Submitted to: Free Radical Biology and Medicine
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/30/2012
Publication Date: 6/8/2012
Publication URL: http://handle.nal.usda.gov/10113/56805
Citation: Dekrey, E.E., Picklo, M.J. 2012. NAD(P)H:quinone oxidoreductase 1 activity reduces hypertrophy in 3T3-L1 adipocytes. Free Radicals in Biology and Medicine. 53:(2012)690-700. Interpretive Summary: Obesity is associated with elevated oxidative stress. This elevation may be through an increase in the formation of reactive oxygen species (ROS) and secondary products such as lipid peroxidation products. On the other hand, a decrease in antioxidant defense pathways can elevate steady-state levels of ROS. This present work examined how anti-oxidant defense proteins change during the formation of adipose cells. Our data demonstrate that the Nrf2 anti-oxidant defense pathway is downregulated as fat (adipose) cells mature. However, this defense pathway can be stimulated through application of the phytochemical sulforaphane. This work is the first to demonstrate a shift in cellular anti-oxidant defenses as fat cells form. These data will be useful for understanding how adipose cells change during obesity and why they may be more sensitive to toxicity during obesity. These data also show that the cellular defenses can be increased nutritionally.
Technical Abstract: The nuclear factor E2-related factor 2 (Nrf2)/Kelch-like ECH-associated protein 1 (Keap1) pathway responds to oxidative stress via control of the expression of several antioxidant genes. Recent efforts demonstrate that Nrf2 modulates development of adiposity and adipogenesis. However little is known about in situ disposition of Nrf2, Keap1, and one of its target proteins NAD(P)H:quinone oxidoreductase 1 (NQO1) during adipogenesis. Based on data in literature, we hypothesized that adipocyte differentiation would increase the Nrf2/Keap1 pathway and NQO1 expressions. Using murine 3T3-L1 adipocytes, we mapped an increase in Nrf2 (2.5-fold) and NQO1 (6-fold) protein at limited clonal expansion and post-mitotic growth arrest (days 1-3) stages and a decrease (5- and 4-fold, respectively) in expression in terminally differentiated (day 8) adipocytes that lasted for several days afterward. Conversely, NQO1, Nrf2, and Keap1 mRNA expression were all increased (1.4-, 2-, and 2-fold, respectively) in differentiated adipocytes (days 11-14), indicating a discrepancy between steady-state mRNA levels and the resulting protein. Treatment of differentiated 3T3-L1 adipocytes with glycogen synthase kinase-3ß (GSK-3ß) inhibitor, LiCl, led to 1.9-fold increase in NQO1 protein. Sulforaphane enhanced, NQO1 protein (10-fold) and Nrf2 nuclear protein (2.5-fold). These data demonstrate a biphasic response of Nrf2 and NQO1 during adipocyte differentiation and that NQO1 expression in mature adipocytes is regulated by Keap1- and GSK-3ß-dependent mechanisms. Furthermore, these data demonstrate a discrepancy between mRNA expression and protein content for NQO1, Nrf2, and Keap-1 in differentiating adipocytes.