S1P Stimulates Erythropoietin Production in Mouse Renal Interstitial Fibroblasts by S1P1 and S1P3 Receptor Activation and HIF-2α Stabilization.

Redona Hafizi,Andrea Huwiler,Faik Imeri,Roland H Wenger

doi:10.3390/ijms22179467

Abstract

Erythropoietin (Epo) is the critical hormone for erythropoiesis. In adults, Epo is mainly produced by a subset of interstitial fibroblasts in the kidney, with minor amounts being produced in the liver and the brain. In this study, we used the immortalized renal interstitial fibroblast cell line FAIK F3-5 to investigate the ability of the bioactive sphingolipid sphingosine 1-phosphate (S1P) to stimulate Epo production and to reveal the mechanism involved. Stimulation of cells with exogenous S1P under normoxic conditions (21% O2) led to a dose-dependent increase in Epo mRNA and protein levels and subsequent release of Epo into the medium. S1P also enhanced the stabilization of HIF-2α, a key transcription factor for Epo expression. S1P-stimulated Epo mRNA and protein expression was abolished by HIF-2α mRNA knockdown or by the HIF-2 inhibitor compound 2. Furthermore, the approved S1P receptor modulator FTY720, and its active form FTY720-phosphate, both exerted a similar effect on Epo expression as S1P. The effect of S1P on Epo was antagonized by the selective S1P1 and S1P3 antagonists NIBR-0213 and TY-52156, but not by the S1P2 antagonist JTE-013. Moreover, inhibitors of the classical MAPK/ERK, the p38-MAPK, and inhibitors of protein kinase (PK) C and D all blocked the effect of S1P on Epo expression. Finally, the S1P and FTY720 effects were recapitulated in the Epo-producing human neuroblastoma cell line Kelly, suggesting that S1P receptor-dependent Epo synthesis is of general relevance and not species-specific. In summary, these data suggest that, in renal interstitial fibroblasts, which are the primary source of plasma Epo, S1P1 and 3 receptor activation upregulates Epo under normoxic conditions. This may have a therapeutic impact on disease situations such as chronic kidney disease, where Epo production is impaired, causing anemia, but it may also have therapeutic value as Epo can mediate additional tissue-protective effects in various organs.

Highlights

The prevalence of chronic kidney disease (CKD) is constantly increasing worldwide.In 2019, CKD affected 15% of the U.S population [1]
We demonstrate for the first time that sphingosine 1-phosphate (S1P) is able to stimulate Epo protein synthesis and secretion in renal fibroblast-like cells in culture even under normoxic conditions, suggesting that S1P may contribute to erythropoiesis
The best-characterized stimulus for renal Epo production is the hypoxia-induced stabilization of the transcription factor hypoxia-inducible factor (HIF)-2α, which binds to hypoxia response elements (HREs) in the Epo promoter and enhancer regions and activates Epo transcription and de novo protein synthesis [57,70]

Summary

Introduction

The prevalence of chronic kidney disease (CKD) is constantly increasing worldwide.In 2019, CKD affected 15% of the U.S population [1]. Tissue fibrosis is the consequence of continuous chronic inflammation and immune response in the kidney, leading to dysregulation of repair processes, tissue remodelling, and extracellular matrix deposition, which cumulates in the progressive loss of kidney function and end-stage renal disease and renal failure [2,3]. A major complication that develops is anemia, affecting most patients in the late stages of CKD. Anemia is associated with a reduced quality of life and increased cardiovascular disease, hospitalization, and mortality [4]. The reason for this complication is an inadequate production of erythropoietin (Epo), which is the main hormone driving erythropoiesis, regulating the oxygen-load of the blood [5,6,7,8]

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