1,720,985 research outputs found
The skeletal ciliopathies
No full textWithin the broad and growing spectrum of human ciliopathies is a range of linked and overlapping disorders that present with skeletal features. These have been coined the skeletal ciliopathies. The syndromes have, to this point, been largely attributed to alterations in cellular Hedgehog signalling during development. However, a huge surge in fundamental discovery and clinical research has unveiled a plethora of roles for cilia in biology. This implicates a range of molecular and cell processes in the pathogenesis of skeletal ciliopathies. Our understanding of bi-directional interactions between cilia and the extracellular matrix remains in its infancy. The identification of genes and causal mutations defines skeletal ciliopathies. Some of these genes, and the proteins they encode, are now being explored further, by means of cell, animal, and other model approaches, seeking to understand the molecular underpinnings of disease. However, given the relatively recent appreciation of links between cilia biology and human disease, there is much work to be done. This chapter will briefly introduce the primary cilium and its associated ‘ciliome’, before describing the ciliary-associated skeletal disorders and the genes with which they are associated. Where possible, it will expand upon our current mechanistic understanding.</p
P127 Disrupting the cartilage mechanostat: the role of the ciliary protein IFT88 in the adolescent growth plate
No full textBackground/sims: as long bone elongation draws to a close, the cartilaginous growth plate begins to ossify in preparation of growth plate fusion. Previous embryonic developmental in vivo work has identified the crucial Parathyroid Hormone-related Protein-Indian hedgehog (PTHrP-Ihh) feedback loop that is responsible for the proliferation of chondrocytes at the epiphysis, whilst also allowing for the hypertrophic differentiation of chondrocytes before ossification at the diaphysis. Indian hedgehog signalling relies upon the microtubule-based organelle the primary cilium, as disruption to either results in similar musculoskeletal phenotypes. Here, we asked for the first time whether juvenile and adolescent primary cilia disruption affected chondrocyte differentiation in the growth plate.Methods: we used a chondrocyte-specific conditional knockout (AggrecanCreERT2; Ift88fl/fl, cKO) of a key primary ciliary protein (Ift88) administering tamoxifen at (4, 6, 8 weeks-of-age) to both cKO and control (Ift88fl/fl) animals, collecting two weeks later (6, 8, 10-weeks-of-age). Immunohistochemistry was performed using type X collagen (ColX), a specific marker of hypertrophic chondrocytes.Results: deletion of IFT88 resulted in large bi-lateral cartilaginous regions filled with disorganised ColX positive hypertrophic chondrocytes, indicating failed ossification. Our results indicate that deletion of IFT88 does not impact hypertrophic differentiation, but disrupts ossification processes downstream at the chondro-osseous junction, such as matrix remodelling and angiogenesis, necessary for growth plate closure. Interestingly, this phenotype was observed only in the bi-lateral most loaded regions of the tibia whilst the middle was unaffected.Conclusion: this observation indicates that the primary cilium could be involved in transducing mechanically regulated biophysical and signalling cues in the adolescent growth plate
Movement-stimulated hyaluronan (HA) secretion into joints in vivo is mediated by phospholipase C and parallel map kinase pathways
No full textMechanoadaptation: articular cartilage through thick and thin
Full text linkThe articular cartilage is exquisitely sensitive to mechanical load. Its structure is largely defined by the mechanical environment and destruction in osteoarthritis is the pathophysiological consequence of abnormal mechanics. It is often overlooked that disuse of joints causes profound loss of volume in the articular cartilage, a clinical observation first described in polio patients and stroke victims. Through the 1980s, the results of studies exploiting experimental joint immobilisation supported this. Importantly, this substantial body of work was also the first to describe metabolic changes that resulted in decreased synthesis of matrix molecules, especially sulfated proteoglycans. The molecular mechanisms that underlie disuse atrophy are poorly understood despite the identification of multiple mechanosensing mechanisms in cartilage. Moreover, there has been a tendency to equate cartilage loss with osteoarthritic degeneration. Here, we review the historic literature and clarify the structural, metabolic and clinical features that clearly distinguish cartilage loss due to disuse atrophy and those due to osteoarthritis. We speculate on the molecular sensing pathways in cartilage that may be responsible for cartilage mechanoadaptation
Are cellular mechanosensors potential therapeutic targets in osteoarthritis?
No full textThe role of mechanical factors in driving osteoarthritis is undisputed, but historically this was largely explained by chronic attrition of the articulating surfaces. The finding that mice deficient in matrix-degrading enzymes were protected from experimental osteoarthritis (OA) suggested an alternative explanation: that mechanosensitive pathways drive the enzymes responsible for cartilage breakdown. Mechanical factors are also important for joint homeostasis and are therefore both good and bad for the joint. Several mechanosensing pathways have been identified in a variety of cell types in vitro and in vivo. Here, we review those pathways with demonstrable roles in chondrocyte mechanotransduction including ion channels, integrins, the primary cilium and the pericellular and intracellular matrices. At least two of these pathways, involving release of FGF2 from the pericellular matrix and activation of TRPV4 are chondroprotective in OA models in vivo. We discuss the potential for modulating selective mechanosensing pathways for therapeutic benefit in OA. © 2014 Future Medicine Ltd
Cilia protein IFT88 regulates extracellular protease activity by optimizing LRP-1–mediated endocytosis
Full text linkMatrix protease activity is fundamental to developmental tissue patterning and remains influential in adult homeostasis. In cartilage, the principal matrix proteoglycan is aggrecan, the protease-mediated catabolism of which defines arthritis; however, the pathophysiologic mechanisms that drive aberrant aggrecanolytic activity remain unclear. Human ciliopathies exhibit altered matrix, which has been proposed to be the result of dysregulated hedgehog signaling that is tuned within the primary cilium. Here, we report that disruption of intraflagellar transport protein 88 (IFT88), a core ciliary trafficking protein, increases chondrocyte aggrecanase activity in vitro. We find that the receptor for protease endocytosis in chondrocytes, LDL receptor–related protein 1 (LRP-1), is unevenly distributed over the cell membrane, often concentrated at the site of cilia assembly. Hypomorphic mutation of IFT88 disturbs this apparent hot spot for protease uptake, increases receptor shedding, and results in a reduced rate of protease clearance from the extracellular space. We propose that IFT88 and/or the cilium regulates the extracellular remodeling of matrix—independently of Hedgehog regulation—by enabling rapid LRP-1–mediated endocytosis of proteases, potentially by supporting the creation of a ciliary pocket. This result highlights new roles for the cilium’s machinery in matrix turnover and LRP-1 function, with potential relevance in a range of diseases.—Coveney, C. R., Collins, I., Mc Fie, M., Chanalaris, A., Yamamoto, K., Wann, A. K. T. Cilia protein IFT88 regulates extracellular protease activity by optimizing LRP-1–mediated endocytosis
The Role of the Primary Cilium in Chondrocyte Response to Mechanical Loading
No full textArticular cartilage, like many other living tissues, experiences a complex physiological mechanical loading environment which regulates cell function and tissue homeostasis through a process of mechanotransduction. The underlying signalling pathways and mechanotransduction mechanisms are poorly understood but recent studies point to the involvement of a fascinating and previously over looked cellular organelle called the primary cilium. In other cell types, including epithelial cells and osteocytes, primary cilia have been shown to function as mechanoreceptors. This appears to involve deflection of the cilium in response to fluid shear forces which then activates calcium signalling pathways. In this chapter we examine the structure and function of the primary cilium and its potential role in mechanotransduction in articular chondrocytes. In particular we review exciting recent studies which suggest that the primary cilium mediates chondrocyte mechanotransduction through regulation of purinergic calcium signalling leading to changes in extracellular matrix synthesis. Furthermore we examine how other cilia-mediated mechanotransduction pathways, most notably hedgehog signalling, are also regulated by mechanical forces thereby controlling cell proliferation and tissue development. Finally we describe the regulation of primary cilia structure and how mechanical forces may influence the complex balance of cilia assembly and disassembly leading to alterations in cilia function. In summary this chapter explores the rapidly evolving area of primary cilia and their response to mechanical forces with a particular focus on articular cartilage for which mechanical loading is critical for homeostasis and functionality. Understanding the role of the primary cilium in mechanobiology will aid the development of novel therapeutic strategies for pathologies, such as osteoarthritis, that involve disruption of primary cilia function.</p
The role and uses of antibodies in COVID-19 infections: a living review
No full textCoronavirus disease 2019 has generated a rapidly evolving field of research, with the global scientific community striving for solutions to the current pandemic. Characterizing humoral responses towards SARS-CoV-2, as well as closely related strains, will help determine whether antibodies are central to infection control, and aid the design of therapeutics and vaccine candidates. This review outlines the major aspects of SARS-CoV-2-specific antibody research to date, with a focus on the various prophylactic and therapeutic uses of antibodies to alleviate disease in addition to the potential of cross-reactive therapies and the implications of long-term immunity
British Society for Matrix Biology Autumn Meeting 2022: "Matrix in Development"
No full textIntroduction: In postnatal development, chondro-osseous transitions such as endochondral ossification (EO) are regulated by rapid matrix turnover, mineralisation and chondro-osseous transdifferentiation, all disrupted in osteoarthritis (OA). We are exploring how force governs these transitions of cartilage to bone; previous studies from our group indicate cartilage matrix and chondrocyte phenotypic plasticity in the growth plate, and stability in articular cartilage, is mechanoregulated. Here, we describe exploitation of a human ‘developmental biology-inspired platform’ alongside in vivo studies, to study cartilage mineralisation.Materials and Methods: In vivo studies reveal chondro-osseous transitions are inhibited by forces. We synthesise GelMA using click chemistry to generate hydrogels with compressive moduli of 3–5 kPa. Buoyancy-driven gradients of BMP-2 within hydrogels seeded with hMSCs were cultured for 28 days. qPCR, histology and immunohistochemistry assessed, cartilage, hypertrophic and bone markers. Uniaxial cyclic compression (0.5 Hz, 10% strain) was applied using Electroforce5500. Cells from Confetti-UBCre mice are being used for lineage tracing studies.Results: MSC-laden GelMA constructs showed differential gene expression across the gradient, indicating tri-phasic osteochondral tissue formation within 28 days. Runx2/Sox9 immunostaining confirmed osteochondral differentiation, increased expression of SPP1, SP7, Runx2, Col1 indicated osteogenesis at one end, while distinct expression of Col10 and Runx2 in the central region marked cellular hypertrophy. The effects of cyclic loading on cell signalling, hyaline cartilage formation and thickness, calcification and phenotypic plasticity/stability are being assessed and compared with in vivo findings.Discussion: These data validate the formation of a humanised osteochondral gradient recapitulating developmental processes, in vitro. It is hypothesised that the generated osteochondral tissues will reflect the results of phenotypic changes in cells and ECM regulation, under physiological and pathological loads. The model will be integrated with snRNA sequencing and lineage tracing, to study trans-differentiation. This approach provides an experimentally tractable mechanobiology model and clinically conformant osteochondral tissue development model enabling fundamental biology and disease modelling across scales
Understanding how mechanical forces shape the hypertrophic niche by exploiting a developmental engineering model of endochondral ossification
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