A Synthetic Peptide, CK2.3, Inhibits RANKL-Induced Osteoclastogenesis through BMPRIa and ERK Signaling Pathway

Abstract

<jats:p>The skeletal system plays an important role in the development and maturation process. Through the bone remodeling process, 10% of the skeletal system is renewed every year. Osteoblasts and osteoclasts are two major bone cells that are involved in the development of the skeletal system, and their activity is kept in balance. An imbalance between their activities can lead to diseases such as osteoporosis that are characterized by significant bone loss due to the overactivity of bone-resorbing osteoclasts. Our laboratory has developed a novel peptide, CK2.3, which works as both an anabolic and anti-resorptive agent to induce bone formation and prevent bone loss. We previously reported that CK2.3 mediated mineralization and osteoblast development through the SMAD, ERK, and AKT signaling pathways. In this study, we demonstrated the mechanism by which CK2.3 inhibits osteoclast development. We showed that the inhibition of MEK by the U0126 inhibitor rescued the osteoclast development of RAW264.7 induced by RANKL in a co-culture system with CK2.3. We observed that CK2.3 induced ERK activation and BMPRIa expression on Day 1 after stimulation with CK2.3. While CK2.3 was previously reported to induce the SMAD signaling pathway in osteoblast development, we did not observe any changes in SMAD activation in osteoclast development with CK2.3 stimulation. Understanding the mechanism by which CK2.3 inhibits osteoclast development will allow CK2.3 to be developed as a new treatment for osteoporosis.</jats:p>

Differentiation of Cells Isolated from Human Femoral Heads into Functional Osteoclasts

“…Osteoclastogenesis and the activity of osteoclasts are reliant on osteoblasts [ 16 , 27 , 28 , 29 , 30 ]. Osteoblasts secrete two proteins that are necessary for osteoclast function and differentiation: macrophage colony stimulating factor (M-CSF) and receptor activator of nuclear factor kappa-β ligand (RANKL) [ 31 , 32 , 33 ].…”

“…The M-CSF and RANKL signaling pathways promote cell differentiation, survival, and proliferation by activating the Akt, Erk, NF-κB, and MAPK pathways [ 18 ]. It has previously been reported that murine RAW264.7 cells of the monocyte/macrophage lineage respond to these factors and can be used as a model for studying osteoclastogenesis [ 16 , 27 ]. However, the effects of M-CSF and RANKL in bone marrow cells isolated directly from human femoral heads remains unclear.…”

The Role of BMP Signaling in Osteoclast Regulation

“…The difference in RANK signaling is that Tumor Necrosis Factor Receptor-associated Factor Protein 6 (TRAF6) rather than XIAP recruits TAB1/TAB2 to the RANK receptor, activating TAK1. MAPK signaling converges to increase the expression and translocation of NFATc1a, an essential transcription factor that leads to the upregulation of osteoclast genes for fusion and activation [ 69 , 73 , 137 , 138 , 139 , 140 ] This overlap in MAPK signaling between the RANKL pathway and the BMP pathway may contribute to the enhancement of osteoclastogenesis ( Figure 5 ).…”

“…Nevertheless, the dual impact on bone formation and bone resorption makes the BMP pathway a potential therapeutic target for osteoporosis. The peptide CK2.3 utilizes the BMP pathway in the absence of a BMP ligand to stimulate osteoblast mineralization and inhibit osteoclast resorption [ 140 , 189 , 190 , 191 , 192 ]. Furthermore, CK2.3 increases mineralization in osteoporotic patients where BMP2 is not [ 167 ].…”

Special Issue “Feature Papers in Journal of Developmental Biology”

“…In the first article [ 1 ], Nguyen and colleagues investigated bone remodeling and cell signaling between the following two types of bone cells: osteoblasts and osteoclasts. They report that a peptide inhibitor of osteoclast development promotes bone formation by activating ERK and promoting the expression of BMPR1a.…”