GelMA Hydrogel Stiffness Modulates IL-6- and BMP-2-Induced Immune Dysregulation in Human Mesenchymal Stem Cells.

Background

Fracture healing requires a coordinated inflammatory response, and its dysregulation, as seen in polytrauma, can impair bone regeneration. Human mesenchymal stem cells (hMSCs) play a central role in fracture repair through osteogenic differentiation and also via their secretome, which regulates local inflammation, angiogenesis, and tissue regeneration. Interleukin-6 (IL-6), an early pro-inflammatory cytokine, contributes to fracture healing by promoting MSC recruitment and osteogenic differentiation, whereas bone morphogenetic protein-2 (BMP-2) is a key osteoinductive factor that drives bone formation. However, the combined effects of IL-6 and BMP-2 on the hMSC secretome remain poorly understood.

Methods

We cultured hMSCs in osteogenic media supplemented with recombinant IL-6 (1-20 ng/mL) alone or combined with recombinant BMP-2 (1 ng/mL) on tissue culture plastic (TCP) and within gelatin methacryloyl (GelMA) hydrogels of low (~3 kPa), medium (~15 kPa), and high (~30 kPa) stiffness. Osteogenic differentiation was assessed by alkaline phosphatase (ALP) activity and calcium deposition; cytokine profiling was performed using a multiplex antibody array.

Results

When cultured on TCP, IL-6 suppressed ALP activity by day 21. Co-treatment with IL-6 and BMP-2 induced a dysregulated secretome with concurrent upregulation of pro-inflammatory markers (MIP-1α, TNF-α, and GM-CSF) and anti-inflammatory mediators (IL-10, TGF-β1, and VEGF). This hyperinflammatory response was attenuated when hMSCs were encapsulated in GelMA, with high-stiffness gels most effectively suppressing pro-inflammatory chemokines and medium-stiffness gels yielding the highest ALP activity.

Conclusions

These findings suggest that mechanically tuned GelMA hydrogels modulate immune and osteogenic responses of hMSCs in vitro, warranting further investigation in the context of scaffold design for fracture care.