In recent years, he has been a star of laboratories who has made his way to the general public … The intestinal microbiota, since it is about him, is seen adorned with many virtues if not intriguing powers and not always beneficial: whether in the context of purely digestive diseases or neurological or psychiatric diseases, it is now considered to be a full-fledged player in the development of certain pathologies.
In addition, being easily accessible, appearing to be easily analyzed or modified, scientists ask themselves the question: if it can induce pathologies, could it also help to cure them or even prevent their appearance? How far can we use it to improve our health?
To answer, we must briefly re-specify what a microbiota is: a complex whole, composed of a large and varied cohort of microorganisms, including bacteria, fungi, viruses and archaea. A microbiota is also integrated into an ecosystem: there can therefore be as many microbiotas as there are ecosystems … hence the need to specify their outlines. And remember that each of our organs in contact with an external environment (not just the intestine) has its own microbiota – skin, mouth, lungs, etc. All together, they form the human microbiota.
Each time one of our organs is in contact with the external environment, a specific microbiota is set up: in our mouth, our skin or our lungs or intestines © Julie Borgèse / Inserm Mibiogate (via The Conversation)
The importance of these microbiota is partly due to the fact that their microorganisms develop in a strategic place: at the edge of our organs, where they constitute a buffer zone between internal environment and external environment. Through their interactions with our cells, they are able to dampen variations in these environments and often represent the first means of excluding pathogens. The gut microbiota, for example, interacts with the outer cells (or epithelial barrier) of the intestine, the immune system, and the enteric nervous system (part of the autonomic nervous system that controls the digestive system).
Our body offers them a place to live in return for beneficial assistance in many cases. But an imbalance will contribute, or may even be the cause of the development of chronic diseases. While it seems easy to restore balance by correcting the microbiota involved, let us not forget the influence of the other scales in the balance: the host and the external environment.
The weight of the intestinal microbiota on our health
The gut microbiota contains 10 to 14 bacteria and 100 times more genes than the entire human genome. It plays an essential role in the development of the immune system, the nervous system and the metabolism of its host.
Heterogeneity of the human gut microbiota along the digestive tract © Clemence Defois / Wikimedia CC BY-SA 4.0
A thousand bacterial species, belonging to five main phyla (Bacteroidetes, Firmicutes, Actinobacteria, Proteobacteria and Verrucomicrobia), make up the healthy human fecal microbiota. Its composition is essential for the maintenance of intestinal homeostasis and reflects, to a varying extent, the overall health of the host.
A group of researchers from the Loire region has focused their research on the regulation of organ barriers where microbiota are established and their relationships (the MiBiogate project). If these barriers are not airtight, they are crossed in a very controlled manner in healthy individuals. In our intestine, it is the layer of cells of the digestive epithelium which constitutes this more or less porous barrier. Its permeability is regulated according to its own state as well as that of the intestinal microbiota, the immune system and the enteric nervous system.
Dysfunctions are observed in various digestive (chronic inflammatory bowel disease) or extra-digestive (type 2 diabetes, obesity, autism spectrum disorders, Parkinson’s disease) pathologies. However, these pathologies are themselves associated with “dysbiosis”: an alteration in the composition and functions of the intestinal microbiota.
Many studies therefore seek to determine to what extent, by improving our microbiota, we could strengthen our barrier, and thus our health.
The intestinal barrier is the layer of cells found on the outer surface of our gut. It is in direct contact with the local microbiota. It is she who manages what we take in from our food. If it is altered, our health suffers © Julie Borgèse / Inserm Mibiogate (via The Conversation)
Fundamental interactions
In 2013, the first studies implicated dysbiosis in the genesis of pathologies such as obesity or non-alcoholic fatty liver disease, showing that the implantation of a microbiota from a sick mouse to a healthy mouse will lead to the development of pathological characters.
Conversely, the New England Journal of Medicine reports a study showing that transplantation of healthy fecal matter is effective, in the vast majority of cases, in treating infection with the bacteria
Clostridium difficile. This bacterium develops following a depletion of the microbiota, often after antibiotic therapy, and causes severe diarrhea, inflammation of the digestive system. Nearly 14,000 Americans die from it each year.
Extract from the comic “You will die less stupid” © Marion Montaigne / éditions Delcourt
Since then, many studies have sought to understand host-microbiota interactions. The Mibiogate consortium thus pools the expertise and tools of its specialists. This enabled him, for example, to observe that vesicles from bacteria could contribute to the worsening of metabolic pathologies, such as non-alcoholic fatty liver disease which can develop into cirrhosis.
Thanks to five thesis projects, the Mibiogate consortium is broadening its perspective and its field of research. The microbiota-barrier interactions of various organs are now being studied, in particular through the development of bioinformatics tools and applications. Tools that open the door to a still unexplored section of knowledge relating to these interactions.
Research to control our microbiota
In addition to studying its interactions, Mibiogate addresses the questions of “how?” ” and when ? »Intervene to improve or restore them effectively.
Regarding the “how” already. Different strategies for modulating or controlling the microbiota exist: through food, prebiotics or cocktails of probiotics. In addition to these direct methods, we must take into account that our state of stress, the quality of our sleep and our physical activity, then that by changing the activity of the fermenter that we are, we will modify our microbiota. These global enrichment strategies are complemented by the use of products from the microbiota, post-biotics, which should have a higher and more targeted efficiency, but all this is still under study.
Through our food, we should be able to modulate or even control our microbiota. What for example to support it when we are under stress, tired, etc © Julie Borgèse / Inserm Mibiogate (via The Conversation)
For the “When”: determining the origin of the development of chronic diseases in order to understand why, how and when it can be taken over is an important line of current research. By characterizing the time windows that determine the composition and activity of the intestinal microbiota, the objective is to be able to offer adapted therapeutic solutions and especially preventive strategies.
Our hypothesis would be that a defect in its correct establishment could underlie the development of future pathologies. Indeed, chronic diseases take a long time to set in and very often patients do not show symptoms for several years: we can assume that they have an early origin, from the fetal stage. This is the concept of the developmental origin of health and disease (DOHaD).
Much research tends to show that there is a link between exposure to environmental factors during the first 1000 days of life (from conception to the child’s two years) and the occurrence of a chronic disease. In particular, this research suggests that it is then that the components of the host’s microbiota, immune system and metabolism can be modulated and interact differently to protect or cause the development of these diseases in adulthood. This is when it is necessary to act to establish the compositions of the microbiota in a lasting way.
In adulthood, we observe a resilience of the intestinal microbiota when it has been able to establish itself correctly: if it can be modified by an environmental factor (stress, diet, tobacco, physical activity, pollution, antibiotics, etc.), it regains its initial signature, characteristic of its host, shortly after the removal of the disturbing environmental factor.
As you will have understood, adopting the right strategy to modulate your microbiota and avoid developing a chronic disease is still in its infancy. Nevertheless, a feature common to many studies is that the poverty of our microbiota is associated with different pathological states while its richness and diversity reflect the resistance of an organism and its healthy character. So let’s cultivate our microbiota!
This analysis was written by Malvyne Rolli-Derkinderen, doctor specializing in neurogastroenterology at the University of Nantes.
The original article was published on the website of The Conversation.
