Polymeric design of cell culture materials that guide the differentiation of human pluripotent stem cells

Abstract

Human pluripotent stem cells (hPSCs), including embryonic stem cells (hESCs) and induced pluripotent stem cells (hiPSCs), have the potential to differentiate into many cell types that originate from the three germ layers, such as dopamine-secreting cells and insulin-secreting cells for the treatment of Alzheimer's disease and diabetes, respectively. However, it is challenging to guide hPSC differentiation into desired cell lineages due to their varying differentiation ability. A reasonable strategy is to mimic the stem cell microenvironment for the differentiation of hPSCs into specific cell lineages using optimal polymeric biomaterials for hPSC culture. This review summarizes various methods for differentiating hPSCs cultured on polymeric biomaterials and discusses the optimal methods and cell culture polymeric biomaterials for hPSC differentiation into specific cell lineages. The recent trend in protocols avoids embryoid body (EB, aggregated cells) formation because EBs contain different types of cells. The combination of appropriate differentiation protocols and cell culture polymeric biomaterials for the differentiation of hPSCs into specific cell lineages will produce a large quantity of highly pure GMP-grade differentiated cells for use in translational medicine.

Introduction

There is a shortage of tissues and organs for patients who suffer damage or loss of their tissues or organs. Pluripotent stem cells, such as embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs), are an attractive cell source for regenerating or reconstructing damaged tissues and organs [1], [2], [3], [4], which have more pluripotency and high differentiation ability compared to adult stem cells such as bone marrow-derived mesenchymal stem cells and adipose-derived stem cells. iPSCs have similar properties to ESCs, and they were originally generated by reprogramming somatic cells by transduction with pluripotency-related genes [5], [6], [7]. Currently, iPSCs can also be generated by reprogramming somatic cells with pluripotency-related proteins or with epigenetic-modifying small molecules [8], [9], [10], [11]. Pluripotent stem cells (PSCs) generated from ESCs and iPSCs have the potential to differentiate into many cell types that originate from the three germ layers: endoderm cells (β cells, hepatocytes, and lung cells), mesoderm cells (osteoblasts, chondrocytes, myocytes, and blood cells), and ectoderm cells (neurons, astrocytes, dendrocytes, and epidermal cells). However, it is challenging to guide PSC, especially human PSC (hPSC), differentiation into desired cell lineages due to their varying differentiation ability.

The stem cell differentiation is guided by several different factors in the hPSC microenvironment: (1) bioactive molecules, such as growth factors, cytokines, vitamins, and small molecules; (2) cell–cell interactions, such as in co-cultures; (3) physical factors, such as shear stress, oxygen concentration, and the elasticity of the cell culture biomaterials; and (4) cell–biomaterial interactions in cell culture (Fig. 1) [3]. A reasonable strategy is to mimic the stem cell microenvironment for the differentiation of hPSCs into specific cell lineages using optimal biomaterials for hPSC culture. Although human adult stem cells, such as bone marrow-derived stem cells, amniotic fluid stem cells, and adipose-derived stem cells, can be differentiated using simple methods, such as stem cell cultivation on biomaterials in induction medium, the method for differentiating hPSCs is more complicated due to the high pluripotency and differentiation ability of hPSCs as well as different culture methods for hPSCs compared to human adult stem cells. Furthermore, hPSCs are generally cultured (a) on feeder cells, such as mouse embryonic fibroblasts (feeder layer culture), (b) on Matrigel, or (c) on specific biomaterials to maintain pluripotency [3], [12]; human adult stem cells can be simply cultured on conventional tissue culture polystyrene (TCPS) dishes. Therefore, the hPSC differentiation protocol is completely different from that for human adult stem cells.

There are several excellent original articles that have focused on the methods for differentiating hPSCs into specific cell lineages, such as cardiomyocytes, hepatocytes, neurons, and pancreatic cells [13], [14], [15], [16], [17]. However, to the best of our knowledge, no systematic review exists that focuses on the differentiation of hPSCs into specific cell lineages upon culture on different biomaterials. Therefore, this review summarizes various methods for differentiating hPSCs cultured on biomaterials and discusses the optimal biomaterials for hPSC differentiation into specific cell lineages. Table 1a, Table 1b, Table 1c, Table 1d, Table 1e summarizes the genes and/or proteins used to evaluate the differentiation of stem cells into the three germ layers (endoderm, mesoderm, and ectoderm).