The Role of 12/15-Lipoxygenase in the Expression of Interleukin-6 and Tumor Necrosis Factor-α in Macrophages

Abstract

12/15-lipoxygenase (12/15-LO) enzyme and products have been associated with inflammation and atherosclerosis. However, the mechanism of effects of the 12/15-LO products has not been fully clarified. To study the role of 12/15-LO in cytokine expression, experiments with direct additions of the12/15-LO products, 12(S)-hydroxyeicosa tetraenoic acid or 12(S)-hydroperoxyeicosa-5Z, 8Z, 10E, or 14Z-tetraenoic acid to macrophages were first carried out, and results showed that the 12/15-LO products stimulated mRNA and protein expression of IL-6 and TNF-alpha in a dose-dependent manner. In contrast, an inactive analogue of 12(S)-hydroxyeicosa tetraenoic acid had no effect. To further explore the role of endogenous 12/15-LO in cytokine expression, we used an in vitro and in vivo model to test the effect of 12/15-LO overexpression. The models included Plox-86 cells, a J774A.1 cell line that stably overexpresses leukocyte-type 12/15-LO and primary mouse peritoneal macrophages (MPMs) from 12/15-LO transgenic mice. The results showed a clear increase in IL-6 and TNF-alpha expression in Plox-86 cells and MPMs from 12/15-LO transgenic mice, compared with mock-transfected J774A.1 cells and MPMs from control C57BL6 mice. IL-1beta, IL-12, and monocyte chemoattractant protein (MCP)-1 mRNA were also increased in Plox-86 cells. These data clearly suggest a clear role of 12/15-LO pathway in cytokine production. We also demonstrated that signaling pathways including protein kinase C, p38 MAPK (p38), c-jun NH(2)-terminal kinase as well as nicotinamide adenine dinucleotide phosphate oxidase are important for 12-(S)-hydroxyeicosatetraenoic acid-induced increases in IL-6 and TNF-alpha gene expression. These results suggest a potentially important mechanism linking 12/15-LO activation to chronic inflammation and atherosclerosis.

Polymorphisms in inflammation associated genes ALOX15 and IL-6 are associated with bone properties in young women and fracture in elderly

“…In the elderly women the results appear contradictory; no appreciable genotype related differences on BMD or QUS yet a tendency towards higher fracture incidence despite lower CRP levels. We interpret these observations to support a role for ALOX15 in modulating inflammatory cytokines [12] while suggesting that fractures are not directly related to increased inflammatory activity, at least not as reflected by serum CRP levels [39]. Unfortunately, other inflammatory biomarkers were not available and neither fracture nor CRP was available in PEAK--25, which is an undoubted limitation of the study.…”

“…This region, which was also identified in an early meta--analysis of genome wide association studies (GWAS) for femoral neck BMD [10], includes the genes encoding arachidonate 12--lipoxygenase (ALOX12) and arachidonate 15--lipoxygenase (ALOX15). Lipid metabolites are produced from the polyunsaturated arachidonic acid [11], some of which have pro--inflammatory effects [12] and have been suggested to play role in chronic inflammation [13].…”

“…Activation of PPARγ--dependent pathways promotes adipogenesis at the expense of osteoblastogenesis, promotes osteoclast differentiation [24] and has an proinflammatory role [25]. Metabolites generated by ALOX12/15 also directly activate expression of the proinflammatory cytokine interleukin 6 (IL--6) [12], whose levels are elevated in inflammatory states [26]. Polymorphisms in IL6 and PPARG have been associated with osteoporosis [27--31].…”

Inflammatory responses to secondary organic aerosols (SOA) generated from biogenic and anthropogenic precursors

“…Several of these genes directly affect the production of inflammatory cytokines measured in this study. For instance, studies have observed that arachidonate 12-lipoxygenase (ALOX12) products induce the production of both TNF-α and IL-6 in macrophages (Wen et al, 2007). As such, a similar response level regardless of SOA formation condition may be observed depending on the biological endpoints measured.…”

“…Cellular responses induced by SOA exposure were measured, including intracellular ROS/RNS production and levels of tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6). Intracellular ROS/RNS production serves as a general indicator of oxidative stress, whereas TNF-α and IL-6 are pro-inflammatory cytokines indicative of the inflammatory response (Henkler et al, 2010;Kishimoto, 2003;Wang et al, 2003). TNF-α is a hallmark biomarker involved in triggering a number of cellular signaling cascades.…”