Figure 6. Impact of circulatory factors on gross disc morphology. H&E staining of lumbar disc was performed to assess the gross morphological changes with aging. Compared to discs of Y-Y mice, discs of O-O mice exhibited increasing loss of a distinct NP/AF boundary (black arrows), loss of AF structure in which the AF lamellae become less concentric and more serpentine, with each lamellae spaced farther apart (yellow arrowheads), loss of NP matrix, indicated by large empty space gaps (red arrowheads) and fissures/clefts (black arrowheads). These degradative changes were also observed in Y-O mice but blunted in the O-Y mice, suggesting the global influences of blood factors on disc aging phenotype. Disc sections from four representative mice of each group (Y-Y, Y-O, O-Y, O-O) are shown. Scale bar = 50μm of H&E stained disc sections.