The effect of IL-17A and combined mechanical injury on meniscal tissue integrity in vitro

Abstract Objective Meniscal integrity is crucial for knee joint stability and prevention of osteoarthritis (OA) development. Recent studies suggested that mechanical overload and interleukin (IL)-17A may be important intertwined players in meniscal degeneration, but a direct impact of IL-17A on the meniscus has not been investigated. Therefore, the aim of this study was to analyze the effect of IL-17A on meniscal tissue with and without combined mechanical injury (MI). Methods Meniscal explant disks (1 mm height, 3 mm diameter) were isolated from the lower surface of bovine menisci and exposed to IL-17A [0-100 ng/ml] and/or MI (single compression, 50% strain, strain rate 1 mm/sec). After three days of incubation in a serum-free medium the proteoglycan release (sGAG; DMMB assay), mRNA level of matrix-degrading enzymes (qRT-PCR), aggrecan degradation (NITEGE immunostaining), and cell death (histomorphometry of nuclear blebbing/apoptosis and condensed nuclei/unspecified cell death) was determined. Statistics: one-way ANOVA with Tukeys multiple comparisons or Kruskal-Wallis-post hoc test. Results IL-17A increased sGAG release in a dose-dependent manner. MI also induced release of sGAG, but the combination with IL-17A raised this effect to a significant level even for an IL-17A concentration which showed no significant effect on its own. Both, IL-17A and MI individually affected the mRNA levels for ADAMTS-4 and MMP-13 slightly, but the combination of both induced a significant increase in mRNA levels. Signals for the ADAMTS-4-related aggrecan neoepitope NITEGE were elevated by IL-17A in superficial explant tissue and by MI in superficial and deeper areas. The combination of both stimuli intensified this signal further. MI increased the number of cells with condensed nuclei significantly and induced apoptosis in a small proportion of cells. IL-17A alone had no significant impact on the amount of condensed nuclei but increased the number of apoptotic cells slightly and even more in combination with MI. Conclusion IL-17A induces matrix degeneration in meniscal tissue which in combination with a trauma intensifies significantly. The latter might be responsible for a post-traumatic joint environment that promotes meniscal degeneration and subsequently OA, and highlights IL-17A as a potential target in PTOA therapy.