Hyperosmolarity-induced lipid droplet formation depends on ceramide production by neutral sphingomyelinase 2

J Lipid Res. 2012 Nov;53(11):2286-95. doi: 10.1194/jlr.M026732. Epub 2012 Aug 15.

Abstract

Hyperosmolarity (HO) imposes a remarkable stress on membranes, especially in tissues in direct contact with the external environment. Our efforts were focused on revealing stress-induced lipid changes that precede the inflammatory cytokine response in human corneal epithelial cells exposed to increasing osmolarity. We used a lipidomic analysis that detected significant and systematic changes in the lipid profile, highly correlated with sodium concentrations in the medium. Ceramides and triglycerides (TGs) were the most-responsive lipid classes, with gradual increases of up to 2- and 3-fold, respectively, when compared with control. The source of ceramide proved to be sphingomyelin hydrolysis, and neutral sphingomyelinase 2 (NSM2) activity showed a 2-fold increase 1 h after HO stress, whereas transcription increased 3-fold. Both TG accumulation and IL-8 secretion were shown to be dependent on ceramide production by specific knock-down of NSM2. In HCE cells, diglyceride acyltransferase 1 was responsible for the TG synthesis, but the enzyme activity had no effect on cytokine secretion. Hence, NSM2 plays a key role in the cellular response to hyperosmolar stress, and its activity regulates both cytokine secretion and lipid droplet formation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cell Line
  • Chromatography, Liquid
  • Cornea / cytology
  • Enzyme-Linked Immunosorbent Assay
  • Epithelial Cells / metabolism*
  • Humans
  • Interleukin-8 / metabolism
  • Mass Spectrometry
  • Microscopy, Fluorescence
  • Osmotic Pressure / physiology*
  • Sphingomyelin Phosphodiesterase / metabolism*
  • Sphingomyelins / metabolism

Substances

  • Interleukin-8
  • Sphingomyelins
  • Sphingomyelin Phosphodiesterase