Laminin α1 Chain Synthesis in the Mouse Developing Lung: Requirement for Epithelial–Mesenchymal Contact and Possible Role in Bronchial Smooth muscle Development

Abstract

Laminins, the main components of basement membranes, are heterotrimers consisting of α, β, and γ polypeptide chains linked together by disulfide bonds. Laminins-1 and -2 are both composed of β1 and γ1 chains and differ from each other on their α chain, which is α1 and α2 for laminin-1 and -2, respectively. The present study shows that whereas laminins-1 and -2 are synthesized in the mouse developing lung and in epithelial–mesenchymal cocultures derived from it, epithelial and mesenchymal monocultures lose their ability to synthesize the laminin α1 chain. Synthesis of laminin α1 chain however returns upon re-establishment of epithelial–mesenchymal contact. Cell–cell contact is critical, since laminin α1 chain is not detected in monocultures exposed to coculture-conditioned medium or in epithelial–mesenchymal cocultures in which heterotypic cell–cell contact is prevented by an interposing filter. Immunohistochemical studies on cocultures treated with brefeldin A, an inhibitor of protein secretion, indicated both epithelial and mesenchymal cells synthesize laminin α1 chain upon heterotypic cell– cell contact. In a set of functional studies, embryonic lung explants were cultured in the presence of monoclonal antibodies to laminin α1, α2, and β/γ chains. Lung explants exposed to monoclonal antibodies to laminin α1 chain exhibited alterations in peribronchial cell shape and decreased smooth muscle development, as indicated by low levels of smooth muscle α actin and desmin. Taken together, our studies suggest that laminin α1 chain synthesis is regulated by epithelial–mesenchymal interaction and may play a role in airway smooth muscle development.

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

“…In some experiments, the main airways, including the peribronchial mesenchyme, were microdissected from fresh or cultured murine lungs and trypsinized. The peribronchial mesenchymal cells were then further selected by 45 minutes' differential plating (19) and immediately lysed for SRF isoform evaluation.…”

Mesenchymal-epithelial interactions in lung development and repair: are modeling and remodeling the same process?

“…Regardless of the organ of origin, embryonic mesenchymal cells remain undifferentiated in culture if forced to stay round and become SM cells if allowed to elongate, even if the cells come from an organ that would not normally develop significant SM, such as the kidney (52). In the embryonic lung, the process of cell elongation is promoted, at least in part, by the developing bronchial basement membrane (35,37,51). New epithelial-mesenchymal contacts produced during branching morphogenesis stimulate the synthesis of laminin-␣ 1 chain by both cell types (37).…”

Monoclonal anti-mouse laminin antibodies: AL-1 reacts with laminin α1 chain, AL-2 with laminin β1 chain, and AL-4 with the coiled-coil domain of laminin β1 chain

“…The α1 chain has also been implicated in kidney stem cell conversion into epithelial cells (Klein et al, 1988), lung development (Schuger et al, 1997), and mammary epithelial cell polarization (Gudjonsson et al, 2002). This is in line with evidence that α1 chain expression is largely limited to epithelial cells in embryos as well as to some epithelia in adult mice (Falk et al, 1999).…”