Expression and Roles of Individual HIF Prolyl 4-Hydroxylase Isoenzymes in the Regulation of the Hypoxia Response Pathway along the Murine Gastrointestinal Epithelium.

Franziska Dengler,Sofia Sova,Joni M Mäki,Peppi Koivunen,Antti M Salo,Johanna Myllyharju

doi:10.3390/ijms22084038

Abstract

The HIF prolyl 4-hydroxylases (HIF-P4H) control hypoxia-inducible factor (HIF), a powerful mechanism regulating cellular adaptation to decreased oxygenation. The gastrointestinal epithelium subsists in “physiological hypoxia” and should therefore have an especially well-designed control over this adaptation. Thus, we assessed the absolute mRNA expression levels of the HIF pathway components, Hif1a, HIF2a, Hif-p4h-1, 2 and 3 and factor inhibiting HIF (Fih1) in murine jejunum, caecum and colon epithelium using droplet digital PCR. We found a higher expression of all these genes towards the distal end of the gastrointestinal tract. We detected mRNA for Hif-p4h-1, 2 and 3 in all parts of the gastrointestinal tract. Hif-p4h-2 had significantly higher expression levels compared to Hif-p4h-1 and 3 in colon and caecum epithelium. To test the roles each HIF-P4H isoform plays in the gut epithelium, we measured the gene expression of classical HIF target genes in Hif-p4h-1−/−, Hif-p4h-2 hypomorph and Hif-p4h-3−/− mice. Only Hif-p4h-2 hypomorphism led to an upregulation of HIF target genes, confirming a predominant role of HIF-P4H-2. However, the abundance of Hif-p4h-1 and 3 expression in the gastrointestinal epithelium implies that these isoforms may have specific functions as well. Thus, the development of selective inhibitors might be useful for diverging therapeutic needs.

Highlights

The adaptation of a cell to hypoxia is regulated by hypoxia-inducible factor (HIF), which consists of an oxygen-dependent α-subunit (HIF1α, HIF2α, HIF3α) and a constitutively expressed β-subunit [1]
We investigated the pression levels of the Hif-p4h isoforms 1, 2, 3 and P4h-tm as well as Fih1, Hif1a and Hif2a expression levels of the Hif-p4h isoforms 1, 2, 3 and P4h-tm as well as Fih1, Hif1a and in the murine jejunum, caecum and colon epithelium applying droplet digital PCR
The gastrointestinal epithelium generally exists at very low pO2

Summary

Introduction

The adaptation of a cell to hypoxia is regulated by hypoxia-inducible factor (HIF), which consists of an oxygen-dependent α-subunit (HIF1α, HIF2α, HIF3α) and a constitutively expressed β-subunit [1]. The HIF prolyl 4-hydroxylases (HIF-P4Hs 1, 2 and 3, known as PHDs 1, 2 and 3 and EglNs 2, 1 and 3, respectively) control the accumulation of HIF by oxygen-dependent hydroxylation of at least one of two critical proline residues in the α-subunit [2,3]. This hydroxylation targets the HIFα subunit for rapid proteasomal degradation under normoxic conditions. The first P4HI to treat anaemia in patients suffering from a chronic kidney disease received permission for clinical use only recently [9,10]

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