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

Abstract

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+/-25 pg/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.

Norepinephrine-induced acute heart failure in transgenic mice overexpressing erythropoietin

“…It has been demonstrated previously that the plasma levels of Epo which are about 10 -12-fold increased in Epo-tg6 mice resulting in a hematocrit of 0.75 -0.80 [1,2,6]. In the present study, heart function was comparable in Epo-tg6 and WT mice under baseline resting conditions (Table 1).…”

“…In addition to the incomplete myocardial relaxation, the mechanism(s) underlying NE-induced myocardial ischemia in the Epo-tg6 mice likely also include increased oxygen diffusion distances due to myocyte hypertrophy which further impairs oxygen delivery. Moreover, the Epo-tg6 mice seem to be well adapted to increased blood volume and viscosity as discussed earlier [1,5,6]. Although not analyzed in this study, it seems reasonable to suggest that any vasoconstriction or increase in oxygen and metabolic requirements of the myocardium induced by NE may exceed the capacity of these compensatory mechanisms thereby contributing to myocardial ischemia.…”

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] and by grants of BMBF (NBL-3-Förderung; Kennzeichen 01ZZ0106).…”

“…Enhanced bioavailability of NO by induction and activation of the endothelial NO synthase (eNOS) seems to be part of the mechanism to compensate for the high hematocrit. Indeed, eNOS levels and NO-mediated endothelium-dependent vasorelaxation are significantly increased in the Epo-tg6 mice despite concomitant expression of the vasoconstrictor endothelin-1 (ET-1) [1,5,6].…”

An Erythropoietin Gene Polymorphism in the Hypoxia-Responsive Element at Position 3434 Is Possibly Associated with Hypertension

“…Transgenic EPO-overexpressing mice demonstrate an increased tubular expression of the prepro-ET-1 promotor sequence [13] and an activation of the tissue ET system [14] . On the other hand, these animals show increased endothelial NO synthase levels, NO-mediated endothelium-dependent relaxation and circulating and vascular tissue NO levels [7] .…”