cyclic-gmp and Retinal-Diseases

Tightly regulated control of cGMP levels is critical for proper functioning of photoreceptors, and mutations in cGMP synthesis or degradation factors can lead to various forms of retinal disorder. Here we review heterogenous human retinal disorders associated with mutant retinal guanylate cyclases (RetGCs) and phosphodiesterase 6 (PDE6), and describe how zebrafish are being used to examine phototransduction components and their roles in these diseases. Though mutations in RetGCs and PDE6 lead to retinal disorders, there is a lack of molecular and biochemical data on routes of subsequent photoreceptor degeneration and visual impairment. Use of animal model systems provides important information to connect in vitro biochemical analyses of mutant genes with clinically observed pathologies of human retinal diseases. Zebrafish are an excellent in vivo system to generate animal models of human retinal disorders and study photoreceptor components, and have already provided valuable data on retinal diseases caused by phototransduction component mutations.

Topics: 3',5'-Cyclic-GMP Phosphodiesterases; Animals; Cyclic GMP; Guanylate Cyclase; Humans; Photoreceptor Cells, Vertebrate; Retinal Diseases; Zebrafish

Progressive visual impairment leading to blindness is often associated with inherited retinal dystrophies. These disorders correlate in most cases with mutations in genes that code for proteins of the visual transduction system in rod and cone photoreceptor cells. Recent progress has highlighted the involvement of a neuronal calcium sensor protein that is specifically expressed in rod and cone cells and operates as a guanylate cyclase-activating protein (GCAP). A group of patients suffering from cone or cone-rod dystrophies carry mutations in the GCAP1 gene, and biochemical analysis of GCAP1 function revealed that for most of these mutations GCAP1 exhibits a disturbance in its Ca(2+)-sensing and its guanylate cyclase-activating properties. Cellular consequences of different GCAP1 mutations are compared and discussed.

Topics: Animals; Corneal Dystrophies, Hereditary; Cyclic GMP; Guanylate Cyclase-Activating Proteins; Humans; Light Signal Transduction; Models, Biological; Retinal Diseases

Calcium feedback in vertebrate photoreceptors regulates synthesis of cGMP, a second messenger in phototransduction. The decrease in the free intracellular Ca(2+) concentrations caused by illumination stimulates two isoforms of retinal membrane guanylyl cyclase (RetGC) via Ca(2+)-sensor proteins and thus contributes to photoreceptor recovery and light adaptation. Unlike other members of the membrane guanylyl cyclase family, retinal guanylyl cyclases do not have identified extracellular peptide ligands. Recoverin-like proteins, GCAP-1 and GCAP-2, interact with the intracellular portion of the cyclases and stimulate its activity through dimerization of the cyclase subunits. Several mutations that affect the function of photoreceptor guanylyl cyclase and the activator protein have been linked to various forms of congenital human retinal diseases, such as Leber congenital amaurosis, cone and cone-rod dystrophy.

Topics: Adaptation, Physiological; Animals; Calcium; Calcium-Binding Proteins; Cyclic GMP; Dimerization; Guanylate Cyclase; Guanylate Cyclase-Activating Proteins; Humans; Light; Models, Molecular; Photoreceptor Cells; Receptors, Cell Surface; Retinal Diseases; Signal Transduction; Vision, Ocular

Nitric oxide synthase (NOS), the enzyme that catalyzes the formation of nitric oxide from L-arginine, exists in three major isoforms, neuronal, endothelial, and immunologic. Neuronal and endothelial isoforms are constitutively expressed, and require calcium for activation. Both of these isoforms can be induced (i.e., new protein synthesis occurs) under appropriate conditions. The immunologic isoform is not constitutively expressed, and requires induction usually by immunologic activation; calcium is not necessary for its activation. Neuronal and immunologic NOS have been detected in the retina. Neuronal NOS may be responsible for producing nitric oxide in photoreceptors and bipolar cells. Nitric oxide stimulates guanylate cyclase of photoreceptor rod cells and increases calcium channel currents. In the retina of cats, NOS inhibition impairs phototransduction as assessed by the electroretinogram. Inducible nitric oxide synthase, found in Müller cells and in retinal pigment epithelium, may be involved in normal phagocytosis of the retinal outer segment, in infectious and ischemic processes, and in the pathogenesis of diabetic retinopathy. Nitric oxide contributes to basal tone in the retinal circulation. To date, findings are conflicting with respect to its role in retinal autoregulation. During glucose and oxygen deprivation, nitric oxide may increase blood flow and prevent platelet aggregation, but it may also mediate the toxic effects of excitatory amino acid release. This reactive, short-lived gas is involved in diverse processes within the retina, and its significance continues to be actively studied.

Topics: Animals; Choroid; Cyclic GMP; Cytokines; Humans; Hyperemia; Ischemia; Nitric Oxide; Nitric Oxide Synthase; Photoreceptor Cells; Pigment Epithelium of Eye; Rabbits; Rats; Retina; Retinal Diseases; Retinal Vessels; Vision, Ocular

Over the past two decades there has been an explosive growth in our understanding of phototransduction, leading to the development of a comprehensive scheme for the process. On the basis of this scheme the finer details of the process are being elucidated. Additional protein components and pathways have been identified, successful quantitative models of parts of the process have been developed, and a detailed understanding of the molecular basis of physiological function has begun to emerge. Here we summarize the most recent developments.

Topics: Animals; Calcium; Cyclic GMP; Feedback; Humans; Models, Neurological; Retinal Cone Photoreceptor Cells; Retinal Diseases; Rod Cell Outer Segment; Signal Transduction

Topics: Adenylyl Cyclases; Animals; Anura; Calcium; Cattle; Cell Membrane; Cyclic AMP; Cyclic GMP; Disease Models, Animal; Enzyme Activation; GTP Phosphohydrolases; Phosphoric Diester Hydrolases; Photic Stimulation; Photoreceptor Cells; Retinal Diseases; Rhodopsin; Vision, Ocular

Nitric oxide (NO) acts as essential regulator of vasculogenesis and angiogenesis and is critical for arteriogenesis. Whether NO's effects in vivo are mediated through NO-sensitive guanylyl cyclase (NO-GC) and thus by cGMP-dependent mechanisms has been only poorly addressed. Mice lacking NO-GC globally or specifically in smooth muscle cells (SMC) or endothelial cells (EC) were subjected to two established models for arteriogenesis and angiogenesis, namely hindlimb ischemia and oxygen-induced retinopathy. Our data clearly show the involvement of NO-GC in the recovery of blood flow after hindlimb ischemia, and this effect could be attributed to NO-GC in SMC. In the retina, global deletion of NO-GC led to reduced oxygen-induced vessel loss and hypoxia-induced capillary regrowth, whereas pathological neovascularization was increased. These effects were also seen in mice with SMC-specific NO-GC deletion but not in animals lacking NO-GC in EC. Intriguingly, NO-GC was found to be strongly expressed in retinal pericytes. Our data prove the involvement of NO-GC in growth and plasticity of hindlimb and retinal vasculature after ischemic/hypoxic insult.

Topics: Animals; Cyclic GMP; Endothelial Cells; Exons; Guanylate Cyclase; Hindlimb; Hypoxia; Image Processing, Computer-Assisted; Immunohistochemistry; Ischemia; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; Myocytes, Smooth Muscle; Neovascularization, Pathologic; Nitric Oxide; Oxygen; Pericytes; Receptors, Cytoplasmic and Nuclear; Retina; Retinal Diseases; Signal Transduction; Soluble Guanylyl Cyclase; Time Factors

To investigate whether nitric oxide (NO) and/or cGMP protects the retina from chemical ischemia and underlie somatostatin's neuroprotective effects.. Eyecups of female Sprague-Dawley rats were incubated with PBS or the chemical ischemia mixture [iodoacetic acid (5 mM)/sodium cyanate (25 mM)] in the absence or presence of (1) arginine (0.05-2.0 mM), the substrate of nitric oxide synthase (NOS); (2) the NO donors sodium nitroprusside (SNP; 0.25-4.0 mM), 3-morpholinosydnonimine (SIN-1; 0.1, 0.3, 1.0 mM), SIN-1 (0.1 mM)/L-cysteine (5 mM, peroxynitrite scavenger), and NONOate (1, 5, 10 microM, slow NO releaser); (3) 8-Br-cGMP (0.1, 0.5, 1.0 mM); (4) BIM23014 (sst(2) receptor agonist; 1 microM), alone or in the presence of (5) the NOS inhibitor N(gamma)-monomethyl-L-arginine (NMMA; 0.5 mM); or (6) the guanylyl cyclase inhibitors 1H-[1,2,4]oxadiazolol [4,3-a]quinoxalin-1-one (ODQ;100 microM) and NS2028 (50 microM) for 60 minutes, at 5%CO(2)/air in 37 degrees C. The effect of SIN-1 (0.1, 0.3, 1.0, or 3.0 mM) on the retina was also examined. Subsequently, the eyecups were fixed and sectioned for choline acetyltransferase (ChAT) immunoreactivity and TUNEL staining.. Arginine and SNP had no effect on the chemical ischemia-induced toxicity. SIN-1, NONOate, and 8-Br-cGMP produced a concentration-dependent protective effect, as shown by ChAT immunoreactivity. TUNEL staining also confirmed the neuroprotective effect of these agents. L-cysteine partially reduced the SIN-1-induced protective effect. SIN-1 alone was toxic only at the highest concentration used (3 mM). NMMA, ODQ, and NS2028 reversed the protective effect of BIM23014.. The results suggest that a NO/peroxynitrite/cGMP mechanism may be important in the protection of the retina from ischemic insult. Furthermore, the NO/sGC/cGMP pathway is involved in the neuroprotective effects of sst(2) ligands against retinal ischemia.

Topics: Animals; Choline O-Acetyltransferase; Cyclic GMP; Dose-Response Relationship, Drug; Enzyme Inhibitors; Female; Fluorescent Antibody Technique, Indirect; In Situ Nick-End Labeling; Ischemia; Molsidomine; Nitric Oxide; Peptides, Cyclic; Rats; Rats, Sprague-Dawley; Retinal Diseases; Retinal Vessels; Somatostatin; Spermine

Absorption of light by visual pigments initiates the phototransduction pathway that results in degradation of the intracellular pool of cyclic-GMP (cGMP). This hydrolysis promotes the closing of cGMP-gated cation channels and consequent hyperpolarization of rod and cone photoreceptor cell membranes. Guanylate cyclase-activating proteins (GCAPs) are a family of proteins that regulate retinal guanylate cyclase (GC) activity in a Ca2+-dependent manner. At high [Ca2+], typical of the dark-adapted state (approximately 500 nM), GCAPs inhibit retinal GCs. At the low [Ca2+] (approximately 50 nM) that occurs after the closing of cGMP-gated channels, GCAPs activate retinal GCs to replenish dark-state cGMP levels. Here, we report the crystal structure of unmyristoylated human GCAP3 with Ca2+ bound. GCAP3 is an EF-hand Ca2+-binding protein with Ca2+ bound to EF2, 3 and 4, while Ca2+ binding to EF-hand 1 is disabled. GCAP3 contains two domains with the EF-hand motifs arranged in a tandem array similar to GCAP2 and members of the recoverin subfamily of Ca2+-binding proteins. Residues not involved in Ca2+ binding, but conserved in all GCAPs, cluster around EF1 in the N-terminal domain and may represent the interface with GCs. Five point mutations in the closely related GCAP1 have been linked to the etiology of cone dystrophies. These residues are conserved in GCAP3 and the structure suggests important roles for these amino acids. We present a homology model of GCAP1 based on GCAP3 that offers insight into the molecular mechanism underlying the autosomal dominant cone dystrophies produced by GCAP1 mutations.

Topics: Calcium; Crystallography, X-Ray; Cyclic GMP; Guanylate Cyclase; Guanylate Cyclase-Activating Proteins; Humans; Models, Molecular; Molecular Sequence Data; Protein Structure, Tertiary; Retinal Cone Photoreceptor Cells; Retinal Diseases

The effects of 3 fixatives (formalin, Bouin's solution and glutaraldehyde-paraformaldehyde) on retinal cyclic AMP and GMP content were determined in canine eyes with a known abnormality of cyclic GMP metabolism. Cyclic nucleotides were measured by radioimmunoassay on perchloric acid (PCA)-precipitated retinal samples from fixed (left) and unfixed (right) eyes from nine 6-week-old rod-cone-dysplasia-affected Irish setter dogs. Cyclic AMP values were significantly lower for fixed retinas than for unfixed controls. Retinal cyclic GMP values were also lower from glutaraldehyde-paraformaldehyde-fixed samples, but were not different from control values for formalin- or Bouin's-fixed eyes, when the retina was PCA-precipitated promptly after fixation.

Topics: Animals; Cyclic AMP; Cyclic GMP; Dogs; Fixatives; Histological Techniques; Photoreceptor Cells; Retinal Diseases

Two patients had bull's-eye maculopathy, negative electroretinograms and low level of plasma cyclic guanosine monophosphate. In these cases, single bright-flash electroretinograms were of a negative type and scotopic electroretinograms were reduced in amplitude, whereas photopic electroretinograms were normal or only slightly reduced in amplitude. The negative electroretinograms were considered to result from extensive abnormalities in the inner retinal layer or an abnormal cyclic guanosine monophosphate metabolism in the photoreceptor cells.

Topics: Adult; Cyclic GMP; Dark Adaptation; Electrooculography; Electroretinography; Fluorescein Angiography; Fundus Oculi; Humans; Macula Lutea; Male; Photic Stimulation; Retinal Diseases; Visual Acuity; Visual Fields

Topics: Animals; Cat Diseases; Cats; Cyclic GMP; Electroretinography; Genes, Dominant; Homeostasis; Photoreceptor Cells; Retina; Retinal Diseases; Taurine

Topics: Animals; Cyclic AMP; Cyclic GMP; Dogs; Mice; Mice, Inbred C3H; Photoreceptor Cells; Rats; Rats, Inbred Strains; Retinal Diseases; Vision Disorders

Topics: Animals; Cyclic AMP; Cyclic GMP; Darkness; Genes, Recessive; Heterozygote; Light; Mice; Mice, Inbred Strains; Photoreceptor Cells; Retina; Retinal Diseases