Mechanical strain promotes osteoblast ECM formation and improves its osteoinductive potential

Yong Guo,Yu-xian Yan,Lu Liu,Chun-qiu Zhang,Qin-xin Hao,Xi-zheng Zhang,Qiang-cheng Zeng,Cai-hong Shi,Rui-xin Li

doi:10.1186/1475-925x-11-80

Abstract

BackgroundThe extracellular matrix (ECM) provides a supportive microenvironment for cells, which is suitable as a tissue engineering scaffold. Mechanical stimulus plays a significant role in the fate of osteoblast, suggesting that it regulates ECM formation. Therefore, we investigated the influence of mechanical stimulus on ECM formation and bioactivity.MethodsMouse osteoblastic MC3T3-E1 cells were cultured in cell culture dishes and stimulated with mechanical tensile strain. After removing the cells, the ECMs coated on dishes were prepared. The ECM protein and calcium were assayed and MC3T3-E1 cells were re-seeded on the ECM-coated dishes to assess osteoinductive potential of the ECM.ResultsThe cyclic tensile strain increased collagen, bone morphogenetic protein 2 (BMP-2), BMP-4, and calcium levels in the ECM. Compared with the ECM produced by unstrained osteoblasts, those of mechanically stimulated osteoblasts promoted alkaline phosphatase activity, elevated BMP-2 and osteopontin levels and mRNA levels of runt-related transcriptional factor 2 (Runx2) and osteocalcin (OCN), and increased secreted calcium of the re-seeded MC3T3-E1 cells.ConclusionMechanical strain promoted ECM production of osteoblasts in vitro, increased BMP-2/4 levels, and improved osteoinductive potential of the ECM. This study provided a novel method to enhance bioactivity of bone ECM in vitro via mechanical strain to osteoblasts.

Highlights

The extracellular matrix (ECM) is a non-cellular component of tissues and contains various protein fibers interwoven in a hydrated gel composed of a network of glycosaminoglycan chains that are secreted by resident cells to provide a mechanical support for cell growth, adhesion, proliferation, differentiation, morphology, and gene expression [1,2,3]
Mechanical strain elevates hydroxyproline and calcium content and increases Bone morphogenetic protein (BMP)-2 and BMP-4 protein levels in osteoblast ECM After subjecting MC3T3-E1 cells to a mechanical tensile strain of 2500 με at 0.5 Hz for 1 h/day, the ECM hydroxyproline and calcium content, which was produced by the strained cells and attached to dishes, were both increased compared with those of ECM produced by non-stimulated cells
After exposing the cells to mechanical strain for 7 days, western blot analysis indicated that the bone morphogenetic protein 2 (BMP-2) and BMP-4 levels in the ECM were both greater than that in the control group (Figure 2B), suggesting that mechanical strain elevated the levels of collagen, calcium, and BMP-2/4 in osteoblast ECMs

Summary

Introduction

The extracellular matrix (ECM) is a non-cellular component of tissues and contains various protein fibers interwoven in a hydrated gel composed of a network of glycosaminoglycan chains that are secreted by resident cells to provide a mechanical support for cell growth, adhesion, proliferation, differentiation, morphology, and gene expression [1,2,3]. The ECM is a potent regulator of cell function and differentiation, and provides a supportive microenvironment for mammalian cells in vitro; it is a very suitable scaffold material for tissue engineering [4,5]. Mechanical strain promotes matrix mineralization of osteoblasts [8,9] and increases the expression of ECM-related proteins of osteoblasts, including osteonectin, osteopontin (OPN), osteocalcin (OCN), bone morphogenetic protein 2 (BMP-2), and type I collagen [10]. Mechanical strain of osteoblasts promotes matrix-bound vascular endothelial growth factor (mVEGF) synthesis, which has angiogenic properties in vivo [11,12]. In these studies, most of ECM-related proteins were intracellular. We investigated the influence of mechanical stimulus on ECM formation and bioactivity

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Discussion

Conclusion