Stromal‐Like Cells and Retinal Pigment Epithelium Modulate Choroidal Sprouting Through Galectin‐1‐Dependent and Independent Pathways

Outer retinal function depends on two supporting tissues: the retinal pigment epithelium (RPE) and the choroid. Limited molecular information is available on the intercellular networks that sustain RPE/choroid tissue in both healthy and pathological states. Galectin-1 (Gal1), a β-galactoside-binding lectin, has recently emerged as a key regulator of angiogenesis and a potential therapeutic target in vascular pathologies, including age-related macular degeneration. Here, we studied the expression of Gal1 in the outer retina and its regulatory role in the RPE/choroid under physiological and pathological conditions. Our findings indicate that Gal1 is predominantly associated with stromal cells in the RPE/choroid. In Gal1-deficient (Lgals1^-/-) mice, the RPE/choroid ultrastructure and gene expression profiles were altered, and choroidal explants exhibited reduced sprouting compared to those of wild-type mice. Consistently, recombinant Gal1 promoted choroidal sprouting under hypoxic conditions, and stromal-like cells modulated pro-angiogenic and antiangiogenic gene expression in vitro under pathological conditions. Interestingly, Gal1 was also expressed by the RPE, with apical secretion under normoxia that shifted toward a basolateral phenotype under hypoxia. These findings identify stromal-like cells and RPE as key sources of Gal1 in the choroid, highlighting its distinct roles in maintaining RPE/choroid homeostasis in healthy or pathological microenvironments.