The Impact of Sphingosine Kinases on Inflammation-Induced Cytokine Release and Vascular Endothelial Barrier Integrity

• Published in: International journal of molecular sciences 2022-11, Vol.23 (21), p.12848
• Main Authors: Thuy, Andreas V., Reimann, Christina-Maria, Ziegler, Anke C., Gräler, Markus H.
• Format: Article
• Language: English
• Subjects: Bone marrow; Cell culture; Cytokines; Dendritic cells; Endothelial cells; Enzymes; Immune system; Infections; Inflammation; Innate immunity; Interferon; Investigations; Lipopolysaccharides; Liver; Lymphocytes; Macrophages; Metabolism; Plasma; Rodents; Sepsis; Sphingosine 1-phosphate; Stability; Stimulation; Tumor necrosis factor-TNF; Weight loss; γ-Interferon
• ISSN: 1422-0067; 1661-6596; 1422-0067
• DOI: 10.3390/ijms232112848

Sphingosine kinases type 1 and 2 (SphK1/2) are required for the production of the immune modulator sphingosine 1-phosphate (S1P). SphK1 deficient mice (SphK1−/−) revealed 50% reduced S1P in plasma, while SphK2−/− mice demonstrated 2–3 times increased S1P levels in plasma. Since plasma S1P is a potent inducer of vascular endothelial cell (VEC) barrier stability, we hypothesized that higher and lower levels of S1P in SphK2−/− and SphK1−/− mice, respectively, compared to wild type (wt) mice should translate into decreased and increased severity of induced systemic inflammation due to improved or damaged VEC barrier maintenance. To our surprise, both SphK1−/− and SphK2−/− mice showed improved survival rate and earlier recovery from inflammation-induced weight loss compared to wt mice. While no difference was observed in VEC barrier stability by monitoring Evans blue leakage into peripheral tissues, SphK1−/− mice demonstrated a distinct delay and SphK2−/− mice an improved resolution of early pro-inflammatory cytokine release in plasma. Ex vivo cell culture experiments demonstrated that bone marrow-derived dendritic cells (BMDC) generated from SphK1−/− and SphK2−/− mice responded with decreased interferon-γ (IFN-γ) production upon stimulation with lipopolysaccharides (LPS) compared to wt BMDC, while activation-induced cytokine expression of lymphocytes and macrophages was not majorly altered. Ex vivo stimulation of macrophages with IFN-γ resulted in increased cytokine release. These results suggest that SphK1/2 are involved in production and secretion of IFN-γ by DC. DC-derived IFN-γ subsequently stimulates the production and secretion of a large panel of inflammatory cytokines by macrophages, which belong to the main cytokine-releasing cells of the early innate immune response. Inhibitors of SphK1/2 may therefore be attractive targets to dampen the early cytokine response of macrophages as part of the innate immune response.