Nucleus pulposus (NP) cell senescence is a typical pathological feature within the degenerative intervertebral disc. As a potential inducing and aggregating factor of disc degeneration, mechanical overloading affects disc biology in multiple ways. The present study was to investigate the NP cell senescence-associated phenotype under intermittent high compression in an ex vivo disc bioreactor culture, and the role of the p38–MAPK pathway in this regulatory process. Porcine discs were cultured in culture chambers of a self-developed mechanically active bioreactor and subjected to different magnitudes of dynamic compression (low-magnitude and high-magnitude: 0.1 and 1.3 MPa at a frequency of 1.0 Hz for 2 h per day respectively) for 7 days. Non-compressed discs were used as controls. The inhibitor SB203580 was used to study the role of the p38–MAPK pathway in this process. Results showed that intermittent high-magnitude compression clearly induced senescence-associated changes in NP cells, such as increasing β-galactosidase-positive NP cells, decreasing PCNA-positive NP cells, promoting the formation of senescence-associated heterochromatic foci (SAHF), up-regulating the expression of senescence markers (p16 and p53), and attenuating matrix production. However, inhibition of the p38–MAPK pathway partly attenuated the effects of intermittent high-magnitude (1.3 MPa) compression on those described NP cell senescence-associated parameters. In conclusion, intermittent high-magnitude compression can induce NP cell senescence-associated changes in an ex vivo disc bioreactor culture, and the p38–MAPK pathway is involved in this process.

Mechanical stimuli obviously affect disc nucleus pulposus (NP) biology. Previous studies have indicated that static compression exhibits detrimental effects on disc biology compared with dynamic compression. To study disc NP cell senescence under static compression and dynamic compression in a disc organ culture, porcine discs were cultured and subjected to compression (static compression: 0.4 MPa for 4 h once per day; dynamic compression: 0.4 MPa at a frequency of 1.0 Hz for 4 h once per day) for 7 days using a self-developed mechanically active bioreactor. The non-compressed discs were used as controls. Compared with the dynamic compression, static compression significantly promoted disc NP cell senescence, reflected by the increased senescence-associated β-galactosidase (SA-β-Gal) activity, senescence-associated heterochromatic foci (SAHF) formation and senescence markers expression, and the decreased telomerase (TE) activity and NP matrix biosynthesis. Static compression accelerates disc NP cell senescence compared with the dynamic compression in a disc organ culture. The present study provides that acceleration of NP cell senescence may be involved in previously reported static compression-mediated disc NP degenerative changes.

Diabetes mellitus (DM) is an important risk factor of intervertebral disc degeneration. However, how DM affects annulus fibrosus (AF) biology remains unclear. The present study was aimed to investigate the effects and mechanism of high glucose on AF cell biology. Rat AF cells were cultured in baseline medium and culture medium with 0.2 M glucose. The inhibitor 4-PBA was added along with the high glucose culture medium to study the role of endoplasmic reticulum (ER) stress in this process. Compared with the control cells, high glucose significantly increased cell apoptosis ratio and caspase-3/9 activity, up-regulated mRNA/protein expression of Bax and caspase-3/cleaved caspase-3, but down-regulated mRNA/protein expression of Bcl-2. Moreover, high glucose increased mRNA and protein expression of CHOP, ATF-6 and GRP78. However, once ER stress was inhibited by the inhibitor 4-PBA in the high glucose group, cell apoptosis ratio and caspase-3/9 activity were decreased, mRNA/protein expression of Bax and caspase-3/cleaved caspase-3 was down-regulated, but mRNA/protein expression of Bcl-2 was up-regulated. In conclusion, high glucose condition can promote AF cell apoptosis through inducing ER stress. The present study helps us understand the mechanism of disc degeneration in DM patients.

No abstract