P20 | RNASEQ AND HISTOCHEMICAL STAININGS ASSESS BIOCHEMICAL AND STRUCTURAL CHANGES IN THE MOUSE INTERVERTEBRAL DISC ACROSS THE LIFESPAN

A. Hallmark¹, A. Ali², C. Dahia³ | ¹Hospital for Special Surgery, New York, USA; ²Department of Medicine, Columbia University, New York, USA; ³Hospital for Special Surgery, Weill Cornell Medicine

The intervertebral disc (IVD) is the largest avascular and aneural tissue in the body. IVDs form the joint in the spine, helping to provide flexibility and resist compressive forces in young and healthy individuals. However, following injury, or with natural aging, the IVD undergoes natural structural and molecular changes leading to its degeneration, and is a leading cause of disability, affecting over 70% of adults, but with no cure. Each IVD has a proteoglycan-rich core made up of the nucleus pulposus (NP). NP is laterally surrounded by collagen-rich annulus fibrosus (AF). The extracellular matrix (ECM) is crucial for IVD hydration, structure, and function. Here, using the mouse as a model system, we analyzed the molecular changes in NP and AF cells from one week to one year of age using bulk RNA sequencing. Results showed that ECM content and turnover were impacted by age in both NP and AF cells. Next, using an array of histochemical staining methods, we analyzed the changes in the lumbar IVD structure and biochemical composition across the lifespan, from newborn to over two years of age. Due to the high collagen and proteoglycan content of the IVD, safranin-O and fast green, or picrosirius red, are generally used to determine biochemical changes in the IVD. Here, using additional staining methods, including Masson’s trichrome and Movat pentachrome, we observed that, in addition to changes in collagen and proteoglycan content with age, the aging mouse IVDs were vascularized and had a high amount of endogenous fibrin forming fibrinoids. Next, we determined the clinical relevance of these findings using clinical samples obtained under an IRB-approved study, following informed consent, and validated the presence of fibrinoids in degenerated human IVDs. To our knowledge, this is the first study to describe the presence of fibrinoid in the IVDs, which was made possible by the histochemical staining approach.