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Critical Role of Sphingolipid Pathway Components in Murine Radiation-Induced Lung Injury: Protection by Sphingosine-1-Phosphate Analogues

ABSTRACT: Clinically significant radiation-induced lung injury (RILI) is associated with significant morbidity and mortality and a common toxicity in patients administered thoracic radiotherapy. While the molecular etiology of RILI is poorly understood, we previously characterized a murine model of RILI in which alterations in lung endothelial barrier integrity surfaced as a potentially important pathobiologic event. In these studies, inhibition of HMG-CoA reductase activity (simvastatin) reduced murine RILI-associated lung inflammation and vascular leak and attenuated radiation-induced dysregulation of sphingolipid metabolic pathway genes identified by genome-wide lung gene expression profiling. In the present study, we test the hypothesis that sphingolipid signaling components serve as important modulators of RILI pathobiology and novel therapeutic targets. Sphingolipid involvement in murine RILI was confirmed by radiation-induced increases in lung expression of sphingosine kinase (SphK) isoforms 1 and 2 and increases in the ratio of ceramide to cumulative sphingosine-1-phosphate (S1P) and dihydro-S1P (DHS1P) levels in plasma, bronchoalveolar lavage (BAL) fluid and lung tissue following 25 Gy exposure (6 weeks). Moreover, genetically-engineered mice with either targeted deletion of SphK1 (SphK1-/-), or with reduced expression of selective members of the S1P receptor family (S1PR1+/-, S1PR2-/-, S1PR3-/-,), exhibited marked susceptibility to RILI-mediated lung inflammation. Finally, we assessed the efficacy of three potent vascular barrier-protective S1P analogues FTY720 (FTY), fTysiponate (fTyS) and SEW-2871 (SEW) in attenuating indices of RILI. The phosphonate analogue, fTyS, and to a lesser degree SEW, exhibited significant attenuation of RILI and RILI-induced gene dysregulation compared to control RILI-challenged mice (6 weeks). In contrast, FTY failed to significantly alter physiologic or genomic changes compared to RILI-challenged controls. Together, these results support the targeting of sphingolipid components as a novel and effective therapeutic strategy in RILI.

ORGANISM(S): Mus musculus

PROVIDER: GSE25295 | GEO | 2010/11/17

SECONDARY ACCESSION(S): PRJNA134777

REPOSITORIES: GEO

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Project description:Clinically significant radiation-induced lung injury (RILI) is associated with significant morbidity and mortality and a common toxicity in patients administered thoracic radiotherapy. While the molecular etiology of RILI is poorly understood, we previously characterized a murine model of RILI in which alterations in lung endothelial barrier integrity surfaced as a potentially important pathobiologic event. In these studies, inhibition of HMG-CoA reductase activity (simvastatin) reduced murine RILI-associated lung inflammation and vascular leak and attenuated radiation-induced dysregulation of sphingolipid metabolic pathway genes identified by genome-wide lung gene expression profiling. In the present study, we test the hypothesis that sphingolipid signaling components serve as important modulators of RILI pathobiology and novel therapeutic targets. Sphingolipid involvement in murine RILI was confirmed by radiation-induced increases in lung expression of sphingosine kinase (SphK) isoforms 1 and 2 and increases in the ratio of ceramide to cumulative sphingosine-1-phosphate (S1P) and dihydro-S1P (DHS1P) levels in plasma, bronchoalveolar lavage (BAL) fluid and lung tissue following 25 Gy exposure (6 weeks). Moreover, genetically-engineered mice with either targeted deletion of SphK1 (SphK1-/-), or with reduced expression of selective members of the S1P receptor family (S1PR1+/-, S1PR2-/-, S1PR3-/-,), exhibited marked susceptibility to RILI-mediated lung inflammation. Finally, we assessed the efficacy of three potent vascular barrier-protective S1P analogues FTY720 (FTY), fTysiponate (fTyS) and SEW-2871 (SEW) in attenuating indices of RILI. The phosphonate analogue, fTyS, and to a lesser degree SEW, exhibited significant attenuation of RILI and RILI-induced gene dysregulation compared to control RILI-challenged mice (6 weeks). In contrast, FTY failed to significantly alter physiologic or genomic changes compared to RILI-challenged controls. Together, these results support the targeting of sphingolipid components as a novel and effective therapeutic strategy in RILI. Four mice were treated with PBS as a control. Three mice were treated with (S)-FTY-phosphonate (0.1mg/kg) as a drug control. Three mice were treated with SEW-2871 (0.1mg/kg) as a drug control. Three mice were treated with FTY720 (0.1mg/kg) as a drug control. Three mice were treated with administered radiation (25 Gy) alone. Three mice were treated with both administered radiation (25 Gy) and (S)-FTY-phosphonate (0.1mg/kg). Three mice were treated with both administered radiation (25 Gy) and SEW-2871 (0.1mg/kg). Three mice were treated with both administered radiation (25 Gy) and FTY720 (0.1mg/kg).

Project description:Background: Myeloid cells (MCs) reside in the aortic intima at regions predisposed to atherosclerosis. Systemic inflammation triggers reverse transendothelial migration (RTM) of intimal MCs into arterial blood, which orchestrates a protective immune response that clears intracellular pathogens from the arterial intima. Molecular pathways that regulate RTM remain poorly understood. Sphingosine-1-phosphate (S1P) is a lipid mediator that regulates immune cell trafficking by signaling via five G protein-coupled receptors (S1PRs). We investigated the role of S1P in the RTM of aortic intimal MCs. Methods: Intravenous injection of lipopolysaccharide (LPS) was used to model a systemic inflammatory stimulus that triggers RTM. CD11c+ intimal MCs in the lesser curvature of the ascending aortic arch were enumerated by en face confocal microscopy. Local gene expression was evaluated by transcriptomic analysis of microdissected intimal cells. Results: In wild-type C57BL/6 mice, LPS induced intimal cell expression of S1pr1, S1pr3, and sphingosine kinase 1 (Sphk1, a kinase responsible for S1P production). Pharmacological modulation of multiple S1PRs blocked LPS-induced RTM and modulation of S1PR1 and S1PR3 reduced RTM in an additive manner. Cre-mediated deletion of S1pr1 in MCs blocked LPS-induced RTM, confirming a role for myeloid-specific S1PR1 signaling. Global or hematopoietic deficiency of Sphk1 reduced plasma S1P levels, the abundance of CD11c+ MCs in the aortic intima and blunted LPS-induced RTM. In contrast, plasma S1P levels, the abundance of intimal MCs, and LPS-induced RTM were rescued in Sphk1-/- mice transplanted with Sphk1+/+ or mixed Sphk1 +/+ and -/- bone marrow. Stimulation with LPS increased endothelial permeability and intimal MC exposure to circulating factors such as S1P. Conclusions: Functional and expression studies support a novel role for S1P signaling in the regulation of LPS-induced RTM as well as the homeostatic maintenance of aortic intimal MCs. Our data provides insight into how circulating plasma mediators help orchestrate intimal MC dynamics.

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Critical Role of Sphingolipid Pathway Components in Murine Radiation-Induced Lung Injury: Protection by Sphingosine-1-Phosphate Analogues

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