Capillary Defects and Exaggerated Inflammatory Response in the Airways of EphA2-Deficient Mice

Abstract

Both Eph receptors and ephrin ligands have been implicated in blood vessel and neuronal development. Recent studies suggested that EphA2 inhibition reduces tumor angiogenesis, but its role in blood vessel development and inflammation is unclear. We examined these issues using either airways of pathogen-free, EphA2-deficient mice at various ages or EphA2-deficient mice whose airways were inflamed by either Mycoplasma pulmonis infection or ovalbumin sensitization and challenge. EphA2-deficient mice had fewer capillaries, a greater number of endothelial sprouts, and greater capillary diameters than age-matched, wild-type control mice. Moreover, capillaries in EphA2-deficient mice had significantly less pericyte coverage, suggesting abnormal interactions between endothelial cells and pericytes. These differences were apparent in early postnatal life but decreased during progression into adulthood. In inflamed airways, significantly more angiogenesis and lymphangiogenesis, a greater number of infiltrating leukocytes, and higher expression levels of inflammatory cytokine mRNA were present in EphA2-deficient mice after M. pulmonis infection. Additionally, in allergic airway inflammation with ovalbumin sensitization and challenge, a greater number of lymphatic sprouts and infiltrating leukocytes, higher mRNA expression levels of TH2 cytokines and chemokines related to allergic airway inflammation, and enhanced airway hyper-responsiveness were present in EphA2-deficient mice. We conclude that defective pericyte coverage causes capillary defects, abundant endothelial sprouts, and thick capillary diameters in EphA2-deficient mice, indicating that these animals have exaggerated responses to airway inflammation.

Point Mutations in Dimerization Motifs of the Transmembrane Domain Stabilize Active or Inactive State of the EphA2 Receptor Tyrosine Kinase

“…Structural studies revealed several sites that are involved in ligand-dependent and ligand-independent EphA2 oligomerization. These sites were found along the extended extracellular domain (ECD), 3 consisting of fibronectin III repeats (FN1 and FN2), ligand-binding domains (LBDs) and cysteine-rich domains, as well as in a cytoplasmic sterile ␣ motif domain situated after the tyrosine kinase domain (TKD) (7,9,10). The functional importance of EphA2 oligomerization via the ECD was confirmed by using site-directed mutagenesis and cellbased signaling assays (7,10).…”

Steroid-Resistant Lymphatic Remodeling in Chronically Inflamed Mouse Airways

“…39 It is well known that initial lymphatics in many tissues 40 -43 including airways 17 do not have a prominent covering of pericytes and basement membrane. Because pericytes and basement membrane are generally believed to stabilize newly formed blood vessels in tumors 44,45 and in inflamed airways, 46 the reason than newly formed lymphatics are resistant to regression despite their lack of pericyte and basement membrane coverage remains unknown. Blood and lymphatic endothelial cells showed distinct reactions to M. pulmonis infection and to dexamethasone treatment, suggesting that the factors responsible for growth and maintenance are distinct from each other.…”

EphrinB2 Reverse Signaling Protects against Capillary Rarefaction and Fibrosis after Kidney Injury

“…EphA2 has been reported to regulate interactions between ECs and pericytes. 21 We therefore studied the kidney microvascular responses in EphA2-deficient mice. No differences were found in PTC density and number of myofibroblasts that appear in control and d4 UUO kidneys of WT and EphA2-deficient mice, suggesting minor roles of EphA2 in kidney injury (Supplemental Figure 7).…”