Dopamine selectively regulates pediatric sclera/choroid interactions through the stimulation of exosome-associated retinoic acid

Postnatal eye growth is critical for healthy vision and yet, how this process is regulated at the cellular level is still unclear. The choroid is thought to play a crucial role in relaying signals from the retina to the sclera to modulate eye growth, but which cells are targeted and how they interact is not known. Using primary cultures of pediatric and adult human choroid and sclera stromal fibroblasts, we investigated the effect of choroid-conditioned medium (CCM) on scleral fibroblasts contractile activity. We show that CCM activates pediatric scleral fibroblast contraction, with age and antero-posterior location differences. Upon exposure to dopamine, a known negative regulator of eye growth, pediatric - but not adult - choroid cells lose their ability to stimulate scleral fibroblasts. Using RNA-Sequencing, we show that dopamine stimulates pathways linked to ribosomal activation, translation and exosome release exclusively in pediatric choroid cells. Removing exosomes from the CCM rescued the ability of dopamine-treated choroid cells to stimulate scleral fibroblasts. We further identify retinoic acid as the active exosome-associated compound preventing scleral fibroblast activation. Mechanistically, we show that CCM stimulates actomyosin-mediated protrusive activity in scleral fibroblasts. This is prevented when scleral cells are exposed to dopamine-CCM, and fully rescued upon exosome removal or ALDH1 inhibition. We thus propose that pediatric choroid stromal cells specifically relay dopamine-mediated retinal signals to the sclera during post-natal eye growth, operating through changes in secretome - including the production of exosome-associated retinoic acid - rather than gene expression changes. SIGNIFICANCEEye size is critical to optimal vision but the exact cellular and molecular mechanisms regulating it are still unknown. Failure to properly regulate postnatal eye growth leads to elongated eyes and myopia. Myopia is expected to affect half of the world population by 2050, with many at risk of blinding complications. Eye growth and homeostasis are supported by the sclera and the choroid, but how the two tissues interact to regulate eye growth is unknown. We use here human cells to demonstrate direct, age-specific, interactions between the two cell types and provide a rationale for the known negative effect of dopamine on eye growth, with significant implications for future studies as well as for the understanding and treatment of myopia.