Recapitulating monocyte extravasation to the synovium in an organotypic microfluidic model of the articular joint

Abstract

The synovium of osteoarthritis (OA) patients can be characterized by an abnormal accumulation of macrophages originating from extravasated monocytes. Since targeting monocyte extravasation may represent a promising therapeutic strategy, our aim was to develop an organotypic microfluidic model recapitulating this process. Synovium and cartilage were modeled by hydrogel-embedded OA synovial fibroblasts and articular chondrocytes separated by a synovial fluid channel. The synovium compartment included a perfusable endothelialized channel dedicated to monocyte injection. Monocyte extravasation in response to chemokines and OA synovial fluid was quantified. The efficacy of chemokine receptor antagonists, RS-504393 (CCR2 antagonist) and Cenicriviroc (CCR2/CCR5 antagonist) in inhibiting extravasation was tested pre-incubating monocytes with the antagonists before injection. After designing and fabricating the chip, culture conditions were optimized to achieve an organotypic model including synovial fibroblasts, articular chondrocytes, and a continuous endothelial monolayer expressing intercellular adhesion molecule-1 and vascular cell adhesion molecule-1. A significantly higher number of monocytes extravasated in response to the chemokine mix (p < 0.01) and OA synovial fluid (p < 0.01), compared to a control condition. In both cases, endothelium pre-activation enhanced monocyte extravasation. The simultaneous blocking of CCR2 and CCR5 proved to be more effective (p < 0.001) in inhibiting monocyte extravasation in response to OA synovial fluid than blocking of CCR2 only (p < 0.01). The study of extravasation in the model provided direct evidence that OA synovial fluid induces monocytes to cross the endothelium and invade the synovial compartment. The model can be exploited either to test molecules antagonizing this process or to investigate the effect of extravasated monocytes on synovium and cartilage cells.

Human Organ-on-a-Chip Microphysiological Systems to Model Musculoskeletal Pathologies and Accelerate Therapeutic Discovery

“…As an example, a recently published joint-on-chip model includes vascularized synovium and articular cartilage PDMS compartments separated by lined trapezoidal posts 90 µm apart creating micropores for cellular transmigration ( Mondadori et al, 2021 ). Monocytes were introduced into the vascularized channel ± TNF-α and shear stress activation and monitored their transmigration into the osteoarthritic (OA) synovial fluid and cartilage compartments, identifying higher transmigration in the presence of OA synovial fluid compared to control medium alone.…”

Cutting-Edge Technologies for Inflamed Joints on Chip: How Close Are We?

“…(E) i: Real picture of the cartilage-on-chip model and overview of the encapsulated chondrocytes in a hydrogel scaffold; ii: stimulation for the diffusion of biomolecules through circular chamber and channel (Adapted from ( 109 ). (F) Components of the synovium-on-chip model and schematic representation of the developed joint microenvironment [Adapted from ( 110 )].…”

“…However, no protein localization was specified through immunochemistry. In another study, the role of macrophages and neutrophils in an osteoarthritic knee have been investigated by combining both mechanical and immune regulators ( 110 ). Here, Mondadori and colleagues developed an articular joint microfluidic in vitro model that was comprised of two compartments (cartilage and synovium) separated by a channel for the synovial fluid ( Figure 3F ).…”

The Added Value of the “Co” in Co-Culture Systems in Research on Osteoarthritis Pathology and Treatment Development

“…Complex systems can nowadays easily be reconstructed in organ-on-a-chip approaches. Monocyte extravasation in response to chemokines or the synovial fluid in OA was studied in a joint-on-a-chip-model including OA patient-derived synovial fluid, fibrin hydrogel-embedded OA chondrocytes and OA synovial fibroblasts, as well as perfusable endothelialized channels for monocyte injection ( Mondadori et al, 2021 ) ( Figure 3B ). To mimic shear stress present in the channel, laminar flow of the medium was applied.…”

“…Addition of a chemokine mix (CCL 2, CCL 3, CCL 4, and CCL 5) to the synovial fluid-mimicking compartment further stimulated monocyte extravasation. OA synovial fluid was similarly able to increase monocyte extravasation significantly, suggesting that synovial fluid might be relevant for monocyte extravasation in vivo ( Mondadori et al, 2021 ). This model was used to test a CCR2 chemokine receptor antagonist and an antagonist for chemokine receptors CCR2 and CCR5.…”