Proteolytic processing of LRP2 on RPE cells regulates BMP activity to control eye size and refractive error. Danio rerio

We compare dissected ocular tissues from wild-type and lrp2-/- mutant adult zebrafish in order to examine the genetic pathways underlying the enlarged eye phenotype observed in the absence of Lrp2. ABSTRACT: Mutations in LRP2, a transmembrane receptor, cause ocular enlargement and high-myopia. LRP2 is expressed by the RPE and eye ciliary epithelia, binding many extracellular ligands, including Bmp4 and Shh. Signaling mediated by LRP2 is very context-dependent, and how multiple pathways are coordinated is unknown. Transcriptome analyses of ocular tissues revealed that controlled, sustained BMP signaling from the RPE is critical for normal eye growth and emmetropia (proper refraction). Using human iPSC-derived RPE, and zebrafish, we demonstrate that BACE sheddase-dependent LRP2 cleavage produces a soluble domain that binds BMP4, inhibiting its signaling. We propose that controlled proteolytic cleavage of LRP2 makes two ligand-binding receptor forms available: a soluble BMP trap, and a membrane-bound RPE signaling facilitator. By modulating LRP2 cleavage, cells can fine-tune and coordinate multiple signaling pathways. This data supports the concept that LRP2 acts as a homeostasis node that buffers and integrates diverse signaling to regulate emmetropic eye growth. Overall design: Examination of whole eyes, sclera/choroid, RPE and retina in wild-type and lrp2-/- mutant zebrafish at 1 month post-fertilization.