Investigating the role of the extracellular matrix (ECM) on pluripotent stem cell differentiation towards retinal lineages

Abstract

Human pluripotent stem cells (hPSCs) can be differentiated into retinal organoids to study inherited and age related retinal dystrophies, to screen new drugs and to use them as replacement tissues. Published evidence suggests that retinal pigmented epithelium (RPE) and decellularised extracellular matrix (ECM) from RPE and neural retina contain several ECM molecules that are important for retinal development and synaptic formation between various cell types. To date, there has been limited detailed analysis of ECM components distribution during human retinal ontogenesis and the functional importance of several components is poorly understood. In this study, the expression of key ECM components in adult mouse and monkey retina, developing and adult human retina and hPSC-derived retinal organoids was studied. The results demonstrate that different ECM components have distinct distribution patterns throughout the adult retina of different species and a well conserved expression pattern between adult and developing human retinae. Furthermore, the expression of ECM components examined in retinal organoids was found to recapitulate at large human retinal development in vivo. The functional role of ECM on the differentiation of hPSC-derived retinal organoids was investigated either via blocking the action of two ECMs: cluster of differentiation 44 (CD44) and interphotoreceptor matrix proteoglycan 1 (IMPG1) in the organoids or via supplementation of culture media with RPE conditioned medium, decellularised ECM of neural retina or RPE. The findings indicate that IMPG1 and CD44 play an important role on photoreceptor development, their inner and outer segments, connecting cilia and IPM formation; with IMPG1 acting earlier and having more significant effect than CD44. All three supplements enhanced the light response in retinal organoids suggesting a beneficial effect of ECM on the development and function of hPSC-derived retinal organoids. Together, the study highlights a conserved expression of ECMs between human adult and developing retinae and retinal organoids as well as an important role for ECM in retinal development in vitro.