Increased Secretion of Adrenomedullin from Cultured Human Astrocytes by Cytokines

Adrenomedullin, originally discovered from pheochromocytoma, is a member of the calcitonin gene-related peptide family. The production and secretion of adrenomedullin by cultured human astrocytes were studied by northern blot analysis and radioimmunoassay. Northern blot analysis showed the expression of adrenomedullin mRNA in cultured human astrocytes. Immunoreactive adrenomedullin concentrations in the culture medium were 29.6+/-1.2 fmol/10(5) cells/24 h (mean +/- SEM, n = 4). Treatment with interferon-gamma (100 U/ml), tumor necrosis factor-alpha (1 and 10 ng/ml), or interleukin-1beta (1 and 10 ng/ml) for 24 h caused >20-fold increases in immunoreactive adrenomedullin levels in the culture medium of human astrocytes. On the other hand, northern blot analysis showed only small increases (approximately 40%) in the adrenomedullin mRNA expression of human astrocytes with either 100 U/ml interferon-gamma or 10 ng/ml interleukin-1beta and no noticeable change with tumor necrosis factor-alpha. Reverse phase HPLC of the medium extracts of human astrocytes treated with interferon-gamma, tumor necrosis factor-alpha, or interleukin-1beta showed that most of immunoreactive adrenomedullin was eluted in the position of adrenomedullin-(1-52). On the other hand, immunoreactive adrenomedullin in the medium of human astrocytes without cytokine treatment was eluted earlier than the adrenomedullin standard, suggesting that this immunoreactive adrenomedullin represents adrenomedullin with some modifications or fragments of the adrenomedullin precursor. The present study has shown the production and secretion of adrenomedullin by human astrocytes and increased secretion of adrenomedullin by cytokines.