Warm blooded animals constantly regulate their body temperatures in order to maintain an important survival balance, known as thermal homeostasis. Given its significance, scientists have tried various ways to measure heat produced from metabolic processes in our cells. Unfortunately, current approaches have fallen short in providing researchers with a precise snapshot of how and where this heat is produced.
To address this problem, a team of scientists from in Japan reported a clever approach in Nature Methods that describes a non-invasive technique to accurately visualize heat production. The team was composed of researchers from Kyoto University's Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Department of Technology and Ecology, Hall of Global Environmental Studies, and Institute for Integrated Cell-Material Sciences.
By fusing two proteins, one found in Salmonella bacteria -- called TlpA -- that is sensitive to heat changes and another that emits green fluorescent light, the researchers were able to create biosensors for detecting temperature fluctuations.
"We took advantage of the behavior TlpA exhibits when it heats up," said Reiko Sakaguchi, a co-author in the study. "The protein has arm-like structures that form pairs at lower temperatures but separate as temperatures increase. Since the green fluorescent protein is connected to these arms, the strength of the light signal we can detect depends on their state; it emitted strongly when the arms were paired and weakly when alone."
When the researchers used the sensors in cells, they were able to direct them precisely to specific areas by attaching a unique tag that acted like a zip code for delivering mail. The study went on to demonstrate the protein's ability to visualize heat produced in specific compartments within cells such as the mitochondria and endoplasmic reticulum as well as in fat tissue and skeletal muscle, which are important producers of heat during cold temperatures and physical movement.
"The next step is to apply these sensors to living animals, such as mice," said principal investigator Yasuo Mori.