VEGF in the lung: a role for novel isoforms.

Vascular endothelial cell growth factor (VEGF) is a potent mitogen and permogen that increases in the plasma and decreases in the alveolar space in respiratory diseases such as acute respiratory distress syndrome (ARDS). This observation has led to controversy over the role of this potent molecule in lung physiology and disease. We hypothesized that some of the VEGF previously detected in normal lung may be of the anti-angiogenic family (VEGF(xxx)b) with significant potential effects on VEGF bioactivity. VEGF(xxx)b protein expression was assessed by indirect immunohistochemistry in normal and ARDS tissue. Expression of VEGF(xxx)b was also detected by immunoblotting in normal lung tissue, primary human alveolar type II (ATII) cells, and bronchoalveolar lavage (BAL) fluid in normal subjects and by ELISA in normal, "at risk," and ARDS subjects. The effect of VEGF(165) and VEGF(165)b on both human primary endothelial cells and alveolar epithelial cell proliferation was assessed by [(3)H]thymidine uptake. We found that VEGF(165)b was widely expressed in normal healthy lung tissue but is reduced in ARDS lung. VEGF(121)b and VEGF(165)b were present in whole lung, BAL, and ATII lysate. The proliferative effect of VEGF(165) on both human primary endothelial cells and human alveolar epithelial cells was significantly inhibited by VEGF(165)b (P < 0.01). These data demonstrate that the novel VEGF(xxx)b family members are expressed in normal lung and are reduced in ARDS. A specific functional effect on primary human endothelial and alveolar epithelial cells has also been shown. These data suggest that the VEGF(xxx)b family may have a role in repair after lung injury.

Vascular Endothelial Growth Factor (VEGF) isoform expression and activity in human and murine lung injury.

BACKGROUND: The properties of vascular endothelial growth factor (VEGF) as a potent vascular permogen and mitogen have led to investigation of its potential role in lung injury. Alternate spliced VEGF transcript generates several isoforms with potentially differing functions. The purpose of this study was to determine VEGF isoform expression and source in normal and ARDS subjects and investigate the expression and regulation of VEGF isoforms by human alveolar type 2 (ATII) cells. METHODS: VEGF protein expression was assessed immunohistochemically in archival normal and ARDS human lung tissue. VEGF isoform mRNA expression was assessed in human and murine lung tissue. Purified ATII cells were cultured with proinflammatory cytokines prior to RNA extraction/cell supernatant sampling/proliferation assay. MEASUREMENTS AND MAIN RESULTS: VEGF was expressed on alveolar epithelium, vascular endothelium and alveolar macrophages in normal and ARDS human lung tissue. Increases in VEGF expression were detected in later ARDS in comparison to both normal subjects and early ARDS (p < 0.001). VEGF121, VEGF165 and VEGF189 isoform mRNA expression increased in later ARDS (p < 0.05). The ratio of soluble to cell-associated isoforms was lower in early ARDS than normal subjects and later ARDS and also in murine lung injury. ATII cells constitutionally produced VEGF165 and VEGF121 protein which was increased by LPS (p < 0.05). VEGF165 upregulated ATII cell proliferation (p < 0.001) that was inhibited by soluble VEGF receptor 1 (sflt) (p < 0.05). CONCLUSION: These data demonstrate that changes in VEGF isoform expression occur in ARDS which may be related to their production by and mitogenic effect on ATII cells; with potentially significant clinical consequences.