S1P ₂ /G _12/13 Signaling Negatively Regulates Macrophage Activation and Indirectly Shapes the Atheroprotective B1-Cell Population

Abstract

Objectives— Monocyte/macrophage recruitment and activation at vascular predilection sites plays a central role in the pathogenesis of atherosclerosis. Heterotrimeric G proteins of the G 12/13 family have been implicated in the control of migration and inflammatory gene expression, but their function in myeloid cells, especially during atherogenesis, is unknown. Approach and Results— Mice with myeloid-specific deficiency for G 12/13 show reduced atherosclerosis with a clear shift to anti-inflammatory gene expression in aortal macrophages. These changes are because of neither altered monocyte/macrophage migration nor reduced activation of inflammatory gene expression; on the contrary, G 12/13 -deficient macrophages show an increased nuclear factor-κB–dependent gene expression in the resting state. Chronically increased inflammatory gene expression in resident peritoneal macrophages results in myeloid-specific G 12/13 -deficient mice in an altered peritoneal micromilieu with secondary expansion of peritoneal B1 cells. Titers of B1-derived atheroprotective antibodies are increased, and adoptive transfer of peritoneal cells from mutant mice conveys atheroprotection to wild-type mice. With respect to the mechanism of G 12/13 -mediated transcriptional control, we identify an autocrine feedback loop that suppresses nuclear factor-κB–dependent gene expression through a signaling cascade involving sphingosine 1-phosphate receptor subtype 2, G 12/13 , and RhoA. Conclusions— Together, these data show that selective inhibition of G 12/13 signaling in macrophages can augment atheroprotective B-cell populations and ameliorate atherosclerosis.

Selective coupling of the S1P 3 receptor subtype to S1P-mediated RhoA activation and cardioprotection

“…CYM-51736, an S1P 3 selective receptor agonist derived from CYM-5541 [29], also increased active RhoA (Figure 3E), albeit to a lesser extent (approximately 1.5 fold) than S1P (approximately 2.5-fold). As further support, we measured active RhoA in the presence of an S1P 2 receptor selective antagonist, JTE-013, which has been used at 1 μM to show S1P 2 selective signaling [41]. We observed that JTE-013 did not block RhoA activation by S1P (Figure 3F), further indicating S1P 3 but not S1P 2 involvement.…”

“…The studies reported here show that signaling via the S1P 3 receptor to RhoA in cardiomyocytes of the isolated, perfused heart is both sufficient and required for cardioprotection in ex vivo I/R. Akt activation by S1P 2 and S1P 3 could contribute, along with the S1P 3 -mediated RhoA activation, to the protective effect of S1P on cardiomyocytes observed in vivo , either by direct actions on cardiomyocytes or S1P-mediated effects on non-cardiac cells [41, 63]. …”

Sphingosine-1-Phosphate Receptor-2 Antagonists: Therapeutic Potential and Potential Risks

“…It was concluded that S1P 2 signaling retained macrophages in the plaques, where they promoted inflammation ( Skoura et al, 2011 ). Recently, it was shown that a knockout of both Gα 12 and Gα 13 in myeloid cells protected LDL receptor-deficient mice from atherosclerosis, which is of importance here, since the S1P 2 receptor was identified as the major G 12/13 activator in the relevant cells, which were identified as peritoneal macrophages ( Grimm et al, 2016 ). In brief, the authors showed that the alternative, anti-inflammatory polarization of aortic macrophages in those mice was an indirect effect, mediated by activation of atheroprotective B cells through classical, pro-inflammatory peritoneal macrophages.…”

“…In brief, the authors showed that the alternative, anti-inflammatory polarization of aortic macrophages in those mice was an indirect effect, mediated by activation of atheroprotective B cells through classical, pro-inflammatory peritoneal macrophages. Importantly, in both bone marrow-derived and peritoneal macrophages from myeloid G 12/13 knockout mice, pro-inflammatory cytokines were strongly upregulated, and this was mimicked by JTE-013 in wild-type macrophages ( Grimm et al, 2016 ). Thus, the study suggested that G 12/13 , and S1P 2 as major G 12/13 activator in macrophages, decreased rather than increased pro-inflammatory cytokine production, but nevertheless, atherosclerosis was attenuated by inhibition of this pathway ( Grimm et al, 2016 ).…”

Macrophages

“…53 In an intriguing study, NF-κB activation in resident peritoneal macrophages, which is controlled by an S1P2/ Gα 12/13 signaling pathway, promoted B1a cell expansion and activation, which led to increased production of natural IgM antibodies against oxidation-specific epitopes and protection against atherosclerosis. 54 The results suggest an interesting strategy of local targeting of peritoneal macrophages to limit atherosclerosis.…”