Except for epidermis and liver, little is known about endogenous expression of 1-O-acylceramides (1-OACs) in mammalian tissue. Therefore, we screened several organs (brain, lung, liver, spleen, lymph nodes, heart, kidney, thymus, small intestine, and colon) from mice for the presence of 1-OACs by LC-MS2. In most organs, low levels of about 0.25-1.3 pmol 1-OACs/mg wet weight were recorded. Higher levels were detected in liver, small and large intestines, with about 4-13 pmol 1-OACs/mg wet weight. 1-OACs were esterified mainly with palmitic, stearic, or
oleic acids. Esterification with saturated very long-chain
fatty acids, as in epidermis, was not observed. Western-type diet induced 3-fold increased 1-OAC levels in mice livers while
ceramides were unaltered. In a mouse model of
Farber disease with a decrease of
acid ceramidase activity, we observed a strong, up to 50-fold increase of 1-OACs in lung, thymus, and spleen. In contrast, 1-OAC levels were reduced 0.54-fold in liver. Only in lung 1-OAC levels correlated to changes in
ceramide levels - indicating tissue-specific mechanisms of regulation.
Glucosylceramide synthase deficiency in liver did not cause changes in 1-OAC or
ceramide levels, whereas increased
ceramide levels in
glucosylceramide synthase-deficient small intestine caused an increase in 1-OAC levels. Deficiency of Dgat1 in mice resulted in a reduction of 1-OACs to 30% in colon, but not in small intestine and liver, going along with constant free
ceramides levels. From these data, we conclude that Dgat1 as well as lysosomal lipid metabolism contribute in vivo to homeostatic 1-OAC levels in an organ-specific manner.