Location: Arkansas Children's Nutrition CenterTitle: Palmitate Antagonizes Wnt/Beta-catenin Signaling in 3T3-L1 Pre-adipocytes Author
Submitted to: Obesity
Publication Type: Abstract Only
Publication Acceptance Date: 6/30/2008
Publication Date: 10/15/2008
Citation: Shankar, K., Harrell, A., Ronis, M.J., Badger, T.M. 2008. Palmitate antagonizes wnt/beta-catenin signaling in 3T3-L1 pre-adipocytes [abstract]. Obesity. 16(1):182P. Interpretive Summary:
Technical Abstract: Long chain saturated free fatty acids such as palmitate (PA) produce insulin resistance, endoplasmic reticulum stress, and apoptosis in mature adipocytes and pre-adipocytes. In pre-adipocytes, saturated free fatty acids also promote adipogenic induction in the presence of adipogenic hormones. Wnt/beta-catenin signaling is both anti-apoptotic and anti-adipogenic in pre-adipocytes and down-regulation of wnt/beta-catenin signaling by free fatty acids may underlie both pro-adipogenic and pro-apoptotic effects in these cells. In the present studies, we have examined the effect of PA on wnt/beta-catenin signaling in 3T3-L1 pre-adipocytes. Confluent 3T3-L1 cells were treated with either 0, 50, 100, or 250 microM PA (Na-palmitate conjugated to BSA, 3:1). Analyses of whole cell RIPA lysates showed significantly lower beta-catenin levels at 250 microM PA (p<0.05). Cytoplasmic and nuclear beta-catenin levels were decreased at concentrations above 250 microM and GSK3 beta phosphorlyation at Ser 21/9 was reduced (p<0.05), while not affecting total GSK3 beta levels. Lithium chloride, a GSK3 beta inhibitor, led to increased (p<0.05) cytosolic and nuclear beta-catenin levels. However, co-treatment with PA (250 microM) attenuated lithium chloride induced beta-catenin levels. Real-time PCR analyses revealed PA (250 microM) decreased mRNA levels of wnt receptors, frizzled 1 and 2 by 5 and 2 fold respectively, while mRNA levels of the wnt signaling antagonist, Sfrp2 were increased 2.5 fold over controls. mRNA expression of the ER stress marker, Chop10 was also increased about 4 fold following treatment with 250 microM PA. Finally, we examined whether wnt-induced beta-catenin signaling was affected by PA. TOPFlash reporter assays revealed that 3T3-L1 pre-adipocytes showed a 4.5 fold increase in luciferase activity following wnt-3a (50 ng/ml) treatment. However, co-treatment of PA (400 microM) with wnt-3a completely abolished wnt-3a induced beta-catenin signaling. The role of MAPK and JNK signaling in PA-mediated antagonism of wnt/beta-catenin signaling is being studied. These data collectively indicate that PA significantly dysregulates wnt/beta-catenin signaling in pre-adipocytes.