Prostaglandin F2α negatively regulates bone resorption in murine osteoclast development

The prevention of latanoprost on osteoclastgenesis in vitro and lipopolysaccharide-induced murine calvaria osteolysis in vivo

Identification of agents that inhibit osteoclast formation and function is important for the treatment of osteolytic diseases which feature excessive osteoclast formation and bone resorption. Latanoprost (LTP), an analog of prostaglandin F2α, is a medication which works to lower pressure inside the eyes. Prostaglandin F2α was reported to regulate bone metabolism, however, the effect of LTP in osteoclastogenesis is still unknown. Here, we found that LTP suppressed RANKL-induced osteoclastogenesis in a dose-dependent manner as illustrated by TRAP activity and TRAP staining. In addition, the osteoclast function was also reduced by LTP treatment, as indicated in less osteoclastic resorption pit areas. Furthermore, LTP inhibited the mRNA expressions of osteoclast marker genes such as TRAP and cathepsin K. In order to illustrate its molecular mechanism, we examined the changing of mRNA and protein levels of NFATc1 and c-fos by LTP treatment, as well as the phosphorylation of ERK, AKT, JNK, and p38. The results suggested that LTP inhibited RANKL-induced osteoclastgenesis and function by inhibiting ERK, AKT, JNK, and p38 cascade, following by the c-fos/NFATc1 pathway. In agreement with in vitro results, using an in vivo lipopolysaccharide-induced murine calvaria osteolysis mouse model, we found that administration of LTP was able to reverse the lipopolysaccharide-induced bone loss. Together, these data demonstrated that LTP attenuated the bone loss in lipopolysaccharide-induced murine calvaria osteolysis mice through inhibiting osteoclast formation and function. Our study thus provided the evidences that LTP was a potential treatment option against osteolytic bone diseases.

Prostaglandin F2α: a bone remodeling mediator

Prostaglandin F2α (PGF2α) plays multiple roles on bone metabolism by regulating a wide range of signaling pathways. PGF2α, via activation of PKC, stimulates Na-dependent inorganic phosphate (Pi) transport system in osteoblasts; up-regulates interleukin (IL)-6 synthesis; increases vascular endothelial growth factor (VEGF). In addition, PGF2α acts as a strong mitogenic and survival agent on osteoblasts, and these effects are, at least in part, mediated by the binding of fibroblast growth factor-2 (FGF-2) to the specific receptor FGFR1. The understanding of PGF2α intracellular network, albeit complex to clarify, provides molecular bases useful to identify the players of osteoblast proliferation, apoptosis, and the associated angiogenic processes. Indeed, the molecular mechanism that underline PGF2α-regulated bone metabolism may be a promising platform for the development of novel targeted therapies in the treatment of bone disorders and disease.

Biasing the prostaglandin F2α receptor responses toward EGFR-dependent transactivation of MAPK

The G protein-coupled prostaglandin F2α (PGF2α) receptor [F prostanoid (FP) receptor] has been implicated in many physiological events including cardiovascular, respiratory, immune, reproductive, and endocrine responses. Binding of PGF2α to FP receptor elicits inositol production and protein kinase C-dependent MAPK activation through Gα(q) coupling. Here we report that AL-8810, previously characterized as an orthosteric antagonist of PGF2α-dependent, Gα(q)-mediated signaling, potently activates ERK1/2 in a protein kinase C-independent manner. Rather, AL-8810 promoted ERK1/2 activation via an epidermal growth factor receptor transactivation mechanism in both human embryonic kidney 293 cells and in the MG-63 osteoblast-like cells, which express endogenous FP receptors. Neither AL-8810- nor PGF2α-mediated stimulation of FP receptor promoted association with β-arrestins, suggesting that MAPK activation induced by these ligands is independent of β-arrestin's signaling scaffold functions. Interestingly, the spatiotemporal activation of ERK1/2 promoted by AL-8810 and PGF2α showed almost completely opposite responses in the nucleus and the cytosol. Finally, using [(3)H]thymidine incorporation, we noted differential regulation of PGF2α- and AL-8810-induced cell proliferation in MG-63 cells. This study reveals, for the first time, the signaling biased nature of FP receptor orthosteric ligands toward MAPK signaling. Our findings on the specific patterns of ERK1/2 activation promoted by FP receptor ligands may help dissect the distinct roles of MAPK in FP receptor-dependent physiological responses.

International Union of Basic and Clinical Pharmacology. LXXXIII: classification of prostanoid receptors, updating 15 years of progress

It is now more than 15 years since the molecular structures of the major prostanoid receptors were elucidated. Since then, substantial progress has been achieved with respect to distribution and function, signal transduction mechanisms, and the design of agonists and antagonists (http://www.iuphar-db.org/DATABASE/FamilyIntroductionForward?familyId=58). This review systematically details these advances. More recent developments in prostanoid receptor research are included. The DP(2) receptor, also termed CRTH2, has little structural resemblance to DP(1) and other receptors described in the original prostanoid receptor classification. DP(2) receptors are more closely related to chemoattractant receptors. Prostanoid receptors have also been found to heterodimerize with other prostanoid receptor subtypes and nonprostanoids. This may extend signal transduction pathways and create new ligand recognition sites: prostacyclin/thromboxane A(2) heterodimeric receptors for 8-epi-prostaglandin E(2), wild-type/alternative (alt4) heterodimers for the prostaglandin FP receptor for bimatoprost and the prostamides. It is anticipated that the 15 years of research progress described herein will lead to novel therapeutic entities.