Joint injuries can often lead to joint disease in both humans and other animals, but a new study looking at a particular biological lubricant suggests we might have to rethink how these diseases actually develop.
Researchers took a close look at the lubricin protein in dogs that had suffered injuries similar to anterior cruciate ligament (ACL) injuries in humans, concluding that it might be one of the early biomarkers, or warning signs, for diseases, including osteoarthritis.
Lubricin is essential in keeping joints functional and well oiled, but there's no scientific consensus about how different injuries affect its production. No one has looked at its relationship to ACL-like injuries in dogs before, despite knee ligament injuries being common problems for our canine pets.
"Lubricin is crucial for normal joint function and the lubrication of cartilage," says professor in equine health Heidi Reesink, from Cornell University. "We know that if a person or animal doesn't make that protein, they will develop devastating joint disease affecting all the major weight-bearing joints."
"The dogma in this field has been that lubricin decreases in joint disease."
What the researchers found was that lubricin levels actually went up in the joints of the dogs that had suffered ACL-like injuries – concentrations were around 16 times greater than those in a control group of uninjured canines.
These higher concentrations started as soon as a day after the injury in some cases and lasted for up to a year, depending on the animal. It's almost as if the protein is overproduced before it dries up.
Crucially, in three cases where the ACL-like injuries led to arthritis in the dogs, the increased lubricin levels were noticeable before any signs of the disease had shown up in x-ray examinations.
"This indicates that the presence of increased lubricin might actually be a biomarker for predicting future osteoarthritis," says Reesink. "We also saw increased lubricin in dogs months to years after they injured their ACLs, suggesting that lubricin might be an indicator of ongoing joint instability."
That's important because there are limited ways to treat joint diseases. Knee osteoarthritis affects more than 12 percent of the US population between the age of 25-74, as well as 20 percent of dogs older than a year. Being able to catch it early – and maybe introduce treatments or adapt behaviour – could go a long way to alleviating pain for millions of people and their canine companions.
Of course, this study only deals with dogs, but lubricin production is common across all mammals, and this spike in lubricin after injury may be seen in humans, too. That's on the to-do list for the researchers, as well as more extensive studies involving dogs.
With so many people affected by joint disease, future research in this area will be closely watched – and let's hope it leads to improved treatment options.
"We can help both animals and humans by potentially coming up with better diagnostics, by more fully understanding how these molecules work and designing therapies beneficial to both, by taking advantage of these naturally occurring cases and improving orthopaedic care," says Reesink.
The research has been published in Scientific Reports.