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Blocking the age-linked enzyme 15-PGDH regrows knee cartilage in old mice
Stanford scientists restored lost knee cartilage in old mice by blocking 15-PGDH, an enzyme whose levels climb with age, a study in Science reports. The result is a credible preclinical lead for a drug against osteoarthritis, a disease that no current medicine reliably slows or reverses.
The Scientist · Science desk
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What happened
- The same inhibitor helped protect mice from osteoarthritis after knee injuries resembling ACL tears in people.
- The repair came from chondrocytes already in the joint, which changed their gene activity and shifted toward a more youthful state without any stem cell contribution.
- The group had already shown that blocking 15-PGDH increased muscle mass and endurance in old mice, while raising it in young mice weakened their muscles.
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Why it matters
- capability Because the responsive human tissue came from joints already being replaced, the inhibitor works on cartilage at the disease stage where surgery is now the usual endpoint.
- exposure An oral version would act on muscle, bone, nerve and blood as well as cartilage, so safety testing has to cover every tissue where 15-PGDH regulates ageing.
- constraint Until the inhibitor is tested in patients, these results give surgeons and patients no basis for putting off a knee or hip replacement.
- cost Osteoarthritis accounts for roughly $65 billion a year in direct US health care costs, and a drug that spares joints would draw on that spending if it works in people.
Helen Blau runs Stanford's Baxter Laboratory for Stem Cell Biology [14], so her team first went looking for stem cells as the source of the new cartilage. Earlier results pointed that way. 15-PGDH has been linked to regeneration of bone, nerve and blood cells [9], and in many of those tissues healing depends on tissue-specific stem cells multiplying and maturing into specialized cells [7]. Cartilage did something else. The chondrocytes already in the joint changed their patterns of gene activity and shifted toward a more youthful state [6]. "We were looking for stem cells, but they are clearly not involved. It's very exciting," Blau said [10].
Each arm of the design tests a different thing. Old mice that had lost cartilage to ageing test one route to osteoarthritis. Mice with an ACL-like knee injury test another [1][2]. The third arm uses human tissue. Those samples were collected during knee replacement surgeries [3], from joints damaged far enough that surgery was the remaining option [12]. That cartilage still began producing new tissue after exposure to the inhibitor [3]. Mamta Singla and Yu Xin (Will) Wang are the lead authors [4].
Nidhi Bhutani, an associate professor of orthopaedic surgery and the other senior author [4], made the larger claim. "Until now, there has been no drug that directly treats the cause of cartilage loss. But this gerozyme inhibitor causes a dramatic regeneration of cartilage beyond that reported in response to any other drug or intervention," she said [15]. That ranking against every other intervention is the authors' own. Testing it will take the effect sizes in the Science paper [4].
The release does not report how many animals were treated, how much cartilage returned, how long treatment ran, whether the mice moved more easily or showed less pain, or what "functional" meant for the human samples. Cartilage treated in the lab after removal from a patient is also outside a working knee. It carries no body weight, and it does not face years of further wear.
The researchers say a version that works in people could become an oral medicine or an injection that reduces the need for knee and hip replacements [16]. The route matters. The group's earlier work showed 15-PGDH regulates ageing outside the joint: a small-molecule blocker increased muscle mass and endurance in old mice, and raising the protein in young mice made their muscles shrink and weaken [8]. A pill would reach muscle, bone, nerve and blood along with cartilage [17].
In my view the work earns the word "lead". The target already had ageing biology behind it in muscle [8]. The cartilage response appeared in two separate mouse models [1][2], and end-stage human tissue responded too [3]. The condition is the one the release states itself: the restoration holds "at least in mice" [13]. If it carries over, the patient pool is large. Osteoarthritis affects about one in five US adults and accounts for roughly $65 billion a year in direct health care costs [11], and current treatments mainly control pain and other symptoms [12].
What to watch
- The effect sizes, animal numbers and functional outcomes in the Science paper, especially whether treated mice showed less pain or better joint use.
- Whether the Stanford group or a licensee moves a 15-PGDH inhibitor into human trials, and whether it chooses an oral or injected route.
- An independent lab reproducing the finding that chondrocytes, not stem cells, produce the new cartilage.