Wharton’s Jelly-derived mesenchymal stem cells suppress apoptosis of nucleus pulposus cells in intervertebral disc degeneration via Wnt pathway

Y.-T. Zhao, Y. Qin, J.-S. Yang, D.-G. Huang, H.-M. Hu, X.-D. Wang, S.-F. Wu, D.-J. Hao

Department of Spine Surgery, Honghui Hospital, Xi’an Jiaotong University, Xi’an, China.zytqy@163.com

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• Orthopedics

OBJECTIVE: Aberrant apoptosis of nucleus pulposus cells (NPCs) is one of the most remarkable pathological changes in intervertebral disc degeneration (IDD) development. Albeit the advances in the application of stem cell-based therapy in IDD treatment, the molecular mechanisms underlying the anti-apoptotic actions of mesenchymal stem cell (MSC) remain poorly elucidated.

PATIENTS AND METHODS: The expression patterns of apoptosis-related proteins and Wnt/β-catenin-related genes in NP samples isolated from patients with mild or severe IDD were compared by performing immunoblot assay and quantitative real-time polymerase chain reaction (qRT-PCR), respectively. NPCs were in vitro treated with compression to induce apoptosis and then co-cultured with Wharton’s Jelly-derived MSCs without direct interaction. After that, flow cytometry was carried out to detect the apoptosis rate of NPCs and the activity of Wnt/β-catenin pathway was determined. DKK-1 was used to inhibit Wnt signaling, in prior to evaluation of the effects of WJ-MSCs on apoptosis within the co-cultured NPCs.

RESULTS: Compared to the mild IDD group, there was a significant increase in the expression of Caspase-3 and Bax in the NP tissues from severe IDD patients, whereas Bcl-2 displayed an opposite result. In addition, the expression of Wnt 3a, Wnt 5a, Wnt 10a, GSK-3β, cyclinD1 and β-catenin was notably augmented in parallel with IDD progression. After compression treatment, the proportion of apoptotic NPCs was increased, which was then dramatically reversed by WJ-MSCs co-culture. Likewise, WJ-MSCs suppressed compression-induced Wnt-related gene expression and blocking Wnt/β-catenin pathway using DKK-1 enhanced the anti-apoptotic impacts of WJ-MSCs. In the presence of DKK-1, there was no significant difference between NPCs co-cultured with WJ-MSCs and those cells cultured alone.

CONCLUSIONS: WJ-MSCs attenuate the compression-induced apoptosis in NPCs and inhibit the activation of Wnt/β-catenin signaling. Blocking Wnt/β-catenin pathway further facilitates the actions of WJ-MSCs in anti-apoptosis, indicating that Wnt/β-catenin signaling plays a crucial role in this process and may function as a potential therapeutic target for IDD treatment.

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