Neurovascular crosstalk between retinal interneurons and intraretinal capillaries is required for murine visual function

Abstract

Purpose: The neurosensory retina is highly organized, with neurons and blood vessels architecturally layered to meet metabolic demands. These neurovascular units, which represent a functional interaction between neurons, vasculature, and glia, are critical to the maintenance of retinal tissue. Our previous work has demonstrated that amacrine and horizontal cells are required for generating and maintaining the intraretinal vasculature through precise regulation of hypoxia-inducible and pro-angiogenic factors. In this study we delineated the role of these cells in the formation of vascular plexus layers, using various transgenic approaches.

Methods: Transgenic mice with floxed VHL, HIF-1α, HIF-2α and/or VEGF alleles were mated with mice specifically expressing Cre recombinase in amacrine and horizontal cells (Ptf1a-Cre mice) to generate cell-type specific genetic knockouts. Additionally, amacrine and horizontal cells were genetically ablated using Ptf1a-Cre and forced expression of diphtheria toxin (DT) receptors. Ptf1a-Cre;VEGF knockout mice were also crossed with two different retinal degeneration models, rd10 and Vldlr knockout mice. To determine the effect of an attenuated intermediate plexus on visual function, scotopic and photopic electroretinography (ERG), or optokinetic response were done in these mutants.

Results: Genetic perturbation of VHL/HIF/VEGF signaling in amacrine/horizontal cells demonstrates that they are required for proper retinal vascular patterning and maintenance. Amacrine/horizontal cell dysfunction leads to attenuation of the intraretinal vasculature and significant defects in visual function. A reduction in both scotopic (rod-driven) and photopic (cone-driven) sensitivity, as well as significantly reduced optokinetic reflexes were observed in ptf1a-Cre; VEGFKO and VHLKO mice. Photoreceptor atrophy occurred earlier and faster in two animal models of human retinal degeneration following VEGF deletion in amacrine cells.

Conclusions: Amacrine and horizontal cells are critical components of the functional neurovascular unit in the intraretinal vasculature. They maintain retinal homeostasis and visual function by supporting the intermediate plexus, which delivers necessary nutrients to photoreceptors. This is accomplished through regulation of the VEGF/VHL/HIF signaling pathway.