ALOX5
Polyunsaturated fatty acid 5-lipoxygenase (EC 1.13.11.-) (Arachidonate 5-lipoxygenase) (EC 1.13.11.34) (5-LO) (5-lipoxygenase) [LOG5]
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Accumulation of senescent cells is associated with the progression of pulmonary fibrosis, but mechanisms accounting for this linkage are not well understood. To explore this issue, we investigated whether a class of biologically active profibrotic lipids, the leukotrienes (LT), is part of the senescence-associated secretory phenotype. The analysis of conditioned medium (CM), lipid extracts, and gene expression of LT biosynthesis enzymes revealed that senescent cells secreted LT, regardless of the origin of the cells or the modality of senescence induction. The synthesis of LT was biphasic and followed by antifibrotic prostaglandin (PG) secretion. The LT-rich CM of senescent lung fibroblasts (IMR-90) induced profibrotic signaling in naive fibroblasts, which were abrogated by inhibitors of ALOX5, the principal enzyme in LT biosynthesis. The bleomycin-induced expression of genes encoding LT and PG synthases, level of cysteinyl LT in the bronchoalveolar lavage, and overall fibrosis were reduced upon senescent cell removal either in a genetic mouse model or after senolytic treatment. Quantification of ALOX5 cells in lung explants obtained from idiopathic pulmonary fibrosis (IPF) patients indicated that half of these cells were also senescent (p16Ink4a ). Unlike human fibroblasts from unused donor lungs made senescent by irradiation, senescent IPF fibroblasts secreted LTs but failed to synthesize PGs. This study demonstrates for the first time to our knowledge that senescent cells secrete functional LTs, significantly contributing to the LT pool known to cause or exacerbate IPF.
MeSH Terms
- Animals
- Arachidonate 5-Lipoxygenase
- Bleomycin
- Bronchoalveolar Lavage Fluid
- Cell Line
- Cellular Senescence
- Culture Media, Conditioned
- Disease Models, Animal
- Disease Progression
- Fibroblasts
- Gene Expression Profiling
- Gene Expression Regulation
- Humans
- Idiopathic Pulmonary Fibrosis
- Leukotrienes
- Lipoxygenase Inhibitors
- Lung
- Male
- Mice
- Primary Cell Culture
- Prostaglandins
- Signal Transduction
Keywords
- Cell Biology
- Cellular senescence
- Eicosanoids
- Fibrosis
- Pulmonology
Most mammalian genomes involve several genes encoding for functionally distinct arachidonate lipoxygenase (ALOX isoforms). Proinflammatory leukotrienes are formed [i]via[/i] the ALOX5 pathway, but 12/15-lipoxygenating ALOX isoforms have been implicated in the biosynthesis of pro-resolving mediators. [i]In vitro[/i] mutagenesis of the triad determinants abolished the leukotriene synthesizing activity of ALOX5, but the biological consequences of these alterations have not been studied. To fill this gap, we created [i]Alox5[/i] knock-in mice, which express the 12/15-lipoxygenating Phe359Trp Ala424Ile Asn425Met Alox5 triple mutant and characterized its phenotypic alterations. The mouse Alox5 triple mutant functions as arachidonic acid 15-lipoxygenating enzyme, which also forms 12S-hydroxy and 8S-hydroxy arachidonic acid. In contrast to the wild-type enzyme, the triple mutant effectively oxygenates linoleic acid to 13S-hydroxy linoleic acid (13S-HODE), which functions as activating ligand of the type-2 nuclear receptor peroxisome proliferator-activated receptor gamma (PPARγ). Knock-in mice expressing the mutant enzyme are viable, fertile, and develop normally. The mice cannot synthesize proinflammatory leukotrienes but show significantly attenuated plasma levels of lipolytic endocannabinoids. When aging, the animals gained significantly more body weight, which may be related to the fivefold higher levels of 13-HODE in the adipose tissue. These data indicate for the first time that [i]in vivo[/i] mutagenesis of the triad determinants of mouse Alox5 abolished the biosynthetic capacity of the enzyme for proinflammatory leukotrienes and altered the catalytic properties of the protein favoring the formation of 13-HODE. [i]In vivo[/i] triple mutation of the mouse [i]Alox5[/i] gene impacts the body weight homeostasis of aging mice [i]via[/i] augmented formation of the activating PPARγ ligand 13-HODE.
MeSH Terms
- Aging
- Alanine
- Animals
- Arachidonate 5-Lipoxygenase
- Asparagine
- Body Weight
- Female
- Gene Knock-In Techniques
- Leukotrienes
- Linoleic Acid
- Male
- Mice
- Mutation
- PPAR gamma
- Phenylalanine
Keywords
- eicosanoids
- inflammation
- leukotrienes
- lipoxygenase
- resolvins