AQP4‑knockout alleviates the lipopolysaccharide‑induced inflammatory response in astrocytes via SPHK1/MAPK/AKT signaling

Int J Mol Med. 2018 Sep;42(3):1716-1722. doi: 10.3892/ijmm.2018.3749. Epub 2018 Jun 29.

Abstract

To date, aquaporin‑4 (AQP4) has been considered as a critical contributor to neuroinflammation, but little is known about the underlying mechanism. Previous studies have shown that a critical enzyme involved in the sphingomyelin cycle, sphingosine kinase 1 (SPHK1), is implicated in inflammatory processes and contributes to chronic neuroinflammation. The present study investigated the role of AQP4 in proinflammatory cytokine release from astrocytes, with an emphasis on the SPHK1/mitogen‑activated protein kinase (MAPK)/protein kinase B (AKT) pathway. Using primary cultures isolated from AQP4+/+ and AQP4‑/‑ embryos, the production of tumor necrosis factor‑α (TNF‑α)/interleukin‑6 (IL‑6) from astrocytes challenged by lipopolysaccharide (LPS) was compared. The results showed increased secretion of TNF‑α/IL‑6 in the two groups following LPS treatment, but a significantly lower level was observed in the AQP4‑/‑ group compared with that in the AQP4+/+ group. Although upregulation of SPHK1 was detected in the two genotypes, only a mild increase in SPHK1 was found in the AQP4‑/‑ genotype. The phosphorylation of MAPK/AKT was also confirmed to be attenuated in the AQP4‑/‑ group, suggesting decreased MAPK/AKT signaling over time in AQP4‑/‑ astrocytes. Overall, the study findings demonstrated that AQP4 deficiency alleviates proinflammatory cytokine release from astrocytes, in association with the SPHK1/MAPK/AKT pathway. This data improves our understanding of AQP4 in neuroinflammatory events, highlighting a novel profile of SPHK1 as a potential target for the treatment of CNS inflammation.

MeSH terms

  • Animals
  • Aquaporin 4 / genetics*
  • Aquaporin 4 / metabolism
  • Astrocytes / enzymology*
  • Astrocytes / metabolism
  • Astrocytes / pathology*
  • Cell Survival / drug effects
  • Cells, Cultured
  • Cytokines / metabolism
  • Gene Knockout Techniques*
  • Inflammation / pathology*
  • Lipopolysaccharides
  • Mice, Knockout
  • Mitogen-Activated Protein Kinases / metabolism*
  • Phosphotransferases (Alcohol Group Acceptor) / metabolism*
  • Proto-Oncogene Proteins c-akt / metabolism*

Substances

  • Aquaporin 4
  • Cytokines
  • Lipopolysaccharides
  • Phosphotransferases (Alcohol Group Acceptor)
  • sphingosine kinase
  • Proto-Oncogene Proteins c-akt
  • Mitogen-Activated Protein Kinases