Circulating Fibrocytes: Cellular Mediators of Tissue Fibrosis

Fibrosis is a pathological condition resulting from an excessive tissue response during the repair process, often affecting various tissues such as the skin, organs, and joints, posing a significant threat to global health. Researchers have made substantial efforts to explore the endogenous mechanisms underlying fibrosis in recent years and have developed several therapeutic strategies to block this process. Historically, research on fibrotic diseases has focused on identifying highly relevant therapeutic targets and developing effective antifibrotic drugs. However, due to the complexity of the mechanisms of fibrosis and its effector cells, the effectiveness of antifibrotic therapies remains limited. With the advancement of high-throughput omics technologies and machine learning tools, we now have a clearer understanding of cellular heterogeneity, intercellular interactions, and the specific roles of cells in various biological processes. This enables tracking the trajectory of different cell types during the fibrotic process, facilitating early identification and discovery of new targets for fibrosis treatment, and conducting more precise targeted research. Supported by these novel technologies, numerous studies have revealed that, in addition to normal fibroblasts, a group of bone marrow-derived fibrocytes also contributes to the fibrosis of both parenchymal and non-parenchymal organs and tissues. Circulating fibrocytes are hematopoietic-derived cells that are recruited to injury sites during injury, disease, and aging, acting as participants in inflammation and tissue repair, and directly or indirectly promoting fibrosis in various tissues throughout the body. This review summarizes the general characteristics of circulating fibrocytes, the molecular mechanisms involved in their recruitment to different tissues, the process of their differentiation into fibroblasts, their potential roles in various diseases, and the latest research developments in this field. Given the key role of circulating fibrocytes in fibrosis across multiple tissues, they may serve as promising targets for the development of novel antifibrotic therapies.