A Novel Primary Cilium-Mediated Mechanism Through which Osteocytes Regulate Metastatic Behavior of Both Breast and Prostate Cancer Cells

Bone metastases are a common cause of suffering in breast and prostate cancer patients, however, the interaction between bone cells and cancer cells is poorly understood. Using a series of co-culture, conditioned media, human cancer spheroid, and organ-on-a-chip experiments, this study reveals that osteocytes suppress cancer cell proliferation and increase migration via tumor necrosis factor alpha (TNF-α) secretion. This action is regulated by osteocyte primary cilia and associated intraflagellar transport protein 88 (IFT88). Furthermore, it shows that cancer cells block this mechanism by secreting transforming growth factor beta (TGF-β), which disrupts osteocyte cilia and IFT88 gene expression. This bi-directional crosstalk signaling between osteocytes and cancer cells is common to both breast and prostate cancer. This study also proposes that osteocyte inhibition of cancer cell proliferation decreases as cancer cells increase, producing more TGF-β. Hence, a positive feedback loop develops accelerating metastatic tumor growth. These findings demonstrate the importance of cancer cell-osteocyte signaling in regulating breast and prostate bone metastases and support the development of therapies targeting this pathway.

Human vascularised synovium-on-a-chip: a mechanically stimulated, microfluidic model to investigate synovial inflammation and monocyte recruitment

Healthy synovium is critical for joint homeostasis. Synovial inflammation (synovitis) is implicated in the onset, progression and symptomatic presentation of arthritic joint diseases such as rheumatoid arthritis and osteoarthritis. Thus, the synovium is a promising target for the development of novel, disease-modifying therapeutics. However, target exploration is hampered by a lack of good pre-clinical models that accurately replicate human physiology and that are developed in a way that allows for widespread uptake. The current study presents a multi-channel, microfluidic, organ-on-a-chip (OOAC) model, comprising a 3D configuration of the human synovium and its associated vasculature, with biomechanical and inflammatory stimulation, built upon a commercially available OOAC platform. Healthy human fibroblast-like synoviocytes (hFLS) were co-cultured with human umbilical vein endothelial cells (HUVECs) with appropriate matrix proteins, separated by a flexible, porous membrane. The model was developed within the Emulate organ-chip platform enabling the application of physiological biomechanical stimulation in the form of fluid shear and cyclic tensile strain. The hFLS exhibited characteristic morphology, cytoskeletal architecture and matrix protein deposition. Synovial inflammation was initiated through the addition of interleukin-1β(IL-1β) into the synovium channel resulting in the increased secretion of inflammatory and catabolic mediators, interleukin-6 (IL-6), prostaglandin E2 (PGE2), matrix metalloproteinase 1 (MMP-1), as well as the synovial fluid constituent protein, hyaluronan. Enhanced expression of the inflammatory marker, intercellular adhesion molecule-1 (ICAM-1), was observed in HUVECs in the vascular channel, accompanied by increased attachment of circulating monocytes. This vascularised human synovium-on-a-chip model recapitulates a number of the functional characteristics of both healthy and inflamed human synovium. Thus, this model offers the first human synovium organ-chip suitable for widespread adoption to understand synovial joint disease mechanisms, permit the identification of novel therapeutic targets and support pre-clinical testing of therapies.

YAP activation inhibits inflammatory signalling and cartilage breakdown associated with reduced primary cilia expression

OBJECTIVE

To clarify the role of YAP in modulating cartilage inflammation and degradation and the involvement of primary cilia and associated intraflagellar transport (IFT).

METHODS

Isolated primary chondrocytes were cultured on substrates of different stiffness (6-1000 kPa) or treated with YAP agonist lysophosphatidic acid (LPA) or YAP antagonist verteporfin (VP), or genetically modified by YAP siRNA, all ± IL1β. Nitric oxide (NO) and prostaglandin E2 (PGE2) release were measured to monitor IL1β response. YAP activity was quantified by YAP nuclear/cytoplasmic ratio and percentage of YAP-positive cells. Mechanical properties of cartilage explants were tested to confirm cartilage degradation. The involvement of primary cilia and IFT was analysed using IFT88 siRNA and ORPK cells with hypomorphic mutation of IFT88.

RESULTS

Treatment with LPA, or increasing polydimethylsiloxane (PDMS) substrate stiffness, activated YAP nuclear expression and inhibited IL1β-induced release of NO and PGE2, in isolated chondrocytes. Treatment with LPA also inhibited IL1β-mediated inflammatory signalling in cartilage explants and prevented matrix degradation and the loss of cartilage biomechanics. YAP activation reduced expression of primary cilia, knockdown of YAP in the absence of functional cilia/IFT failed to induce an inflammatory response.

CONCLUSIONS

We demonstrate that both pharmaceutical and mechanical activation of YAP blocks pro-inflammatory signalling induced by IL1β and prevents cartilage breakdown and the loss of biomechanical functionality. This is associated with reduced expression of primary cilia revealing a potential anti-inflammatory mechanism with novel therapeutic targets for treatment of osteoarthritis (OA).

Organ-on-a-Chip and Microfluidic Platforms for Oncology in the UK

Organ-on-chip systems are capable of replicating complex tissue structures and physiological phenomena. The fine control of biochemical and biomechanical cues within these microphysiological systems provides opportunities for cancer researchers to build complex models of the tumour microenvironment. Interest in applying organ chips to investigate mechanisms such as metastatsis and to test therapeutics has grown rapidly, and this review draws together the published research using these microfluidic platforms to study cancer. We focus on both in-house systems and commercial platforms being used in the UK for fundamental discovery science and therapeutics testing. We cover the wide variety of cancers being investigated, ranging from common carcinomas to rare sarcomas, as well as secondary cancers. We also cover the broad sweep of different matrix microenvironments, physiological mechanical stimuli and immunological effects being replicated in these models. We examine microfluidic models specifically, rather than organoids or complex tissue or cell co-cultures, which have been reviewed elsewhere. However, there is increasing interest in incorporating organoids, spheroids and other tissue cultures into microfluidic organ chips and this overlap is included. Our review includes a commentary on cancer organ-chip models being developed and used in the UK, including work conducted by members of the UK Organ-on-a-Chip Technologies Network. We conclude with a reflection on the likely future of this rapidly expanding field of oncological research.

Techniques for Visualization and Quantification of Primary Cilia in Chondrocytes

Primary cilia regulate and coordinate a variety of cell signaling pathways important in chondrocyte physiology and cartilage development, health, and disease. Despite this, the chondrocyte primary cilium and its associated role in cartilage biology remains poorly understood. Key to elucidating primary cilia structure and function in chondrocytes is the ability to visualize this unique structure. Here we describe materials and methods for immunofluorescence labeling, microscopy, and measurement of chondrocyte primary cilia.

Collagen pre-strain discontinuity at the bone—Cartilage interface

The bone-cartilage unit (BCU) is a universal feature in diarthrodial joints, which is mechanically-graded and subjected to shear and compressive strains. Changes in the BCU have been linked to osteoarthritis (OA) progression. Here we report existence of a physiological internal strain gradient (pre-strain) across the BCU at the ultrastructural scale of the extracellular matrix (ECM) constituents, specifically the collagen fibril. We use X-ray scattering that probes changes in the axial periodicity of fibril-level D-stagger of tropocollagen molecules in the matrix fibrils, as a measure of microscopic pre-strain. We find that mineralized collagen nanofibrils in the calcified plate are in tensile pre-strain relative to the underlying trabecular bone. This behaviour contrasts with the previously accepted notion that fibrillar pre-strain (or D-stagger) in collagenous tissues always reduces with mineralization, via reduced hydration and associated swelling pressure. Within the calcified part of the BCU, a finer-scale gradient in pre-strain (0.6% increase over ~50μm) is observed. The increased fibrillar pre-strain is linked to prior research reporting large tissue-level residual strains under compression. The findings may have biomechanical adaptative significance: higher in-built molecular level resilience/damage resistance to physiological compression, and disruption of the molecular-level pre-strains during remodelling of the bone-cartilage interface may be potential factors in osteoarthritis-based degeneration.

Oscillations of the circadian clock protein, BMAL-1, align to daily cycles of mechanical stimuli: a novel means to integrate biological time within predictive in vitro model systems

PURPOSE

In vivo, the circadian clock drives 24-h rhythms in human physiology. Isolated cells in vitro retain a functional clockwork but lack necessary timing cues resulting in the rapid loss of tissue-level circadian rhythms. This study tests the hypothesis that repeated daily mechanical stimulation acts as a timing cue for the circadian clockwork. The delineation and integration of circadian timing cues into predictive in vitro model systems, including organ-on-a-chip (OOAC) devices, represent a novel concept that introduces a key component of in vivo physiology into predictive in vitro model systems.

METHODS

Quiescent bovine chondrocytes were entrained for 3 days by daily 12-h bouts of cyclic biaxial tensile strain (10%, 0.33 Hz, Flexcell) before sampling during free-running conditions. The core clock protein, BMAL-1, was quantified from normalised Western Blot signal intensity and the temporal oscillations characterised by Cosinor linear fit with 24-h period.

RESULTS

Following entrainment, the cell-autonomous oscillations of the molecular clock protein, BMAL-1, exhibited circadian (24 h) periodicity (p < 0.001) which aligned to the diurnal mechanical stimuli. A 6-h phase shift in the mechanical entrainment protocol resulted in an equivalent shift of the circadian clockwork. Thus, repeated daily mechanical stimuli synchronised circadian rhythmicity of chondrocytes in vitro.

CONCLUSION

This work demonstrates that daily mechanical stimulation can act as a timing cue that is sufficient to entrain the peripheral circadian clock in vitro. This discovery may be exploited to induce and sustain circadian physiology within into predictive in vitro model systems, including OOAC systems. Integration of the circadian clock within these systems will enhance their potential to accurately recapitulate human diurnal physiology and hence augment their predictive value as drug testing platforms and as realistic models of human (patho)physiology.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s44164-022-00032-x.

Abstract 2642: Using 3-Dimensional in vitro models to unravel the complexity of the metastatic microenvironment in high-grade serous ovarian cancer

Studying the complexity of the tumor microenvironment (TME) still represents a challenge in research. The intricate communication within the stroma - fibroblast, immune cells, endothelial cells and the extracellular matrix (ECM) - and the malignant cell compartment sustains every stage of cancer progression and resistance to cancer therapies, but it is difficult to model this using human cells. Using a multi-level deconstruction of human metastases as a template and validation, we developed multicellular models of high-grade serous ovarian cancer (HGSOC) with increased complexity. The different models - tri-, tetra- and penta-cultures - consist of different combinations of primary adipocytes, fibroblasts, mesothelial cells, HGSOC cells and myeloid cells that mimic the structure and the composition of a human omental metastatic tissue. In HGSOC biopsies, we previously identified a prognostic matrisome signature and a number of pathways correlating ECM deposition and disease progression. This knowledge combined with the versatile nature of our platforms has allowed us to identify the contributions of each cell type in supporting tumor progression and ECM remodeling. For instance, 14-day tri-culture of malignant cells, adipocytes and fibroblasts was sufficient to replicate the deposition of specific ECM proteins and the prognostic matrisome signature seen in human omental metastases. Moreover, we found that TGFβR and Hedgehog signaling pathways act together on the fibroblasts to stimulate ECM production. In addition, in the tetra-culture model, we identified platelets as promoters of early metastatic invasion by activating mesothelial cells. As the immune system plays an important role in HGSOC tumor microenvironment, we have now added myeloid cells to form a more complex penta-culture in which we can analyze the behavior and impact of myeloid cells. In conclusion, the multicellular models presented here could be a new resource to study new and established cancer therapies and provide a useful tool to better understand the molecular mechanisms that drive cancer progression.

Citation Format: Beatrice Malacrida, Robin Delaine-Smith, Sam Nichols, Eleni Maniati, Roanne L. Jones, Martin M. Knight, Oliver M. Pearce, Frances R. Balkwill. Using 3-Dimensional in vitro models to unravel the complexity of the metastatic microenvironment in high-grade serous ovarian cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2642.

A human multi-cellular model shows how platelets drive production of diseased extracellular matrix and tissue invasion

Guided by a multi-level "deconstruction" of omental metastases, we developed a tetra (four cell)-culture model of primary human mesothelial cells, fibroblasts, adipocytes, and high-grade serous ovarian cancer (HGSOC) cell lines. This multi-cellular model replicated key elements of human metastases and allowed malignant cell invasion into the artificial omental structure. Prompted by findings in patient biopsies, we used the model to investigate the role of platelets in malignant cell invasion and extracellular matrix, ECM, production. RNA (sequencing and quantitative polymerase-chain reaction), protein (proteomics and immunohistochemistry) and image analysis revealed that platelets stimulated malignant cell invasion and production of ECM molecules associated with poor prognosis. Moreover, we found that platelet activation of mesothelial cells was critical in stimulating malignant cell invasion. Whilst platelets likely activate both malignant cells and mesothelial cells, the tetra-culture model allowed us to dissect the role of both cell types and model the early stages of HGSOC metastases.

Modelling TGFβR and Hh pathway regulation of prognostic matrisome molecules in ovarian cancer

In a multi-level "deconstruction" of omental metastases, we previously identified a prognostic matrisome gene expression signature in high-grade serous ovarian cancer (HGSOC) and twelve other malignancies. Here, our aim was to understand how six of these extracellular matrix (ECM) molecules, COL11A1, cartilage oligomeric matrix protein, FN1, versican, cathepsin B, and COL1A1, are upregulated in cancer. Using biopsies, we identified significant associations between TGFβR activity, Hedgehog (Hh) signaling, and these ECM molecules and studied the associations in mono-, co-, and tri-culture. Activated omental fibroblasts (OFs) produced more matrix than malignant cells, directed by TGFβR and Hh signaling cross talk. We "reconstructed" omental metastases in tri-cultures of HGSOC cells, OFs, and adipocytes. This combination was sufficient to generate all six ECM proteins and the matrisome expression signature. TGFβR and Hh inhibitor combinations attenuated fibroblast activation and gel and ECM remodeling in these models. The tri-culture model reproduces key features of omental metastases and allows study of diseased-associated ECM.

Mechanical Stimulation Modulates Osteocyte Regulation of Cancer Cell Phenotype

Breast and prostate cancers preferentially metastasise to bone tissue, with metastatic lesions forming in the skeletons of most patients. On arriving in bone tissue, disseminated tumour cells enter a mechanical microenvironment that is substantially different to that of the primary tumour and is largely regulated by bone cells. Osteocytes, the most ubiquitous bone cell type, orchestrate healthy bone remodelling in response to physical exercise. However, the effects of mechanical loading of osteocytes on cancer cell behaviour is still poorly understood. The aim of this study was to characterise the effects of osteocyte mechanical stimulation on the behaviour of breast and prostate cancer cells. To replicate an osteocyte-controlled environment, this study treated breast (MDA-MB-231 and MCF-7) and prostate (PC-3 and LNCaP) cancer cell lines with conditioned media from MLO-Y4 osteocyte-like cells exposed to mechanical stimulation in the form of fluid shear stress. We found that osteocyte paracrine signalling acted to inhibit metastatic breast and prostate tumour growth, characterised by reduced proliferation and invasion and increased migration. In breast cancer cells, these effects were largely reversed by mechanical stimulation of osteocytes. In contrast, conditioned media from mechanically stimulated osteocytes had no effect on prostate cancer cells. To further investigate these interactions, we developed a microfluidic organ-chip model using the Emulate platform. This new organ-chip model enabled analysis of cancer cell migration, proliferation and invasion in the presence of mechanical stimulation of osteocytes by fluid shear stress, resulting in increased invasion of breast and prostate cancer cells. These findings demonstrate the importance of osteocytes and mechanical loading in regulating cancer cell behaviour and the need to incorporate these factors into predictive in vitro models of bone metastasis.

Polycystin-2 Is Required for Chondrocyte Mechanotransduction and Traffics to the Primary Cilium in Response to Mechanical Stimulation

Primary cilia and associated intraflagellar transport are essential for skeletal development, joint homeostasis, and the response to mechanical stimuli, although the mechanisms remain unclear. Polycystin-2 (PC2) is a member of the transient receptor potential polycystic (TRPP) family of cation channels, and together with Polycystin-1 (PC1), it has been implicated in cilia-mediated mechanotransduction in epithelial cells. The current study investigates the effect of mechanical stimulation on the localization of ciliary polycystins in chondrocytes and tests the hypothesis that they are required in chondrocyte mechanosignaling. Isolated chondrocytes were subjected to mechanical stimulation in the form of uniaxial cyclic tensile strain (CTS) in order to examine the effects on PC2 ciliary localization and matrix gene expression. In the absence of strain, PC2 localizes to the chondrocyte ciliary membrane and neither PC1 nor PC2 are required for ciliogenesis. Cartilage matrix gene expression (Acan, Col2a) is increased in response to 10% CTS. This response is inhibited by siRNA-mediated loss of PC1 or PC2 expression. PC2 ciliary localization requires PC1 and is increased in response to CTS. Increased PC2 cilia trafficking is dependent on the activation of transient receptor potential cation channel subfamily V member 4 (TRPV4) activation. Together, these findings demonstrate for the first time that polycystins are required for chondrocyte mechanotransduction and highlight the mechanosensitive cilia trafficking of PC2 as an important component of cilia-mediated mechanotransduction.

Activation of TRPV4 by mechanical, osmotic or pharmaceutical stimulation is anti-inflammatory blocking IL-1β mediated articular cartilage matrix destruction

OBJECTIVE

Cartilage health is maintained in response to a range of mechanical stimuli including compressive, shear and tensile strains and associated alterations in osmolality. The osmotic-sensitive ion channel Transient Receptor Potential Vanilloid 4 (TRPV4) is required for mechanotransduction. Mechanical stimuli inhibit interleukin-1β (IL-1β) mediated inflammatory signalling, however the mechanism is unclear. This study aims to clarify the role of TRPV4 in this response.

DESIGN

TRPV4 activity was modulated glycogen synthase kinase (GSK205 antagonist or GSK1016790 A (GSK101) agonist) in articular chondrocytes and cartilage explants in the presence or absence of IL-1β, mechanical (10% cyclic tensile strain (CTS), 0.33 Hz, 24hrs) or osmotic loading (200mOsm, 24hrs). Nitric oxide (NO), prostaglandin E₂ (PGE₂) and sulphated glycosaminoglycan (sGAG) release and cartilage biomechanics were analysed. Alterations in post-translational tubulin modifications and primary cilia length regulation were examined.

RESULTS

In isolated chondrocytes, mechanical loading inhibited IL-1β mediated NO and PGE₂ release. This response was inhibited by GSK205. Similarly, osmotic loading was anti-inflammatory in cells and explants, this response was abrogated by TRPV4 inhibition. In explants, GSK101 inhibited IL-1β mediated NO release and prevented cartilage degradation and loss of mechanical properties. Upon activation, TRPV4 cilia localisation was increased resulting in histone deacetylase 6 (HDAC6)-dependent modulation of soluble tubulin and altered cilia length regulation.

CONCLUSION

Mechanical, osmotic or pharmaceutical activation of TRPV4 regulates HDAC6-dependent modulation of ciliary tubulin and is anti-inflammatory. This study reveals for the first time, the potential of TRPV4 manipulation as a novel therapeutic mechanism to supress pro-inflammatory signalling and cartilage degradation.

Mechanical Stimulation: A Crucial Element of Organ-on-Chip Models

Organ-on-chip (OOC) systems recapitulate key biological processes and responses in vitro exhibited by cells, tissues, and organs in vivo. Accordingly, these models of both health and disease hold great promise for improving fundamental research, drug development, personalized medicine, and testing of pharmaceuticals, food substances, pollutants etc. Cells within the body are exposed to biomechanical stimuli, the nature of which is tissue specific and may change with disease or injury. These biomechanical stimuli regulate cell behavior and can amplify, annul, or even reverse the response to a given biochemical cue or drug candidate. As such, the application of an appropriate physiological or pathological biomechanical environment is essential for the successful recapitulation of in vivo behavior in OOC models. Here we review the current range of commercially available OOC platforms which incorporate active biomechanical stimulation. We highlight recent findings demonstrating the importance of including mechanical stimuli in models used for drug development and outline emerging factors which regulate the cellular response to the biomechanical environment. We explore the incorporation of mechanical stimuli in different organ models and identify areas where further research and development is required. Challenges associated with the integration of mechanics alongside other OOC requirements including scaling to increase throughput and diagnostic imaging are discussed. In summary, compelling evidence demonstrates that the incorporation of biomechanical stimuli in these OOC or microphysiological systems is key to fully replicating in vivo physiology in health and disease.

Solution-Processed Epitaxial Growth of Arbitrary Surface Nanopatterns on Hybrid Perovskite Monocrystalline Thin Films

Semiconductor surface patterning at the nanometer scale is crucial for high-performance optical, electronic, and photovoltaic devices. To date, surface nanostructures on organic-inorganic single-crystal perovskites have been achieved mainly through destructive methods such as electron-beam lithography and focused ion beam milling. Here, we present a solution-based epitaxial growth method for creating nanopatterns on the surface of perovskite monocrystalline thin films. We show that high-quality monocrystalline arbitrary nanopatterns can form in solution with a low-cost simple setup. We also demonstrate controllable photoluminescence from nanopatterned perovskite surfaces by adjusting the nanopattern parameters. A seven-fold enhancement in photoluminescence intensity and a three-time reduction of the surface radiative recombination lifetime are observed at room temperature for nanopatterned MAPbBr₃ monocrystalline thin films. Our findings are promising for the cost-effective fabrication of monocrystalline perovskite on-chip electronic and photonic circuits down to the nanometer scale with finely tunable optoelectronic properties.

Nanoscale Mapping Reveals Functional Differences in Ion Channels Populating the Membrane of Primary Cilia

BACKGROUND/AIMS

The primary cilium is a nanoscale membrane protrusion believed to act as a mechano-chemical sensor in a range of different cell types. Disruptions in its structure and signalling have been linked to a number of medical conditions, referred to as ciliopathies, but remain poorly understood due to lack of techniques capable of investigating signal transduction in cilia at nanoscale. Here we set out to use latest advances in nanopipette technology to address the question of ion channel distribution along the structure of primary cilium.

METHODS

We used glass nanopipettes and Scanning Ion Conductance Microscopy (SICM) to image 3D topography of intact primary cilia in inner medullary collecting duct (IMCD) cells with nanoscale resolution. The high-resolution topographical images were then used to navigate the nanopipette along the structure of each cilium and perform spatially resolved single-channel recordings under precisely controlled mechanical and chemical stimulation.

RESULTS

We have successfully obtained first single-channel recordings at specific locations of intact primary cilia. Our experiments revealed significant differences between the populations of channels present at the ciliary base, tip and within extra-ciliary regions in terms of mean conductance and sensitivity to membrane displacement as small as 100 nm. Ion channels at the base of cilium, where mechanical strain is expected to be the highest, appeared particularly sensitive to the mechanical displacement.

CONCLUSION

Our results suggest the distribution of ion channels in the membrane of primary cilia is non-homogeneous. The relationship between the location and function of ciliary ion channels could be key to understanding signal transduction in primary cilia.

Proteoglycan degradation mimics static compression by altering the natural gradients in fibrillar organisation in cartilage

Structural and associated biomechanical gradients within biological tissues are important for tissue functionality and preventing damaging interfacial stress concentrations. Articular cartilage possesses an inhomogeneous structure throughout its thickness, driving the associated variation in the biomechanical strain profile within the tissue under physiological compressive loading. However, little is known experimentally about the nanostructural mechanical role of the collagen fibrils and how this varies with depth. Utilising a high-brilliance synchrotron X-ray source, we have measured the depth-wise nanostructural parameters of the collagen network in terms of the periodic fibrillar banding (D-period) and associated parameters. We show that there is a depth dependent variation in D-period reflecting the pre-strain and concurrent with changes in the level of intrafibrillar order. Further, prolonged static compression leads to fibrillar changes mirroring those caused by removal of extrafibrillar proteoglycans (as may occur in aging or disease). We suggest that fibrillar D-period is a sensitive indicator of localised changes to the mechanical environment at the nanoscale in soft connective tissues.

Statement of Significance

Collagen plays a significant role in both the structural and mechanical integrity of articular cartilage, allowing the tissue to withstand highly repetitive loading. However, the fibrillar mechanics of the collagen network in cartilage are not clear. Here we find that cartilage has a spatial gradient in the nanostructural collagen fibril pre-strain, with an increase in the fibrillar pre-strain with depth. Further, the fibrillar gradient changes similarly under compression when compared to an enzymatically degraded tissue which mimics age-related changes. Given that the fibrils potentially have a finite capacity to mechanically respond and alter their configuration, these findings are significant in understanding how collagen may alter in structure and gradient in diseased cartilage, and in informing the design of cartilage replacements.

An in vitro investigation of the inflammatory response to the strain amplitudes which occur during high frequency oscillation ventilation and conventional mechanical ventilation

Children randomised in the neonatal period to high frequency oscillatory ventilation (HFOV) or conventional mechanical ventilation (CMV) in the United Kingdom Oscillation study (UKOS) had superior lung function at 11 to 14 years of age. During HFOV, much smaller tidal volumes, but a higher mean airway distending pressure is delivered, hence, a possible explanation for a volume dependent effect on long term lung function could be an increase in inflammation in response to higher tidal volumes and strains. We tested that hypothesis by assessing interleukin-6 (IL-6) and -8 (IL-8) release from A549 alveolar analogue cells following biaxial mechanical strain applied at 0.5 Hz occurring during conditions mimicking strain during CMV (5-20% strain) and conditions mimicking strain during HFOV (17.5% ± 2.5% strain) for up to 4 h. Cyclic strain of 5-20%, occurring during CMV, increased levels of both IL-6 and IL-8 compared to unstrained controls, while 17.5% ± 2.5% strain, occurring during HFOV, was associated with significantly lower levels of IL-6 (46.31 ± 2.66 versus 56.79 ± 3.73 pg/mL) and IL-8 (1340.2 ± 74.9 versus 2522 ± 248 pg/mL) secretion compared to conditions occurring during CMV at four hours. These results may provide a possible explanation for the superior lung function in 11-14-year-old children who had been supported in the neonatal period by HFOV.

Oncometabolite induced primary cilia loss in pheochromocytoma

Primary cilia are sensory organelles involved in regulation of cellular signaling. Cilia loss is frequently observed in tumors; yet, the responsible mechanisms and consequences for tumorigenesis remain unclear. We demonstrate that cilia structure and function is disrupted in human pheochromocytomas - endocrine tumors of the adrenal medulla. This is concomitant with transcriptional changes within cilia-mediated signaling pathways that are associated with tumorigenesis generally and pheochromocytomas specifically. Importantly, cilia loss was most dramatic in patients with germline mutations in the pseudohypoxia-linked genes SDHx and VHL. Using a pheochromocytoma cell line derived from rat, we show that hypoxia and oncometabolite-induced pseudohypoxia are key drivers of cilia loss and identify that this is dependent on activation of an Aurora-A/HDAC6 cilia resorption pathway. We also show cilia loss drives dramatic transcriptional changes associated with proliferation and tumorigenesis. Our data provide evidence for primary cilia dysfunction contributing to pathogenesis of pheochromocytoma by a hypoxic/pseudohypoxic mechanism and implicates oncometabolites as ciliary regulators. This is important as pheochromocytomas can cause mortality by mechanisms including catecholamine production and malignant transformation, while hypoxia is a general feature of solid tumors. Moreover, pseudohypoxia-induced cilia resorption can be pharmacologically inhibited, suggesting potential for therapeutic intervention.

Cobalt ions stimulate a fibrotic response through matrix remodelling, fibroblast contraction and release of pro-fibrotic signals from macrophages

Many studies report the adverse responses to metal-on-metal (MoM) hip prostheses, with tissues surrounding failed MoM hip prostheses revealing abundant tissue necrosis and fibrosis. These local effects appear to be initiated by metal ions released from the prosthesis causing the secretion of inflammatory mediators. However, little is known about the effect of the metal ions on tissue remodelling and pseudotumor formation, which are also associated with the failure of MoM hip prostheses. The peri-prosthetic soft tissue masses can lead to pain, swelling, limited range of joint movement and extensive tissue lesion. To elucidate this cellular response, a multidisciplinary approach using both two- and three-dimensional (2D and 3D) in vitro culture systems was employed to study the effects of Co2+ and Cr3+ on human fibroblast activation and mechanobiology. Co2+ induced a fibrotic response, characterised by cytoskeletal remodelling and enhanced collagen matrix contraction. This was associated with increased cell stiffness and contractile forces as measured by atomic force microscopy and traction force microscopy, respectively. These effects were triggered by the generation of reactive oxygen species (ROS). Moreover, this fibrotic response was enhanced in the presence of macrophages, which increased the prevalence of a-smooth muscle actin (a-SMA)-positive fibroblasts and collagen synthesis. Cr3+ did not show any significant effect on fibroblast activation. Co2+ promoted matrix remodelling by fibroblasts that was further enhanced by macrophage signalling. Use of alternative implant materials or manipulation of this fibrotic response could provide an opportunity for enhancing the success of prostheses utilising CoCr alloys.

Cobalt (II) ions and nanoparticles induce macrophage retention by ROS-mediated down-regulation of RhoA expression

Histological assessments of synovial tissues from patients with failed CoCr alloy hip prostheses demonstrate extensive infiltration and accumulation of macrophages, often loaded with large quantities of particulate debris. The resulting adverse reaction to metal debris (ARMD) frequently leads to early joint revision. Inflammatory response starts with the recruitment of immune cells and requires the egress of macrophages from the inflamed site for resolution of the reaction. Metal ions (Co²⁺ and Cr³⁺) have been shown to stimulate the migration of T lymphocytes but their effects on macrophages motility are still poorly understood. To elucidate this, we studied in vitro and in vivo macrophage migration during exposure to cobalt and chromium ions and nanoparticles. We found that cobalt but not chromium significantly reduces macrophage motility. This involves increase in cell spreading, formation of intracellular podosome-type adhesion structures and enhanced cell adhesion to the extracellular matrix (ECM). The formation of podosomes was also associated with the production and activation of matrix metalloproteinase-9 (MMP9) and enhanced ECM degradation. We showed that these were driven by the down-regulation of RhoA signalling through the generation of reactive oxygen species (ROS). These novel findings reveal the key mechanisms driving the wear/corrosion metallic byproducts-induced inflammatory response at non-toxic concentrations.

Statement of significance

Adverse tissue responses to metal wear and corrosion products from CoCr alloy implants remain a great challenge to surgeons and patients. Macrophages are the key regulators of these adverse responses to the ions and debris generated. We demonstrated that cobalt, rather than chromium, causes macrophage retention by restructuring the cytoskeleton and inhibiting cell migration via ROS production that affects Rho Family GTPase. This distinctive effect of cobalt on macrophage behaviour can help us understand the pathogenesis of ARMD and the cellular response to cobalt based alloys, which provide useful information for future implant design and biocompatibility testing.

Deconstruction of a Metastatic Tumor Microenvironment Reveals a Common Matrix Response in Human Cancers

We have profiled, for the first time, an evolving human metastatic microenvironment by measuring gene expression, matrisome proteomics, cytokine and chemokine levels, cellularity, extracellular matrix organization, and biomechanical properties, all on the same sample. Using biopsies of high-grade serous ovarian cancer metastases that ranged from minimal to extensive disease, we show how nonmalignant cell densities and cytokine networks evolve with disease progression. Multivariate integration of the different components allowed us to define, for the first time, gene and protein profiles that predict extent of disease and tissue stiffness, while also revealing the complexity and dynamic nature of matrisome remodeling during development of metastases. Although we studied a single metastatic site from one human malignancy, a pattern of expression of 22 matrisome genes distinguished patients with a shorter overall survival in ovarian and 12 other primary solid cancers, suggesting that there may be a common matrix response to human cancer.Significance: Conducting multilevel analysis with data integration on biopsies with a range of disease involvement identifies important features of the evolving tumor microenvironment. The data suggest that despite the large spectrum of genomic alterations, some human malignancies may have a common and potentially targetable matrix response that influences the course of disease. Cancer Discov; 8(3); 304-19. ©2017 AACR.This article is highlighted in the In This Issue feature, p. 253.

Tissue stiffening promotes keratinocyte proliferation via activation of epidermal growth factor signaling

Tissue biomechanics regulate a wide range of cellular functions, but the influences on epidermal homeostasis and repair remain unclear. Here, we examined the role of extracellular matrix stiffness on human keratinocyte behavior using elastomeric substrates with defined mechanical properties. Increased matrix stiffness beyond normal physiologic levels promoted keratinocyte proliferation but did not alter the ability to self-renew or terminally differentiate. Activation of epidermal growth factor (EGF) signaling mediated the proliferative response to matrix stiffness and depended on focal adhesion assembly and cytoskeletal tension. Comparison of normal skin with keloid scar tissue further revealed an up-regulation of EGF signaling within the epidermis of stiffened scar tissue. We conclude that matrix stiffness regulates keratinocyte proliferation independently of changes in cell fate and is mediated by EGF signaling. These findings provide mechanistic insights into how keratinocytes sense and respond to their mechanical environment and suggest that matrix biomechanics may play a role in the pathogenesis keloid scar formation.

The Secret Life of Collagen: Temporal Changes in Nanoscale Fibrillar Pre-Strain and Molecular Organization during Physiological Loading of Cartilage

Articular cartilage is a natural biomaterial whose structure at the micro- and nanoscale is critical for healthy joint function and where degeneration is associated with widespread disorders such as osteoarthritis. At the nanoscale, cartilage mechanical functionality is dependent on the collagen fibrils and hydrated proteoglycans that form the extracellular matrix. The dynamic response of these ultrastructural building blocks at the nanoscale, however, remains unclear. Here we measure time-resolved changes in collagen fibril strain, using small-angle X-ray diffraction during compression of bovine and human cartilage explants. We demonstrate the existence of a collagen fibril tensile pre-strain, estimated from the D-period at approximately 1-2%, due to osmotic swelling pressure from the proteoglycan. We reveal a rapid reduction and recovery of this pre-strain which occurs during stress relaxation, approximately 60 s after the onset of peak load. Furthermore, we show that this reduction in pre-strain is linked to disordering in the intrafibrillar molecular packing, alongside changes in the axial overlapping of tropocollagen molecules within the fibril. Tissue degradation in the form of selective proteoglycan removal disrupts both the collagen fibril pre-strain and the transient response during stress relaxation. This study bridges a fundamental gap in the knowledge describing time-dependent changes in collagen pre-strain and molecular organization that occur during physiological loading of articular cartilage. The ultrastructural details of this transient response are likely to transform our understanding of the role of collagen fibril nanomechanics in the biomechanics of cartilage and other hydrated soft tissues.

Chondrocyte expansion is associated with loss of primary cilia and disrupted hedgehog signalling

Tissue engineering-based therapies targeting cartilage diseases, such as osteoarthritis, require in vitro expansion of articular chondrocytes. A major obstacle for these therapies is the dedifferentiation and loss of phenotype accompanying chondrocyte expansion. Recent studies suggest that manipulation of hedgehog signalling may be used to promote chondrocyte re-differentiation. Hedgehog signalling requires the primary cilium, a microtubule-based signalling compartment, the integrity of which is linked to the cytoskeleton. We tested the hypothesis that alterations in cilia expression occurred as consequence of chondrocyte dedifferentiation and influenced hedgehog responsiveness. In vitro chondrocyte expansion to passage 5 (P5) was associated with increased actin stress fibre formation, dedifferentiation and progressive loss of primary cilia, compared to primary (P0) cells. P5 chondrocytes exhibited ~50 % fewer cilia with a reduced mean length. Cilia loss was associated with disruption of ligand-induced hedgehog signalling, such that P5 chondrocytes did not significantly regulate the expression of hedgehog target genes (GLI1 and PTCH1). This phenomenon could be recapitulated by applying 24 h cyclic tensile strain, which reduced cilia prevalence and length in P0 cells. LiCl treatment rescued cilia loss in P5 cells, partially restoring hedgehog signalling, so that GLI1 expression was significantly increased by Indian hedgehog. This study demonstrated that monolayer expansion disrupted primary cilia structure and hedgehog signalling associated with chondrocyte dedifferentiation. This excluded the possibility to use hedgehog ligands to stimulate re-differentiation without first restoring cilia expression. Furthermore, primary cilia loss during chondrocyte expansion would likely impact other cilia pathways important for cartilage health and tissue engineering, including transforming growth factor (TGF), Wnt and mechanosignalling.

Reduced primary cilia length and altered Arl13b expression are associated with deregulated chondrocyte Hedgehog signaling in alkaptonuria

Alkaptonuria (AKU) is a rare inherited disease resulting from a deficiency of the enzyme homogentisate 1,2-dioxygenase which leads to the accumulation of homogentisic acid (HGA). AKU is characterized by severe cartilage degeneration, similar to that observed in osteoarthritis. Previous studies suggest that AKU is associated with alterations in cytoskeletal organization which could modulate primary cilia structure/function. This study investigated whether AKU is associated with changes in chondrocyte primary cilia and associated Hedgehog signaling which mediates cartilage degradation in osteoarthritis. Human articular chondrocytes were obtained from healthy and AKU donors. Additionally, healthy chondrocytes were treated with HGA to replicate AKU pathology (+HGA). Diseased cells exhibited shorter cilia with length reductions of 36% and 16% in AKU and +HGA chondrocytes respectively, when compared to healthy controls. Both AKU and +HGA chondrocytes demonstrated disruption of the usual cilia length regulation by actin contractility. Furthermore, the proportion of cilia with axoneme breaks and bulbous tips was increased in AKU chondrocytes consistent with defective regulation of ciliary trafficking. Distribution of the Hedgehog-related protein Arl13b along the ciliary axoneme was altered such that its localization was increased at the distal tip in AKU and +HGA chondrocytes. These changes in cilia structure/trafficking in AKU and +HGA chondrocytes were associated with a complete inability to activate Hedgehog signaling in response to exogenous ligand. Thus, we suggest that altered responsiveness to Hedgehog, as a consequence of cilia dysfunction, may be a contributing factor in the development of arthropathy highlighting the cilium as a novel target in AKU.

Topography of calcium phosphate ceramics regulates primary cilia length and TGF receptor recruitment associated with osteogenesis

The surface topography of synthetic biomaterials is known to play a role in material-driven osteogenesis. Recent studies show that TGFβ signalling also initiates osteogenic differentiation. TGFβ signalling requires the recruitment of TGFβ receptors (TGFβR) to the primary cilia. In this study, we hypothesize that the surface topography of calcium phosphate ceramics regulates stem cell morphology, primary cilia structure and TGFβR recruitment to the cilium associated with osteogenic differentiation. We developed a 2D system using two types of tricalcium phosphate (TCP) ceramic discs with identical chemistry. One sample had a surface topography at micron-scale (TCP-B, with a bigger surface structure dimension) whilst the other had a surface topography at submicron scale (TCP-S, with a smaller surface structure dimension). In the absence of osteogenic differentiation factors, human bone marrow stromal cells (hBMSCs) were more spread on TCP-S than on TCP-B with alterations in actin organization and increased primary cilia prevalence and length. The cilia elongation on TCP-S was similar to that observed on glass in the presence of osteogenic media and was followed by recruitment of transforming growth factor-β RII (p-TGFβ RII) to the cilia axoneme. This was associated with enhanced osteogenic differentiation of hBMSCs on TCP-S, as shown by alkaline phosphatase activity and gene expression for key osteogenic markers in the absence of additional osteogenic growth factors. Similarly, in vivo after a 12-week intramuscular implantation in dogs, TCP-S induced bone formation while TCP-B did not. It is most likely that the surface topography of calcium phosphate ceramics regulates primary cilia length and ciliary recruitment of p-TGFβ RII associated with osteogenesis and bone formation. This bioengineering control of osteogenesis via primary cilia modulation may represent a new type of biomaterial-based ciliotherapy for orthopedic, dental and maxillofacial surgery applications.

STATEMENT OF SIGNIFICANCE

The surface topography of synthetic biomaterials plays important roles in material-driven osteogenesis. The data presented herein have shown that the surface topography of calcium phosphate ceramics regulates mesenchymal stromal cells (e.g., human bone marrow mesenchymal stromal cells, hBMSCs) with respect to morphology, primary cilia structure and TGFβR recruitment to the cilium associated with osteogenic differentiation in vitro. Together with bone formation in vivo, our results suggested a new type of biomaterial-based ciliotherapy for orthopedic, dental and maxillofacial surgery by the bioengineering control of osteogenesis via primary cilia modulation.

The 67P/Churyumov-Gerasimenko observation campaign in support of the Rosetta mission

We present a summary of the campaign of remote observations that supported the European Space Agency's Rosetta mission. Telescopes across the globe (and in space) followed comet 67P/Churyumov-Gerasimenko from before Rosetta's arrival until nearly the end of the mission in September 2016. These provided essential data for mission planning, large-scale context information for the coma and tails beyond the spacecraft and a way to directly compare 67P with other comets. The observations revealed 67P to be a relatively 'well-behaved' comet, typical of Jupiter family comets and with activity patterns that repeat from orbit to orbit. Comparison between this large collection of telescopic observations and the in situ results from Rosetta will allow us to better understand comet coma chemistry and structure. This work is just beginning as the mission ends-in this paper, we present a summary of the ground-based observations and early results, and point to many questions that will be addressed in future studies.This article is part of the themed issue 'Cometary science after Rosetta'.

Zonal variation in primary cilia elongation correlates with localized biomechanical degradation in stress deprived tendon

Tenocytes express primary cilia, which elongate when tendon is maintained in the absence of biomechanical load. Previous work indicates differences in the morphology and metabolism of the tenocytes in the tendon fascicular matrix (FM) and the inter-fascicular matrix (IFM). This study tests the hypothesis that primary cilia in these two regions respond differently to stress deprivation and that this is associated with differences in the biomechanical degradation of the extracellular matrix. Rat tail tendon fascicles were examined over a 7-day period of either stress deprivation or static load. Seven days of stress deprivation induced cilia elongation in both regions. However, elongation was greater in the IFM compared to the FM. Stress deprivation also induced a loss of biomechanical integrity, primarily in the IFM. Static loading reduced both the biomechanical degradation and cilia elongation. The different responses to stress deprivation in the two tendon regions are likely to be important for the aetiology of tendinopathy. Furthermore, these data suggest that primary cilia elongate in response to biomechanical degradation rather than simply the removal of load. This response to degradation is likely to have important consequences for cilia signalling in tendon and as well as in other connective tissues. © 2016 The Authors. Journal of Orthopaedic Research Published by Wiley Periodicals, Inc. on behalf of Orthopaedic Research Society. J Orthop Res 34:2146-2153, 2016.

Experimental validation of a flat punch indentation methodology calibrated against unconfined compression tests for determination of soft tissue biomechanics

Mechanical characterisation of soft biological tissues using standard compression or tensile testing presents a significant challenge due to specimen geometrical irregularities, difficulties in cutting intact and appropriately sized test samples, and issues with slippage or damage at the grips. Indentation can overcome these problems but requires fitting a model to the resulting load-displacement data in order to calculate moduli. Despite the widespread use of this technique, few studies experimentally validate their chosen model or compensate for boundary effects. In this study, viscoelastic hydrogels of different concentrations and dimensions were used to calibrate an indentation technique performed at large specimen-strain deformation (20%) and analysed with a range of routinely used mathematical models. A rigid, flat-ended cylindrical indenter was applied to each specimen from which 'indentation moduli' and relaxation properties were calculated and compared against values obtained from unconfined compression. Only one indentation model showed good agreement (<10% difference) with all moduli values obtained from compression. A sample thickness to indenter diameter ratio ≥1:1 and sample diameter to indenter diameter ratio ≥4:1 was necessary to achieve the greatest accuracy. However, it is not always possible to use biological samples within these limits, therefore we developed a series of correction factors. The approach was validated using human diseased omentum and bovine articular cartilage resulting in mechanical properties closely matching compression values. We therefore present a widely useable indentation analysis method to allow more accurate calculation of material mechanics which is important in the study of soft tissue development, ageing, health and disease.

Chondrocyte dedifferentiation increases cell stiffness by strengthening membrane-actin adhesion

OBJECTIVE

Chondrocyte dedifferentiation is known to influence cell mechanics leading to alterations in cell function. This study examined the influence of chondrocyte dedifferentiation in monolayer on cell viscoelastic properties and associated changes in actin organisation, bleb formation and membrane-actin cortex interaction.

METHOD

Micropipette aspiration was used to estimate the viscoelastic properties of freshly isolated articular chondrocytes and the same cells after passage in monolayer. Studies quantified the cell membrane-actin cortex adhesion by measuring the critical pressure required for membrane detachment and bleb formation. We then examined the expression of ezrin, radixin and moesin (ERM) proteins which are involved in linking the membrane and actin cortex and combined this with theoretical modelling of bleb dynamics.

RESULTS

Dedifferentiated chondrocytes at passage 1 (P1) were found to be stiffer compared to freshly isolated chondrocytes (P0), with equilibrium modulus values of 0.40 and 0.16 kPa respectively. The critical pressure increased from 0.59 kPa at P0 to 0.74 kPa at P1. Dedifferentiated cells at P1 exhibited increased cortical F-actin organisation and increased expression of total and phosphorylated ERM proteins compared to cells at P0. Theoretical modelling confirmed the importance of membrane-actin cortex adhesion in regulating bleb formation and effective cellular elastic modulus.

CONCLUSION

This study demonstrates that chondrocyte dedifferentiation in monolayer strengthens membrane-actin cortex adhesion associated with increased F-actin organisation and up-regulation of ERM protein expression. Thus dedifferentiated cells have reduced susceptibility to bleb formation which increases cell modulus and may also regulate other fundamental aspects of cell function such as mechanotransduction and migration.

Adipogenic Differentiation of hMSCs is Mediated by Recruitment of IGF-1r Onto the Primary Cilium Associated With Cilia Elongation

Primary cilia are single non‐motile organelles that provide a highly regulated compartment into which specific proteins are trafficked as a critical part of various signaling pathways. The absence of primary cilia has been shown to prevent differentiation of human mesenchymal stem cells (hMSCs). Changes in primary cilia length are crucial for regulating signaling events; however it is not known how alterations in cilia structure relate to differentiation. This study tested the hypothesis that changes in primary cilia structure are required for stem cell differentiation. hMSCs expressed primary cilia that were labeled with acetylated alpha tubulin and visualized by confocal microscopy. Chemically induced differentiation resulted in lineage specific changes in cilia length and prevalence which were independent of cell cycle. In particular, adipogenic differentiation resulted in cilia elongation associated with the presence of dexamethasone, while insulin had an inhibitory effect on cilia length. Over a 7‐day time course, adipogenic differentiation media resulted in cilia elongation within 2 days followed by increased nuclear PPARγ levels; an early marker of adipogenesis. Cilia elongation was associated with increased trafficking of insulin‐like growth factor‐1 receptor β (IGF‐1Rβ) into the cilium. This was reversed on inhibition of elongation by IFT‐88 siRNA transfection, which also decreased nuclear PPARγ. This is the first study to show that adipogenic differentiation requires primary cilia elongation associated with the recruitment of IGF‐1Rβ onto the cilium. This study may lead to the development of cilia‐targeted therapies for controlling adipogenic differentiation and associated conditions such as obesity. Stem Cells2015;33:1952–1961

Differential effects of LifeAct-GFP and actin-GFP on cell mechanics assessed using micropipette aspiration

The actin cytoskeleton forms a dynamic structure involved in many fundamental cellular processes including the control of cell morphology, migration and biomechanics. Recently LifeAct-GFP (green fluorescent protein) has been proposed for visualising actin structure and dynamics in live cells as an alternative to actin-GFP which has been shown to affect cell mechanics. Here we compare the two approaches in terms of their effect on cellular mechanical behaviour. Human mesenchymal stem cells (hMSCs) were analysed using micropipette aspiration and the effective cellular equilibrium and instantaneous moduli calculated using the standard linear solid model. We show that LifeAct-GFP provides clearer visualisation of F-actin organisation and dynamics. Furthermore, LifeAct-GFP does not alter effective cellular mechanical properties whereas actin-GFP expression causes an increase in the cell modulus. Interestingly, LifeAct-GFP expression did produce a small (~10%) increase in the percentage of cells exhibiting aspiration-induced membrane bleb formation, whilst actin-GFP expression reduced blebbing. Further studies examined the influence of LifeAct-GFP in other cell types, namely chondrogenically differentiated hMSCs and murine chondrocytes. LifeAct-GFP also had no effect on the moduli of these non-blebbing cells for which mechanical properties are largely dependent on the actin cortex. In conclusion we show that LifeAct-GFP enables clearer visualisation of actin organisation and dynamics without disruption of the biomechanical properties of either the whole cell or the actin cortex. Thus the study provides new evidence supporting the use of LifeAct-GFP rather than actin-GFP for live cell microscopy and the study of cellular mechanobiology.

Hedgehog signalling does not stimulate cartilage catabolism and is inhibited by Interleukin-1β

Background

In osteoarthritis, chondrocytes adopt an abnormal hypertrophic morphology and upregulate the expression of the extracellular matrix-degrading enzymes, MMP-13 and ADAMTS-5. The activation of the hedgehog signalling pathway has been established in osteoarthritis and is thought to influence both of these processes. However, the role of this pathway in the initiation and progression of osteoarthritis is unclear as previous studies have been unable to isolate the effects of hedgehog pathway activation from other pathological processes. In this study we test the hypothesis that hedgehog pathway activation causes cartilage degradation in healthy cartilage and in an in vitro model of inflammatory arthritis.

Methods

Isolated articular chondrocytes from the bovine metacarpal-phalangeal joint were stimulated for up to 24 hours with the agonist, recombinant Indian hedgehog (r-Ihh). ADAMTS-5 and MMP-13 gene expression was quantified by real-time PCR. In addition, healthy bovine cartilage explants were treated with r-Ihh or the hedgehog antagonist, cyclopamine, and sGAG release into the media was measured over 72 hours. Studies were repeated using chondrocytes and cartilage explants from human knee joint. Finally, studies were conducted to determine the effect of hedgehog pathway activation on matrix catabolism in the presence of the pro-inflammatory cytokine, IL-1β.

Results

Addition of r-Ihh activated hedgehog signalling, confirmed by upregulation of Gli1 and Ptch1 expression, but did not increase ADAMTS-5 or MMP-13 expression in bovine or human chondrocytes. Furthermore, r-Ihh did not induce sGAG release in healthy bovine or human cartilage explants. IL-1β treatment induced sGAG release, but this response was not altered by the stimulation or inhibition of hedgehog signalling. Hedgehog pathway activation was downregulated by IL-1β. Conversely, r-Ihh weakly suppressed IL-1β-induced ADAMTS-5 expression.

Conclusion

Our results show for the first time that Indian hedgehog does not cause extracellular matrix degradation in healthy ex vivo cartilage or in the presence of IL-1β and that IL-1β downregulates Indian hedgehog induced signalling. Thus, we suggest reported hedgehog induced matrix catabolism in osteoarthritis must be due to its interaction with pathological factors other than IL-1β. Hence, hedgehog signalling and its downstream effects are highly context-dependent.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-015-0891-z) contains supplementary material, which is available to authorized users.

Cytokine preconditioning of engineered cartilage provides protection against interleukin-1 insult

BACKGROUND

During osteoarthritis and following surgical procedures, the environment of the knee is rich in proinflammatory cytokines such as IL-1. Introduction of tissue-engineered cartilage constructs to a chemically harsh milieu may limit the functionality of the implanted tissue over long periods. A chemical preconditioning scheme (application of low doses of IL-1) was tested as a method to prepare developing engineered tissue to withstand exposure to a higher concentration of the cytokine, known to elicit proteolysis as well as rapid degeneration of cartilage.

METHODS

Using an established juvenile bovine model system, engineered cartilage was preconditioned with low doses of IL-1α (0.1 ng/mL, 0.5 ng/mL, and 1.0 ng/mL) for 7 days before exposure to an insult dose (10 ng/mL). The time frame over which this protection is afforded was investigated by altering the amount of time between preconditioning and insult as well as the time following insult. To explore a potential mechanism for this protection, one set of constructs was preconditioned with CoCl2, a chemical inducer of hypoxia, before exposure to the IL-1α insult. Finally, we examined the translation of this preconditioning method to extend to clinically relevant adult, passaged chondrocytes from a preclinical canine model.

RESULTS

Low doses of IL-1α (0.1 ng/mL and 0.5 ng/mL) protected against subsequent catabolic degradation by cytokine insult, preserving mechanical stiffness and biochemical composition. Regardless of amount of time between preconditioning scheme and insult, protection was afforded. In a similar manner, preconditioning with CoCl2 similarly allowed for mediation of catabolic damage by IL-1α. The effects of preconditioning on clinically relevant adult, passaged chondrocytes from a preclinical canine model followed the same trends with low-dose IL-1β offering variable protection against insult.

CONCLUSIONS

Chemical preconditioning schemes have the ability to protect engineered cartilage constructs from IL-1-induced catabolic degradation, offering potential modalities for therapeutic treatments.

Lithium chloride prevents interleukin-1β induced cartilage degradation and loss of mechanical properties

Osteoarthritis is a chronic degenerative disease that affects the articular cartilage. Recent studies have demonstrated that lithium chloride exhibits significant efficacy as a chondroprotective agent, blocking cartilage degradation in response to inflammatory cytokines. However, conflicting literature suggests lithium may affect the physicochemical properties of articular cartilage and thus long-term exposure may negatively affect the mechanical functionality of this tissue. This study aims to investigate the effect of lithium chloride on the biomechanical properties of healthy and interleukin-1β treated cartilage in vitro and examines the consequences of long-term exposure to lithium on cartilage health in vivo. Bovine cartilage explants were treated with lithium chloride for 12 days. Chondrocyte viability, matrix catabolism and the biomechanical properties of bovine cartilage explants were not significantly altered following treatment. Consistent with these findings, long term-exposure (9 months) to dietary lithium did not induce osteoarthritis in rats, as determined by histological staining. Moreover, lithium chloride did not induce the expression of catabolic enzymes in human articular chondrocytes. In an inflammatory model of cartilage destruction, lithium chloride blocked interleukin-1β signaling in the form of nitric oxide and prostaglandin E2 release and prevented matrix catabolism such that the loss of mechanical integrity observed with interleukin-1β alone was inhibited. This study provides further support for lithium chloride as a novel compound for the treatment of osteoarthritis.

The primary cilium influences interleukin-1β-induced NFκB signalling by regulating IKK activity

The primary cilium is an organelle acting as a master regulator of cellular signalling. We have previously shown that disruption of primary cilia assembly, through targeting intraflagellar transport, is associated with muted nitric oxide and prostaglandin responses to the inflammatory cytokine interleukin-1β (IL-1β). Here, we show that loss of the primary cilium disrupts specific molecular signalling events in cytosolic NFκB signalling. The induction of cyclooxygenase 2 (COX2) and inducible nitrous oxide synthase (iNOS) protein is abolished. Cells unable to assemble cilia exhibit unaffected activation of IκB kinase (IKK), but delayed and reduced degradation of IκB, due to diminished phosphorylation of inhibitor of kappa B (IκB) by IKK. This results in both delayed and reduced NFκB p65 nuclear translocation and nuclear transcript binding. We also demonstrate that heat shock protein 27 (hsp27), an established regulator of IKK, is localized to the ciliary axoneme and cellular levels are dramatically disrupted with loss of the primary cilium. These results suggest that the primary cilia compartment exerts influence over NFκB signalling. We propose that the cilium is a locality for regulation of the molecular events defining NFκB signalling events, tuning signalling as appropriate.

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Hypermorphic mutation of IFT88 results in partial loss of the primary cilium.

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Cilia loss leads to inhibition of COX2 and iNOS induction in response to IL-1.

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In cells without cilia, IKK is activated but does not phosphorylate IκB.

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This leads to sustained IκB expression, and reduced and mistimed NFκB signalling.

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We propose the cilium to be a location for hsp27 regulation of IKK activity.

Interleukin-1β sequesters hypoxia inducible factor 2α to the primary cilium

BACKGROUND

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

Primary 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;ift88(fl/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;ift88(fl/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.

Stent encrustation in feline and human artificial urine: does the low molecular weight composition account for the difference?

Anecdotal evidence suggests that the rate of encrustation on JJ stents placed in domesticated cats appears to be decreased as compared to humans. Our study tests the hypothesis that this may be due to specific differences in the chemical composition of human and feline urine. Artificial human and feline urine solutions were used in an in vitro encrustation model where an 80 % stent encrustation could be expected after 7 weeks of incubation. Scanning electron microscopy (SEM) was used to analyse crystal morphology. Energy dispersive X-ray spectrometry (EDS) was used to assess composition weight. The percentage of surface coverage of encrustation on the respective stents was quantified using image J Java plug-in software. No significant difference was observed between both solutions with regard to quality and quantity of stent encrustation. Crystals were formed in both solutions as a mixture of Ca-dihydrate and Ca-monohydrate. The study shows that there is no significant difference in the rate of encrustations on JJ stents incubated in artificial feline or human urine. This suggests that a possible difference in stent encrustation between cats and humans is due to factors other than the inorganic biochemical composition of the urines alone. Keeping in mind a true species difference, analysis of urinary macromolecules and proteins will be the logical next step.

Quantification of chromatin condensation level by image processing

The level of chromatin condensation is related to the silencing/activation of chromosomal territories and therefore impacts on gene expression. Chromatin condensation changes during cell cycle, progression and differentiation, and is influenced by various physicochemical and epigenetic factors. This study describes a validated experimental technique to quantify chromatin condensation. A novel image processing procedure is developed using Sobel edge detection to quantify the level of chromatin condensation from nuclei images taken by confocal microscopy. The algorithm was developed in MATLAB and used to quantify different levels of chromatin condensation in chondrocyte nuclei achieved through alteration in osmotic pressure. The resulting chromatin condensation parameter (CCP) is in good agreement with independent multi-observer qualitative visual assessment. This image processing technique thereby provides a validated unbiased parameter for rapid and highly reproducible quantification of the level of chromatin condensation.

Osmotic challenge drives rapid and reversible chromatin condensation in chondrocytes

Changes in extracellular osmolality have been shown to alter gene expression patterns and metabolic activity of various cell types, including chondrocytes. However, mechanisms by which physiological or pathological changes in osmolality impact chondrocyte function remain unclear. Here we use quantitative image analysis, electron microscopy, and a DNase I assay to show that hyperosmotic conditions (>400 mOsm/kg) induce chromatin condensation, while hypoosmotic conditions (100 mOsm/kg) cause decondensation. Large density changes (p < 0.001) occur over a very narrow range of physiological osmolalities, which suggests that chondrocytes likely experience chromatin condensation and decondensation during a daily loading cycle. The effect of changes in osmolality on nuclear morphology (p < 0.01) and chromatin condensation (p < 0.001) also differed between chondrocytes in monolayer culture and three-dimensional agarose, suggesting a role for cell adhesion. The relationship between condensation and osmolality was accurately modeled by a polymer gel model which, along with the rapid nature of the chromatin condensation (<20 s), reveals the basic physicochemical nature of the process. Alterations in chromatin structure are expected to influence gene expression and thereby regulate chondrocyte activity in response to osmotic changes.

Cell mechanics, structure, and function are regulated by the stiffness of the three-dimensional microenvironment

This study adopts a combined computational and experimental approach to determine the mechanical, structural, and metabolic properties of isolated chondrocytes cultured within three-dimensional hydrogels. A series of linear elastic and hyperelastic finite-element models demonstrated that chondrocytes cultured for 24 h in gels for which the relaxation modulus is <5 kPa exhibit a cellular Young's modulus of ∼5 kPa. This is notably greater than that reported for isolated chondrocytes in suspension. The increase in cell modulus occurs over a 24-h period and is associated with an increase in the organization of the cortical actin cytoskeleton, which is known to regulate cell mechanics. However, there was a reduction in chromatin condensation, suggesting that changes in the nucleus mechanics may not be involved. Comparison of cells in 1% and 3% agarose showed that cells in the stiffer gels rapidly develop a higher Young's modulus of ∼20 kPa, sixfold greater than that observed in the softer gels. This was associated with higher levels of actin organization and chromatin condensation, but only after 24 h in culture. Further studies revealed that cells in stiffer gels synthesize less extracellular matrix over a 28-day culture period. Hence, this study demonstrates that the properties of the three-dimensional microenvironment regulate the mechanical, structural, and metabolic properties of living cells.