf2 but reduced the acetylation of p53, Nrf2, nuclear factor-κB (NF-κB) p65, and forkhead transcriptional factor 1 (FOXO1). Of interest, the stimulatory role of Kaempferol in the nuclear accumulation and activation of SIRT1 and the nuclear levels of Nrf2, as well as in reducing the acetylation of Nrf2, NF-κB p65, and FOXO1, was shown in nuclei of control + Kaempferol-treated cells. Conclusion: Kaempferol protective effect against H₂O₂-induced ARPE-19 damage involves antioxidant and anti-inflammatory effects mediated, at least, by stimulating the nuclear accumulation, activation, and deacetylase ability of SIRT1 and concurrent inhibition of PARP1.

Expression and Localization of Kcne2 in the Vertebrate Retina

Purpose

To characterize the retinal expression and localization of Kcne2, an ancillary (β) ion-channel subunit with an important role in fine-tuning cellular excitability.

Methods

We analyzed available single-cell transcriptome data from tens of thousands of murine retinal cells for cell-type-specific expression of Kcne2 using state-of-the-art bioinformatics techniques. This evidence at the transcriptome level was complemented with a comprehensive immunohistochemical characterization of mouse retina (C57BL/6, ages 8-12 weeks) employing co-labeling techniques and cell-type-specific antibody markers. We furthermore examined how conserved the Kcne2 localization pattern in the retina was across species by performing immunostaining on zebrafish, cowbird, sheep, mice, and macaque.

Results

Kcne2 is distinctly expressed in cone photoreceptors and rod bipolar cells. At a subcellular level, the bulk of Kcne2 immunoreactivity can be observed in the outer plexiform layer. Here, it localizes into cone pedicles and likely the postsynaptic membrane of the rod bipolar cells. Thus, the vast majority of Kcne2 immunoreactivity is observed in a thin band in the outer plexiform layer. In addition to this, faint Kcne2 immunoreactivity can also be observed in cone inner segments and the somata of a small subset of cone ON bipolar cells. Strikingly, the localization of Kcne2 in the outer plexiform layer was preserved among all of the species studied, spanning at least 300 million years of evolution of the vertebrate kingdom.

Conclusions

The data we present here suggest an important and specific role for Kcne2 in the highly specialized photoreceptor-bipolar cell synapse.

Protective effects of delphinidin against H2O2-induced oxidative injuries in human retinal pigment epithelial cells

Age-related macular degeneration (AMD) is now one of the leading causes of blindness in the elderly population and oxidative stress-induced damage to retinal pigment epithelial (RPE) cells occurs as part of the pathogenesis of AMD. In the present study, we evaluated the protective effect of delphinidin (2-(3,4,5-trihydroxyphenyl) chromenylium-3,5,7-triol) against hydrogen peroxide (H₂O₂)-induced toxicity in human ARPE-19 cells and its molecular mechanism. MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay and flow cytometry demonstrated that pretreatment of ARPE-19 cells with delphinidin (25, 50, and 100 μg/ml) significantly increased cell viability and reduced the apoptosis from H₂O₂ (0.5 mM)-induced oxidative stress in a concentration-dependent manner, which was achieved by the inhibition of Bax, cytochrome c, and caspase-3 protein expression and enhancement of Bcl-2 protein. The same tendency was observed in ARPE-19 cells pre-treated with 15 mM of N-acetylcysteine (NAC) before the addition of H₂O₂. Furthermore, pre-incubation of ARPE-19 cells with delphinidin markedly inhibited the intracellular reactive oxygen species (ROS) generation and Nox1 protein expression induced by H₂O₂. Moreover, the decreased antioxidant enzymes activities of superoxide dismutase (SOD), catalase (CAT), and glutathione-peroxidase (GSH-PX) and elevated (MDA) level in H₂O₂-treated cells were reversed to the normal standard by the addition of delphinidin, which was regulated by increasing nuclear Nrf2 protein expression in ARPE-19 cells. Our results suggest that delphinidin effectively protects human ARPE-19 cells from H₂O₂-induced oxidative damage via anti-apoptotic and antioxidant effects.

Calcified nodules in retinal drusen are associated with disease progression in age-related macular degeneration

Drusen are lipid-, mineral-, and protein-containing extracellular deposits that accumulate between the basal lamina of the retinal pigment epithelium (RPE) and Bruch's membrane (BrM) of the human eye. They are a defining feature of age-related macular degeneration (AMD), a common sight-threatening disease of older adults. The appearance of heterogeneous internal reflectivity within drusen (HIRD) on optical coherence tomography (OCT) images has been suggested to indicate an increased risk of progression to advanced AMD. Here, in a cohort of patients with AMD and drusen, we show that HIRD indicated an increased risk of developing advanced AMD within 1 year. Using multimodal imaging in an independent cohort, we demonstrate that progression to AMD was associated with increasing degeneration of the RPE overlying HIRD. Morphological analysis of clinically imaged cadaveric human eye samples revealed that HIRD was formed by multilobular nodules. Nanoanalytical methods showed that nodules were composed of hydroxyapatite and that they differed from spherules and BrM plaques, other refractile features also found in the retinas of patients with AMD. These findings suggest that hydroxyapatite nodules may be indicators of progression to advanced AMD and that using multimodal clinical imaging to determine the composition of macular calcifications may help to direct therapeutic strategies and outcome measures in AMD.

Effects of cisplatin-5-fluorouracil combination therapy on oxidative stress, DNA damage, mitochondrial apoptosis, and death receptor signalling in retinal pigment epithelium cells

AIM

Combination therapies of cisplatin with 5-FU (PF) are an effective solution and have been widely used for the treatment of various categories of cancer including anal, gastrointestinal, and oral cancer, as well as head and neck tumors. The effects of combined PF treatment on vital intracellular signalling pathways in nontargeted cells remain unclear. The aim of this study is to explain the possible mechanisms by which combined PF treatment results in retinal toxicity and to investigate the effects of PF on important vital signalling pathways in ARPE 19 retinal pigmented epithelial cells.

MATERIALS AND METHODS

We analysed the cellular and molecular effects of PF on cell viability, oxidative stress, gene repair response, and induction of apoptosis in ARPE 19 cells using molecular probe fluorescent staining, cell cytometer, RAPD, qRT-PCR, and western blot assays.

RESULTS

We determined that PF causes excessive generation of reactive oxygen species (ROS) and prevents ROS scavenging by suppressing antioxidant systems. We found induction of DNA damage, particularly mismatch and double strand break repair, in ARPE 19 cells treated with PF. In this study, PF also induced both the intrinsic apoptosis pathway and death receptor signalling in ARPE 19 cells.

CONCLUSIONS

Our data proved that PF causes cytotoxicity and genotoxicity, at both the cellular and molecular levels, in ARPE 19 cells following particularly prolonged treatment (48 h). Additionally, our results suggest key molecular signals for prevention strategies that can be developed to reduce the severe side effects of PF chemotherapy.

Relationship between rat retinal degeneration and potassium channel KCNQ5 expression

KCNQ5/Kv7.5 is a low-threshold non-inactivating voltage-gated potassium channel preferentially targeted to excitatory endings in brain neurons. The M-type current is mediated by KCNQ5 channel subunits in monkey retinal pigment epithelium cells and in brain neurons. This study was undertaken to analyze KCNQ5 expression and the interaction signals of KCNQ5 with other proteins in normal rat retina and during photoreceptor degeneration. The KCNQ5 expression pattern was studied by immunocytochemistry and Western blot in normal rat retinas (Sprague-Dawley, SD) and P23H-1 rats as a retinitis pigmentosa model. The physical interactions of KCNQ5 with calmodulin (CaM), vesicular glutamate transporter 1 (VGluT1) and glial fibrillary acidic protein (GFAP) were analyzed by in situ proximity ligation assays and were supported by calcium recording. KCNQ5 expression was found in the plexiform layers, ganglion cell layer and basal membrane of the retinal pigment epithelium. The physical interactions among KCNQ5 and CaM, VGluT1 and GFAP changed with age and during retinal degeneration. The maximal level of KCNQ5/CaM interaction was found when photoreceptors had almost completely disappeared; the KCNQ5/VGluT1 interaction signal decreased and the KCNQ5/GFAP interaction increased in the inner retina, while degeneration progressed. The basal calcium levels in the astrocytes and neurons of P23H-1 were higher than in the control SD retinas. This study demonstrates that KCNQ5 is present in the rat retina where its activity may be moderated by CaM. Retinal degeneration progression in P23H-1 rats can be followed by an interaction between KCNQ5 with CaM in an in situ system. The relationship between KCNQ5 and VGluT1 or GFAP needs to be more cautiously interpreted.