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 ± IL1ß. Nitric oxide (NO) and prostaglandin E2 (PGE2) release were measured to monitor IL1ß 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 IL1ß-induced release of NO and PGE2, in isolated chondrocytes. Treatment with LPA also inhibited IL1ß-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 IL1ß 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).

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.

Frequency-modulated atomic force microscopy localises viscoelastic remodelling in the ageing sheep aorta.

Age-related aortic stiffening is associated with cardiovascular diseases such as heart failure. The mechanical functions of the main structural components of the aorta, such as collagen and elastin, are determined in part by their organisation at the micrometer length scale. With age and disease both components undergo aberrant remodelling, hence, there is a need for accurate characterisation of the biomechanical properties at this length scale. In this study we used a frequency-modulated atomic force microscopy (FM-AFM) technique on a model of ageing in female sheep aorta (young: ~18 months, old: >8 years) to measure the micromechanical properties of the medial layer of the ascending aorta. The novelty of our FM-AFM method, operated at 30kHz, is that it is non-contact and can be performed on a conventional AFM using the ×³cantilever tune' mode, with a spatial (areal) resolution of around 1.6µm(2). We found significant changes in the elastic and viscoelastic properties within the medial lamellar unit (elastic lamellae and adjacent inter-lamellar space) with age. In particular, there was an increase in elastic modulus (Young; geometric mean (geometric SD)=42.9 (2.26)kPa, Old=113.9 (2.57)kPa, P<0.0001), G' and G″ (storage and loss modulus respectively) (Young; G'=14.3 (2.26)kPa, Old G'=38.0 (2.57)kPa, P<0.0001; Young; G″=14.5 (2.56)kPa, Old G″=32.8 (2.52)kPa, P<0.0001). The trends observed in the elastic properties with FM-AFM matched those we have previously found using scanning acoustic microscopy (SAM). The utility of the FM-AFM method is that it does not require custom AFM hardware and can be used to simultaneously determine the elastic and viscoelastic behaviour of a biological sample.