Abstract
Sphingosine Kinase-2 (Sphk2) is responsible for the production of the bioactive lipid Sphingosine-1 Phosphate, a key regulator of tissue repair. Here we address the in vivo significance of Sphingosine Kinase -2 in renal inflammation/fibrosis in response to unilateral ureteral obstruction using both genetic and pharmacological strategies. Obstructed kidneys of Sphk2-/- mice showed reduced renal damage and diminished levels of the renal injury markers TGFβ1 and αSMA when compared to wild type controls. We found a consistently significant increase in anti-inflammatory (M2) macrophages in obstructed Sphk2-/- kidneys by flow cytometry and a decrease in mRNA levels of the inflammatory cytokines, MCP1, TNFα, CXCL1 and ILβ1, suggesting an anti-inflammatory bias in the absence of Sphk2. Indeed, metabolic profiling showed that the pro-inflammatory glycolytic pathway is largely inactive in Sphk2-/- bone marrow-derived macrophages. Furthermore, treatment with the M2-promoting cytokines IL-4 or IL-13 demonstrated that macrophages lacking Sphk2 polarized more efficiently to the M2 phenotype than wild type cells. Bone marrow transplant studies indicated that expression of Sphk2-/- on either the hematopoietic or parenchymal cells did not fully rescue the pro-healing phenotype, confirming that both infiltrating M2-macrophages and the kidney microenvironment contribute to the damaging Sphk2 effects. Importantly, obstructed kidneys from mice treated with an Sphk2 inhibitor recapitulated findings in the genetic model. These results demonstrate that reducing Sphk2 activity by genetic or pharmacological manipulation markedly decreases inflammatory and fibrotic responses to obstruction, resulting in diminished renal injury and supporting Sphk2 as a novel driver of the pro-inflammatory macrophage phenotype.
Highlights
The bioactive lipid Sphingosine-1-Phosphate (S1P) and its five receptors S1PR1-5 play important roles in human health and disease
Permanent unilateral ureteral obstruction was performed on WT and Sphingosine Kinase-2 (Sphk2)-/- mice and both kidneys were harvested at the peak of the early and late inflammatory responses, 3 and 5 days post-surgery
The functional effects of Sphk2 appear to be essentially the opposite of those attributed to Sphk1, as illustrated by studies wherein the genetic absence of Sphk2 is protective in ischemia-reperfusion injury of the kidney [30] and liver [31] by diminishing cell cycle arrest and apoptosis [4]
Summary
The bioactive lipid Sphingosine-1-Phosphate (S1P) and its five receptors S1PR1-5 play important roles in human health and disease. Mice harboring a combined deletion of the two kinases die in utero, while mice with a single isoform deletion are viable. Both isoforms are significantly active at baseline and it is thought that Sphk is primarily responsible for maintaining intracellular and circulating S1P levels. Significant structural homology exists between the two isoforms, but their clearly differential cellular localization and sometimes opposing functions[4,5] may suggest distinctly different roles. While Sphk has historically been more intensely studied due to its prominent role in tumor cell proliferation, recent investigations have increasingly focused on understanding potentially unique functions of Sphk
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
