Lysyl Oxidase Propeptide Promotes Adipogenesis through Inhibition of FGF‐2 Signaling

Abstract

Lysyl oxidase (LOX), an extracellular enzyme, catalyzes the oxidative deamination of lysine residues in collagen and elastin. LOX is synthesized as an inactive 50kd prepro‐protein and secreted where it is cleaved into an active 32kd enzyme and an 18kd propeptide (PP). Fibroblast growth factor‐2 (FGF‐2) leads to the expansion of fibrogenic progenitor cells, and it is reported that PP inhibits FGF‐2 signaling. We hypothesized that PP regulates adipogenesis via inhibition of FGF‐2 signaling. 3T3‐L1 cells were treated with FGF‐2 and adipogenesis was evaluated by expression of PPARγ and Oil‐Red O staining. PP was cloned into pFLAG expression vector and expressed in DH5α cells. 3T3‐L1 cells were allowed to differentiate with PP and adipogenic medium. Recombinant PP inhibited FGF‐2 signaling by up‐regulation of the adipogenic marker PPARγ, whereas the phosphorylation of ERK1/2 and AKT, two key pathways activated by FGF‐2, was reduced. Separately, we cloned PP into pCMV mammalian expression vector, and made a point mutation resulting in an Arg152 to Gln substitution, which is expected to diminish its inhibitory effect on FGF‐2 signaling. Similarly, transfection with WT PP increased expression of PPARγ and C/EBPα, whereas the PP point mutation diminished the adipogenic promoting potential of LOX‐PP. For the first time, our data show that PP enhances adipogenesis, an effect mediated by inhibition of FGF‐2 signaling.