Macrophage phenotype impacts in vitro equine intrasynovial deep digital flexor tenocyte matrix metalloproteinase gene expression and secretion

Abstract

OBJECTIVE To investigate matrix metalloproteinase (MMP) and their inhibitors tissue inhibitor matrix metalloproteinase (TIMP) gene expression and secretion during equine deep digital flexor tendon (DDFT) tenocyte and macrophage (undifferentiated, proinflammatory, and regulatory) co-culture. SAMPLE Third passage DDF tenocytes and donor-matched macrophages differentiated from peripheral blood CD14+ monocytes from 5 healthy horses ages 9–11 years, euthanized for reasons unrelated to musculoskeletal conditions. METHODS Passage 3 DDT tenocyte aggregate cultures were co-cultured with undifferentiated (control), proinflammatory (granulocyte-macrophage colony-stimulating factor; GM-CSF pretreated and lipopolysaccharide + interferon gamma-primed; LPS+IFN-γ) or regulatory (interleukin-4 and interleukin-10-primed; IL-4 + IL-10) macrophages in direct and transwell co-cultures for 72 hours. MMP-1,-2,-3,-9,-13, and TIMP-1,-2 mRNA were measured via realtime Polymerase Chain Reaction (rtPCR). Co-culture media MMP-3,-9, and TIMP-1,-2 concentrations were quantified via ELISA. RESULTS Direct co-culture of DDF tenocytes with proinflammatory macrophages for 72 hours increased MMP-1,-3, and-13 mRNA levels whereas, MMP-9 mRNA levels decreased. Direct and transwell co-culture with proinflammatory and regulatory macrophages resulted in increased MMP-3 and decreased MMP-9 media concentrations. While direct co-culture with regulatory macrophages significantly increased TIMP-1 mRNA, overall, TIMP mRNA and culture media concentrations were largely unchanged. CLINICAL RELEVANCE Cell-to-cell contact between DDF tenocytes and macrophages is not essential to induce MMP gene expression and secretion. Co-culture systems offer a viable in vitro platform to screen and evaluate immunomodulatory properties of therapies aimed at improving equine intrasynovial tendon healing.