This 2009 study surgically induced joint damage in the knees of mice lacking MMP13 and of normal mice. Both lost aggrecan, but by eight weeks the MMP13 knockout mice had less tibial cartilage erosion. Swelling of the cartilage cells and bony outgrowths still developed, so MMP13 mattered for erosion but not for those changes.
Researchers surgically induced joint damage in the knees of MMP13 knockout and wild-type mice and compared them at 4 and 8 weeks. They scored aggrecan loss, cartilage erosion and chondrocyte hypertrophy (enlargement of cartilage cells) in the femur and tibia, measured the size and maturity of osteophytes (bony outgrowths), and stained sections for type X collagen and for a fragment of aggrecan made by MMPs.
In wild-type mice, damage was worse in the tibia than the femur, and tibial erosion grew over time. At 4 weeks the two kinds of mice did not differ in aggrecan loss or erosion. At 8 weeks, knockout mice had less tibial cartilage erosion. Osteophytes were larger in knockout mice at 4 weeks but no different by 8 weeks. Chondrocyte hypertrophy, with type X collagen and the aggrecan fragment, appeared in both. The authors concluded that structural cartilage damage in this model depends on MMP13, and that removing MMP13 limits erosion even when aggrecan is depleted.
Knockout mice lack MMP13 from birth, which is different from lowering it later in life. The abstract does not give the number of mice. The benefit appeared at 8 weeks and in the tibia only, and the study tested no drug or nutrient. Mouse knees are a model, not a guide to results in people.
It is the mirror image of Neuhold's 2001 study: adding active MMP13 caused erosion, and taking MMP13 away reduced it. That erosion was limited even after aggrecan had been lost supports the idea that protecting the collagen still matters after the early aggrecan stage.
Because it acts at the step reviews call irreversible. MMP13 is the main enzyme cutting type II collagen in damaged cartilage, and that collagen renews very slowly. Mice...
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MMP13 cuts type II collagen, the rope-like fibre that gives cartilage its strength. It cleaves each three-stranded collagen molecule at one spot, leaving a three-quarter...
It depends which part is damaged. Reviews describe losing aggrecan, the water-holding molecule in cartilage, as an early and reversible step, and losing type II collagen...