LSD2 appears to represent a new class of regulators, a protein that transduces regulatory signals to a separable core motor machinery. In addition, the demonstration that LSD2 regulates both transport and lipid metabolism suggests a link between lipid-droplet motion and lipid homeostasis.

Lysyl oxidase (LOX) catalyzes the oxidative deamination of lysine residues in collagen and elastin, key components of connective tissue. LOX is synthesized as an inactive 50 kD pre-proenzyme, and secreted to the extracellular matrix where it is cleaved into an active 32 kD LOX, and an 18kD free propeptide (LOX-PP), purportedly an inhibitor of fibroblast growth factor-2 (FGF-2) signaling. Given that adipocytes are distributed inside the connective tissue, it is likely that LOX-PP has an important regulatory role in adipogenesis, which has not been studied. Using NIH 3T3-L1 cells, we observed that FGF-2 inhibited adipogenesis, and LOX-PP promoted adipogenesis of 3T3-L1 cells in the presence of FGF-2; the expression of peroxisome proliferator-activated receptor (PPAR) g and CCAAT-enhancer binding protein (C/EBP) a, two markers of adipogenesis, were enhanced in the presence of LOX-PP. We further observed that LOX-PP down-regulated AKT and ERK1/2, two proliferative signaling proteins down-stream of FGF-2 signaling. Similarly, inhibition of FGF-2 receptor signaling by canofin, a competitive inhibitor of FGF-2 receptor, promoted adipogenesis albeit less effective compared to LOX-PP. To further explore whether LOX-PP promoted adipogenesis through inhibition of FGF-2 signaling, site directed mutagenesis of LOX-PP, resulting in an Arg158 to Gln158 mutation which abolishes the inhibitory activity of LOX-PP to FGF-2 receptor, attenuated the adipogenic promoting properties of LOX-PP. In summary, for the first time, our data show that LOX-PP enhances adipogenesis at least partially through inhibition of FGF-2 receptor signaling. Our data suggest that LOX-PP may serve as a bona fide therapeutic target for regulating adipogenesis and adipose tissue development.

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.