Towards engineering distinct multi-lamellated outer and inner annulus fibrosus tissues

Area of Science:

• Biomaterials Science
• Tissue Engineering
• Orthopaedic Research

Background:

• The annulus fibrosus (AF) in the intervertebral disc (IVD) exhibits zonal cell populations with distinct extracellular matrix (ECM) compositions.
• Outer AF (OAF) cells produce type I collagen, while inner AF (IAF) cells produce type II collagen and proteoglycans.
• Replicating this zonal heterogeneity is crucial for functional bioengineered IVD tissues.

Purpose of the Study:

• To generate multi-lamellated OAF and IAF tissues using polycarbonate urethane (PU) scaffolds.
• To achieve zonal-specific ECM compositions mimicking native AF tissues.
• To investigate the role of specific supplements in directing cellular differentiation and matrix production.

Main Methods:

• Culturing OAF and IAF cells on PU scaffolds.
• Supplementing culture media with insulin-transferrin-selenium (ITS), proline, dexamethasone, and sodium pyruvate.
• Analyzing ECM composition (collagen types, aggrecan) and cellular responses, including mitochondrial activity and glucocorticoid receptor signaling.

Main Results:

• ITS and proline supplementation supported cellularity but did not induce zonal ECM production in IAF cells.
• Dexamethasone and sodium pyruvate successfully promoted type II collagen and aggrecan accumulation in IAF tissues.
• OAF tissues maintained type I collagen production, and dexamethasone enhanced mitochondrial activity, dependent on sodium pyruvate and glucocorticoid receptor signaling.

Conclusions:

• Biologically distinct, multi-lamellated OAF and IAF tissues can be generated in vitro.
• Dexamethasone and sodium pyruvate are key inducers of zonal matrix formation, particularly for IAF tissue engineering.
• This approach represents a significant advancement towards creating functional bioengineered IVD replacements.