Figure 1.
Immunolabeling for collagen VI in the articular cartilage of the mouse tibial plateau cartilage.
Top row: Collagen VI is found exclusively in the pericellular region of chondrocytes in the wild-type PCM (left). Bottom row: Corresponding DIC images overlaid with collagen VI labeling (green) and nuclear staining (red). Cartilage of the Col6a1−/− mice (right) shows no labeling for collagen VI. Scale bar, 50 µm. WT = Col6a1+/+; KO = Col6a1−/−.
Figure 2.
MicroCT measures of trabecular bone structure.
In the tibial epiphysis of collagen VI null mice (Col6a1−/−), the structure model index (SMI, A) shows evidence of rod-like trabeculae from the earliest age, in contrast to the initially plate-like trabeculae of the wild-type mice. The trabecular bone volume (BV, B) is low from an early age and contributes to a higher bone tissue density (BD, D) in 2-month-old Col6a1−/− mice. With increasing age, the Col6a1−/− connectivity density (ConnDens, C) drops significantly at 15 months. Bars are mean ± SEM. Starred bars with no connecting lines are different from all other bars including each other. Horizontal lines connect statistically significantly different values. *p<0.05; **p<0.01. WT = Col6a1+/+; KO = Col6a1−/−.
Figure 3.
MicroCT images of 2-month-old mouse knees, showing the calcified structures of the right knees of a male wild-type mouse (left images: A, C, E) and a male Col6a1−/− mouse (right images: B, D, F).
Top row (A, B) shows a medial view of the knee; note the ossified medial collateral ligament in the Col6a1−/− joint (arrow, B). Middle row (C, D) displays a distal view of the tibial trabecular bone, where the Col6a1−/− trabeculae are rod-like while the wild-type trabeculae are plate-like. Bottom row (E, F) shows a proximal view of the tibial metaphyseal region, where the wild-type bone is immature in comparison to the Col6a1−/− bone. WT = Col6a1+/+; KO = Col6a1−/−.
Figure 4.
Mineral content of the Col6a1−/− tibial metaphysis.
In the tibial metaphysis directly distal to the fibular attachment (25 microCT slices = 0.4 mm), wild-type mice quadrupled their mineral content from 2-months-old to 9-months-old. In contrast, collagen VI null mice already had an intermediate level of mineral content by 2 months of age; this mineral content never changed. Bars are mean ± SEM; those sharing the same letter are not statistically different; bars with different letters: p<0.01. WT = Col6a1+/+; KO = Col6a1−/−.
Figure 5.
Effects of genotype on the joint capsule and subchondral bone.
Joint capsule thickness on the medial side was high in Col6a1−/− mice from the youngest age but almost universally low in wild-type mice until the oldest age (A). Subchondral bone thickness, in contrast, shows that Col6a1−/− bone fails to thicken with age, unlike the wild-type bone (B). Bars are mean ± SEM. Starred bars with no connecting lines are different from all other bars including each other. Starred bar connected by notches on horizontal line to multiple bars is different from those values. *p<0.05, **p<0.01. WT = Col6a1+/+; KO = Col6a1−/−.
Figure 6.
Histologic images revealed differences among wild-type and Col6a1−/− knees at 2, 9, and 15 months.
Coronal tissue slices (7 µm thick) were stained with fast green for collagen (blue) and safranin-O for proteoglycans (proteoglycans), and Harris' hematoxylin for nuclei (black). The left side is lateral while the right side is medial. The collagen VI null knees (right column) include a thick and proteoglycan-rich medial collateral ligament, increased chondrophyte formation on the lateral femur, larger trabeculae in both bones, and at 2 months a more confined growth-plate staining relative to the wild-type knees (left column). Scale bar = 1 mm. WT = Col6a1+/+; KO = Col6a1−/−.
Figure 7.
Effects of genotype on cartilage and joint structure.
Cartilage degradation in Col6a1−/−mice did not significantly increase with age, whereas wild type cartilage increased from 2 to15 months. (A) Bars are mean ± SEM. Osteophyte score was initially low in Col6a1+/+ mice and trended up with age, whereas severity of osteophytes began and remained high among the Col6a1−/− mice (B). Median with quartile bars shown. The combination of the two scores showed trends similar to that of the Modified Mankin score (C). Bars are mean ± SEM. Starred bar connected by notches on horizontal line to multiple bars is different from those values. *p<0.05, **p<0.01. WT = Col6a1+/+; KO = Col6a1−/−.