Overview of how the gut microbiome influence human health

First, let’s talk about the cells that make up your body. Each cell of your body is a living unit that is within a system. And therefore, it needs strategies to communicate with the other cells. The communication between cells is constant and vital, as the maintenance and the coordination of the whole body depends on it. But you may wonder, how are they able to do this? In this video, you will learn more about the communication between the gut microbiome and the host. There are several vias of communication between cells. They will use one way or another depending on the distance that separates the cells and the type of cell.

In general, to communicate with cells close to them, they directly contact through unions or specific receptors on the surface. Or they release chemical signals similar to how immune cells do. In contrast, when cells want to send a message to reach other cells that are far away, they can use two pathways. One is by the release of hormones that travel in the blood until reaching the cells recipient of the signal. This is known as endocrine communication. The second way is exclusive to nerve cells. They release specific chemical signals called neurotransmitters that are specific biomolecules that allow the transmission of information from one nerve cell to another. This is known as neural communication.

Bacteria can produce chemical signals and can establish surface contacts to communicate not only among them but also with our own cells. It is fascinating that bacteria, being much simpler organisms than us, are capable of acting on these communication routes. So by using these pathways, bacteria influences the homeostasis of our body and coevolve with us. Now, let’s have a look at the gut. In the gut, there are thousands of bacteria that live with us. At the same time, the intestinal mucosa is composed of different types of cells. Among them, there are cells of the endocrine, immune, or nervous system that interact with the intestinal microbiota to consequently activate metabolic immune or neuronal pathways in our body.

The gut is the perfect place for intruders to get in. And that is why it is guided by an aggressive army, the immune system. One of the main functions of the immune system is to discriminate which bacteria are pathogenic and which ones are commensal bacteria. To do this, the immune system has specific receptors, such as Toll-Like Receptor, or TLR, on their surface. Gut bacteria can communicate with our immune system by releasing bacterial metabolites that can act as signals for the immune system to create tolerance towards them instead of activating an attack against them. The best examples are short-chain fatty acids that influence the way cells of the immune system work, inducing the development of tolerogenic responses.

Altogether, this crosstalk between the bacteria and the host using these types of signals helps to educate the immune system to cohabit with the gut microbiota. In the last few years, new evidence has emerged about how the influence of the gut microbiota goes much further than the immune system. It has been observed that microbes can stimulate those cells in the gut which produce hormones, known as enteroendocrine cells– entero from gut and endocrine. Some of these hormones can directly influence our appetite and our metabolic state. How does this happen? The release of metabolites, like short-chain fatty acids, plays a role.

These metabolites can also be recognised by receptors expressed on the membrane of enteroendocrine cells, which are ultimately responsible for releasing hormones to the blood to reach the other organs, such as the pancreas or the brain. Finally, it has also been demonstrated that our gut bacteria could talk to our brain, directly influencing our mood through the production of molecules, neurotransmitters, that are able to activate nerve cells or through a more complex pathway to activate certain immune cells that send a message to the brain influencing our behaviour. During the next sections, you will learn more about how the gut microbiota impact these three axes of communication– immune system, metabolism, and brain.