Pattern of prepro-endothelin-1 expression revealed by reporter-gene activity in kidneys of erythropoietin-overexpressing mice

Transgenic overexpression of erythropoietin (Epo) in mice increases haematocrit to a mean of 80% in adult mice, leading to an increase in blood viscosity and volume. As a consequence, renal tissue endothelin-1 (ET-1) concentrations are significantly elevated in erythropoietin-overexpressing (Epo+) mice (mean±S.E.M; Epo+, 798±71; Epo-, 400±25pg/g tissue; P<0.01). To investigate the pattern of expression of the primary translation product of the ET-1 gene, prepro-ET-1, in kidneys of (Epo+) mice, we generated crossbred mice overexpressing the human EPO gene with mice carrying a reporter gene construct expressing the LacZ gene under the control of the human prepro-ET-1 promotor sequence (LacZ+/Epo+). For comparison, we generated (LacZ+/Epo-) mice from the same strains. After Bluo-Gal staining of frozen kidney sections (n = 10 in each group), intracellular blue precipitates as indicators of prepro-ET-1 promotor activity were detectable in tubular and vascular endothelium and glomerular cells in (LacZ+/Epo-) as well as (LacZ+/Epo+) mice. Comparison of the amount of blue precipitates by semiquantitative scoring showed a significant increase in reporter gene activity in tubular epithelium of (LacZ+/Epo+) mice (mean±S.E.M.; LacZ+/Epo+, 1.64±0.18; LacZ+/Epo-, 1.00±0.19; P<0.05). Reporter gene activity was not significantly elevated in epithelium of small intrarenal arteries of (LacZ+/Epo+) mice (mean±S.E.M.; LacZ+/Epo+, 0.86±0.14; LacZ+/Epo-, 0.38±0.21; P = 0.08) and was similar in glomerular cells (mean±S.E.M.; LacZ+/Epo+, 1.28±0.16; LacZ+/Epo-, 1.14±0.21; P = 0.6). The main source of elevated ET-1 tissue concentration in kidneys of (Epo+) mice therefore seems more likely to be tubular than vascular endothelium or glomerular cells.