Injection Reverses Cartilage Loss in Aging knees, Offers Hope for Arthritis Treatment

An injection that blocks the activity of a protein involved in aging reverses naturally occurring cartilage loss in the knee joints of old mice, a Stanford Medicine-led study has found. The treatment also prevented the development of arthritis after knee injuries mirroring the ACL tears often experienced by athletes or recreational exercisers. An oral version of the treatment is already in clinical trials wiht the goal of treating age-related muscle weakness.

Samples of human tissue from knee replacement surgeries-which include both the extracellular scaffolding, or matrix, in the joint as well as cartilage-generating chondrocyte cells-also responded to the treatment by making new, functional cartilage.

The study results suggest it may be possible to regenerate cartilage lost to aging or arthritis with an oral drug or local injection,rendering knee and hip replacement unneeded.

The treatment directly targets the cause of osteoarthritis, a degenerative joint disease that affects 1 of every 5 adults in the United States and is estimated to cost about $65 billion in direct health care costs each year. No drug can currently slow down or reverse the disease; the primary treatments for osteoarthritis are pain control and surgical replacement of the affected joints.

The protein, 15-PGDH-termed a gerozyme due to its increase in prevalence as the body ages-is a master regulator of aging. Gerozymes,identified by the same researchers in 2023,also drive the loss of tissue function. they are a major force behind age-related loss of muscle strength in mice.

Blocking the function of 15-PGDH with a small molecule results in an increase in old animals’ muscle mass and endurance.Conversely,expressing 15-PGDH in young mice causes their muscles to shrink and weaken. The gerozyme has also been implicated in the regeneration of bone, nerve and blood cells.

In each of these tissues, regeneration is due to increases in the proliferation and specialization of cells.

Reversing Cartilage Loss and Addressing ACL Tears with a Novel Approach

Previous research has demonstrated that prostaglandin E2 is essential for muscle stem cell function, and that inhibiting the enzyme 15-PGDH – which degrades prostaglandin E2 – supports regeneration in damaged tissues like muscle, nerve, bone, colon, liver, and blood cells in young mice. Researchers at Blau’s lab, including Bhutani and colleagues, investigated whether 15-PGDH also plays a role in aging cartilage and joints, hypothesizing a similar pathway contributes to cartilage loss with age or injury. Their findings revealed that 15-PGDH levels increased two-fold in the knee cartilage of older mice compared to younger mice.

Experiments involving injections of a small molecule drug inhibiting 15-PGDH activity – both systemically and directly into the joint – showed remarkable results. Knee cartilage,significantly thinner and less functional in older animals,thickened across the joint surface. Further analysis confirmed the regeneration of hyaline, or articular, cartilage by chondrocytes within the joint, rather than the less-functional fibrocartilage. “Cartilage regeneration to such an extent in aged mice took us by surprise,” Bhutani noted, emphasizing the critically important effect observed.

Similar positive outcomes were seen in animals with knee injuries,specifically ACL tears – common in sports involving pivoting,stopping,or jumping. While ACL tears are often surgically repaired, approximately 50% of patients develop osteoarthritis within 15 years. Treatment with the 15-PGDH inhibitor, administered via twice-weekly injections for four weeks post-injury, dramatically reduced the development of osteoarthritis in mice. Control animals exhibited twice the 15-PGDH levels of uninjured peers and developed osteoarthritis within four weeks.

Furthermore, animals treated with the gerozyme inhibitor demonstrated more natural movement and greater weight-bearing capacity on the affected leg compared to untreated animals. “Interestingly, prostaglandin E2 has been implicated in inflammation and pain,” Blau added, “But this research shows that, at normal bi

Scientists Discover Way to Boost Cartilage Repair

For years, scientists haven’t been able to reliably repair damaged cartilage. It’s a huge problem for people with arthritis and sports injuries. Now,that coudl change. Researchers have identified a key enzyme that, when blocked, actually promotes cartilage regrowth.

The study, published in Science on November 27, 2025, focuses on 15-hydroxy prostaglandin dehydrogenase (15-PGDH). It’s an enzyme that breaks down a molecule called PGE2. PGE2 seems crucial for cartilage repair, but 15-PGDH stops it from working effectively.

Researchers found that inhibiting 15-PGDH allows PGE2 to build up. This buildup doesn’t just slow cartilage breakdown-it actively stimulates regeneration.It’s a significant shift in understanding how cartilage heals.

“We were surprised to see such a strong regenerative effect,” says Mamta Singla, lead author of the study. “It wasn’t just about preventing further damage; we were actually seeing cartilage grow back.”

The team tested their findings in mice with osteoarthritis. Blocking 15-PGDH led to noticeable cartilage repair. They saw improvements in joint function and reduced pain. It’s promising, but more research is needed.

This isn’t a cure yet. But it’s a major step forward. Scientists are now working on developing drugs that can safely and effectively inhibit 15-PGDH in humans. They don’t know the long-term effects, so caution is key.

This discovery could revolutionize treatment for osteoarthritis and other cartilage-related conditions. Imagine a future where damaged joints can be healed, not just managed. It’s a hopeful prospect.

Source: Singla, M., et al. Inhibition of 15-hydroxy prostaglandin dehydrogenase promotes cartilage regeneration. Science (2025). DOI: 10.1126/science.adx6649. www.science.org/doi/10.1126/science.adx6649