S-phase kinase-associated protein-2 (Skp2) promotes nucleus pulposus cell proliferation by inhibition of p27 in attenuating intervertebral disc degeneration.

Abstract

Nucleus pulposus (NP) cell proliferation plays a key role during the process of intervertebral disc degeneration (IDD). S-phase kinase-associated protein-2 (Skp2) has been proved as an important regulator for cell growth factors in vitro. Nonetheless, whether Skp2 attenuates IDD by mediating NP cell proliferation still remains unclear. Therefore, the aim of this study was to explore how Skp2 affected NP cell proliferation and the potential mechanism in vitro. In this study, we first collected different degenerated human NP samples and isolated NP cells from these tissues. NP cell degenerated model was established with IL-1β, and the cells were transfected with lentivirus to achieve Skp2 overexpression. Besides, SKPinC1 was used to suppress Skp2 expression in vitro. Western blot, RT-PCR, and immunocytofluorescence were applied to detect genetic differences among groups. Furthermore, cell viability and cell cycle were determined by CCK-8 assay and flow cytometry, respectively. Skp2 expression decreased significantly in degenerated disc samples (p<0.05). IL-1β stimulation significantly promoted NP cell degeneration, which could be reversed by Skp2 overexpression (p<0.05). Meanwhile, Skp2 in IDD significantly inhibited the expression level of medial p27 and promoted cell cycle by CDK2 activation (p<0.05). In addition, Skp2 suppression affected NP cell proliferation in vitro. NP cells exhibited significantly inhibited proliferation ability when down-regulated the expression level of Skp2. Our findings provided a more meritorious viewpoint of Skp2 in NP cell proliferation. Furthermore, the above results suggested that Skp2 was a novel target in the treatment of IDD.