Spatial mapping of collagen content and structure in human intervertebral disk degeneration

Abstract

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.

Imaging Evaluation of Intervertebral Disc Degeneration and Painful Discs—Advances and Challenges in Quantitative MRI

“…Changes in T2 are a result of water content and to what extent water is "bound" or "free". When IVD degeneration occurs, water content decreases and collagen organization changes from a more randomly orientated mesh to more uniform structure with loss of microstructural elements and increased NP collagen polarity [47]. Therefore, the T2 values in the NP tend to decrease with age and degeneration [48,49].…”

Fibrotic alterations in human annulus fibrosus correlate with progression of intervertebral disc herniation

“…This analysis is usually associated with Col I and collagen III (Col III) fibres, although, in this study, the fibres are most probably associated with Col I, since Col III is not abundant in AF and is described only as a pericellular protein within the tissue [ 34 , 35 ]. Nevertheless, this analysis should be performed using second harmonic microscopy [ 36 ]. Figure 2 B shows representative images of hAF samples stained with PSR and imaged under polarized light, while Fig.…”

The Role of Polymorphisms in Collagen-Encoding Genes in Intervertebral Disc Degeneration

“…Collagens are present in all anatomical structures of the spine, including: IVDs; intervertebral joints; ligaments, tendons and muscles; membranes (dura mater, arachnoid, pia mater)-protective layers that surround and nourish the spinal cord; and blood vessels [ 16 , 17 ].…”