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Published on: June 23, 2013
AMP-activated protein kinase suppresses arachidonate 15-lipoxygenase expression in interleukin 4-polarized human
Dmitry Namgaladze1, Ryan G Snodgrass1, Carlo Angioni2
1From the Institute of Biochemistry I, Faculty of Medicine and.
Abstract:
Macrophages respond to the Th2 cytokine IL-4 with elevated expression of arachidonate 15-lipoxygenase (ALOX15). Although IL-4 signaling elicits anti-inflammatory responses, 15-lipoxygenase may either support or inhibit inflammatory processes in a context-dependent manner. AMP-activated protein kinase (AMPK) is a metabolic sensor/regulator that supports an anti-inflammatory macrophage phenotype. How AMPK activation is linked to IL-4-elicited gene signatures remains unexplored. Using primary human macrophages stimulated with IL-4, we observed elevated ALOX15 mRNA and protein expression, which was attenuated by AMPK activation. AMPK activators, e.g. phenformin and aminoimidazole-4-carboxamide 1-β-d-ribofuranoside inhibited IL-4-evoked activation of STAT3 while leaving activation of STAT6 and induction of typical IL-4-responsive genes intact. In addition, phenformin prevented IL-4-induced association of STAT6 and Lys-9 acetylation of histone H3 at the ALOX15 promoter. Activating AMPK abolished cellular production of 15-lipoxygenase arachidonic acid metabolites in IL-4-stimulated macrophages, which was mimicked by ALOX15 knockdown. Finally, pretreatment of macrophages with IL-4 for 48 h increased the mRNA expression of the proinflammatory cytokines IL-6, IL-12, CXCL9, and CXCL10 induced by subsequent stimulation with lipopolysaccharide. This response was attenuated by inhibition of ALOX15 or activation of AMPK during incubation with IL-4. In conclusion, limiting ALOX15 expression by AMPK may promote an anti-inflammatory phenotype of IL-4-stimulated human macrophages.
Insights
AMP-activated protein kinase (AMPK) activation limits arachidonate 15-lipoxygenase (ALOX15) in IL-4-stimulated macrophages. This suggests AMPK promotes an anti-inflammatory macrophage phenotype by reducing pro-inflammatory mediators.
Area of Science:
- Immunology
- Cell Biology
- Molecular Biology
Background:
- Macrophages are key immune cells influenced by Th2 cytokine IL-4.
- IL-4 typically induces anti-inflammatory responses, but its downstream effects can be complex.
- Arachidonate 15-lipoxygenase (ALOX15) expression is upregulated by IL-4, with context-dependent roles in inflammation.
- AMP-activated protein kinase (AMPK) is a metabolic regulator promoting anti-inflammatory macrophage phenotypes.
Purpose of the Study:
- To investigate the link between AMPK activation and IL-4-induced gene expression in human macrophages.
- To determine how AMPK influences ALOX15 expression and its downstream inflammatory effects.
Main Methods:
- Primary human macrophages were stimulated with IL-4.
- AMPK activators (phenformin, AICAR) were used to modulate AMPK activity.
- ALOX15 mRNA and protein levels were measured.
- STAT3 and STAT6 activation, histone acetylation, and cytokine production were assessed.
- ALOX15 knockdown was performed.
Main Results:
- AMPK activation attenuated IL-4-induced ALOX15 expression.
- AMPK inhibited IL-4-evoked STAT3 activation but not STAT6 activation.
- Phenformin prevented STAT6 binding and histone acetylation at the ALOX15 promoter.
- AMPK activation abolished 15-lipoxygenase metabolite production.
- AMPK activation or ALOX15 inhibition reduced IL-4-primed pro-inflammatory cytokine production.
Conclusions:
- AMPK activation limits ALOX15 expression and its associated inflammatory metabolites in IL-4-stimulated macrophages.
- AMPK activation may contribute to an anti-inflammatory macrophage phenotype induced by IL-4.
- Targeting AMPK could be a strategy to modulate macrophage inflammatory responses.
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