Soluble guanylate cyclase modulates alveolarization in the newborn lung

Abstract

Nitric oxide (NO) regulates lung development through incompletely understood mechanisms. NO controls pulmonary vascular smooth muscle cell (SMC) differentiation largely through stimulating soluble guanylate cyclase (sGC) to produce cGMP and increase cGMP-mediated signaling. To examine the role of sGC in regulating pulmonary development, we tested whether decreased sGC activity reduces alveolarization in the normal and injured newborn lung. For these studies, mouse pups with gene-targeted sGC-α1 subunit truncation were used because we determined that they have decreased pulmonary sGC enzyme activity. sGC-α1 knockout (KO) mouse pups were observed to have decreased numbers of small airway structures and lung volume compared with wild-type (WT) mice although lung septation and body weights were not different. However, following mild lung injury caused by breathing 70% O2, the sGC-α1 KO mouse pups had pronounced inhibition of alveolarization, as evidenced by an increase in airway mean linear intercept, reduction in terminal airway units, and decrease in lung septation and alveolar openings, as well as reduced somatic growth. Because cGMP regulates SMC phenotype, we also tested whether decreased sGC activity reduces lung myofibroblast differentiation. Cellular markers revealed that vascular SMC differentiation decreased, whereas myofibroblast activation increased in the hyperoxic sGC-α1 KO pup lung. These results indicate that lung development, particularly during hyperoxic injury, is impaired in mouse pups with diminished sGC activity. These studies support the investigation of sGC-targeting agents as therapies directed at improving development in the newborn lung exposed to injury.

Lysophosphatidic Acid Signaling through the Lysophosphatidic Acid-1 Receptor Is Required for Alveolarization

“…Because our structural data indicated that this period of lung development was significantly affected by the absence of LPA 1 , we compared the matrix protein expression pattern of these cells isolated from LPA 1 KO and WT pups, from z1-mm-thick layers of the lung periphery that excludes large airways and vessels that we obtained with the aid of a dissecting microscope (19). As we have described previously, the fibroblasts that we isolated from the lung periphery of mouse pups were a mixture of a-smooth muscle actin-negative and -positive cells (19), suggesting that they were a mixture of fibroblasts and myofibroblasts that we refer to together as PSFBs. As demonstrated in Figure 7A, tropoelastin mRNA expression was reduced significantly by 42% in LPA 1 -deficient versus WT PSFBs, consistent with the overall reduction in tropoelastin expression we observed in total lung homogenates of LPA 1 KO mice.…”

“…The P4 mouse pup lungs were fixed in situ as described previously (19). The older mouse lungs were fixed in situ after the vasculature was flushed via the right ventricle with ice-cold phosphate-buffered saline to remove blood cells.…”

“…Fibroblasts and myofibroblasts, which are referred to together as PSFBs, were isolated from peripheral slices of 3-week-old LPA 1 KO and WT mouse lungs after enzymatic dissociation, as described (19). Previous work has characterized the identity of these cells (see online supplement for details).…”

Essential Role for Zinc Transporter 2 (ZnT2)-mediated Zinc Transport in Mammary Gland Development and Function during Lactation

“…The irregular shape and narrow distention of the alveolar lumen, determined by the significant reduction of alveolar circularity in lactating ZnT2ko mice (Fig. 5, G and H), suggested impaired alveologenesis (37).…”

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

“…This is supported by data obtained from animal models of neonatal chronic lung disease or BPD, caused by hypoxia-or hyperoxia-induced oxidative stress (8, 31): 1) sGC-␣1-deficient mice show reduced alveolar development (2) and similar to eNOS-deficient mice show an aggravated response toward hypoxic neonatal lung injury (4); 2) treatment with inhaled NO improved aberrant hyperoxia-or bleomycininduced lung development and reduced lung injury in neonatal rats, and in neonatal eNOS-deficient mice with hypoxia-induced lung injury (5,25,35,39); 3) treatment of hyperoxiaexposed neonatal rats with growth factors that activate eNOS, including vascular endothelial growth factor and apelin, improves aberrant alveolar development and attenuates lung injury (14,23,36); and 4) treatment of hyperoxia-or hypoxia-exposed neonatal rats with the cGMP-specific phosphodiesterase 5 inhibitor sildenafil improves aberrant alveolar development and reduces cardiopulmonary disease (13,15,24), but combined inhaled NO and sildenafil did not have a synergistic effect on hypoxia-induced pulmonary hypertension (15). Collectively, these studies indicate that NO-dependent signaling not only modulates lung development but that stimulation of the NO-sGC-cGMP pathway also improves many factors that contribute to aberrant airway, alveolar, and vascular development leading to persistent alveolar simplification, lung inflammation, airway and vascular remodeling, pulmonary hypertension, and fibrosis.…”