Journal
JOURNAL OF ORTHOPAEDIC RESEARCH
Volume 40, Issue 7, Pages 1661-1671Publisher
WILEY
DOI: 10.1002/jor.25190
Keywords
AKT; ALK5; annulus fibrosus; CD146 regulation; cell contractility; SMADs; TGF-beta
Categories
Funding
- AO Foundation
- AOSpine International
- European Union's Horizon2020 research and innovation programme under Marie Sklodowska-Curie Grant [801540]
- Dutch Arthritis Society [LLP12, LLP22]
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CD146 has been shown to play a crucial role in maintaining the cell contractility of human AF cells in vitro. Additionally, TGF-beta upregulates CD146 via the ALK5 signaling cascade, partially through the SMAD2, SMAD4, and AKT pathways, while ERK acts as a potential negative modulator.
The mouse outer annulus fibrosus (AF) was previously shown to contain CD146(+) AF cells, while in vitro culture and exposure to transforming growth factor-beta (TGF-beta) further increased the expression of CD146. However, neither the specific function of CD146 nor the underlying mechanism of TGF-beta upregulation of CD146(+)AF cells have been elucidated yet. In the current study, CD146 expression and its role in cultured human AF cells was investigated studying the cells' capacity for matrix contraction and gene expression of functional AF markers. In addition, TGF-beta pathways were blocked by several pathway inhibitors and short hairpin RNAs (shRNAs) targeting SMAD and non-SMAD pathways to investigate their involvement in TGF-beta-induced CD146 upregulation. Results showed that knockdown of CD146 led to reduction in AF cell-mediated collagen gel contraction, downregulation of versican and smooth muscle protein 22 alpha (SM22 alpha), and upregulation of scleraxis. TGF-beta-induced CD146 upregulation was significantly blocked by inhibition of TGF-beta receptor ALK5, and partially inhibited by shRNA against SMAD2 and SMAD4 and by an Protein Kinase B (AKT) inhibitor. Interestingly, the inhibition of extracellular signal-regulated kinases (ERK) pathway induced CD146 upregulation. In conclusion, CD146 was shown to be crucial to maintain the cell contractility of human AF cells in vitro. Furthermore, TGF-beta upregulated CD146 via ALK5 signaling cascade, partially through SMAD2, SMAD4, and AKT pathway, whereas, ERK was shown to be a potential negative modulator. Our findings suggest that CD146 can potentially be used as a functional marker in AF repair strategies.
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