Influence of the Intervertebral Disc Microenvironment on Matrix Synthesis and Metabolism in Goat Nucleus Pulposus Cells.

Background: The intervertebral disc (IVD) microenvironment plays a crucial role in cellular function and viability. Although the precise cause of IVD degeneration remains unclear, it is associated with progressive disruption of nutrient, metabolite, and pH homeostasis. Despite growing interest in regenerative therapies, the complex IVD microenvironment is often overlooked in preclinical development. This study investigates the effects of clinically relevant combinations of oxygen, glucose, pH, and osmolarity on the metabolic activity and matrix synthesis of goat nucleus pulposus (NP) cells. Materials and Methods: Goat NP cells were embedded in 3D alginate beads and exposed to 24 distinct microenvironments across four factors in combination: oxygen (2% and 5%), glucose (0.5 and 1.0 mM), pH (6.5, 6.8, and 7.1), and osmolarity (350 and 500 mOsm). Alginate beads were primed for 10 days before subjection to altered microenvironmental conditions for a further 14 days. Cell viability, DNA content, glycosaminoglycan (GAG), and collagen synthesis, as well as oxygen consumption and lactate production rates, were quantified. Experimental data informed in silico modeling of a goat IVD, profiling nutrient and metabolite gradients and GAG accumulation to determine the effects of microenvironmental changes at the whole-organ level. Results: pH was the most influential factor, significantly reducing cell viability, DNA content, and GAG production under degenerated conditions at pH 6.5. Collagen production remained unchanged. Oxygen and glucose significantly affected metabolic rates. Combined analysis revealed the interdependent nature of these factors, better reflecting in vivo interactions. In silico modeling demonstrated that microenvironment-driven changes directly altered disc-wide nutrient profiles and long-term GAG accumulation. Conclusion: These findings highlight the critical role of pH in regulating NP cell function and show that interactions between microenvironmental factors impact cell behavior more than isolated effects. Incorporating physiologically relevant microenvironments may improve regenerative therapy development and enhance translation from preclinical models to clinical application.