Overexpression of TIMP-3 in Chondrocytes Produces Transient Reduction in Growth Plate Length but Permanently Reduces Adult Bone Quality and Quantity.

Blandine Poulet,Alexandra Sampson,Mittal Shah,Sandra Shefelbine,Hideaki Nagase,Phoung Vo,Darren Plumb,Hiroyuki Nakamura,Katherine Staines,George Bou-Gharios,Alessandra Carriero,Ke Liu,Andrew A Pitsillides

doi:10.1371/journal.pone.0167971

Blandine Poulet, Alexandra Sampson + Show 11 more

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https://doi.org/10.1371/journal.pone.0167971

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Abstract

Bone development and length relies on the growth plate formation, which is dependent on degradative enzymes such as MMPs. Indeed, deletion of specific members of this enzyme family in mice results in important joint and bone abnormalities, suggesting a role in skeletal development. As such, the control of MMP activity is vital in the complex process of bone formation and growth. We generated a transgenic mouse line to overexpress TIMP3 in mouse chondrocytes using the Col2a1-chondrocyte promoter. This overexpression in cartilage resulted in a transient shortening of growth plate in homozygote mice but bone length was restored at eight weeks of age. However, tibial bone structure and mechanical properties remained compromised. Despite no transgene expression in adult osteoblasts from transgenic mice in vitro, their differentiation capacity was decreased. Neonates, however, did show transgene expression in a subset of bone cells. Our data demonstrate for the first time that transgene function persists in the chondro-osseous lineage continuum and exert influence upon bone quantity and quality.

Highlights

Bone formation is a complex three-dimensional process in which several signaling molecules play a role in controlling skeletal development
Mice that overexpress TIMP3 in chondrocytes under the control of the promoter/enhancer collagen type II (Col2a1) gene were used and we find major defects in bone formation and in bone structure and mechanical properties in adult mice, which suggests a control of bone by chondrocytes, possibly via the transdifferentiation of growth plate hypertrophic chondrocytes into bone cells
Skeletal comparison of Homozygot transgenic (Tg/Tg) mice to WT littermates revealed that most ribs and knee joints showed accumulation of matrix, which stained positively with Alcian blue for proteoglycans, as well as deficient ossification levels consistent with the failure to remodel the matrix in order to facilitate bone formation (Fig 1G)

Summary

Introduction

Bone formation is a complex three-dimensional process in which several signaling molecules play a role in controlling skeletal development. Components of the extracellular matrix (ECM) and their remodelling by matrix metalloproteinases (MMP) play critical roles in cartilage and bone structure and function. The process of endochondral ossification, which is essential for bone formation and growth, involves a cartilage intermediate. During this process, mesenchymal condensation differentiates into a cartilage template, rich in collagen type II. Chondrocytes become hypertrophic and produce a calcified cartilage matrix, which is replaced by bone matrix, rich in collagen type I, produced by invading osteoblasts.

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