November is National Diabetes Month in the United States. Twenty-nine million people in the US live with diabetes. To recognize this awareness month, we spoke with BPS member Roger Cooke, University of California, San Francisco, about his biophysics research related to the disease.
This cartoon shows the 3 states of myosin. In the active state the myosin head is attached to the actin filament producing force and motility. In the super relaxed state, shown above, myosin heads are bound to the core of the thick filament, where they have a very low ATPase activity. In the disordered relaxed state myosin heads extend away from the core of the thick filament where they have a much higher ATPase activity and are available for binding to actin.
What is the connection between your research and diabetes?
Our laboratory has studied the physiology and biophysics of skeletal muscle for many decades. Recently we have concentrated on the metabolic rate of resting skeletal muscle. Skeletal muscle plays a major role in diabetes as it is the organ response for metabolizing a large fraction of the carbohydrate that we consume. Recently we have discovered a mechanism, which we believe can be manipulated to up regulate the metabolic rate of resting muscle, thus metabolizing more carbohydrate. This would be particularly helpful in Type 2 diabetes.
Why is your research important to those concerned about diabetes?
Type 2 diabetes is thought to be caused by or an overconsumption of carbohydrate coupled with a sedentary lifestyle that does not need the carbohydrate as fuel. The excess carbohydrate leads to high levels of serum glucose. Our laboratory has focused on the motor protein myosin, which is responsible for producing the force of active muscle and also responsible for using much of the energy ingested in the form of lipids and carbohydrates. We have shown that myosin in resting muscle has 2 states with vastly different functions and metabolic rates. In one of these, the super relaxed state, the myosin is bound to the core of the thick filament where its metabolic rate is inhibited, See Figure. In the other, the disordered relaxed state, the myosin is free to move about and its metabolic rate is more than10 fold higher. By analogy with another motor, myosin in active muscles is akin to a car racing down the road. Myosin in the disordered relaxed state is similar to a car stopped at a traffic light with the motor idling, and the counterpart of the super relaxed state is a car parked beside the road with the motor off.
For energy economy in resting muscle most of our myosins are in the super relaxed state. If all of these myosins were transferred out of the super relaxed state into the disordered relaxed state they would consume an additional 1000 kilo calories a day. This is a large fraction of the standard daily consumption, which is approximately 2000 kilo calories a day. Thus a pharmaceutical that destabilized the super relaxed state would lead to the metabolism of a greater amount of carbohydrate providing an effective therapy for Type 2 diabetes. Such a pharmaceutical would address one of the fundamental problems in Type 2 diabetes the consumption of more carbohydrates than are required as fuel.
How did you get into this area of research?
In 1978 a group in England showed that purified myosin in a test tube had a much greater activity than it has in living fibers. This observation showed that myosin in vivo spent much of its time in a state that had a very low metabolic rate. I felt that this inhibited state of myosin could have important consequences for resting muscle and whole body metabolic rates. Although we studied this problem for a number of years, we were not able to find an in vitro system that replicates the in vivo activity. In 2009 we started using quantitative epi-fluorescence spectroscopy to measure single nucleotide turnovers in relaxed skinned muscle fibers, and finally we were able to observe the elusive inhibited state of myosin, the super relaxed state. This ability allowed us to now study the properties of this state.
How long have you been working on it?
I have been interested in this problem since the original observation in 1978, described above. However it was not until 2009, and the discovery of the in vitro assays, which allowed us to observe the super relaxed state, that this project became the central focus of our laboratory.
Do you receive public funding for this work? If so, from what agency?
Our work has been funded by the National Institutes of Health.
Have you had any surprise findings thus far?
The Holy Grail in this area of research is to find pharmaceuticals that will destabilize the super relaxed state. Recently we were able to devise new methods of measuring the population of the super relaxed state, methods that were amenable to use in high throughput screens. We screened over 2000 compounds looking for ones that destabilized the super relaxed state. We found only one compound that did so, a compound named piperine, which provides the pungent taste in black pepper. After working for over a year developing assays and running the screen, to our surprise the one molecule we discovered was already known to mitigate Type 2 diabetes in rodents. Although piperine lowered serum glucose, no one knew how it did this. We propose that piperine acts by destabilizing the super relaxed state, thus up-regulating the metabolic rate of resting skeletal muscles. We showed that piperine had no effect on active muscle and no affect in cardiac muscle, both desirable qualities to have in a pharmaceutical targeting resting skeletal muscle to treat Type 2 diabetes. Although piperine is effective in lowering blood glucose in rodents, it only does so at very high doses, too high to be useful as a therapeutic in humans. We now need to find molecules whose action is similar to piperine, but which bind with greater affinity.
What is particularly interesting about the work from the perspective of other researchers?
Our results provide the proof of concept that pharmaceuticals targeting resting muscle metabolic rate, can be found, using the high throughput screens we developed. These new pharmaceuticals have the potential of more effectively treating Type 2 diabetes.
What is particularly interesting about the work from the perspective of the public?
Type 2 diabetes is a growing problem worldwide. Almost 10% of the US public has Type 2 diabetes. Our research holds out the hope that new pharmaceuticals will be found to treat this disorder more effectively than those available today.
Our studies have also shown that the super relaxed state is destabilized when muscles are activated, and that it will remain destabilized for a number of minutes afterwards, due to phosphorylation of myosin. This extended period of destabilization adds to the metabolic cost of activity, particularly during light and intermittent activities. In fact a number of studies have shown that even modest and intermittent activity will improve serum glucose, help prevent weight gain and lead to better health. The worst thing that people can do is to sit for extended periods of in front of a computer or TV screen. For example when working at a computer I get up and walk around the room every 10 minutes or so, and I avoid elevators, taking the stairs to my laboratory on the 4th floor.