Abstract
Purpose: :
Oxidative stress is a major event in etiology and progression of cataract formation. Peroxiredoxin (PRDX) 6 plays a rheostat role in gene expression by optimizing reactive oxygen species (ROS), and thereby providing cytoprotection. We unveiled the novel mechanism of PRDX6 regulation of endoplasmic reticulum (ER) stress and apoptosis by using Prdx6-/--deficient and wild-type lens epithelial cells (LECs) established from Prdx6-deficient mice under normoxic and hypoxic conditions.
Methods: :
Prdx6-/- and Prdx6+/+ LECs from Prdx6-deficient and wild-type mice were exposed to either 1% O2 (hypoxia) or normoxia for 24 or 48 h in a controlled Tri-gas incubator at 37°C. Cell death was evaluated by MTS and TUNEL assays. ROS expression was quantified using H2-DCFH-DA dye. Western blot and real time PCR were used to monitor expression of PRDX6, ER stress-induced molecules; CHOP, Bip/GRP78, ATF4 and Calnexin in Prdx6+/+ and Prdx6-/- cells. PRDX6 linked to TAT transduction domain was used for extrinsic supply of PRDX6 to cells.
Results: :
In Prdx6-/- LECs, ROS levels and apoptosis were higher at normal culture conditions, and significantly increased when exposed to 1% O2 (hypoxia) compared to Prdx6+/+ LECs that survived well with increased PRDX6 expression. Prdx6-deficient LECs revealed markedly elevated expression of mRNA and protein for CHOP and ATF4, transcription factors involved in ER-stress-induced apoptosis, and these factors were further increased in Prdx6-/- LECs under hypoxia. Bip/GRP78 and calnexin, ER chaperons which are known to be induced by ER stress, were also elevated. Under these conditions, a supply of PRDX6 to Prdx6-/- LECs optimized ROS levels and abnormal expressions of ER stress-induced gene and suppressed apoptosis. Coupled with the lower vulnerability of Prdx6+/+ LECs, these findings demonstrate that apoptosis in Prdx6-deficient LECs occurs through the ER stress pathway.
Conclusions: :
These results underscore the importance of PRDX6 in the signaling network of ER-stress regulating LEC homeostasis as its depletion is associated with ER stress-induced apoptosis.
Keywords: oxidation/oxidative or free radical damage • apoptosis/cell death • antioxidants