Figure 4.

Carrier-dependent effects of S1P in atherosclerosis. At least part of the HDL pleiotropic effects are thought to be due to S1P present on HDL, and HDL-associated S1P is bound specifically to ApoM. ApoM is not just a carrier of S1P, but is also an important modifier that increases the total amount of S1P in the body by protecting S1P from degradation. Furthermore, ApoM strengthens the agonist properties of S1P toward S1P₁, which is anti-atherosclerotic, while it weakens the agonist properties for S1P₂, which is pro-atherosclerotic. On the other hand, S1P bound to albumin preferably interacts with S1P₂.