Die Bedeutung von Dystrophin 71 in Müllerzellen bei vasoproliferativen Netzhauterkrankungen
Zusammenfassung der Projektergebnisse
Duchenne muscular dystrophy patients are prone to develop severe vasoproliferative retinopathy in response to hypoxic episodes suggesting that mutations in the dystrophin gene serve as predisposition for the development of vascular abnormalities under hypoxic pressure. In contrast to other tissues, the retina expresses multiple dystrophin isoforms including Dp427, Dp260 and Dp71. Due to its localization to perivascular Müller cell endfeet Dp71 has been attributed a role in vascular homeostasis in the past. Our research results confirmed that Dp71 is predominantly expressed in perivascular Müller cell endfeet while Dp427 and Dp260 expression can be found in multiple retinal cell types including photoreceptor and bipolar cells. Three mutant mouse strains with different mutations in the dystrophin gene leading to loss of Dp427 (Mdx mice), Dp427 + Dp260 (Mdx-4cv mice) or all dystrophin isoforms (Mdx-3cv mice) were used to evaluate the role of each dystrophin isoforms in the development of hypoxia-induced pathological neovascularization. Hypoxic stress was created by the mouse model of oxygen-induced retinopathy (OIR). To our great surprise, we found that mice with an isolated defect in Dp427 developed significantly more preretinal neovascularization compared to wildtype littermate controls while Mdx-4cv and Mdx-3cv mice did not show significant changes in the OIR phenotype. Genetic studies from blood samples of a Duchenne patient with severe neovascular retinopathy also revealed an isolated defect in the full-length dystrophin isoform Dp427. Together, these data strongly suggest that Dp427 is involved in the development of pathological neovascularization. Our study results have strong clinical implications suggesting that Duchenne patients with a mutation in Dp427 should receive routine ophthalmologic exams above the age of 20 to prevent vasoproliferative retinopathy. Further studies involved independent signaling pathways that both play an important role in the interaction of Müller and endothelial cell. Müller cells strongly express ciliary neurotrophic factor (CNTF), a well-studied neurotrophic agent that is currently tested for treatment of retinal degenerative diseases. Our studies showed that supplementation of recombinant CNTF in the OIR model strongly improved retinal vascular abnormalities including pathological neovascularization as well as vasoobliteration. While these effects could partially be explained by a direct STAT3/SOCS3 mediated anti-angiogenic effect of CNTF on vascular endothelial cells, activation of STAT3 was also detected in retinal glial cells. Further studies are needed to better understand the glial component that contributes to the angio-modulatory effect of CNTF treatment. Norrin induced β-catenin signaling represents another important communication pathway between Müller and endothelial cells. In the retina, vascular endothelial cells express the co-receptor Tetraspanin 12 (Tspan12) in order to respond to Norrin. Endogenous expression levels of Norrin, Tspan12 and β-catenin were shown to be upregulated in response to retinal hypoxia in the OIR model. Treatment with a Tspan12 blocking antibody resulted in a decrease in endothelial cell migration and tube formation in vitro and significant improvement in retinal neovascular changes in the OIR as well as VLDLR knock-out mouse model. Tspan12 Ab treatment strongly suppressed β-catenin signaling in vascular endothelial cells while VEGF expression levels remained unaltered. Combination therapy with the anti-VEGF agent Aflibercept showed significant enhancement of the therapeutic potential of each monotherapy and the potential to reduce therapeutic doses of Aflibercept which in turn reduces the risk for off-target effects subsequent to long-term suppression of VEGF signaling.
Projektbezogene Publikationen (Auswahl)
- CNTF attenuates vasoproliferative changes through upregulation of SOCS3 in a mouse-model of oxygen-induced retinopathy. Invest Ophthalmol Vis Sci. 2016;57:4017-4026
Bucher et al.
(Siehe online unter https://doi.org/10.1167/iovs.15-18508)
