Sphingosine‐1‐Phosphate Modulates the Effect of Estrogen in Human Osteoblasts

Abstract

Production of sphingosine-1-phosphate (S1P) is linked to 17β-estradiol (E2) activity in many estrogen-responsive cells; in bone development, the role of S1P is unclear. We studied effects of S1P on proliferation and differentiation of human osteoblasts (hOB). Ten nM E2, 1 μM S1P, or 1 μM of the S1P receptor 1 (S1PR1) agonist SEW2871 increased hOB proliferation at 24 hours. S1PR 1, 2, and 3 mRNAs are expressed by hOB but not S1PR4 or S1PR5. Expression of S1PR2 was increased at 7 and 14 days of differentiation, in correspondence with osteoblast-related mRNAs. Expression of S1PR1 was increased by E2 or S1P in proliferating hOB, whereas S1PR2 mRNA was unaffected in proliferating cells; S1PR3 was not affected by E2 or S1P. Inhibiting sphingosine kinase (SPHK) activity with sphingosine kinase inhibitor (Ski) greatly reduced the E2 proliferative effect. Both E2 and S1P increased SPHK mRNA at 24 hours in hOB. S1P promoted osteoblast proliferation via activating MAP kinase activity. Either E2 or S1P increased S1P synthesis in a fluorescent S1P assay. Interaction of E2 and S1P signaling was indicated by upregulation of E2 receptor mRNA after S1P treatment. E2 and S1P also promoted alkaline phosphatase expression. During osteoblast differentiation, S1P increased bone-specific mRNAs, similarly to the effects of E2. However, E2 and S1P showed differences in the activation of some osteoblast pathways. Pathway analysis by gene expression arrays was consistent with regulation of pathways of osteoblast differentiation; collagen and cell adhesion proteins centered on Rho/Rac small GTPase signaling and Map kinase or signal transducer and activator of transcription (Stat) intermediates. Transcriptional activation also included significant increases in superoxide dismutase 1 and 2 transcription by either S1P or E2. We demonstrate that the SPHK system is a co-mediator for osteoblast proliferation and differentiation, which is mainly, but not entirely, complementary to E2, whose effects are mediated by S1PR1 and S1PR2.

Cytokine-Induced and Stretch-Induced Sphingosine 1-Phosphate Production by Enthesis Cells Could Favor Abnormal Ossification in Spondyloarthritis

“…These results corroborate our previous study that implicated SKs in the mineralization capacity of osteoblasts and chondrocytes . In accordance, the addition of exogenous S1P to human osteoblasts (hOB CC‐2538) has been shown to enhance Bglap2 and Alpl gene expression . These effects on osteoblast differentiation are in addition to those already observed on their proliferation.…”

“…(19) In accordance, the addition of exogenous S1P to human osteoblasts (hOB CC-2538) has been shown to enhance Bglap2 and Alpl gene expression. (48) These effects on osteoblast differentiation are in addition to those already observed on their proliferation. Further, S1P can indeed stimulate the proliferation of rat, bovine, and human primary chondrocytes.…”

Sphingosine‐1‐phosphate (S1P) receptors: Promising drug targets for treating bone‐related diseases

“…Similarly, the formation of S1P can be modulated by treatments targeting SPHK. Using SKi (10 μmol/L), a SPHK inhibitor, in hOB assays further confirmed this hypothesis 49 . Because these enzymes have limited distribution and their activation can be easily controlled, controlling the S1P concentration by regulating enzyme activation has tissue specificity, and they have great advantages over directly regulating S1PRs.…”

The role of sphingosine-1-phosphate in bone remodeling and osteoporosis

“…Various in vitro studies revealed that S1P controls bone formation by regulating OB proliferation and survival. 48 – 52 Dziak et al were one of the first to demonstrate that short-term incubation with S1P leads enhances proliferation rate in primary human osteoblastic cells, as well as in the human osteosarcoma cell lines MG63 and G292, in a pertussis toxin-sensitive manner. Therefore, the researchers suggested the involvement of S1PR1.…”