Quercetin 3-Glucoside Protects Neuroblastoma (SH-SY5Y) Cells in Vitro against Oxidative Damage by Inducing Sterol Regulatory Element-binding Protein-2-mediated Cholesterol Biosynthesis

Ramani Soundararajan,Alexander D Wishart,H.P Vasantha Rupasinghe,Mayi Arcellana-Panlilio,Carolanne M Nelson,Michael Mayne,George S Robertson

doi:10.1074/jbc.m703583200

Abstract

The flavonoid quercetin 3-glucoside (Q3G) protected SH-SY5Y, HEK293, and MCF-7 cells against hydrogen peroxide-induced oxidative stress. cDNA microarray studies suggested that Q3G-pretreated cells subjected to oxidative stress up-regulate the expression of genes associated with lipid and cholesterol biosynthesis. Q3G pretreatment elevated both the expression and activation of sterol regulatory element-binding protein-2 (SREBP-2) only in SH-SY5Y cells subjected to oxidative stress. Inhibition of SREBP-2 expression by small interfering RNA or small molecule inhibitors of 2,3-oxidosqualene:lanosterol cyclase or HMG-CoA reductase blocked Q3G-mediated cytoprotection in SH-SY5Y cells. By contrast, Q3G did not protect either HEK293 or MCF-7 cells via this signaling pathway. Moreover, the addition of isopentenyl pyrophosphate rescued SH-SY5Y cells from the inhibitory effect of HMG-CoA reductase inhibition. Last, Q3G pretreatment enhanced the incorporation of [(14)C]acetate into [(14)C]cholesterol in SH-SY5Y cells under oxidative stress. Taken together, these studies suggest a novel mechanism for flavonoid-induced cytoprotection in SH-SY5Y cells involving SREBP-2-mediated sterol synthesis that decreases lipid peroxidation by maintaining membrane integrity in the presence of oxidative stress.

Highlights

Cholesterol, phospholipids, and sphingolipids are major structural components of the eukaryotic plasma membrane that play an essential role in maintaining membrane integrity
When cholesterol levels are low, SREBP cleavage-activating protein (SCAP) escorts sterol regulatory element-binding protein-2 (SREBP-2) from the endoplasmic reticulum to Golgi, where SREBP-2 is proteolytically cleaved by proteases into a mature form (65 kDa) that translocates to the nucleus and binds to the sterol regulatory element, triggering the transcrip
Treatment with 105 cells/ml and incubated with Q3G (10 ␮M) quercetin 3-glucoside (Q3G) alone did not alter cell viability relative to control cells that were not treated with the flavonoid or exposed to oxidative stress (Fig. 1C). These results indicate that 10 ␮M Q3G provided maximal protection from the loss of cell viability produced by the H2O2 insult, and at this concentration Q3G was not cytotoxic; nor did it alter the rate of cell division (Fig. 1C)

Summary

Introduction

Cholesterol, phospholipids, and sphingolipids are major structural components of the eukaryotic plasma membrane that play an essential role in maintaining membrane integrity. CDNA microarray studies suggested that Q3G-pretreated cells subjected to oxidative stress up-regulate the expression of genes associated with lipid and cholesterol biosynthesis. SH-SY5Y cells treated with H2O2 and horseradish peroxidase showed a 2.5-fold increase in ROS activity compared with untreated control cells (supplemental Fig. 2B).

Results

Conclusion