Modeling The Synovium In Vitro

RA is a chronic inflammatory disease that is challenging to model in vitro. Historically cells have been cultured out of the joint, particularly Type B fibroblast-like synoviocytes (FLS) in monolayer culture conditions, in order to model behavior of disease-specific cells for drug screening as well as potential therapeutic discovery. In order to better recapitulate the in situ tissue microenvironment, improvements were made to various components of in vitro modeling of synovium, a soft lining tissue within diarthroses important both in health and disease. First, in order to obtain healthy, viable, and representative cells from synovial tissue—including resident FLS as well as infiltrating mononuclear cells—current techniques used for tissue disaggregation and cell isolation were optimized, resulting in improved yield and quality of isolated cells. Subsequently, peripheral blood-derived monocytes were used to generate model macrophages and osteoclasts for inclusion in co-culture experiments with FLS in order to model the in vivo interactions between resident Type A (macrophage-like) and Type B (fibroblast-like) synoviocytes as well as resident FLS and giant bone-resorbing cells that form in chronic inflammatory conditions such as RA and mediate destruction of periarticular bone ; coculture experiments yielded interesting observations that may mimic in vivo behavior. Finally, in order to to better reflect three-dimensional in situ interactions between resident FLS and matrix components, FLS were plated in micromass culture using Matrigel. These initial experiments with 3D culture appeared to better reflect certain aspects of FLS behavior in vivo, particularly in response to TNFɑ, a pro-inflammatory cytokine involved in RA pathogenesis