PUTTING THE CARTILAGE BEFORE THE HORSE

With horses, being able to move is everything. A horse will do everything in its power to keep on its feet, because without motion it knows it will fall prey to any predator that comes around. And most horse owners want to see their animals able to perform, whether it is for trail riding or as a multi-million dollar racehorse. Not only that, but we’d like to know they are not in pain when doing so.

To that end, Dr. Jamie MacLeod has been continuing his studies of diseases and conditions of the equine bones, joints, and musculature at the Maxwell H. Gluck Equine Research Center. One of the center’s newest researchers, MacLeod holds the John S. and Elizabeth A. Knight Chair in Musculoskeletal Science. He comes to the Gluck Center from Cornell University where he expanded on his burgeoning interest in equine movement and, more specifically, the effects of work and movement on joint cartilage (also called articular cartilage).

Ideally, articular cartilage is smooth and unblemished. It is the most abundant type of cartilage found in the body and lines the bones in the joints, as well as providing cushioning for weight bearing on the bones. It allows the bones to slide over each other with minimal resistance. It’s no surprise that movement causes wear and tear to the cartilage. But this natural process can become a problem when the wear is extreme or there is injury to the cartilage. Most of the time when this happens, arthritis sets in.

“Lameness is the main reason that the athletic careers of horses are limited,” MacLeod said. “It’s a huge problem.”

For reasons that are not well understood, MacLeod said, cartilage does not heal well. In contrast, bones usually heal without difficulty. And the mystery is that many mammals bones start out as cartilage when they are in the fetal stage. Most of the cartilage forms into bone as the fetus develops.

He said the more a horse is used and the more strenuous his activity, the more wear and tear there is on the cartilage. So if a horse is put to work at an early age, it follows that it will have more wear on its cartilage than a horse that begins working later in life. And, MacLeod added, the type of work the horse does will determine which joints will be most affected.

“A race horse injury will be different than what is seen in a show jumper or a draft animal. Horses often accumulate joint injuries throughout their lives—just like people do. If you ask a premier race horse to be athletic early in its life, it will accumulate injuries or at least aches and pains earlier in life,” he said.

What MacLeod is focusing his research efforts on is the study of gene expression in chondrocytes. Gene expression refers to the sequence of a gene’s DNA which alters to become the structures and functions of a cell. Chondrocytes are the cells that synthesize and maintain the cartilage throughout life. He feels gene expression promises a better solution to healing cartilage than surgery. In the same vein, he is looking to new information supplied by the Equine Genome Project (see Horse Cures of the Future: A Map Would Help) and microarrays (the study of microscopic DNA spots to measure gene expression). He said these two research strategies will provide he and other equine researchers with more powerful solutions to assist them in their experiments.

With a better understanding of chondrocyte cell biology, MacLeod hopes to answer the questions of what can be done to prevent cartilage damage and, should such damage occur, what can be done to help the cartilage to heal. Both answers mean a lot in the equine world—and to the field human medicine as well--since the disease process of arthritis caused either by sudden trauma or life’s normal wear on joint cartilage is very similar in horses and people.