Bone-destructive diseases such as osteoporosis and chronic inflammatory arthritis affect millions of people worldwide, causing pain, fractures, and decreased quality of life. These conditions often result from the dysregulation of osteoclasts—specialized cells responsible for breaking down bone tissue. Today, many promising treatments target the receptor activator of nuclear factor kappa B ligand (RANKL)-RANK-tumor necrosis factor receptor-associated factor 6 (TRAF6) signaling pathway, which controls osteoclast formation. When the protein RANKL binds to its receptor RANK on osteoclast precursor cells, it triggers a cascade of signals through an adapter molecule called TRAF6, ultimately leading to the formation of mature osteoclasts.
While effective, these therapies come with severe limitations in either potency or specificity. Because the RANKL-RANK-TRAF6 signaling pathway is involved in many vital biological processes, including immune system function and mammary gland development, drugs that broadly inhibit this pathway can cause diverse side effects. Moreover, synthetic peptides previously developed to target the RANK-TRAF6 interaction have shown limited efficacy, requiring high concentrations to achieve meaningful effects. These issues highlight the need for more targeted interventions that can tightly modulate osteoclast development without disrupting other essential cellular processes.
Against this backdrop, a research team led by Professor Kiyotaka Nishikawa from the Department of Molecular Life Sciences, Doshisha University, Japan, has developed a novel compound that could be useful for treating bone-destructive diseases. Their study, published in Communications Biology on April 22, 2025, describes a tetravalent peptide that regulates the interaction between RANK and TRAF6 by fine-tuning specific downstream signals. The research was co-authored by Dr. Masataka Anzai and Assistant Professor Miho Watanabe-Takahashi, also from Doshisha University.
First, the team used an innovative screening method to identify promising tetravalent peptide structures. This led them to WHD-tet, which binds to TRAF6 through a multivalent interaction. They then developed a cell-permeable form of this peptide, called CR4-WHD-tet, which efficiently inhibited osteoclast development in lab cultures at concentrations significantly lower than previously known compounds.
What makes this discovery particularly noteworthy is how the peptide works. Rather than completely blocking all downstream signals, it specifically inhibits the recruitment of a protein called MKK3 to TRAF6. In turn, this prevents the activation of p38-MAPK, a critical signaling molecule in late-stage osteoclast development. "The tetravalent peptide we identified here is potentially a novel type of therapeutic agent for osteoclast-related diseases with fewer side effects than conventional medications," explains Prof. Nishikawa.
When tested in mice, CR4-WHD-tet effectively prevented bone loss in a RANKL-induced bone disease model. Notably, the peptide accumulated preferentially in bone tissue due to its acidic amino acid composition, enhancing its therapeutic potential. Additionally, it did not disrupt the function of osteoblasts—the cells responsible for building new bone—suggesting a highly targeted effect on bone resorption without compromising bone formation.
Beyond its therapeutic potential, this research has revealed important new insights into the mechanisms of osteoclastogenesis. The study demonstrated that MKK3 plays a crucial role in the late stage of osteoclast differentiation, specifically affecting the nuclear localization of p38-MAPK. This finding helps clarify the temporal dynamics of signaling pathways during osteoclast development, shedding light on the different molecular mechanisms that are at play during early versus late stages of differentiation.
Overall, this work represents a significant advancement in the treatment of bone-destructive diseases, offering hope for therapies that can effectively maintain bone density while minimizing unwanted effects on other biological systems. "Our study's new strategic concept of fine-tuning, rather than blocking, disease-related downstream signals pave the way for the development of new types of therapeutics," notes Prof. Nishikawa.
With any luck, further efforts in this field will lead to treatments that can significantly improve the quality of life of the millions of patients suffering from bone-destructive diseases.
About Professor Kiyotaka Nishikawa from Doshisha University, Japan
Professor Kiyotaka Nishikawa obtained Master's and PhD degrees from The University of Tokyo in 1986 and 1989, respectively. He joined Doshisha University in 2008, where he currently serves as a full Professor. He specializes in molecular and cellular biology, covering topics such as peptide engineering, host–pathogen interactions, and intracellular trafficking. He has over 60 scientific publications to his name.
Funding information
This work was supported by grants from the Japan Society for the Promotion of Science (JSPS; KAKENHI grant number JP22J11001), the Japan Science and Technology (JST; SPRING grant number JPMJSP2129), and the Joint Research Project of the Institute of Medical Science, The University of Tokyo.
