Equine skeletal muscle cell research is limited because researchers must obtain muscle tissue from horses to test. However, this method might soon be relied on less, thanks to a recent research breakthrough by a scientist team based in Ireland.

“In our study, we successfully established, from primary muscle tissue, equine skeletal muscle cell lines that are phenotypically (referring to the observable characteristics) equivalent to primary equine muscle and grow prosperously in culture,” said Mary Rooney, PhD, research fellow at Trinity College Dublin’s School of Biochemistry and Immunology, in Ireland.

In other words, these immortal myoblasts (embryonic precursors of muscle cells) grow continually and abundantly in the laboratory. The cells can return to a primary state as the temperature of their growth environment changes, said Rooney. In this state myoblasts can be induced to differentiate and develop into mature muscle cells researchers can study.

Studying Racehorse Muscle Cells

In the study, Rooney established skeletal muscle cell lines from primary muscle tissue in the Thoroughbreds’ gluteus medius muscle. All three cell lines are valid models of Thoroughbred horse skeletal muscle, she said, and provide a useful source of in vitro (in culture/laboratory) equine skeletal muscle cells to study for research purposes. The cells differ genetically because they were derived from different horses, which also allowed the researchers to study the DNA sequence related to speed aptitude in Thoroughbreds.

The researchers found the maximum respiration rate of muscle cells from endurance-type horses was significantly higher than that of sprint horse cells. Cellular respiration allows the cells to generate energy, which is particularly important when horses are exercising. “This finding is consistent with the fact that the endurance horses’ muscle has significantly more oxidative fibers (more mitochondria),” said Rooney.

Mitochondria are the cells’ power plants, so the higher their number, the more energy that can be created within those cells. Mitochondria produce ATP (adenosine triphosphate), which is the energy supply of cells, and cells with higher energy demands, such as those found in muscles, contain higher numbers of mitochondria to meet increased energy needs.

Advancing Equine Muscle Research

The availability of an in vitro cell model of equine skeletal muscle benefits the equine industry and scientists because researchers can use these cell lines in the laboratory for equine muscle research. “Performing research in vitro minimizes the requirement to obtain muscle biopsies, which can be ethically undesirable and logistically and economically challenging,” Rooney said.

When working with biopsy samples of equine skeletal muscle, researchers are limited in what they can study depending on the amount of muscle tissue obtained from horses and its condition. The cell line model, however, provides researchers with sufficient and regular samples to perform a broad range of functional analyses and offers an ethically prudent and valuable resource that can advance equine muscle research, Rooney added.

The study, “Conditionally immortalized equine skeletal muscle cell lines for in vitro analysis,” appeared in Biochemistry and Biophysics Reports in March 2023.