Insulin-Like Growth Factor-1 and Bone Morphogenetic Protein-2 Jointly Mediate Prostaglandin E2-Induced Adipogenic Differentiation of Rat Tendon Stem Cells

Junpeng Liu,You Zhou,Xiangzhou Liu,Kanglai Tang,Lei Chen,Maria Cristina Vinci

doi:10.1371/journal.pone.0085469

Junpeng Liu, You Zhou + Show 4 more

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https://doi.org/10.1371/journal.pone.0085469

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Abstract

Tendinopathy is characterized histopathologically by lipid accumulation and tissue calcification. Adipogenic and osteogenic differentiation of tendon stem cells (TSCs) are believed to play key roles in these processes. The major inflammatory mediator prostaglandin E2 (PGE2) has been shown to induce osteogenic differentiation of TSCs via bone morphogenetic protein-2 (BMP-2), and BMP-2 has also been implicated in adipogenic differentiation of stem cells. We therefore examined the mechanisms responsible for PGE2-induced adipogenesis in rat TSCs in vitro. Insulin-like growth factor-1 (IGF-1) mRNA and protein were significantly up-regulated in PGE2-stimulated TSCs, measured by quantitative reverse transcription-polymerase chain reaction and enzyme-linked immunosorbent assay, respectively. Incubation with specific inhibitors of cAMP, cAMP-dependent protein kinase A (PKA), and CCAAT/enhancer binding protein-δ (CEBPδ) demonstrated that IGF-1 up-regulation occurred via a cAMP/PKA/CEBPδ pathway. Furthermore, neither IGF-1 nor BMP-2 alone was able to mediate adipogenic differentiation of TSCs, but IGF-1 together with BMP-2 significantly increased adipogenesis, indicated by Oil Red O staining. Moreover, knock-down of endogenous IGF-1 and BMP2 abolished PGE2-induced adipogenic differentiation. Phosphorylation of CREB and Smad by IGF-1 and BMP-2, respectively, were required for induction of the adipogenesis-related peroxisome proliferator-activated receptor γ2 (PPARγ2) gene and for adipogenic differentiation. In conclusion, IGF-1 and BMP-2 together mediate PGE2-induced adipogenic differentiation of TSCs in vitro via a CREB- and Smad-dependent mechanism. This improved understanding of the mechanisms responsible for tendinopathies may help the development of more effective therapies.

Highlights

Tendons are constantly subjected to stress and mechanical loading, which can lead to acute tendon injuries, and to chronic degenerative tendinopathies [1]
We investigated the roles of Insulin-like growth factor-1 (IGF-1) and bone morphogenetic protein-2 (BMP-2) in prostaglandin E2 (PGE2)-induced adipogenic differentiation of cultured rat tendon stem cells (TSCs), and defined the roles of downstream cAMP response elementbinding protein (CREB) and Smad signaling in the effects of IGF-1
PGE2 induces adipogenic differentiation To define the role of PGE2 in adipogenesis, rat TSCs were incubated with increasing doses of PGE2 for 7 d, or with 100 ng/ ml PGE2 for different time

Summary

Introduction

Tendons are constantly subjected to stress and mechanical loading, which can lead to acute tendon injuries, and to chronic degenerative tendinopathies [1]. The Achilles, patella, elements of the rotator cuff, forearm extensors, biceps brachi and tibialis posterior tendons are most vulnerable to tendinopathies [2], which are a common clinical problem in both athletes and the general public They involve degenerative changes exacerbated by overuse and mechanical loading [2], and are characterized histopathologically by lipid accumulation and tissue calcification [3,4,5,6]. PGE2 treatment may result in degenerative changes of the tendon characterized by lipid accumulation and tissue calcification, partly by inducing the differentiation of TSCs into non-tenocytes, including adipocytes and osteocytes [9,11,21]

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