Macrophage polarization in fish transcriptional profiles and metabolic changes

Macrophages of higher vertebrates can display a range of functional phenotypes, while the chief M1 and M2 activation states appear to operate under the guidance of primordially-conserved principles. We have been studying the evolutionary conservation of these M1 and M2 macrophage activation states in teleost carp, mainly by measuring functional responses such as nitric oxide production (M1) and arginase activity (M2). However, the picture of M1 and M2 activation states in teleosts is still far from complete. To complement our understanding of teleost macrophage polarization we first studied activation-state specific gene expression profiles through an unbiased whole transcriptome approach in addition to functional assays. Secondly, we studied the conservation of bioenergetic and metabolic pathways paramount to activation-state specific functions.

Here we report differential transcriptional profiles for M1 (LPS stimulated) and M2 (exogenous cAMP stimulated) carp macrophages and discuss the conservation of these profiles, which include multiple conserved markers. In addition, we show an enhanced M1 profile when IFN-γ is combined with LPS.

Although essential to direct and support macrophage activation-state specific functions, conservation of bioenergetic and metabolic pathways have not been studied in detail in polarized carp macrophages. Generally, mammalian M1 macrophages show relatively high glycolysis rates while M2 macrophages are geared towards oxidative phosphorylation to generate energy. We studied whether the enhancement of these specific energy metabolism pathways is conserved. We optimized for carp macrophages the determination of cellular oxygen consumption rate (OCR) as a measure for oxidative phosphorylation, and the determination of extracellular acidification rate (ECAR) as a measure for glycolysis, using the Seahorse real-time Mito Stress Test. We have gained insight in the energy metabolism pathways utilized by carp macrophages driven to M1 or M2 activation states by using specific parameters measured with this test. Both our whole transcriptome approach and assays to measure bioenergetic and metabolic pathways provide valuable additions to studies addressing the evolutionary conservation of M1 and M2 macrophage activation states.