3.1 In a rabbit model of impingement knee cartilage injury, we
found an innate immune response mechanism at the early stage of injury.
As described above, We applied Borrelli’s method in rabbits to verify
the pathological changes of impingement knee cartilage injury. According
to the experimental plan, after the surgery of rabbit, we have selected
1, 2 and 4 weeks as the detection time points for research. At 1 week
after injury, the articular cartilage was significantly degenerated in
rabbits with impingement knee cartilage injury ,as shown by HE and
safranin-O & fast green staining(Fig. 1A,B) and the Mankin’s scores
were also signifificantly increased compared with those of control
rabbits in 0 week (Fig. 1C). All joint specimens obtained were
photographed for observation prior to histological examination,We can
observe the repair of articular cartilage injury at different time
points, the cartilaginous surface of the joint after injury is repaired
to varying degrees over time (Fig.S1).As time went on, the degree of
cartilage damage gradually decreased, and the cartilage damage was
significantly improved four weeks later. We also performed MRI scanning
and marked imaging on the articular surface of different groups of
rabbit joints, and observed that the normal articular cartilage surface
was clear and smooth, with complete morphology and uniform thickness.
Form the result,1 week after the injury, the cartilage injury site was
obvious and clear, as it is showed by the red arrow marks. Cartilage
damage was still visible 2 weeks later, however, after 4 weeks the
cartilage basically returned to normal (Fig.1D).
Meanwhile, one week after the injury, the expression of MMP13 and MMP9,a
molecule directly involved in cartilage degradation, was significantly
increased compared with control rabbits of 0 week ,and the expression of
MMPs decreased gradually with the extension of injury time. To further
quantitatively detect the expression of genes related to cartilage
repair, molecular markers COL1A1, COL2A1, MMP9, MMP13 and ADAMTS-5 were
selected to be observed at different time points after cartilage injury.
The results indicated that the expression levels of COL1A1, COL2A1 and
MMP9 gradually increased 1 week after impaction, and reached a peak at 2
weeks after injury. Meanwhile, the expressions of MMP13 and ADAMTS-5
peaked in the first week after injury, and then decreased gradually
(Fig.1E-I). In order to further verify damage, we further tested the
protein level of the cartilage,
result of western blot showed
that the expressions of COL1A1, COL2A1 and MMP9 were the highest in the
second week, while the expressions of mmp13 and ADAMTS5 were the highest
in the third week (Fig.1H,S2).
Based on these results, we successfully constructed an animal model of
cartilage impact injury, and further verified the changes of different
injury factors during the injury process through histology and molecular
studies.