Elevated sphingosine 1-phopshate (S1P) concentration was observed in type 2 diabetes mellitus (T2D). On the other side, 1α,25-dihydroxyvitamin D3 (1,25(OH)2D3) can influence the formation of sphingosine 1-phopshate (S1P) and the expression of S1P receptors, which are known to be involved in T2D. In order to evaluate mechanisms for the antiinflammatory potential of 1,25(OH)2D3, we investigated whether 1,25(OH)2D3 alters S1P signaling and metabolism in human CD14+ monocytes. Primary monocytes isolated from healthy controls (HC) and T2D patients were treated for 24 h with 10 nM 1,25(OH)2D3 in the absence or presence of 500 IU/ml interleukin-(IL)-1β. Thereafter, sphingosine kinase (SPHK)1, SPHK2 and S1P receptor 1-5 (S1P1-5) mRNA expression levels were measured by TaqMan™ analyses. Sphingolipid levels in cell supernatant were determined by high-performance liquid chromatography/tandem mass spectrometry (LC-MS/MS). 1,25(OH)2D3 treatment downregulated S1P1 and S1P2 mRNA expression compared to untreated monocytes of HC and T2D patients. In contrast, SPHK1, S1P3 and S1P4 mRNA expression levels were upregulated by 1,25(OH)2D3 treatment compared to the respective controls. Furthermore, reduced S1P2 and increased S1P3 and S1P4 mRNA expression levels upon treatment with 1,25(OH)2D3 occurred in the presence of IL-1β. Additionally, S1P levels in cell supernatants were decreased in monocytes from HC and T2D patients by 1,25(OH)2D3 with or without IL-1β costimulation. The levels of sphingosine in cell supernatants were not influenced by 1,25(OH)2D3. Overall, our results demonstrate for the first time that 1,25(OH)2D3 treatment can influence S1P receptor and SPHK expression and S1P levels in primary monocytes of both HC and subjects with T2D. These findings justify further investigations into the sphingolipid metabolism and potential benefits of vitamin D treatment in diabetes.
Keywords: 1α,25-dihydroxyvitamin D(3); Monocytes; S1P receptors; Sphingolipid metabolism; Sphingosine 1-phosphate; Sphingosine kinase; Type 2 diabetes mellitus.
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