Fernandes, DC; Manoel, AHO; Laurindo, FRM
Mechanisms of NADPH oxidase regulation remain open. Recently, we showed through loss-of-function experiments that vascular NADPH oxidase is functionally regulated by associated Protein Disulfide Isomerase (PDI), a thioredoxin superfamily oxidoreductase chaperone. Here, through overexpression experiments, we further investigated the role of PDI on vascular NADPH oxidase. Rabbit VSMC were transiently transfected with wild-type PDI (wt-PDI) or PDI with serine mutations in all 4 thioredoxin-motif cysteines (mut-PDI), inducing ~2-fold increase in PDI expression. Overexpression of wt or mut-PDI enhanced (2.5- fold) basal cellular O2•− and H2O2 production (DHE-HPLC and Amplex Red assays) and membrane NADPH oxidase activity, in association with a ~3-fold increase in Nox1, but not Nox4 mRNA expression. However, further ROS production and NADPH oxidase activity triggered by angiotensin II (AII, 100 nM, 4h) were totally lost in transfected cells, together with Nox1 mRNA levels (with exception of mut-PDI transfected VSMC, which had further increase in Nox1 mRNA). Nox4 mRNA was unaffected by aII in control or transfected VSMC. These data suggest preemptive Nox1 activation due to PDI overexpression. Since PDI thiols are known to catalyze trans-nitrosation reactions, we assessed whether NO modulates PDI effects on Nox. VSMC were exposed to GSNO (100μM, 5h), with no change in protein PDI levels. in non-transfected VSMC, GSNO strongly decreased (by 60%) basal Nox1 mRNA, with no changes in NADPH oxidase activity or VSMC H2O2 production. However, VSMC became irresponsive to aII (added 1h after starting GSNO incubation), with no further change in Nox1 mRNA, NADPH oxidase activity or H2O2 production. in PDI-transfected cells, GSNO prevented the baseline increases in Nox1 mRNA levels (by 60%), NADPH oxidase activity (65%) and cellular H2O2 (60%). Further responses of all such variables to aII were abrogated. Importantly, wt- or mut-PDI transfection had similar effects, indicating that NO inhibits the preemptive PDI overexpression-mediated Nox1 activation by mechanisms unrelated to PDI thiols. Such data further strengthen the role of PDI as a regulator of NADPH oxidase (Support: FAPESP, CNPq Redoxoma).
