Background/Purpose: Mechanotransduction is a cell’s ability to translate mechanical stimuli into biochemical signals and has been implicated in signaling pathways involving differentiation and proliferation. Mechanical stress at entheses and adjacent tissues has additionally been implicated in the pathogenesis of spondyloarthropathies, such as ankylosing spondylitis and psoriatic arthritis, by triggering inflammation. However, the mechanisms underlying these processes remain unclear. This project aims to establish an in vitro system to study the effects of mechanical stress on mesenchymal stem cells and osteoblasts, specifically examining mineralization and cytokine production.

Methods: Mechanical stress was applied to rat calvarial mesenchymal stem cells (MSCs) using the Flexcell FX-5000 Tension System. This instrument uses a computer-controlled vacuum pump to apply uniform axial strain to cells plated on silicone bottomed Bioflex plates. For osteogenic differentiation, 3% uniform axial strain was applied to the cells. After applying strain for 5 days, cells were cultured in osteogenic medium (OS+) to induce differentiation. Mineralization was measured with Alizarin red stain after 28 days. For measuring cytokine secretion upon stress, MSCs were subjected to 24 hours of 10% strain. ELISA was used to quantify cytokine secretion into cell culture supernatants at 24, 48, and 72h after stimulation. For all experiments, non-stretched cells were used as controls.

Results: For MSCs cultured in OS+ for 28d, overall mineralization was 2 to 3-fold higher than MSCs cultured in OS-, as expected. In OS+ conditions, stress resulted in a 12% decrease in mineralization for stretched cells compared to non-treated controls (p < 0.05). In addition, stress increased secretion of RANTES and IL-6 from MSCs, as determined by ELISA. For RANTES, stretch led to a 130% increase in production at 24h, a 56% increase at 48h, and a 43% increase 72h after stimulation (p = 0.06; p < 0.001; p < 0.01, respectively). For IL-6, stretch led to a 324% increase in production at 24h, an 85% increase 48h, and a 55% increase 72h after stimulation (p < 0.01; p < 0.05; p < 0.05, respectively).

Conclusion: These results suggest that mechanical stress can alter osteogenic ability and cytokine secretion from MSCs. RANTES and IL-6 have been previously shown to play a positive role in bone formation, so further studies are needed to determine whether these mediators have a biological effect during osteogenesis in this system. Future studies will focus on optimizing the system and then using it to study the role of ankylosing spondylitis risk genes in MSC and osteoblast function.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/investigating-the-role-of-mechanical-stress-in-spondyloarthritis-pathogenesis/