Purinergic Signaling Mediates PTH and Fluid Flow-Induced Osteoblast Proliferation.

Yanghui Xing,Liang Song,Yingying Zhang,Chunjing Tao,Tengyu Zhang,Jian Li,Xiao Wang

doi:10.1155/2021/6674570

Abstract

Both parathyroid hormone (PTH) and mechanical signals are able to regulate bone growth and regeneration. They also can work synergistically to regulate osteoblast proliferation, but little is known about the mechanisms how PTH and mechanical signals interact with each other during this process. In this study, we investigated responses of MC3T3-E1 osteoblasts to PTH and oscillatory fluid flow. We found that osteoblasts are more sensitive to mechanical signals in the presence of PTH according to ERK1/2 phosphorylation, ATP release, CREB phosphorylation, and cell proliferation. PTH may also reduce the osteoblast refractory period after desensitization due to mechanical signals. We further found that the synergistic responses of osteoblasts to fluid flow or ATP with PTH had similar patterns, suggesting that synergy between fluid flow and PTH may be through the ATP pathway. After we inhibited ATP effects using apyrase in osteoblasts, their synergistic responses to mechanical stimulation and PTH were also inhibited. Additionally, knocking down P2Y2 purinergic receptors can significantly attenuate osteoblast synergistic responses to mechanical stimulation and PTH in terms of ERK1/2 phosphorylation, CREB phosphorylation, and cell proliferation. Thus, our results suggest that PTH enhances mechanosensitivity of osteoblasts via a mechanism involving ATP and P2Y2 purinergic receptors.

Highlights

Mechanical signals play very important roles in regulating bone growth and remodeling [1, 2]
We first examined the effect of parathyroid hormone (PTH) on MC3T3-E1 osteoblastic cells in terms of ERK1/2 phosphorylation in response to oscillatory fluid flow
If we pretreated cells with thapsigargin (5 μM), an endoplasmic reticulum (ER) ATPase inhibitor, we found that cell responses to PTH and fluid flow were significantly decreased in terms of ERK1/2 phosphorylation (Figure 3(b))

Summary

Introduction

Mechanical signals play very important roles in regulating bone growth and remodeling [1, 2]. Oscillatory fluid flow, a potent and widely used mechanical stimulus for bone cells, can induce osteoblast intracellular calcium mobilization, MAPK activation, ATP release, c-fos expression, and other intracellular events and subsequently regulates bone metabolism [3,4,5]. PTH enhances osteoblast proliferation, inhibits osteoblast apoptosis, and reactivates lining cells to resume their matrix synthesizing function through a series of pathways, including cAMP, PKA, Runx, and Wnt signals [9,10,11]. Both mechanical stimulation and PTH are able to regulate osteoblast metabolism and bone remodeling; their synergistical effects on bone are of great interests of researchers. Relative P-ERK expression Static Flow 1 min Flow 3 min Flow 5 min Flow 7 min Flow 9 min

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Discussion

Conclusion