Sonic Hedgehog Signaling Regulates Myofibroblast Function during Alveolar Septum Formation in Murine Postnatal Lung

Abstract

Sonic Hedgehog (Shh) signaling regulates mesenchymal proliferation and differentiation during embryonic lung development. In the adult lung, Shh signaling maintains mesenchymal quiescence and is dysregulated in diseases such as idiopathic pulmonary fibrosis and chronic obstructive pulmonary disease. Our previous data implicated a role for Shh in postnatal lung development. Here, we report a detailed analysis of Shh signaling during murine postnatal lung development. We show that Shh pathway expression and activity during alveolarization (postnatal day [P] 0-P14) are distinct from those during maturation (P14-P24). This biphasic pattern is paralleled by the transient presence of Gli1;α-smooth muscle actin (α-SMA) myofibroblasts in the growing alveolar septal tips. Carefully timed inhibition of Hedgehog (Hh) signaling during alveolarization defined mechanisms by which Shh influences the mesenchymal compartment. First, interruption of Hh signaling at earlier time points results in increased lung compliance and wall structure defects of increasing severity, ranging from moderately enlarged alveolar airspaces to markedly enlarged airspaces and fewer secondary septa. Second, Shh signaling is required for myofibroblast differentiation: Hh inhibition during early alveolarization almost completely eliminates Gli1;α-SMA cells at the septal tips, and Gli1-lineage tracing revealed that Gli1 cells do not undergo apoptosis after Hh inhibition but remain in the alveolar septa and are unable to express α-SMA. Third, Shh signaling is vital to mesenchymal proliferation during alveolarization, as Hh inhibition decreased proliferation of Gli1 cells and their progeny. Our study establishes Shh as a new alveolarization-promoting factor that might be affected in perinatal lung diseases that are associated with impaired alveolarization.

Hedgehog signaling regulates the expression levels of inflammatory mediators in cigarette‑induced airway inflammation

“…Previous data implicated a role of Hh in postnatal lung development; the interruption of Hh signaling at earlier time points leads to enlarged alveolar airspaces. In the adult lung, the Hh pathway maintains mesenchymal quiescence and is dysregulated in disease such as COPD (5). These results suggest that the Hh pathways underlie the initiation, maintenance, proliferation, and survival of CSE-transformed epithelial cells.…”

Secondary crest myofibroblast PDGFRα controls the elastogenesis pathway via a secondary tier of signaling networks during alveologenesis

“…Until recently, SCMFs remained inaccessible to isolation and analysis. We, and others, have shown that SCMFs are a subclass of lung mesodermal cells that are targeted by hedgehog signaling, and thus can be tagged and isolated using Gli1-cre ERT2 , a high-fidelity hedgehog reporter (Ahn and Joyner, 2004;Li et al, 2015;Kugler et al, 2017).…”

Failure to Down-Regulate miR-154 Expression in Early Postnatal Mouse Lung Epithelium Suppresses Alveologenesis, with Changes in Tgf-β Signaling Similar to those Induced by Exposure to Hyperoxia

“…The process of alveologenesis mainly takes part in the period of P0-P14 in mice (approximately equivalent to the first 6 months after birth in humans). Afterwards, from P14 through P28, the maturation of the alveoli occurs [1]. Many different signaling ligands and receptors are involved in the process of alveolarization: absence of Platelet derived growth factor alpha (Pdgfα) leads to lack of Pdgf receptor α expressing cells, which potentially form a progenitor population for the α-smooth muscle actin-expressing alveolar myofibroblasts [2][3][4].…”

“…Many different signaling ligands and receptors are involved in the process of alveolarization: absence of Platelet derived growth factor alpha (Pdgfα) leads to lack of Pdgf receptor α expressing cells, which potentially form a progenitor population for the α-smooth muscle actin-expressing alveolar myofibroblasts [2][3][4]. Sonic hedgehog (Shh) signaling is also required for proper alveolar myofibroblast differentiation [1]. In addition, in a newborn murine hypoalveologenesis model, Perl et al showed that the re-alveolarization induced by application of retinoic acid is dependent on Fgf signaling [4].…”