Fibrocytes: A Critical Review and Practical Guide

Abstract

Fibrocytes are hematopoietic-derived cells that directly contribute to tissue fibrosis by producing collagen following injury, during disease, and with aging. The lack of a fibrocyte-specific marker has led to the use of multiple strategies for identifying these cells in vivo. This review will detail how past studies were performed, report their findings, and discuss their strengths and limitations. The motivation is to identify opportunities for further investigation and promote the adoption of best practices during future study design.

Old age promotes retinal fibrosis in choroidal neovascularization through circulating fibrocytes and profibrotic macrophages

“…Fibrocytes in the BM and blood were identified by flow cytometry using CD45 and collagen-1 as markers [ 22 ] (Fig. 2 A).…”

“…Fibrocytes are hematopoietic-derived collagen-1-producing cells. Once formed in the bone marrow (BM), they move to blood circulation and can migrate to the spleen and peripheral tissues [ 22 ]. When an injury occurs, fibrocytes are recruited and differentiate into myofibroblasts, which contribute to wound healing and fibrosis [ 22 ].…”

“…Once formed in the bone marrow (BM), they move to blood circulation and can migrate to the spleen and peripheral tissues [ 22 ]. When an injury occurs, fibrocytes are recruited and differentiate into myofibroblasts, which contribute to wound healing and fibrosis [ 22 ]. Although there is no consensus on fibrocytes-specific markers, the cells are generally identified by their hematopoietic origin (e.g., express CD34 and CD45) and their ability to produce collagen-1/3 [ 22 ].…”

“…When an injury occurs, fibrocytes are recruited and differentiate into myofibroblasts, which contribute to wound healing and fibrosis [22]. Although there is no consensus on fibrocytes-specific markers, the cells are generally identified by their hematopoietic origin (e.g., express CD34 and CD45) and their ability to produce collagen-1/3 [22]. Altered circulating fibrocytes have been linked to idiopathic pulmonary fibrosis and atrial fibrosis [23][24][25], although their function is affected by age and their role in age-related retinal fibrosis remain unknown.…”

Current Perspectives on Nucleus Pulposus Fibrosis in Disc Degeneration and Repair

“…A subset of fibroblasts expressing FSP-1 were identified in the heart, kidneys and skin [ 78 ], while an FSP-1 expressing myeloid-monocytic cell lineage was found to be involved in liver injury [ 79 ]. Myofibroblasts could be derived from mesenchymal stromal cells [ 80 ], epithelial–mesenchymal transition (EMT, [ 81 ]), circulating fibrocytes [ 82 ], pericytes [ 83 ] and macrophages [ 6 ]. In both cultured disc cells and a mouse annulus puncture-induced IDD model, treatment with bleomycin, a commonly used fibrosis-inducing agent, resulted in the expression of fibroblastic markers [ 26 ].…”