Mechano-Hypoxia Conditioning of Engineered Human Meniscus

Meniscus fibrochondrocytes (MFCs) experience simultaneous hypoxia and mechanical loading in the knee, conditions that have promising applications in human meniscus tissue engineering. We hypothesized that “mechano-hypoxia conditioning,” using mechanical loading such as dynamic compression (DC) and cyclic hydrostatic pressure (CHP), would enhance development of human meniscus fibrocartilage extracellular matrix in vitro. MFCs from inner human meniscus surgical discards were pre-cultured on porous type I collagen scaffolds with TGF-β3 supplementation to form baseline tissues with newly-formed matrix. They were then treated with DC or CHP under hypoxia (HYP, 3% O2) for 5 days. DC was the more effective load regime, and combined HYP/DC enhanced gene expression of fibrocartilage precursors. The individual treatments of DC and HYP regulated thousands of genes and combined in an overwhelmingly additive rather than synergistic manner. Baseline tissues were then treated with a short course of DC (5 vs 60 minutes, 10-20% vs 30-40% strain) with different pre-culture durations (3 vs 6 weeks). Longer courses of loading had diminishing returns in terms of gene regulation. There was a dose-effect for higher DC strains, whereas outcomes were mixed for different MFC donors in pre-culture durations. Finally, baseline tissues were conditioned for 3 weeks with mechano-hypoxia conditioning to assess mechanical and protein-level outcomes. There were 1.8 to 5.1-fold gains in the dynamic modulus relative to baseline in HYP/DC, but matrix outcomes were equal or inferior to static controls. Long-term mechano-hypoxia conditioning was effective in suppressing hypertrophic markers (e.g., COL10A1 10-fold suppression vs static/normoxia). Applied appropriately, mechano-hypoxia conditioning can support meniscus fibrocartilage development in vitro and may be useful as a strategy for developing non-hypertrophic articular cartilage using mesenchymal stem cells. Examination completed using 12 sequenced samples. These came from 3 meniscus donors (4 samples per donor). Each donor had 2 samples treated in hypoxia and 2 in normoxia. In each oxygen tension, the treatments were Dynamic Compression (DC) or Static Vehicle Control (Stat). Each individual sample came from pooled equal masses of RNA from 4 biological replicates in the same condition from the same donor.