Tenocyte Response to Interleukin-1 Beta Depends on Substrate Stiffness: Implication to the Etiology of Tendon Inflammation

摘要

Early responses to tendon overloading involve functional changes of tenocytes from anabolic (producing matrix protein) to catabolic (breaking down matrix proteins) state. These changes are thought to be induced by a combination of changes in extracellular mechanical environment as well as extrinsic inflammatory stimulation such as interleukin-1 β (IL-1 β), which stimulates tenocyte catabolism. However, detailed mechanisms are still largely unknown. We have focused on cellular tension as a possible regulator of tenocyte catabolism and inflammatory responses. The present study was performed to investigate if tenocyte response to IL-1 β stimulation can be regulated by cellular tension. Tenocytes isolated from rabbit Achilles tendons were seeded onto one of the following substrates: glass or PDMS-made micropillar substrate (3 µm diameter, 6 µm spacing in a hexagonal lattice with a pillar height of 2, 4 or 8 µm). Substrate stiffness was the highest in glass and the lowest in 8 µm-height micropillars. Following a 24-h incubation, IL-1β was administrated at 0 pM (control), 1 pM, 10 pM or 100 pM. IL-1β culture was performed for 3 days. Cell shapes and mRNA expression of matrix metalloproteinase-1 (MMP-1) in each condition was assessed. It was demonstrated that cell shape was remarkably influenced by both substrate stiffness and the concentration of IL-1 β. Cell area was significantly decreased with lowering substrate stiffness and increasing IL-1β concentration. The expression of MMP-1 mRNA was also influenced by both the substrate stiffness and ILl β concentration. These findings suggest that cellular tension, which is thought to reflect the substrate stiffness, is a key mechanical factor in the regulation of tenocyte functions, in particular their responses to inflammatory stimulation.