Intermittent Administration of Parathyroid Hormone 1-34 Enhances Osteogenesis of Human Mesenchymal Stem Cells by Regulating Protein Kinase Cδ

Human mesenchymal stem cells (hMSCs) can differentiate into osteoblasts and are regulated by chemical cues. The recombinant N-terminal (1-34 amino acids) fragment of the parathyroid hormone (PTH (1-34)) is identified to promote osteogenesis. The osteoanabolic effects of intermittent PTH (1-34) treatment are linked to a complex consisting of signaling pathways; additionally, protein kinase C (PKC) act as mediators of multifunctional signaling transduction pathways, but the role of PKC delta (PKC delta), a downstream target in regulating osteoblast differentiation during intermittent administration of PTH (1-34) is less studied and still remains elusive. The purpose of this study is to examine the role of PKC delta during intermittent and continuous PTH (1-34) administration using osteoblast-lineage-committed hMSCs. Relative gene expression of osteoblast-specific genes demonstrated significant upregulation of RUNX2, type I Collagen, ALP, and Osterix and increased alkaline phosphatase activity in the presence of PTH (1-34). Intermittent PTH (1-34) administration increased PKC activity at day 7 of osteogenic differentiation, whereas inhibition of PKC activity attenuated these effects. In addition, the specific isoform PKC delta was activated upon treatment. These findings demonstrate that intermittent PTH (1-34) treatment enhances the osteogenesis of hMSCs by upregulating osteoblast-specific genes via PKC delta activation.