Mechanism of CK2.3, a Novel Mimetic Peptide of Bone Morphogenetic Protein Receptor Type IA, Mediated Osteogenesis

Abstract

Background: Osteoporosis is a degenerative skeletal disease with a limited number of treatment options. CK2.3, a novel peptide, may be a potential therapeutic. It induces osteogenesis and bone formation in vitro and in vivo by acting downstream of BMPRIA through releasing CK2 from the receptor. However, the detailed signaling pathways, the time frame of signaling, and genes activated remain largely unknown. Methods: Using a newly developed fluorescent CK2.3 analog, specific inhibitors for the BMP signaling pathways, Western blot, and RT-qPCR, we determined the mechanism of CK2.3 in C2C12 cells. We then confirmed the results in primary BMSCs. Results: Using these methods, we showed that CK2.3 stimulation activated OSX, ALP, and OCN. CK2.3 stimulation induced time dependent release of CK2β from BMPRIA and concurrently CK2.3 colocalized with CK2α. Furthermore, CK2.3 induced BMP signaling depends on ERK1/2 and Smad1/5/8 signaling pathways. Conclusion: CK2.3 is a novel peptide that drives osteogenesis, and we detailed the molecular sequence of events that are triggered from the stimulation of CK2.3 until the induction of mineralization. This knowledge can be applied in the development of future therapeutics for osteoporosis.

Aberrant BMP2 Signaling in Patients Diagnosed with Osteoporosis

“…Additionally, our lab has developed a novel peptide, CK2.3, that also utilizes the BMP signaling pathway to induce the SMAD-dependent and SMAD-independent signaling cascades. We have previously shown CK2.3′s efficacy in multiple cell and animal models with its pro-osteoblast and anti-osteoclast effects [20][21][22]. We have also shown that CK2.3 activates ERK and SMAD signaling in C2C12 cells [22].…”

“…Activated ERK (or pERK) expression was significantly decreased after BMP2 stimulation, which indicates that SMAD independent signaling is altered in OP (Figure 1). CK2.3 has been shown to act through the ERK signaling pathway in C2C12 cells [22], and it also significantly increased expression of pERK in cells isolated from patients diagnosed with OP. This suggests that CK2.3 acts through the ERK pathway in humans as well, and that CK2.3 can rescue aberrant BMP signaling.…”

“…This peptide (CK2.3) is designed to bind to CK2 and prohibit its interaction with the BMPRIa receptor at the corresponding phosphorylation site, but not to inhibit CK2 from binding to BMPRIa completely. CK2.3 has been shown to increase bone formation and decrease bone resorption in various animal models [15,[20][21][22]. It has also been shown to elicit its response primarily through the ERK pathway, and the SMAD pathway to a lesser extent [22].…”

“…CK2.3 has been shown to increase bone formation and decrease bone resorption in various animal models [15,[20][21][22]. It has also been shown to elicit its response primarily through the ERK pathway, and the SMAD pathway to a lesser extent [22]. CK2.3 also increased mineralization in OP patients, when BMP2 did not, showing the increased potential of CK2.3 as a novel OP therapeutic, especially if there is a mis-regulation within the canonical BMP signaling cascade [15].…”

Osteoporosis: From Molecular Mechanisms to Therapies

“…Park and colleagues have identified a bioactive compound, kukoamine B, from fractionation of Lycii Radicis Cortex (LRC) extract, which reverses bone loss in ovariectomized mice by enhancing osteoblast differentiation [7]. Interestingly, Vrathasha and colleagues describe how they developed a blocking peptide CK2.3 that induces osteogenesis and bone formation by acting downstream of bone morphogenetic protein receptor type IA (BMPRIA) [8]. Liao and colleagues suggest that exercise improves bone mineral density and bone microstructure in mild chronic kidney disease-mineral bone disorder (CKD-MBD) by inhibiting sclerostin production, without altering serum minerals [9], while Jeong and Kim have summarized the complex relationship between osteoporosis and chronic liver disease [10].…”