Factor XIII (FXIII) is a transglutaminase enzyme that catalyses the formation of ε-(γ-glutamyl)lysyl isopeptide bonds into protein substrates. The plasma form, FXIIIA2B2, has an established function in haemostasis, with fibrin being its principal substrate. A deficiency in FXIII manifests as a severe bleeding diathesis emphasising its crucial role in this pathway. The FXIII-A gene (F13A1) is expressed in cells of bone marrow and mesenchymal lineage. The cellular form, a homodimer of the A subunits denoted FXIII-A, was perceived to remain intracellular, due to the lack of a classical signal peptide for its release. It is now apparent that FXIII-A can be externalised from cells, by an as yet unknown mechanism. Thus, three pools of FXIII-A exist within the circulation: plasma where it circulates in complex with the inhibitory FXIII-B subunits, and the cellular form encased within platelets and monocytes/macrophages. The abundance of this transglutaminase in different forms and locations in the vasculature reflect the complex and crucial roles of this enzyme in physiological processes. Herein, we examine the significance of these pools of FXIII-A in different settings and the evidence to date to support their function in haemostasis and wound healing
Bibliographical noteAuthor Contributions: F.S.M.A. wrote the manuscript; C.S.W. supervised the research and wrote the manuscript; N.J.M. supervised the research and wrote the manuscript. All authors have read and agreed to the published version of the manuscript.
Funding: Fahad S.M. Alshehri is supported by Royal Embassy of Saudi Arabia Cultural Bureau (KFMCS74). Claire S. Whyte and Nicola J. Mutch were supported by the British Heart Foundation project grants (PG/15/82/31721 and PG/20/17/35050).
Acknowledgments: All figures were prepared with https://biorender.com/ (accessed on 16 March 2021).
- Factor XIII-A
- cellular FXIII-A
- wound healing