Shutting off a gene implicated in insulin resistance leads to damaged mitochondria and decreased exercise capacity in mice.
Health researchers have known for decades that Type 2 diabetes results from a phenomenon called insulin resistance, but what causes insulin resistance has remained a mystery. Now, researchers at the Stanford University School of Medicine and the University of Wisconsin have begun to untangle a web of connections that includes a gene; mitochondria, which produce energy for cells; insulin resistance; and how well the body’s metabolism functions. “We’ve identified a mechanism for insulin resistance that involves a gene that ties insulin resistance to mitochondrial function,” said Joshua Knowles, MD, PhD, an assistant professor of cardiovascular medicine at Stanford.
A paper describing the work was published in the Oct. 4 issue of the journal Cell Reports.
Previous work by Knowles and his team linked a variant of a human gene called NAT2 with insulin resistance in humans. In mice, suppressing a similar gene, called Nat1, caused metabolic dysfunction, including decreased insulin sensitivity and higher levels of blood sugar, insulin and triglycerides. The new study shows that suppressing the expression of the Nat1 gene in mice interferes with the function of mitochondria — cell structures that make ATP.
In addition, mice whose Nat1 gene had been eliminated gained more weight and had larger fat cells and higher levels of biomarkers indicating inflammation than did regular mice, even though all the mice got the same amount of food and water. The mice without Nat1 also had a decreased ability to use fat for energy, said Knowles, and they were also pretty slow on the exercise wheel.
Exactly why the Nat1–free mice have trouble running is something Knowles and his colleagues are still working out. “Is that physically an effect on muscle, skeletal muscle? Is that an effect on the heart? We don't know exactly yet,” he said. Upcoming work will focus on identifying a factor that links all these metabolic effects.