Neural retina-specific Aldh1a1 controls dorsal choroidal vascular development via Sox9 expression in retinal pigment epithelial cells

Abstract

VEGF secreted from retinal pigment epithelial (RPE) cells is responsible for the choroidal vascular development; however, the molecular regulatory mechanism is unclear. We found that Aldh1a1–/– mice showed choroidal hypoplasia with insufficient vascularization in the dorsal region, although Aldh1a1, an enzyme that synthesizes retinoic acids (RAs), is expressed in the dorsal neural retina, not in the RPE/choroid complex. The level of VEGF in the RPE/choroid was significantly decreased in Aldh1a1–/– mice, and RA-dependent enhancement of VEGF was observed in primary RPE cells. An RA-deficient diet resulted in dorsal choroidal hypoplasia, and simple RA treatment of Aldh1a1–/– pregnant females suppressed choroid hypoplasia in their offspring. We also found downregulation of Sox9 in the dorsal neural retina and RPE of Aldh1a1–/– mice and RPE-specific disruption of Sox9 phenocopied Aldh1a1–/– choroidal development. These results suggest that RAs produced by Aldh1a1 in the neural retina directs dorsal choroidal vascular development via Sox9 upregulation in the dorsal RPE cells to enhance RPE-derived VEGF secretion.

Retinoic acid signaling in vascular development

“…RA is produced by multiple cells of the retina starting early in development, but not by retinal pigment epithelial cells (RPE) or cells of the choroid (Goto et al, 2018; Matt et al, 2005; McCaffery, Tempst, Lara, & Dräger, 1991). RA is essential for proper embryonic eye development as genetic deletion of either the enzymes that make RA or RA receptors lead to severe eye formation defects (Dupé et al, 2003; Fan et al, 2003; Kastner et al, 1994; Kastner et al, 1997; Lohnes et al, 1994; Matt et al, 2005).…”

“…Whole body knockouts of Raldh1 , the RA synthesizing enzyme expressed in the postnatal retinal, do not have retinal defects but do show impaired choroidal vascular development (Goto et al , 2018). Analysis of the Raldh1 −/− knockout mice shows that RA produced by cells in the retina stimulate RPE cells to produce VEGFA and in the absence of Raldh1, RPE cells make less VEGF (Goto et al, 2018). Development of the choroidal vascular is dependent on VEGFA produced by the RPE cells (Saint-Geniez, Kurihara, Sekiyama, Maldonado, & D’Amore, 2009) and Vitamin A deficient mice also have same choroidal vascular defects (Goto et al , 2018).…”

“…Analysis of the Raldh1 −/− knockout mice shows that RA produced by cells in the retina stimulate RPE cells to produce VEGFA and in the absence of Raldh1, RPE cells make less VEGF (Goto et al, 2018). Development of the choroidal vascular is dependent on VEGFA produced by the RPE cells (Saint-Geniez, Kurihara, Sekiyama, Maldonado, & D’Amore, 2009) and Vitamin A deficient mice also have same choroidal vascular defects (Goto et al , 2018). Thus, these initial studies are consistent with a role for RA in retinal vascular development.…”

“…The mouse retinal vasculature forms postnatally, where at birth the retinal nourishment is provided by hyaloid and choroidal vessels that form embryonically (Connolly, Hores, Smith, & D'Amore, 1988;Fruttiger, 2007;Selvam, Kumar, & Fruttiger, 2018;Stahl et al, 2010). Retinal vascular formation starts with the superficial plexus, which forms from P0 to P7 as RA is produced by multiple cells of the retina starting early in development, but not by retinal pigment epithelial (RPE) cells or cells of the choroid (Goto et al, 2018;Matt et al, 2005;McCaffery, Tempst, Lara, & Dräger, 1991). RA is essential for proper embryonic eye development as genetic deletion of either the enzymes that make RA or RA receptors lead to severe eye formation defects (Dupé et al, 2003;Fan et al, 2003;Kastner et al, 1994;Lohnes et al, 1994;Matt et al, 2005).…”

“…If RA is delivered systemically to mice in a model of retinopathy of prematurity (ROP), RA treatment can prevent the loss of VEGFA and improves vascular growth . Whole body knockouts of Raldh1, the RA synthesizing enzyme expressed in the postnatal retinal, do not have retinal defects but do show impaired choroidal vascular development (Goto et al, 2018). Analysis of the Raldh1 −/− knockout mice shows that RA produced by cells in the retina stimulate RPE cells to produce VEGFA and in the absence of Raldh1, RPE cells make less VEGF (Goto et al, 2018).…”