Sphingosine-1-Phosphate Modulates the Effect of Estrogen in Human Osteoblasts.

Michelle R Witt,Duangrat Tantikanlayaporn,Lisa J Robinson,Harry C Blair,Irina L Tourkova,Quitterie Larrouture,Pawinee Piyachaturawat,Jianhua Luo

doi:10.1002/jbm4.10037

Michelle R Witt, Duangrat Tantikanlayaporn + Show 6 more

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https://doi.org/10.1002/jbm4.10037

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Abstract

ABSTRACTProduction 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. © 2018 The Authors JBMR Plus is published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

Highlights

Balanced bone formation by osteoblasts and bone resorption by osteoclasts is required to maintain bone mass
NAD(P)H-dependent cellular oxidoreductase enzymes were not affected by S1P and estrogen treatment
Estradiol protects bone mass in a number of contexts and is known to suppress production of RANKL, which induces production of bone-degrading osteoclasts.[19]. Estrogen signaling has genomic and nongenomic components, including estrogen signaling in bone.[13]. In non-bone cells, including breast cancer, an important nongenomic signal downstream of estrogen is production of sphingosine-1-phosphate via sphingosine kinase-1 (SPHK1)/ 2.(6,20) Our work demonstrates, using assays of fluorescently labeled S1P production, that estrogen or S1P, directly or indirectly, induce S1P production (Fig. 3B); PCR for the sphingosine kinase 1, SPHK1, and Western blots were consistent

Summary

Introduction

Balanced bone formation by osteoblasts and bone resorption by osteoclasts is required to maintain bone mass. S1P modifies proliferation, differentiation, migration, survival, and calcium homeostasis in a variety of cells by coupling receptor of activation to a variety of downstream activators including Map kinases and transcription factors.[9] S1P is irreversibly degraded by S1P lyase to palmitaldehyde, and its phosphorylation is reversed by phosphatases.[10] Several plasma membrane sphingosine-1 phosphate receptors[11] mediate pathophysiological effects of S1P; because of specific links of individual receptors to effects, receptor-specific inhibitors are potential therapeutic agents.[12]. Molecular Pathway analysis using Affymetrix arrays to study whole-genome mRNA expression showed that S1P and estradiol have many similar effects on osteoblast proliferation and differentiation, differences were revealed by study of effects on individual pathways including RANKL/osteoprotegerin signaling

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