ABSTRACT
INTRODUCTION/OBJECTIVES: The protein delta homolog 1 (DLK1) has been reported to have an important role as inhibitor of adipogenesis. Understanding its mode of action can be a promising approach to cope with the formation of obesity. However, data on DLK1 signaling are not consistent, and especially its role as negative regulator of Notch receptors is discussed controversially. METHODS: DLK1 effects have been investigated in differentiated 3T3-L1 cells by Adipokine Profiler Array, enzyme-linked immunosorbent assay and quantitative real-time PCR (qRT-PCR). In vivo effects of DLK1 on adipogenesis have been studied by the DLK1 treatment of pregnant C57BL/6NTac mice and the phenotypical characterization of the offspring fed on chow or high-fat diet (HFD). Furthermore, gene expression of key adipogenesis genes in adipose tissue (AT) samples was observed by qRT-PCR. RESULTS: In 3T3-L1 cells, DLK1 was found to be an inhibitor of Notch1 signaling. Gene expression of Notch1 and Hes1 was lowered by 53% and 65%, respectively, and the expression of protein target PAI-1 was decreased by 51%. The offspring of DLK1-treated pregnant mice were fed chow or HFD starting from week 4. At week 18, a larger proportion of visceral AT was determined on HFD after DLK1 treatment (P=0.011), whereas adipocyte size was reduced (P=0.007 for maximal size). This was affiliated to an upregulation of adipocyte differentiation. The underlying mechanism was found in an increased expression of the Notch1 receptor gene and protein in AT of the offsprings independently of the diet. However, feeding a chow diet resulted in a decreased expression of Notch1 target genes Hes1 and RBP-Jκ, whereas under HFD these genes were upregulated. CONCLUSIONS: Treatment of mice with recombinant human DLK1 during pregnancy has significant effects on AT of the offspring. This can be associated with counter-regulatory changes in the Notch1 signaling cascade.
