P16 deficiency attenuates intervertebral disc degeneration by adjusting oxidative stress and nucleus pulposus cell cycle.

Hui Che,Zhen Zhang,Cory J Xian,You Li,Jie Li,Liping Wang,Dengshun Miao,Yongxin Ren,Jianghui Dong,Huan Liu,Cheng Ma,Jingyi Qin

doi:10.7554/elife.52570

Abstract

The cell cycle regulator p16 is known as a biomarker and an effector of aging. However, its function in intervertebral disc degeneration (IVDD) is unclear. In this study, p16 expression levels were found to be positively correlated with the severity of human IVDD. In a mouse tail suspension (TS)-induced IVDD model, lumbar intervertebral disc height index and matrix protein expression levels were reduced significantly were largely rescued by p16 deletion. In TS mouse discs, reactive oxygen species levels, proportions of senescent cells, and the senescence-associated secretory phenotype (SASP) were all increased, cell cycling was delayed, and expression was downregulated for Sirt1, superoxide dismutase 1/2, cyclin-dependent kinases 4/6, phosphorylated retinoblastoma protein, and transcription factor E2F1/2. However, these effects were rescued by p16 deletion. Our results demonstrate that p16 plays an important role in IVDD pathogenesis and that its deletion attenuates IVDD by promoting cell cycle and inhibiting SASP, cell senescence, and oxidative stress.

Highlights

Intervertebral disc degeneration (IVDD) refers to the physiological and pathological process of natural degeneration and aging of the intervertebral disc, which is the basis of various clinical spinal diseases (Silagi et al, 2018)
Numerous studies have proven that p16 contributes to IVDD pathogenesis, few have focused on the role of p16 in humans
An unbiased comparison of p16 expression in nucleus pulposus (NP) cells from IVDD patients with varying Pfirrmann scores showed that p16 expression is positively correlated with the degree of human disc degeneration

Summary

Introduction

Intervertebral disc degeneration (IVDD) refers to the physiological and pathological process of natural degeneration and aging of the intervertebral disc, which is the basis of various clinical spinal diseases (Silagi et al, 2018). In mouse fat tissue, muscles or eyes, removing the cells that contain high levels of p16 delays aging-associated disorders It was still unknown whether deactivating the gene that codes p16 in senescent cells could delay disc degeneration. The human intervertebral disc is a non-vascular tissue, and its annulus fibrosus (AF) and inner layer nucleus pulposus (NP) rely mainly on the penetration of the end plate to provide nutrition In this chronically high osmotic pressure, low pH, hypoxic and low-nutrition environment, the cells are less active. The systemic clearance of p16-positive senescent cells and conditional Cdkn2a gene deletion have been shown to mitigate age-associated IVDD in mice, mostly by suppressing the senescenceassociated secretory phenotype (SASP), improving matrix homeostasis, and reducing apoptosis (Novais et al, 2019; Patil et al, 2019). The present study aimed to highlight the influence of p16 on disc degeneration, mainly focusing on oxidative stress and human NP cell proliferation, and verified this effect in mice that have homozygous deletion of Cdkn2a

Results

Discussion

Findings

Materials and methods