H. Mirazi, S. Wood
University of New England,
United States
Keywords: microphysiological systems, osteoarthritis (OA), joint on a chip
Summary:
Fluid shear stress (FSS) above 5 dyn/cm² has a catabolic impact on articular chondrocytes.[1] FSS of 10-20 dyn/cm² is widely known to increase levels of osteogenic gene expression in many different osteoblastic cell types.[2] However, it is not as well understood how FSS levels influence the behavior of synoviocytes, which include fibroblast- and macrophage-like synoviocytes. Nevertheless, 12 dyn/cm2 FSS induces THP-1-derived human macrophages to secrete inflammatory cytokines (i.e., TNF -α, IL-1β)[3] that are pertinent to the pathogenesis of osteoarthritis (OA). Notably, prior studies were focused almost exclusively on cells in monoculture, whereas here, we examine the effects of FSS under co-culture conditions. In this study, the multi-tissue nature of the joint as an organ was recapitulated by co-culturing human osteoblasts, articular chondrocytes, dermal fibroblasts, and THP-1-derived macrophages in Ibidi µ-Slide I Luer chips linked together in series. Different channel heights were utilized for each cell type to allow for exposure to physiologically relevant FSS levels specific for each cell type under a single volumetric flow rate. To establish a model of healthy joint cell co-culture, cell viability across a 5-day duration using a single shared cell culture media was assessed using multiple assays, including PrestoBlue™ assessment of viability, MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide] assessment of metabolic activity, and lactate dehydrogenase (LDH) cytotoxicity evaluation. To model the OA disease state, macrophages were either separately exposed to lipopolysaccharides (LPS) and interferon‐gamma (IFN‐γ) prior to co-culture or exposed to inflammatory levels of FSS during co-culture to induce secretion of inflammatory cytokines relevant to OA pathogenesis. Results for Day 1 are shown in Figure 1. Secretion of catabolic enzymes commonly associated with OA were evaluated following up to 5 days of co-culture by utilizing immunoblots of conditioned media to assess levels of MMP-13 and MMP-1 secretion by chondrocytes.