Engineering the human pluripotent stem cell microenvironment to direct cell fate

Abstract

Human pluripotent stem cells (hPSCs), including both embryonic stem cells and induced pluripotent stem cells, offer a potential cell source for research, drug screening, and regenerative medicine applications due to their unique ability to self-renew or differentiate to any somatic cell type. Before the full potential of hPSCs can be realized, robust protocols must be developed to direct their fate. Cell fate decisions are based on components of the surrounding microenvironment, including soluble factors, substrate or extracellular matrix, cell-cell interactions, mechanical forces, and 2D or 3D architecture. Depending on their spatio-temporal context, these components can signal hPSCs to either self-renew or differentiate to cell types of the ectoderm, mesoderm, or endoderm. Researchers working at the interface of engineering and biology have identified various factors which can affect hPSC fate, often based on lessons from embryonic development, and they have utilized this information to design in vitro niches which can reproducibly direct hPSC fate. This review highlights culture systems that have been engineered to promote self-renewal or differentiation of hPSCs, with a focus on studies that have elucidated the contributions of specific microenvironmental cues in the context of those culture systems. We propose the use of microsystem technologies for high-throughput screening of spatial-temporal presentation of cues, as this has been demonstrated to be a powerful approach for differentiating hPSCs to desired cell types.

Keywords: Cell culture engineering; Differentiation; Ectoderm; Embryonic stem cells; Endoderm; Induced pluripotent stem cells; Mesoderm; Microenvironment; Niche; Self-renewal.

Figure 1

Schematic illustrating the traditional paradigm for engineering methods to manipulate PSC fate decisions by investigating the roles of individual microenvironmental cues and how the incorporation of these cues can instruct a cell to differentiate towards a particular lineage.

Figure 2

Relative progress on engineering microenvironments to achieve various hPSC cell fates. The arrow thickness is proportional to the amount of research that has been conducted in directing hPSCs toward that specific cell fate.

Figure 3

Outline of strategies for deriving (a) MSCs and their derivatives, (b) hematopoietic and vascular cells, and (c) DE and its derivatives from hPSCs using soluble factors.

Figure 4

Schematic illustrating how a new paradigm for designing culture systems to guide PSC fate decisions should take into account the combinatorial effect of microenvironmental cues as opposed to the individual contributions of each cue on a cell’s fate. In addition, the dynamic nature of a cell undergoing differentiation should be taken into account since the effects of these microenvironmental factors are contextually dependent on the state of the cell. A final consideration is the ability of the cell to continually modify its microenvironment, which can change the combinatorial net signal on itself or neighboring cells.