Using hiPSCs to develop physiologically-relevant outer retina tissue mimetics

点击翻译按钮获取中文摘要

The outer blood retina barrier (oBRB) comprises of the retinal pigment epithelium (RPE) cells and underlying fenestrated choriocapillaris (CC) that interfaces with the blood supply. The RPE-CC complex functions synergistically to support photoreceptor cell health that is critical for vision. Consistently, dysfunction of the RPE- CC leads to retinal degeneration in myraid eye diseases, including age-related macular degeneration (AMD), the single biggest cause of irreversible blindness in adults > 50 years of age in the US. However, the lack of in vitro tissue mimetics that faithfully recapitulate the RPE-CC complex has significantly impaired the study of normal and diseased physiology of the oBRB. A major challenge for the development of RPE-CC tissue mimetics is our limited understanding of human retinogenesis. This is especially relevant to the CC layer in which the majority of inferences are drawn from histological studies of embryonic human retina. Human induced pluripotent stem cells (hiPSCs) provide a unique platform to develop in vitro oBRB models. Indeed, several studies have now shown that specific cell types relevant to the RPE-CC complex, including RPE, endothelial cells (ECs) and mesenchymal stem cells (MSCs) can be differentiated from hiPSCs. Furthermore, we have recently developed a primitive RPE-CC tissue mimetic by exploiting the versatility of poly(ethylene glycol)(PEG) hydrogel-based engineered ECM (eECM) and hiPSC-derived target cells to emulate the spatial organization of RPE, ECs, and mesenchyme. The RPE-CC tissue mimetic is able to recapitulate important physiological features of the in vivo RPE-CC complex, such as CC-like fenestrated vasculature, that had previously been elusive in vitro. Although this model provides a framework for physiological RPE-CC development, it currently has several limitations, including unoptimized eECM biochemical and biophysical cues, lack of developmentally-instructed temporal cell- cell cues, and absence of vascular perfusion, resulting in a tissue model that does not fully recapitulate in vivo structure (e.g., well-defined Bruch’s membrane-like ECM and CC spatial angioarchitecture) and function (e.g., nutrient transport and macromolecular diffusion). In this proposal, we hypothesize that better understanding of the eECM requirements (Aim 1), ii) incorporation of temporal developmental cues (Aim 2), and integration of vascular perfusion, (Aim 3) will promote development of modular, spatially relevant, and functional RPE-CC tissue mimetic(s). Ultimately, the development of a physiological and modular human outer retina (RPE-CC) tissue mimetic will have important implications for subsequent disease modeling, drug screening, and transplantation studies.