Extensive mechanical tension promotes annulus fibrosus cell senescence through suppressing cellular autophagy

Abstract

Background: Mechanical load contributes a lot to the initiation and progression of disc degeneration. Annulus fibrosus (AF) cell biology under mechanical tension remains largely unclear. Objective: The present study was aimed to investigate AF cell senescence under mechanical tension and the potential role of autophagy. Methods: Rat AF cells were cultured and experienced different magnitudes (5% elongation and 20% elongation) of mechanical tension for 12 days. Control AF cells were kept static. Cell proliferation, telomerase activity, cell cycle fraction, and expression of senescence-related molecules (p16 and p53) and matrix macromolecules (aggrecan and collagen I) were analyzed to evaluate cell senescence. In addition, expression of Beclin-1 and LC3, and the ratio of LC3-II to LC3-I were analyzed to investigate cell autophagy. Results: Compared with the control group and 5% tension group, 20% tension group significantly decreased cell proliferation potency and telomerase activity, increased G1/G0 phase fraction, and up-regulated gene/protein expression of p16 and p53, whereas down-regulated gene/protein expression of aggrecan and collagen I. In addition, autophagy-related parameters such as gene/protein expression of Beclin-1 and LC3, and the ratio of LC3-II to LC3-I, were obviously suppressed in the 20% tension group. Conclusion: High mechanical tension promotes AF cell senescence though suppressing cellular autophagy. The present study will help us to better understand AF cell biology under mechanical tension and mechanical load-related disc degeneration.

Cell Senescence: A Nonnegligible Cell State under Survival Stress in Pathology of Intervertebral Disc Degeneration

“…Selective elimination of senescent NP cells protects tail suspension- (TS-) induced IDD mice from disc degeneration. Similar relationship between mechanical stress and cell senescence is proved in AF and EP cells [ 46 , 47 ]. Further investigation indicated that the increased oxidative stress acted as a causative intermediator during mechanical factor-associated SIPS in degenerated discs [ 50 ].…”

“…As the functional cells in discs during intervertebral disc growth, NP, AF, and EP cells are in charge of ECM anabolic balance in separate regions, which play a key role in maintaining normal extracellular microenvironment [ 43 ]. These functional cells derived from degenerative discs all undergo the decline of proliferating potential, with high expressions of SA- β -gal and p16 (Ink4a) as well as decreased telomere length [ 4 , 46 , 47 ]. Interestingly, these senescence-associated changes in EPs seem to appear later than in AF and NP [ 46 ].…”

Transforming growth factor-β1-regulated Fas/FasL pathway activation suppresses nucleus pulposus cell apoptosis in an inflammatory environment

“…Until now, the accurate pathogenesis of disc degeneration is not clear. It has been established that NP cell apoptosis is the main cause of disc degeneration and gradually increases with advancing age [6,25,26]. Besides, increased content of inflammatory cytokines is another important feature within the degenerative disc NP region [27].…”

Upregulation of P53 promotes nucleus pulposus cell apoptosis in intervertebral disc degeneration through upregulating NDRG2

“…Here, we provided evidence that P53 is a positive regulator of NDRG2. Numerous studies have documented upregulated P53 levels in annulus fibrosus cells (Zhao et al, 2019) and in NP cells in IVDD (Zhao et al, 2019). The results in these studies are in agreement with our findings, which demonstrated that P53 was upregulated in IVDD, and the exogenous P53 overexpression could up‐regulate NDRG2.…”