Neurite Mistargeting and Inverse Order of Intraretinal Vascular Plexus Formation Precede Subretinal Vascularization in Vldlr Mutant Mice.

Verity Johnson,Mengqing Xiang,Harald J Junge,Zhe Chen,Jing Chen

doi:10.1371/journal.pone.0132013

Abstract

In the retina blood vessels are required to support a high metabolic rate, however, uncontrolled vascular growth can lead to impaired vision and blindness. Subretinal vascularization (SRV), one type of pathological vessel growth, occurs in retinal angiomatous proliferation and proliferative macular telangiectasia. In these diseases SRV originates from blood vessels within the retina. We use mice with a targeted disruption in the Vldl-receptor (Vldlr) gene as a model to study SRV with retinal origin. We find that Vldlr mRNA is strongly expressed in the neuroretina, and we observe both vascular and neuronal phenotypes in Vldlr-/- mice. Unexpectedly, horizontal cell (HC) neurites are mistargeted prior to SRV in this model, and the majority of vascular lesions are associated with mistargeted neurites. In Foxn4-/- mice, which lack HCs and display reduced amacrine cell (AC) numbers, we find severe defects in intraretinal capillary development. However, SRV is not suppressed in Foxn4-/-;Vldlr-/- mice, which reveals that mistargeted HC neurites are not required for vascular lesion formation. In the absence of VLDLR, the intraretinal capillary plexuses form in an inverse order compared to normal development, and subsequent to this early defect, vascular proliferation is increased. We conclude that SRV in the Vldlr-/- model is associated with mistargeted neurites and that SRV is preceded by altered retinal vascular development.

Highlights

Retinal vascular diseases are a leading cause of impaired vision and blindness
We found that the onset of vascular lesion formation was at postnatal day 12 (P12) when multiple isolectinB4 positive endothelial cells invaded the normally avascular outer nuclear layer (ONL) predominantly in the central retina (Fig 1A)
We observed the formation of retinal rosettes and reactive gliosis in Vldlr-/- retinas, but only after the outer limiting membrane (OLM) was doi:10.1371/journal.pone.0132013.g001

Summary

Introduction

Retinal vascular diseases are a leading cause of impaired vision and blindness. The subretinal space contains photoreceptor segments, and is the target of harmful neovascularization in several vision threatening pathologies, including retinal angiomatous proliferation (RAP). Vldlr-/- mice develop vascular lesions that extend from capillaries in the OPL into the subretinal space [4]. We report the unexpected finding that HC neurites are mistargeted into the ONL and subretinal space prior to SRV in Vldlr-/- mice, and that most vascular lesions are associated with mistargeted neurites. We use Foxn4-/-; Vldlr-/- double knockout mice to show that SRV can occur in the absence of HCs. Our analysis of early postnatal development establishes that SRV in Vldlr-/- mice is preceded by developmental defects including an inverse order of intraretinal capillary plexus formation and a subsequent increase in vascular cell proliferation

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Discussion