Stretch-induced alternative splicing of serum response factor promotes bronchial myogenesis and is defective in lung hypoplasia
Yan Yang, Safedin Beqaj, Paul Kemp, Ilana Ariel, Lucia Schuger
Yan Yang, Safedin Beqaj, Paul Kemp, Ilana Ariel, Lucia Schuger
View: Text | PDF
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

×

Figure 3

Options: View larger image (or click on image) Download as PowerPoint
(a) Determination of periluminal mesenchymal cell elongation caused by d...
(a) Determination of periluminal mesenchymal cell elongation caused by different concentrations of dextran within the airways. Since mesenchymal cell boundaries are indistinguishable in vivo, we measured the distance between the centers of adjacent nuclei (the more the stretch, the more the distance). Each column represents the mean measurement of 40 distances ± SD. (b) Immunoblots show modulation of SM protein synthesis in embryonic lung organ cultures by dextran-induced peribronchial cell stretch. A dose-response increase in SM protein synthesis is seen in day-11 lung explants containing dextran inside the airways after 24 hours in culture (lanes 3–5). No SM protein synthesis is observed when dextran is present in the culture medium outside the lung, preventing development of intraluminal pressure (lane 2). Minimal synthesis of SM proteins is seen in the control lung explants in which some hydrostatic pressure is likely to be produced by the fluid secreted by epithelial cells (lane 1). (c–e) Immunofluorescence shows modulation of bronchial myogenesis in embryonic lung organ cultures by dextran-induced peribronchial cell stretching. Day-11 lung explants were cultured for 24 hours and then immunostained for SM α-actin as whole-mount preparations. (c) SM α-actin in lung explants cultured without dextran. Notice the occurrence of some bronchial SM development (arrows). (d) SM α-actin in lung explants cultured with 5% dextran inside the airways, where significant bronchial myogenesis took place (arrows). (e) In lung explants cultured in the presence of 1% dextran in the culture medium, notice the absence of bronchial SM development. Results shown in b–e are representative of three experiments, each performed on duplicate lung explants per treatment. Bar, 100 μm.