Abstract
In the pulmonary vasculature, mechanical forces such as cyclic stretch induce changes in vascular signaling, tone and remodeling. Nitric oxide is a potent regulator of soluble guanylate cyclase (sGC), which drives cGMP production, causing vasorelaxation. Pulmonary artery smooth muscle cells (PASMCs) express inducible nitric oxide synthase (iNOS), and while iNOS expression increases during late gestation, little is known about how cyclic stretch impacts this pathway. In this study, PASMC were subjected to cyclic stretch of 20% amplitude and frequency of 1 Hz for 24 h and compared to control cells maintained under static conditions. Cyclic stretch significantly increased cytosolic oxidative stress as compared to static cells (62.9 ± 5.9% vs. 33.3 ± 5.7% maximal oxidation), as measured by the intracellular redox sensor roGFP. Cyclic stretch also increased sGCβ protein expression (2.5 ± 0.9-fold), sGC activity (1.5 ± 0.2-fold) and cGMP levels (1.8 ± 0.2-fold), as well as iNOS mRNA and protein expression (3.0 ± 0.9 and 2.6 ± 0.7-fold, respectively) relative to control cells. An antioxidant, recombinant human superoxide dismutase (rhSOD), significantly decreased stretch-induced cytosolic oxidative stress, but did not block stretch-induced sGC activity. Inhibition of iNOS with 1400 W or an iNOS-specific siRNA inhibited stretch-induced sGC activity by 30% and 68% respectively vs. static controls. In conclusion, cyclic stretch increases sGC expression and activity in an iNOS-dependent manner in PASMC from fetal lambs. The mechanism that produces iNOS and sGC upregulation is not yet known, but we speculate these effects represent an early compensatory mechanism to counteract the effects of stretch-induced oxidative stress. A better understanding of the interplay between these two distinct pathways could provide key insights into future avenues to treat infants with pulmonary hypertension.
Highlights
At the time of transition from the fetal to neonatal pattern of circulation, blood vessels in the neonatal pulmonary vasculature are acutely exposed to mechanical forces such as shear stress from the movement of circulating blood, intra-luminal stretch determined by pressure from heart propulsions, and extra-luminal stretch induced by respiratory cycles
Past studies presumed eNOS to be the predominant source of Nitric oxide (NO) production in the pulmonary vasculature; more recent studies suggest that inducible nitric oxide synthase (iNOS) is an important isoform in generating the NO-mediated fall in pulmonary vascular resistance during the transition of pulmonary circulation from fetal to neonatal life [3]
Cyclic stretch for 24 h induced soluble guanylate cyclase (sGC) activity in untreated Pulmonary artery smooth muscle cells (PASMCs) (Figure 2B; 2.3 ± 0.5-fold vs. untreated static PASMC), but recombinant human superoxide dismutase (rhSOD) had no impact on the cyclic-stretch induced sGC activity (Figure 2B)
Summary
At the time of transition from the fetal to neonatal pattern of circulation, blood vessels in the neonatal pulmonary vasculature are acutely exposed to mechanical forces such as shear stress from the movement of circulating blood, intra-luminal stretch determined by pressure from heart propulsions, and extra-luminal stretch induced by respiratory cycles. Recent reports suggest that pathologic levels of stretch increase production of reactive oxygen species (ROS) via increased NADPH oxidase activity. These ROS may in turn trigger vasoconstriction in chronic hypertension, stimulate vascular remodeling or angiogenesis, or induce vascular barrier dysfunction in the pulmonary circulation damaged by ventilator-induced lung injury [1,2]. The iNOS isoform has been shown to be expressed in the airway epithelium and vascular smooth muscle in late-gestation ovine fetal lung, and some groups speculate that cyclic stretch and increased oxygen exposure of distal airway epithelium may directly activate iNOS, leading to vasorelaxation [3,4]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
