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2018 ; 20
(1
): 67
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Osteoclasts degrade bone and cartilage knee joint compartments through different
resorption processes
#MMPMID29636095
Löfvall H
; Newbould H
; Karsdal MA
; Dziegiel MH
; Richter J
; Henriksen K
; Thudium CS
Arthritis Res Ther
2018[Apr]; 20
(1
): 67
PMID29636095
show ga
BACKGROUND: Osteoclasts have been strongly implicated in osteoarthritic cartilage
degradation, at least indirectly via bone resorption, and have been shown to
degrade cartilage in vitro. The osteoclast resorption processes required to
degrade subchondral bone and cartilage-the remodeling of which is important in
the osteoarthritic disease process-have not been previously described, although
cathepsin K has been indicated to participate. In this study we profile
osteoclast-mediated degradation of bovine knee joint compartments in a novel in
vitro model using biomarkers of extracellular matrix (ECM) degradation to assess
the potential of osteoclast-derived resorption processes to degrade different
knee joint compartments. METHODS: Mature human osteoclasts were cultured on ECMs
isolated from bovine knees-articular cartilage, cortical bone, and osteochondral
junction ECM (a subchondral bone-calcified cartilage mixture)-in the presence of
inhibitors: the cystein protease inhibitor E-64, the matrix metalloproteinase
(MMP) inhibitor GM6001, or the vacuolar-type H(+)-ATPase (V-ATPase) inhibitor
diphyllin. Biomarkers of bone (calcium and C-terminal type I collagen (CTX-I))
and cartilage (C2M) degradation were measured in the culture supernatants.
Cultures without osteoclasts were used as background samples.
Background-subtracted biomarker levels were normalized to the vehicle condition
and were analyzed using analysis of variance with Tukey or Dunnett's T3 post hoc
test, as applicable. RESULTS: Osteochondral CTX-I release was inhibited by E-64
(19% of vehicle, p = 0.0008), GM6001 (51% of vehicle, p = 0.013), and E-64/GM6001
combined (4% of vehicle, p = 0.0007)-similarly to bone CTX-I release. Diphyllin
also inhibited osteochondral CTX-I release (48% of vehicle, p = 0.014), albeit
less than on bone (4% of vehicle, p 0.0001). Osteochondral C2M release was only
inhibited by E-64 (49% of vehicle, p = 0.07) and GM6001 (14% of vehicle, p =
0.006), with complete abrogation when combined (0% of vehicle, p = 0.004).
Cartilage C2M release was non-significantly inhibited by E-64 (69% of vehicle, p
= 0.98) and was completely abrogated by GM6001 (0% of vehicle, p = 0.16).
CONCLUSIONS: Our study supports that osteoclasts can resorb non-calcified and
calcified cartilage independently of acidification. We demonstrated both
MMP-mediated and cysteine protease-mediated resorption of calcified cartilage.
Osteoclast functionality was highly dependent on the resorbed substrate, as
different ECMs required different osteoclast processes for degradation. Our novel
culture system has potential to facilitate drug and biomarker development aimed
at rheumatic diseases, e.g. osteoarthritis, where pathological osteoclast
processes in specific joint compartments may contribute to the disease process.