Von Hippel-Lindau protein in the RPE is essential for normal ocular growth and vascular development

Abstract

SUMMARYMolecular oxygen is essential for the development, growth and survival of multicellular organisms. Hypoxic microenvironments and oxygen gradients are generated physiologically during embryogenesis and organogenesis. In the eye, oxygen plays a crucial role in both physiological vascular development and common blinding diseases. The retinal pigment epithelium (RPE) is a monolayer of cells essential for normal ocular development and in the mature retina provides support for overlying photoreceptors and their vascular supply. Hypoxia at the level of the RPE is closely implicated in pathogenesis of age-related macular degeneration. Adaptive tissue responses to hypoxia are orchestrated by sophisticated oxygen sensing mechanisms. In particular, the von Hippel-Lindau tumour suppressor protein (pVhl) controls hypoxia-inducible transcription factor (HIF)-mediated adaptation. However, the role of Vhl/Hif1a in the RPE in the development of the eye and its vasculature is unknown. In this study we explored the function of Vhl and Hif1a in the developing RPE using a tissue-specific conditional-knockout approach. We found that deletion of Vhl in the RPE results in RPE apoptosis, aniridia and microphthalmia. Increased levels of Hif1a, Hif2a, Epo and Vegf are associated with a highly disorganised retinal vasculature, chorioretinal anastomoses and the persistence of embryonic vascular structures into adulthood. Additional inactivation of Hif1a in the RPE rescues the RPE morphology, aniridia, microphthalmia and anterior vasoproliferation, but does not rescue retinal vasoproliferation. These data demonstrate that Vhldependent regulation of Hif1a in the RPE is essential for normal RPE and iris development, ocular growth and vascular development in the anterior chamber, whereas Vhl-dependent regulation of other downstream pathways is crucial for normal development and maintenance of the retinal vasculature.KEY WORDS: Von Hippel-Lindau factor, Hypoxia-inducible factor 1, Microphthalmia, Angiogenesis, Mouse

Late neuroprogenitors contribute to normal retinal vascular development in a Hif2a-dependent manner

“…Overall, the results indicated that Cre-mediated recombination in retinal neuroprogenitors is not limited to ocular pigmented tissues as originally described (Lange et al, 2012;Mori et al, 2002).…”

“…As we previously reported a major role for Hif1a regulation in whole eye development by employing the same transgenic line (Lange et al, 2012), we compared eye size and morphology over time and observed no effect ( Fig. S1B,C).…”

Pharmacological Restoration of Visual Function in a Zebrafish Model of von-Hippel Lindau Disease

“…Difficulty modelling VHL disease in rodents due to embryonic lethality has stunted the progress towards elucidating the molecular mechanisms contributing to retinal hemangioblastoma growth and ultimate vision loss in humans. A conditional RPE-specific Vhl knockout mouse model developed aniridia, microphthalmia, retinal neovascularisation and RPE-specific cell death [25]. Additional deletion of HIF-α resulted in proper iris development and normal ocular growth, suggesting these processes require VHL-dependent regulation of HIF-α in the RPE.…”

“…Additional deletion of HIF-α resulted in proper iris development and normal ocular growth, suggesting these processes require VHL-dependent regulation of HIF-α in the RPE. Moreover, Vegf expression and the development of abnormal retinal neovascularisation persisted in the double knockout mouse which suggests a HIF-independent regulation of vascular formation in the mouse retina [25]. .…”

Increased expression of hypoxia-inducible factor-1 alpha and its impact on transcriptional changes and prognosis in malignant tumours of the ocular adnexa

“…HIF-1α immunohistochemistry was performed in a standardised matter, as previously described [8]. In brief, antigen retrieval was achieved by exposing slides in citrate buffer to 95°C in a steamer for 1 h. Following incubation with a protein block and a blocking agent against endogenous peroxidase, the sections were incubated with primary monoclonal antibodies against HIF-1α (Novus Biologicals ® NB 100-105 diluted in a 1:8000 proportion for SCC/papilloma, 1:4000 for melanoma/nevi and 1:2000 for lymphoma/RLH) for 24 h at 4°C.…”