CK2.3 inhibits osteoclastogenesis in a proliferation-independent manner
Date
2021
Authors
Journal Title
Journal ISSN
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Publisher
University of Delaware
Abstract
The role of BMPs in bone homeostasis and repair led to the approval of BMP2 by the Federal Drug Administration (FDA) for anterior lumbar interbody fusion (ALIF) to increase the bone formation in the treated area. However, recent research shows that patients treated with BMP2 caused the stimulation of both osteoblast mineralization and osteoclast absorption, raising concerns of potential complications with long-term treatment. The increase in absorption activity is the result of direct stimulation of osteoclasts by BMP2 working synergistically with the RANK signaling pathway. The dual effect of BMPs on bone resorption and mineralization highlights the essential role of BMPs in bone homeostasis and bone diseases. ☐ Osteoporosis is the most common bone disease known, costing the United States over 16 billion dollars in 2002 alone. To address this, our lab developed a therapeutic for osteoporosis that targets the dual function of the BMP-signaling pathway. We designed a peptide called Casein Kinase 2.3 (CK2.3), which increased bone mineral density in vivo by binding to Casein kinase 2 (CK2), and removing it from the intercellular domain of BMPR1a activating the BMP pathway. In vitro, CK2.3 increased osteoblast activity in cells derived from patients with osteoporosis, where BMP2 failed to create a response (Durbano, 2020). Furthermore, CK2.3 decreases osteoclastogenesis in vitro by modulating noncanonical BMPR dependent ERK1/2 phosphorylation (Nguyen, 2020). However, the cellular response to aberrant ERK1/2 phosphorylation that results in decreased osteoclastogenesis is still not known. Since ERK signaling is known to induce proliferation in osteoclast progenitors, I hypothesis that CK2.3 will induce proliferation of osteoclast progenitors. ☐ To elucidate the effects of CK2.3 on osteoclastogenesis, the impacts of CK2.3 on the proliferation of monocytes/macrophage RAW 264.7 cells were determined. CK2.3 did not affect the proliferation of RAW26.7 cells; however, RAW 264.7 cells have only 2.5% osteoclast generation, suggesting high background levels of proliferation in undifferentiated cells. ☐ A new cell model utilizing primary cells extracted from human femoral heads was created. The culturing process was refined for the human osteoclast progenitor cells to produce up to 98% TRAP-positive cells. Of these, 30% were multinucleated TRAP cells indicative of mature osteoclasts. ☐ CK2.3 inhibited osteoclastogenesis in the new human cell model. The increase of osteoclasts upon RANKL stimulation was abolished with the treatment of CK2.3. Similar to the results in RAW 264.7 cells, CK2.3 did not affect the proliferation of human primary cells. Only BMP2 treatment groups showed increased cell number over a 5-day culturing period. Altogether, CK2.3 inhibits osteoclastogenesis in a proliferation-independent manner. This knowledge will help decipher the effects of CK2.3 on osteoclasts and the risk of potential side effects.
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Keywords
Osteoclastogenesis, Bone homeostasis