Osteoblast-mediated Osteoclastogenesis in Response to Breast Cancer Cell Condition Media

Open Access
Author:
Baron, Andrew Ellis
Area of Honors:
Biochemistry and Molecular Biology
Degree:
Bachelor of Science
Document Type:
Thesis
Thesis Supervisors:
  • Andrea Marie Mastro, Thesis Supervisor
  • Chen Pei David Tu, Honors Advisor
  • Scott Brian Selleck, Faculty Reader
Keywords:
  • osteoclasts
  • osteoblasts
  • breast cancer
  • metastasis
  • inflammatory repsonse
  • osteoclastogenesis
  • vicious cycle
  • TRAP stain
Abstract:
The bone microenvironment is a dynamic system in which bone is constantly being degraded and rebuilt. In addition to being responsible for the building up of bone, osteoblasts also directly influence the bone-degrading cells, osteoclasts. Breast cancer preferentially metastasizes to this bone microenvironment, thus beginning what is referred to as the “vicious cycle.” When the cancer cells reach their niche, they secrete parathyroid hormone-related protein (PTHrP), which stimulates osteoblasts to release increased levels of receptor activator to nuclear factor κB ligand (RANKL). This cytokine promotes osteoclast bone resorption activity and differentation. As the osteoclasts continually resorb the bone matrix, they release embedded growth factors, such as transforming growth factor-β (TGF-β), which complete the cycle by promoting tumor cell proliferation. In addition to causing the vicious cycle, cancer cells also cause osteoblasts to undergo an inflammatory response, which not only inhibits their function, but also causes them to release pro-inflammatory cytokines. These cytokines in turn, promote osteoclastogenesis, or the differentiation and activation of precursor cells in the bone marrow into multinucleated, mature osteoclasts, perpetuating osteolysis. We hypothesize that the osteoblast inflammatory response occurs after breast cancer cells metastasize to the bone is partially responsible for enhanced levels of osteoclast activity, specifically through increasing the number of differentiated osteoclasts. In this study, the importance of all three cell types in the cycle was emphasized by monitoring osteoclastogenesis in response to various condition media. Pre-osteoclasts were exposed to condition media from osteoblasts, and breast cancer cells as well as combinations of their media for 21 days and then assayed for mature osteoclast markers. The results of these series of experiments demonstrate that medium that includes cytokines of the osteoblastic inflammatory response is capable of increasing osteoclastogenesis compared to baseline values. These data provide important information regarding possible intervention sites for halting the vicious cycle and thereby decreasing the painful osteolysis that is associated with breast cancer bone metastases.