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Published on: April 29, 2015
Cre/lox Studies Identify Resident Macrophages as the Major Source of Circulating Coagulation Factor XIII-A
Cora M L Beckers1, Kingsley R Simpson1, Kathryn J Griffin1
1From the Leeds Institute for Cardiovascular and Metabolic Medicine, LIGHT Laboratories, University of Leeds, United Kingdom (C.M.L.B., K.R.S., K.J.G., J.M.B., L.T.C., K.A.S., P.A.C., M.T.K., P.J.G., R.J.P.); and Clinical Research Institute of Montreal, McGill University, Canada (J.V.).
Objective:
To establish the cellular source of plasma factor (F)XIII-A.
Approach And Results:
A novel mouse floxed for the F13a1 gene, FXIII-Aflox/flox (Flox), was crossed with myeloid- and platelet-cre-expressing mice, and cellular FXIII-A mRNA expression and plasma and platelet FXIII-A levels were measured. The platelet factor 4-cre.Flox cross abolished platelet FXIII-A and reduced plasma FXIII-A to 23±3% (P<0.001). However, the effect of platelet factor 4-cre on plasma FXIII-A was exerted outside of the megakaryocyte lineage because plasma FXIII-A was not reduced in the Mpl-/- mouse, despite marked thrombocytopenia. In support of this, platelet factor 4-cre depleted FXIII-A mRNA in brain, aorta, and heart of floxed mice, where FXIII-Apos cells were identified as macrophages as they costained with CD163. In the integrin αM-cre.Flox and the double copy lysozyme 2-cre.cre.Flox crosses, plasma FXIII-A was reduced to, respectively, 75±5% (P=0.003) and 30±7% (P<0.001), with no change in FXIII-A content per platelet, further consistent with a macrophage origin of plasma FXIII-A. The change in plasma FXIII-A levels across the various mouse genotypes mirrored the change in FXIII-A mRNA expression in aorta. Bone marrow transplantation of FXIII-A+/+ bone marrow into FXIII-A-/- mice both restored plasma FXIII-A to normal levels and replaced aortic and cardiac FXIII-A mRNA, while its transplantation into FXIII-A+/+ mice did not increase plasma FXIII-A levels, suggesting that a limited population of niches exists that support FXIII-A-releasing cells.
Conclusions:
This work suggests that resident macrophages maintain plasma FXIII-A and exclude the platelet lineage as a major contributor.
Insights
Resident macrophages, not platelets, are the primary source of plasma factor XIII-A (FXIII-A). This study utilized genetically modified mice to demonstrate that macrophages maintain circulating FXIII-A levels.
Area of Science:
- Hematology
- Cell Biology
- Molecular Biology
Background:
- Plasma factor XIII-A (FXIII-A) is crucial for hemostasis and wound healing.
- The cellular origin of plasma FXIII-A has been debated, with both myeloid and platelet lineages being considered.
Purpose of the Study:
- To definitively establish the cellular source of plasma factor XIII-A (FXIII-A).
- To investigate the contribution of myeloid and platelet lineages to circulating FXIII-A levels.
Main Methods:
- Generation of novel mouse models with floxed F13a1 gene crossed with myeloid- and platelet-specific Cre-recombinase expressing mice.
- Quantification of cellular FXIII-A mRNA expression, plasma FXIII-A levels, and platelet FXIII-A content.
- Bone marrow transplantation experiments to assess cellular contribution to FXIII-A production.
Main Results:
- Deletion of FXIII-A in platelets significantly reduced plasma FXIII-A, but this effect was independent of megakaryocyte lineage.
- FXIII-A mRNA was depleted in macrophages within various tissues (brain, aorta, heart) upon platelet-specific Cre expression.
- Myeloid-specific Cre expression (integrin αM-cre and lysozyme 2-cre) significantly reduced plasma FXIII-A levels, correlating with FXIII-A mRNA in aorta.
- Bone marrow transplantation confirmed that a specific niche supports FXIII-A-releasing cells, likely macrophages.
Conclusions:
- Resident macrophages are the primary source of plasma factor XIII-A (FXIII-A).
- The platelet lineage is not a major contributor to circulating FXIII-A levels.
- These findings have implications for understanding coagulation disorders and FXIII-A-related therapies.
