Paracrine functions of fibrocytes to promote lung fibrosis

Abstract

Fibrocytes are derived from the bone marrow and are found in the circulation. They can be recruited to sites of injury and contribute to repair/remodeling. In vitro evidence suggests that fibrocytes may differentiate into fibroblasts to promote lung fibrosis. However, in vivo evidence for this is sparse. This review summarizes recent literature which may suggest that fibrocytes function to promote fibrosis via paracrine actions. In this way, secretion of growth factors, proteases and matricellular proteins may strongly influence the actions of resident epithelial and mesenchymal cells to promote repair and resolution or to tip the scale toward pathologic remodeling.

Keywords::

• bone marrow
• chemokines
• growth factors
• mesenchymal cells
• periostin

Financial & competing interests disclosure

KK Kim was supported by NIH HL108904. BB Moore was supported by NIH HL115618. The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed.

No writing assistance was utilized in the production of this manuscript.

Key issues

• Fibrocytes are a unique cell type with features of circulating bone marrow-derived leukocytes and fibroblasts. These cells have been identified by many groups, they express leukocyte and fibroblast markers and they are often found in increased numbers in a variety of fibrotic diseases.

• Because fibrocytes are circulating cells found in the blood there is real potential for using fibrocytes as a biomarker for diagnosis, prognosis and response to specific treatments.

• Fibrocytes can be recruited and activated by specific chemokines/cytokines and they can secrete a number of important profibrotic factors leading to recruitment and activation of other fibrogenic effector cells.

• Fibrocyte-derived factors can influence the behavior of multiple cell types therefore they may have a large impact in orchestrating fibrogenesis.

• Fibrocytes have a unique profile of receptors and secreted proteins suggesting that they may have a unique function during fibrogenesis and potentially offer a novel target for therapeutic intervention.

Notes