Lysyl oxidase mediates regeneration of chondrocytes and extracellular matrix in the construction of tissue-engineered cartilage in vitro

Cartilage tissue engineering affords great promise for cartilage tissue regeneration in clinical practice. Unfortunately, in vitro engineered cartilage falls short of mechanical properties compared to natural cartilage, which has not yet become the mainstream of cartilage defect repair. Notably, the collagen fiber structure in the extracellular matrix (ECM) of chondrocytes accounts for the mechanical properties of engineered cartilage. Specifically, massive collagen fibers in ECM are covalently cross-linked by lysyl oxidase (LOX) to form a rigid cross-linked structure, contributing to certain mechanical properties. Accordingly, LOX may be a key enzyme for improving the mechanical properties of tissue-engineered cartilage in vitro. As reported, transforming growth factor-β1 (TGF-β1) can activate LOX via the SMAD-independent MAPK pathway, and β-aminopropionitrile (BAPN), an irreversible inhibitor of LOX, directly represses the cross-linking between macromolecules in the ECM of chondrocytes. In the present study, we intervened in cartilage regeneration in vitro using the aforementioned activator and inhibitor of LOX, thereby evaluating the quality and mechanical properties of tissue-engineered cartilage and further investigating the role of LOX in cartilage regeneration in vitro. Our results demonstrated that TGF-β1 improved the mechanical properties of cartilage in vitro at both two-dimensional and three-dimensional constructs by activating LOX. Therefore, further experimental studies are warranted to probe the activators of LOX and their mechanisms in cartilage regeneration in vitro.