Tendon injuries are associated with the formation of inferior, disorganized scar tissue at the tendon bone insertion site and high failure rates. Two major processes are discussed being key players: the inflammatory reaction upon tear and the remodeling process of the tendon. In a previous study we demonstrated that the profile of MMPs and TIMPs, being key factors of tendon modeling and remodeling, is altered in tenocytes of rotator cuff tears from donors with higher age (>65 years) and degenerative status (high degree of muscle fatty infiltration)[1]. But do these cells also show different expression of inflammatory cytokines or react different upon cytokine stimulation? The aim of our project was to analyze the expression of inflammatory cytokines in human tenocyte-like cells (hTLCs) on mRNA-level and the responsiveness to cytokine stimulation regarding differences between varying donor characteristics such as age, sex and the degenerative status of the tendon.

TLCs were isolated from SSP tendon biopsies from 16 male and 14 female donors undergoing arthroscopic or open shoulder surgery. Cells from each donor (passage 1 or 2) were seeded in a 6-well plate and RNA was isolated after 7 days of culture. Quantitative Real-Time PCR was performed to analyze the expression of IL-6, IL-1β, TNF-α, IL-10, IL-33, TGF-β1 and COX-2. Furthermore, hTLCs of 12 male donors were stimulated for 3 days with a combination of TNF-α and IFN-γ (10ng/ml). The effect of the cytokines was analyzed by flow cytometry regarding surface marker expression: ICAM (CD54), VCAM (CD106), and Major Histocompatibility Complex (MHC)-class I and MHC-class II. Statistics: Mann-Whitney-U-Test, Spearman´s-Rho-correlation, p≤0.05.

Gene expression analysis revealed high levels of IL-6, TGF-β1 and COX-2 in hTLCs but low expression of TNF-α and IL-10. No differences in the expression of the inflammatory cytokines were found between low and high fatty infiltration or with respect to age. The stimulation of the hTLCs with TNF-α and IFN-γ increased the number of ICAM and VCAM positive cells up to 100% and 97±5%, respectively. MHC-class II was not expressed on unstimulated cells but 77±17% MHC-class II positive cells were present after stimulation. All unstimulated cells were positive for MHC-class I, but the MFI (Mean Fluorescent Intensity) increased after stimulation. No significant difference in the expression of surface markers was detected when comparing tenocytes of donors with low and high muscle fatty infiltration.

In contrast to the significant changes in expression levels of MMPs and TIMPs in tenocytes of donors with different age and degenerative status[1], we could not detect any significant changes in the expression of inflammatory cytokines or in the responsiveness of these tenocytes upon cytokine stimulation. All tenocytes showed the potential to respond to inflammatory processes. This indicates that the response of the tenocytes to inflammatory stimuli seems to be independent of donor characteristics, whereas the tendon remodeling might depend on age and degenerative status of the donor.