Electronic Theses and Dissertations

Identifier

5976

Date

2017

Document Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Biology

Committee Chair

Judith A Cole

Committee Member

Carlos Estrano

Committee Member

Charles A Lessman

Committee Member

Omar Skalli

Abstract

Parathyroid hormone PTH (1-34)’s ability to increase bone formation has made it therapeutically beneficial, but its impact on bone resorption and chance of osteosarcoma limits its usefulness. In mice, bovine PTH (7-34) induces bone formation without bone resorption, suggesting its usefulness in osteoporosis. However, PTH (7-34)’s impact on bone function must be comparable to or better than that produced by PTH (1-34) and its effect on bone in the presence of endogenous PTH has not been assessed. Using human Saos2 osteosarcoma cells, we examined the effects of PTH (1-34) and PTH (7-34), alone and in combination, on second messenger production, DNA synthesis, ERK and Akt activation, activity of pro-apoptotic caspase 3, and changes in expression of selected genes. PTH (1-34) increased cAMP, a response competitively antagonized by PTH (7-34). PTH (7-34) alone reduced basal cAMP production, indicating it is an inverse agonist in these cells. PTH (1-34) also increased intracellular calcium. While PTH (7-34) had no effect alone, it enhanced the effect of PTH (1-34) on calcium at low doses. A 24 h treatment with PTH (1-34) increased cell number, while PTH (7-34) had no effect alone and blocked the responses to PTH (1-34). PTH (1-34) produced a rapid increase in ERK activity at 5 min while PTH (7-34) slowly increased ERK activity with a maximal response appearing between 30-60 min. However, ERK activation was lost when both peptides were present. While PTH (1-34) decreased Akt activity and PTH (7-34) had no effect, when both peptides were present together, Akt activity increased at low dose of PTH (1-34). In general, PTH (1-34) decreased expression of genes involved in osteoblast differentiation (Runx2, osteocalcin, and Col1A1) a response mimicked by PTH (7-34). Co-incubation with both peptides produced responses comparable to PTH (1-34) alone. PTH (1-34) stimulates pro-proliferative genes (p21cip1, BMP2) and increased RANKL/OPG ratio while PTH (7-34) did not. Taken together, these data suggest that PTH (7-34) may not be a suitable anabolic agent in vivo.

Comments

Data is provided by the student.

Library Comment

Dissertation or thesis originally submitted to the local University of Memphis Electronic Theses & dissertation (ETD) Repository.

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