AMPK-Mediated mTORC1 Regulation in Macrophage Metabolism and Polarization

Abstract

The fundamental interplay between immunity and metabolism (immunometabolism) transcends a staggering number of chronic diseases and underpins current and future therapeutic efforts. AMP-activated protein kinase (AMPK) generally promotes catabolic and anti-inflammatory pathways. In contrast, the mechanistic target of rapamycin complex 1 (mTORC1) initiates anabolic and pro-inflammatory pathways. While it is known that AMPK can inhibit mTORC1 activation via two specific targets (Raptor and TSC2), the physiological importance of this signalling axis remains completely unknown. With the help of collaborators, a novel point mutant mouse model where the phosphorylation sites on TSC2 (Ser1387) and Raptor (Ser722/792) have been mutated to alanine (double knock-in mice; DKI) was generated. With these mice, the objective was to map the importance of this signalling axis in macrophage immunometabolism. Using bone marrow-derived macrophages (BMDM) from DKI and wild-type control mice, the lack of phosphorylation of both TSC2 and Raptor was first validated. Moreover, downstream signalling to mTORC1 targets was consistent with a basal increase in mTORC1 activity. Next, macrophages were polarized using validated immune stressors such as bacterial endotoxin and interleukin 4. Changes in metabolic signature and immune responses were assessed by measuring transcript and surface expression markers, expression of metabolic enzymes, and cytokine profiles of these cells. Given that immunometabolism underpins several fundamental macrophage responses, this research seeks to identify how specific metabolic signalling pathways can affect macrophage immune responses in culture to potentially inform how these cells behave under acute and chronic inflammation conditions in vivo.