MMP2 and myopia: Based on the findings, we propose that Chrnb4 modulates myopia progression through a multi-layered signaling network involving dopamine and the TGF-β/MMP-2/TIMP-1 axis, as outlined below (see schematic framework): Functional Localization and Upstream Regulation of Chrnb4 encodes the β4 subunit of the nicotinic acetylcholine receptor (nAChR), predominantly expressed in retinal amacrine cells, bipolar cells, and scleral fibroblasts.