Norrin mediates neuroprotective effects on retinal ganglion cells via activation of the Wnt/beta-catenin signaling pathway and the induction of neuroprotective growth factors in Muller cells

Noninvasive topical loading for manganese-enhanced MRI of the mouse visual system

PURPOSE

To evaluate topical loading as an alternative to intravitreal injection for Mn(2+)-enhanced magnetic resonance imaging (MEMRI) of the visual system.

METHODS

Topical administration of 0.5 to 1.5 M MnCl(2) and intravitreal injections with 0.5 μL 100 mM and 2 μL 1 M MnCl(2) for mouse MEMRI were conducted, followed by immunohistochemistry. In another mouse group, two topical administrations of 1 M Mn(2+) were applied to the same animals 7 days apart, to evaluate the use of MEMRI in a time course study. Dynamic imaging was also conducted to reveal how Mn(2+) travels to the retina. MEMRI with topically loaded MnCl(2) was also conducted in eyes with retinal ischemia, to evaluate whether the enhancements required healthy neurons.

RESULTS

After 1 day, topical administration of 1 M and 1.5 M MnCl(2) rendered significant signal enhancement (up to 20%) in the superior colliculus (P < 0.05) that was equivalent to that of the 2-μL 1 M injection. Repeated exposure to Mn(2+) showed reproduced enhancement. Dynamic imaging showed significant enhancement in the iris, retina, and lens boundary, but not in the vitreous space. In retinal ischemic eyes, no enhancement of MEMRI was detected in the optic nerves. The immunohistochemistry of the optic nerve (1.5 mm anterior to the chiasm) and retina showed no injury 1 week after Mn(2+) topical administrations to each mouse.

CONCLUSIONS

The results demonstrated the feasibility of using topical administration of Mn(2+) for MEMRI. Topically loaded Mn(2+) did not diffuse into the vitreous space, but was it may have been absorbed into the iris to diffuse or travel via the capillary circulation to reach the retina.

The Wnt signaling pathway protects retinal ganglion cell 5 (RGC-5) cells from elevated pressure

The Wnt pathway is an essential signaling cascade that regulates survival and differentiation in the retina. We recently demonstrated that retinal ganglion cells (RGCs) have constitutively active Wnt signaling in vivo. However, the role of Wnt in RGC viability or function is unknown. In this study, we investigated whether Wnt protects the retinal ganglion cell line RGC-5 from elevated pressure, oxidative stress, and hypoxia injuries. Expression of RGC marker genes in the RGC-5 cultures was confirmed by immunocytochemistry and PCR. We demonstrated that the Wnt3a ligand significantly reduced pressure-induced caspase activity in RGC-5 cells (n = 5, P = 0.03) and decreased the number of TUNEL-positive cells (n = 5, P = 0.0014). Notably, Wnt3a-dependent protection was reversed by the Wnt signaling inhibitor Dkk1. In contrast, Wnt3a did not protect RGC-5 cells from oxidative stress or hypoxia. Furthermore, Wnt3a significantly increased growth factor expression in the presence of elevated pressure but not in the presence of oxidative stress and hypoxia. These results indicate that Wnt3a induces injury-specific survival pathways in RGC-5 cells, potentially by upregulating neuroprotective growth factors. Therefore, activation of the Wnt pathway by Wnt3a could be investigated further as a tool to develop novel molecular therapeutic strategies for the prevention of RGC death in retinal disease.

Retinal vascular disease and the pathogenesis of facioscapulohumeral muscular dystrophy. A signalling message from Wnt?

The peripheral retinal vascular abnormality which accompanies FSHD belongs morphologically and clinically to a class of developmental 'retinal hypovasculopathies' caused by abnormalities of 'Wnt' signalling, which controls retinal angiogenesis. Wnt signalling is also fundamental to myogenesis. This paper integrates modern concepts of myogenic cell signalling and of transcription factor expression and control with data from the classic early ophthalmic and myology embryology literature. Together, they support an hypothesis that abnormalities of Wnt signalling, which activates myogenic programs and transcription factors in myoblasts and satellite cells, leads to defective muscle regeneration in FSHD. The selective vulnerability of different FSHD muscles (notably facial muscle, from the second branchial arch) might reflect patterns of transcription factor redundancies. This hypothesis has implications for FSHD research through study of transcription factors patterning in normal human muscles, and for autologous cell transplantation.

A novel nonsense mutation in the NDP gene in a Chinese family with Norrie disease

PURPOSE

Norrie disease (ND), a rare X-linked recessive disorder, is characterized by congenital blindness and, occasionally, mental retardation and hearing loss. ND is caused by the Norrie Disease Protein gene (NDP), which codes for norrin, a cysteine-rich protein involved in ocular vascular development. Here, we report a novel mutation of NDP that was identified in a Chinese family in which three members displayed typical ND symptoms and other complex phenotypes, such as cerebellar atrophy, motor disorders, and mental disorders.

METHODS

We conducted an extensive clinical examination of the proband and performed a computed tomography (CT) scan of his brain. Additionally, we performed ophthalmic examinations, haplotype analyses, and NDP DNA sequencing for 26 individuals from the proband's extended family.

RESULTS

The proband's computed tomography scan, in which the fifth ventricle could be observed, indicated cerebellar atrophy. Genome scans and haplotype analyses traced the disease to chromosome Xp21.1-p11.22. Mutation screening of the NDP gene identified a novel nonsense mutation, c.343C>T, in this region.

CONCLUSIONS

Although recent research has shown that multiple different mutations can be responsible for the ND phenotype, additional research is needed to understand the mechanism responsible for the diverse phenotypes caused by mutations in the NDP gene.