Sphingosine Kinase 1 Deficiency Exacerbates LPS-Induced Neuroinflammation

<div><p>The pathogenesis of inflammation in the central nervous system (CNS), which contributes to numerous neurodegenerative diseases and results in encephalopathy and neuroinflammation, is poorly understood. Sphingolipid metabolism plays a crucial role in maintaining cellular processes in the CNS, and thus mediates the various pathological consequences of inflammation. For a better understanding of the role of sphingosine kinase activation during neuroinflammation, we developed a bacterial lipopolysaccharide (LPS)-induced brain injury model. The onset of the inflammatory response was observed beginning 4 hours after intracerebral injection of LPS into the lateral ventricles of the brain. A comparison of established neuroinflammatory parameters such as white matter rarefactions, development of cytotoxic edema, astrogliosis, loss of oligodendrocytes, and major cytokines levels in wild type and knockout mice suggested that the neuroinflammatory response in SphK1−/− mice was significantly upregulated. At 6 hours after intracerebroventricular injection of LPS in SphK1−/− mice, the immunoreactivity of the microglia markers and astrocyte marker glial fibrillary acidic protein (GFAP) were significantly increased, while the oligodendrocyte marker O4 was decreased compared to WT mice. Furthermore, western blotting data showed increased levels of GFAP. These results suggest that SphK1 activation is involved in the regulation of LPS induced brain injury.</p> <h3>Research Highlights</h3><p>• Lipopolysaccharide (LPS) intracerebral injection induces severe neuroinflammation. • Sphingosine kinase 1 deletion worsens the effect of the LPS. • Overexpression of SphK1 might be a potential new treatment approach to neuroinflammation.</p> </div

(A) Western blot analysis of the GFAP protein expressed in the total brain extract.

<p>(<b>B</b>) Statistical analysis of the integrated densities of the bands of the western blot. Significance was reached in wild type group after LPS induction (*p<0.0001) and in saline injected group between wild type and SphK1−/− animals (**p<0.001).</p

Immunohistochemistry using anti- CD 68 and ferritin light chain antibodies.

<p>(<b>A</b>) Two-way ANOVA analysis revealed significant difference (*p = 0.0451) in anti-CD68 (FITC) staining after LPS 1 mg/kg intracerebroventricular injection in wild type and SphK1−/− mice. (<b>B</b>) Bonferroni’s multiple comparison of the anti-ferritin light chain staining (TRITC) determined significance between wild type LPS 1 mg/kg vs. SphK1−/− LPS 1 mg/kg (**p = 0.0181) and in mutant group after LPS injury (*p = 0.0123).</p