Zoledronic acid (ZA) is a bisphosphonate that is used to prevent skeletal fractures
in patients with cancer, as well as for treating osteoporosis. Complete mechanism
of action of ZA is not understood, and their actions on the osteoblasts are confusing.
Epigenetic changes such as DNA methylation are regulatory mechanisms that control
stem cell differentiation. In this situation, ZA induces osteoblastic differentiation
in MSC, but regulatory mechanisms are unknown. Gene specific methylation of
RUNX2, OSX, DLX5 and BSP genes and global methylation status were evaluated
by methylation specific PCR (MSP) and specific antibody, respectively. Also, the
effect of ZA on the BSP gene expression was evaluated by RT-PCR.
MSP present 3 different methylation patterns. Global methylation assay present
hypomethylation in osteoblastic differentiation period. RT-PCR present BSP gene
expression in differentiated MSCs but not in undifferentiated MSC.
ZA didn�t change RUNX2, DLX5 methylation status in differentiated than
undifferentiated MSCs. Therefore, MSCs are heterogeneous populations because
they were methylated and unmethylated in same time. But, OSX promoter
methylation status hypomethylated during osteoblastic differentiation. This finding
shows that OSX gene regulation followed from epigenetic changes such as promoter
hypomethylation. BSP methylation status shows that its expression independent
from epigenetic modifications. Also, expression of RUNX2, DLX5 and BSP may
be influenced from other epigenetic changes such as histone modifications. This
confirm new epigenetic hypothesis that says epigenetic changes in the human
methylome is dynamic changes during differentiation.
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