Biology subjects

Ormsby, R. T.

Publications and source records attributed to Ormsby, R. T..

3 recordsLinked to original sources

bioRxiv2025

TWEAK and Fn14 expression in osteoarthritis: evidence for TWEAK-induced RANKL release from chondrocytes

ObjectiveA role for TWEAK expression and that of its receptor Fn14 by osteoblasts and synovial tissue has been proposed in the pathogenesis of osteoarthritis (OA). Here, we examined whether the cartilage in OA was also a source and target of TWEAK. DesignArticular cartilage samples from 24 patients undergoing hip or knee replacement surgery for OA were investigated for TWEAK and Fn14 expression by both immunostaining and real-time RT-PCR. Samples were graded according to the Pritzker scale from grade 0 (normal) through increasing levels of cartilage damage (grades 1-3). Human primary chondrocytes isolated from OA cartilage were treated with combinations of recombinant TWEAK and TNF and examined for acute effects on TWEAK, FN14, RANKL and ADAM17 mRNA levels. Released soluble RANKL levels were measured by ELISA. ResultsImmunostaining indicated that the majority (21/24) of OA cartilage samples expressed low levels of TWEAK protein and high levels of Fn14, however, expression did not appear to vary with respect to OA grade. TWEAK mRNA levels were elevated in grade 2 OA cartilage compared to grade 0 (p < 0.05), while Fn14 mRNA levels appeared elevated across all damage grades, significantly in grade 2 samples. Primary chondrocytes treated with TNF, alone or in combination with TWEAK, exhibited early upregulated Fn14 mRNA expression. TWEAK induced RANKL mRNA expression. while both TWEAK and TNF induced the mRNA expression of the RANKL sheddase, ADAM17. Consistent with these findings, TWEAK and TNF both induced soluble RANKL release by chondrocytes. ConclusionsThe expression and regulation of TWEAK and Fn14 is a feature of human OA articular cartilage, suggesting a pathogenetic role. TNF may prime chondrocytes for TWEAK reactivity by upregulating Fn14 expression. The TWEAK and TNF induction of ADAM17 expression and sRANKL release by chondrocytes points to a further disease pathway in human OA.

pathology↗

bioRxiv2022

The Effects of Vitamin E Analogues α-Tocopherol and γ-Tocotrienol on the Human Osteocyte Response to Ultra-high Molecular Weight Polyethylene Wear Particles

Polyethylene (PE) liners are a common bearing surface of orthopaedic prostheses. Wear particles of ultra-high molecular weight PE (UHMWPE) contribute to periprosthetic osteolysis, a major cause of aseptic loosening. Vitamin E is added to some PE liners to prevent oxidative degradation. Osteocytes, an important cell type for controlling both bone mineralisation and bone resorption, have been shown to respond UHMWPE particles by upregulating pro-osteoclastogenic and osteocytic osteolysis. Here, we examined the effects of the vitamin E analogues -tocopherol and {gamma}-tocotrienol alone or in the context of UHMWPE particles on human osteocyte gene expression and mineralisation behaviour. Human osteoblasts differentiated to an osteocyte-like stage were exposed to UHMWPE wear particles in the presence or absence of either -Tocopherol or {gamma}-Tocotrienol. Both -Tocopherol and {gamma}-Tocotrienol induced antioxidant-related gene expression. UHMWPE particles independently upregulated antioxidant gene expression, suggesting an effect of wear particles on oxidative stress. Both vitamin E analogues strongly induced OPG mRNA expression and {gamma}-Tocotrienol also inhibited RANKL mRNA expression, resulting in a significantly reduced RANKL:OPG mRNA ratio (p < 0.01) overall. UHMWPE particles reversed the suppressive effect of -Tocopherol but not of {gamma}-Tocotrienol on this pro-osteoclastogenic index. UHMWPE particles also upregulated osteocytic-osteolysis related gene expression. Vitamin E analogues alone or in combination with UHMWPE particles also resulted in upregulation of these genes. Consistent with this, both vitamin E analogues promoted calcium release from mineralised cultures of osteocyte-like cells. Our findings suggest that while vitamin E may suppress osteocyte support of osteoclastogenesis in the presence of UHMWPE particles, the antioxidant effect may induce osteocytic osteolysis, which could promote periprosthetic osteolysis. It will be important to conduct further studies of vitamin E to determine the long-term effects of its inclusion in prosthetic materials.

cell biology↗

bioRxiv2020

Sclerostin directly stimulates osteocyte synthesis of fibroblast growth factor-23

Osteocyte produced fibroblast growth factor 23 (FGF23) is the key regulator of serum phosphate (Pi) homeostasis. The interplay between parathyroid hormone (PTH), FGF23 and other proteins that regulate FGF23 production and serum Pi levels is complex and incompletely characterised. Evidence suggests that the protein product of the SOST gene, sclerostin (SCL), also a PTH target and also produced by osteocytes, plays a role in FGF23 expression, however the mechanism for this effect is unclear. Part of the problem of understanding the interplay of these mediators is the complex multi-organ system that achieves Pi homeostasis in vivo. In the current study, we sought to address this using a unique cell line model of the osteocyte, IDG-SW3, known to express FGF23 at both the mRNA and protein levels. In cultures of differentiated IDG-SW3 cells, both PTH1-34 and recombinant human (rh) SCL remarkably induced Fgf23 mRNA expression dose-dependently within 3 hours. Both rhPTH1-34 and rhSCL also strongly induced C-terminal FGF23 protein secretion. Secreted intact FGF23 levels remained unchanged, consistent with constitutive post-translational cleavage of FGF23 in this cell model. Both rhPTH1-34 and rhSCL treatments significantly suppressed mRNA levels of Phex, Dmp1 and Enpp1 mRNA, encoding putative negative regulators of FGF23 levels, and induced Galnt3 mRNA expression, encoding N-acetylgalactosaminyl-transferase 3 (GalNAc-T3), which protects FGF23 from furin-like proprotein convertase-mediated cleavage. The effect of both rhPTH1-34 and rhSCL was antagonised by pre-treatment with the NF-{kappa}{beta} signalling inhibitors, BAY11 and TPCK. RhSCL also stimulated FGF23 mRNA expression in ex vivo cultures of human bone. These findings provide evidence for the direct regulation of FGF23 expression by sclerostin. Locally expressed sclerostin via the induction of FGF23 in osteocytes thus has the potential to contribute to the regulation of Pi homeostasis.

physiology↗