The protein neural retina leucine zipper (Nrl) is a basic motif-leucine zipper transcription factor that is preferentially expressed in rod photoreceptors. It acts synergistically with Crx to regulate rhodopsin transcription. Missense mutations in human NRL have been associated with autosomal dominant retinitis pigmentosa. Here we report that deletion of Nrl in mice results in the complete loss of rod function and super-normal cone function, mediated by S cones. The photoreceptors in the Nrl-/- retina have cone-like nuclear morphology and short, sparse outer segments with abnormal disks. Analysis of retinal gene expression confirms the apparent functional transformation of rods into S cones in the Nrl-/- retina. On the basis of these findings, we postulate that Nrl acts as a 'molecular switch' during rod-cell development by directly modulating rod-specific genes while simultaneously inhibiting the S-cone pathway through the activation of Nr2e3.

Neurotrophic factors are agents with a promising ability to retard progression of neurodegenerative diseases and are effective in slowing photoreceptor degeneration in animal models of retinitis pigmentosa. Here we report a human clinical trial of a neurotrophic factor for retinal neurodegeneration. In this Phase I safety trial, human ciliary neurotrophic factor (CNTF) was delivered by cells transfected with the human CNTF gene and sequestered within capsules that were surgically implanted into the vitreous of the eye. The outer membrane of the encapsulated cell implant is semipermeable to allow CNTF to reach the retina. Ten participants received CNTF implants in one eye. When the implants were removed after 6 months, they contained viable cells with minimal cell loss and gave CNTF output at levels previously shown to be therapeutic for retinal degeneration in rcd1 dogs. Although the trial was not powered to form a judgment as to clinical efficacy, of seven eyes for which visual acuity could be tracked by conventional reading charts, three eyes reached and maintained improved acuities of 10 -15 letters, equivalent to two-to three-line improvement on standard Snellen acuity charts. A surgically related choroidal detachment in one eye resulted in a transient acuity decrease that resolved with conservative management. This Phase I trial indicated that CNTF is safe for the human retina even with severely compromised photoreceptors. The approach to delivering therapeutic proteins to degenerating retinas using encapsulated cell implants may have application beyond disease caused by genetic mutations.clinical trial ͉ neurodegeneration ͉ retinitis pigmentosa ͉ photoreceptor ͉ macular degeneration R etinitis pigmentosa (RP) describes a set of neurodegenerative retinal diseases that cause the death of photoreceptor cells and lead to progressive vision loss and blindness. More than 39 genetic loci and genes have been implicated in monogenic forms of RP (1), underscoring the complexity of its pathogenic mechanisms. With the exception of vitamin A nutritional supplementation (2), no treatments have been shown to be effective across the range of these disorders. Regardless of the initial causative genetic defect, the end result is photoreceptor cell death. The multiplicity of mechanisms stimulated a search for therapeutic agents that are effective in slowing photoreceptor death regardless of the causative genetic mutation.Intervention studies have indicated the possibility of using neurotrophic factors as therapeutic agents for RP (3). Specifically, ciliary neurotrophic factor (CNTF) is effective at retarding retinal degeneration in at least 13 animal RP models, including rd-PDE6b mice (4, 5), rds-peripherin mice (4, 6-10), transgenic rats expressing P23H or S334ter mutant rhodopsin (7, 10), Rdy cats (11), rcd1-PDE6b dogs (7), rhodopsin-knockout mice (9), and rd͞rd mice, nr͞nr mice, and Q334ter rhodopsin transgenic mice (4).CNTF also appears effective for retarding cellular and functional losses in neurodegenerative diseases ...

Stargardt-like macular dystrophy (STGD3, MIM 600110) and autosomal dominant macular dystrophy (adMD) are inherited forms of macular degeneration characterized by decreased visual acuity, macular atrophy and extensive fundus flecks. Genetic mapping data suggest that mutations in a single gene may be responsible for both conditions, already known to bear clinical resemblance. Here we limit the minimum genetic region for STGD3 and adMD to a 0.6-cM interval by recombination breakpoint mapping and identify a single 5-bp deletion within the protein-coding region of a new retinal photoreceptor-specific gene, ELOVL4, in all affected members of STGD3 and adMD families. Bioinformatic analysis of ELOVL4 revealed that it has homology to a group of yeast proteins that function in the biosynthesis of very long chain fatty acids. Our results are therefore the first to implicate the biosynthesis of fatty acids in the pathogenesis of inherited macular degeneration.

Existing models of the primate photopic electroretinogram (ERG) attribute the light-adapted b–wave to activity of depolarizing bipolar cells (DBCs), mediated through a release of potassium that is monitored by Müller cells. However, possible ERG contributions from OFF-bipolar cells (HBCs) and horizontal cells (HzCs) have not been explored. We examined the contribution of these hyperpolarizing second-order retinal cells to the photopic ERG of monkey by applying glutamate analogs to suppress photoreceptor transmission selectively to HBC/HzCs vs. DBCs.ERGs of Macaca monkeys were recorded at the cornea before and after intravitreal injection of drugs. Photopic responses were elicited by bright 200–220 ms flashes on a steady background of 3.3 log scotopic troland to suppress rod ERG components.2–amino-4–phosphonobutyric acid (APB), which blocks DBC light responses, abolished the photopic b–wave and indicated that DBC activity is requisite for photopic b–wave production.However, applying cis–2,3–piperidine dicarboxylic acid (PDA) and kynurenic acid (KYN), to suppress HBCs/HzCs and third-order neurons, revealed a novel ERG response that was entirely positive and was sustained for the duration of the flash. The normally phasic b–wave was subsumed into this new response. Applying n–methyl-dl-aspartate (NMA) did not replicate the PDA+KYN effect, indicating that third-order retinal cells are not involved. This suggests that HBC/HzC activity is critical for shaping the phasic b–wave.Components attributable to depolarizing vs. hyperpolarizing cells were separated by subtracting waveforms after each drug from responses immediately before. This analysis indicated that DBCs and HBC/HzCs each can produce large but opposing field potentials that nearly cancel and that normally leave only the residual phasic b–wave response in the photopic ERG.Latency of the DBC component was 5–9 ms slower than the HBC/HzC component. However, once activated, the DBC component had a steeper slope. This resembles properties known for the two types of cone synapses in lower species, in which the sign-preserving HBC/HzC synapse has faster kinetics but probably lower gain than the slower sign-inverting G-protein coupled DBC synapse.A human patient with “unilateral cone dystrophy” was found to have a positive and sustained ERG that mimicked the monkey ERG after PDA+KYN, indicating that these novel positive photopic responses can occur naturally even without drug application.These results demonstrate that hyperpolarizing second-order neurons are important for the primate photopic ERG. A “Push-Pull Model” is proposed in which DBC activity is requisite for b–wave production but in which HBC/HzC activity limits the amplitude and controls the shape of the primate photopic b–wave.

Recessive splice site and nonsense mutations of PCDH15, encoding protocadherin 15, are known to cause deafness and retinitis pigmentosa in Usher syndrome type 1F (USH1F). Here we report that non-syndromic recessive hearing loss (DFNB23) is caused by missense mutations of PCDH15. This suggests a genotype-phenotype correlation in which hypomorphic alleles cause non-syndromic hearing loss, while more severe mutations of this gene result in USH1F. We localized protocadherin 15 to inner ear hair cell stereocilia, and to retinal photoreceptors by immunocytochemistry. Our results further strengthen the importance of protocadherin 15 in the morphogenesis and cohesion of stereocilia bundles and retinal photoreceptor cell maintenance or function.

X-linked retinitis pigmentosa (XLRP) is a clinically and genetically heterogeneous degenerative disease of the retina. At least five loci have been mapped for XLRP; of these, RP2 and RP3 account for 10%-20% and 70%-90% of genetically identifiable disease, respectively. However, mutations in the respective genes, RP2 and RPGR, were detected in only 10% and 20% of families with XLRP. Mutations in an alternatively spliced RPGR exon, ORF15, have recently been shown to account for 60% of XLRP in a European cohort of 47 families. We have performed, in a North American cohort of 234 families with RP, a comprehensive screen of the RP2 and RPGR (including ORF15) genes and their 5' upstream regions. Of these families, 91 (39%) show definitive X-linked inheritance, an additional 88 (38%) reveal a pattern consistent with X-linked disease, and the remaining 55 (23%) are simplex male patients with RP who had an early onset and/or severe disease. In agreement with the previous studies, we show that mutations in the RP2 gene and in the original 19 RPGR exons are detected in <10% and approximately 20% of XLRP probands, respectively. Our studies have revealed RPGR-ORF15 mutations in an additional 30% of 91 well-documented families with X-linked recessive inheritance and in 22% of the total 234 probands analyzed. We suggest that mutations in an as-yet-uncharacterized RPGR exon(s), intronic changes, or another gene in the region might be responsible for the disease in the remainder of this North American cohort. We also discuss the implications of our studies for genetic diagnosis, genotype-phenotype correlations, and gene-based therapy.

The RS-KO mouse mimics structural features of human X-linked juvenile retinoschisis with dissection through, and disorganization of, multiple retinal layers. The Rs1h-KO functional deficit results in an electronegative ERG waveform that is characteristic of human retinoschisis disease and that implicates a synaptic transmission deficit in the absence of retinoschisin protein. Replacement therapy by supplementing normal Rs1h protein in the adult Rs1h-KO mouse restored the normal ERG configuration. This indicates that gene therapy is a viable strategy of therapeutic intervention even in the postdevelopmental adult stage of XLRS disease.

A single locus at 11q23 is implicated in a complex ocular phenotype involving RPE and CE, tissues of neuroectodermal origin. All individuals with either LAZ and/or macular degeneration carry the same CTRP5 S163R mutation, which is transmitted in autosomal dominant manner.