Abstract
ObjectivesAnemia is a known driver for hypoxia inducible factor (HIF) which leads to increased renal erythropoietin (EPO) synthesis. Bone marrow (BM) EPO receptor (EPOR) signals are transduced through a JAK2-STAT5 pathway. The origins of anemia of chronic kidney disease (CKD) are multifactorial, including impairment of both renal EPO synthesis as well as intestinal iron absorption. We investigated the HIF- EPO- EPOR axis in kidney, BM and proximal tibia in anemic juvenile CKD rats.MethodsCKD was induced by 5/6 nephrectomy in young (20 days old) male Sprague-Dawley rats while C group was sham operated. Rats were sacrificed 4 weeks after CKD induction and 5 minutes after a single bolus of IV recombinant human EPO. An additional control anemic (C-A) group was daily bled for 7 days.ResultsHemoglobin levels were similarly reduced in CKD and C-A (11.4 ± 0.3 and 10.8±0.2 Vs 13.5±0.3 g/dL in C, p<0.0001). Liver hepcidin mRNA was decreased in CA but increased in CKD. Serum iron was unchanged while transferrin levels were mildly decreased in CKD. Kidney HIF2α protein was elevated in C-A but unchanged in CKD. Kidney EPO protein and mRNA levels were unchanged between groups. However, BM EPO protein (which reflects circulating EPO) was increased in C-A but remained unchanged in CKD. BM and proximal tibia EPOR were unchanged in C-A but decreased in CKD. Proximal tibial phospho-STAT5 increased after the EPO bolus in C but not in CKD.ConclusionsCompared to blood loss, anemia in young CKD rats is associated with inappropriate responses in the HIF-EPO-EPO-R axis: kidney HIF2α and renal EPO are not increased, BM and bone EPOR levels, as well as bone pSTAT5 response to EPO are reduced. Thus, anemia of CKD may be treated with additional therapeutic avenues beyond iron and EPO supplementation.
Highlights
Anemia prevalence in chronic kidney disease (CKD) increases as disease worsens, reaching 73% in children with stage 4 disease [1]
Kidney HIF2α protein was elevated in control anemic (C-A) but unchanged in CKD
Bone marrow (BM) and proximal tibia EPO receptor (EPOR) were unchanged in C-A but decreased in CKD
Summary
Anemia prevalence in chronic kidney disease (CKD) increases as disease worsens, reaching 73% in children with stage 4 disease [1]. The appearance of this complication is associated with increased morbidity and mortality, as well as quality of life impairment [2]. Anemia of CKD is thought to be due to impaired renal erythropoietin (EPO) synthesis, since the kidney’s tubulointerstitial cells are the main synthesis site for this hormone after birth [3]. Other factors that have been found to be impaired in CKD are iron homeostasis as well as deficiency of folic acid and vitamin B12. In CKD there is no clear inverse correlation between anemia degree and EPO serum levels [8], suggesting that other mechanisms are of importance beyond EPO deficiency
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