Developmental changes in erythropoietin receptor expression of fetal mouse liver

Promotion of neurite outgrowth and protective effect of erythropoietin on the retinal neurons of rats

OBJECTIVE

To clarify the effect of erythropoietin (EPO) on neurite outgrowth of the cultured retinal neurocytes, and investigate whether EPO might potentially be beneficial in protecting cultured retinal neurocytes suffering from glutamate-induced cytotoxity.

METHODS

After the retinal neurocytes were cultured for 48 hours, the culture media was replaced with serum-free media, and the cultured retinal cells were exposed to 1.0 U/ml, 3.0 U/ml and 6.0 U/ml EPO for another 48 hours; then the cells were stained with Sudan Black B, and the neurite outgrowth of those cells were evaluated by an image-analysis system. After the retinal neurocytes were cultured for 48 hours, the cells were cultured in serum-free media containing 5 mM or 10 mM glutamate, and the cells were incubated in the presence or absence of Epo (1.0 U/ml, 3.0 U/ml, 6.0 U/ml respectively) for another 48 hours. The survival and apoptosis rates of those cells were estimated by MTT assay and fluorescein isothiocyanate (FITC)-annexin V/propidium Iodide (PI) flow cytometry respectively.

RESULTS

EPO induced a stable improvement of neurite outgrowth of retinal neurocytes in a dose-dependent manner. Compared with the control group, the neurite outgrowth length increased to 162.8% at 6.0 U/ml EPO exposure. EPO had no any significant effect on the survival and apoptosis rates of the retinal neurocytes cultured in serum-free media, but it was beneficial in promoting the survival and decreasing the early and total apoptosis rates of the cultured retinal neurocytes suffering from glutamate-induced cytotoxicity.

CONCLUSION

EPO had a significant biological effect on neurite outgrowth of the dissociated retinal neurocytes in vitro. EPO was beneficial in promoting the survival and decreasing the apoptosis rates of the cultured retinal neurocytes suffering from glutamate-induced cytotoxicity.

Safety of high-dose recombinant erythropoietin in a neonatal rat model

BACKGROUND

High-dose recombinant erythropoietin (rEpo) is neuroprotective in neonatal animal models of brain injury, but the long-term consequences of neonatal exposure have not been studied.

OBJECTIVES

We hypothesized that multiple injections of high-dose rEpo during the neonatal period would be safe, and would improve neurologic outcomes after exposure to neonatal hypoxia or hypoxic-ischemic injury.

METHODS

Three experimental groups of Sprague-Dawley rats were assessed: (1) normoxia, (2) hypoxia and (3) hypoxia-ischemia. Groups 1 and 2 were given 0, 2,500 or 5,000 U/kg rEpo subcutaneously for the first 5 days of life (P1-P5). Group 2 animals also underwent 2 h of hypoxia (8% O(2)) daily from P1-P3. Group 3 animals underwent right carotid artery ligation followed by hypoxia (8% O(2) x 90 min) on P7, followed by either vehicle or rEpo (2,500 U/kg subcutaneously QD x3). We evaluated short- and long-term physiologic and behavioral outcomes. Major organs were evaluated grossly and histologically.

RESULTS

rEpo treatment transiently raised hematocrit, prevented hypoxia-induced delays in geotaxis and growth, improved forelimb strength, promoted liver growth in males, lowered the adult platelet count, but did not alter other CBC indices or histology. rEpo prevented hypoxia-ischemia-induced learning impairment and substantia nigra neuron loss.

CONCLUSIONS

Repeated treatment of newborn rats with high-dose rEpo was safe under all conditions tested. rEpo treatment improved the development of hypoxia-exposed newborns and prevented the learning impairment and dopamine neuron loss due to unilateral hypoxic-ischemic brain injury.

ERK-mediated production of neurotrophic factors by astrocytes promotes neuronal stem cell differentiation by erythropoietin

Erythropoietin (EPO), a hematopoietic factor, is also required for normal brain development, and its receptor is localized in brain. Our previous study showed that EPO promotes differentiation of neuronal stem cells into astrocytes. Since astrocytes have influence on the neuronal function, we investigated whether EPO-activated astrocytes could stimulate differentiation of neuronal stem cells into neurons. EPO did not promote neuronal differentiation of neuronal stem cells isolated from 17 day embryos, however, neuronal differentiation was promoted when the neuronal stem cells were co-cultured with astrocyte isolated from post neonatal (Day 1) rat brain. Moreover, neuronal differentiation was further promoted when the neuronal stem cells were cultured with astrocyte culture medium treated by EPO (10U/ml) showing increase of morphological differentiation, and expression of neuronal differentiation marker proteins, neurofilament, and tyrosine hydroxylase. The promoting effect of EPO-treated astrocyte medium was also found in the differentiation of PC12 cells. EPO-promoted morphological differentiation of neuronal stem cells as well as astrocytes was dose dependently reduced by treatment with anti-EPO receptor antibodies in culture with astrocyte culture medium. To clarify whether EPO itself or via production of well-known neurotropic factor could promote neuronal cell differentiation, we determined the level of neurotropic factors in the EPO-treated astrocytes. Compared to untreated astrocytes, EPO-treated astrocytes increased about 2-fold in beta-NGF and 3-4-fold in BMP2, but did not increase BNDF and NT-3 levels. Since the previous study showed that extracellular signal-regulated kinase (ERK) is involved in activation of astrocytes by EPO, we determined whether generation of neurotrophic factor may also be involved with the ERK pathway. In the presence of ERK inhibitor, PD98059, the generation of beta-NGF was diminished in a dose dependent manner consistent with the inhibiting effect on neuronal differentiation. These data demonstrate that EPO promotes neuronal cell differentiation through increased release of beta-NGF and BMP2 from astrocytes, and this effect may be associated with ERK pathway signals.

EPO receptor-mediated ERK kinase and NF-kappaB activation in erythropoietin-promoted differentiation of astrocytes

Erythropoietin (EPO), a hematopoietic factor, is also required for normal brain development, and its receptor is localized in brain. Therefore, it is possible that EPO could act as a neurotropic factor inducing differentiation of neurons. In the present study, we investigated whether EPO can promote differentiation of neuronal stem cells into astrocytes. In primary culture of cortical neuronal stem cells isolated from post neonatal (Day 1) rat brain, EPO dose (0.1-10U/ml) dependently promoted initiation of morphological differentiation of astrocyte and expression of an astrocyte marker protein, glial fibrillary acidic protein (GFAP). Expression of EPO receptor was also increased during morphological differentiation of astrocytes. EPO-induced increased morphological differentiation of astrocytes and GFAP expression were reduced by treatment with anti-EPO and EPO receptor antibodies. Since our previous study showed that activation of MAPK family and transcription factors is differentially involved in neuronal cell differentiation, we further determined the activation of MAP kinase family and NF-kappaB during morphological differentiation of astrocytes. Concomitant with the progression of the morphological differentiation of astrocytes, ERK(2) but not JNK(1) and p38 MAPK as well as NF-kappaB were activated. However, in the presence of PD98,059, an inhibitor of ERK, and salicylic acid, an NF-kappaB inhibitor, the EPO-induced morphological differentiation of astrocytes and expression of FGAP and EPO receptor were reduced. Conversely, treatment with anti-EPO and EPO receptor antibodies also reduced EPO-induced ERK(2) and NF-kappaB activation. These data demonstrate that EPO can promote differentiation of neuronal stem cells into astrocytes in an EPO receptor dependent manner, and this effect may be associated with the activation of ERK kinase and NF-kappaB pathway.

Production and processing of erythropoietin receptor transcripts in brain

The expression of erythropoietin receptor (EpoR) in brain and neuronal cells, and hypoxia-responsive production of erythropoietin (Epo) in the brain suggests that the function of Epo as a survival or viability factor may extend beyond hematopoietic tissue and erythroid progenitor cells. Epo, produced by astrocytes and neurons, can be induced by hypoxia by severalfold, and in animal models Epo administration is neuroprotective to ischemic challenge. We characterized the human EpoR transcript in brain and neuronal cells to determine its contribution in regulating the Epo response in brain. Screening of a human brain cDNA library and quantitative analysis of EpoR transcripts indicate that the EpoR gene locus is transcriptionally active in brain. In addition to the proximal promoter that is active in hematopoietic cells, a significant proportion of transcripts originates far upstream from the EpoR coding region. Unlike erythroid cells with efficient splicing of EpoR transcripts to its mature form, brain EpoR transcripts are inefficiently or alternately processed with a bias towards the 3' coding region. In human EpoR transgenic mice, anemic stress induces expression of the transgene and endogenous EpoR gene in hematopoietic tissue and brain. In culture of neuronal cells, hypoxia induces EpoR expression and increases sensitivity to Epo. Induction of EpoR expression appears to be a consequence of increased transcription from the upstream region and proximal promoter, and a shift towards increased processing efficiency. These data suggest that in contrast to erythropoiesis where erythroid progenitor cells express high levels of EpoR and are directly responsive to Epo stimulation, the neuroprotective effect of Epo and its receptor may require two molecular events: the induction of Epo production by hypoxia and an increase in EpoR expression in neuronal cells resulting in increased sensitivity to Epo.

Erythropoietin stimulates proliferation of human renal carcinoma cells

BACKGROUND

We reported recently that normal human, rat, and mouse tubular cells express authentic erythropoietin-receptors (EPO-R) through which EPO stimulates mitogenesis. The present study examines whether EPO could elicit such a proliferative and thereby potentially detrimental response in cells of human renal-cell carcinoma (RCC).

METHODS

Nephrectomy samples were screened from patients with RCC (one chromophilic, two clear cell) as well as cell lines of human (Caki-2, 786-0) and mouse (RAG) renal adenocarcinomas for expression of EPO-R transcripts and protein. Cells were further tested for specific 125I-EPO binding and mitogenic response to EPO.

RESULTS

Authentic EPO-R transcripts and protein (approximately 72 kD) were detected in renal tumors and cell lines. Tumors showed low-level EPO expression, while cell lines did not. In cells, specific 125I-EPO binding to a single class of EPO-R (apparent Kd 1. 3 to 1.4 nmol/L, Bmax 2.2 to 2.6 fmol/mg protein) was observed. EPO stimulated cell proliferation dose dependently, and the individual mitogenic effects of either EPO or 10% newborn calf serum were markedly amplified when both were coadministered.

CONCLUSION

These data are the first to demonstrate, to our knowledge, that human RCCs express EPO-R message and protein and that receptor activation stimulates their proliferation in vitro. If these mitogenic effects of EPO are also operative in patients with RCC, endogenous EPO or its administration for the treatment of anemia could potentially hasten proliferation of renocellular malignancies.

Human, rat, and mouse kidney cells express functional erythropoietin receptors

BACKGROUND

Erythropoietin (EPO), secreted by fibroblast-like cells in the renal interstitium, controls erythropoiesis by regulating the survival, proliferation, and differentiation of erythroid progenitor cells. We examined whether renal cells that are exposed to EPO express EPO receptors (EPO-R) through which analogous cytokine responses might be elicited.

METHODS

Normal human and rat kidney tissue and defined cell lines of human, rat, and mouse kidney were screened, using reverse transcription-polymerase chain reaction, nucleotide sequencing, ligand binding, and Western blotting, for the expression of EPO-R. EPO's effects on DNA synthesis and cell proliferation were also examined.

RESULTS

EPO-R transcripts were readily detected in cortex, medulla, and papilla of human and rat kidney, in mesangial (human, rat), proximal tubular (human, mouse), and medullary collecting duct cells (human). Nucleotide sequences of EPO-R cDNAs from renal cells were identical to those of erythroid precursor cells. Specific 125I-EPO binding revealed a single class of high- to intermediate-affinity EPO-Rs in each tested cell line (kD 96 pm to 1. 4 nm; Bmax 0.3 to 7.0 fmol/mg protein). Western blots of murine proximal tubular cell membranes revealed an EPO-R protein of approximately 68 kDa. EPO stimulated DNA synthesis and cell proliferation dose dependently.

CONCLUSION

This is the first direct demonstration, to our knowledge, that renal cells possess EPO-Rs through which EPO stimulates mitogenesis. This suggests currently unrecognized cytokine functions for EPO in the kidney, which may prove beneficial in the repair of an injured kidney while being potentially detrimental in renal malignancies.

Erythropoietin concentrations and erythropoiesis in newborns suffering from renal agenesis and congenital kidney diseases

We studied serum concentrations of erythropoietin (EPO) in the cord blood of 31 newborns. In patients with renal agenesis (n = 6), the EPO levels were 68.2 (23-177) mU/ml (median, range). These values are clearly above EPO levels in the reference groups (median/range: < 30 weeks 11.0 (5.5-17.5) mU/ml; 30-32 weeks 18.1 (5.5-136) mU/ml; 33-34 weeks 17.7 (8.3-423) mU/ml; 35-37 weeks 17.3 (5.5-272) mU/ml; > or = 38 weeks 17.8 (8.7-40.3) mU/ml). Neonates with polycystic kidney diseases (n = 12, EPO 23.5 (9.7-491) mU/ml) and with severe bilateral hydronephrosis due to obstructive uropathy (n = 13, 18.6 (7.5-30.7) mU/ml) showed no difference to the reference groups. In all groups there were only slight differences in haemoglobin/haematocrit values.

CONCLUSION

In spite of renal agenesis and severe congenital kidney diseases, erythropoiesis is sufficiently maintained during fetal life. The liver of congenitally kidney-damaged fetuses is sufficiently able to compensate the reduction in--or lack of--renal EPO production.

The ontogeny of the biological role and production of erythropoietin

In has been long recognized that erythropoiesis in adults is under control of erythropoietin, a glycoprotein produced mainly by adult kidneys in inverse relation to oxygen availability. Increasing evidence indicates nowadays that EPO is also an essential growth factor for red cell precursors at different sites of fetal erythropoiesis. The primary site of EPO production during fetal and neonatal life is the liver, and the fetus has been shown to be able to increase EPO production in response to hypoxia through intrinsic oxygen sensing mechanisms of hepatocytes. Thus despite different sites of both erythropoiesis and EPO production a similar oxygen dependent feedback control of red cell formation appears to operate during all stages of development. EPO levels in fetal blood are potentially useful parameters of fetal stress, and, as in adults, the availability of recombinant EPO raises the possibility to modulate erythropoiesis in the perinatal period.