11-cis-retinal and Genetic-Diseases--Inborn

Molecules that are incorrectly folded or defectively assembled are recognised by cellular quality control mechanisms. This leads such conformationally abnormal molecules to intracellular retention and eventual degradation. A number of diseases caused by mutations that interfere with proper processing and intracellular trafficking of key cell surface proteins have been described. These include a particular variant of hypogonadotropic hypogonadism, which results from mislocalisation of the gonadotropin-releasing hormone (GnRH) receptor. It has been shown recently that membrane expression and function of misfolded GnRH receptor mutants can be rescued by a peptidomimetic antagonist of GnRH (IN3) that permeates into the cell and reaches the abnormally manufactured nascent receptor, stabilising a conformation compatible with cell-surface transport and reversing intracellular retention. This approach seems applicable for the development of defined therapeutic strategies for an array of diseases caused by incorrectly routed cell surface or secreted proteins.

Topics: Amino Acid Sequence; Amino Acid Substitution; Animals; Aquaporin 2; Cell Membrane; Cystic Fibrosis Transmembrane Conductance Regulator; Drug Design; Drug Resistance; Genes, Recessive; Genetic Diseases, Inborn; Gonadotropin-Releasing Hormone; GTP-Binding Protein alpha Subunits, Gq-G11; Humans; Hypogonadism; Models, Molecular; Molecular Chaperones; Molecular Sequence Data; Mutation, Missense; Point Mutation; Protein Conformation; Protein Folding; Protein Transport; Receptors, Cell Surface; Receptors, LHRH; Rhodopsin; Signal Transduction; Structure-Activity Relationship

The function of the retina is to detect light and to send appropriate signals to the brain in response. Inherited diseases that cause the retina to degenerate, leading to either partial or total blindness, affect approximately 1 in 3000 people. Rapid progress is being made in identifying the genetic causes of common, inherited retinal diseases, such as retinitis pigmentosa and macular degeneration, as well as some of the rare forms of retinal disease. Linkage studies of large families and candidate-gene screening of known retinal genes have already identified 59 independent genetic loci that can cause retinal degeneration. The astounding genetic and clinical heterogeneity that is being revealed is a 'nightmare' for those interested in molecular diagnostics but, at the same time, provides great insight into functional aspects of the normal retina.

Topics: Chromosome Mapping; Genetic Diseases, Inborn; Humans; Models, Biological; Pedigree; Retina; Retinal Degeneration; Rhodopsin

Retinitis Pigmentosa (RP) is a mostly incurable inherited retinal degeneration affecting approximately 1 in 4000 individuals globally. The goal of this work was to identify drugs that can help patients suffering from the disease. To accomplish this, we screened drugs on a zebrafish autosomal dominant RP model. This model expresses a truncated human rhodopsin transgene (Q344X) causing significant rod degeneration by 7 days post-fertilization (dpf). Consequently, the larvae displayed a deficit in visual motor response (VMR) under scotopic condition. The diminished VMR was leveraged to screen an ENZO SCREEN-WELL REDOX library since oxidative stress is postulated to play a role in RP progression. Our screening identified a beta-blocker, carvedilol, that ameliorated the deficient VMR of the RP larvae and increased their rod number. Carvedilol may directly on rods as it affected the adrenergic pathway in the photoreceptor-like human Y79 cell line. Since carvedilol is an FDA-approved drug, our findings suggest that carvedilol can potentially be repurposed to treat autosomal dominant RP patients.

Topics: Animals; Animals, Genetically Modified; Behavior, Animal; Cell Line; Drug Evaluation, Preclinical; Genetic Diseases, Inborn; Humans; Mutation; Retinal Rod Photoreceptor Cells; Retinitis Pigmentosa; Rhodopsin; Transgenes; Vision, Ocular; Zebrafish

The aim of this study was to unravel the molecular pathogenesis of an unusual retinitis pigmentosa (RP) phenotype observed in a Turkish consanguineous family. Homozygosity mapping revealed two candidate genes, SAMD7 and RHO. A homozygous RHO mutation c.448G > A, p.E150K was found in two affected siblings, while no coding SAMD7 mutations were identified. Interestingly, four non-coding homozygous variants were found in two SAMD7 genomic regions relevant for binding of the retinal transcription factor CRX (CRX-bound regions, CBRs) in these affected siblings. Three variants are located in a promoter CBR termed CBR1, while the fourth is located more downstream in CBR2. Transcriptional activity of these variants was assessed by luciferase assays and electroporation of mouse retinal explants with reporter constructs of wild-type and variant SAMD7 CBRs. The combined CBR2/CBR1 variant construct showed significantly decreased SAMD7 reporter activity compared to the wild-type sequence, suggesting a cis-regulatory effect on SAMD7 expression. As Samd7 is a recently identified Crx-regulated transcriptional repressor in retina, we hypothesize that these SAMD7 variants might contribute to the retinal phenotype observed here, characterized by unusual, recognizable pigment deposits, differing from the classic spicular intraretinal pigmentation observed in other individuals homozygous for p.E150K, and typically associated with RP in general.

Topics: Amino Acid Substitution; Animals; Female; Genetic Diseases, Inborn; Homeodomain Proteins; Humans; Male; Mice; Mutation, Missense; Pregnancy; Protein Domains; Response Elements; Retinitis Pigmentosa; Rhodopsin; Trans-Activators; Turkey

Retinol dehydrogenase 12 (RDH12) is an NADP(+)-dependent oxidoreductase that in vitro catalyzes the reduction of all-trans-retinaldehyde to all-trans-retinol or the oxidation of retinol to retinaldehyde depending on substrate and cofactor availability. Recent studies have linked the mutations in RDH12 to severe early-onset autosomal recessive retinal dystrophy. The biochemical basis of photoreceptor cell death caused by mutations in RDH12 is not clear because the physiological role of RDH12 is not yet fully understood. Here we demonstrate that, although bi-directional in vitro, in living cells, RDH12 acts exclusively as a retinaldehyde reductase, shifting the retinoid homeostasis toward the increased levels of retinol and decreased levels of bioactive retinoic acid. The retinaldehyde reductase activity of RDH12 protects the cells from retinaldehyde-induced cell death, especially at high retinaldehyde concentrations, and this protective effect correlates with the lower levels of retinoic acid in RDH12-expressing cells. Disease-associated mutants of RDH12, T49M and I51N, exhibit significant residual activity in vitro, but are unable to control retinoic acid levels in the cells because of their dramatically reduced affinity for NADPH and much lower protein expression levels. These results suggest that RDH12 acts as a regulator of retinoic acid biosynthesis and protects photoreceptors against overproduction of retinoic acid from all-trans-retinaldehyde, which diffuses into the inner segments of photoreceptors from illuminated rhodopsin. These results provide a novel insight into the mechanism of retinal degeneration associated with mutations in RDH12 and are consistent with the observation that RDH12-null mice are highly susceptible to light-induced retinal apoptosis in cone and rod photoreceptors.

Topics: Alcohol Oxidoreductases; Amino Acid Substitution; Animals; Apoptosis; Gene Expression Regulation, Enzymologic; Genetic Diseases, Inborn; Homeostasis; Humans; Light; Macaca mulatta; Mice; Mice, Mutant Strains; Mutation, Missense; NADP; Oxidation-Reduction; Photoreceptor Cells; Retinal Diseases; Retinaldehyde; Rhodopsin; Tretinoin

Night blindness is a frequent concomitant of retinal disorders, many of which are of genetic origin. Through the use of quantitative noninvasive test procedures it has been possible to study patients with these hereditary conditions and to show that the visual abnormalities often result from defects in the functional properties of the rod photoreceptors. More important, the uniqueness of the functional disturbance in the various types of night-blinding disorders suggests that each involves a specific aspect of the rod's internal machinery, i.e., the molecular processes devoted to transduction, intercellular communication, and the renewal of cellular components. Knowledge gained from the study of these clinical entities and from the investigation of experimental animals regarding the cellular events involved in these vital processes have enabled us to formulate tentative hypothesis as to the molecular bases of the hereditary defects.

Topics: Genetic Diseases, Inborn; Horseradish Peroxidase; Humans; Neuromuscular Junction; Neurotransmitter Agents; Night Blindness; Photoreceptor Cells; Retinal Diseases; Retinitis Pigmentosa; Rhodopsin; Synapses; Synaptic Transmission