In animal experiments, researchers have discovered tachykinin, a gut hormone that specifically regulates hunger for protein. The study also shows that it affects sleep and can influence how long the animals live. People also produce tachykinin in the gut, which may also regulate appetite and sleep and influences lifespan in similar ways. A researcher says that developing drugs that regulate hunger and satiety for specific types of foods could help improve health.
Researchers have been focusing intensely on discovering gut hormones that could be useful in enabling healthy weight regulation.
Now they have identified tachykinin as a new and interesting gut hormone that appears to regulate hunger for protein. It also appears to be involved in regulating sleep and influencing lifespan – at least in fruit flies.
The research was published recently in Nature Metabolism.
“With the success of weight-loss drugs based on gut hormones, researchers began to wonder whether other gut hormones could have similar effects that could counteract obesity and improve health. The gut may be the largest hormone-producing organ and therefore produces many types of gut hormones, and the same gut cells can produce several types of hormones in combination. This research involves discovering how the various gut hormones affect the body’s functions and health,” explains a researcher behind the study, Kim Rewitz, Professor, Department of Biology, University of Copenhagen, Denmark.
Silenced 220 different genes in the gut
The search for new and interesting hormones and their functions often begins in fruit flies, as did Kim Rewitz and colleagues.
The researchers turned off 220 genes in fruit flies that are active in the endocrine gut cells make hormones.
By switching off the genes one by one, the researchers observed the functions of each gene and whether any are linked to producing potentially useful gut hormones.
The researchers specifically silenced genes that were likely to regulate the fruit flies’ appetite or other aspects of their physiology, such as sleep and lifespan.
“Hunger, sleep and lifespan are often connected. For example, it is hard to sleep if you are hungry. We also know that lower calorie intake is associated with a longer lifespan, especially if animals are fed less protein,” says Kim Rewitz.
Loss of appetite for protein
The large-scale screen uncovered several interesting gut hormones, many with functions that were previously unknown.
While the researchers have presented findings on other gut hormones in several other scientific articles, the study in Nature Metabolism focused on tachykinin.
Their findings show that tachykinin specifically affects the appetite for protein.
When fruit flies eat a lot of protein, the endocrine cells in the gut secrete tachykinin. This makes the animal lose their appetite for more protein and instead increase their cravings for sugar.
Kim Rewitz says that another identified gut hormone has the opposite effect of causing the fruit flies to lose their cravings for sugar but increase appetite for protein.
“Nature has designed organisms cleverly so that they become hungry for the nutrients they lack and feel full when they have had enough. The interesting thing here is that tachykinin does not just make the animal more or less hungry – it changes what type of food it prefers to eat,” notes Kim Rewitz.
The researchers also found that tachykinin works through another hormone to send a message to the brain and curb the appetite for protein.
They also discovered how the cells in the gut detect protein and then release tachykinin, which signals to the body that protein is present and ultimately affects the brain to produce a feeling of satiety specifically for protein.
Also affects sleep and well-being
In further studies, the researchers also discovered that when mice eat protein, it activates the same signalling system in the gut and triggers the release of tachykinin.
This suggests that the signalling pathway is conserved across species and may also play a role in humans. The researchers also found that tachykinin affects sleep in fruit flies – something that Kim Rewitz considers especially interesting.
Fruit flies normally take a siesta in the middle of the day, and if they have eaten protein and thus released tachykinin, they become more awake. This suggests that the gut not only controls appetite but adjust sleep patterns depending on what has been eaten.
When the researchers turned off the gene responsible for producing tachykinin in the gut, this effect disappeared.
They also discovered that silencing the gene for tachykinin in the gut made the fruit flies live longer – pointing to a surprising new role for gut hormones in controlling lifespan, according to Kim Rewitz.
“Virtually nothing is known about how gut hormones affect lifespan. Here we see a direct effect of a gut hormone, tachykinin, on lifespan. And it makes sense that tachykinin influences lifespan by acting as a link between protein intake and its effects on the body and behaviour in these animals,” he adds.
Targeting satiety and hunger related to specific types of foods
Kim Rewitz says that it will be exciting to continue studying tachykinin to discover more about it and its potential use in future medicines.
The idea is that there will be more focus in the future on creating healthy weight loss instead of just weight loss. Developing medicine creating more appetite for healthy foods and less appetite for unhealthy foods could be interesting.
“In recent years, we have started to understand more broadly how the hormones secreted in the gut help regulate various aspects of our health. The more we can learn about these hormones, the easier it will be to discover how to optimally ensure good health, whether through medication or through other means,” concludes Kim Rewitz.
