1,741,298 research outputs found
Interleukin-1β sequesters hypoxia inducible factor 2α to the primary cilium.
Full text linkBACKGROUND: The primary cilium coordinates signalling in development, health and disease. Previously we have shown that the cilium is essential for the anabolic response to loading and the inflammatory response to interleukin-1β (IL-1β). We have also shown the primary cilium elongates in response to IL-1β exposure. Both anabolic phenotype and inflammatory pathology are proposed to be dependent on hypoxia-inducible factor 2 alpha (HIF-2α). The present study tests the hypothesis that an association exists between the primary cilium and HIFs in inflammatory signalling. RESULTS: Here we show, in articular chondrocytes, that IL-1β-induces primary cilia elongation with alterations to cilia trafficking of arl13b. This elongation is associated with a transient increase in HIF-2α expression and accumulation in the primary cilium. Prolyl hydroxylase inhibition results in primary cilia elongation also associated with accumulation of HIF-2α in the ciliary base and axoneme. This recruitment and the associated cilia elongation is not inhibited by blockade of HIFα transcription activity or rescue of basal HIF-2α expression. Hypomorphic mutation to intraflagellar transport protein IFT88 results in limited ciliogenesis. This is associated with increased HIF-2α expression and inhibited response to prolyl hydroxylase inhibition. CONCLUSIONS: These findings suggest that ciliary sequestration of HIF-2α provides negative regulation of HIF-2α expression and potentially activity. This study indicates, for the first time, that the primary cilium regulates HIF signalling during inflammation
Depletion of chondrocyte primary cilia reduces the compressive modulus of articular cartilage
Full text linkAbstractPrimary cilia are slender, microtubule based structures found in the majority of cell types with one cilium per cell. In articular cartilage, primary cilia are required for chondrocyte mechanotransduction and the development of healthy tissue. Loss of primary cilia in Col2aCre;ift88fl/fl transgenic mice results in up-regulation of osteoarthritic (OA) markers and development of OA like cartilage with greater thickness and reduced mechanical stiffness. However no previous studies have examined whether loss of primary cilia influences the intrinsic mechanical properties of articular cartilage matrix in the form of the modulus or just the structural properties of the tissue. The present study describes a modified analytical model to derive the viscoelastic moduli based on previous experimental indentation data. Results show that the increased thickness of the articular cartilage in the Col2aCre;ift88fl/fl transgenic mice is associated with a reduction in both the instantaneous and equilibrium moduli at indentation strains of greater than 20%. This reveals that the loss of primary cilia causes a significant reduction in the mechanical properties of cartilage particularly in the deeper zones and possibly the underlying bone. This is consistent with histological analysis and confirms the importance of primary cilia in the development of a mechanically functional articular cartilage
Heat shock induces rapid resorption of primary cilia
Full text linkPrimary cilia are involved in important developmental and disease pathways, such as the regulation of neurogenesis and tumorigenesis. They function as sensory antennae and are essential in the regulation of key extracellular signalling systems. We have investigated the effects of cell stress on primary cilia. Exposure of mammalian cells in vitro, and zebrafish cells in vivo, to elevated temperature resulted in the rapid loss of cilia by resorption. In mammalian cells loss of cilia correlated with a reduction in hedgehog signalling. Heat-shock-dependent loss of cilia was decreased in cells where histone deacetylases (HDACs) were inhibited, suggesting resorption is mediated by the axoneme-localised tubulin deacetylase HDAC6. In thermotolerant cells the rate of ciliary resorption was reduced. This implies a role for molecular chaperones in the maintenance of primary cilia. The cytosolic chaperone Hsp90 localises to the ciliary axoneme and its inhibition resulted in cilia loss. In the cytoplasm of unstressed cells, Hsp90 is known to exist in a complex with HDAC6. Moreover, immediately after heat shock Hsp90 levels were reduced in the remaining cilia. We hypothesise that ciliary resorption serves to attenuate cilia-mediated signalling pathways in response to extracellular stress, and that this mechanism is regulated in part by HDAC6 and Hsp90
Primary cilia disassembly down regulates mechanosensitive hedgehog signalling: a feedback mechanism controlling ADAMTS-5 expression in chondrocytes
Full text linkSummaryObjectiveHedgehog signalling is mediated by the primary cilium and promotes cartilage degeneration in osteoarthritis. Primary cilia are influenced by pathological stimuli and cilia length and prevalence are increased in osteoarthritic cartilage. This study aims to investigate the relationship between mechanical loading, hedgehog signalling and cilia disassembly in articular chondrocytes.MethodsPrimary bovine articular chondrocytes were subjected to cyclic tensile strain (CTS; 0.33 Hz, 10% or 20% strain). Hedgehog pathway activation (Ptch1, Gli1) and A Disintegrin And Metalloproteinase with Thrombospondin Motifs 5 (ADAMTS-5) expression were assessed by real-time PCR. A chondrocyte cell line generated from the Tg737ORPK mouse was used to investigate the role of the cilium in this response. Cilia length and prevalence were quantified by immunocytochemistry and confocal microscopy.ResultsMechanical strain upregulates Indian hedgehog expression and activates hedgehog signalling. Ptch1, Gli1 and ADAMTS-5 expression were increased following 10% CTS, but not 20% CTS. Pathway activation requires a functioning primary cilium and is not observed in Tg737ORPK cells lacking cilia. Mechanical loading significantly reduced cilium length such that cilia became progressively shorter with increasing strain magnitude. Inhibition of histone deacetylase 6 (HDAC6), a tubulin deacetylase, prevented cilia disassembly and restored mechanosensitive hedgehog signalling and ADAMTS-5 expression at 20% CTS.ConclusionsThis study demonstrates for the first time that mechanical loading activates primary cilia-mediated hedgehog signalling and ADAMTS-5 expression in adult articular chondrocytes, but that this response is lost at high strains due to HDAC6-mediated cilia disassembly. The study provides new mechanistic insight into the role of primary cilia and mechanical loading in articular cartilage
Primary cilia elongation in response to interleukin-1 mediates the inflammatory response
Full text linkPrimary cilia are singular, cytoskeletal organelles present in the majority of mammalian cell types where they function as coordinating centres for mechanotransduction, Wnt and hedgehog signalling. The length of the primary cilium is proposed to modulate cilia function, governed in part by the activity of intraflagellar transport (IFT). In articular cartilage, primary cilia length is increased and hedgehog signaling activated in osteoarthritis (OA). Here, we examine primary cilia length with exposure to the quintessential inflammatory cytokine interleukin-1 (IL-1), which is up-regulated in OA. We then test the hypothesis that the cilium is involved in mediating the downstream inflammatory response. Primary chondrocytes treated with IL-1 exhibited a 50 % increase in cilia length after 3 h exposure. IL-1-induced cilia elongation was also observed in human fibroblasts. In chondrocytes, this elongation occurred via a protein kinase A (PKA)-dependent mechanism. G-protein coupled adenylate cyclase also regulated the length of chondrocyte primary cilia but not downstream of IL-1. Chondrocytes treated with IL-1 exhibit a characteristic increase in the release of the inflammatory chemokines, nitric oxide and prostaglandin E2. However, in cells with a mutation in IFT88 whereby the cilia structure is lost, this response to IL-1 was significantly attenuated and, in the case of nitric oxide, completely abolished. Inhibition of IL-1-induced cilia elongation by PKA inhibition also attenuated the chemokine response. These results suggest that cilia assembly regulates the response to inflammatory cytokines. Therefore, the cilia proteome may provide a novel therapeutic target for the treatment of inflammatory pathologies, including OA
Tethered fleximags as artificial cilia
Full text linkFlexible superparamagnetic filaments ('fleximags') are very slender elastic filaments, which can be driven by distributed magnetic torques to mimic closely the behaviour of biological flagella. Previously, fleximags have been used as a basis for artificial micro-swimmers capable of transporting small cargos Dreyfus et al. (Nature, vol. 437, 2005, p. 862). Here, we demonstrate how these filaments can be anchored to a wall to make carpets of artificial micro-magnetic cilia with tunable densities. We analyse the dynamics of an artificial cilium under both planar and three-dimensional beating patterns. We show that the dynamics are controlled by a single characteristic length scale varying with the inverse square root of the driving frequency, providing a mechanism to break the fore and aft symmetry and to generate net fluxes and forces. However, we show that an effective geometrical reciprocity in the filament dynamics creates intrinsic limitations upon the ability of the artificial flagellum to pump fluid when driven in two dimensions
Bardet-Biedl syndrome proteins control cilia length through regulation of actin polymerisation.
Full text linkPrimary cilia are cellular appendages important for signal transduction and sensing the environment. Bardet-Biedl syndrome proteins form a complex that is important for several cytoskeleton-related processes such as ciliogenesis, cell migration and division. However, the mechanisms by which BBS proteins may regulate the cytoskeleton remain unclear. We discovered that Bbs4 and Bbs6 deficient renal medullary cells display a characteristic behaviour comprising poor migration, adhesion and division with an inability to form lamellipodial and filopodial extensions. Moreover, fewer mutant cells were ciliated (48% ± 6 for wild-type cells vs 23% ± 7 for Bbs4 null cells; P-value < 0.0001) and their cilia were shorter (2.55 μm ± 0.41 for wild-type cells vs 2.16 μm ± 0.23 for Bbs4 null cells; P-value < 0.0001). Whilst the microtubular cytoskeleton and cortical actin were intact, actin stress fibre formation was severely disrupted, forming abnormal apical stress fibre aggregates. Furthermore, we observed over-abundant focal adhesions in Bbs4, Bbs6 and Bbs8-deficient cells. In view of these findings and the role of RhoA in regulation of actin filament polymerisation, we showed that RhoA-GTP levels were highly upregulated in the absence of Bbs proteins. Upon treatment of Bbs4-deficient cells with chemical inhibitors of RhoA, we were able to restore cilia length and number as well as the integrity of the actin cytoskeleton. Together these findings indicate that Bbs proteins play a central role in the regulation of the actin cytoskeleton and control cilia length through alteration of RhoA levels
Particle Transport by Cilia Arrays in Parallel-Wall Channels
No full textCilia are thin hair-like organelles projecting from a cell body, which are found in many unicellular and multicellular organisms. Individual cilia in ciliary arrays often coordinate their motion, leading to formation of metachronal waves that can propel a uni- cellular organism in a fluid or generate particle and fluid transport along a cellular layer. For example, clean-up functions in living organs are carried out by coordinated oscillations in cilia carpets. Numerous mathematical models and simulations have been developed to investigate the mechanism of metachronal wave formation and cilia dynamics. However, much less is known about particle transport by cilia, which is an interesting and important re- search topic. This thesis aims to use a simplified rower model of the arrays of hydrodynamically coupled cilia to investigate particle transport by metachronal waves. In circular rower models cilia are represented by spherical beads (rowers) moving on prescribed trajectories that mimic the motion of cilia tips. Such models have been successful in explaining the cilia beating coordination and the mechanism of propagation of metachronal waves but the problem of particle transport has not been addressed. Here, a circular rower model that includes hydrodynamic interactions between the rowers and free particles in a parallel-wall channel has been implemented to investigate this problem. Accurate incorporation of hydrodynamic interactions into the model is essential for quantifying particle transport. In our model, metachronal waves are generated by placing consecutive rowers at a constant phase difference in the initial configuration. Various system parameters, such as the wavelength and direction of the metachronal wave, particle position with respect to a rower array, and the channel width, affect the transport rate. In this thesis, a large set of numerical simulations has been performed and analyzed to understand how the transport in cilia arrays depends on these parameters. The results obtained explain how fast (or slow) a particle can be transported by a cilia array and how this transport is affected by the hydrodynamic interactions and by changes of system parameters. Some cases of interesting behavior of both the rower arrays and transported particles have been elucidated, including looped particle trajectories (associated with backflow patterns) and instabilities in cilia array motion. Our results are not only relevant for understanding particle transport by cilia arrays in vivo but can also be used in the development of artificial microfluidic cilia systems for biomedical applications.Embargo status: Restricted until 09/2025. To request the author grant access, click on the PDF link
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Cilia in Brain Development and Disease
No full textThe development of the vertebrate brain follows a tightly coordinated course of partially concomitant events. Progressive regionalization of larger brain areas into defined progenitor fields depends on the locally restricted action of specific gene sets involved in patterning. Within discrete progenitor fields further dynamic morphogenetic processes ensure proper maturation through controlled cell proliferation, differentiation and migration. Proper cell placement is crucial for subsequent neuronal wiring, which leads to functional connectivity and neuronal circuits, and there by ensures proper brain function. Cilia are microtubule-based cell protrusions encased by a specialized membrane. Depending on cell type cilia serve as signaling centers or function in (cell) motility. In their function as specialized signaling compartments cilia are involved in the reception and transduction of multiple signals from the environment of a cell. Cilia are abundantly present in many different regions of the vertebrate brain. The importance of cilia function can be found throughout all and at all levels of brain morphogenetic processes. We focus on the role of cilia in the predominant SHH signaling pathway and give an overview of its impact on various cilia-associated and -dependent brain patterning events. We then discuss and summarize the functions of cilia in subsequent morphogenetic processes like stem cell niche proliferation, cell migration and neuronal wiring, as well as the role of cilia during later stages of brain development andin the adult brain. Ciliopathies comprise a group of human disorders associated with genetic mutations that alter cilia structure and function. We describe a few well-established ciliopathies with associated neurological phenotypes. As an example for a human brain condition with a more tenuous connection to cilia we present dyslexia, or reading disorder. This chapter focuses on the role of cilia in the predominant Sonic Hedghog signaling pathway and provides an overview of its impact on various cilia-associated and -dependent brain patterning events. It discusses and summarizes the functions of cilia in subsequent morphogenetic processes like stem cell niche proliferation, cell migration and neuronal wiring, as well as the role of cilia during later stages of brain development and in the adult brain. Ciliopathies comprise a group of human disorders associated with genetic mutations that alter cilia structure and function. The chapter describes a few well-established ciliopathies with associated neurological phenotypes. As an example for a human brain condition with a more tenuous connection to cilia the present dyslexia, or reading disorder. The notion that the human brain is the most complex object in the universe may be a narcissistic statement. Vertebrates inhabit very diverse environmental niches. It is therefore not surprising that their brains have evolved various specializations
Cilia-mediated signalling in the embryonic nodes: A computational fluid-structure-protein interaction (FSPI) model
No full textThis paper was presented at the 2nd Micro and Nano Flows Conference (MNF2009), which was held at Brunel University, West London, UK. The conference was organised by Brunel University and supported by the Institution of Mechanical Engineers, IPEM, the Italian Union of Thermofluid dynamics, the Process Intensification Network, HEXAG - the Heat Exchange Action Group and the Institute of Mathematics and its Applications.The breaking of left-right symmetry in the mammalian embryo is believed to occur in a transient embryonic structure, the node, when cilia create a leftward flow of liquid. It has been widely confirmed that this nodal flow is the first sign of left-right differentiation; however, the mechanism through which embryonic cilia produce their movement and how the leftward flow confers laterality are still requiring investigation. The ciliary motility in the embryonic node involves complex dynein activations and the handed information is transmitted to the cells by the flow produced by cilia, either mechanically and/or by advection of a chemical species. In this paper, we present a computational model of ciliary ultrastructure (protein-structure model) and discuss the scenarios that incorporate this internal microtubule-dynein system with the external fluidic environment (fluid-structure-protein interaction model, FSPI). By employing
computational fluid dynamics, deformable mesh computational techniques and fluid-structure interaction analysis, and solving the three-dimensional unsteady transport equations, the protein-triggered mechanism of
nodal ciliary motility has been studied, which is a primary component for the FSPI model. Future work regarding the integrative model is discussed, that will provide more accurate quantitative information on the
flow rate, ciliary motion, and molecule/ particle transport in the embryonic node and support the plausibility of hypotheses regarding left-right information transmission
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