SDF1/CXCR4 axis facilitates the angiogenesis via activating the PI3K/AKT pathway in degenerated discs

Symptomatic degenerative disc disease (DDD) is considered the leading cause of chronic lower back pain (LBP). As one of the main features of intervertebral disc degeneration (IDD), vascular ingrowth plays a crucial role in the progression of LBP. Stromal cell-derived factor 1 (SDF1) and its receptor C-X-C receptor 4 (CXCR4) were reported to be overexpressed in the degenerated intervertebral discs, suggesting that they may be involved in the pathogenesis of IDD. Moreover, SDF1 has been identified to induce neovascularization in rheumatoid arthritis disease. However, the roles of the SDF1/CXCR4 axis in the neovascularization of IDD remain unclear. Therefore, the objective of the present study was to elucidate whether the SDF1/CXCR4 axis takes part in neovascularization in degenerated intervertebral discs and its underlying mechanisms. Adenovirus infection was used to upregulate SDF1 expression in primary nucleus pulposus cells (NPCs). The effects of SDF1 on the proliferation and angiogenesis of vascular endothelial cells (VECs) were assessed by Cell Counting Kit-8 and tube formation assays after VECs were treated with the supernatants derived from SDF1 overexpressed or not treated NPCs. Transwell chambers using the supernatants from NPCs as chemokines were applied to assess VEC migration and invasion. AMD3100, MK-2206 and SF1670 were used to antagonize CXCR4, AKT serine/threonine kinase 1 (AKT) and phosphatase and tensin homolog (PTEN) in VECs. The results revealed that SDF1 overexpression significantly increased the ratio of phosphorylated AKT to AKT and decreased PTEN expression in NPCs, as well as enhanced the proliferation, migration, invasion and angiogenesis abilities of VECs. However, these effects induced by SDF1 overexpression in NPCs were all reversed when VECs were pretreated with AMD3100 or MK-2206, whereas enhanced by SF1670 treatment. Collectively, the present study indicated that enhancement of the SDF1/CXCR4 axis in NPCs can significantly accelerate angiogenesis by regulating the PTEN/phosphatidylinositol-3-kinase/AKT pathway.