Your Horse's Cartilage Has Bling
Within the rubberlike cartilage that helps pad and protect your horse’s joints are tons of specialized cells and nutrients. Oh, and crystals—microscopic protein crystals, that is.

While these crystals might not have the same financial value as precious stone crystals, they do appear to have significant mechanical value to the horse. These crystals exist in equine cartilage cells’ mitochondria—responsible for each cell’s energy production and respiration—and they can grow so big that they stretch the mitochondria’s size, sometimes to the length of the entire cell.

Austrian and German researchers say these intramitochondrial crystals are unique: So far, horses are the only species found to have crystals in their cartilage cell mitochondria. And this, they said, could be related to horse joints’ exceptional capacity to withstand great levels of mechanical stress.

“At the moment we do not have any indication that there is a pathologic relation or harmful influence causing these protein aggregations, and the investigated horses were absolutely healthy,” said Dirk Barnewitz, DrMedVet, of the Research Centre for Medical Technics and Biotechnology, in Bad Langensalza, Germany.

Barnewitz and Sylvia Nürnberger, PhD, of the Department of Trauma Surgery at the Medical University of Vienna, in Austria, and colleagues described these protein crystals in equine cartilage cells after examining them under microscope in a recent study. They also looked for crystals in cartilage cell mitochondria of other species (including chickens, rats, pigs, sheep, cattle, and humans), but that search turned up zero results. Previous research revealed that there are no such crystals in cat or dog cartilage, either.

Crystals do exist in the mitochondria of certain kinds of other cells, however. Mostly, they appear in lower-level life forms like single-cell protozoa, or invertebrates, the researchers said. Scientists have also detected protein crystals in the mitochondria of certain diseased mammal cells, mostly liver and muscle cells, with pathologies such as ischemia (lack of blood flow), starvation, alcohol intoxication, and myopathies (muscle tissue diseases), Nürnberger and Barnewitz said.

But that doesn’t mean our horses have cartilage pathologies just because they have these crystals—or that they’re lower-life forms. While the explanation for their existence is not yet clear, it appears to be related to mechanical stress, they said, because the crystals are larger and more numerous in cartilage areas that receive the most stress. Furthermore, they’re far more abundant in growing horses—specifically, yearlings.

“We will continue to investigate this phenomenon, to find out if there is a relation to any other clinical relevant physiological condition,” Barnewitz said. “At the moment there is no reason to be scared. We will update the community if we find any clinically relevant aspects.”

In the meantime, the crystals could lead to opportunities to discover biomarkers that indicate mechanical stress levels on the cartilage, they added. “The crystals themselves will not be suitable as a clinical biomarker since biopsies would be necessary, which is far too invasive for routine diagnostics,” said Nürnberger. “However, studies of the physiological background of the protein aggregations could bring up biomarkers that are more easily obtainable.”

Their research is ongoing.

The study, “Giant crystals inside mitochondria of equine chondrocytes,” was published in Histochemistry and Cell Biology.