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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Figure 5

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(a) RT-PCR and immunoblot demonstrate the presence of SRFΔ5 in fresh (un...
(a) RT-PCR and immunoblot demonstrate the presence of SRFΔ5 in fresh (uncultured) mouse undifferentiated peribronchial mesenchymal cells on day 11 (E11) and absence of SRFΔ5 with concomitant increment in SRF on day 14 (E14), after the peribronchial cells become SM cells. S18 represents an internal control. The increment in SRF isoforms was best seen at the protein rather than at the message level. (b) RT-PCR shows SRF and SRFΔ5 mRNA changes along with cell spread–induced SM differentiation in culture. Notice the increment in SRF mRNA and the decrease and disappearance of SRFΔ5 mRNA. (c) RT-PCR demonstrates rapid disappearance of SRFΔ5 mRNA and increments in SRF mRNA upon 4 hours of sustained stretch. The same change is seen at the protein level after 12 hours in the immunoblot in the lower panel. (d) Effect of peribronchial mesenchymal cell stretch on SRF and SRFΔ5 isoforms in lung organ cultures. One percent dextran inside the airways led to suppression of SRFΔ5 and increase in SRF (lane 2), whereas dextran in the medium outside the lung explants maintained the SRF isoform profile characteristic of undifferentiated mesenchymal cells (lane 3). (e and f) Effect of cell spreading (e) and stretching (f) on SRFΔ5 in human fetal mesenchymal cells. Notice that the very low levels of SRFΔ5 mRNA found in the human cells are likely a reflection of their more advanced stage of SM differentiation. Results shown are representative of three experiments, each done on duplicate samples per treatment.