Endothelial SRF/MRTF ablation causes vascular disease phenotypes in murine retinae
Christine Weinl, Heidemarie Riehle, Dongjeong Park, Christine Stritt, Susanne Beck, Gesine Huber, Hartwig Wolburg, Eric N. Olson, Mathias W. Seeliger, Ralf H. Adams, Alfred Nordheim
Christine Weinl, Heidemarie Riehle, Dongjeong Park, Christine Stritt, Susanne Beck, Gesine Huber, Hartwig Wolburg, Eric N. Olson, Mathias W. Seeliger, Ralf H. Adams, Alfred Nordheim
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Research Article Vascular biology

Endothelial SRF/MRTF ablation causes vascular disease phenotypes in murine retinae

Abstract

Retinal vessel homeostasis ensures normal ocular functions. Consequently, retinal hypovascularization and neovascularization, causing a lack and an excess of vessels, respectively, are hallmarks of human retinal pathology. We provide evidence that EC-specific genetic ablation of either the transcription factor SRF or its cofactors MRTF-A and MRTF-B, but not the SRF cofactors ELK1 or ELK4, cause retinal hypovascularization in the postnatal mouse eye. Inducible, EC-specific deficiency of SRF or MRTF-A/MRTF-B during postnatal angiogenesis impaired endothelial tip cell filopodia protrusion, resulting in incomplete formation of the retinal primary vascular plexus, absence of the deep plexi, and persistence of hyaloid vessels. All of these features are typical of human hypovascularization-related vitreoretinopathies, such as familial exudative vitreoretinopathies including Norrie disease. In contrast, conditional EC deletion of Srf in adult murine vessels elicited intraretinal neovascularization that was reminiscent of the age-related human pathologies retinal angiomatous proliferation and macular telangiectasia. These results indicate that angiogenic homeostasis is ensured by differential stage-specific functions of SRF target gene products in the developing versus the mature retinal vasculature and suggest that the actin-directed MRTF-SRF signaling axis could serve as a therapeutic target in the treatment of human vascular retinal diseases.

Authors

Christine Weinl, Heidemarie Riehle, Dongjeong Park, Christine Stritt, Susanne Beck, Gesine Huber, Hartwig Wolburg, Eric N. Olson, Mathias W. Seeliger, Ralf H. Adams, Alfred Nordheim

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Figure 2

Avascular zones, distal microaneurysms, and lack of deep plexi in SrfiECKO retinae at P10.

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Avascular zones, distal microaneurysms, and lack of deep plexi in SrfiEC...
(A) ILB4-stained retinal flat-mounts. Red arrow indicates recessed angiogenic front in the SrfiECKO primary plexus. Images are composites (see Methods). (B) Radial outgrowth, expressed as percent of control. n = 19 retinae (control); 9 retinae (SrfiECKO). (C) Higher magnification of ILB4-stained retinal flat-mounts. White arrows indicate microaneurysms in SrfiECKO retinae. (D) EM image of blood vessels near the inner limiting membrane (ILM) to visualize the primary plexus. P, pericyte; L, lumen; BL, basal lamina. (E and F) ILB4-stained retinal capillaries of (E) the primary plexus and (F) deep plexi, which revealed complete absence of deeper capillaries in SrfiECKO retinae. (G) EM image visualizing deep plexi. OPL, outer plexiform layer. (H) Semiquantitative RT-PCR of mRNA expression in purified ECs of P10 retinae. n = 4 (Srf); 3 (Kdr and Actb); 5 (Cdh5). mRNA levels were normalized to Gapdh and expressed as percent of control. (I) Western blot analysis of 2 representative pairs of control and SrfiECKO P10 whole retinal tissue. (J) Quantitation of Western blot. SRF (n = 5) and VEGF-R2 (n = 4) levels were normalized to GAPDH and expressed as percent of control. Scale bars: 1 mm (A), 100 μm (C), 2 μm (D and G, left), 50 μm (E and F), 5 μm (G, right). *P < 0.05, **P < 0.01 vs. respective control.