How do I taste: researchers identify new taste chemical pathway

Taste might not at first glance be considered one of our most important senses, but when you consider how invaluable it is in helping to identify toxic materials, and the role it plays in the brain’s reward centre, it becomes clear how vital it is to our wellbeing.

Despite taste’s importance, we still know surprisingly little about the role it plays and the mechanisms related to brain chemistry. Recently though, scientists at the University of Buffalo have identified a new chemical pathway that further explains how we taste bitter, sweet and savoury (umami) flavours, opening up avenues for further research in the fields of taste, nutrition, and the fight against obesity.

Upsetting the status quo

In the past, scientists believed that only one protein, transient receptor potential melastatin 5 (TRPM5), was responsible for the detection of bitter, sweet and umami flavours, and that without this receptor the brain would not be able to receive these signals, but according to the University of Buffalo’s research a second protein, TRPM4, also contributes to taste.

“When we looked at the literature we saw that people were reporting that without the TRPM5 protein they had reduced experience, but not that it was abolished. We looked at TRPM4 and found that it’s also expressed in taste cells, so we started trying to figure out what it was doing,” explains lead researcher Dr Kathryn Medler, “Our research shows that you need both TRPM4 and TRPM5 to have a normal taste response, and if you only have one then you can still taste things, but not normally.” It is only if both TRPM4 and TRPM5 are missing that a person would experience a lack of salty, sweet or umami flavours.

The finding links up to previous research that Medler’s team carried out around the topic of obesity and taste signalling, meaning the TRPM4 discovery could lead to new research avenues in nutritional study. “We took genetically identical mice and gave one of them a high-fat diet so they developed obesity. The development of obesity caused the taste system to not work as well,” said Medler, “Our hypothesis is that if you don’t taste things as well, then you’re not receiving the right signals in your brain to tell you that you’re full.”

The importance of our sense of taste

According to Medler, our sense of taste was most likely the first sensory system to evolve in the form of the detection of chemicals in the environment, a trait that is critical to any organism’s survival. “In our modern society we don’t think of a taste deficit as very important because grocery stores etc. tell us what is safe, but if for whatever reason we were dropped out in the middle of nowhere and we were trying to find food out in the wilderness, then our taste system is going to become very important.”

And yet despite the intrinsic importance of taste, we still don’t fully understand taste mechanisms and their relationship with the reward centre of the brain. When a person is found to have a reduced sense of taste, they tend to lose their appetite, which can be extremely detrimental to health.

The most common factors affecting the efficiency of our sense of taste are old age, and chemotherapy. An unfortunate side effect of chemo is that it targets continuously generating cells, which includes the regenerative cells related to taste. Chemo patients then tend to lose weight as a result of reduced appetite – further study into these factors could change the way we combat these issues. “If we can understand how this system works better, then we can develop systems to counteract some of those problems that can develop in society,” says Medler.