Cyclic strain modulates resistance to oxidant stress by increasing G6PDH expression in smooth muscle cells

Vascular smooth muscle cells (VSMC) may be subjected to mechanical forces, such as cyclic strain, that promote the formation of reactive oxygen specie s (ROS). We hypothesized that VSMC modulate this adverse milieu by increasi ng the expression of glucose-6-phosphate dehydrogenase (G6PDH) to maintain or restore intracellular glutathione (GSH) levels. Cyclic strain increased superoxide formation, which resulted in diminished GSH because of an increa se in oxidized glutathione formation; there was also an increase in glutath ione peroxidase and glutathione reductase activities. G6PDH activity and pr otein expression were enhanced concomitant with decreases in GSH levels and remained elevated until intracellular GSH levels were restored. To confirm the role of G6PDH in repleting GSH stores, we inhibited G6PDH activity wit h DHEA or inhibited enzyme expression with an antisense oligodeoxynucleotid e. Diminished G6PDH activity or expression was associated with persistently depleted GSH levels and inhibition of the cyclic strain-mediated increase in glutathione reductase activity. These observations demonstrate that cycl ic strain promotes oxidant stress in VSMC, which, in turn, induces G6PDH ex pression. When G6PDH is inhibited, GSH levels are not restored because of i mpaired glutathione reductase activity. These data suggest that G6PDH is a critical determinant of the response to oxidant stress in VSMC.