The hypoxia-inducible factor (HIF) co-ordinates the adaptive transcriptional response to hypoxia in metazoan cells. The hypoxic sensitivity of HIF is conferred by a family of oxygen-sensing enzymes termed HIF hydroxylases. This family consists of three prolyl hydroxylases (PHD1-3) and a single asparagine hydroxylase termed factor inhibiting HIF (FIH). It has recently become clear that HIF hydroxylases are functionally non-redundant and have discrete but overlapping physiological roles. Furthermore, altered abundance or activity of these enzymes is associated with a number of pathologies. Pharmacological HIF-hydroxylase inhibitors have recently proven to be both tolerated and therapeutically effective in patients. In this review, we focus on the physiology, pathophysiology and therapeutic potential of the PHD1 isoform, which has recently been implicated in diseases including inflammatory bowel disease, ischaemia and cancer.

Background Pouchitis is the most common long-term complication after restorative proctocolectomy with ileal pouch–anal anastomosis (IPAA) for ulcerative colitis (UC) or familial adenomatous polyposis (FAP), which can eventually progress to pouch failure, necessitating permanent stoma construction. Hypoxia-inducible transcription factor prolyl hydroxylase–containing enzymes (PHD1, PHD2, and PHD3) are molecular oxygen sensors that control adaptive gene expression through hypoxia-inducible factor (HIF). Emerging evidence supports PHDs as being therapeutic targets in intestinal inflammation. However, pharmacological inhibition of PHDs has not been validated as a treatment strategy in pouchitis. Methods PHD1-3 mRNA and protein expression were analyzed in mucosal pouch and prepouch ileal patient biopsies. After establishment of a preclinical IPAA model in rats, the impact of the pan-PHD small-molecule inhibitor dimethyloxalylglycine (DMOG) on dextran sulfate sodium (DSS)–induced pouchitis was studied. Clinical and molecular parameters were investigated. Results PHD1, but not PHD2 or PHD3, was overexpressed in pouchitis in biopsies of patients with IPAA for UC but not FAP. In addition, PHD1 expression correlated with disease activity. DMOG treatment profoundly mitigated DSS-induced pouchitis in a rodent IPAA model. Mechanistically, DMOG restored intestinal epithelial barrier function by induction of tight junction proteins zona occludens-1 and claudin-1 and alleviation of intestinal epithelial cell apoptosis, thus attenuating pouch inflammation. Conclusions Together, these results establish a strong therapeutic rationale for targeting PHD1 with small-molecule inhibitors in pouchitis after IPAA for UC.

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Colitis-associated colorectal cancer (CAC) is a severe complication of inflammatory bowel disease (IBD). HIF-prolyl hydroxylases (PHD1, PHD2, and PHD3) control cellular adaption to hypoxia and are considered promising therapeutic targets in IBD. However, their relevance in the pathogenesis of CAC remains elusive. We induced CAC in Phd1-/-, Phd2+/-, Phd3-/-, and WT mice with azoxymethane (AOM) and dextran sodium sulfate (DSS). Phd1-/- mice were protected against chronic colitis and displayed diminished CAC growth compared to WT mice. In Phd3 -/- mice, colitis activity and CAC growth remained unaltered. In Phd2+/- mice, colitis activity was unaffected, but CAC growth was aggravated. Mechanistically, Phd2 deficiency (i) increased the number of tumor-associated macrophages (TAMs) in AOM/DSS-induced tumors, (ii) promoted the expression of EGFR ligand epiregulin ( Ereg) in macrophages, and (iii) augmented signal transducer and activator of transcription 3 (STAT3) and extracellular signal-regulated kinase 1/2 (ERK1/2) signaling which at least in part contributed to aggravated tumor cell proliferation in colitis-associated tumors. Consistently, Phd2 deficiency in hematopoietic ( Vav:Cre-Phd2f/f) but not in intestinal epithelial cells ( Villin:Cre-Phd2f/f) increased CAC growth. In conclusion, the three different PHD isoenzymes have distinct and non-redundant, either promoting (PHD1), diminishing (PHD2), or neutral effects (PHD3) on CAC growth. KBK received funding from the German Cancer Aid. MJS. received funding from the German Research Foundation (DFG; STR 1570/1-1) and the Braun Foundation (Braun®; BBST-D-18-00018). MSch received funding from the German Federal Ministry of Education and Research (BMBF; 031L0084). JMH received funding from the Heidelberg Stiftung Chirurgie. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.