Bioengineered Systems and Designer Matrices That Recapitulate the Intestinal Stem Cell Niche
2018; Elsevier BV; Volume: 5; Issue: 3 Linguagem: Inglês
10.1016/j.jcmgh.2018.01.008
ISSN2352-345X
AutoresYuli Wang, Raehyun Kim, Samuel S. Hinman, Bailey Zwarycz, Scott T. Magness, Nancy L. Allbritton,
Tópico(s)Planarian Biology and Electrostimulation
ResumoThe 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. 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. SummaryGradients of ligands, growth factors, receptors, extracellular matrix, metabolites, and gases along the crypt (colon) and crypt-villus (small intestine) axis drive maintenance of intestinal stem cells, orderly differentiation, and movement of epithelial cells from the intestinal stem cell niche to the luminal intestinal epithelium. Advances in biomaterials and microdevices enable reconstruction of this complex microenvironment, replicating the key architectural features and physiological functions of the in vivo intestinal epithelium. Gradients of ligands, growth factors, receptors, extracellular matrix, metabolites, and gases along the crypt (colon) and crypt-villus (small intestine) axis drive maintenance of intestinal stem cells, orderly differentiation, and movement of epithelial cells from the intestinal stem cell niche to the luminal intestinal epithelium. Advances in biomaterials and microdevices enable reconstruction of this complex microenvironment, replicating the key architectural features and physiological functions of the in vivo intestinal epithelium. The phrase stem cell niche refers to a specific anatomic tissue location that provides a microenvironment enabling intestinal stem cells (ISCs) to remain in an undifferentiated state and promote self-renewal.1Sailaja B.S. He X.C. Li L.H. 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In the colon, crypts also are present in densely packed arrays, but feed cells onto a flat luminal surface. Although there are functional differences between the small intestine and colon, remarkable similarities exist in the ordered arrangement of crypts, for example, the location of the stem cell zone at the base of the crypt, and the differentiation and migration pattern of epithelial cells. ISCs divide to produce progenitor cells known as transit-amplifying (TA) cells, which reside above the ISCs within the crypt. The TA cells undergo several additional cell divisions as they migrate upward along the crypt axis and their progeny terminally differentiate into a variety of cell lineages. Absorptive enterocytes represent the majority of cells in the small intestine, while a host of secretory lineages including goblet, enteroendocrine, tuft, and M cells contribute to the functional epithelium. When these cells reach the villus tip in the small intestine or flat luminal surface in the colon, they undergo anoikis and exfoliate into the intestinal lumen to finish a self-renewal cycle that lasts approximately 3–5 days for mice and 5–7 days for human beings.2Barker N. Adult intestinal stem cells: critical drivers of epithelial homeostasis and regeneration.Nat Rev Mol Cell Biol. 2014; 15: 19-33Crossref PubMed Scopus (538) Google Scholar, 3Fuchs E. Chen T. A matter of life and death: self-renewal in stem cells.EMBO Rep. 2013; 14: 39-48Crossref PubMed Scopus (0) Google Scholar An exception to the upward migration of differentiated epithelial cells is the secretory Paneth cell in the small intestine and a Paneth-like cell (cKit+) cell in the colon, which remains at the crypt base intercalated among ISCs.7Rothenberg M.E. Nusse Y. Kalisky T. Lee J.J. Dalerba P. Scheeren F. Lobo N. Kulkarni S. Sim S. Qian D. Beachy P.A. Pasricha P.J. Quake S.R. Clarke M.F. 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Although rodent models laid the foundation for understanding ISC biology and the niche in vivo, 3-dimensional (3D) organoid and monolayer models of the small intestinal and colonic epithelium have fueled progress toward in vitro recapitulation of the ISC niche microenvironment to study both epithelial function and pathology.5Sato T. Vries R.G. Snippert H.J. Van De Wetering M. Barker N. Stange D.E. Van Es J.H. Abo A. Kujala P. Peters P.J. Single Lgr5 stem cells build crypt villus structures in vitro without a mesenchymal niche.Nature. 2009; 459: 262-265Crossref PubMed Scopus (0) Google Scholar, 20Krausova M. Korinek V. Wnt signaling in adult intestinal stem cells and cancer.Cell Signal. 2014; 26: 570-579Crossref PubMed Scopus (226) Google Scholar, 21Sato T. Stange D.E. Ferrante M. Vries R.G.J. van Es J.H. van den Brink S. van Houdt W.J. Pronk A. van Gorp J. Siersema P.D. Clevers H. 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Enterohemorrhagic Escherichia coli reduces mucus and intermicrovillar bridges in human stem cell-derived colonoids.Cell Mol Gastroenterol Hepatol. 2016; 2: 48-62Abstract Full Text Full Text PDF PubMed Google Scholar However, conventional organoid and monolayer culture systems do not fully recapitulate the microarchitecture of gut epithelium and cannot support the formation of gradients across geometric structures because of the nature of conventional culture systems. To develop high-fidelity, physiologically relevant in vitro models, new culture systems need to incorporate these in vivo gradients. Although there is clear evidence for factor gradients that drive gut epithelial dynamics, visualizing, measuring, and re-creating these gradients has historically been technically challenging. This review focuses on the direct and indirect evidence for in vivo gradients that impact ISC biology and gut epithelial dynamics, and then presents the current state-of-the-art technologies and platforms for the in vitro culture of gut epithelium, particularly as they relate to lab-on-chip and microfluidic culture devices. Growth factor gradients commonly are associated with fundamental mechanisms that underlie ISC maintenance and differentiation. Paneth cells have been the focus of much attention as an ISC niche cell by secreting factors that set up gradients to regulate stemness. A number of studies have shown that Paneth cells are dispensable for ISC maintenance and suggest that other niche cells generate factor gradients that function similar to those set up by Paneth cells.28Bastide P. Darido C. Pannequin J. Kist R. Robine S. Marty-Double C. Bibeau F. Scherer G. Joubert D. Hollande F. Blache P. Jay P. 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Extracellular matrix, integrins, and growth factors as tailors of the stem cell niche.Curr Opin Cell Biol. 2012; 24: 645-651Crossref PubMed Scopus (227) Google Scholar These studies have merely scratched the surface on a complex cellular and molecular balance that is required to maintain the ISC-driven renewal of the epithelium. The full complement of growth factors, ECM components, and cell types involved in regenerating the epithelial monolayer are not yet fully appreciated. Moreover, noncanonical gradients such as tissue stiffness, gases, and microbial metabolites likely play critical roles but are technically difficult to study in vivo. Understanding these physical properties is of substantial interest to those investigating the broad and diverse factors that regulate gut biology, and is essential for efforts to engineer functional intestinal and colonic tissues. The following section is a brief review of the current state of in vivo gradients and highlights gaps in knowledge as new avenues for investigation. Modern advances in understanding ISC biology are based largely on studies that define genetic pathways and mechanisms that govern ISC maintenance and differentiation. Among these are the wingless-related integration site (Wnt), bone morphogenetic protein (BMP), and Notch pathways, which classically are studied as key contributors to epithelial renewal in homeostasis, disease, and injury. Arguably, the Wnt/β-catenin signaling pathway has been a central focus of studies that have heavily influenced the current state in the field.4Clevers H.C. Bevins C.L. Paneth cells: maestros of the small intestinal crypts.Ann Rev Physiol. 2013; 75: 289-311Crossref PubMed Scopus (0) Google Scholar, 15Pinto D. Gregorieff A. Begthel H. Clevers H. Canonical Wnt signals are essential for homeostasis of the intestinal epithelium.Genes Dev. 2003; 17: 1709-1713Crossref PubMed Scopus (700) Google Scholar, 20Krausova M. Korinek V. Wnt signaling in adult intestinal stem cells and cancer.Cell Signal. 2014; 26: 570-579Crossref PubMed Scopus (226) Google Scholar Wnts are secreted ligands that bind their cognate receptors and function to regulate ISC maintenance and differentiation. Sox9 is largely a downstream Wnt target gene and shows a distinct expression gradient with higher expression at the base of the crypt in the ISC zone and lower expression through the TA zone, suggesting that Wnt signaling also is present in a gradient that mimics its downstream target genes.32Formeister E.J. Sionas A.L. Lorance D.K. Barkley C.L. Lee G.H. Magness S.T. 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Distinct levels of Sox9 expression mark colon epithelial stem cells that form colonoids in culture.Am J Physiol Gastrointest Liver Physiol. 2012; 302: G10-G20Crossref PubMed Scopus (51) Google Scholar In fact, 9 Wnts are expressed in the small intestine of mice and are regionally expressed along the crypt-villus axis.30Farin H.F. Van Es J.H. Clevers H. Redundant sources of Wnt regulate intestinal stem cells and promote formation of Paneth cells.Gastroenterology. 2012; 143: 1518-1529Abstract Full Text Full Text PDF PubMed Scopus (310) Google Scholar Contrary to popular assumptions, it appears that Wnt3 gradients may be formed not by simple diffusion, but rather by "plasma membrane dilution" as cells divide.36Farin H.F. Jordens I. Mosa M.H. Basak O. Korving J. Tauriello D.V. de Punde
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