The Skeletal Phenotype of Chondroadherin Deficient Mice

Lovisa Hessle,Patrik Önnerfjord,Gunhild A Stordalen,Dick Heinegård,Sverre-Henning Brorson,Christina Wenglén,Elizabeth K Tanner,Christiane Petzold,Finn P Reinholt,Espen S Baekkevold

doi:10.1371/journal.pone.0063080

Abstract

Chondroadherin, a leucine rich repeat extracellular matrix protein with functions in cell to matrix interactions, binds cells via their α2β1 integrin as well as via cell surface proteoglycans, providing for different sets of signals to the cell. Additionally, the protein acts as an anchor to the matrix by binding tightly to collagens type I and II as well as type VI. We generated mice with inactivated chondroadherin gene to provide integrated studies of the role of the protein. The null mice presented distinct phenotypes with affected cartilage as well as bone. At 3–6 weeks of age the epiphyseal growth plate was widened most pronounced in the proliferative zone. The proteome of the femoral head articular cartilage at 4 months of age showed some distinct differences, with increased deposition of cartilage intermediate layer protein 1 and fibronectin in the chondroadherin deficient mice, more pronounced in the female. Other proteins show decreased levels in the deficient mice, particularly pronounced for matrilin-1, thrombospondin-1 and notably the members of the α1-antitrypsin family of proteinase inhibitors as well as for a member of the bone morphogenetic protein growth factor family. Thus, cartilage homeostasis is distinctly altered. The bone phenotype was expressed in several ways. The number of bone sialoprotein mRNA expressing cells in the proximal tibial metaphysic was decreased and the osteoid surface was increased possibly indicating a change in mineral metabolism. Micro-CT revealed lower cortical thickness and increased structure model index, i.e. the amount of plates and rods composing the bone trabeculas. The structural changes were paralleled by loss of function, where the null mice showed lower femoral neck failure load and tibial strength during mechanical testing at 4 months of age. The skeletal phenotype points at a role for chondroadherin in both bone and cartilage homeostasis, however, without leading to altered longitudinal growth.

Highlights

Bone and cartilage are both made up of relatively few cells embedded in an abundant extracellular matrix (ECM)
CHAD mediates adhesion of isolated chondrocytes via two mechanisms: one is binding via the a2b1 integrin [11] an interaction that can mediate signalling between chondrocytes and their extracellular matrix [12]; the other interaction is between the C-terminal chondroadherin sequence and cell surface proteoglycans such as syndecans that can act as receptors (Haglund et al, 2013)
We found that CHAD plays roles in the cartilage development and maturation of the growth plate at young age and in the molecular composition of articular cartilage in adults as well as in bone homeostasis and function

Summary

Introduction

Bone and cartilage are both made up of relatively few cells embedded in an abundant extracellular matrix (ECM). Collagen fibrils and the negatively charged proteoglycan aggrecan, forming large aggregates with hyaluronic acid, constitute the major structural assemblies of the matrix These two components provide tissue with tensile strength and resistance against compressive forces, respectively. Several SLRPs have roles in bridging between cells and matrix by providing for interactions with cell surface receptors such as syndecans (CHAD and PRELP) and integrins (CHAD and OSAD) at the same time as binding to structural matrix proteins, fibril forming collagens exemplified in Camper et al., 1997, Haglund et al, 2011, and Haglund et al, 2013. As CHAD can interact with structural extracellular matrix (ECM) molecules as well as with cells in the tissue, the protein may provide a mechanism for regulating cell activities in relation to ECM structure, and play a role in both cartilage and bone homeostasis. We found that CHAD plays roles in the cartilage development and maturation of the growth plate at young age and in the molecular composition of articular cartilage in adults as well as in bone homeostasis and function

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Results

Conclusion