INTRODUCTION

      SPARC is a matricellular collagen-binding glycoprotein that modulates the interaction of cells with the extracellular matrix (ECM) through its regulation of cell adhesion and matrix assembly. SPARC is widely expressed in bone and tendon, therefore, we investigated the involvement of SPARC in tendon development.

METHODS

      We identify the role of SPARC during tendon development in SPARC^-/- mice, using methods including histology, RT-qPCR, stem cell differentiation assays, immunohistochemistry, wstern blotting, treadmill training and 3d in vitro loading model.

RESULTS

      We have found that tendons from adult SPARC^-/- mice exhibit hypoplastic tendons at load bearing region throughout the body, moreover, the phenotype developed at around 3 weeks post-natally, when mice have become actively mobile. Achilles tendon gene profile showed no significant difference at 10 days post-natal between wild type and SPARC^-/- mice, whereas increased osteogenic and adipogenic markers and decreased tenogenic marker were detected at 3 weeks post-natal in SPARC^-/- mice compared to wild type mice. To investigate the effect of mechanical loading on tendon development, TDSCs was isolated from both WT and SPARC^-/- mice and subjected to uni-axial loading in our novel 3D in vitro loading developmental model. Result showed mechanical loading increased the phosphorylation of AKT in both TDSCs, however, S6K activation was inhibited without SPARC causing reduced collagen type I production. To confirm the in vitro data, 7 weeks old mice were trained using treadmill for 16 days. Micro-CT analysis showed increased Achilles tendon size in WT mice after training, whereas decreased tendon size with some partial rupture was observed in SPARC^-/- mice.

DISCUSSION

      Our data demonstrate SPARC plays a critical role in the mechanosencing mechanism in tendon tissue. Lacking SPARC can reduce the type I collagen production stimulated by mechanical stimulation resulted in unpaired tendon development and compromised remodeling.