Fatal Bilateral Chylothorax in Mice Lacking the Integrin α9β1

Abstract

Members of the integrin family of adhesion receptors mediate both cell-cell and cell-matrix interactions and have been shown to play vital roles in embryonic development, wound healing, metastasis, and other biological processes. The integrin ␣9␤1 is a receptor for the extracellular matrix proteins osteopontin and tenacsin C and the cell surface immunoglobulin vascular cell adhesion molecule-1. This receptor is widely expressed in smooth muscle, hepatocytes, and some epithelia. To examine the in vivo function of ␣9␤1, we have generated mice lacking expression of the ␣9 subunit. Mice homozygous for a null mutation in the ␣9 subunit gene appear normal at birth but develop respiratory failure and die between 6 and 12 days of age. The respiratory failure is caused by an accumulation of large volumes of pleural fluid which is rich in triglyceride, cholesterol, and lymphocytes. ␣9 ؊/؊ mice also develop edema and lymphocytic infiltration in the chest wall that appears to originate around lymphatics. ␣9 protein is transiently expressed in the developing thoracic duct at embryonic day 14, but expression is rapidly lost during later stages of development. Our results suggest that the ␣9 integrin is required for the normal development of the lymphatic system, including the thoracic duct, and that ␣9 deficiency could be one cause of congenital chylothorax.Integrins are heterodimeric receptors for extracellular matrix and cell surface counterreceptors, which play important roles in embryonic development, inflammation, wound healing, and tumorigenesis (8, 9, 15). The integrin ␤1 subunit pairs with at least 12 ␣ subunits, forming the largest subfamily of integrins. Ablation of the ␤1 gene produces early embryonic lethality (3, 17), and most null mutations described for individual ␤1-associated ␣ subunits cause severe but individually distinct developmental phenotypes (10).␣9␤1 is a member of the ␤1 family that recognizes tenascin C (23, 26), osteopontin (16,24), and vasular cell adhesion molecule-1 (VCAM-1) (20) as ligands. Immunostaining of mouse tissue has shown that this integrin is expressed in skeletal and cardiac muscle, visceral smooth muscle, hepatocytes, airway epithelium, squamous epithelium, and choroid plexus epithelium (13,21). Wound healing experiments performed on mouse corneas (18,19) suggest that ␣9 may play a role in corneal epithelial migration and differentiation. In mouse embryos, ␣9 expression was not detected prior to embryonic day 12.5 (E12.5) (21), suggesting that this integrin is unlikely to play a general role in the earliest stages of tissue morphogenesis.In vitro experiments demonstrate that ␣9␤1 mediates cell adhesion as well as cell migration on all three known ligands (16,20,26). In addition, ␣9-transfected SW480 cells use ␣9␤1 to proliferate on tenascin-C (25), and these effects are associated with phosphorylation of the integrin signaling intermediates focal adhesion kinase and paxillin and with activation of the mitogen-activated protein kinase isoform, erk2. However, the in vivo function(s) ...

Role for ephrinB2 in postnatal lung alveolar development and elastic matrix integrity

“…However, because ephrinB2 ⌬V/⌬V mutants typically died before 2 weeks of age, a lethality not always seen in other mouse lines with chylothorax (Huang et al, 2000;Ayadi et al, 2001), we reasoned that perhaps these animals had a second problem which contributed to early lethality. During histopathological inspection of postnatal ephrinB2 ⌬V/⌬V mutants, we found that their lungs showed severe airspace enlargement (see below).…”

“…However, the available evidence suggests that the lung abnormalities in ephrinB2 ⌬V/⌬V mice are not a direct result of the abnormal lymphatic function in the same mice (Makinen et al, 2005). Lung airspace enlargement has not been reported in other mouse models of chylothorax (Huang et al, 2000;Ayadi et al, 2001), nor has chylothrorax been reported in mouse models of abnormal alveolar development, suggesting that these two systems can develop independently of each other. Second, examination of mutant lung Tenascin-C immunonreactivity in wild-type lung is distributed as immunoreactive puncta (arrows) with a spidery intervening network.…”

Generation and Characterization of Telomerase-Transfected Human Lymphatic Endothelial Cells with an Extended Life Span

“…Lymphatic markers include LYVE-1, a lymphatic endothelial receptor for the extracellular matrix/lymphatic fluid glycosaminoglycan hyaluronan; 1 Prox-1, a homeobox gene product involved in regulating early lymphatic development; 2 podoplanin, a glomerular podocyte membrane mucoprotein; 3 and vascular endothelial growth factor receptor-3 (VEGFR-3), a transmembrane tyrosine kinase receptor for vascular endothelial growth factors-C (VEGF-C) and VEGF-D. 4,5 Recent reports indicate that the expression of the integrin ␣9 subunit is restricted to lymphatic endothelium. 6 Use of these markers has permitted the isolation of relatively pure populations of BECs and LECs using fluorescence-activated cell sorting (FACS) 7 or immunomag-netic beads. 8,9 Initial characterization of these populations highlighted major differences between the two cell types.…”

Developmental and pathological lymphangiogenesis: from models to human disease

“…It may be signiWcant that integrin 9 1 binds VEGF-C and VEGF-D, and endothelial adhesion to and migration on the lymphangiogenic vascular endothelial growth factors (VEGF-C and -D) are 9 1-dependent (Vlahakis et al 2005). Mice deWcient in the integrin 9 chain die of chylothorax during the early postnatal period, suggesting an underlying function for integrin 9 1 in the normal development of the lymphatic system, including the thoracic duct (Huang et al 2000).…”