Inhibition of prolyl hydroxylases (PHDs) leads to the induction of a transcriptional program that, in the gut, promotes intestinal epithelial cell survival. PHD inhibitors have recently been suggested as a promising alternative treatment for inflammatory bowel disease (IBD). In this study, we explored the colonic mucosal expression of the different PHD-isoforms (PHD1, 2 and 3) in order to identify the key isoform(s) involved in the pathogenesis of IBD.

The mRNA expression of inflammatory cytokines (IL-8 and TNF-α), an apoptosis marker (caspase 3) and PHD1, 2 and 3 was analysed in biopsies of IBD patients (UC and CD), patients with infectious colitis and healthy controls using qRT-PCR. PHD protein levels were evaluated using western blot. Cellular localization of PHD 1, 2 and 3 was determined by immunohistochemistry.

PHD1 was significantly up-regulated in IBD patients, both at the mRNA (UC: p < 0.0001 and CD: p < 0.05) and at the protein level (UC: p < 0.05 and CD: p < 0.05), and showed a very good correlation with the expression of the inflammatory cytokines IL-8 and TNF-α and the apoptosis marker caspase 3. Colonic mucosal PHD2 mRNA and protein expressions were not altered in IBD. PHD3 expression was increased in inflamed biopsies from UC patients (p < 0.0001), but only at the mRNA level. PHD1 and PHD2 expression was found both in the colonic lamina propria and the epithelium while PHD3 was mainly located in the endothelium of blood vessels.

In this exploratory expression analysis, PHD1 comes forward as the primary therapeutic target for UC and, to a lesser extent, for (colonic) CD.