Dickkopf-1 promotes the differentiation and adipocytokines secretion via canonical Wnt signaling pathway in primary cultured human preadipocytes

Abstract

Dickkopf-1, a newly recognized antagonist for canonical Wnt signaling, is secreted in the early stage of human adipose-derived stem cells (ASCs) adipogenic differentiation. This study was aimed to investigate whether human recombinant DKK-1 (rhDKK-1) could affect the differentiation and metabolism as well as adipocytokines secretion in primary cultured human ASCs. Human ASCs were isolated from omental adipose tissue and induced to adipogenic differentiation in the absence or presence of Wnt signaling antagonist rhDKK-1 and agonist SB216763, respectively. mRNA and protein expression profiles of adipogenic factors during the differentiation process were analyzed using quantitative RT-PCR and Western blotting. Adipocytokines secretion levels in the culture medium were measured by ELISA method. Our results showed that DKK-1 was already expressed during the early stage of adipogenesis and reached the peak on the 9th day. Exogenous rhDKK-1 exposure accelerated the differentiation by up-regulating PPAR-γ and C/EBP-α, down-regulating Wnt3a, Wnt10b and β-catenin, without affecting non-canonical Wnt signaling marker (Wnt5a). In addition, rhDKK-1 treatment increased the secretion of leptin, RBP4, TNF-α and adiponectin during differentiation. rhDKK-1 treatment also significantly increased the intracellular accumulation of lipids and lipolysis. Thus, Wnt signal pathway agonist SB216763 down-regulated DKK-1 transcriptional and secretion levels during adipogenic process. Our results suggest that rhDKK-1 could promote ASCs differentiation and increase adipocytokines secretion via canonical Wnt signaling pathway.