A key role for cyclic nucleotide gated (CNG) channels in cGMP-related retinitis pigmentosa.

The rd1 natural mutant is one of the first and probably the most commonly studied mouse model for retinitis pigmentosa (RP), a severe and frequently blinding human retinal degeneration. In several decades of research, the link between the increase in photoreceptor cGMP levels and the extremely rapid cell death gave rise to a number of hypotheses. Here, we provide clear evidence that the presence of cyclic nucleotide gated (CNG) channels in the outer segment membrane is the key to rod photoreceptor loss. In Cngb1(-/-) × rd1 double mutants devoid of regular CNG channels, cGMP levels are still pathologically high, but rod photoreceptor viability and outer segment morphology are greatly improved. Importantly, cone photoreceptors, the basis for high-resolution daylight and colour vision, survived and remained functional for extended periods of time. These findings strongly support the hypothesis of deleterious calcium (Ca(2+))-influx as the cause of rapid rod cell death and highlight the importance of CNG channels in this process. Furthermore, our findings suggest that targeting rod CNG channels, rather than general Ca(2+)-channel blockade, is a most promising symptomatic approach to treat otherwise incurable forms of cGMP-related RP.

ARMS2 is a constituent of the extracellular matrix providing a link between familial and sporadic age-related macular degenerations.

PURPOSE: SNPs in chromosomal region 10q26 harboring PLEKHA1, ARMS2, and Htra1 showed the strongest association with age-related macular degeneration. Recent evidence suggests that in patients homozygous for the risk allele, the lack of synthesis of the poorly characterized ARMS2 is causative of this disorder. The present study was undertaken to gain an understanding of the genuine (patho)physiological role of this protein. METHODS: ARMS2-interacting proteins were identified by using a yeast two-hybrid system and validated by coprecipitation. Immunofluorescence was applied to reveal the localization of ARMS2 in transfected cells and in human eyes. Western blot analyses were performed on extra- and intracellular fractions of ARMS2-expressing cells to demonstrate the secretion of ARMS2. RESULTS: Contrary to previous reports, this study showed that ARMS2 is a secreted protein that binds several matrix proteins. Notably, ARMS2 directly interacts with fibulin-6 (hemicentin-1). Mutations in the fibulin-6 gene have been demonstrated to cause familial AMD. ARMS2 also interacts with further extracellular proteins, several of which have been implicated in macular dystrophies. Although ARMS2 apparently lacks any classic targeting sequence, it is translocated to the endoplasmic reticulum in cultured cells before secretion. ARMS2 is mostly confined to choroid pillars in human eyes, representing a part of extracellular matrix and corresponding to the principal sites of drusen formation. CONCLUSIONS: The pivotal role of the extracellular matrix in the progression of AMD is underlined by the abnormal deposition of extracellular debris in the macula, observed frequently in affected individuals. The results have shown that ARMS2 may be necessary for proper matrix function.

STAT6 as an asthma candidate gene: polymorphism-screening, association and haplotype analysis in a Caucasian sib-pair study.

The human signal transducer and activator of transcription 6 (STAT6) gene represents one of the most promising candidate genes for asthma and other inflammatory diseases on the chromosomal region 12q13-q24. Therefore we screened all 23 exons, including parts of the neighbouring introns, as well as the promoter region for common polymorphisms and tested them for linkage/association with asthma and related traits (total serum IgE level, eosinophil cell count and SLOPE of the dose-response curve after bronchial challenge) in a Caucasian sib-pair study (108 families with at least two affected children). We could identify 13 single nucleotide polymorphisms (SNPs), which are all non-coding. A recently described dinucleotide (GT) repeat in exon 1 was also examined. Besides the confirmation of the four alleles described elsewhere we could identify a new one, named allele A5. Neither the SNPs nor the GT repeat showed linkage/association to asthma. Two intronic SNPs and one SNP in the 3'untranslated region of the gene showed weak association to total IgE levels (P = 0.0200, 0.0260 and 0.0280, respectively), whereas a significant association was found between a SNP in intron 18 and an increase in total IgE levels (P = 0.0070). However, the most promising effect was seen between allele A4 of the GT repeat polymorphism and an increase in eosinophil cell count (P = 0.0010). From these findings we conclude that the human STAT6 gene is rather involved in the development of eosinophilia and changes in total IgE levels than contributing to the pathogenesis of asthma.