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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 -
Scientific Reports Sep 2021Vertebrate photoreceptors contain large numbers of closely-packed mitochondria which sustain the high metabolic demands of these cells. These mitochondria populations...
Vertebrate photoreceptors contain large numbers of closely-packed mitochondria which sustain the high metabolic demands of these cells. These mitochondria populations are dynamic and undergo fusion and fission events. This activity serves to maintain the population in a healthy state. In the event of mitochondrial damage, sub-domains, or indeed whole mitochondria, can be degraded and population homeostasis achieved. If this process is overwhelmed cell death may result. Death of photoreceptors contributes to loss of vision in aging individuals and is associated with many eye diseases. In this study we used serial block face scanning electron microscopy of adult Macaca fascicularis retinae to examine the 3D structure of mitochondria in rod and cone photoreceptors. We show that healthy-looking photoreceptors contain mitochondria exhibiting a range of shapes which are associated with different regions of the cell. In some photoreceptors we observe mitochondrial swelling and other changes often associated with cellular stress. In rods and cones that appear stressed we identify elongated domains of mitochondria with densely-packed normal cristae associated with photoreceptor ciliary rootlet bundles. We observe mitochondrial fission and mitochondrion fragments localised to these domains. Swollen mitochondria with few intact cristae are located towards the periphery of the photoreceptor inner-segment in rods, whilst they are found throughout the cell in cones. Swollen mitochondria exhibit sites on the mitochondrial inner membrane which have undergone complex invagination resulting in membranous, electron-dense aggregates. Membrane contact occurs between the mitochondrion and the photoreceptor plasma membrane in the vicinity of these aggregates, and a series of subsequent membrane fusions results in expulsion of the mitochondrial aggregate from the photoreceptor. These events are primarily associated with rods. The potential fate of this purged material and consequences of its clearance by retinal pigment epithelia are discussed.
Topics: Animals; Cell Membrane; Imaging, Three-Dimensional; Macaca fascicularis; Microscopy, Electron, Scanning; Mitochondria; Mitochondrial Membranes; Retinal Cone Photoreceptor Cells; Retinal Rod Photoreceptor Cells
PubMed: 34552195
DOI: 10.1038/s41598-021-98409-7 -
Ophthalmic Genetics Jun 2022Rods and cones are photoreceptor neurons in the retina that are required for visual sensation in vertebrates, wherein the perception of vision is initiated when these...
BACKGROUND
Rods and cones are photoreceptor neurons in the retina that are required for visual sensation in vertebrates, wherein the perception of vision is initiated when these neurons respond to photons in the light stimuli. The photoreceptor cell is structurally studied as outer segments (OS) and inner segments (IS) where proper protein sorting, localization, and compartmentalization are critical for phototransduction, visual function, and survival. In human retinal diseases, improper protein transport to the OS or mislocalization of proteins to the IS and other cellular compartments could lead to impaired visual responses and photoreceptor cell degeneration that ultimately cause loss of visual function.
RESULTS
Therefore, studying and identifying mechanisms involved in facilitating and maintaining proper protein transport in photoreceptor cells would help our understanding of pathologies involving retinal cell degeneration in inherited retinal dystrophies, age-related macular degeneration, and Usher Syndrome.
CONCLUSIONS
Our mini-review will discuss mechanisms of protein transport within photoreceptors and introduce a novel role for an unconventional motor protein, MYO1C, in actin-based motor transport of the visual chromophore Rhodopsin to the OS, in support of phototransduction and visual function.
Topics: Animals; Humans; Protein Transport; Retina; Retinal Cone Photoreceptor Cells; Retinal Degeneration; Retinal Rod Photoreceptor Cells; Vision, Ocular
PubMed: 35470760
DOI: 10.1080/13816810.2022.2062391 -
Stem Cells and Development Nov 2023Retinitis pigmentosa (RP) is a prevalent inherited retinal degenerative disease resulting from photoreceptor and pigment epithelial apoptosis. The is the most commonly...
Retinitis pigmentosa (RP) is a prevalent inherited retinal degenerative disease resulting from photoreceptor and pigment epithelial apoptosis. The is the most commonly associated pathogenic gene in RP. However, mutations (c.512C>T P171L) have been infrequently reported, and the RP pathogenesis caused by these mutations remains unclear. The objective of this study was to investigate the impact of (c.512C>T P171L) mutation on retinal cell differentiation and elucidate the underlying mechanisms of RP. An effective retinal organoid induction scheme for inhibiting the Wnt signaling pathway was selected for further experiments, and the established cell line HES-406 was demonstrated to be heterozygous for c.512C>T, with a normal karyotype and pluripotency potential. Furthermore, the development of HES-406 organoids may be delayed, and apoptosis detection and co-localization revealed that HES-406 organoids had more apoptotic cells than HES-90 in the outer nuclear layer (ONL), mutant RHO protein was mislocalized in the endoplasmic reticulum (ER), and stress-related and apoptotic gene expression increased. Overall, our study elucidated a possible mechanism by which ER stress caused by RHO P171L protein mislocalization may lead to ONL cell apoptosis.
Topics: Humans; Rhodopsin; Retinal Rod Photoreceptor Cells; Retinitis Pigmentosa; Endoplasmic Reticulum Stress; Apoptosis; Mutation
PubMed: 37470211
DOI: 10.1089/scd.2023.0034 -
International Journal of Molecular... Mar 2022In the vertebrate retina, the light-sensitive photoreceptor rods and cones constantly undergo renewal by generating new portions of the outer segment and shedding their... (Review)
Review
In the vertebrate retina, the light-sensitive photoreceptor rods and cones constantly undergo renewal by generating new portions of the outer segment and shedding their distal, spent tips. The neighboring RPE provides the critical function of engulfing the spent material by phagocytosis. RPE phagocytosis of shed rod outer segment fragments is a circadian process that occurs in a burst of activity shortly after daily light onset with low activity at other times, a rhythm that has been reported for many species and over 50 years. In this review, we compare studies on the rhythm and quantity of RPE phagocytosis using different in vivo model systems and assessment methods. We discuss how measurement methodology impacts the observation and analysis of RPE phagocytosis. Published studies on RPE phagocytosis investigating mice further suggest that differences in genetic background and housing conditions may affect results. Altogether, a comparison between RPE phagocytosis studies performed using differing methodology and strains of the same species is not as straightforward as previously thought.
Topics: Animals; Circadian Rhythm; Mice; Phagocytosis; Retina; Retinal Pigment Epithelium; Retinal Rod Photoreceptor Cells
PubMed: 35409021
DOI: 10.3390/ijms23073661 -
Cells Aug 2023HK2 and PKM2 are two main regulators of aerobic glycolysis. Photoreceptors (PRs) use aerobic glycolysis to produce the biomass necessary for the daily renewal of their...
HK2 and PKM2 are two main regulators of aerobic glycolysis. Photoreceptors (PRs) use aerobic glycolysis to produce the biomass necessary for the daily renewal of their outer segments. Previous work has shown that HK2 and PKM2 are important for the normal function and long-term survival of PRs but are dispensable for PR maturation, and their individual loss has opposing effects on PR survival during acute nutrient deprivation. We generated double conditional (dcKO) mice lacking HK2 and PKM2 expression in rod PRs. Western blotting, immunofluorescence, optical coherence tomography, and electroretinography were used to characterize the phenotype of dcKO animals. Targeted and stable isotope tracing metabolomics, qRT-PCR, and retinal oxygen consumption were performed. We show that dcKO animals displayed early shortening of PR inner/outer segments, followed by loss of PRs with aging, much more rapidly than either knockout alone without functional loss as measured by ERG. Significant alterations to central glucose metabolism were observed without any apparent changes to mitochondrial function, prior to PR degeneration. Finally, PR survival following experimental retinal detachment was unchanged in dcKO animals as compared to wild-type animals. These data suggest that HK2 and PKM2 have differing roles in promoting PR neuroprotection and identifying them has important implications for developing therapeutic options for combating PR loss during retinal disease.
Topics: Animals; Mice; Retinal Rod Photoreceptor Cells; Citric Acid Cycle; Metabolomics; Oxygen Consumption; Retina; Animals, Wild
PubMed: 37626853
DOI: 10.3390/cells12162043 -
Optics Letters Sep 2020Noninvasive, objective measurement of rod function is as significant as that of cone function, and for retinal diseases such as retinitis pigmentosa and age-related...
Noninvasive, objective measurement of rod function is as significant as that of cone function, and for retinal diseases such as retinitis pigmentosa and age-related macular degeneration, rod function may be a more sensitive biomarker of disease progression and efficacy of treatment than cone function. Functional imaging of single human rod photoreceptors, however, has proven difficult because their small size and rapid functional response pose challenges for the resolution and speed of the imaging system. Here, we describe light-evoked, functional responses of human rods and cones, measured noninvasively using a synchronized adaptive optics optical coherence tomography (OCT) and scanning light ophthalmoscopy (SLO) system. The higher lateral resolution of the SLO images made it possible to confirm the identity of rods in the corresponding OCT volumes.
Topics: Humans; Light; Ophthalmoscopy; Retinal Cone Photoreceptor Cells; Retinal Rod Photoreceptor Cells
PubMed: 32870829
DOI: 10.1364/OL.398868 -
The Journal of Neuroscience : the... Aug 2021Epigenetic modifiers are increasingly being investigated as potential therapeutics to modify and overcome disease phenotypes. Diseases of the nervous system present a...
Epigenetic modifiers are increasingly being investigated as potential therapeutics to modify and overcome disease phenotypes. Diseases of the nervous system present a particular problem as neurons are postmitotic and demonstrate relatively stable gene expression patterns and chromatin organization. We have explored the ability of epigenetic modifiers to prevent degeneration of rod photoreceptors in a mouse model of retinitis pigmentosa (RP), using rd10 mice of both sexes. The histone modification eraser enzymes lysine demethylase 1 (LSD1) and histone deacetylase 1 (HDAC1) are known to have dramatic effects on the development of rod photoreceptors. In the RP mouse model, inhibitors of these enzymes blocked rod degeneration, preserved vision, and affected the expression of multiple genes including maintenance of rod-specific transcripts and downregulation of those involved in inflammation, gliosis, and cell death. The neuroprotective activity of LSD1 inhibitors includes two pathways. First, through targeting histone modifications, they increase accessibility of chromatin and upregulate neuroprotective genes, such as from the Wnt pathway. We propose that this process is going in rod photoreceptors. Second, through nonhistone targets, they inhibit transcription of inflammatory genes and inflammation. This process is going in microglia, and lack of inflammation keeps rod photoreceptors alive. Retinal degenerations are a leading cause of vision loss. RP is genetically very heterogeneous, and the multiple pathways leading to cell death are one reason for the slow progress in identifying suitable treatments for patients. Here we demonstrate that inhibition of LSD1and HDAC1 in a mouse model of RP leads to preservation of rod photoreceptors and visual function, retaining of expression of rod-specific genes, and with decreased inflammation, cell death, and Müller cell gliosis. We propose that these epigenetic inhibitors cause more open and accessible chromatin, allowing expression of neuroprotective genes. A second mechanism that allows rod photoreceptor survival is suppression of inflammation by epigenetic inhibitors in microglia. Manipulation of epigenetic modifiers is a new strategy to fight neurodegeneration in RP.
Topics: Animals; Cell Death; Disease Models, Animal; Epigenesis, Genetic; Female; Histone Deacetylase 1; Histone Deacetylase Inhibitors; Histone Demethylases; Male; Mice; Mice, Inbred C57BL; Nerve Degeneration; Retinal Rod Photoreceptor Cells; Retinitis Pigmentosa; Tranylcypromine
PubMed: 34193554
DOI: 10.1523/JNEUROSCI.3102-20.2021 -
Ophthalmology Sep 2019
Topics: Genetic Therapy; Humans; Mutation; Retinal Cone Photoreceptor Cells; Retinal Dystrophies; Retinal Rod Photoreceptor Cells
PubMed: 31443790
DOI: 10.1016/j.ophtha.2019.03.007 -
The Journal of Neuroscience : the... Apr 2022Deactivation of G-protein-coupled receptors (GPCRs) involves multiple phosphorylations followed by arrestin binding, which uncouples the GPCR from G-protein activation....
Deactivation of G-protein-coupled receptors (GPCRs) involves multiple phosphorylations followed by arrestin binding, which uncouples the GPCR from G-protein activation. Some GPCRs, such as rhodopsin, are reused many times. Arrestin dissociation and GPCR dephosphorylation are key steps in the recycling process. evidence suggests that visual arrestin (ARR1) binding to light-activated, phosphorylated rhodopsin hinders dephosphorylation. Whether ARR1 binding also affects rhodopsin dephosphorylation is not known. We investigated this using both male and female mice lacking ARR1. Mice were exposed to bright light and placed in darkness for different periods of time, and differently phosphorylated species of rhodopsin were assayed by isoelectric focusing. For WT mice, rhodopsin dephosphorylation was nearly complete by 1 h in darkness. Surprisingly, we observed that, in the KO rods, rhodopsin remained phosphorylated even after 3 h. Delayed dephosphorylation in KO rods cannot be explained by cell stress induced by persistent signaling, since it is not prevented by the removal of transducin, the visual G-protein, nor can it be explained by downregulation of protein phosphatase 2A, the putative rhodopsin phosphatase. We further show that cone arrestin (ARR4), which binds light-activated, phosphorylated rhodopsin poorly, had little effect in enhancing rhodopsin dephosphorylation, whereas mice expressing binding-competent mutant ARR1-3A showed a similar time course of rhodopsin dephosphorylation as WT. Together, these results reveal a novel role of ARR1 in facilitating rhodopsin dephosphorylation G-protein-coupled receptors (GPCRs) are transmembrane proteins used by cells to receive and respond to a broad range of extracellular signals that include neurotransmitters, hormones, odorants, and light (photons). GPCR signaling is terminated by two sequential steps: phosphorylation and arrestin binding. Both steps must be reversed when GPCRs are recycled and reused. Dephosphorylation, which is required for recycling, is an understudied process. Using rhodopsin as a prototypical GPCR, we discovered that arrestin facilitated rhodopsin dephosphorylation in living mice.
Topics: Animals; Arrestin; Female; GTP-Binding Proteins; Male; Mice; Phosphorylation; Retinal Rod Photoreceptor Cells; Rhodopsin
PubMed: 35332081
DOI: 10.1523/JNEUROSCI.0141-22.2022