Collagen plays a key structural role in both the annulus fibrosus (AF) and nucleus pulposus (NP) of intervertebral disks (IVDs). Changes in collagen content with degeneration suggest a shift from collagen type II to type I within the NP, and the activation of pro-inflammatory factors is indicative of fibrosis throughout. While IVD degeneration is considered a fibrotic process, an increase in collagen content with degeneration, reflective of fibrosis, has not been demonstrated. Additionally, changes in collagen content and structure in human IVDs with degeneration have not been characterized with high spatial resolution. The collagen content of 23 human lumbar L2/3 or L3/4 IVDs was quantified using second harmonic generation imaging (SHG) and multiple image processing algorithms, and these parameters were correlated with the Rutges histological degeneration grade. In the NP, SHG intensity increased with degeneration grade, suggesting fibrotic collagen deposition. In the AF, the entropy of SHG intensity was reduced with degeneration indicating increased collagen uniformity and suggesting less-organized lamellar structure. Collagen orientation entropy decreased throughout most IVD regions with increasing degeneration grade, further supporting a loss in collagen structural complexity. Overall, SHG imaging enabled visualization and quantification of IVD collagen content and organization with degeneration. There was an observed shift from an initially complex structure to more uniform structure with loss of microstructural elements and increased NP collagen polarity, suggesting fibrotic remodeling.

Background Back and neck pain are leading causes of global disability that are associated with intervertebral disc (IVD) degeneration. Causes of IVD degeneration are multifactorial, and diet, age, and diabetes have all been linked to IVD degeneration. Advanced glycation endproducts (AGEs) accumulate in the IVD as a result of aging, diet, and diabetes, and AGE accumulation in the IVD has been shown to induce oxidative stress and catabolic activity that result in collagen damage. An association between AGE accumulation and IVD degeneration is emerging, yet mechanism behind this association remains unclear. The Receptor for AGEs (RAGE) is thought to induce catabolic responses in the IVD, and the AGE receptor Galectin 3 (Gal3) had a protective effect in other tissue systems but has not been evaluated in the IVD. Methods This study used an IVD organ culture model with genetically modified mice to analyze the roles of RAGE and Gal3 in an AGE challenge. Results Gal3 was protective against an AGE challenge in the murine IVD ex vivo, limiting collagen damage and biomechanical property changes. Gal3 receptor levels in the AF significantly decreased upon an AGE challenge. RAGE was necessary for AGE‐induced collagen damage in the IVD, and RAGE receptor levels in the AF significantly increased upon AGE challenge. Discussion These findings suggest both RAGE and Gal3 are important in the IVD response to AGEs and highlight Gal3 as an important receptor with protective effects on collagen damage. This research improves understanding the mechanisms of AGE‐induced IVD degeneration and suggests Gal3 receptor modulation as a potential target for preventative and therapeutic treatment for IVD degeneration.