45 - Suppression of site IQ electron leak attenuates lung epithelial cell proliferation

Abstract

Hyperoxia contributes to the development of acute lung injury in neonates and adults. Hyperoxia enhances cellular oxidative stress, yet mitochondrially derived reactive oxygen species (ROS) are poorly defined. Mitochondrial superoxide (O2•–) is produced as a consequence of electron leak during the reduction of molecular oxygen by oxidative phosphorylation. The primary sites electron leak include complex I (IQ) and III (IIIQo). Suppressors of site IQ electron leak (S1QEL) and site IIIQo electron leak (S3QEL) decrease O2•– production without affecting oxidative phosphorylation. These studies tested the hypothesis that S1QEL and S3QEL will attenuate the effects of hyperoxia on cell proliferation. Murine airway epithelial cells (mtCC) were cultured in room air (21% O2; RA) or hyperoxia (85% O2; HO) for 24 hours in the presence or absence of DMSO, 1 µM S1QEL or 1 µM S3QEL. Cell numbers were determined by Bio-Rad TC20 cell counter and cell viability assessed by trypan blue exclusion. Data (n=3) were analyzed by 2-way ANOVA followed by Tukey’s post-hoc analyses. Our data indicated independent effects of hyperoxia and S1QEL on total cell number. Hyperoxic exposure decreased cell numbers by 57% vs RA exposed cells (p=0.003). In RA exposed cells, S1QEL treatment decreased cell numbers by 52% (p=0.006). There were no differences between DMSO and S1QEL-treated HO-exposed groups. There was no effect of S3QEL on cell numbers. There were no independent effects of hyperoxia, S1QEL, or S3QEL on viable cell numbers. Hyperoxic exposure decreased mtCC numbers. Though neither compound prevented hyperoxia-induced decreases in mtCC numbers, S1QEL treatment decreased mtCC numbers but not viability in RA. Given the lack of a comparable effect of S3QEL, we interpret these novel data to indicate that complex I derived O2•- contributes to mtCC proliferation. This unique contribution of mitochondrially derived oxidants toward lung epithelial proliferation has not been reported.