The hypoxia inducible factor/erythropoietin (EPO)/EPO receptor pathway is disturbed in a rat model of chronic kidney disease related anemia

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.

Intermittent Hypoxia Exposure Can Prevent Reductions in Hemoglobin Concentration After Intense Exercise Training in Rats

“…The blood samples collected using EDTA-lacking tubes were centrifuged at 3,000 rpm/min for 20 min at room temperature to collect the serum for EPO measurements (see below). Kidneys were collected and homogenized to measure EPO (see below) as previously described (Garrido et al, 2015;Landau et al, 2018). The rats were then killed by an overdose of the anesthetic.…”

Regulation of Fibroblast Growth Factor 23 by Iron, EPO, and HIF

“…Iron deficiency and iron deficiency-induced anemia is a frequent co-morbidity arising in chronic kidney disease (81) with the incidence and prevalence of the diagnosis increasing as renal function declines (82). Iron deficiency during renal failure is multifaceted, but is frequently due to reduced EPO synthesis (83). Therefore, replacement therapy with recombinant EPO is a primary avenue for correcting iron deficiency and anemia in this patient population.…”

Experimental modulation of Interleukin 1 shows its key role in chronic kidney disease progression and anemia

“…We have previously reported that anemia in juvenile CKD rats is associated with inappropriate responses in the HIF-EPO-EPO-R axis 27 : the typical response to anemia induced hypoxia (increased HIF2 leading to increased renal EPO, which controls EPO-R and TFR expression) was shown to be deranged in CKD. The current study now shows an accentuated anemia when inflammation is further increased in the RaKO-CKD group in comparison to WT-CKD (Fig.…”