Osteoarthritis (OA) is a degenerative disease characterised by progressive loss of
articular cartilage which affects millions of people globally. Although the leading
causes of OA are still elusive, the increasing body of evidence indicates that the
predisposing factors such as lifestyle, age, injuries and genetics associated with the
onset of OA. The regeneration of the degraded cartilage tissue in OA is mediated by
the tissue-resident stem cells. However, in advanced OA, the regenerative and tissue
repair capability of tissue-resident stem cells is compromised as a result of diseases
condition and leads to an unusual stem cell nature. Mesenchymal stem cells (MSCs)
have been implicated in the pathogenesis of OA and, in turn, the progression of the
disease could be therapeutically modulated by MSCs. However, it remains unclear
whether the defective tissue-resident MSCs contributes to the pathogenesis of OA by
a depleted stem cell pool or loss of the chondrogenic differentiation potential which
impedes on the proper execution of stem cell functions. Therefore, this study aimed to
explore the biological properties of human non-OA and OA cartilage-derived MSCs
(C-MSCs) as well as to determine whether the defects in human OA C-MSCs are
results of an inherent genetic make-up or acquired from the exposure of pathological
OA inflammatory environment.
A small fraction of non-weight bearing human articular cartilage from non-OA
subjects and OA patients were harvested during the arthroscopy session. Patients
(n=11) were selected based on the grade 4 osteoarthritis according to the Kleegren and
Lawrence score system, and five cartilage samples were obtained from nonosteoarthritic
donors undergoing knee surgery or arthroscopy due to the sports injury.
The optimised enzymatic digestion and serial plating methods were used to generate cartilage-derived MSCs. The differences in biological features of OA compared to
non-OA C-MSCs as well as that of non-OA C-MSCs cultured in OA synovial fluid
were investigated through a series of proliferation, cell cycle and apoptosis assays.
The secretome profile and the global gene expression were performed through
cytokine antibody arrays and microarray, respectively.
Mesenchymal stem cells were successfully generated from the human OA cartilage
tissues along with non-OA cartilage. As compared to the human non-OA C-MSCs, the
counterpart from OA exhibited compromised cell qualities in term of ill-defined
morphology specifically at late passages, lower colony forming ability, reduced
chondrogenesis when induced, a higher tendency towards osteogenic and adipogenic
differentiation. However, the immunophenotypic profile between these two groups
remained relatively same. Additionally, human OA C-MSCs also demonstrated slower
growth kinetics, prolonged doubling time, increased susceptibility to senescence
especially at late passages, reduced proliferation and poor immunosuppressive ability
against T cells. It was also observed that during the in vitro culture expansion, the
human OA C-MSCs underwent escalated level of cellular senescence in late passage
(80%), apoptosis (i.e. 18.33±0.1% early apoptosis, 6.46±0.2% late apoptosis at
passage 3 and 20.09±0.1% early apoptosis, 8.42±0.2% late apoptosis at passage 6),
exhibited G0/G1 cell cycle arrest (i.e. 78.68±3.17% of cells in G0/G1 phase, at passage
3 while passage 6 had 93.23±2.64% of cells in G0/G1 phase) with a secretome profile
that reveals the downregulation of anti-inflammatory cytokines such as IL-1, IL-6, and
IL-10, as well as aberrations in gene expression.
Analysis of OA synovial fluid indicated with presence of proinflammatory cytokines
that associated with OA pathophysiology while pre-treated non-OA C-MSCs with OA
synovial fluid exhibited increased apoptosis (i.e. 28.42±0.66% early apoptosis and
12.11±0.47% late apoptosis) and inhibition of proliferation via cell cycle arrest
(i.e.78.62±4.38% of cells in G0/G1 phase and 12.42±1.53% of cells in S phase). These
findings suggest that the catabolic and inflammatory agents in the synovial fluid could
be implicated in cartilage tissue degradation, and may also be involved in the alteration
of the inherent genetic makeup of cartilage tissue-resident MSCs which is evident
from the aberrant gene expression. The microarray-based gene expression analysis of
OA C-MSCs indicated dysregulation of essential genes of cell proliferation and
survival, whereas the gene expression of non-OA MSCs treated with OA synovial
fluid revealed dysregulation of cartilage metabolism. The KEGG pathway analysis
based on the dysregulated gene expression showed the involvement of several key
signalling pathways especially Wnt signalling, cell adhesion molecule pathway, Ras
signalling pathway, cytokine-cytokine receptor interaction pathway.
In conclusion, the biological features of OA C-MSCs are negatively affected by OA
disease. It could be possible that the inflammatory condition of OA synovial fluid
impedes the functional properties of cartilage tissue-resident MSCs. Thus, treatment
strategies for OA should be strategized by allotting an appropriate concern to the inflammatory condition that limits the function of tissue stem cells and therapeutically
transplanted stem cells
