Developmental Regulation of the Laminin α5 Chain Suggests a Role in Epithelial and Endothelial Cell Maturation

Abstract

We have previously shown that mouse and bovine endothelial cells express a novel 400-kDa laminin alpha chain complexed to beta1 and gamma1 laminin chains. We describe here purification of this laminin isoform from the conditioned medium of a mouse peripheral lymph node endothelial cell line, SVEC. The laminin alpha chain was isolated from the laminin complex, subjected to Edman digestion, and the amino acid sequences of the resulting peptides were determined. Amino acid sequence revealed 100% identity to the predicted amino acid sequence of the recently reported laminin alpha5 gene. A monoclonal antibody to the laminin alpha5 chain was raised (4G6), allowing investigation of its distribution in embryonic, newborn, and mature mouse tissues. The laminin alpha5 chain was expressed mainly by epithelial, endothelial, and myogenic cells: In both embryonic and mature tissues the laminin alpha5 chain was strongly expressed by epithelial cells, the bronchi of the lungs and the developing kidney tubules being the sites of strongest expression. However, laminin alpha5 was not associated with early stages of epithelial cell development, but rather with epithelial cell maturation. Widespread expression of laminin alpha5 in endothelial cells was apparent only in tissues of mature mice, its appearance correlating approximately with sexual maturity. During embryogenesis and in newborn tissues, laminin alpha5 occurred in basement membranes of larger blood vessels only, excluding a role in angiogenic processes. Smooth muscle and skeletal muscle cells were the only other cell types which showed considerable laminin alpha5 expression, with skeletal muscle exhibiting a developmentally regulated pattern of expression: The laminin alpha5 chain occurred in skeletal muscle fiber basement membranes early in embryogenesis (E13-E15) but decreased with development, remaining strongly expressed only at the neuromuscular junction. The data show that laminin alpha5 expression is associated with epithelial and endothelial cell maturation, implicating a role for this laminin chain in the maintenance of differentiated epithelial and endothelial cell phenotype.

A High Endothelial Venule Secretory Protein, Mac25/Angiomodulin, Interacts with Multiple High Endothelial Venule-Associated Molecules Including Chemokines

“…such as fibronectin and vitronectin. In addition, it failed to bind various LN isoforms that are also expressed in the blood vascular basal lamina, including LN-8 and -10/11 (32)(33)(34). Thus, these results extend previous observations (11) and indicate that mac25/ AGM interacts with restricted members of the ECM proteins that are expressed in the basal lamina of HEVs.…”

Endothelial basement membrane laminin 511 is essential for shear stress response

“…The Tie2 promoter drives Cre recombinase expression in the Tek‐Cre::Lama5 −/− mice and is active in all endothelial cells by E9.5 (Kisanuki et al , 2001) prior to any Lama5 endothelial expression (Sorokin et al , 1997). All experiments were conducted according to German and Swedish Animal Welfare guidelines.…”

“…Laminin 411 is ubiquitously expressed in all endothelial basement membranes from the first stages of tube formation (Hallmann et al , 2005) and has been shown to play a role in angiogenesis in some tissues (Stenzel et al , 2011). By contrast, laminin α5 first appears surrounding arteries when the heart commences to beat (E10) and when blood pressure is initiated, and only much later in basement membranes of microvessels (Sorokin et al , 1997); it has been implicated in immune cell extravasation (Sixt et al , 2001a; Wu et al , 2009). Both laminin isoforms have been reported to interact with β1‐integrins (Kikkawa et al , 2000; Nielsen & Yamada, 2001; Sixt et al , 2001b) and laminin 511 also with the RGD‐binding integrins (Sasaki & Timpl, 2001).…”

Venular basement membranes contain specific matrix protein low expression regions that act as exit points for emigrating neutrophils

“…The data presented also demonstrate that the alterations in the size of LE regions in the vascular BM are directly caused by emigrating neutrophils and are transient in nature, returning toward basal dimensions within 24 h after initiation of transmigration. The latter reinforces the fact that the vascular BM is a dynamic and not a static and rigid structure (6,28). Vascular endothelial cells have been reported to respond rapidly to proinfl ammatory cytokines with altered expressions of the vascular laminin isoforms, laminins 8 and 10, resulting in local changes in the underlying basement membrane (6, 13, 37) and adaptation to the physiological needs of the tissue.…”

“…To investigate the expression of venular BM constituents, cremaster muscles were immunostained for laminin 8 (α4β1γ1 chains) and 10 (α5β1γ1 chains), the principal vascular laminin isoforms (6,(12)(13), in parallel with other key basement membrane components, collagen type IV (25), perlecan (26), and nidogen-2 (27), using a panel of wellcharacterized anti-mouse antibodies (28). Immunostaining of unstimulated whole cremasteric muscles with a rabbit anti-laminin α5 (LN-α5) chain polyclonal antibody (405), detecting the laminin 10 isoform, consistently indicated a dis continuous expression profi le of this matrix protein in venules but not arterioles (both at 20-40 μm in diameter).…”