The role of transglutaminase 2 in cell motility processes and its effect on cutaneous wound healing

Transglutaminase 2 (TG2) is a multi-functional protein that catalyses post-translational protein modification by transamidation, and it functions as a G-protein to α1B- and α1D-adrenergic receptors via GTP-binding and hydrolysis, as well as being an adaptor-like molecule bridging between the extracellular environment and cell surface adhesion receptors. The aim of this work was to investigate the role of TG2 in murine cutaneous wound healing and the relevant cell motility processes of cell adhesion, spreading and migration.Full-thickness, 5mm-diameter, skin wounds were made on congenic 129T2/SvEmsJ wildtype (129T2-TG2+/+) or TG2 knockout (129T2-TG2-/-) mice by punch biopsy. Wound areas were monitored until closure. 129T2-TG2-/- mice had a slower rate of wound closure during the initial wound-healing phase relative to their wildtype counterpart. This delayed closure rate was rescued with a single application, immediately post-wounding, of purified TG2 to the wounds.Cell adhesion, spreading, and migration studies were performed in-vitro utilising primary murine embryonic fibroblasts (MEFs), a cell type relevant in the early stages of wound healing. Relative to wildtype, MEFs from 129T2-TG2-/- mice were impaired in cell adhesion, spreading, and migration, and, in concurrence with the in vivo results, TG2 addition rescued these processes in 129T2-TG2-/- and enhanced them in wildtype fibroblasts. TG2 addition also overcame inhibition of integrin cell adhesion receptors mediated by their competitive inhibitor, RGD. Blocking both integrin- and syndecan-mediated adhesion drastically reduced fibroblast adhesion. This was not rescuable in either genotype by TG2 addition and, moreover, 129T2-TG2-/- MEF adhesion remained reduced relative to TG2+/+ MEFs, even with TG2 addition. This suggests an inherent TG2 effect that is independent of TG2 interaction with integrins or syndecans. Interestingly, congenic C57Bl/6 (B6.Cg-) TG2+/+ and TG2-/- wound closure as well as fibroblast properties were similar to those of 129T2-TG2-/-, and significantly impaired relative to 129T2-TG2+/+. This correlated with lower TG2 expression levels in B6.Cg-TG2+/+ than in 129T2-TG2+/+ mice.The data presented here demonstrate a role for TG2 in the physiological process of cutaneous wound healing suggest a potential use for TG2 as a therapeutic agent in the treatment of wounds through its effects on fibroblast dynamics