Expression and Regulation of 12/15-lipoxygenases in Human Primary Macrophages

Objectives: Atherosclerosis is a chronic disease characterized by two main features, lipid retention and inflammation. The 12/15-lipoxygenases play a two-faced role in atherosclerosis with pro-inflammatory effects through oxidation of LDL and anti-inflammatory effects through lipid mediator synthesis. In cells involved in atherosclerosis the 12-lipoxygenase ALOX12 and the two 15-lipoxygenases, ALOX15 and ALOX15B may be expressed but their expression has not yet been investigated in detail.

Methods: To investigate the regulation of ALOX12, ALOX15 and ALOX15B in human macrophages we measured basal mRNA and protein expression during differentiation of monocytes to macrophages and stimulated expression in macrophages.

Results: The results show an increase of ALOX15B during the differentiation of monocytes to macrophages, while the expression of ALOX12 and ALOX15 remains on the same low level. Stimulation of macrophages with a set of cytokines and with hypoxia revealed that IL-4, IL-13, LPS and hypoxia further increase the ALOX15B mRNA. Western blot analysis showed that IL-4, LPS and hypoxia increase the ALOX15B protein expression, whereas IL-13 has no effect on the protein levels. IL-4 and IL-13 also enhance ALOX15 mRNA and protein expression, whereas none of the stimuli has an impact on ALOX12 expression.

Conclusion: In summary, these data suggest that ALOX15B is the mainly expressed 12/15-lipoxygenase in human macrophages and that its expression is induced by IL-4, LPS and hypoxia. IL-4 and IL-13 also increase the expression of ALOX15, however, only IL-4 stimulation seems to drive ALOX15 expression to levels higher than the basal expression of ALOX15B. Hence, ALOX15B may play a major role in human atherosclerosis.