Ricerc@Sapienza

Abstract: Changes in cell–matrix and cell-to-cell adhesion patterns are dramatically fostered by
the microgravity exposure of living cells. The modification of adhesion properties could promote
the emergence of a migrating and invasive phenotype. We previously demonstrated that short
exposure to the simulated microgravity of human keratinocytes (HaCaT) promotes an early epithelial–
mesenchymal transition (EMT). Herein, we developed this investigation to verify if the cells maintain
the acquired invasive phenotype after an extended period of weightlessness exposure. We also
evaluated cells’ capability in recovering epithelial characteristics when seeded again into a normal
gravitational field after short microgravity exposure. We evaluated the ultra-structural junctional
features of HaCaT cells by Transmission Electron Microscopy and the distribution pattern of vinculin
and E-cadherin by confocal microscopy, observing a rearrangement in cell–cell and cell–matrix
interactions. These results are mirrored by data provided by migration and invasion biological assay.
Overall, our studies demonstrate that after extended periods of microgravity, HaCaT cells recover an
epithelial phenotype by re-establishing E-cadherin-based junctions and cytoskeleton remodeling,
both being instrumental in promoting a mesenchymal–epithelial transition (MET). Those findings
suggest that cytoskeletal changes noticed during the first weightlessness period have a transitory
character, given that they are later reversed and followed by adaptive modifications through which
cells miss the acquired mesenchymal phenotype