Activation of aryl hydrocarbon receptor mediates suppression of hypoxia-inducible factor-dependent erythropoietin expression by indoxyl sulfate

Abstract

Indoxyl sulfate (IS) is a representative uremic toxin that accumulates in the blood of patients with chronic kidney disease (CKD). In addition to the involvement in the progression of CKD, a recent report indicates that IS suppresses hypoxia-inducible factor (HIF)-dependent erythropoietin (EPO) production, suggesting that IS may also contribute to the progression of renal anemia. In this report, we provide evidence that aryl hydrocarbon receptor (AhR) mediates IS-induced suppression of HIF activation and subsequent EPO production. In HepG2 cells, IS at concentrations similar to the blood levels in CKD patients suppressed hypoxia- or cobalt chloride-induced EPO mRNA expression and transcriptional activation of HIF. IS also induced AhR activation, and AhR blockade resulted in abolishment of IS-induced suppression of HIF activation. The HIF transcription factor is a heterodimeric complex composed of HIF-α subunits (HIF-1α and HIF-2α) and AhR nuclear translocator (ARNT). IS suppressed nuclear accumulation of the HIF-α-ARNT complex accompanied by an increase of the AhR-ARNT complex in the nucleus, implying the involvement of interactions among AhR, HIF-α, and ARNT in the suppression mechanism. In rats, oral administration of indole, a metabolic precursor of IS, inhibited bleeding-induced elevation of renal EPO mRNA expression and plasma EPO concentration and strongly induced AhR activation in the liver and renal cortex tissues. Collectively, this study is the first to elucidate the detailed mechanism by which AhR plays an indispensable role in the suppression of HIF activation by IS. Hence, IS-induced activation of AhR may be a potential therapeutic target for treating renal anemia.

Iron suppresses erythropoietin expression via oxidative stress-dependent hypoxia-inducible factor-2 alpha inactivation

“…Therefore, HepG2 cells, a human hepatoma cell line, have been used as EPO-producing cells in in vitro experiments. [19][20][21] Similarly, we used HepG2 cells to investigate the mechanism of iron on EPO regulation in this study. HepG2 cell was purchased from the Japanese Collection of Research Bioresources (Osaka, Japan).…”

Influence of AHRR Pro189Ala polymorphism on kidney functions

“…Asai et al showed that administering rats with the precursor indole increases levels of serum indoxyl sulfate and suppresses erythropoietin production although their proposed mechanisms differ from the present hypothesis. 3) On the other hand, proximal tubular cells comprise a main target of indoxyl sulfate because high levels of OAT3 are expressed in these cells 33) and proximal tubular cell dysfunction closely correlates with reduced eGFR. Therefore, the present results might reflect a difference in the amount of AHRR expression induced by indoxyl sulfate between cells that produce erythropoietin and proximal tubular cells.…”

“…2) These findings indicate that indoxyl sulfate is involved in not only CKD progression and the pathogenesis of CKD-related diseases, but also the development of aging-induced diseases. [2][3][4][5][6][7][8][9][10][11][12][13][14] Activation of the aryl hydrocarbon receptor (AHR; also called the dioxin receptor) has recently received focus in terms of mechanisms of indoxyl sulfate-induced pathogenesis and disease progression because indoxyl sulfate is its ligand. 15) After binding to indoxyl sulfate, AHR complexes translocate from the cytoplasm to the nucleus where they dimerize with AHR nuclear translocator/ Hypoxia-inducible factor-1β (ARNT/HIF-1β).…”

The harmful effect of indoxyl sulfate on neovascularization in chronic kidney disease

“…Inactivation of AhR by inhibitor or small, interfering RNA abolishes the suppressive effect of IS on HIF activation in HepG2 cells. 8 In these cells, IS suppresses nuclear accumulation of the HIF-a-ARNT complex in inverse proportion to the increase in amount of the AhR-ARNT complex in the nucleus. 8 So, AhR activation by IS could be the missing link between IS and HIF inhibition (Figure 1).…”

“…8 In these cells, IS suppresses nuclear accumulation of the HIF-a-ARNT complex in inverse proportion to the increase in amount of the AhR-ARNT complex in the nucleus. 8 So, AhR activation by IS could be the missing link between IS and HIF inhibition (Figure 1). IS may be a therapeutic target for the impaired neovascularization in CKD patients.…”