Diurnal Asymmetric Loading Modulates Cell Phenotype in Intervertebral Disc

Area of Science:

• Biomechanical Engineering
• Cell Biology
• Spinal Research

Background:

• The intervertebral disc (IVD) is susceptible to degeneration influenced by mechanical loading.
• Understanding the effects of different loading patterns on IVD cells is crucial for developing effective treatments.
• Ex vivo models provide a controlled environment to study IVD responses to mechanical stimuli.

Purpose of the Study:

• To investigate how asymmetric dynamic loading, alone or with static loading, affects IVD cell morphology and biology.
• To evaluate the impact of different loading regimes on the structural integrity and cellular responses of bovine caudal IVDs.

Main Methods:

• Bovine caudal intervertebral discs (IVDs) were subjected to four loading conditions: parallel dynamic load with free swelling, parallel dynamic load with static load, wedge dynamic load with free swelling, and wedge dynamic load with static load.
• IVD height loss and histological changes were assessed.
• Cell viability, gene expression (ACAN, MMP1, MMP13), and nucleus pulposus (NP) morphology were analyzed.

Main Results:

• Dynamic loading with free swelling maintained cell viability and physiological gene expression.
• Dynamic loading followed by static loading led to degeneration, characterized by reduced cell viability and altered gene expression (lower anabolic, higher catabolic).
• Wedge loading with free swelling upregulated ACAN expression, while wedge loading with static loading showed increased MMP1 and MMP13 expression, with NP protrusion observed.

Conclusions:

• Continuous static loading after dynamic loading negatively impacts IVD cell phenotype in an ex vivo model.
• Temporary reduction of mechanical stress on the IVD may mitigate degeneration.
• Asymmetric loading followed by static loading can effectively mimic pathological changes seen in IVD degeneration and spinal deformity.