Injury site-derived proteoglycan glypican-3 suppresses growth plate cartilage bony repair and bone fracture healing
Chief Investigator: Dr Yu-Wen Su
Funding Amount: $75,000
Recipient: University of South Australia
Two major challenges in paediatric orthopaedics are (1) the faulty or unwanted bony repair of injured growth plate and (2) failure and/or delay in bone fracture healing, which cause high morbidities and burden. Our recent data suggest that injury site-derived proteoglycan glypican-3 suppresses growth plate bony repair and bone healing. Using a rat model of growth plate repair and bone healing, the proposed work will reveal functions and action mechanism of glypican-3 in growth plate repair and bone healing, and define if glypican-3 can serve as a target for developing strategies blocking growth plate faulty repair and enhancing bone healing.
Researchers: Dr Yu-Wen (Michelle) Su, Dr Liping Wang, A/Prof Bruce Foster, Prof Cory Xian
Research Completed: 2021
In Australia, about 10% of bone fractures in children/adolescents cannot heal or have delayed healing, and 20% of these fractures also involve the growth plate (a cartilage located at the ends of a long bone responsible for bone growth) which is often “faultily” repaired by bone. For both problems, that cause high morbidities and high healthcare expense/burden, a better mechanistic understanding is required for the causative factors, and there is a major need for better therapies. In this CRF-funded project, we achieved excellent outcomes from two related studies, which are summarized as follows.
Firstly, we investigated roles of bone morphogenetic protein (BMP) signalling at the growth plate dysrepair. Using a rat growth plate repair model, we demonstrated increased BMP signalling at the repair site and that blocking BMP signalling inhibited the bony repair. In addition, we also observed enhanced BMP signalling at the adjacent uninjured growth plate cartilage and that blocking BMP signalling can attenuate cartilage degeneration of the uninjured growth plate. These findings suggest critical roles of BMP signalling for growth plate bony repair within the injury site and premature degeneration at the adjacent uninjured growth plate cartilage. These findings have been recently published (Su YW et al 2021 BONE) (see below publication list). Secondly, as a step to study factors that can modulate repair at the growth plate and bone, we investigated potential functions of glypicans (GPCs, some heparan sulphate proteoglycans) in regulating BMP signalling and repair of the injured growth plate and bone. Using a rat growth plate and bone injury repair model, our gene expression analyses showed GPC1 downregulation but GPC3 upregulation during the bony repair at the growth plate injury site. To investigate potential roles of GPC3 in regulating the bony repair, rats with growth plate and bone injury received local treatment (via chitosan hydrogel) with GPC3 protein or anti-GPC3 neutralising antibody or vehicle. Analyses showed a reduction in bone volume and expression of osteogenic transcription factor Runx2 and bone protein osteocalcin within the growth plate and bone injury sites following GPC3 protein treatment. Anti-GPC3 antibody treatment appeared to have opposite trends. GPC3 protein treatment significantly reduced BMP signalling activation (as shown by phosphorylated Smad1/5/8 (pSmad1/5/8) immunopositive staining and mRNA expression of BMP downstream targeted gene Id1). This study suggests that locally expressed GPC3 or exogenously delivered GPC3 protein can suppress BMP signalling and bony repair within the growth plate and bone injury site. Furthermore, our in vitro studies also demonstrated that GPC3, but not GPC1, is a major negative regulator of BMP activities in osteogenic cells. Work is in progress preparing a manuscript for publication reporting our findings on GPC3.
Key Outcomes: Failure and delay in bone healing and the faulty bony repair of injured growth plate remain two major paediatric orthopaedic challenges, which demand a better mechanistic understanding for the underlying causative factors and better therapies. This study has identified critical roles of BMP signalling in growth plate dysrepair. This study has also found activity of the matrix protein glypican-3 in suppressing BMP signalling and thus the bony repair at injured growth plate and bone.
The following papers have acknowledged the CRF funding support:
1. Su YW, Wong DSK, Fan J, Chung R, Wang L, Chen Y, Xian CH, Yao L, Wang L, Foster BK, Xu J, Xian CJ. Enhanced BMP signalling causes growth plate cartilage dysrepair in rats. Bone 2021 Feb 3;115874. doi: 10.1016/j.bone.2021.115874.
2. Zhang YL, Liu L, Peymanfar Y, Anderson P, Xian CJ (2021). Roles of microRNAs in osteogenesis or adipogenesis differentiation of bone marrow stromal progenitor cells. Int J Mol Sci 2021 Jul 5;22(13):7210. doi: 10.3390/ijms22137210