The endothelium, a key actor in organ development and hPSC-derived organoid vascularization

Abstract

Over the last 4 decades, cell culture techniques have evolved towards the creation of in vitro multicellular entities that incorporate the three-dimensional complexity of in vivo tissues and organs. As a result, stem cells and adult progenitor cells have been used to derive self-organized 3D cell aggregates that mimic the morphological and functional traits of organs in vitro. These so-called organoids were first generated from primary animal and human tissues, then human pluripotent stem cells (hPSCs) arose as a new tool for organoid generation. Due to their selfrenewal capacity and differentiation potential, hPSCs are an unlimited source of cells used for organoids. Today, hPSC-derived small intestinal, kidney, brain, liver, and pancreas organoids, among others, have been produced and are promising in vitro human models for diverse applications, including fundamental research, drug development and regenerative medicine. However, achieving in vivo-like organ complexity and maturation in vitro remains a challenge. Current hPSC-derived organoids are often limited in size and developmental state, resembling embryonic or fetal organs rather than adult organs. The use of endothelial cells to vascularize hPSC-derived organoids may represent a key to ensuring oxygen and nutrient distribution in large organoids, thus contributing to the maturation of adult-like organoids through paracrine signaling. Here, we review the current state of the art regarding vascularized hPSC-derived organoids (vhPSC-Orgs). We analyze the progress achieved in the generation of organoids derived from the three primary germ layers (endoderm, mesoderm and ectoderm) exemplified by the pancreas, liver, kidneys and brain. Special attention will be given to the role of the endothelium in the organogenesis of the aforementioned organs, the sources of endothelial cells employed in vhPSC-Org protocols and the remaining challenges preventing the creation of ex vivo functional and vascularized organs.

Electrophysiological Analysis of Brain Organoids: Current Approaches and Advancements

“…Finally, a significant effort has been made to vascularize brain organoids in recent years. Without vascularization, significant cell death is observed in the inner regions of brain organoids, limiting proper development and analysis ( Lancaster et al, 2013 ; Vargas-Valderrama et al, 2020 ). Several strategies have been employed to vascularize brain organoids.…”

Induced Pluripotent Stem Cells (iPSCs) in Vascular Research: from Two- to Three-Dimensional Organoids

“…In addition, iPSCs also offer other advantages, such as the ethical renunciation of hESCs, the avoidance of immune reactions upon implantation, the generation of gene-edited cells with isogenic background, and the scalable production of cellular materials for research [ 9 , 19 , 20 ]. Recently, organoids have aided the investigation of diseases, which can be achieved with a homogeneous and well-defined iPSC-derived EC line [ 21 ].…”

Engineering neurovascular organoids with 3D printed microfluidic chips

“…The presence of a vascular network has been hypothesized to be a key missing feature in these models which could account for some of these limitations. Indeed, the endothelium plays an critical role in the development of tissues and organs, functioning as a site of nutrient and waste exchange as well as a paracrine signalling centre which directs differentiation, patterning and morphogenesis (3).…”

“…The presence of a vascular network has been hypothesized to be a key missing feature in these models which could account for some of these limitations. Indeed, the endothelium plays an critical role in the development of tissues and organs, functioning as a site of nutrient and waste exchange as well as a paracrine signalling centre which directs differentiation, patterning and morphogenesis (3). For example, the endothelium plays an in important role in the initiation of cortical neurogenesis as well as in the outgrowth of the liver bud by surrounding the embryonic hepatic endoderm, thereby delimitating the mesenchymal domain (4).…”

“… (A) Differentiation protocol for the generation of hPSC derived vascular networks on chip. ( B ) IHC image of vascular cells on chip at day 7 with sprouts present in the interface (2) between channels (1) and the organoid culture chamber (3) (scale: 100μm). ( C ) Bright field images of the organoid culture chamber showing sprout progression and graphs quantifying sprout progression (n=3;Avg.…”