Oxidant Stress Mediates the Effects of Inflammatory Lipids on PTH Responsiveness in Osteoblasts
Authors:Jamie Garcia , Xin Li, Jinxiu Lu, Yin Tintut
Mentor:Yin Tintut , Adjunct Professor David Geffen School of Medicine , University of California Los Angeles
High fat diet over an extended period of time can cause hyperlipidemia. Hyperlipidemia, the consistently high concentration of low-density lipoprotein (LDL) or lipids in the blood, causes an accumulation of lipid oxidation products in the subendothelial spaces of arteries and bone. Prolonged accumulation of these lipids leads to oxidative modifications and elicits an inflammatory reaction. The project is investigating if oxidant stress is mediating the pathway from oxidized lipid to parathyroid hormone receptor (PTH1R) expression. This pathway is important because if PTH1R expression is reduced, downstream processes such as osteoblastic differentiation will be affected. Evidence suggests that the presence of hyperlipidemia reduces PTH1R expression. The inflammatory lipids inhibit osteoblastic differentiation and decrease response to intermittent parathyroid hormone treatment (iPTH). The hypothesis is that oxidant stress mediates the effects of inflammatory lipids on PTH1R expression in osteoblasts. Calvarial preosteoblasts (MC3T3-E1) were plated to determine PTH1R gene expression at 2, 4, 6, 8, 10, and 12 days by real-time RT-qPCR. This PTH1R time course experiment showed that expression of the PTH1R gene peaked after 4 days. MC3T3-E1 cells were also plated and treated with the enzyme, xanthine oxidase (5mu/mL, 10mu/mL, and 25mu/mL), and the substrate, xanthine (25uM). Xanthine and xanthine oxidase (XXO) are known to produce oxidant stress. Results showed that PTH1R expression was inhibited in a dose dependent manner by XXO. Pretreatment of MC3T3-E1 cells with XXO reduces PTH-induced expression of Nurr1 and PTH1R. Our preliminary experiments showed that oxidant stress might be mediating osteoblastic differentiation and PTH1R levels.