In situ hybridization was used to quantitate the cells that produce erythropoietin (EP) in the renal cortices of mice with varying severities of acute anemia and of mice recovering from severe, acute anemia. The number of EP-producing cells in the renal cortex increased in an exponential manner as hematocrit was decreased. Individual EP-producing cells had very similar densities of silver grains in autoradiograms regardless of whether they were from normal mice or from slightly, moderately or severely anemic animals. With increasingly severe anemia, total renal EP mRNA levels and serum EP concentrations showed increases that correlated with the number of renal EP-producing cells. These results indicate that as mice become more anemic, additional cells are recruited to produce EP rather than the cells already producing EP being stimulated to increase their individual production. In mildly and moderately anemic animals, small clusters of EP-producing cells were found in the inner cortex with large areas of cortex containing no EP-producing cells. In severely anemic mice, EP-producing cells were found throughout the inner cortex with only a very few found scattered in the outer cortex and outer medulla. The data indicate that only a subset of total renal interstitial cells produce EP. During recovery from severe, acute anemia, the numbers of EP-producing cells decreased exponentially as hematocrits rose and correlated with decreases in total renal EP mRNA and serum EP concentrations. These results suggest that following an acute blood loss and during the recovery from a blood loss, the capacity to deliver oxygen, as represented by hematocrit, is the major regulator of EP production.
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"Most of the present knowledge of the O 2 - sensing mechanism in control of Epo production has been based on in vitro studies utilising human hepatoma cells ( lines Hep3B and HepG2 ) . Noteworthily , the mechanisms of the renal and the hepatic Epo expression differ . ( i ) Renal cells respond in an all - or - nothing fashion to hypoxia ( Koury et al . 1989 ) , whereas hepatoma cells respond in a graded way . ( ii ) The hypoxia - response elements ( HREs ) in control of the Epo gene are located upstream in the kidney ( between 9 . 5 and 14 kb 5 to Epo ) but downstream in the liver ( within 0 . 7 kb 3 to Epo ) according to studies in transgenic mice ( Kochling et al . 1998 ) . In both tissu"
[Show abstract][Hide abstract] ABSTRACT: The hormone erythropoietin (Epo) maintains red blood cell mass by promoting the survival, proliferation and differentiation of erythrocytic progenitors. Circulating Epo originates mainly from fibroblasts in the renal cortex. Epo production is controlled at the transcriptional level. Hypoxia attenuates the inhibition of the Epo promoter by GATA-2. More importantly, hypoxia promotes the availability of heterodimeric (α/β) hypoxia-inducible transcription factors (predominantly HIF-2) which stimulate the Epo enhancer. The HIFs are inactivated in normoxia by enzymatic hydroxylation of their α-subunits. Three HIF-α prolyl hydroxylases (PHD-1, -2 and -3) initiate proteasomal degradation of HIF-α, while an asparaginyl hydroxylase ('factor inhibiting HIF-1', FIH-1) inhibits the transactivation potential. The HIF-α hydroxylases contain Fe(2+) and require 2-oxoglutarate as co-factor. The in vivo response is dynamic, i.e. the concentration of circulating Epo increases initially greatly following an anaemic or hypoxaemic stimulus and then declines despite continued hypoxia. Epo and angiotensin II collaborate in the maintenance of the blood volume. Whether extra-renal sites (brain, skin) modulate renal Epo production is a matter of debate. Epo overproduction results in erythrocytosis. Epo deficiency is the primary cause of the anaemia in chronic kidney disease and a contributing factor in the anaemias of chronic inflammation and cancer. Here, recombinant analogues can substitute for the hormone.
The Journal of Physiology 11/2010; 589(Pt 6):1251-8. DOI:10.1113/jphysiol.2010.195057 · 5.04 Impact Factor
"RB 0 = 0.49 (Koury et al., 1989). and suggests that mEpo synthesis may reach 100-fold times of the basal synthesis for acute anaemia episodes as the experimental ones described in Koury et al. (1989) and by Angelillo-Scherrer et al. (2008). In addition, the model predicts that, as a result of the physiological feedback loop, levels of hematocrit higher than the basal level may induce a smooth inhibition in the mEpo synthesis, both observations are in perfect accordance with the homeostatic nature of erythropoiesis. "
[Show abstract][Hide abstract] ABSTRACT: We develop a multi-level model, using ordinary differential equations, based on quantitative experimental data, accounting for murine erythropoiesis. At the sub-cellular level, the model includes a description of the regulation of red blood cell differentiation through Epo-stimulated JAK2-STAT5 signalling activation, while at the cell population level the model describes the dynamics of (STAT5-mediated) red blood cell differentiation from their progenitors. Furthermore, the model includes equations depicting the hypoxia-mediated regulation of hormone erythropoietin blood levels. Take all together, the model constitutes a multi-level, feedback loop-regulated biological system, involving processes in different organs and at different organisational levels. We use our model to investigate the effect of deregulation in the proteins involved in the JAK2-STAT5 signalling pathway in red blood cells. Our analysis results suggest that down-regulation in any of the three signalling system components affects the hematocrit level in an individual considerably. In addition, our analysis predicts that exogenous Epo injection (an already existing treatment for several blood diseases) may compensate the effects of single down-regulation of Epo hormone level, STAT5 or EpoR/JAK2 expression level, and that it may be insufficient to counterpart a combined down-regulation of all the elements in the JAK2-STAT5 signalling cascade.
[Show abstract][Hide abstract] ABSTRACT: The cellular site of erythropoietin (epo) production within the mammalian kidney is still not completely understood. In the
present study, we examined the expression of epo mRNA in microdissected rat nephron segments by RT-PCR after induction of
epo expression with cobalt chloride. Erythropoietin mRNA was not detected in nephron segments from saline injected rats. In
cobalt chloride injected animals, epo mRNA was found in the majority of samples from the cortical region of the nephron, PCT,
and CAL. Medullary tubule preparations (MCT and MAL) were mostly negative for epo mRNA, and glomeruli were uniformly negative.
The induction of epo transcripts in tubular cells by cobalt chloride was paralleled by stimulation of the major transport
enzyme in the kidney, namely, Na−K ATPase in a tubular profile similar to that of induction of epo transcripts. These results
support some earlier findings that epo gene expression in response to cobalt salt stimulation of rat kidney occurs in transporting
tubular epithelial cells.
Cell Biochemistry and Biophysics 30(1):153-166. · 1.68 Impact Factor