Stretch-induced alternative splicing of serum response factor promotes bronchial myogenesis and is defective in lung hypoplasia
Yan Yang, … , Ilana Ariel, Lucia Schuger
Yan Yang, … , Ilana Ariel, Lucia Schuger
Published December 1, 2000
Citation Information: J Clin Invest. 2000;106(11):1321-1330. https://doi.org/10.1172/JCI8893.
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Article

Stretch-induced alternative splicing of serum response factor promotes bronchial myogenesis and is defective in lung hypoplasia

Abstract

Smooth muscle (SM) develops only in organs and sites that sustain mechanical tensions. Therefore, we determined the role of stretch in mouse and human bronchial myogenesis. Sustained stretch induced expression of SM proteins in undifferentiated mesenchymal cells and accelerated the differentiation of cells undergoing myogenesis. Moreover, bronchial myogenesis was entirely controlled in lung organ cultures by the airway intraluminal pressure. Serum response factor (SRF) is a transcription factor critical for the induction of muscle-specific gene expression. Recently, a SRF-truncated isoform produced by alternative splicing of exon 5 has been identified (SRFΔ5). Here we show that undifferentiated mesenchymal cells synthesize both SRF and SRFΔ5 but that SRFΔ5 synthesis is suppressed during bronchial myogenesis in favor of increased SRF production. Stretch induces the same change in SRF alternative splicing, and its myogenic effect is abrogated by overexpressing SRFΔ5. Furthermore, human hypoplastic lungs related to conditions that hinder cell stretching continue to synthesize SRFΔ5 and show a marked decrease in bronchial and interstitial SM cells and their ECM product, tropoelastin. Taken together, our findings indicate that stretch plays a critical role in SM myogenesis and suggest that its decrease precludes normal bronchial muscle development.

Authors

Yan Yang, Safedin Beqaj, Paul Kemp, Ilana Ariel, Lucia Schuger

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Immunohistochemistry showing paucity of visceral SM cells in human fetal...
Immunohistochemistry showing paucity of visceral SM cells in human fetal hypoplastic lungs. Shown are histological sections from normal lung (a), hypoplastic lung caused by oligohydramnion (b), and hypoplastic lung caused by diaphragmatic hernia (c), all at 22 weeks of gestation, immunostained for SM α-actin. There is a significant decrease in bronchial and interstitial SM cells (arrows) in the hypoplastic lungs (b and c), particularly in those compressed by intrathoracic herniation of abdominal viscerae due to diaphragmatic hernia (c). The vascular musculature seems unaffected (arrowheads). In the same hypoplastic lung shown in b, the epithelial cells, immunostained for low–molecular-weight cytokeratins (e), and the endothelial cells, immunostained for PECAM-1 (g), show no changes compared with controls (d and f). Photos (h and i) demonstrate immunohistochemistry showing decrease in tropoelastin deposition in human hypoplastic lungs. (h) Histological sections from the normal lung at 20 weeks of gestation demonstrate tropoelastin deposition around bronchi and bronchioli and at scattered interstitial sites (arrows). (i) Histological sections from same age hypoplastic lung reveals essentially no tropoelastin deposition, with the exception of vascular SM that shows no changes in tropoelastin when compared with controls (arrowheads). Bar, 60 μm in a–e and h and i. Bar, 100 μm in f and g. (j) RT-PCR and immunoblot show stretch-induced upregulation of tropoelastin expression in mouse lung embryonic mesenchymal cells undergoing myogenic differentiation. (k) Immunoblot shows stretch-induced upregulation of tropoelastin synthesis in human lung embryonic mesenchymal cells undergoing myogenic differentiation. Results shown in j and k are representative of three experiments conducted in duplicate sample per treatment.