Proceedings of The Physiological Society

Europhysiology 2018 (London, UK) (2018) Proc Physiol Soc 41, PCA069

Poster Communications

Novel Epo regulating transcription factors

D. Maric1,5, M. Chantillon2, L. Yerly1, B. Gardie3, H. Cario4, D. Hoogewijs1,5

1. University of Fribourg, Fribourg, Switzerland. 2. University of Duisburg-Essen, Essen, Germany. 3. University of Nantes, Nantes, France. 4. University Medical Center Ulm, Ulm, Germany. 5. National Center of Competence in Research Kidney Control of Homeostasis, University of Zurich, Zurich, Switzerland.

Erythropoietin (Epo) is the key hormone promoting red blood cell production in response to hypoxia and anemia. While the kidneys are the primary site of adult Epo synthesis, the liver is the main source during development. Epo is induced by the activation of the hypoxia-inducible factor (HIF) pathway in response to hypoxia and anemia, contributing to restore the normal plasmatic oxygen levels (Wenger et al., 2010). However, under pathological conditions, such as erythrocytosis, Epo plasma levels are high, leading to a dramatic increase of the red blood cell mass and resulting in blood hyperviscosity and thrombosis. Whereas a number of mutations in genes involved in the oxygen-sensing pathway have been identified, for the majority of congenital secondary erythrocytosis patients the cause remains unknown (Keohane et al., 2013; McMullin et al., 2008). We previously identified a functional distal hypoxia response element (5'-HRE) within the so-called kidney-inducible element, which is exploited in the current study to hunt for additional Epo regulating mechanisms (Storti et al., 2014). Apart from the hypoxia-inducible factor 2-alpha (HIF-2α), the transcription factors GATA and the hepatocyte nuclear factor 4-alpha (HNF4a) no other transcription factors have been shown to regulate Epo expression (Jelkmann et al., 2010). The tight tissue-specific and conditional control of Epo transcriptional regulation strongly suggests that other transcription factors might be involved in its expression regulation. An improved understanding of the molecular mechanism underlying Epo regulation is of major importance in view of the current development of various therapeutic strategies to modulate endogenous Epo levels. To identify novel factors regulating Epo production we are sequencing various regulatory regions of the Epo locus in patients with unknown cause of erythrocytosis. In a complementary approach we employ a 5'-HRE-dependent reporter gene assay screening procedure for transcription factors regulating Epo expression. Identified factors will be studied on their potential regulation of endogenous Epo expression under siRNA interference conditions and endogenous DNA binding will be validated by ChIP assays. Moreover, co-overexpression studies of candidate factors with various HIF-2 mutants found in patients with congenital erythrocytosis will also be performed.

Where applicable, experiments conform with Society ethical requirements