The University of Hong Kong The University of Hong Kong, Hong Kong
Abstract: The depletion of extracellular matrix-producing nucleus pulposus (NP) cells and long-lived progenitors leads to progressive degenerative changes in the intervertebral disc (IVD) over a lifetime. While pluripotent stem cells hold potential for deriving notochordal and NP cells, they face challenges in translational medicine. Conversely, adult MSCs may serve as a promising alternative for deriving NP progenitors, although an optimal differentiation protocol is still lacking. Tie2 and GD2 expressing adult NP progenitor cells have been reported to exhibit in vitro clonogenicity and in vivo self-renewal ability. Through microarray analysis of the transcriptome in rat primitive NP and costal cartilage, we identified preferential expressions of Cdh2, Krt19, and Car3 in rat primitive NP. Further in silico analysis of signaling pathways suggested that rat primitive NP exhibits low MAP kinase activity in TGF-β signaling. Mesenchymal stem cells (MSCs) have been demonstrated to differentiate into NP-like cells via TGF-β stimulation. Here, we hypothesized that human bone marrow MSCs could differentiate into NP progenitor-like cells through MAP kinase interference coupled with TGF-β1 mediated chondrogenic induction (MICCI). To this end, we confirmed the protein expression of CDH2 in Colonies Formation Units-Spherical (CFU-S) as a unique marker of human NP progenitors. Additionally, QPCR showed strong upregulations of CDH2 at Day 1 and NP-associated markers (COL2A1, ACAN, CD24 and KRT19) from Day 7 to Day 21 in MEK1/2 inhibitor-treated MSC micro-pellets. On the other hand, TGF-β1 could stimulate CFU-S formation in human NP cells. Interestingly, the ability to form CFU-S was reduced with TGF-β1 in the presence of a MEK inhibitor. This may suggest that TGF-β1 promotes the proliferation of dormant NP cells into progenitor colonies. MEK1/2 inhibition could couple with TGF-β1-induced nucleopulpogenic differentiation of progenitors into committed NP-like cells.
Funding Source: Health and Medical Research Fund (HMRF) 9202236
