Functional humanization of 15-lipoxygenase-1 (Alox15) protects mice from dextran sodium sulfate induced intestinal inflammation.

Background: Mammalian arachidonic acid lipoxygenases (ALOXs) have previously been implicated in the pathogenesis of inflammatory disease, and pro- as well as anti-inflammatory activities have been reported. The human genome involves six functional ALOX genes and each of them encodes for a functionally distinct enzyme. ALOX15 is one of these isoforms and the majority of mammalian ALOX15 orthologs including mouse Alox15 convert arachidonic acid to its 12-hydroperoxy derivative. In contrast, human ALOX15 forms 15-hydroperoxy arachidonic acid instead. This difference in the catalytic properties of the two mammalian ALOX15 orthologs may be of biological relevance since arachidonic acid 15-lipoxygenating ALOX-isoforms exhibit an improved biosynthetic capacity for pro-resolving mediators. We recently generated Alox15 knock-in mice, which homozygously express a humanized Alox15 mutant (Leu353Phe) instead of the wildtype enzyme. These animals should be protected from the development of inflammatory symptoms in whole animal inflammation models if the biosynthesis of pro-resolving mediators plays a major role.

Methods: To explore whether functional humanization of mouse Alox15 might impact the pathogenesis of inflammatory diseases we tested Alox-KI mice in comparison with wildtype control animals in two whole animal inflammation models (dextran sodium sulfate induced colitis, Freund's complete adjuvant induced paw edema). In these experiments we quantified the severity of inflammatory symptoms during the acute phase of inflammation and during the resolution period.

Results: We found that Alox15 knock-in mice are strongly protected from the development of inflammatory symptoms in the dextran sodium sulfate colitis model when the loss of body weight was used as major readout parameter. Quantification of the colon tissue oxylipidomes revealed that the colon concentrations of resolvin D5 were elevated in Alox15-KI mice and thus, this mediator might contribute to the protective effect induced by our genetic manipulation. However, other specialized pro-resolving mediators, such as maresin-2, neuroprotectin-1, and lipoxins, may not play a major role for the protective response. In the Freund's complete adjuvant induced paw edema inflammation model no protective effect was observed.

Conclusions: Taken together, our data suggest that humanization of the reaction specificity of mouse Alox15 (Leu353Phe mutation) exhibits differential effects in two mouse inflammation models.