Sphingosine-1-phosphate (S1P), a potent bioactive
lipid, is emerging as a central mediator in
inflammation and immune responses. We have previously implicated S1P and its synthetic
enzyme sphingosine kinase (SK) in inflammatory and autoimmune disorders, including
inflammatory bowel disease and
rheumatoid arthritis. Generation of S1P requires phosphorylation of
sphingosine by SK, of which there are two
isoforms. Numerous studies have implicated SK1 in immune cell trafficking,
inflammation and autoimmune disorders. In this study, we set out to determine the role of SK and S1P in
lupus nephritis (LN). To this end, we examined S1P and dihydro-S1P (dh-S1P) levels in serum and kidney tissues from a mouse model of LN. Interestingly dh-S1P was significantly elevated in serum and kidney tissue from LN mice, which is more readily phosphorylated by SK2. Therefore, we employed the use of the specific SK2 inhibitor,
ABC294640 in our murine model of LN. Treatment with
ABC294640 did not improve vascular or interstitial pathology associated with LN. However, mice treated with the SK2 inhibitor did demonstrate decreases in glomerular pathology and accumulation of B and T cells in the spleen these were not statistically different from lpr mice treated with vehicle. LN mice treated with
ABC294640 did not have improved urine
thromboxane levels or urine
proteinuria measurements. Both S1P and dh-S1P levels in circulation were significantly reduced with
ABC294640 treatment; however, dh-S1P was actually elevated in kidneys from LN mice treated with
ABC294640. Together these data demonstrate a role for SKs in LN; however, they suggest that inhibition of SK1 or perhaps both SK
isoforms would better prevent elevations in S1P and dh-S1P and potentially better protect against LN.