In vitro and in vivo evidence for stimulation of bone resorption by an EP4 receptor agonist and basic fibroblast growth factor: Implications for their efficacy as bone anabolic agents

Abstract

Prostaglandin E2 receptor subtype 4 agonists (EP4A) and basic fibroblast growth factor (FGF2) stimulate bone formation, but their effects on bone resorption are controversial. To provide additional insight into the skeletal effects of EP4A and FGF2, their regulation of expression of genes associated with bone formation and resorption in aged ovariectomized (OVX) rats and in cultured mouse bone marrow cells was determined. RNA was isolated from lumbar vertebrae of OVX rats (16 months of age) treated daily for 3 weeks with FGF2 or EP4A and processed for quantitative real time-PCR analyses. mRNA expression for the receptor activator of NF-κB ligand (RANKL) and cathepsin K (CTSK), but not osteoprotegerin (OPG), were upregulated by both FGF2 and EP4A. Addition of FGF2 and EP4A to the medium of cultured mouse bone marrow cells increased the formation of tartrate resistant acid phosphatase (TRAP) positive cells, upregulated the expression of RANKL and CTSK, and downregulated expression for OPG. EP4A also increased the formation of actin rings, an indicator of osteoclast activation, in a dose dependent manner in osteoclasts cultured on bone slices and triggered the formation of pits as revealed by a pitting assay. Gene expression for osterix (OSX) and IGF-2, genes associated with bone formation, was significantly greater in FGF2-treated OVX rats compared with EP4A-treated OVX rats. These findings at the molecular level are consistent with previous tissue-level histomorphometric findings, and at the doses tested, support the contention that FGF2 has a stronger bone anabolic effect than EP4A. The results of these in vivo and in vitro analyses clarify the effects of FGF2 and EP4A on bone formation and resorption, and provide insight into differences in the efficacy of two potential bone anabolic agents for restoration of lost bone mass in the osteopenic, estrogen-deplete skeleton.

In vivo identification of Bmp2-correlation networks during fracture healing by means of a limb-specific conditional inactivation of Bmp2

“…First, we found that Fgf2 was not present in the WT pre-fracture network (Figure 2, upper left panel), but demonstrated connections with Ctsk, Myod, Postn and Tnn in the WT post-fracture network. This result is, at least in part, confirmed by the studies of Downey et al, who reported Fgf2 induction of bone formation via Ctsk(27). In contrast, in the cKO group, Fgf2 was connected with MCAM, MMP9, Postn and Tbx4 before fracture and lost connections with all except PTHrP post-fracture.…”

Effectiveness of combined salmon calcitonin and aspirin therapy for osteoporosis in ovariectomized rats

“…In aged rats administered an agonist of prostaglandin E, RANKL gene expression in the rat vertebrae was increased, while OPG was unaffected. In cultured bone marrow cells in vitro , prostaglandin E agonists increased RANKL gene expression in bone marrow cells and reduced OPG gene expression ( 46 ). Prostaglandin production is primarily mediated by COX-2 in osteoblasts ( 47 ).…”

Prostaglandin EP4 Selective Agonist AKDS001 Enhances New Bone Formation by Minimodeling in a Rat Heterotopic Xenograft Model of Human Bone

“…EP4 receptors have been identified as promising targets for osteoporosis treatment and bone regeneration in both in vitro ( Suzawa et al, 2000 ; Nakagawa et al, 2007 ; Downey et al, 2009 ; Minamizaki et al, 2009 ; Kanayama et al, 2018 ) and in vivo ( Tanaka et al, 2004 ; Toyoda et al, 2005 ; Iwaniec et al, 2007 ; Downey et al, 2009 ; Kanayama et al, 2018 ) preclinical studies using a variety of animal species. However, the clinical therapeutic effect of EP4 receptor agonists on human bone tissue has not yet been proven.…”