Borrelidin Isolated from Streptomyces sp. Inhibited Adipocyte Differentiation in 3T3-L1 Cells via Several Factors...

An inhibitor of 3T3-L1 adipocyte differentiation was isolated from Streptomyces sp. TK08330 and identified by spectroscopy as the 18-membered macrolide borrelidin. Treatment with 1.0 μM borrelidin suppressed intracellular lipid accumulation by 80% and inhibited the expression of adipocyte-specific genes. Borrelidin suppressed the mRNA expression of two master regulators of adipocyte differentiation, peroxisome proliferator-activated receptor gamma (PPARγ) and CCAAT/enhancer binding protein (C/EBPα). Studies on well-known upstream regulators of PPARγ revealed that borrelidin down-regulated C/EBPδ mRNA expression but did not affect expression of C/EBPβ. Borrelidin increased mRNA expression of negative regulators of differentiation such as GATA-binding protein (GATA) 3, Krüppel-like factor (KLF) 3 and KLF7, as well as positive regulators, KLF4, KLF6 and KLF15, at early stages of differentiation. To elucidate a primary mediator of borrelidin differentiation inhibitory activity, small interfering RNA (siRNA) transfection experiments were performed. The mRNA expression of PPARγ, which was down-regulated by borrelidin, was not changed by KLF3 and KLF7 siRNA treatment. In contrast, expression of PPARγ in GATA-3 siRNA-treated cells was not significantly different from that of control siRNA-treated cells. Borrelidin significantly inhibited lipid accumulation in control siRNA-treated cells, and treatment with GATA-3 siRNA slightly reduced the inhibitory effect of borrelidin. These results indicate that borrelidin inhibited adipocyte differentiation partially via GATA-3.