How do stem cells work? We know some things. For example, stem cells can both differentiate (turn into) another cell and excrete chemicals to coordinate a repair response. They can transfer good mitochondrial batteries to a dying cell with bad batteries. They can also transfer some of their RNA into another cell and make it produce proteins. Now a new study also suggests that stem cells injected into a joint may be able to wake up local cartilage repair cells.
To understand the new research, you need to understand the structure of a joint. We’ll use the knee as an example. Joints consist of a variety of structures that all work in unison to provide smooth and proper movement. These include bones (in the knee, this would be the distal end of the femur, or the upper-leg bone, and the proximal end of the tibia, or lower-leg bone), ligaments (e.g., anterior cruciate ligament, or ACL), muscles, nerves, and cushioning and shock absorbing structures (in the knee, this would be the cartilage and meniscus).
Arthritis affects the cartilage and bone, damaging it and wearing it down further and further over time. In mild and moderate arthritis, the cartilage has been worn down or damaged to some degree, but there is still cartilage remaining. Severe arthritis occurs when it has reached the point of bone-on-bone arthritis and no cartilage remains. There are many things that can put us at risk for arthritis, such as hypertension, metabolic syndrome, a low-fat, high-carb diet, a sedentary lifestyle, NSAIDs, steroid injections, and surgeries that remove shock absorbing material. Injuries, such as a vehicle accident, can also lead to arthritis.
In our experience and based on our published studies, stem cell therapy can be a helpful treatment for knee pain stemming from arthritic knees, but how, exactly, does this work? A new study provides one of likely many answers to this question.
The new study set out to answer this question: is it the mesenchymal stem cells themselves regenerating damaged cartilage, or are they stimulating the local cells to wake up and repair the cartilage? Frankly, we have many studies which all suggest a different mechanism of action for stem cells, like all of the ones described above. So this study was never going to be definitive, but more designed to see if in this experimental design, stem cells worked a certain way.
This was a complex study in which mice were bred to recognize donor cells as their own host cells (to replicate a bone marrow stem cell therapy in which a patient’s own stem cells are harvested and reinjected). The researchers found that while the stem cells do attach to the damaged cartilage and that this is indeed imperative to regenerate the cartilage, in this study, it isn’t actually the injected stem cells that regenerate the cartilage—at least not directly. Instead, the action of the injected stem cells, the study found, is necessary to stimulate the local cells (knee, shoulder, etc.) to wake up and repair the cartilage.
Keep in mind that while stem cells can facilitate the repair of damaged cartilage via our local cells in mild arthritis, none of these cells can create new cartilage where none exists (e.g., bone-on-bone arthritis). So if you are falling under the spell of one of the many clinics out there promising to heal your severe bone-on-bone arthritis with some type of stem cell therapy, it simply isn’t true. No stem cells, regardless of the source, have the ability to do this. Injections of your own bone marrow stem cells may be able to provide long-term relief in these cases, but they simply can’t grow a new joint.
Also, make sure you keep the above study in context, as we have lots of studies showing many ways stem cells work and none is definitive, including this study. For example, we have research showing that the stem cells can stay in the joint and turn into cartilage and others that show that the cells only act as an orchestra leader for the symphony of repair.
The upshot? It’s always interesting to see new studies on how stem cells work. I’m sure we’ll see more of these studies coming down the pike in the future!
About the Author
Christopher J. Centeno, M.D. is an international expert and specialist in regenerative medicine and the clinical use of mesenchymal stem cells in orthopedics. He is board certified in physical medicine as well as rehabilitation and in pain management through The American Board of Physical Medicine and Rehabilitation.…