Background/Purpose:  In healthy cartilage, there is a balance between anabolic and catabolic activities of chondrocytes that maintains the functional integrity of the extracellular matrix. However, during osteoarthritis (OA), chondrocytes become more catabolically active and express matrix degrading enzymes, such MMPs and ADAMTSs. This process results in a net loss of the extracellular matrix and therefore leads to cartilage damage. Previously we found, that the anti-inflammatory cytokine Interleukin 37 (IL37) is able to counter-regulate the catabolic status of chondrocytes by reducing the IL1β-driven expression of pro-inflammatory cytokines and catabolic enzymes. The goal of this study was to investigate the effect of IL37 on content and synthesis of extracellular matrix molecules in human OA cartilage explants.

Methods: Human cartilage was obtained from sixteen OA patients undergoing total knee or hip arthroplasty. Biopsy punches of 4 mm in diameter were made to equalize explant size. After culturing overnight, explants were incubated for 48 h with three doses (1-10 ng/ml) of recombinant-IL37 (rec-IL37). Sulfated glycosaminoglyans (GAG) were measured in the supernatant with the DMB assay and RNA was extracted from explants to analyze gene expression of extracellular matrix molecules and cartilage degrading enzymes. In addition, nitric oxide (NO) was measured in the supernatant using Griess reagens, because NO is an important effector molecule that may suppress cartilage matrix synthesis. 

Results:  Adding rec-IL37 (100ng/ml) to OA cartilage explants caused a significant reduction in GAG release in the supernatant of, on average, 32% in sixteen donors. Gene expression of the extracellular matrix molecules aggrecan and collagen type II was not different between rec-IL37 treated groups and controls in the five patients analyzed so far. This indicates that rec-IL37 does not inhibit GAG release by inhibiting the synthesis of the proteoglycan aggrecan. We did observe a reduction in the gene expression of the matrix degrading enzyme MMP3 after stimulation with 1 ng/ml rec-IL37. However, high doses of rec-IL37 did not significantly reduce MMP3 expression. Furthermore, we did not observe an effect of rec-IL37 on gene expression of MMP13 and ADAMTS5, which suggests that rec-IL37 does not inhibit GAG release by inhibiting expression of these enzymes. Another mechanism to prevent GAG release is via inhibition of NO synthesis, but NO levels in the supernatant were comparable between rec-IL37 treated groups and the control group. However, we did observe a trend towards increased gene expression of the metalloproteinase inhibitor TIMP3 in rec-IL37 treated groups, as a possible mechanism for reduced GAG release.

Conclusion:  Our data show that rec-IL37 reduces GAG release out of OA cartilage explants. The mechanism behind this process is most likely positioned downstream of catabolic gene expression, and possibly runs via modulation of matrix degrading enzyme activity. Our results indicate that IL37 can maintain cartilage matrix integrity under OA conditions.

« Back to 2016 ACR/ARHP Annual Meeting

ACR Meeting Abstracts - https://acrabstracts.org/abstract/il37-rescues-human-oa-cartilage-explants-from-gag-release/