The intervertebral disc is a complex and dynamic structure that provides spinal stability, mobility and flexibility. It is comprised of a central nucleus pulposus (NP), enveloped by the annulus fibrosus (AF) and sandwiched between two cartilaginous endplates. With aging and degeneration, biochemical changes result in disc biomechanics changes, and thereby function. However, as a major cause of low back pain, the aetiology of IVD degeneration remains unclear. Few studies have examined the IVD proteome and currently lacking is a reference proteome of healthy and aged IVD with spatial information.
Here, we compared the proteomic landscape of 3 lower lumbar IVD (L3/4, L4/5, L5/S1) of one young (16YO) and one aged (59YO) cadaveric donor, respectively. IVD were MRI-imaged, and segments representing the NP, IAF and OAF were analysed by mass spectrometry. Mass spectrometry data were obtained, and also compared with our in-house data set of the NP transcriptome, providing a first comprehensive map incorporating both regulatory and functional aspects.
We identified over 3000 proteins in young and aged IVD. Our acquired MRI images facilitated an integration between IVD clinical images and proteomic signatures. This is the first study which allowed for a thorough proteomic intra- and inter-discal comparison, with both young and aged IVD, highlighting regional (NP, IAF, OAF) differences within and between discs. Aged NP had increases of proteins related to cellular stress and matrix degradation in addition to a shift in the dominating types of proteoglycans, highlighting the importance of matrix in intervertebral disc maintenance. Our study identified that IAF showed more similarities with NP than with the OAF, and that there were specific clusters of proteins that were upregulated in IAF and OAF, which suggests that these two compartments have different roles in the IVD.
Our study provides mechanistic insights into IVD homeostasis in health, aging and degeneration.