Sphingosine-1-phosphate promotes osteogenesis by stimulating osteoblast growth and neovascularization in a vascular endothelial growth factor-dependent manner.

Sphingosine-1-phosphate (S1P) plays multiple roles in bone metabolism and regeneration. Here, we have identified a novel S1P-regulated osteoanabolic mechanism functionally connecting osteoblasts (OBs) to the highly specialized bone vasculature. We demonstrate that S1P/S1PR3 signaling in OBs stimulates vascular endothelial growth factor a (VEGFa) expression and secretion to promote bone growth in an autocrine and boost osteogenic H-type differentiation of bone marrow endothelial cells in a paracrine manner. VEGFa-neutralizing antibodies and VEGF receptor inhibition by axitinib abrogated OB growth in vitro and bone formation in male C57BL/6J in vivo following S1P stimulation and S1P lyase inhibition, respectively. Pharmacological S1PR3 inhibition and genetic S1PR3 deficiency suppressed VEGFa production, OB growth in vitro, and inhibited H-type angiogenesis and bone growth in male mice in vivo. Together with previous work on the osteoanabolic functions of S1PR2 and S1PR3, our data suggest that S1P-dependent bone regeneration employs several nonredundant positive feedback loops between OBs and the bone vasculature. The identification of this yet unappreciated aspect of osteoanabolic S1P signaling may have implications for regular bone homeostasis as well as diseases where the bone microvasculature is affected such as age-related osteopenia and posttraumatic bone regeneration.

Sphingosine-1-phosphate (S1P) is a signaling lipid that regulates bone growth and regeneration. In the present study, a novel regenerative mechanism was connected to S1P signaling within the bone. Activation of its receptor S1PR3 in bone-forming osteoblasts led to secretion of vascular endothelial growth factor a (VEGFa), the most potent vessel-stimulating factor. This stimulated the development of specialized vessels of the bone marrow, the H-type vessels, that supported overall bone regeneration. These findings foster our understanding of regular bone metabolism and suggest that S1P-based drugs may help treat diseases such as age-related osteopenia and posttraumatic bone regeneration, conditions crucially dependent on functional bone microvasculature.

Sphingosine-1-phosphate suppresses GLUT activity through PP2A and counteracts hyperglycemia in diabetic red blood cells.

Red blood cells (RBC) are the major carriers of sphingosine-1-phosphate (S1P) in blood. Here we show that variations in RBC S1P content achieved by altering S1P synthesis and transport by genetic and pharmacological means regulate glucose uptake and metabolic flux. This is due to S1P-mediated activation of the catalytic protein phosphatase 2 (PP2A) subunit leading to reduction of cell-surface glucose transporters (GLUTs). The mechanism dynamically responds to metabolic cues from the environment by increasing S1P synthesis, enhancing PP2A activity, reducing GLUT phosphorylation and localization, and diminishing glucose uptake in RBC from diabetic mice and humans. Functionally, it protects RBC against lipid peroxidation in hyperglycemia and diabetes by activating the pentose phosphate pathway. Proof of concept is provided by the resistance of mice lacking the S1P exporter MFSD2B to diabetes-induced HbA1c elevation and thiobarbituric acid reactive substances (TBARS) generation in diabetic RBC. This mechanism responds to pharmacological S1P analogues such as fingolimod and may be functional in other insulin-independent tissues making it a promising therapeutic target.

Sphingosine-1-Phosphate (S1P) Lyase Inhibition Aggravates Atherosclerosis and Induces Plaque Rupture in ApoE-/-Mice.

Altered plasma sphingosine-1-phosphate (S1P) concentrations are associated with clinical manifestations of atherosclerosis. However, whether long-term elevation of endogenous S1P is pro- or anti-atherogenic remains unclear. Here, we addressed the impact of permanently high S1P levels on atherosclerosis in cholesterol-fed apolipoprotein E-deficient (ApoE-/-) mice over 12 weeks. This was achieved by pharmacological inhibition of the S1P-degrading enzyme S1P lyase with 4-deoxypyridoxine (DOP). DOP treatment dramatically accelerated atherosclerosis development, propagated predominantly unstable plaque phenotypes, and resulted in frequent plaque rupture with atherothrombosis. Macrophages from S1P lyase-inhibited or genetically deficient mice had a defect in cholesterol efflux to apolipoprotein A-I that was accompanied by profoundly downregulated cholesterol transporters ATP-binding cassette transporters ABCA1 and ABCG1. This was dependent on S1P signaling through S1PR3 and resulted in dramatically enhanced atherosclerosis in ApoE-/-/S1PR3-/- mice, where DOP treatment had no additional effect. Thus, high endogenous S1P levels promote atherosclerosis, compromise cholesterol efflux, and cause genuine plaque rupture.