Mechanism of the Mitogen-Activated Protein Kinases/Mammalian Target of Rapamycin Pathway in the Process of Cartilage Endplate Stem Cell Degeneration Induced by Tension Load

Abstract

Study Design Basic Research. Objective Intervertebral disc degeneration (IVDD) is caused by the cartilage endplate (CEP). Cartilage endplate stem cell (CESC) is involved in the recovery of CEP degeneration. Tension load (TL) contributes a lot to the initiation and progression of IVDD. This study aims to investigate the regulatory mechanism of the Mitogen-activated protein kinases/Mammalian target of rapamycin (MAPK/mTOR) pathway during TL-induced CESC degeneration. Methods CESCs were isolated from New Zealand big-eared white female rabbits (6 months old). FX-4000T cell stress loading system was applied to establish a TL-induced degeneration model of CESCs. Western blotting was used to detect the level of mTOR pathway-related proteins and autophagy markers LC3-Ⅱ, Beclin-1, and p62 in degenerative CESCs. The expression of MAPK pathway-related proteins JNK and extracellular signal-regulated kinases (ERK) in degenerated CESCs was inhibited by cell transfection to explore whether JNK and ERK play a regulatory role in TL-induced autophagy in CESCs. Results In the CESC degeneration model, the mTOR pathway was activated. After inhibition of mTOR, the autophagy level of CESCs was increased, and the degeneration of CESCs was alleviated. The MAPK pathway was also activated in the CESC degeneration model. Inhibition of JNK expression may alleviate TL-induced CEP degeneration by inhibiting Raptor phosphorylation and activating autophagy. Inhibition of ERK expression may alleviate TL-induced CEP degeneration by inhibiting mTOR phosphorylation and activating autophagy. Conclusion Inhibition of JNK and ERK in the MAPK signaling family alleviated TL-induced CESC degeneration by inhibiting the phosphorylation of Raptor and mTOR in the mTOR pathway.

Stress-Activated Protein Kinases in Intervertebral Disc Degeneration: Unraveling the Impact of JNK and p38 MAPK

“…When JNK was inhibited, the protein levels of the autophagy markers microtubule-associated protein 1 light chain 3 beta-II (LC3-II) and Beclin-1 increased, while the protein levels of p62 decreased. This suggests that the downregulation of JNK may mitigate TL-induced CEP degeneration through the activation of autophagy [26]. Additionally, p38 MAPK is considered to play a crucial role in inhibiting the activation of autophagy.…”

“…JNK and p38 MAPK can also increase the content of intracellular reactive oxygen species (ROS), leading to oxidative stress damage, and affect the excessive accumulation of iron in cells, leading to the occurrence of ferroptosis [24,25]. Additionally, inhibition of JNK and p38 MAPK significantly increases the level of intracellular autophagy in NP cells, thus delaying apoptosis and ECM degradation [26,27]. However, the specific signal transduction mechanism of JNK and p38 MAPK in IDD is not clear and needs further exploration.…”

Signaling Mechanisms of Stem Cell Therapy for Intervertebral Disc Degeneration

“…Inhibition of the JNK signaling pathway alleviates degeneration of stem cells derived from CEP, NP, and bone marrow [ 119 ]. For example, oxidative stress during the transplant of BMSC to degenerative discs may cause cell toxicity and poor survival of BMSCs.…”

Cartilage Endplate-Derived Stem Cells for Regeneration of Intervertebral Disc Degeneration: An Analytic Study

“…56,59,60,64,66 Eight studies discussed the fate of CESCs in IDD. 54,57,61,63,[68][69][70]76 Eight studies elaborated on the biological potential of CESCs in intervertebral disc regeneration. 55,67,[71][72][73][74][75]77…”

“…These findings provide substantial evidence of CESCs in the CE. Subsequent research has identified CESCs in other species, including rats 70,71,73-75 and rabbits, 76 further broadening the scope of knowledge in this field.…”