Knock-In Mice Expressing a 15-Lipoxygenating Alox5 Mutant Respond Differently to Experimental Inflammation Than Reported Alox5−/− Mice

Eugenia Marbach-Breitrück,Dominika Labuz,Laura Kutzner,Dagmar Heydeck,Hartmut Kuhn,Silvina Romero-Suarez,Karsten H Weylandt,Michael Rothe,Pallu Reddanna,Lothar H Wieler,Carmen Infante-Duarte,Nadine Rohwer,Halina Machelska,Nils Helge Schebb

doi:10.3390/metabo11100698

Abstract

Arachidonic acid 5-lipoxygenase (ALOX5) is the key enzyme in the biosynthesis of pro-inflammatory leukotrienes. We recently created knock-in mice (Alox5-KI) which express an arachidonic acid 15-lipoxygenating Alox5 mutant instead of the 5-lipoxygenating wildtype enzyme. These mice were leukotriene deficient but exhibited an elevated linoleic acid oxygenase activity. Here we characterized the polyenoic fatty acid metabolism of these mice in more detail and tested the animals in three different experimental inflammation models. In experimental autoimmune encephalomyelitis (EAE), Alox5-KI mice displayed an earlier disease onset and a significantly higher cumulative incidence rate than wildtype controls but the clinical score kinetics were not significantly different. In dextran sodium sulfate-induced colitis (DSS) and in the chronic constriction nerve injury model (CCI), Alox5-KI mice performed like wildtype controls with similar genetic background. These results were somewhat surprising since in previous loss-of-function studies targeting leukotriene biosynthesis (Alox5−/− mice, inhibitor studies), more severe inflammatory symptoms were observed in the EAE model but the degree of inflammation in DSS colitis was attenuated. Taken together, our data indicate that these mutant Alox5-KI mice respond differently in two models of experimental inflammation than Alox5−/− animals tested previously in similar experimental setups.

Highlights

The arachidonic acid lipoxygenases (ALOX-isoforms) are lipid-peroxidizing enzymes [1,2], which have been implicated in the biosynthesis of pro- and anti-inflammatory mediators [3,4]
In our Alox5-KI mice, the Alox5 gene was modified by site-directed mutagenesis of the triad determinants to reach two independent goals: i) Inactivation of the arachidonic acid 5-lipoxygenase activity and the leukotriene synthase activity of Alox5
As the first consequence of this alteration, we expected that the Alox5-KI mice might perform like Alox5−/− mice in animal disease models, in which leukotrienes may play a major patho-physiological role. ii) Upregulation of the arachidonic acid 15-lipoxygenating activity

Summary

Introduction

The arachidonic acid lipoxygenases (ALOX-isoforms) are lipid-peroxidizing enzymes [1,2], which have been implicated in the biosynthesis of pro- and anti-inflammatory mediators [3,4]. In the mouse genome a single ortholog exists for each human gene, but in addition a functional Aloxe gene is present in the Alox gene cluster on mouse chromosome 17 [5]. ALOX5 orthologs catalyze the conversion of arachidonic acid to 5,6-epoxyleukotriene (LTA4). This unstable intermediate is further hydrolyzed by LTA4 hydrolase [9] to leukotriene B4 (LTB4) or is alternatively converted by LTC4 synthase [10] to leukotriene C4 (LTC4). Alox5-deficient mice were protected from inflammation in different animal disease models [16], and administration of a lipid-rich Western diet to these animals induced the formation of aortic aneurisms [17]

Methods

Results

Discussion

Conclusion