Defect in Vascular Endothelial Growth Factor Expression Leads to Vessel Loss in the Lungs of Mitogen‐Activated Protein Kinase Phosphatase‐1 Deficient Mice

Abstract

Role of MAP kinase phosphatase‐1 (MKP‐1), a critical regulator of neovascularization and angiogenesis, in the regulation of vascular endothelial growth factor (VEGF) expression is unknown. We tested the hypothesis that VEGF expression and subsequent vessel development in the lung are regulated by MKP‐1 using MKP‐1 deficient (MKP‐1−/−) and wilt‐type (MKP‐1+/+) mice. Animals (4‐5 weeks old) were exposed to sea level (SL), Denver altitude (DA; 5280 feet) and severe altitude (HYP; 17,000 feet) for 6 weeks. Substrate of MKP‐1, p38 MAP kinase levels were greatest in vessels, respiratory epithelium, and interstitial cells of the lungs of MKP‐1−/− mice. Smooth muscle actin expression was increased in the lungs of MKP‐1 null mice. Vessel (<50µm in diameter) numbers as measured by vessel to alveoli ratio was markedly decreased whereas wall thickness of the vessel was augmented in hypoxia‐exposed lungs of MKP‐1 deficient mice. Immunoreactivities against anti‐VEGF as well as anti‐Ki67 antibodies were greatest in the lungs of MKP‐1+/+ mice. To evaluate the mechanisms of hypoxia‐induced loss of vessel in the lungs of MKP‐1 deficient mice, embryonic fibroblasts (MEFs) were isolated and VEGF level was evaluated by ELISA. Hypoxia‐stimulated increase in VEGF expression (8‐fold) was maximally inhibited by the JNK1/2 antagonist (SP600125) in wild‐type MEFs. However, VEGF expression was upregulated by < 1‐fold only upon exposure to hypoxia in MKP‐1 deficient MEFs. Our data strongly suggest that MKP‐1 plays a critical role in lung vessel development through the regulation of hypoxia‐stimulated VEGF expression.