A team of scientists from Duke University Health Center have found that the human body has the ability to repair joint cartilage, which causes osteoarthritis. This is an ability previously thought restricted to animals such as the salamander and zebra fish. The study was published in Science Advances in October 2019. The article is currently available to read in full online on the journal’s website.
The scientists explained that animals such as zebrafish and axolotl were able to regenerate lost limbs by using a circuit of microRNA which were conserved across species. Humans are not able to regenerate a lost limb, but the fact that it was believed that they were unable to heal fully from the damage of repetitive joint use or from a single substantial injury, often sports-related which can lead to osteoarthritis was called into question.
The scientists extracted cartilage from the ankle, the knee and the hip and checked it for the amount of microRNA it contained. They used proteomic tools to check the proteins present in the samples. They also assessed the extent to which cartilage proteins reflected the amount of microRNA. This helped they to assess the regenerative qualities of the human joints, based on the age of the cartilage it contained. The tissues were obtained via waste surgical specimens from patients who had received total arthroplasty surgery. Healthy cartilage was collected during surgery for acute trauma to the joint. The surgeon noted whether or not osteoarthritis was present.
The scientists found that young cartilage could be found in ankles, and these joints were usually able to heal quickly from injury. They found that cartilage in the knees was the next young and that cartilage in the hips was the oldest type of cartilage which made it more difficult to heal. These findings were linked with the way that limb repair took place within the animals that had that ability: often they were able regenerate the tip of a tail or the end of a leg very easily. Injuries to human hips or knees can take a lot longer to heal.
The scientists found that humans also had microRNA which helped them to repair joint tissue. The molecules were found at a higher concentration in the ankle, then the knee then the hip and concentrations were at their highest in the top layer of cartilage as opposed to the deeper layers. The slower healing process meant that osteoarthritis was more likely to develop in the joint.
The scientists suggested that the microRNA molecules could be used to develop treatments which could help fully regenerate the joint cartilage of a joint that has turned arthritic. Understanding what is missing when comparing the human molecules to the salamander’s could help scientists learn how to regenerate a part or whole of an injured limb. The ability to repair could also be transferred to tissue other than cartilage.
Limitations of the study included the way the scientists chose to extract the molecules dictated the type of molecules they extracted. Not all of the molecules were extracted and tested. This meant that only some of them were accounted for. The structure of the molecules also made it more difficult for this study to work with them and meant that scientists probably underestimated their number. The scientists suggested areas for further study to help enhance their knowledge and to help develop an injection-based treatment to help repair and limit degeneration of joint tissues due to osteoarthritis.
Hsueh, M-F., et al., Analysis of “old” proteins unmasks dynamic gradient of cartilage turnover in human limbs, Science Advances, October 2019, Vo 5(10)