Date of Completion

9-23-2013

Embargo Period

9-23-2013

Keywords

Aging, bone, osteoprogenitors, bone regeneration, fibroblast growth factor 2, bone morphogenetic protein 2, calvarial defect

Major Advisor

Liisa T. Kuhn

Associate Advisor

Anne M. Delany

Associate Advisor

A. Jon Goldberg

Associate Advisor

Golria A. Gronowicz

Field of Study

Biomedical Science

Degree

Doctor of Philosophy

Open Access

Campus Access

Abstract

The primary goal of our studies is to increase bone regeneration in aging animals. Bone morphogenetic protein 2 (BMP-2) is an osteogenic agent able to differentiate osteoprogenitor cells into mature, functional osteoblast which produce bone. In the elderly, inadequate number and decreased responsiveness of osteoprogenitor cells reduce BMP-2 efficacy. Much higher and potentially dangerous doses of BMP-2 are generally needed in elderly patients. To lower these potentially harmful doses of BMP-2 in older patients, we proposed the use of a second factor, fibroblast growth factor 2, (FGF-2). We hypothesized that FGF-2 could stimulate the proliferation of osteoprogenitor and that this effect could potentiate low dose BMP-2 induced bone formation.

Firstly, we found that low doses of FGF-2 (0.0016 – 1.6 ng/mL) stimulates the proliferation of osteoprogenitor cells from young and old mouse and human bone and that exposure to low doses of FGF-2 stimulated an increase in expression of the osteoprogenitor cell marker, activated leukocyte cell adhesion molecule (ALCAM or CD166), in both mouse and human bone in vitro.

Secondly, co-delivery of low dose FGF-2 and BMP-2 was shown to increase in vitro mineralization of osteoprogenitors from old mouse and human bone. In old mouse calvaria-derived cells, FGF-2 (0.16 ng/mL) in combination with BMP-2 (50 ng/mL) resulted in more mineralization than BMP-2 alone. In neonatal mouse calvarial cells, sequential delivery of low-dose FGF-2 and low-dose BMP-2 (5 ng/mL) was more stimulatory than co-delivery, whereas in old cultures from human bone, co-delivery of FGF-2 and BMP-2 was optimal.

Finally, we show that in vivo, in a mouse critical-sized calvarial defect, low dose FGF-2 (5 ng) increases defect bridging in old mice treated with low doses of BMP-2 (2 mg). Defect bridging was increased by 28% when 5 ng FGF-2 was combined with 2 mg BMP-2 in old mice, compared to BMP-2 alone. A significant 18% increase in % BV/TV was observed. BMP-2 treatment alone was sufficient for healing in young mice.

Together, these data indicate that low dose FGF-2 and BMP-2 treatment is a potentially beneficial treatment for bone regeneration in old animals in which osteoprogenitor number and responsiveness may be reduced.

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