Arthritis, or more properly osteoarthritis, is a disease of the joints that results in breakdown of the protective cartilage and eventually the bone. It often affects the joints in the hands, neck, lower back, knees, and hips. The symptoms of osteoarthritis include: pain in the joint, loss of movement, and stiffness. Osteoarthritis is usually caused by a prior injury to the joint commonly sports related like sprains or ligament tears. There are also genetic conditions that increase a person’s risk for osteoarthritis by affecting the normal development of the joint. Approximately 30 million people in the US have osteoarthritis and take a daily anti-inflammatory to control their pain. Recently, researchers from the US have shown that by removing old cells from the damaged joints they could prevent the onset of osteoarthritis in mice.
When cells age or become damaged they enter a state known as senescence. In this state, cells no longer grow or divide and their metabolism slows down. Numerous research has shown that by removing senescent cells from a tissue you can kick start the growth and metabolism of that tissue. With this in mind, Jeon and colleagues hypothesized that removal of senescent cells from the knee joint of mice who suffered an ACL injury would prevent the future onset of osteoarthritis. To do this, they took mice who had a gene inserted into their DNA to make senescent cells glow green and then injured their ACL. The researchers saw that, over time, green senescent cells accumulated in the cartilage and joint fluid of the mouse. When they removed these cells the knee joint pain was reduced, osteoarthritis markers went down, and new cartilage began to grow to repair the damage. To confirm these results, the researchers injected a molecule that selectively kills senescent cells into the joints of old mice and found that they also had reduced pain and new cartilage growth. Finally, the team grew cells isolated from the joints of patients with osteoarthritis and began to remove those cells that were senescent. By removing these cells, they found that markers of inflammation went down and the levels of key cartilage producing genes went up.
This study is an exciting step towards finding a cure for osteoarthritis, one that could be easy to administer with very few side effects. The results still need to be validated in some larger animals and we still need to design a safe drug to remove senescent cells but there now exists the possibility to prevent and reverse osteoarthritis.
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