Limiting S1P production with Nogo-B

Sci. Signal.  15 Sep 2015:
Vol. 8, Issue 394, pp. ec263
DOI: 10.1126/scisignal.aad4206

Sphingosine-1-phosphate (S1P) is produced by endothelial cells and red blood cells to regulate vascular tone and barrier function. S1P is a ceramide metabolite, and the rate-limiting enzyme in the biosynthesis of ceramide is serine palmitoyltransferase (SPT), which is an enzyme located in the endoplasmic reticulum (ER). Nogo-A, Nogo-B, and Nogo-C are members of the reticulon-4 family of proteins that are associated with the ER, with Nogo-B the abundant form in the vasculature. Cantalupo et al. determined that mice lacking both Nogo-A and Nogo-B globally (Nogo-A/B–deficient mice) were hypotensive without impaired vascular smooth muscle contractility, had increased abundance of the phosphorylated (active) form of endothelial nitric oxide synthase (eNOS), and exhibited enhanced flow-induced vasodilation and reduced pressure-induced vasoconstriction compared with wild-type mice. Mice with endothelial cell–specific knockout of Nogo-A/B exhibited similar vascular phenotypes, consistent with an important role for Nogo-B in the endothelial cells. Mass spectrometry analysis of sphingolipids from endothelial cells of the lungs and vascular smooth muscles of the Nogo-A/B–deficient mice showed that the amounts of particular ceramide species and the direct precursor of S1P were increased specifically in the endothelial cells compared with the same cells from wild-type mice. Consistent with this biochemical result, the Nogo-A/B–deficient mice had increased amounts of S1P in the circulation. The amount of S1P in the culture medium from Nogo-A/B–deficient endothelial cells was increased compared with that in the medium from control cells, and pharmacological inhibition of SPT with myriocin inhibited S1P production in cells from both the deficient and control animals. Nogo-B and a transmembrane subunit of SPT from overexpressing cultured cells or from mouse lung lysates coimmunoprecipitated, and SPT activity was increased in microsomal preparations from lungs of Nogo-A/B–deficient mice, indicating that Nogo-B inhibited SPT activity. Administration of myriocin to the Nogo-A/B–deficient mice normalized blood pressure and the amount of NO in the plasma, eliminated differences in flow-induced vasodilation between the deficient mice and wild-type mice, and increased myogenic tone to the same extent as occurred in wild-type mice. Application of an S1P receptor antagonist to isolated mesenteric arteries showed that those from the Nogo-A/B–deficient mice exhibited a greater increase in vascular tone than did those from the control mice, consistent with an increase in autocrine S1P signaling in the endothelial cells of the Nogo-A/B–deficient mice. In an angiotensin II–induced mouse model of hypertension, the the Nogo-A/B–deficient mice exhibited a milder increase in blood pressure than did the control Ang II–treated mice and mesenteric arteries from the Nogo-A/B–deficient mice exhibited a greater induced vasodilation response and a reduction in an induced vasoconstriction response. Thus, this study suggests that endothelial cell S1P biosynthesis, which is limited by Nogo-B, is an important contributor to the regulation of vascular tone.

A. Cantalupo, Y. Zhang, M. Kothiya, S. Galvani, H. Obinata, M. Bucci, F. J. Giordano, X.-C. Jiang, T. Hla, A. Di Lorenzo, Nogo-B regulates endothelial sphingolipid homeostasis to control vascular function and blood pressure. Nat. Med. 21, 1028–1037 (2015). [PubMed]