Visualizing cell arrangements
In vivo , ECM molecules including fibronectins, collagens, and
laminins not only affect signaling properties and cell function but also
modulate overall tissue architecture with direct consequences on cell
arrangements and tissue organization.[57] To
better understand the effects of specific ECM proteins on the cell
organization, we used immunohistochemistry staining for HepG2 and HSC
cells in whole mount spheroids to visualize the impact of ECM modified
MPs on arrangements (Figure 7) . Although HepG2 cell
distribution was homogenous, we observed distinct localization of HSCs
toward the periphery of spheroids, generating a distinct outer layer of
similar thickness in all groups. This also correlates with E-cadherin
staining results (Figure 6B ). The contacting area of the
hepatocytes contains collagen fibrils, [58]resulting in a membrane thickening which we also observed in our images
(the purple ring at the edge of all groups). We observed that groups
treated with laminin-511 and 521 resulted in localization of some HSCs
toward the center of spheroids, perhaps because PFC-laminin 511/521 MPs
stimulate cells to change position relative to their neighbors toward
contact strengthening. This finding lends support to prior findings and
confirms that interactions between cells and the ECM at integrin-based
adhesion sites allow cells to sense their physical surroundings and
adjust mechanisms of migration and anchorage.[59]Thus, besides organization, our co culture system provides a similar
physicochemical structure that more closely mimics in vivo tissue
counterparts.