Pristimerin Protects Against OVX-Mediated Bone Loss by Attenuating Osteoclast Formation and Activity via Inhibition of RANKL-Mediated Activation of NF-κB and ERK Signaling Pathways

Abstract

Introduction

Osteoporosis is an osteolytic bone condition characterized by decreased bone strength and increased bone fragility. It is the result of elevated formation or activity of bone-resorbing osteoclasts. Although current therapeutic agents are efficacious against osteoclast-mediated bone loss, detrimental side effects preclude the long-term use of these agents. Pristimerin (PRI) is a naturally occurring quinone-methide triterpenoid that has been revealed to exert anti-inflammatory and anti-tumor effects via regulating various signaling cascades including NF-κB and MAPK activation.

Methods

The bone marrow macrophages were used to confirm the anti-osteoclastic and anti-resorptive functions of PRI in vitro. An in vivo ovariectomy (OVX) model was applied to verify the function of PRI protecting bone loss.

Results

PRI abolished the early activation of NF-κB and ERK MAPK signal cascades thereby thwarting the downstream expression of c-Fos and NFATc1, which prevented the production of mature osteoclasts. In vivo, PRI protects mice against ovariectomy (OVX)-mediated bone loss by diminishing osteoclast formation and bone resorptive activity.

Conclusion

Our study shows that PRI demonstrates therapeutic potential in the effective treatment against osteoclast-induced osteolytic diseases like osteoporosis.

Keywords:

• osteoporosis
• osteoclast
• pristimerin
• ERK
• NF-κB

Acknowledgments

This work is supported by the Natural Science Foundation of China (No.81770254, No.81970236) and Natural Science Foundation of Guangxi Province (2018GXNSFAA050092).

Abbreviations

PRI, pristimerin; NF-κB, nuclear factor-κB; M-CSF, macrophage-colony stimulating factor; RANKL, receptor activator of nuclear factor-κB ligand; FBS, fetal bovine serum; TNF, tumor necrosis factor; MAPK, mitogen-activated protein kinase; NFATc1, nuclear factor of activated T-cells 1; Dc-stamp, dendritic cell-specific transmembrane protein; Trap/Acp5, tartrate resistant acid phosphatase; Ctsk, cathepsin K; Mmp-9, matrix metalloproteinase-9; α-MEM, Minimum Essential Medium Alpha Modification; CCK-8, cell counting kit-8; DAPI, 4′,6-diamidino-2-phenylindole; BMMs, bone marrow macrophages; PFA, paraformaldehyde; PBS, phosphate-buffered saline; BSA, bovine serum albumin; PCR, polymerase chain reaction; cDNA, complementary DNAs; TBST, tris buffered saline with tween; SDS-PAGE, sodium dodecyl sulfatepolyacrylamide gel electrophoresis; c-Fos, protooncogene; JNK, c-Jun N-terminal kinase; ERK, extracellular signal-regulated kinase; OVX, ovariectomy; BMD, bone mineral density; Conn.Dn, connectivity density; Tb.N, trabecular number; Tb.Sp, trabecular separation; Tb.Th, trabecular thickness; BV/TV, percentage bone volume per tissue volume.

Data Sharing Statement

All data generated or analysed during this study are included in this published article.The data that support the findings of this study are available from the corresponding author upon reasonable request.

Ethics Statement

This work fully considered and protected the rights and interests of the study objects. The use of animals in experiments was approved by the ethics Committee of Guangxi medical university (SYXK 2020-0004). All experimental procedures were performed in conformity with institutional guidelines for the care and use of laboratory animals Guangxi medical university, China. This project meets the criteria of the Ethical Review Committee.

Author Contributions

All authors made a significant contribution to the work reported, whether that is in the conception, study design, execution, acquisition of data, analysis and interpretation, or in all these areas; took part in drafting, revising or critically reviewing the article; gave final approval of the version to be published; have agreed on the journal to which the article has been submitted; and agree to be accountable for all aspects of the work.

Disclosure

The authors report no conflicts of interest for this work.