Hypoxic conditions stimulate the release of B‐type natriuretic peptide from human retinal pigment epithelium cell culture

PURPOSE: A-type peptide, a natriuretic peptide belonging to the natriuretic peptide family, has been shown to be increased in the vitreous of patients suffering from diabetic retinopathy and that human retina has a well-developed natriuretic peptide system. The stimulus to which the synthesis of natriuretic peptides responded in these patients has, however, remained unknown. As the natriuretic peptides have recently been shown to respond to hypoxic conditions, the genes of both A-type and B-type have a hypoxia-response element (HRE) in their promoter sequence, we therefore hypothesized that hypoxia in the human retinal pigment epithelium will increase the secretion of NT-proBNP, the most common natriuretic peptide monitored in clinical medicine. METHODS: We used cultured human retinal pigment epithelium cell line (ARPE-19) which was exposed either to normoxia or to hypoxia for 2 hr, 4 hr, 6 hr and 24 hr. NT-proBNP was measured with enzyme immunoassay, VEGF with ELISA and HIF-1α with Western blotting. RESULTS: Hypoxia induced VEGF 165 release in culture medium and HIF-1α expression in cultured ARPE-19 cells. Time-dependent NT-proBNP release was detected when the ARPE-19 cells were cultured under normoxia. When hypoxia was induced, a statistically significant increase in NT-proBNP release was demonstrated in the culture medium. CONCLUSIONS: Hypoxic conditions increase the release of a natriuretic peptide from retinal pigment epithelium (RPE) cells. The secretion of VEGF was also enhanced. The responses were associated with the up-regulation of the HIF-1α transcription factor. These results explain the previous findings from patients with diabetes, which also suggest that hypoxia is a ubiquitous stimulus for the secretion of natriuretic peptides in human body.