Transcriptional profiling of the murine intervertebral disc and age-associated changes in the nucleus pulposus

Abstract

<b>Purpose/Aim</b>: The intervertebral disc (IVD) is composed of cell types whose subtle phenotypic differences allow for the formation of distinct tissues. The role of the nucleus pulposus (NP) in the initiation and progression of IVD degeneration is well established; however, the genes and pathways associated with NP degeneration are poorly characterized.<b>Materials and Methods</b>: Using a genetic strategy for IVD lineage-specific fluorescent reporter expression to isolate cells, gene expression and bioinformatic analysis was conducted on the murine NP at 2.5, 6, and 21 months-of-age and the annulus fibrosus (AF) at 2.5 and 6 months-of-age. A subset of differentially regulated genes was validated by qRT-PCR.<b>Results</b>: Transcriptome analysis identified distinct profiles of NP and AF gene expression that were remarkably consistent at 2.5 and 6 months-of-age. <i>Prg4, Cilp, Ibsp</i> and <i>Comp</i> were increased >50-fold in the AF relative to NP. The most highly enriched NP genes included <i>Dsc3</i> and <i>Cdh6</i>, members of the cadherin superfamily, and microRNAs <i>mir218-1</i> and <i>mir490</i>. Changes in the NP between 2.5 and 6 months-of-age were associated with up-regulation of molecular functions linked to laminin and Bmp receptor binding (including up-regulation of <i>Bmp5</i> & <i>7</i>), with the most up-regulated genes being <i>Mir703, Shh</i>, and <i>Sfrp5</i>. NP degeneration was associated with molecular functions linked to alpha-actinin binding (including up-regulation of <i>Ttn</i> & <i>Myot</i>) and cytoskeletal protein binding, with the overall most up-regulated genes being <i>Rnu3a, Snora2b</i> and <i>Mir669h</i>.<b>Conclusions</b>: This study provided insight into the phenotypes of NP and AF cells, and identified candidate pathways that may regulate degeneration.