Muscle Men: Lab-grown cells mirror source’s characteristics

Researchers studying muscle cells maintained in petri dishes have found that the cells burn sugar and fat with the same efficiency as do the people from whom the cells were isolated. The finding may give scientists a leg up on understanding the mechanisms behind obesity and type-2 diabetes.

Previous research had examined the muscles of people who were both obese and resistant to the effects of insulin, a hormone that lowers sugar concentrations in blood. Such individuals’ muscles don’t burn fat as well as the muscles of people without these conditions do. Other studies showed that muscles in obese, insulin-resistant people have trouble switching between using fat and sugar as fuel.

Researchers haven’t been sure whether these characteristics arise from the muscles themselves or whether the muscle tissues are reacting to different concentrations of hormones and other molecules that circulate in a person’s blood.

To investigate that question, Steven R. Smith and his colleagues at the Pennington Biomedical Research Center in Baton Rouge, La., recruited 16 healthy men between ages 18 and 29. The volunteers ranged from lean to obese.

Smith’s team ran each of the men through a battery of tests, including measurements of body-fat composition, insulin sensitivity, and rates of sugar and fat metabolism. Not surprisingly, the men who were lean and had normal insulin sensitivity burned fat more efficiently than did those who were overweight and insulin resistant. Slim, insulin-sensitive individuals also switched more effectively between metabolizing fat and sugar than the other volunteers did.

The researchers then removed a tissue sample from a leg muscle in each volunteer and grew the cells for several weeks in the lab. That isolated the cells from the influences of the men’s individual body chemistries, says Smith.

“If something is intrinsic to the muscle cells, the ability of the cells to burn fat or glucose [in the lab] should match up with what we see in people in the clinic,” Smith says. “That’s what we found.”

When the research team bathed each cell sample in a high-fat broth, the cells metabolized the fat with about the same efficiency as the person who had given them did. Further tests showed that the cells likewise mirrored their owner’s capability to switch back and forth between burning sugar and fat.

Smith says that his team isn’t sure whether muscle cells contribute to weight gain and insulin resistance or whether having these conditions reduces a muscle’s ability to metabolize sugar and fat. He and his colleagues report their results in the July Journal of Clinical Investigation.

The new research “opens a lot of possibilities” for studying metabolic disorders, says David E. Kelley, an endocrinologist at the University of Pittsburgh School of Medicine.

Finding why muscle-cell metabolism differs between lean and heavy individuals “may give some fresh insight on treating obesity and diabetes,” Kelley says.