Myeloid-Specific Rictor Deletion Induces M1 Macrophage Polarization and Potentiates In Vivo Pro-Inflammatory Response to Lipopolysaccharide

Abstract

The phosphoinositide-3-kinase (PI3K)/protein kinase B (Akt) axis plays a central role in attenuating inflammation upon macrophage stimulation with toll-like receptor (TLR) ligands. The mechanistic target of rapamycin complex 2 (mTORC2) relays signal from PI3K to Akt but its role in modulating inflammation in vivo has never been investigated. To evaluate the role of mTORC2 in the regulation of inflammation in vivo, we have generated a mouse model lacking Rictor, an essential mTORC2 component, in myeloid cells. Primary macrophages isolated from myeloid-specific Rictor null mice exhibited an exaggerated response to TLRs ligands, and expressed high levels of M1 genes and lower levels of M2 markers. To determine whether the loss of Rictor similarly affected inflammation in vivo, mice were either fed a high fat diet, a situation promoting chronic but low-grade inflammation, or were injected with lipopolysaccharide (LPS), which mimics an acute, severe septic inflammatory condition. Although high fat feeding contributed to promote obesity, inflammation, macrophage infiltration in adipose tissue and systemic insulin resistance, we did not observe a significant impact of Rictor loss on these parameters. However, mice lacking Rictor exhibited a higher sensitivity to sceptic shock when injected with LPS. Altogether, these results indicate that mTORC2 is a key negative regulator of macrophages TLR signalling and that its role in modulating inflammation is particularly important in the context of severe inflammatory challenges. These observations suggest that approaches aimed at modulating mTORC2 activity may represent a possible therapeutic approach for diseases linked to excessive inflammation.

Macrophage Activation and Polarization: Nomenclature and Experimental Guidelines

“…Other mutations in the mTOR pathway have produced disparate results. However, systematic investigation of mTOR pathway mutants using the principles described here will likely resolve why rapamycin treated macrophages and macrophages from Raptor, Rictor and TSC1 mutants have diverse phenotypes (Ai et al, 2014; Byles et al, 2013; Festuccia et al, 2014; Weichhart et al, 2008). Some of these mutants are summarized in Figure 1C.…”

Insulin resistance causes inflammation in adipose tissue

“…Three lines of evidence suggest that our findings are not due to confounding effects of ectopic knockout of Rictor in macrophages. First, Rictor expression was unchanged in macrophages isolated from the HFD-fed AdRiKO mice compared with those from control mice (Supplemental ), had no effect on macrophages in WAT of mice fed a HFD (43).…”

The Mechanistic Target of Rapamycin: The Grand ConducTOR of Metabolism and Aging

“…Similarly, we now believe that the effect of rapamycin on the insulin content and mass of pancreatic beta cells in vivo is mediated in part by diminished mTORC2 signaling (Barlow et al, 2012; Yang et al, 2012). Recent work has identified many important roles for mTORC2 in the immune system, in T cells, B cells and macrophages (Byles et al, 2013; Festuccia et al, 2014). In T cells, mTORC2 promotes TH2 differentiation via the SGK1-mediated degradation of JunB (Heikamp et al, 2014).…”