Cryptic fragment α4 LG4-5 derived from laminin α4 chain inhibits de novo adipogenesis by modulating the effect of fibroblast growth factor-2

Cleavage of the extracellular matrix (ECM) by proteolysis unmasks cryptic sites and generates novel fragments with biological activities functionally distinct from those of the intact ECM molecule. The laminin G-like (LG)4-5 fragment has been shown to be excised from the laminin α4 chain in various tissues. However, the functional role of this fragment has remained unknown to date. To investigate this, we prepared α4 LG1-3 and α4 LG4-5 fragments by elastase digestion of recombinant α4 LG1-5, and examined their effects on de novo adipogenesis in mice at the site of injection of basement membrane extract (Matrigel) and fibroblast growth factor (FGF)-2. Although the addition of whole α4 LG1-5 suppressed adipogenesis to some extent, the α4 LG4-5 fragment could strongly suppress adipogenesis at a concentration of less than 20 nm. Addition of the α4 LG4 module, which contains a heparin-binding region, had a suppressive effect, but this was lost in mutants with reduced heparin-binding activity. In addition, antibodies against the extracellular domain of syndecan-2 and -4, which are known receptors for the α4 LG4 module, suppressed adipogenesis. Thus, these results suggest that the cryptic α4 LG4-5 fragment derived from the laminin α4 chain inhibits de novo adipogenesis by modulating the effect of FGF-2 through syndecans.