Cyclic strain alters the expression and release of angiogenic factors by human tendon cells.

Rouhollah Mousavizadeh,Alex Scott,Hayedeh Behzad,Vincent Duronio,Shahram Khosravi,Robert G Mccormack,James H-C Wang

doi:10.1371/journal.pone.0097356

Abstract

Angiogenesis is associated with the tissue changes underlying chronic overuse tendinopathy. We hypothesized that repetitive, cyclic loading of human tendon cells would lead to increased expression and activity of angiogenic factors. We subjected isolated human tendon cells to overuse tensile loading using an in vitro model (1 Hz, 10% equibiaxial strain). We found that mechanically stimulated human tendon cells released factors that promoted in vitro proliferation and tube formation by human umbilical vein endothelial cells (HUVEC). In response to cyclic strain, there was a transient increase in the expression of several angiogenic genes including ANGPTL4, FGF-2, COX-2, SPHK1, TGF-alpha, VEGF-A and VEGF-C, with no change in anti-angiogenic genes (BAI1, SERPINF1, THBS1 and 2, TIMP1-3). Cyclic strain also resulted in the extracellular release of ANGPTL4 protein by tendon cells. Our study is the first report demonstrating the induction of ANGPTL4 mRNA and release of ANGPTL4 protein in response to cyclic strain. Tenocytes may contribute to the upregulation of angiogenesis during the development of overuse tendinopathy.

Highlights

Tendinopathy is a common overuse injury, prevalent among both athletes and workers [1]
Incubation of human umbilical vein endothelial cells (HUVEC) cells with the conditioned media from 24 hours strained and unstrained tendon cells showed that cyclic strain resulted in the accumulation of angiogenic factors, since media from loaded tendon cells increased the proliferation of HUVEC cells
Profiling the expression of angiogenic factors by Human Angiogenesis RT2 Profiler PCR Array showed that cyclic strain increased the expression of several angiogenic factors, including some that have already been identified as playing a role in tendinopathy, such as VEGF and COX2, along with some novel genes (Fig. 3)

Summary

Introduction

Tendinopathy is a common overuse injury, prevalent among both athletes and workers [1]. The disorder is often considered a mechanically driven pathology, as repetitive or forceful loading of tendons are well established risk factors [2]. Repetitive strain and shear are thought to induce matrix degeneration in tendon tissue, making the tissue susceptible to damage and eventually to overuse injury [3]. The mechanisms which precede the development of symptomatic injury have not been fully described but are felt to be multifactorial, with repetitive strain being an important risk factor [4,5]. It must be acknowledged that the colour Doppler signal typically associated with tendinopathy may represent angiogenesis, but increased blood flow in vessels which are already present. Angiogenesis may be accompanied by neurogenesis, i.e, nerves may be proliferating along with neovessels in mechanically loaded tendon tissue increasing the level of substance

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