FTY720 enhances osteogenic differentiation of bone marrow mesenchymal stem cells in ovariectomized rats

The role of SphK/S1P/S1PR signaling pathway in bone metabolism

There are a large number of people worldwide who suffer from osteoporosis, which imposes a huge economic burden, so it is necessary to explore the underlying mechanisms to achieve better supportive and curative care outcomes. Sphingosine kinase (SphK) is an enzyme that plays a crucial role in the synthesis of sphingosine-1-phosphate (S1P). S1P with paracrine and autocrine activities that act through its cell surface S1P receptors (S1PRs) and intracellular signals. In osteoporosis, S1P is indispensable for both normal and disease conditions. S1P has complicated roles in regulating osteoblast and osteoclast, respectively, and there have been exciting developments in understanding how SphK/S1P/S1PR signaling regulates these processes in response to osteoporosis therapy. Here, we review the proliferation, differentiation, apoptosis, and functions of S1P, specifically detailing the roles of S1P and S1PRs in osteoblasts and osteoclasts. Finally, we focus on the S1P-based therapeutic approaches in bone metabolism, which may provide valuable insights into potential therapeutic strategies for osteoporosis.

Controlled mechanical loading improves bone regeneration by regulating type H vessels in a S1Pr1-dependent manner

Despite the best treatment, approximately 10% of fractures still face undesirable repair and result in delayed unions or non-unions. Dynamic mechanical stimulation promotes bone formation, when applied at the correct time frame, with optimal loading magnitude, frequency, and repetition. Controlled mechanical loading significantly increases osteogenic cells during the matrix deposition phase of bone repair. In the bone defect, the blood vessel network guides the initial bone formation activities. A unique blood vessel subtype (Type H) exists in bone, which expresses high levels of CD31 and endomucin, and functions to couple angiogenesis and osteogenesis. However, how this form of controlled mechanical loading regulates the Type H vessels and promotes bone formation is still not clear. Sphingosine 1-phosphate (S1P) participates in the bone anabolic process and is a key regulator of the blood vessel. Its receptor, sphingosine 1-phosphate receptor 1 (S1Pr1), is a mechanosensitive protein that regulates vascular integrity. Therefore, we hypothesis that controlled anabolic mechanical loading promotes bone repair by acting on Type H vessels. To study the effect of S1Pr1 on loading induced-bone repair, we utilized a stabilized tibial defect model, which allows for the application of anabolic mechanical loading. Mechanical loading upregulated S1Pr1 within the entire defect, with up to 80% expressed in blood vessels, as observed by deep tissue imaging. Additionally, S1Pr1 antagonism by W146 inhibited the anabolic effects of mechanical loading. We showed that mechanical loading or activating S1Pr1 could induce YAP nuclear translocation, a key regulator in the cell's mechanical response, in endothelial cells (ECs) in vitro. Inhibition of S1Pr1 in endothelial cells by siRNA reduced loading-induced YAP nuclear translocation and expressions of angiogenic genes. In vivo, YAP nuclear translocation in Type H vessels was up-regulated after mechanical loading but was inhibited by antagonizing S1Pr1. S1Pr1 agonist, FTY720, increased bone volume and Type H vessel volume, similar to that of mechanical stimulation. In conclusion, controlled anabolic mechanical loading enhanced bone formation mainly through Type H vessels in a S1Pr1-dependent manner.

FTY720 administration results in a M2 associated immunoregulatory effect that positively influences the outcome of alveolar bone repair outcome in mice

The alveolar bone repair process may be influenced by multiple local and systemic factors, which include immune system cells and mediators. Macrophages allegedly play important roles in the repair process, and the transition of an initial inflammatory M1 profile into a pro-reparative M2 profile theoretically contributes to a favorable repair outcome. In this context, considering immunoregulatory molecules as potential targets for improving bone repair, this study evaluated the role of the immunoregulatory molecule FTY720, previously described to favor the development of the M2 phenotype, in the process of alveolar bone healing in C57Bl/6 (WT) mice. Experimental groups submitted to tooth extraction and maintained under control conditions or treated with FTY720 were evaluated by microtomographic (μCT), histomorphometric, immunohistochemical and molecular analysis to characterize healing and host response features at 0, 1, 3, 7 and 14 days. Our results demonstrated that the FTY720 group presented higher bone tissue density, higher bone tissue volume, greater tissue volume fraction, greater number and thickness of trabeculae and a higher number of osteoblasts and osteoclasts than the control group. Accordingly, the bone markers BMP2, BMP7, ALPL, SOST and RANK mRNA expressions increased in the FTY720 treated group. Furthermore, the levels of FIZZ, ARG2 and IL-10 mRNA increased in the FTY720 group together with the presence of CD206⁺ cells, suggesting that the boost of bone formation mediated by FTY720 involves an increased polarization and activity of M2 macrophages in healing sites. Thus, our results demonstrate that FTY720 favored the process of alveolar bone repair, probably trough a strengthened M2 response, associated with an increased expression of markers osteogenic differentiation and activity markers. Immunoregulatory strategies based in the modulation of macrophage polarization profile can comprise effective tools to improve the bone repair process.

The Mechanosensory Role of Osteocytes and Implications for Bone Health and Disease States

Bone homeostasis is a dynamic equilibrium between bone-forming osteoblasts and bone-resorbing osteoclasts. This process is primarily controlled by the most abundant and mechanosensitive bone cells, osteocytes, that reside individually, within chambers of porous hydroxyapatite bone matrix. Recent studies have unveiled additional functional roles for osteocytes in directly contributing to local matrix regulation as well as systemic roles through endocrine functions by communicating with distant organs such as the kidney. Osteocyte function is governed largely by both biochemical signaling and the mechanical stimuli exerted on bone. Mechanical stimulation is required to maintain bone health whilst aging and reduced level of loading are known to result in bone loss. To date, both in vivo and in vitro approaches have been established to answer important questions such as the effect of mechanical stimuli, the mechanosensors involved, and the mechanosensitive signaling pathways in osteocytes. However, our understanding of osteocyte mechanotransduction has been limited due to the technical challenges of working with these cells since they are individually embedded within the hard hydroxyapatite bone matrix. This review highlights the current knowledge of the osteocyte functional role in maintaining bone health and the key regulatory pathways of these mechanosensitive cells. Finally, we elaborate on the current therapeutic opportunities offered by existing treatments and the potential for targeting osteocyte-directed signaling.

Down-regulated microRNA-199a-3p enhances osteogenic differentiation of bone marrow mesenchymal stem cells by targeting Kdm3a in ovariectomized rats

Osteoporosis is a prevalent systemic skeletal disorder entailing bone fragility and increased fracture risk, often emerging in post-menopausal life. Emerging evidence implicates the dysregulation of microRNAs (miRNAs or miRs) in the progression of osteoporosis. This study investigated the effect of miR-199a-3p on osteoporosis and its underlying mechanism. We first examplished an ovariectomized (OVX)-induced rat osteoporosis model, and then isolated mesenchymal stem cells (MSCs) from bone marrow of the model rats. The overexpression and knock down of miR-199a-3p were conducted in OVX rats and MSCs to verify the role of miR-199a-3p on MSC differentiation. Calcium nodules were measured using alizarin red S (ARS) staining. RT-qPCR and Western blot assay were performed to measure the expression of miR-199a-3p, Kdm3a and osteogenic differentiation-related markers in rat tissues and cells. The correlation between miR-199a-3p and Kdm3a was confirmed using dual-luciferase reporter assay. The enrichment of Kdm3a at the Erk2 and Klf2 promoter was assessed using chromatin immunoprecipitation (ChIP) assay. Isolated MSCs were positive for CD29, CD44, CD90, and CD45, suggesting successful isolation of MSCs. There was increased expression of miR-199a-3p and inhibited osteogenic differentiation in OVX rats. Kdm3a was negatively targeted by miR-199a-3p. Our results also demonstrated that Kdm3a elevated the expression of Erk2 and Erk2 by promoting Erk2 and Klf2 demethylation, which further contributed to osteogenic differentiation. Overall, our results revealed a regulatory network of miR-199a-3p in osteogenic differentiation, highlighting miR-199a-3p as a potential target for therapeutic interventions in osteoporosis.

Fingolimod increases oligodendrocytes markers expression in epidermal neural crest stem cells

Epidermal neural crest stem cells (EPI-NCSCs) are propitious candidates for cell replacement therapy and supplying neurotrophic factors in the neurological disorders. Considering the potential remyelinating and regenerative effects of fingolimod, in this study, we evaluated its effects on EPI-NCSCs viability and the expression of neurotrophic and oligodendrocyte differentiation factors. EPI-NCSCs, extracted from the bulge of rat hair follicles, were characterized and treated with fingolimod (0, 50, 100, 200, 400, 600, 1000, and 5000 nM). The cell viability was evaluated by MTT assay at 6, 24 and 72 h. The expression of neurotrophic and differentiation factors in the cells treated with 100 and 400 nM fingolimod were measured at 24 and 120 h. Fingolimod at 50-600 nM increased the cells viability after 6 h, with no change at the higher concentrations. The highest concentration (5000nM) induced toxicity at 24 and 72 h. NGF and GDNF genes expression were decreased at 120 h, but on the contrary, brain derived neurotrophic factor (BDNF) and neurotrophin 3 (NT3) were increased by both concentrations at both time points. Oligodendrocyte markers including platelet-derived growth factor receptor A (PDGFRα), neuron-glial antigen 2 (NG2) and growth associated protein 43 (GAP43) were elevated at 120 h, which was accompanied with reduce in stemness markers (Nestin and early growth response 1 (EGR1)). Fingolimod increased the expression of neurotrophic factors in EPI-NCSCs, and guided them to oligodendrocyte fate. Therefore, fingolimod in combination with EPI-NCSCs, can be considered as a promising approach for demyelinating neurological disorders.

Fingolimod inhibits proliferation and epithelial-mesenchymal transition in sacral chordoma by inactivating IL-6/STAT3 signalling

Purpose: To explore the sensitivity of the immunosuppressive agent fingolimod (FTY720) in chordoma and determine whether it can serve as an appropriate alternate treatment for unresectable tumours in patients after incomplete surgery.

Methods: Cell viability assays, colony formation assays and EdU assays were performed to evaluate the sensitivity of chordoma cell lines to FTY720. Transwell invasion assays, wound healing assays, flow cytometry, cell cycle analysis, immunofluorescence analysis, Western blotting analysis and enzyme-linked immunosorbent assays (ELISAs) were performed to evaluate cell invasion, epithelial–mesenchymal transition (EMT) and activation of related pathways after treatment with FTY720. The effect of FTY720 was also evaluated in vivo in a xenograft model.

Results: We found that FTY720 inhibited the proliferation, invasion and metastasis of sacral chordoma cells (P < 0.01). FTY720 also inhibited the proliferation of tumour cells in a xenograft model using sacral chordoma cell lines (P < 0.01). The mechanism was related to the EMT and apoptosis of chordoma cells and inactivation of IL-6/STAT3 signalling in vitro and in vivo.

Conclusions: Our findings indicate that FTY720 may be an effective therapeutic agent against chordoma. These findings suggest that FTY720 is a novel agent that can treat locally advanced and metastatic chordoma.

The role of sphingosine 1-phosphate metabolism in bone and joint pathologies and ectopic calcification

Sphingolipids display important functions in various pathologies such as cancer, obesity, diabetes, cardiovascular or neurodegenerative diseases. Sphingosine, sphingosine 1-phosphate (S1P), and ceramide are the central molecules of sphingolipid metabolism. Sphingosine kinases 1 and 2 (SK1 and SK2) catalyze the conversion of the sphingolipid metabolite sphingosine into S1P. The balance between the levels of S1P and its metabolic precursors ceramide and sphingosine has been considered as a switch that could determine whether a cell proliferates or dies. This balance, also called « sphingolipid rheostat », is mainly under the control of SKs. Several studies have recently pointed out the contribution of SK/S1P metabolic pathway in skeletal development, mineralization and bone homeostasis. Indeed, SK/S1P metabolism participates in different diseases including rheumatoid arthritis, spondyloarthritis, osteoarthritis, osteoporosis, cancer-derived bone metastasis or calcification disorders as vascular calcification. In this review, we will summarize the most important data regarding the implication of SK/S1P axis in bone and joint diseases and ectopic calcification, and discuss the therapeutic potential of targeting SK/S1P metabolism for the treatment of these pathologies.

Mammalian sphingosine kinase (SphK) isoenzymes and isoform expression: challenges for SphK as an oncotarget

The various sphingosine kinase (SphK) isoenzymes (isozymes) and isoforms, key players in normal cellular physiology, are strongly implicated in cancer and other diseases. Mutations in SphKs, that may justify abnormal physiological function, have not been recorded. Nonetheless, there is a large and growing body of evidence demonstrating the contribution of gain or loss of function and the imbalance in the SphK/S1P rheostat to a plethora of pathological conditions including cancer, diabetes and inflammatory diseases. SphK is expressed as two isozymes SphK1 and SphK2, transcribed from genes located on different chromosomes and both isozymes catalyze the phosphorylation of sphingosine to S1P. Expression of each SphK isozyme produces alternately spliced isoforms. In recent years the importance of the contribution of SpK1 expression to treatment resistance in cancer has been highlighted and, additionally, differences in treatment outcome appear to also be dependent upon SphK isoform expression. This review focuses on an exciting emerging area of research involving SphKs functions, expression and subcellular localization, highlighting the complexity of targeting SphK in cancer and also comorbid diseases. This review also covers the SphK isoenzymes and isoforms from a historical perspective, from their first discovery in murine species and then in humans, their role(s) in normal cellular function and in disease processes, to advancement of SphK as an oncotarget.