Moderate dynamic compression inhibits pro-catabolic response of cartilage to mechanical injury, tumor necrosis factor-α and interleukin-6, but accentuates degradation above a strain threshold

Abstract

Objective Traumatic joint injury can initiate early cartilage degeneration in the presence of elevated inflammatory cytokines (e.g., TNF-α and IL-6). The positive/negative effects of post-injury dynamic loading on cartilage degradation and repair in vivo is not well-understood. This study examined the effects of dynamic strain on immature bovine cartilage in vitro challenged with TNF-α + IL-6 and its soluble receptor (sIL-6R) with/without initial mechanical injury. Methods Groups of mechanically injured or non-injured explants were cultured in TNF-α + IL-6/sIL-6R for 8 days. Intermittent dynamic compression was applied concurrently at 10%, 20%, or 30% strain amplitude. Outcome measures included sGAG loss (DMMB), aggrecan biosynthesis (35S-incorporation), aggrecanase activity (Western blot), chondrocyte viability (fluorescence staining) and apoptosis (nuclear blebbing via light microscopy), and gene expression (qPCR). Results In bovine explants, cytokine-alone and injury-plus-cytokine treatments markedly increased sGAG loss and aggrecanase activity, and induced chondrocyte apoptosis. These effects were abolished by moderate 10% and 20% strains. However, 30% strain-amplitude greatly increased apoptosis and had no inhibitory effect on aggrecanase activity. TNF+IL-6/sIL-6R downregulated matrix gene expression and upregulated expression of inflammatory genes, effects that were rescued by moderate dynamic strains but not by 30% strain. Conclusions Moderate dynamic compression inhibits the pro-catabolic response of cartilage to mechanical injury and cytokine challenge, but there is a threshold strain-amplitude above which loading becomes detrimental to cartilage. Our findings support the concept of appropriate loading for post-injury rehabilitation.

Synergy between Piezo1 and Piezo2 channels confers high-strain mechanosensitivity to articular cartilage

“…S5). The resulting 50% strain is considered hyperphysiologic and injurious (3,(34)(35)(36). The Ca 2+ transients (Fig.…”

The Regional Sensitivity of Chondrocyte Gene Expression to Coactive Mechanical Load and Exogenous TNF-α Stimuli

“…The interactive effects of mechanical stimuli and cytokines on articular cartilage have been investigated in in vivo [32] and in vitro studies [24,25,33] and the interaction may be dependent on the duration and magnitude of mechanical loading. Continuous passive motion, a low-magnitude load stimulus, attenuated cartilage degradation relative to immobilization in an in vivo model of ag-induced arthritis in rabbits [32].…”

“…Further, low levels of in vitro dynamic compression seem to inhibit the catabolic effects of cytokines on articular chondrocytes [24,25,33], but a loading threshold may exist above which the protective effects of mechanical load are not observed [33]. Consistent with the findings of Li et al [33], dynamic unconfined compression was observed to upregulate CII and aggrecan expression relative to unloaded samples treated with TNF-a and TNF-a treatment was observed to upregulate ADAM-TS expression even in the presence of dynamic compression. Thus, it appears that the interaction between mechanical and biochemical stimuli is complex and it may be an oversimplification to view mechanical loading simply as an anticatabolic stimulus.…”

Correlation between interleukin-6 expression in articular cartilage bone and osteoarthritis

“…As previously described (Li et al, 2013), all cartilage samples were first fixed in 4% paraformaldehyde for 24 h, followed by gradient dehydration (100% ethanol for 30 min, 2 times; 95% ethanol for 30 min; 85% ethanol for 30 min; 75% ethanol for 30 min; and xylene for 10 min, 2 times) and paraffin embedding, and were sectioned into 4-μm thick slices by a microtome (Leica, Germany). Tissue slices were then mounted onto glass slides, which were dried at 62°C, and were re-hydrated by sequential immersion in xylene (5 min, 2 times), 100% ethanol (5 min), 95% ethanol (5 min), 80% ethanol (5 min), 75% ethanol (5 min), and distilled water (2 min).…”