Overexpression of extracellular matrix proteins, increased cell death and reduced cell proliferation contribute to the pathophysiology of microphthalmia across in vitro patient-derived models

Genetic perturbations influencing early eye development can result in microphthalmia, anophthalmia and coloboma (MAC). Over 100 genes are associated with MAC, but little is known about common disease mechanisms. In this study, we generated induced pluripotent stem cell (iPSC) derived optic vesicles (OVs) from two unrelated microphthalmia patients and healthy controls. At day 20, 35 and 50 microphthalmia patient OV diameters were significantly smaller, recapitulating the ‘small eye’ phenotype. RNA-seq analysis revealed upregulation of apoptosis-initiating and extracellular matrix (ECM) genes at day 20 and 35. Western blot and immunohistochemistry revealed increased expression of lumican, nidogen and collagen type IV, suggesting ECM overproduction. Increased apoptosis was observed in microphthalmia OVs with reduced pH3+ cells confirming decreased cell proliferation at day 35. Pharmacological inhibition of caspase-8 activity with Z-IETD-FMK decreased apoptosis in one patient model, highlighting a potential therapeutic approach. These data reveal shared pathophysiological mechanisms contributing to a microphthalmia phenotype.