FSTL1

Follistain-like 1 (Fstl1) is a member of the secreted protein acidic rich in cysteine (SPARC) family and has been implicated in many different signaling pathways, including BMP and TGF-β signaling. In multiple biological and pathological processes, such as immunomodulation, tumorigenesis, vascularization, fibrogenesis and embryonic development, Fstl1 has shown diverse and cell type-specific functions, including the regulation of cell proliferation, apoptosis, differentiation, and migration. In lung development, loss-of-function experiments using null mice have unveiled Fstl1 as a BMP antagonist in regulating alveolar epithelial differentiation/maturation. In addition, Fstl1 has been reported to be ubiquitously expressed in embryonic lung with high levels in mesenchyme surrounding airways and walls of blood vessels. The dynamic spatial expression pattern suggests another potential role of Fstl1 in the development of mesenchymal-derived lineages in the lung, specially ASM and VSM.