Citations

Abstract Preterm infants can develop airway hyperreactivity and impaired bronchodilation following supplemental O 2 (hyperoxia) in early life, making it important to understand mechanisms of hyperoxia effects. Endogenous hydrogen sulfide (H 2 S) has anti‐inflammatory and vasodilatory effects with oxidative stress. There is little understanding of H 2 S signaling in developing airways. We hypothesized that the endogenous H 2 S system is detrimentally influenced by O 2 and conversely H 2 S signaling pathways can be leveraged to attenuate deleterious effects of O 2 . Using human fetal airway smooth muscle (fASM) cells, we investigated baseline expression of endogenous H 2 S machinery, and effects of exogenous H 2 S donors NaHS and GYY4137 in the context of moderate hyperoxia, with intracellular calcium regulation as a readout of contractility. Biochemical pathways for endogenous H 2 S generation and catabolism are present in fASM, and are differentially sensitive to O 2 toward overall reduction in H 2 S levels. H 2 S donors have downstream effects of reducing [Ca 2+ ] i responses to bronchoconstrictor agonist via blunted plasma membrane Ca 2+ influx: effects blocked by O 2 . However, such detrimental O 2 effects are targetable by exogenous H 2 S donors such as NaHS and GYY4137. These data provide novel information regarding the potential for H 2 S to act as a bronchodilator in developing airways in the context of oxygen exposure.

Supplemental O 2 is a primary mode of respiratory therapy for preterm infants. Numerous studies, however, have shown that supplemental O 2 may contribute to the pathophysiology of airway hyperreactivity (AHR) associated with wheezing disorders such as asthma later in childhood. The calcium‐sensitive receptor (CaSR) is a potent modulator of smooth muscle contractility and may be an underlying feature of childhood asthma. In the present study, we investigated whether CaSR is involved in neonatal hyperoxia induced AHR in a mouse model of BPD. We hypothesize that inhibition (CaSR antagonism), downregulation of expression (siRNA), or deletion (CaSR KO mice) of CaSR will attenuate the AHR induced by hyperoxia in neonatal mice. Newborn C57BL/6 wild‐type (background) or CaSR −/− (knockout) mice were randomized on the second day of life and assigned to room air (21% O 2 ) or hyperoxic (40% O 2 ) groups and exposed for seven days, then recovered in room air for two additional weeks. At day P21, AHR was assessed in vitro using precision‐cut living lung slice preparations in response to increasing doses of methacholine (MCh, 0.25–8 μM). Wild‐type lung slices were pre‐incubated for 48 h in a CaSR siRNA sequence (40 nM) or scrambled RNA as a negative control. In another set of experiments, slices were pre‐incubated in a CaSR antagonist – NPS 2143 (10 nM) for 1 h. Airways were imaged and airway reactivity was expressed as percent change from baseline airway lumen area (± SEM). Neonatal hyperoxia significantly increased airway contractile responses to MCh in wild‐type mice with a mean maximal effect (Emax) of 68.4±8.7% decrease in airway lumen area compared to room air controls (47.3±5.8%, p<0.001), indicating AHR. Pre‐incubation (48hrs) with siRNA targeting CaSR or pharmacologic inhibition (NPS 2143, 1hr incubation) of CaSR reversed the hyperoxia‐induced AHR and the contractile responses were normalized to control level, with hyperoxic groups Emax of 44.0±5.2% and 41.3±3.1%, respectively. AHR was not observed in CaSR knockout mice suggesting resistance to hyperoxia exposure. These data suggest that CaSR plays an important role in the long‐term effects of neonatal hyperoxia on AHR. We speculate that CaSR may be a novel therapeutic target to reverse airway hyperreactivity in former preterm infants who had received prior supplemental O 2 therapy. Support or Funding Information Funding: NIH: HL R01 138402 and NIH R01 HL 056470

Continuous positive airway pressure (CPAP) is a common mode of respiratory support for preterm infants. Recent studies from our lab, however, have shown that CPAP may contribute to the pathophysiology of airway hyperreactivity (AHR) associated with wheezing disorders in former preterm infants. The long‐term effects of CPAP on lung‐development, however, still remain largely unknown. Both hyaluronan synthase 3 (HAS3) and the calcium‐sensitive receptor (CaSR) have been associated with various respiratory morbidities. In the present study, we used a neonatal mouse model of daily CPAP treatment to investigate whether the long‐term effects on AHR are associated with changes in airway HAS3 and CaSR expression. Neonatal mice were exposed to CPAP (6cm H 2 O) for 3 hours per day for the first 7 postnatal days. Control animals experienced the same conditions as experimental animals only with no CPAP. On postnatal day 21, the lungs from these animals were harvested for either real time rt‐PCR or immunohistochemistry to assess changes in HAS3 and CaSR expression. We observed increased expression of multiple genes involved in hylauraonan synthesis, most notably has3 , as well as increased CaSR expression, in the lungs of mice two weeks after CPAP ended when compared to control mice. The increased gene expression of has3 and CaSR was also reflected in increased protein expression as confirmed by immunohistochemistry. HAS3 was expressed predominantly in airway epithelium and the increased CaSR expression correlated with increased αSM actin. To further investigate the role of CaSR in CPAP‐induced AHR, CaSR KO mice ( CaSR (−/−) ) were exposed to CPAP and airway reactivity to methacholine challenge was assessed two weeks later (P21 days). Compared to control mice, AHR was not expressed in CaSR (−/−) mice suggesting resistance to CPAP treatment. These data suggest increased airway HAS3 and CaSR may be important modulators of CPAP‐induced AHR and remodeling. Support or Funding Information HLR01138402 HLR01056470

Purpose Epidemiological evidences suggest higher incidence and severity of asthma in pre‐menopausal women and aging men, indicating the role of sex steroids, especially estrogen. Our recent studies demonstrated that airway smooth muscle (ASM) cells from both male and female expresses estrogen receptors (ERα and β) and these receptors differentially regulate intracellular calcium ([Ca 2+ ] i ) which is a key role player in contraction. The degree of force for contraction can also be altered in a Ca 2+ ‐independent manner via RhoA. Both Ca 2+ ‐dependent and Ca 2+ ‐independent pathways in ASM thus together contribute towards the airway contractility. In this study, we hypothesized that the ERs differentially regulate cyclic adenosine monophosphate (cAMP) and RhoA mechanisms, thereby affecting the overall contractility of human ASM cells. Methods Asthmatic and non‐asthmatic primary human ASM cells (isolated from lung tissue, Mayo Clinic, IRB‐approved) were seeded and grown to 70% confluence. After serum‐deprivation, cells were exposed to 1nM 17β‐estradiol (E 2 ), 10nM PPT (ERα agonist) or WAY (ERβ agonist) for 24hr. IBMX (10μM) was used as phosphodiesterase inhibitor and Isoproterol (100nM for 10min) served as a positive control group for estimation of cAMP. In parallel studies, phosphorylation of myosin light chain (MLC 20 ) and myosin phosphatase targeting subunit‐1 (MYPT1) was assessed through Western analyses. Activated RhoA and cAMP measurements were done through ELISA kits. Cell contraction was accessed through traction force microscopy (TFM) using softgel plates coated with collagen and fluorescent beads. Upon treatments, phase‐contrast and fluorescent images were captured before, during and after 10μM histamine exposure and net traction force was calculated using advanced software. Results Prolonged (24h) activation of ERβ significantly increased the baseline cAMP levels whereas ERα activation decreased it. This effect was more profound in asthmatic ASM cells compared to non‐asthmatics. Furthermore, ERβ activation lowered the active RhoA levels in non‐asthmatic human ASM cells. The phosphorylation of MLC 20 and MYPT1 was significantly attenuated with ERβ activation compared to vehicle. TFM studies demonstrated reduced traction force in non‐asthmatic ASM cells treated with ERβ agonist compared to the vehicle, whereas ERα activation did not show any significant changes. Conclusion Our findings highlight the crucial role of divergent ER signaling in regulating Ca 2+ ‐dependent and Ca 2+ ‐independent pathways, which together govern the contractile function of ASM. Particularly, ERβ activation (and not ERα) mediates ASM relaxation by increasing the cAMP, reducing active RhoA and decreasing phosphorylation of MLC 20 /MYPT1. Thus, ERβ activation might serve as a novel target to manage the increased ASM contractility in asthma. Support or Funding Information Acknowledgement Supported by NIH grants R01‐HL0123494 (Venkatachalem), R01‐HL 088029 (Prakash) and R01‐HL142061 (Pabelick, Prakash).