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Cells Jun 2020Phosphoinositides are known to play multiple roles in eukaryotic cells. Although dysregulation of phosphoinositide metabolism in the retina has been reported to cause...
Phosphoinositides are known to play multiple roles in eukaryotic cells. Although dysregulation of phosphoinositide metabolism in the retina has been reported to cause visual dysfunction in animal models and human patients, our understanding of the phosphoinositide composition of the retina is limited. Here, we report a characterization of the phosphoinositide profile of the mouse retina and an analysis of the subcellular localization of major phosphorylated phosphoinositide forms in light-sensitive photoreceptor neurons. Using chromatography of deacylated phosphatidylinositol headgroups, we established PI(4,5)P and PI(4)P as two major phosphorylated phosphoinositides in the retina. Using high-resolution mass spectrometry, we revealed 18:0/20:4 and 16:0/20:4 as major fatty-acyl chains of retinal phosphoinositides. Finally, analysis of fluorescent phosphoinositide sensors in rod photoreceptors demonstrated distinct subcellular distribution patterns of major phosphoinositides. The PI(4,5)P reporter was enriched in the inner segments and synapses, but was barely detected in the light-sensitive outer segments. The PI(4)P reporter was mostly found in the outer and inner segments and the areas around nuclei, but to a lesser degree in the synaptic region. These findings provide support for future mechanistic studies defining the biological significance of major mono- (PI(4)P) and bisphosphate (PI(4,5)P) phosphatidylinositols in photoreceptor biology and retinal health.
Topics: Animals; Fatty Acids; Lipidomics; Mice, Inbred C57BL; Phosphatidylinositols; Phosphorylation; Retina; Retinal Rod Photoreceptor Cells; Subcellular Fractions
PubMed: 32517352
DOI: 10.3390/cells9061417 -
The Journal of Neuroscience : the... Nov 2022At intermediate (mesopic) light levels, rods and cones are both active and can contribute to vision. This presents a challenge to the retina because the visual responses...
At intermediate (mesopic) light levels, rods and cones are both active and can contribute to vision. This presents a challenge to the retina because the visual responses originating with rods and cones are distinct, yet their visual responses must be seamlessly combined. The current study aimed to establish how the circadian clock regulates rod and/or cone vision in these conditions, given the strong time-of-day change in the reliance on each photoreceptor. Visual responses were recorded in the retina and visual thalamus of anaesthetized male mice at distinct circadian time points, and the method of receptor silent substitution was used to selectively stimulate different photoreceptor types. With stimuli designed to only activate rods, responses in the mesopic range were highly rhythmic and peaked in amplitude in the subjective night. This rhythm was abolished following intravitreal injection of the gap junction blocker meclofenamic acid, consistent with a circadian variation in the strength of electrical coupling of photoreceptors. In contrast, responses to stimuli designed to only activate cones were arrhythmic within the mesopic to photopic range when adapted to the background irradiance. The outcome was that combined rod-plus-cone responses showed a stable contrast-response relationship across mesopic-photopic backgrounds in the circadian day, whereas at night, responses were significantly amplified at lower light levels. These data support the idea that the circadian clock is a key regulator of vision, in this case defining the relative amplitude of rod/cone vision across the mesopic transition according to time of day. Although the importance of circadian clocks in regulating vision has been long recognized, less is known about how the clock shapes vision in conditions where both rods and cones are active (mesopic conditions). Here, the novel approach of receptor silent substitution has been applied to trace rod and cone visual responses in mice across the circadian cycle and has identified pronounced rhythms in rod, but not cone, vision. This has the effect of boosting responses in dimmer backgrounds at night at the cost of impaired contrast-response stability across the mesopic to photopic range. Thus, the circadian clock drives anticipatory changes in the relative contribution of rods versus cones to vision, which match the prevailing visual environment.
Topics: Male; Mice; Animals; Retinal Rod Photoreceptor Cells; Mesopic Vision; Retinal Cone Photoreceptor Cells; Retina; Color Vision
PubMed: 36216501
DOI: 10.1523/JNEUROSCI.0486-22.2022 -
FASEB Journal : Official Publication of... Aug 2022Photoreceptors consume glucose supplied by the choriocapillaris to support phototransduction and outer segment (OS) renewal. Reduced glucose supply underlies...
Photoreceptors consume glucose supplied by the choriocapillaris to support phototransduction and outer segment (OS) renewal. Reduced glucose supply underlies photoreceptor cell death in inherited retinal degeneration and age-related retinal disease. We have previously shown that restricting glucose transport into the outer retina by conditional deletion of Slc2a1 encoding GLUT1 resulted in photoreceptor loss and impaired OS renewal. However, retinal neurons, glia, and the retinal pigment epithelium play specialized, synergistic roles in metabolite supply and exchange, and the cell-specific map of glucose uptake and utilization in the retina is incomplete. In these studies, we conditionally deleted Slc2a1 in a pan-retinal or rod-specific manner to better understand how glucose is utilized in the retina. Using non-invasive ocular imaging, electroretinography, and histochemical and biochemical analyses we show that genetic deletion of Slc2a1 from retinal neurons and Müller glia results in reduced OS growth and progressive rod but not cone photoreceptor cell death. Rhodopsin levels were severely decreased even at postnatal day 20 when OS length was relatively normal. Arrestin levels were not changed suggesting that glucose uptake is required to synthesize membrane glycoproteins. Rod-specific deletion of Slc2a1 resulted in similar changes in OS length and rod photoreceptor cell death. These studies demonstrate that glucose is an essential carbon source for rod photoreceptor cell OS maintenance and viability.
Topics: Glucose; Glucose Transporter Type 1; Humans; Retinal Cone Photoreceptor Cells; Retinal Degeneration; Rod Cell Outer Segment
PubMed: 35766190
DOI: 10.1096/fj.202200369R -
Journal of Theoretical Biology Feb 2022Retinitis pigmentosa (RP) is the term used to denote a group of inherited retinal-degenerative conditions that cause progressive sight loss. Individuals with this...
Retinitis pigmentosa (RP) is the term used to denote a group of inherited retinal-degenerative conditions that cause progressive sight loss. Individuals with this condition lose their light-sensitive photoreceptor cells, known as rods and cones, over a period of years to decades; degeneration starting in the retinal periphery, and spreading peripherally and centrally over time. RP is a rod-cone dystrophy, meaning that rod health and function are affected earlier and more severely than that of cones. Rods degenerate due to an underlying mutation, whereas the reasons for cone degeneration are unknown. A number of mechanisms have been proposed to explain secondary cone loss and the spatio-temporal patterns of retinal degeneration in RP. One of the most promising is the trophic factor hypothesis, which suggests that rods produce a factor necessary for cone survival, such that, when rods degenerate, cone degeneration follows. In this paper we formulate and analyse mathematical models of human RP under the trophic factor hypothesis. These models are constructed as systems of reaction-diffusion partial differential equations in one spatial dimension, and are solved and analysed using a combination of numerical and analytical methods. We predict the conditions under which cones will degenerate following the loss of a patch of rods from the retina, the critical trophic factor treatment rate required to prevent cone degeneration following rod loss and the spatio-temporal patterns of cone loss that would result if the trophic factor mechanism alone were responsible for retinal degeneration.
Topics: Humans; Models, Theoretical; Retinal Cone Photoreceptor Cells; Retinal Degeneration; Retinal Rod Photoreceptor Cells; Retinitis Pigmentosa
PubMed: 34687673
DOI: 10.1016/j.jtbi.2021.110938 -
The Journal of Biological Chemistry 2021The Musashi family of RNA-binding proteins is known for its role in stem-cell renewal and is a negative regulator of cell differentiation. Interestingly, in the retina,...
The Musashi family of RNA-binding proteins is known for its role in stem-cell renewal and is a negative regulator of cell differentiation. Interestingly, in the retina, the Musashi proteins MSI1 and MSI2 are differentially expressed throughout the cycle of retinal development, with MSI2 protein displaying robust expression in the adult retinal tissue. In this study, we investigated the importance of Musashi proteins in the development and function of photoreceptor neurons in the retina. We generated a pan-retinal and rod photoreceptor neuron-specific conditional KO mouse lacking MSI1 and MSI2. Independent of the sex, photoreceptor neurons with simultaneous deletion of Msi1 and Msi2 were unable to respond to light and displayed severely disrupted photoreceptor outer segment morphology and ciliary defects. Mice lacking MSI1 and MSI2 in the retina exhibited neuronal degeneration, with complete loss of photoreceptors within 6 months. In concordance with our earlier studies that proposed a role for Musashi proteins in regulating alternative splicing, the loss of MSI1 and MSI2 prevented the use of photoreceptor-specific exons in transcripts critical for outer segment morphogenesis, ciliogenesis, and synaptic transmission. Overall, we demonstrate a critical role for Musashi proteins in the morphogenesis of terminally differentiated photoreceptor neurons. This role is in stark contrast with the canonical function of these two proteins in the maintenance and renewal of stem cells.
Topics: Alternative Splicing; Animals; Cilia; Mice; Mice, Knockout; Nerve Tissue Proteins; Photoreceptor Cells, Vertebrate; RNA-Binding Proteins; Retinal Degeneration; Synaptic Transmission; Vision, Ocular
PubMed: 33168629
DOI: 10.1074/jbc.RA120.015714 -
Photoreceptor-Specific Temporal Contrast Sensitivities in RP1L1-Associated Occult Macular Dystrophy.Investigative Ophthalmology & Visual... Jun 2023The purpose of this study was to compare L-, M-, S-cone-, and rod-driven temporal contrast sensitivities (tCS) in patients with RP1L1-associated autosomal-dominant...
PURPOSE
The purpose of this study was to compare L-, M-, S-cone-, and rod-driven temporal contrast sensitivities (tCS) in patients with RP1L1-associated autosomal-dominant occult macular dystrophy (OMD), and to investigate how photoreceptor degeneration determines which post-receptoral channels dominate perception.
METHODS
Photoreceptor isolating stimuli were created with the silent substitution technique. Photoreceptor-selective tCS deviations (D L-cone/M-cone/S-cone/Rod) were obtained as a function of temporal frequency with identical retinal adaptation, by subtracting tCS from age-corrected normal values. A linear-mixed effects model was used for analysis.
RESULTS
Eleven genetically confirmed patients were included (7 women, 5 men; age = 52.27 ± 14.44 years). Overall, L- and M-cone-driven sensitivity deviations (DL-cone and DM-cone) were more negative than DS-cone; DRod was normal at frequencies between 8 and 12 Hz in all subjects. Rod-driven tCS functions allowed identification of two subgroups of patients: one with band-pass properties and one with low-pass properties, suggesting dominance of different post-receptoral filters. The same filtering properties were observed in L-cone-driven tCS functions. Furthermore, the two subgroups also differed in clinical parameters (spherical equivalent, BCVA, perimetry, and ocular coherence tomography (OCT) reflectivity of the ellipsoid zone relative to the RPE).
CONCLUSIONS
OMD was characterized predominantly by deterioration of L- and M-cone-cone driven function in the perifovea. Rod-driven functions were normal. Differences in the photoreceptor signals were further modified by postreceptoral filters.
Topics: Male; Humans; Female; Adult; Middle Aged; Aged; Electroretinography; Retinal Cone Photoreceptor Cells; Macular Degeneration; Vision, Ocular; Photoreceptor Cells, Vertebrate; Retinal Dystrophies; Eye Proteins
PubMed: 37342031
DOI: 10.1167/iovs.64.7.33 -
Cells Mar 2023Wnt/β-catenin signaling is essential for embryonic eye development in both the anterior eye and retina. WNT2B, a ligand and activator of the Wnt/β-catenin pathway,...
Wnt/β-catenin signaling is essential for embryonic eye development in both the anterior eye and retina. WNT2B, a ligand and activator of the Wnt/β-catenin pathway, assists in the development of the lens and peripheral regions of the eye. In humans mutations are associated with coloboma and WNT2B may also assist in retinal progenitor cell differentiation in chicken, yet the potential role of WNT2B in retinal neuronal development is understudied. This study explored the effects of WNT2B on retinal neuronal and vascular formation using systemic knockout (KO) mice generated by crossing (fl/fl) mice with CMV-cre mice. KO eyes exhibited relatively normal anterior segments and retinal vasculature. Ectopic formation of rod photoreceptor cells in the subretinal space was observed in KO mice as early as one week postnatally and persisted through nine-month-old mice. Other retinal neuronal layers showed normal organization in both thickness and lamination, without detectable signs of retinal thinning. The presence of abnormal photoreceptor genesis was also observed in heterozygous mice, and occasionally in wild type mice with decreased expression levels. Expression of was found to be enriched in the retinal pigment epithelium compared with whole retina. Together these findings suggest that WNT2B is potentially involved in rod photoreceptor genesis during eye development; however, potential influence by a yet unknown genetic factor is also possible.
Topics: Animals; Humans; Mice; beta Catenin; Glycoproteins; Mice, Knockout; Retina; Retinal Pigment Epithelium; Retinal Rod Photoreceptor Cells; Wnt Proteins
PubMed: 37048106
DOI: 10.3390/cells12071033 -
Journal of Anatomy Aug 2023The precise specification of cellular fate is thought to ensure the production of the correct number of neurons within a population. Programmed cell death may be an... (Review)
Review
The precise specification of cellular fate is thought to ensure the production of the correct number of neurons within a population. Programmed cell death may be an additional mechanism controlling cell number, believed to refine the proper ratio of pre- to post-synaptic neurons for a given species. Here, we consider the size of three different neuronal populations in the rod pathway of the mouse retina: rod photoreceptors, rod bipolar cells, and AII amacrine cells. Across a collection of 28 different strains of mice, large variation in the numbers of all three cell types is present. The variation in their numbers is not correlated, so that the ratio of rods to rod bipolar cells, as well as rod bipolar cells to AII amacrine cells, varies as well. Establishing connectivity between such variable pre- and post-synaptic populations relies upon plasticity that modulates process outgrowth and morphological differentiation, which we explore experimentally for both rod bipolar and AII amacrine cells in a mouse retina with elevated numbers of each cell type. While both rod bipolar dendritic and axonal arbors, along with AII lobular arbors, modulate their areal size in relation to local homotypic cell densities, the dendritic appendages of the AII amacrine cells do not. Rather, these processes exhibit a different form of plasticity, regulating the branching density of their overlapping arbors. Each form of plasticity should ensure uniformity in retinal coverage in the presence of the independent specification of afferent and target cell number.
Topics: Mice; Animals; Dendrites; Retina; Amacrine Cells; Axons
PubMed: 35292986
DOI: 10.1111/joa.13653 -
Investigative Ophthalmology & Visual... Nov 2020The purpose of this study was to test the hypothesis that anti-oxidant and / or anti-inflammation drugs that suppress rod death in cyclic light-reared Pde6brd10 mice are...
PURPOSE
The purpose of this study was to test the hypothesis that anti-oxidant and / or anti-inflammation drugs that suppress rod death in cyclic light-reared Pde6brd10 mice are also effective in dark-reared Pde6brd10 mice.
METHODS
In untreated dark-reared Pde6brd10 mice at post-natal (P) days 23 to 24, we measured the outer nuclear layer (ONL) thickness (histology) and dark-light thickness difference in external limiting membrane-retinal pigment epithelium (ELM-RPE) (optical coherence tomography [OCT]), retina layer oxidative stress (QUEnch-assiSTed [QUEST] magnetic resonance imaging [MRI]); and microglia/macrophage-driven inflammation (immunohistology). In dark-reared P50 Pde6brd10 mice, ONL thickness was measured (OCT) in groups given normal chow or chow admixed with methylene blue (MB) + Norgestrel (anti-oxidant, anti-inflammatory), or MB or Norgestrel separately.
RESULTS
P24 Pde6brd10 mice showed no significant dark-light ELM-RPE response in superior and inferior retina consistent with high cGMP levels. Norgestrel did not significantly suppress the oxidative stress of Pde6brd10 mice that is only found in superior central outer retina of males at P23. Overt rod degeneration with microglia/macrophage activation was observed but only in the far peripheral superior retina in male and female P23 Pde6brd10 mice. Significant rod protection was measured in female P50 Pde6brd10 mice given 5 mg/kg/day MB + Norgestrel diet; no significant benefit was seen with MB chow or Norgestrel chow alone, nor in similarly treated male mice.
CONCLUSIONS
In early rod degeneration in dark-reared Pde6brd10 mice, little evidence is found in central retina for spatial associations among biomarkers of the PDE6B mutation, oxidative stress, and rod death; neuroprotection at P50 was limited to a combination of anti-oxidant/anti-inflammation treatment in a sex-specific manner.
Topics: Animals; Cyclic Nucleotide Phosphodiesterases, Type 6; Dark Adaptation; Disease Models, Animal; Female; Immunohistochemistry; Magnetic Resonance Imaging; Male; Mice; Mice, Inbred C57BL; Mice, Mutant Strains; Neuroprotection; Oxidative Stress; Retina; Retinal Degeneration; Retinal Pigment Epithelium; Retinal Rod Photoreceptor Cells; Tomography, Optical Coherence
PubMed: 33156341
DOI: 10.1167/iovs.61.13.14 -
Advances in Protein Chemistry and... 2020Most vertebrates express four arrestin subtypes: two visual ones in photoreceptor cells and two non-visuals expressed ubiquitously. The latter two interact with hundreds... (Review)
Review
Most vertebrates express four arrestin subtypes: two visual ones in photoreceptor cells and two non-visuals expressed ubiquitously. The latter two interact with hundreds of G protein-coupled receptors, certain receptors of other types, and numerous non-receptor partners. Arrestins have no enzymatic activity and work by interacting with other proteins, often assembling multi-protein signaling complexes. Arrestin binding to every partner affects cell signaling, including pathways regulating cell survival, proliferation, and death. Thus, targeting individual arrestin interactions has therapeutic potential. This requires precise identification of protein-protein interaction sites of both participants and the choice of the side of each interaction which would be most advantageous to target. The interfaces involved in each interaction can be disrupted by small molecule therapeutics, as well as by carefully selected peptides of the other partner that do not participate in the interactions that should not be targeted.
Topics: Animals; Arrestins; Binding Sites; Gene Expression Regulation; Genetic Therapy; Humans; Leber Congenital Amaurosis; Molecular Targeted Therapy; Mutation; Protein Binding; Receptors, G-Protein-Coupled; Retinal Rod Photoreceptor Cells; Signal Transduction; Small Molecule Libraries
PubMed: 32312421
DOI: 10.1016/bs.apcsb.2019.11.011