Studies on expression and function of sphingosine 1-phosphate receptor-1 (S1P1) in embryogenesis and the adult

S1P1, a high affinity G-protein coupled receptor for bioactive lipid sphingosine 1-phosphate (S1P), regulates various cellular functions. However, little is known about the physiological roles of S1P1. To improve our understanding of the function of S1P1 in vivo, we investigated the role of S1P1 during limb development, S1P1 expression in the adult tissues, and S1P1 function in adult vasculature and angiogenesis. ^ During limb development, S1P1 is expressed in the vasculature and in mesenchymal tissues in the remodeling areas. S1P1 −/− limbs are hypervascularized and cartilage condensation was absent in the digit areas. The expression of VEGF and HIF-1α are highly elevated in S1P 1 −/− limbs. Endothelium specific S1P1 −/− limbs also exhibit same phenotype. These results indicate that impaired vascular function in S1P1 −/− limbs generates tissue hypoxia, resulting in abnormal limb development. ^ In normal adult tissues, S1P1 is ubiquitously expressed in various cell types, including endothelial cells, neuronal cells, hepatocytes, cardiomyocytes, and spermatids. Interestingly, S1P1 expression in endothelial cells is variable depending on tissues, suggesting that the requirement of S1P1 depends on microenvironment or vascular functions. S1P1 is highly induced in the selective vessels during tumor angiogenesis. ^ To determine the role of S1P1 in adult, small interfering RNA strategy was developed using E. coli RNaseIII (usiRNA). The usiRNA for S1P1 specifically suppressed the expression of S1P 1 and migration toward S1P in endothelial cells in vitro. Intravenous administration of S1P1 usiRNA in vivo resulted in significant suppression of endogenous gene expression in the lung and liver and induced the increase in lung vascular permeability. Local administration of usiRNA into tumor xenografts significantly attenuated tumor growth concomitantly with the suppression of angiogenesis. In addition, usiRNA for S1P1 potently inhibited FGF-2 induced angiogenesis. These data argue for the utility of usiRNA technology in therapeutics and specifically suggest that the S1P 1 receptor may be critical for the tumor angiogenesis. ^ Taken together, S1P1 is critical for the vascular system in adult as well as in embryo. Also, S1P1 is necessary for normal limb development and is expressed in diverse tissues, suggesting that the role of S1P1 is not limited to vascular system.