Follistatin-related protein 1 (FSTL1) is an extracellular glycoprotein whose functional significance in physiological and pathological processes is incompletely understood. Recently, we have shown that FSTL1 acts as a muscle-derived secreted factor that is up-regulated by Akt activation and ischemic stress and that FSTL1 exerts favorable actions on the heart and vasculature. Here, we sought to identify the receptor that mediates the cellular actions of FSTL1. It contains an FS module, a follistatin-like sequence containing 10 conserved cysteine residues. FSTL1 is thought to be an autoantigen associated with rheumatoid arthritis. DIP2A functions as a novel receptor that mediates the cardiovascular protective effects of FSTL1. Experiment results have provided in vivo and in vitro evidence to demonstrate that Fstl1 modulates lung development and alveolar maturation, in part, through BMP4 signaling.

> 90% as determined by SDS-PAGE.