Hydroxyapatite suppression of osteoblast genes requires FGF receptor signaling and phosphate transporter Open Access
Park, Jonathan (2017)
Published
Abstract
Hydroxyapatite (HAp) is the main mineral component of the skeleton and is naturally produced by osteoblasts during bone formation and bone remodeling. Due to its role in skeletal biology, the material is currently being investigated as a therapeutic biomaterial for orthopedic and dental use. Although HAp is a key product of the mineralizing osteoblasts, recent studies have suggested that extracellular HAp is not simply an inert biomaterial, but can suppress osteoblast lineage commitment through regulation of gene expression involved in early osteoblast differentiation. However, the cellular and molecular mechanisms by which HAp regulates osteoblast gene expression are not well delineated. In this study we investigated the mechanism(s) by which HAp suppresses gene expression in an in vitro osteoblast cell model. The study revealed that suppression of key genes, such as alkaline phosphatase, osterix and RUNX2, involved in osteoblast differentiation occurs within the first few hours after osteoblasts are exposed to extracellular HAp. HAp-effects are mediated through both the Fibroblast Growth Factor (FGF) receptor and the Sodium-dependent phosphate (Pi) transporters, but not the calcium-sensing receptor (CaSR). Interestingly, the key osteoblastic transcription factors RUNX2 and osterix--although suppressed by HAp--do not appear to regulate the early osteoblastic differentiation gene alkaline phosphatase. The study identifies previously unknown signaling pathways involved in osteoblast responses to extracellular HAp that down-regulate osteoblast gene expression. These data on the effects of HAp on osteoblast function may have importance in understanding HAp-feedback regulation of physiological mineralization, pathological calcification, and potential biomaterial development.
Table of Contents
Table of Contents
Title…..…………………………………………………………………………………………..........................................................................................................................1
Introduction………………………………………………………………………………............................................................................................................................2
Materials and Methods…..………………………………………………………....................................................................................................................…….....5
Results………………………………………………………………………………………............................................................................................................................8
Discussion……………………………………………………………………………………........................................................................................................................12
Conclusion….………...………………………………………………………………...…….....................................................................................................................16
Figure Legends and Tables….…………………………………………………….…......................................................................................................................17
References……………………………………………………………………………………….....................................................................................................................21
Figures………………………………………………………………………........................................................................................................................................A1
Figure 1: Time course of HAp-regulated gene expression…………….....................................................................................................................A1
Figure 2: Inhibition of FGF receptor and Sodium-dependent Phosphate Co-Transporter
provides partial blockage of HAp-induced changes in alkaline phosphatase expression…......................................................................................A2
Figure 3: Simultaneous inhibition of FGF receptor and Sodium-dependent Phosphate Co-Transporter provides full blockage of HAp-induced changes
in down-regulated gene expression…………………………………………………………………………………........................................................................................A3
Figure 4: HAp stimulates the down-regulation of FGF receptor 2 gene expression…............................................................................................A4
Figure 5: HAp rapidly stimulates the signaling proteins ERK1/2……………...…………................................................................................................A5
Figure 6: HAp stimulates the phosphorylation of FGF receptor 2 proteins……...…….…...........................................................................................A6
Figure 7: HAp stimulates the up-regulation of Sodium-dependent Phosphate Co-Transporter family SLC20A1 & SLC20A2………….……………………….........A7
Figure 8: Western blot of osteoblast transcription factors..……..…………………….....................................................................................................A8
Figure 9: Schematic of potential mechanism by which HAp regulates gene expression........................................................................................A9
About this Honors Thesis
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