Specific Cell – Biomaterial Interactions for In Vivo-Like In Vitro Tissue Models from Human Pluripotent Stem Cells
Year: 2019
Type: dissertation
Abstract: There is an urgent need for better in vitro cell models to increase efficacy and cost-efficiency in drug development. Current simple models poorly mimic the natural in vivo cell environment. Human pluripotent stem cells (hPSCs) could serve as a limitless source for all the cells in the human body, but for most cell types, such as hepatocytes, efficient differentiation protocols do not exist. The signals that control cell behavior in vivo and in vitro are generated from growth factors (GFs), cell-extracellular matrix (ECM), and cell-cell interactions. The role of the ECM in cell behavior has only recently gained attention. Natural ECM of cells is a tissue-specific and complex three-dimensional (3D) array of various macromolecules. It provides physical, mechanical, and biochemical signals to cells. Mimicking the entire natural environment for cells is difficult, and it is, therefore, important to recognize the key components providing the essential signals. New materials, such as unmodified cellulose nanofibril (CNF) hydrogel, have been developed to tackle the technical difficulties that the ECM proteins have in 3D cell culture models, but the interactions of these materials with cells are not well known. Integrins with 18 subtypes are the main mediators of the cell – biomaterial interactions. The presentation and activation of these subtypes are important mediators in hPSC maintenance and differentiation. The activation of integrins can be caused by inside-out signaling through other integrins or receptors and outside-in activation through ECM molecules, divalent cations, or GFs. Hence it is vital to be able to measure these interactions in order to design good in vitro cell models. One of the most versatile instruments to quantify cell – biomaterial interactions and integrin activation is the atomic force microscope (AFM). The aim of this thesis is to study the hPSC interactions with biomaterials and use this information to better understand the cell behavior in vitro. The adhesion data of the AFM-based colloidal probe microscopy (CPM) correlate and predict cell adhesion on materials in vitro. Using CPM, we quantitatively tested the role of integrin density as well as integrin activation, enabled by cell viability and divalent cations, in these interactions. We observed that ECM proteins laminin-521 and laminin-511—detected in acellular matrix produced by hepatic progenitor cells—improved hPSC differentiation to hepatic cells. Cells in 3D cultures have more in vivo-like functions, and we, therefore, tested if the created differentiation protocol could be used to stepwise induce hPSCs specification to hepatic organoids in a CNF hydrogel. With CPM we found that CNF has only weak, nonspecific interactions with cells and maybe therefore CNF is not providing the signals needed for hPSC differentiation. The differentiation efficiency of hPSCs in CNF hydrogel is lower compared to matrix-free suspension culture. In conclusion, this thesis provides new quantitative information about cell – biomaterial interactions with a particular focus on hPSC cells, and laminin and CNF biomaterials. The implications of these interactions on in vitro cell cultures and stem cell differentiation to hepatic cells are analyzed.
Source: Työväentutkimus Vuosikirja
Author: Riina Harjumäki
Language: English
Subfield: Cell Biology
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W2996191893