Mathematical modelling of cytokines, MMPs and fibronectin fragments in osteoarthritic cartilage

Diffusive mediator feedbacks control the health-to-disease transition of skin inflammation

The spatiotemporal dynamics of inflammation provide vital insights into the understanding of skin inflammation. Skin inflammation primarily depends on the regulatory feedback between pro- and anti-inflammatory mediators. Healthy skin exhibits fading erythema. In contrast, diseased skin exhibits expanding erythema with diverse patterns, which are clinically classified into five types: circular, annular, arcuate, gyrate, and polycyclic. Inflammatory diseases with expanding erythema are speculated to result from the overproduction of pro-inflammatory mediators. However, the mechanism by which feedback selectively drives the transition from a healthy fading erythema to each of the five types of diseased expanding erythema remains unclear. This study theoretically elucidates the imbalanced production between pro- and anti-inflammatory mediators and prospective treatment strategies for each expanding pattern. Our literature survey showed that eleven diseases exhibit some of the five expanding erythema, thereby suggesting a common spatiotemporal regulation underlying different patterns and diseases. Accordingly, a reaction-diffusion model incorporating mediator feedback reproduced the five observed types of diseased expanding and healthy fading patterns. Importantly, the fading pattern transitioned to the arcuate, gyrate, and polycyclic patterns when the productions of anti-inflammatory and pro-inflammatory mediators were lower and higher, respectively than in the healthy condition. Further depletion of anti-inflammatory mediators caused a circular pattern, whereas further overproduction of pro-inflammatory mediators caused an annular pattern. Mechanistically, the bistability due to stabilization of the diseased state exhibits circular and annular patterns, whereas the excitability exhibits the gyrate, polycyclic, arcuate, and fading patterns as the threshold of pro-inflammatory mediator concentration relative to the healthy state increases. These dynamic regulations of diffusive mediator feedback provide effective treatment strategies for mediator production wherein skins recover from each expanding pattern toward a fading pattern. Thus, these strategies can estimate disease severity and risk based on erythema patterns, paving the way for developing noninvasive and personalized treatments for inflammatory skin diseases.

A dynamical model of TGF-β activation in asthmatic airways

Excessive activation of the regulatory cytokine transforming growth factor $\beta $ (TGF-$\beta $) via contraction of airway smooth muscle (ASM) is associated with the development of asthma. In this study, we develop an ordinary differential equation model that describes the change in density of the key airway wall constituents, ASM and extracellular matrix (ECM), and their interplay with subcellular signalling pathways leading to the activation of TGF-$\beta $. We identify bistable parameter regimes where there are two positive steady states, corresponding to either reduced or elevated TGF-$\beta $ concentration, with the latter leading additionally to increased ASM and ECM density. We associate the former with a healthy homeostatic state and the latter with a diseased (asthmatic) state. We demonstrate that external stimuli, inducing TGF-$\beta $ activation via ASM contraction (mimicking an asthmatic exacerbation), can perturb the system irreversibly from the healthy state to the diseased one. We show that the properties of the stimuli, such as their frequency or strength, and the clearance of surplus active TGF-$\beta $, are important in determining the long-term dynamics and the development of disease. Finally, we demonstrate the utility of this model in investigating temporal responses to bronchial thermoplasty, a therapeutic intervention in which ASM is ablated by applying thermal energy to the airway wall. The model predicts the parameter-dependent threshold damage required to obtain irreversible reduction in ASM content, suggesting that certain asthma phenotypes are more likely to benefit from this intervention.

A chemo-mechano-biological modeling framework for cartilage evolving in health, disease, injury, and treatment

BACKGROUND AND OBJECTIVE

Osteoarthritis (OA) is a pervasive and debilitating disease, wherein degeneration of cartilage features prominently. Despite extensive research, we do not yet understand the cause or progression of OA. Studies show biochemical, mechanical, and biological factors affect cartilage health. Mechanical loads influence synthesis of biochemical constituents which build and/or break down cartilage, and which in turn affect mechanical loads. OA-associated biochemical profiles activate cellular activity that disrupts homeostasis. To understand the complex interplay among mechanical stimuli, biochemical signaling, and cartilage function requires integrating vast research on experimental mechanics and mechanobiology-a task approachable only with computational models. At present, mechanical models of cartilage generally lack chemo-biological effects, and biochemical models lack coupled mechanics, let alone interactions over time.

METHODS

We establish a first-of-its kind virtual cartilage: a modeling framework that considers time-dependent, chemo-mechano-biologically induced turnover of key constituents resulting from biochemical, mechanical, and/or biological activity. We include the "minimally essential" yet complex chemical and mechanobiological mechanisms. Our 3-D framework integrates a constitutive model for the mechanics of cartilage with a novel model of homeostatic adaptation by chondrocytes to pathological mechanical stimuli, and a new application of anisotropic growth (loss) to simulate degradation clinically observed as cartilage thinning.

RESULTS

Using a single set of representative parameters, our simulations of immobilizing and overloading successfully captured loss of cartilage quantified experimentally. Simulations of immobilizing, overloading, and injuring cartilage predicted dose-dependent recovery of cartilage when treated with suramin, a proposed therapeutic for OA. The modeling framework prompted us to add growth factors to the suramin treatment, which predicted even better recovery.

CONCLUSIONS

Our flexible framework is a first step toward computational investigations of how cartilage and chondrocytes mechanically and biochemically evolve in degeneration of OA and respond to pharmacological therapies. Our framework will enable future studies to link physical activity and resulting mechanical stimuli to progression of OA and loss of cartilage function, facilitating new fundamental understanding of the complex progression of OA and elucidating new perspectives on causes, treatments, and possible preventions.

Disturbances in Metabolic Pathways and the Identification of a Potential Biomarker Panel for Early Cartilage Degeneration in a Rabbit Anterior Cruciate Ligament Transection Model

OBJECTIVE

This study aimed to assess the association between synovial fluid (SF) metabolites and magnetic resonance imaging (MRI) measurements of cartilage biochemical composition to identify potential SF biomarkers for detecting the early onset of cartilage degeneration in a rabbit model.

METHODS

Both knees of 12 New Zealand White rabbits were used. The anterior cruciate ligament transection (ACLT) model was performed on right knees, and the sham surgery on left knees. MRI UTE-T2* scanning and SF sample collection were performed on ACLT knees at 4 and 8 weeks postsurgery and on sham surgery knees at 4 weeks postsurgery. Ultra-performance liquid chromatography-mass spectrometry and multivariate statistical analysis were used to distinguish samples in three groups. Pathway and receiver operating characteristic analyses were utilized to identify potential metabolite biomarkers.

RESULTS

There were 12 knees in sham surgery models, 11 in ACLT models at 4 weeks postsurgery, and 10 in ACLT models at 8 weeks postsurgery. UTE-T2* values for the lateral tibia cartilage showed significant decreases over the study period. Levels of 103 identified metabolites in SF were markedly different among three groups. Furthermore, 24 metabolites were inversely correlated with UTE-T2* values of the lateral tibia cartilage, while hippuric acid was positively correlated with UTE-T2* values of the lateral tibia cartilage. Among 25 potential markers, N1-acetylspermidine, 2-amino-1,3,4-octadecanetriol, l-phenylalanine, 5-hydroxy-l-tryptophan, and l-tryptophan were identified as potential biomarkers with high area under the curve values and Pearson correlation coefficients.

CONCLUSION

Five differential metabolites in SF were found as potential biomarkers for the early detection of cartilage degeneration in the rabbit ACLT model.

Cartilage Protective and Immunomodulatory Features of Osteoarthritis Synovial Fluid-Treated Adipose-Derived Mesenchymal Stem Cells Secreted Factors and Extracellular Vesicles-Embedded miRNAs

Intra-articular administration of adipose-derived mesenchymal stem cells (ASCs), either in vitro expanded or within adipose tissue-based products obtained at point-of-care, has gained popularity as innovative regenerative medicine approach for osteoarthritis (OA) treatment. ASCs can stimulate tissue repair and immunomodulation through paracrine factors, both soluble and extracellular vesicles (EV) embedded, collectively defining the secretome. Interaction with the degenerative/inflamed environment is a crucial factor in understanding the finely tuned molecular message but, to date, the majority of reports have described ASC-secretome features in resting conditions or under chemical stimuli far from the in vivo environment of degenerated OA joints. In this report, the secretory profile of ASCs treated with native synovial fluid from OA patients was evaluated, sifting 200 soluble factors and 754 EV-embedded miRNAs. Fifty-eight factors and 223 EV-miRNAs were identified, and discussed in the frame of cartilage and immune cell homeostasis. Bioinformatics gave a molecular basis for M2 macrophage polarization, T cell proliferation inhibition and T reg expansion enhancement, as well as cartilage protection, further confirmed in an in vitro model of OA chondrocytes. Moreover, a strong influence on immune cell chemotaxis emerged. In conclusion, obtained molecular data support the regenerative and immunomodulatory properties of ASCs when interacting with osteoarthritic joint environment.

Macroscale mesenchymal condensation to study cytokine-driven cellular and matrix-related changes during cartilage degradation

Understanding the pathophysiological processes of cartilage degradation requires adequate model systems to develop therapeutic strategies towards osteoarthritis (OA). Although different in vitro or in vivo models have been described, further comprehensive approaches are needed to study specific disease aspects. This study aimed to combine in vitro and in silico modeling based on a tissue-engineering approach using mesenchymal condensation to mimic cytokine-induced cellular and matrix-related changes during cartilage degradation. Thus, scaffold-free cartilage-like constructs (SFCCs) were produced based on self-organization of mesenchymal stromal cells (mesenchymal condensation) and (i) characterized regarding their cellular and matrix composition or secondly (ii) treated with interleukin-1β (IL-1β) and tumor necrosis factor α (TNFα) for 3 weeks to simulate OA-related matrix degradation. In addition, an existing mathematical model based on partial differential equations was optimized and transferred to the underlying settings to simulate the distribution of IL-1β, type II collagen degradation and cell number reduction. By combining in vitro and in silico methods, we aimed to develop a valid, efficient alternative approach to examine and predict disease progression and effects of new therapeutics.

Anti‑chondrocyte apoptosis effect of genistein in treating inflammation‑induced osteoarthritis

Osteoarthritis (OA) is a chronic disease that is mainly characterized by chondrocyte degeneration. Inflammatory mediators participate in the development of OA, leading to chondrocyte apoptosis and destruction of the cartilage. Genistein is the major active component of isoflavone, with a chemical composition and a biological effect that is similar to that of estrogens, which prevents the degradation of cartilage; however, its underlying mechanisms of action remain unknown. The aim of the present study was to investigate the anti-apoptotic effects of genistein on chondrocytes for the treatment of inflammation-induced OA. Interleukin (IL)-1β was used to establish a chondrocyte OA model. After treatment with different concentrations of genistein, western blotting identified that expression levels of collagen II and aggrecan were increased in a concentration-dependent manner, while caspase 3 expression gradually decreased after genistein application. Moreover, flow cytometry and ELISA results demonstrated that genistein could decrease chondrocyte apoptosis and reduce the levels of tumor necrosis factor (TNF)-α in a dose-dependent manner. Furthermore, the in vitro data were evaluated in an OA rat model. Genistein increased the collagen and acid glycosaminoglycan content, as well as decreased the levels of TNF-α and IL-1β. Genistein also promoted the expression levels of collagen II and aggrecan in the articular cartilage, and decreased the expression of caspase 3, thus alleviating cartilage degradation. In conclusion, the results indicated that genistein mediated inflammation and had an anti-apoptotic role in treating OA. Therefore, genistein may serve as an alternative treatment for OA.

Profile of Matrix-Remodeling Proteinases in Osteoarthritis: Impact of Fibronectin

The extracellular matrix (ECM) is a complex and specialized three-dimensional macromolecular network, present in nearly all tissues, that also interacts with cell surface receptors on joint resident cells. Changes in the composition and physical properties of the ECM lead to the development of many diseases, including osteoarthritis (OA). OA is a chronic degenerative rheumatic disease characterized by a progressive loss of synovial joint function as a consequence of the degradation of articular cartilage, also associated with alterations in the synovial membrane and subchondral bone. During OA, ECM-degrading enzymes, including urokinase-type plasminogen activator (uPA), matrix metalloproteinases (MMPs), and a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTSs), cleave ECM components, such as fibronectin (Fn), generating fibronectin fragments (Fn-fs) with catabolic properties. In turn, Fn-fs promote activation of these proteinases, establishing a degradative and inflammatory feedback loop. Thus, the aim of this review is to update the contribution of ECM-degrading proteinases to the physiopathology of OA as well as their modulation by Fn-fs.

Moderate Fluid Shear Stress Could Regulate the Cytoskeleton of Nucleus Pulposus and Surrounding Inflammatory Mediators by Activating the FAK-MEK5-ERK5-cFos-AP1 Signaling Pathway

We first applied moderate fluid shear stress to nucleus pulposus cells. The correlation of AP-1 with type II collagen, proteoglycan, Cytokeratin 8 protein, MAP-1, MAP-2, and MAP-4 and the correlation of AP-1 with IL-1β, TNF-α, IL-6, IL-8, MIP-1, MCP-1, and NO were detected. Our results document that moderate fluid shear stress could activate the FAK-MEK5-ERK5-cFos-AP1 signaling pathway. AP1 could downregulate the construct factors of cytoskeleton such as type II collagen, proteoglycan, Cytokeratin 8 protein, MAP-1, MAP-2, and MAP-4 in nucleus pulposus cell after the fluid shear stress was loaded. AP1 could upregulate the inflammatory factors such as IL-1β, TNF-α, IL-6, IL-8, MIP-1, MCP-1, and NO in nucleus pulposus cell after the fluid shear stress was loaded. Taken together, our data suggested that moderate fluid shear stress may play an important role in the cytoskeleton of nucleus pulposus and surrounding inflammatory mediators by activating the FAK-MEK5-ERK5-cFos-AP1 signaling pathway, thereby affecting cell degeneration.

Fragments generated upon extracellular matrix remodeling: Biological regulators and potential drugs

The remodeling of the extracellular matrix (ECM) by several protease families releases a number of bioactive fragments, which regulate numerous biological processes such as autophagy, angiogenesis, adipogenesis, fibrosis, tumor growth, metastasis and wound healing. We review here the proteases which generate bioactive ECM fragments, their ECM substrates, the major bioactive ECM fragments, together with their biological properties and their receptors. The translation of ECM fragments into drugs is challenging and would take advantage of an integrative approach to optimize the design of pre-clinical and clinical studies. This could be done by building the contextualized interaction network of the ECM fragment repertoire including their parent proteins, remodeling proteinases, and their receptors, and by using mathematical disease models.