Project List

How Do Osteoclasts Survive?

enlarge image

Fig. 1: This is a co-culture of osteoclasts (purple multinucleated cells - red arrow) and mesenchymal stromal cells (mononuclear cells - blue arrow). The cells have been treated for 150 minutes with a chemical inhibitor of the enzyme PI3Kinase prior to fixation. Nuclei are stained with Hoechst 33258 to reveal chromatin morphology. Large, normal nuclei are seen in the stromal cells whereas osteoclast nuclei are condensed, exhibiting chromatin condensation that is indicative of apoptosis. These data suggest that osteoclasts are highly sensitive to PI3Kinase inhibition compared to stromal cells.

This project focuses on discovering the molecular mechanisms by which osteoclasts survive. This may be critical to the design of effective anti-osteoclast therapies, as targeting survival rates will provide candidate mechanisms to reduce bone loss. One aspect of this project is to study Transforming Growth Factor Beta (TGF-ß), which induces osteoclast apoptosis. Our focus in these studies is to determine how TGF-ß directs osteoclast apoptosis.

The Mechanisms By Which TGF-ß Influences Osteoclast Differentiation.

enlarge image

Fig. 2: This is of osteoclasts stained for Tartrate Resistant Acid Phosphatase (TRAP). The top panel cells are osteoclasts differentiated from precursors that do not express TIEG (knockout) and the bottom panel cells are osteoclasts that differentiated from an equal number of normal precursors. Both mononuclear and multinucleated cells (arrows) are TRAP positive, but there are many more osteoclasts in cultures from TIEG knockout precursors. These data show that precursors lacking TIEG protein have an enhanced capacity to differentiate compared to precursors expressing TIEG protein.

TGF-ß-Inducible Early Gene (TIEG) is rapid response gene that is regulated by members of the TGF-ß family. The bones from mice that lack TIEG are smaller and break more easily, indicating that TIEG expression is critical for normal bone development. We have discovered that osteoclast precursors that lack TIEG have an enhanced ability to differentiate into osteoclasts. In addition, osteoblastic cells lacking TIEG are less able to support osteoclast differentiation and are defective in the ability to make bone in culture. We are currently seeking to determine the molecular bases of these defects.

The Role of TGF-ß In Estrogen’s Protective Effects On Bone.

enlarge image

Fig. 3: This is a comparison of the architecture of trabecular bone in the spine. On the left is a scan of a normal spine trabecular structure and on the right is a scan of the spine of an osteoporotic individual. This comparison shows that normal trabecular bone is thicker, more abundant, and forms more connections throughout the structure than the trabecular bone of an osteoporotic individual.

Estrogen treatment prevents the bone loss associated with postmenopausal osteoporosis. Osteoclasts and bone forming osteoblasts respond to estrogen treatment with increased TGF-ß production. Since TGF-ß has multiple influences on bone metabolism, we are focusing on discovering how TGF-ß effects on the myriad cells found in bone participate in estrogen’s protective effects on bone.

Exploration Of A Small Molecule Therapy To Target Both Tumors That Metastasize To Bone and Osteoclast-mediated Bone Loss

enlarge image

Fig. 4:Fluorescence imaging of the in vivo effect of 2ME₂ on bone marrow- and mammary pad-injected 4T1/Red cells in Balb/c mice. 50 mg/kg/d 2ME₂ significantly inhibited tumor growth in bones (Cicek et al, Nov 1st. 2007 Cancer Research).

(headed by Dr. Muzaffer Cicek, Assistant Professor). We are examining the mechanisms by which small molecule therapies target osteoclast differentiation and survival to slow osteolytic breast cancer tumor progression. We have discovered that the krupple-like transcription factor TIEG1 is rapidly induced by a naturally occurring estrogen metabolite, 2-methoxyestradiol (2ME₂) and are investigating the role of TIEG induction in suppression of breast cancer progression.