An in Vitro Study on Tissue Repair: Impact of Unloading on Cells Involved in the Remodelling Phase

Abstract

The number of astronauts involved in longlasting missions and extra-vehicular activities is going to increase in the future. Consequently, the chance of injury due to traumatic events or unexpected emergency surgery will also increase and medical evacuation times to earth will be prolonged. Hence, the need to address requirements for surgery and trauma care in non terrestrial environments will be a priority. Tissue repair in weightlessness should therefore be regarded as a major issue not enough studied to date. Wound healing is a complex multi-step process, crucial to the survival of the organism. It starts with an inflammatory phase followed by a remodelling phase. During repair, the extracellular matrix (ECM) is sequentially remodelled by the concerted action of different cell types, in order to rebuild a functional tissue. The available literature concerning wound healing with mechanical unloading presents controversial results. However, many studies indicate impairment of the healing processes. Here we present a study on the behaviour of cells involved in the remodelling phase of repair, e.g. fibroblasts and endothelial cells, in response to microgravity (μg). In particular, their adhesion/migration, cytoskeleton organization, production of ECM molecules and receptors have been investigated. Cell response to pulsed Nd:YAG laser irradiation has also been investigated in order to evaluate the possibility to use laser irradiation for counteracting the effect of μg on wound healing. In μg, we observed alterations in production/assembling of ECM molecules. Increased fibronectin (FN) and laminin (LM) could be the cause for impaired ECM rebuilding and altered cell adhesion/migration. Treatment with Nd:YAG laser pulses induced organized fibrillogenesis and favoured endothelial cell spreading and monolayer formation. These findings open the way for a better understanding of tissue repair mechanisms in space and future clinical applications on earth.

Modeled Microgravity Affects Fibroblast Functions Related to Wound Healing

“…Its decrease, although not statistically significant (p > 0.05), is consistent with the α-SMA decrease and the lower adhesion ability. These results are in agreement with the findings of our previous experiments, in which significant alterations in the distribution of actin filaments and α5β1 integrins were observed (Monici et al 2011). Also, other authors reported on the effects of cytoskeleton disruption in fibroblasts (Bohmer et al 1996) and μginduced downregulation of genes involved in cytoskeleton organization and adhesion (Beck et al 2014).…”

“…Some studies reported that exposure to microgravity may induce skin atrophy (Neutelings et al 2015), delay and impair wound healing (Davidson et al 1999;Delp 2008;Radek et al 2008), and alter processes involved in it, such as inflammation, apoptosis, cell migration, collagen formation, and ECM deposition (Infanger et al 2006;Pietsch et al 2011;Morbidelli et al 2005;Monici et al 2006Monici et al , 2011Chung and Erickson 1997).…”

“…In WI-38 fibroblasts, space flight induced changes in gene expression, mostly associated with cellular stress signaling, directing the cells to either apoptotic death or premature senescence (Liu and Wang 2008). Following exposure to microgravity, modeled by a Random Positioning Machine (RPM), fetal fibroblasts showed alterations in distribution of α5β1 integrins and the network of actin filaments (Monici et al 2011). Culturing fetal murine fibroblasts in a RPM induced oxidative stress-responsive genes and downregulated genes involved in cytoskeleton organization and adhesion (Beck et al 2014).…”

Effect of Unloading Condition on the Healing Process and Effectiveness of Platelet Rich Plasma as a Countermeasure: Study on In Vivo and In Vitro Wound Healing Models

“…In the in vitro wound healing models (scratched fibroblast monolayers) exposed to unloading conditions, the ability of fibroblasts to migrate was significantly decreased, as assessed by both scratch and Boyden chamber assays. Previous studies demonstrated an altered production of ECM molecules, such as fibronectin and collagen I, in fibroblasts and endothelial cells cultured in µg simulated by RPM [30]. A relationship could be speculated between inability to migrate and altered ECM production, which could be also a cause of the scarce de novo formation of reparative connective tissue observed in the leeches exposed to µg (Figure 4).…”

“…In vitro studies on immune cells, fibroblasts, endothelial, and epithelial cells cultured both in real and modeled µg conditions show alterations of functions involved in wound healing, such as phagocytosis, adhesion/migration, apoptosis, proliferation, intercellular cross-talking, production of inflammatory mediators, ECM molecules, growth factors, and so on [26][27][28][29][30][31][32].…”