Tailored Integrin–Extracellular Matrix Interactions to Direct Human Mesenchymal Stem Cell Differentiation

Abstract

Integrins provide the primary link between mesenchymal stem cells (MSCs) and their surrounding extracellular matrix (ECM), with different integrin pairs having specificity for different ECM molecules or peptide sequences contained within them. It is widely acknowledged that the type of ECM present can influence MSC differentiation; however, it is yet to be determined how specific integrin-ECM interactions may alter this or how they change during differentiation. We determined that human bone marrow-derived mesenchymal stem cells (hMSCs) express a broad range of integrins in their undifferentiated state and show a dramatic, but transient, increase in the level of α5 integrin on day 7 of osteogenesis and an increase in α6 integrin expression throughout adipogenesis. We used a nonfouling polystyrene-block-poly(ethylene oxide)-copolymer (PS-PEO) surface to present short peptides with defined integrin-binding capabilities (RGD, IKVAV, YIGSR, and RETTAWA) to hMSCs and investigate the effects of such specific integrin-ECM contacts on differentiation. hMSCs cultured on these peptides displayed different morphologies and had varying abilities to differentiate along the osteogenic and adipogenic lineages. The peptide sequences most conducive to differentiation (IKVAV for osteogenesis and RETTAWA and IKVAV for adipogenesis) were not necessarily those that were bound by those integrin subunits seen to increase during differentiation. Additionally, we also determined that presentation of RGD, which is bound by multiple integrins, was required to support long-term viability of hMSCs. Overall we confirm that integrin-ECM contacts change throughout hMSC differentiation and show that surfaces presenting defined peptide sequences can be used to target specific integrins and ultimately influence hMSC differentiation. This platform also provides information for the development of biomaterials capable of directing hMSC differentiation for use in tissue engineering therapies.

Vitronectin-Based, Biomimetic Encapsulating Hydrogel Scaffolds Support Adipogenesis of Adipose Stem Cells

“…29 Although there are a few common changes of integrin subunit expression between BM-MSCs and ASCs (like the increase in a6), there are more notably some potentially important differences. One such difference is the lack of increase in a5 and aV in the BM-MSCs.…”

“…28 The expression levels of some of these proteins have previously been shown to change, in vitro, during differentiation of ASCs down various lineages. 1,[29][30][31] During osteogenic differentiation increased deposition of collagens I and IV have been observed, 1,29 whereas chondrogenic differentiation shows increases in collagen II. 2,3,32 Changes in ECM expression of adipogenically differentiated mesenchymal cells isolated from bone marrow have been studied previously.…”

“…2,3,32 Changes in ECM expression of adipogenically differentiated mesenchymal cells isolated from bone marrow have been studied previously. 4,5,[27][28][29]33 However, little work has been done examining adipogenesis in the more readily abundant cell population from fat lipoaspirate.…”

“…They interact with the surrounding ECM and relay messages from the extracellular environment to the cells, as well as from the cell to the ECM. 7,34 Based on previous work showing that BM-MSCs change their integrin expression profile during other types of differentiation, 8,[29][30][31]37 we hypothesized that the integrin profile of ASCs being directed toward an adipogenic lineage will alter in response to a changing ECM environment. We further hypothesize that we can utilize various small integrininteracting peptides, incorporated into a three-dimensional (3D) scaffold, to promote adipogenic differentiation of this stem cell population.…”

“…There are at least eight known integrins that can bind to laminin 28,54 and adipocytes use a small number of these. 33 While integrin expression of BM-MSC-derived adipocytes has been examined previously, 29 the expression of integrins in adipocytes derived from lipoaspirate, compared to their undifferentiated counterparts, has yet to be examined fully. Using immunocytochemistry, we characterized the expression of integrin subunits in undifferentiated ASCs and ASC-derived adipocytes that had been differentiated for 21 days (Fig.…”