Oxygen dose responsiveness of human fetal airway smooth muscle cells

Abstract

Maintenance of blood oxygen saturation dictates supplemental oxygen administration to premature infants, but hyperoxia predisposes survivors to respiratory diseases such as asthma. Although much research has focused on oxygen effects on alveoli in the setting of bronchopulmonary dysplasia, the mechanisms by which oxygen affects airway structure or function relevant to asthma are still under investigation. We used isolated human fetal airway smooth muscle (fASM) cells from 18-20 postconceptual age lungs (canalicular stage) to examine oxygen effects on intracellular Ca(2+) ([Ca(2+)](i)) and cellular proliferation. fASM cells expressed substantial smooth muscle actin and myosin and several Ca(2+) regulatory proteins but not fibroblast or epithelial markers, profiles qualitatively comparable to adult human ASM. Fluorescence Ca(2+) imaging showed robust [Ca(2+)](i) responses to 1 μM acetylcholine (ACh) and 10 μM histamine (albeit smaller and slower than adult ASM), partly sensitive to zero extracellular Ca(2+). Compared with adult, fASM showed greater baseline proliferation. Based on this validation, we assessed fASM responses to 10% hypoxia through 90% hyperoxia and found enhanced proliferation at <60% oxygen but increased apoptosis at >60%, effects accompanied by appropriate changes in proliferative vs. apoptotic markers and enhanced mitochondrial fission at >60% oxygen. [Ca(2+)](i) responses to ACh were enhanced for <60% but blunted at >60% oxygen. These results suggest that hyperoxia has dose-dependent effects on structure and function of developing ASM, which could have consequences for airway diseases of childhood. Thus detrimental effects on ASM should be an additional consideration in assessing risks of supplemental oxygen in prematurity.

Therapeutic potential of soluble guanylate cyclase modulators in neonatal chronic lung disease

“…The increased Ca 2ϩ response in fetal human airway smooth muscle cells in hyperoxia-exposed cells is in line with previous data demonstrating a concentration-dependent increased proliferative response under mild to moderate hyperoxia (30 -50%) and hypoxia, whereas proliferation was reduced under high oxygen levels in these cells (60 -90%; see Ref. 18). These complimentary proliferative responses to moderate and high oxygen levels were recently confirmed in neonatal mice in which exposure to hyperoxia increased thickness of the airway smooth muscle layer, with a more severe response under moderate hyperoxia (40%) compared with high oxygen levels (70%; see Refs.…”

“…In this issue of Am J Physiol Lung Cell Mol Physiol, Britt et al (10) investigated the interaction between hyperoxia and sGC on Ca 2ϩ responses in human fetal airway smooth muscle cells. Fetal human airway smooth muscle cells are substantially different from adult human airway smooth muscle cells in their proliferative and Ca 2ϩ -signaling characteristics and exhibit marked changes in the expression profile of contractile proteins, receptors, and Ca 2ϩ -signaling effectors (18). They demonstrated that, upon exposure to moderate hyperoxia, fetal human airway smooth muscle cells show an increased histamine-induced Ca 2ϩ response that could be blunted by sGC activators and stimulators in a protein kinase G-dependent way.…”

“…Fetal human airway smooth muscle cells are not only different from adult human airway smooth muscle cells in their proliferative, Ca 2ϩ -signaling, and contractile characteristics (18), but these cells also respond to cigarette smoke extract with increased proliferation and extracellular matrix protein expression (41). This is of clear relevance to the development of asthma, since fetal exposure to maternal smoking increases asthma susceptibility and the development of airway smooth muscle mass (9).…”

Severity of neonatal hyperoxia determines structural and functional changes in developing mouse airway

“…We have previously documented that exposure to Ͼ95% oxygen upregulates epithelial arginase in neonatal rat pups, which would be expected to increase lung collagen content and potentially restrict airway constriction (1). Furthermore, we have shown that levels of supplemental oxygen Ͼ60% cause apoptosis in human fetal ASM cells in contrast to the ASM proliferation observed at lower levels of oxygen exposure (6). This is consistent with the inhibition of apoptosis observed in lung cells of neonatal rats exposed to 60% compared with 95% oxygen (23).…”

Coming to terms with tissue engineering and regenerative medicine in the lung

“…In turn, these ECM components are themselves modulated by diseases such as asthma, COPD, and pulmonary fibrosis (i.e., many of the same diseases that are indications for lung transplantation). Factors such as altered oxygen levels (2,16,69,110,120,157,210,221,226), environmental influences (23,211), and inflammatory and profibrotic mediators (3,4,9,30,154,209,229) can modulate the expression of collagens, fibronectin, elastin. and other important lung ECM components.…”