Hyperosmolarity-induced lipid droplet formation depends on ceramide production by neutral sphingomyelinase 2.
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.
Helsinki Eye Lab, Department of Ophthalmology, Haartmaninkatu 4 C,  University of Helsinki, 00290 Helsinki,  Finland.
Alexandra
A
Robciuc
Tuulia
T
Hyötyläinen
Matti
M
Jauhiainen
Juha M
JM
Holopainen
D002460:Cell Line; D002853:Chromatography, Liquid; D003315:Cornea / Q000166:cytology; D004797:Enzyme-Linked Immunosorbent Assay; D004847:Epithelial Cells / Q000378:metabolism*; D006801:Humans; D016209:Interleukin-8 / Q000378:metabolism; D013058:Mass Spectrometry; D008856:Microscopy, Fluorescence; D009997:Osmotic Pressure / Q000502:physiology*; D013108:Sphingomyelin Phosphodiesterase / Q000378:metabolism*; D013109:Sphingomyelins / Q000378:metabolism
D016209:Interleukin-8; D013109:Sphingomyelins; D013108:Sphingomyelin Phosphodiesterase