Sphingomyelin Degradation is a Key Factor in Dentin and Bone Mineralization: Lessons from the <i>fro/fro</i> Mouse

Abstract

Lipids play major biological roles as components of cell membranes (Vance and Vance, 1991). They are involved in cell proliferation, differentiation and survival (Cutler and Mattson, 2001). Impairment of lipid functions has direct consequences on cell functions, as demonstrated by nutritional and genetic pathologies related to lipid metabolism. As components of the extracellular matrix (ECM) of mineralized tissues, lipids have been far less studied. Their presence is now well recognized, but their role in biological and pathological mineralizations is far from being elucidated. The total lipid content of bones has been reported to range from 1–10%. In dental tissues, the total lipid content is 0.26–0.36% in dentin, 0.014% of which are phospholipids, and 0.60% in enamel, among which 12.5% are phospholipids (0.075% of total enamel) (see for review Goldberg and Boskey, 1996). Compared with the major dentin ECM components, namely the phosphorylated proteins of the SIBLING family, lipids appear as minor components. Due to the low ratio between lipids and the total ECM molecules and to the fact that the major part of the lipid fraction is lost after routine fixation and processing for light and electron microscopy, they have been less investigated than other matrix components easier to preserve and analyze.