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Inherited retinal dystrophies (iRDs) are a group of genetically and clinically heterogeneous conditions resulting from mutations in over 250 genes. Here, homozygosity mapping and whole-exome sequencing (WES) in a consanguineous family revealed a homozygous missense mutation, c.973C>T (p.His325Tyr), in RCBTB1. In affected individuals, it was found to segregate with retinitis pigmentosa (RP), goiter, primary ovarian insufficiency, and mild intellectual disability. Subsequent analysis of WES data in different cohorts uncovered four additional homozygous missense mutations in five unrelated families in whom iRD segregates with or without syndromic features. Ocular phenotypes ranged from typical RP starting in the second decade to chorioretinal dystrophy with a later age of onset. The five missense mutations affect highly conserved residues either in the sixth repeat of the RCC1 domain or in the BTB1 domain. A founder haplotype was identified for mutation c.919G>A (p.Val307Met), occurring in two families of Mediterranean origin. We showed ubiquitous mRNA expression of RCBTB1 and demonstrated predominant RCBTB1 localization in human inner retina. RCBTB1 was very recently shown to be involved in ubiquitination, more specifically as a CUL3 substrate adaptor. Therefore, the effect on different components of the CUL3 and NFE2L2 (NRF2) pathway was assessed in affected individuals’ lymphocytes, revealing decreased mRNA expression of NFE2L2 and several NFE2L2 target genes. In conclusion, our study puts forward mutations in RCBTB1 as a cause of autosomal-recessive non-syndromic and syndromic iRD. Finally, our data support a role for impaired ubiquitination in the pathogenetic mechanism of RCBTB1 mutations., SCOPUS: ar.j, info:eu-repo/semantics/published

Wolfram syndrome 1 (WFS1, OMIM 222300), a rare genetic disorder characterized by optic nerve atrophy, deafness, diabetes insipidus and diabetes mellitus, is caused by mutations of WFS1, encoding WFS1/wolframin. Non-syndromic WFS1 variants are associated with the risk of diabetes mellitus due to altered function of wolframin in pancreatic islet cells, expanding the importance of wolframin. This study extends a previous report for the monkey retina, using immunohistochemistry to localize wolframin on cryostat and paraffin sections of human retina. In addition, the human retinal pigment epithelial (RPE) cell line termed ARPE-19 and retinas from both pigmented and albino mice were studied to assess wolframin localization. In the human retina, wolframin was expressed in retinal ganglion cells, optic axons and the proximal optic nerve. Wolframin expression in the human retinal pigment epithelium (RPE) was confirmed with intense cytoplasmic labeling in ARPE-19 cells. Strong labeling of the RPE was also found in the albino mouse retina. Cryostat sections of the mouse retina showed a more extended pattern of wolframin labeling, including the inner nuclear layer (INL) and photoreceptor inner segments, confirming the recent report of Kawano et al. [Kawano, J., Tanizawa, Y., Shinoda, K., 2008. Wolfram syndrome 1 (Wfs1) gene expression in the normal mouse visual system. J. Comp. Neurol. 510, 1-23]. Absence of these cells in the human specimens despite the use of human-specific antibodies to wolframin may be related to delayed fixation. Loss of wolframin function in RGCs and the unmyelinated portion of retinal axons could explain optic nerve atrophy in Wolfram Syndrome 1.

BACKGROUND: Glucose is the most important metabolic substrate of the retina and maintenance of normoglycemia is an essential challenge for diabetic patients. Glycemic excursions could lead to cardiovascular disease, nephropathy, neuropathy and retinopathy. A vast body of literature exists on hyperglycemia namely in the field of diabetic retinopathy, but very little is known about the deleterious effect of hypoglycemia. Therefore, we decided to study the role of acute hypoglycemia in mouse retina. METHODOLOGY/PRINCIPAL FINDINGS: To test effects of hypoglycemia, we performed a 5-hour hyperinsulinemic/hypoglycemic clamp; to exclude an effect of insulin, we made a hyperinsulinemic/euglycemic clamp as control. We then isolated retinas from each group at different time-points after the clamp to analyze cells apoptosis and genes regulation. In parallel, we used 661W photoreceptor cells to confirm in vivo results. We showed herein that hypoglycemia induced retinal cell death in mouse via caspase 3 activation. We then tested the mRNA expression of glutathione transferase omega 1 (Gsto1) and glutathione peroxidase 3 (Gpx3), two genes involved in glutathione (GSH) homeostasis. The expression of both genes was up-regulated by low glucose, leading to a decrease of reduced glutathione (GSH). In vitro experiments confirmed the low-glucose induction of 661W cell death via superoxide production and activation of caspase 3, which was concomitant with a decrease of GSH content. Moreover, decrease of GSH content by inhibition with buthionine sulphoximine (BSO) at high glucose induced apoptosis, while complementation with extracellular glutathione ethyl ester (GSHee) at low glucose restored GSH level and reduced apoptosis. CONCLUSIONS/SIGNIFICANCE: We showed, for the first time, that acute insulin-induced hypoglycemia leads to caspase 3-dependant retinal cell death with a predominant role of GSH content.