Curcumin abates hypoxia-induced oxidative stress based-ER stress-mediated cell death in mouse hippocampal cells (HT22) by controlling Prdx6 and NF-κB regulation

Abstract

Oxidative stress and endoplasmic reticulum (ER) stress are emerging as crucial events in the etiopathology of many neurodegenerative diseases. While the neuroprotective contributions of the dietary compound curcumin has been recognized, the molecular mechanisms underlying curcumin's neuroprotection under oxidative and ER stresses remains elusive. Herein, we show that curcumin protects HT22 from oxidative and ER stresses evoked by the hypoxia (1% O(2) or CoCl(2) treatment) by enhancing peroxiredoxin 6 (Prdx6) expression. Cells exposed to CoCl(2) displayed reduced expression of Prdx6 with higher reactive oxygen species (ROS) expression and activation of NF-κB with IκB phosphorylation. When NF-κB activity was blocked by using SN50, an inhibitor of NF-κB, or cells treated with curcumin, the repression of Prdx6 expression was restored, suggesting the involvement of NF-κB in modulating Prdx6 expression. These cells were enriched with an accumulation of ER stress proteins, C/EBP homologous protein (CHOP), GRP/78, and calreticulin, and had activated states of caspases 12, 9, and 3. Reinforced expression of Prdx6 in HT22 cells by curcumin reestablished survival signaling by reducing propagation of ROS and blunting ER stress signaling. Intriguingly, knockdown of Prdx6 by antisense revealed that loss of Prdx6 contributed to cell death by sustaining enhanced levels of ER stress-responsive proapoptotic proteins, which was due to elevated ROS production, suggesting that Prdx6 deficiency is a cause of initiation of ROS-mediated ER stress-induced apoptosis. We propose that using curcumin to reinforce the naturally occurring Prdx6 expression and attenuate ROS-based ER stress and NF-κB-mediated aberrant signaling improves cell survival and may provide an avenue to treat and/or postpone diseases associated with ROS or ER stress.

Delivery of a protein transduction domain-mediated Prdx6 protein ameliorates oxidative stress-induced injury in human and mouse neuronal cells

“…Quantitation by H 2 -DCF-DA dye (13,25) demonstrated that Prdx6 acted to protect cells by reducing their oxidative load (Fig. 2C, black bar vs. gray bar).…”

“…Absorbance was measured at 405 nm using a microtiter plate ELISA reader. Transactivation activities were adjusted for transfection efficiencies using GFP/SEAP values (13,23).…”

“…Recent reports show ROS-driven oxidative stress as a cause of neuronal cell death that ultimately leads to age-related degenerative diseases (13,44). To evaluate whether loss of Prdx6 in neuronal cells is associated with increased ROS expression and decreased cell viability during oxidative stress, we exposed primary cell culture of HCN-2 to different concentrations of paraquat, a superoxide generator (12,19).…”

“…Prdx 1 through Prdx5 have 2-Cys; Prdx6 has 1-Cys at position 47 (Cys47). The antioxidant protein Prdx6 has GSH peroxidase as well as acidic Ca 2ϩ -independent phospholipase activities (aiPLA 2 ) (13,25,43). Prdx6 uses redoxactive Cys47 to reduce peroxides and protect cells from membrane, DNA, and protein damage mediated by lipid peroxidation (12,43).…”

“…The proapoptotic and antiapoptotic roles of NF-B depend on cell types and cellular microenvironment as well as levels of intracellular ROS (45). Several published reports have shown that NF-B is a regulator of several genes, and by doing so it exerts its proapoptotic and antiapoptotic roles (13,39). Thus it seems reasonable that modulation of ROS production at certain levels might alter the activity of NF-B, leading to repression of Prdx6 in cells.…”