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Review
, 5 (3), 440-453.e1
eCollection

Bioengineered Systems and Designer Matrices That Recapitulate the Intestinal Stem Cell Niche

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Review

Bioengineered Systems and Designer Matrices That Recapitulate the Intestinal Stem Cell Niche

Yuli Wang et al. Cell Mol Gastroenterol Hepatol.

Abstract

The relationship between intestinal stem cells (ISCs) and the surrounding niche environment is complex and dynamic. Key factors localized at the base of the crypt are necessary to promote ISC self-renewal and proliferation, to ultimately provide a constant stream of differentiated cells to maintain the epithelial barrier. These factors diminish as epithelial cells divide, migrate away from the crypt base, differentiate into the postmitotic lineages, and end their life span in approximately 7 days when they are sloughed into the intestinal lumen. To facilitate the rapid and complex physiology of ISC-driven epithelial renewal, in vivo gradients of growth factors, extracellular matrix, bacterial products, gases, and stiffness are formed along the crypt-villus axis. New bioengineered tools and platforms are available to recapitulate various gradients and support the stereotypical cellular responses associated with these gradients. Many of these technologies have been paired with primary small intestinal and colonic epithelial cells to re-create select aspects of normal physiology or disease states. These biomimetic platforms are becoming increasingly sophisticated with the rapid discovery of new niche factors and gradients. These advancements are contributing to the development of high-fidelity tissue constructs for basic science applications, drug screening, and personalized medicine applications. Here, we discuss the direct and indirect evidence for many of the important gradients found in vivo and their successful application to date in bioengineered in vitro models, including organ-on-chip and microfluidic culture devices.

Keywords: 3D, 3-dimensional; BMP, Bone morphogenetic protein; Bioengineering; ECM, extracellular matrix; Eph, erythropoietin-producing human hepatocellular receptor; Ephrin, Eph family receptor interacting proteins; Gradients; IFN-γ, interferon-γ; ISC, intestinal stem cell; Intestinal Epithelial Cells; NO, nitric oxide; SFCA, short-chain fatty acids; Stem Cell Niche; TA, transit amplifying; Wnt, wingless-related integration site.

Figures

Figure 1
Figure 1
Gradients in the intestine in vivo. (A) The large intestine possesses chemical gradients spanning the crypt long axis. These gradients include ECM proteins, growth factors and their receptors, inflammatory mediators, and microbial metabolites. Numerous gaseous gradients also are present including oxygen from the arterial system, NO from inflammatory cells and the vasculature, and microbial-derived gases such as H2S and S2O. (B) A multitude of gradients span the crypt/villus long axis in the small intestine. The concentration of ECM proteins, growth factors and their receptors, and inflammatory mediators varies along the length of the crypt/villus unit. The oxygen gradient is much shallower than that of the large intestine because of the absence of the vast numbers of oxygen-scavenging microbes. Because microbial numbers are greatly decreased relative to that in the large intestine, few microbial metabolite gradients have been characterized. (B and C) The shaded triangles show only the gradient direction because the quantitative shape of the gradient is unknown. EGF, epidermal growth factor; IL, interleukin; TNF, tumor necrosis factor.
Figure 2
Figure 2
Gradients formed across intestinal tissue in vitro. (A) Generation of in vitro human, small intestine crypt-villus arrays. Left panel: Schematic of the gradient of growth factors (W, Wnt3A; R, R-spondin 3; N, noggin). Middle panels: Brightfield and fluorescence images of a polarized crypt-villus unit under the 3-growth factor gradient and opposing DAPT gradient. Mature enterocytes (red, alkaline phosphatase [ALP]) and proliferative cells (green, 5-ethynyl-20-deoxyuridine [EdU]) also are marked. DNA or nuclei are shown in blue. Right panel: Immunofluorescence staining (olfactomedin [Olfm4]/keratin 20 [KRT20]) of a cross-section through in vitro human small intestinal tissue under the combined growth factor and DAPT gradient. Scale bars: 100 μm. Reproduced by permission from Elsevier from Biomaterials, 2017: 128, 44-55. (B) Generation of in vitro human colon crypts. Left panel: Schematic of the gradient of growth factors (Wnt3A, R-spondin, noggin). Differentiated and stem/proliferative cells are shown in red and green, respectively. Middle panels: Brightfield and fluorescence side views of in vitro–formed crypts (EdU, green; ALP, red; DNA, blue). Right panel: Cross-section of in vitro crypt immunostained for KRT20 (red) and Olfm4 (green). Scale bars: 100 μm. (C) Modulation of in vitro human crypts by SCFAs. Left panel: Biochemical gradients applied to the tissue. Middle and right panels: Side view of representative crypts from the arrays under different SCFA gradients (EdU, green; ALP, red). Scale bar: 100 μm. Reproduced by permission under a Creative Commons Attribution-NonCommercial-No Derivatives License from Elsevier from Cellular and Molecular Gastroenterology Hepatology. (D) Bioengineered tissues on silk scaffolds mimic in vivo luminal oxygen levels. Left panels: Schematic of a 3D tissue and quantification of luminal partial pressure of oxygen (Po2) in the presence of confluent Caco-2 tumor cells. Right panels: Oxygen levels were detected in situ by using engineered oxygen-sensing fluorescent Yersinia pseudotuberculosis (red). The absence of green fluorescent protein (GFP) fluorescence and the presence of expressed mini singlet-oxygen generator (arrowheads) indicates the presence of anaerobic conditions. Reproduced under a Creative Commons Attribution 4.0 International License from Sci. Rep. 5, 13708. (E) Matrix mechanical properties control ISC proliferation. Upper panels: ISC colonies were formed within enzymatically cross-linked poly(ethylene glycol) (PEG) hydrogels modified with Arg (R)-Gly (G)-Asp (D) (RGD) and of varying stiffness. Yes-associated protein (YAP) immunofluorescence is shown in green. Scale bar: 50 μm. Lower panel: ISC colony-forming efficiency of ISCs embedded in degradable (DG) or nondegradable (N-DG) PEG gels of varying stiffness. GM6001 is a broad-spectrum matrix metalloproteinase inhibitor.
Supplemental Graphical Summary
Supplemental Graphical Summary

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