|89th Annual Meeting Abstracts
Fibrocytes, the fibroblast progenitor cells of hematopoietic lineage, enhance cutaneous wound healing in diabetic mice.
Bin Chen, MD, PhD, George Murphy, MD, Dennis Orgill, MD, PhD, Lifei Guo, MD, PhD.
Brigham and Women's Hospital, Boston, MA, USA.
Fibrocytes are newly identified mesenchymal progenitor cells that can rapidly and specifically migrate into the site of tissue injury at the time of injury. They are derived from bone marrow and mature from a subpopulation of CD14 peripheral blood mononuclear cells. Fibrocytes are characterized by co-expression of hematopoietic cell markers such as CD11b, CD34, CD45, and CD13 as well as fibroblast markers such as collagen type I, fibronectin, and vimentin. Under permissive conditions, fibrocytes can further differentiate into myofibroblasts both in vitro and in vivo. There is increasing evidence that these circulating cells play a key role in pulmonary injury repair. We would like to investigate their role in cutaneous wound healing.
Mouse fibrocytes were isolated from the peripheral blood of wild type B6.Cg-m +/+ Lepr control mice. These cells were cultured and passaged as needed to day 28 after initial isolation. Their surface markers were examined, including those of CD11b, CD45, Collagen I, and α-SMA, over the course of their maturation. Real time PCR was performed to assay expression of various chemokines and growth factors. These expression profiles were compared to those of normal mouse dermal fibroblasts. Harvested fibrocytes at day 28, fibroblasts, both labeled with a fluorescent dye (PKH-26), or PBS, were then injected into the tail vein of a diabetic B6.Cg-m +/+ Leprdb/db mouse with a cutaneous full thickness dorsal wound. Wound contracture and re-epithelialization were recorded and analyzed with digital photography. Biopsies were taken at multiple time points. Fluorescent staining of the wounded tissue section was examined for presence of PKH-26 stained cells. Epidermal proliferation and dermal neo-vascularization were compared across the three experimental groups. Statistical analysis was performed where necessary.
We have showed that as these fibrocytes mature in vitro, they start to lose their hematopoietic markers such as CD11b and CD45 and at the same time, gain markers of a myofibroblast, such as collagen I and α-SMA. In addition, throughout their maturation process, they consistently express higher levels of chemokines (MCP-1, MIP-1a & 2a, and CXCR4) and certainly growth factors (TGF-β1, PDGF, and basic-FGF) than their mature dermal fibroblast counterpart. More remarkably, when intravenously injected into the diabetic mice with excisional dorsal wounds, they enhance wound healing, not only by accelerated dermal contraction, but also by faster re-epithelialization than either fibroblasts or PBS. Not surprisingly, PKH-26 labeled fibrocytes are found at the wound edge as early as day one post-injection, whereas injected dermal fibroblasts never migrate to the wound edges. Immunohistochemistry reveal higher rate of epidermal proliferation and denser dermal neo-vascularization in wounds of those diabetic mice with intravenous fibrocytes injection.
Fibrocytes are believed to be hematopoietic progenitor cells of mature fibroblasts. They have been previously implicated in pulmonary injury repair. Our study represents the first evidence of its role in cutaneous wound healing. This can potentially expand how one looks at the wound healing not only from a basic science standpoint but also, more practically, from a clinical and therapeutic standpoint.