Fungi in the microbiota may play a role in teen depression
According to a Chinese study on teenagers, bacteria are not the only gut microbes involved in depression. Microscopic fungi found in the colon could also be responsible.
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Is depression linked to the microscopic fungi that populate the gut alongside bacteria and viruses?
So suggests a study on adolescent patients, the results of which have recently been published in the Journal of Affective Disorders1, further proof for the existence of a gut-brain axis.
Gut fungi of 300 teenagers have been closely examined
To this end, Chinese researchers recruited 145 teenagers aged between 12 and 18 years who suffered from depression. They collected 2 g of stool from each teenager and analyzed the fungal (i.e., the mycobiota) and bacterial composition of their gut microbiota. They then compared these analyses to those of the stools of 110 children with no mental health problems.
Firstly, there were significant differences in mycobiota composition between the teens who suffered from depression and those who did not.
The authors noted the existence of a “fungal (sidenote: Dysbiosis Generally defined as an alteration in the composition and function of the microbiota caused by a combination of environmental and individual-specific factors. Levy M, Kolodziejczyk AA, Thaiss CA, et al. Dysbiosis and the immune system. Nat Rev Immunol. 2017;17(4):219-232. ) ” in the former group, with the depressed teens having more Saccharomyces and Apiotrichum than the latter group but less Aspergillus and Xeromyces. This type of dysbiosis had already been noted in children suffering from autism and Rett syndrome.
These findings are interesting because previous studies have shown that fungi can synthesize molecules that are able to reach the brain and induce depressive behavior. For example, Aspergillus can indirectly modulate inflammation of the central nervous system and modify its functioning.
The mycobiota, crucial to human health
Less abundant than bacteria (they make up a mere 0.1% of gut microorganisms), less well known and less studied, the microscopic fungi in the microbiota (i.e., the “mycobiota”) are nonetheless crucial to health.
According to a review published in 2022 in The Lancet2 :
- They play an important role in regulating homeostasis and immunity;
- Fungal imbalances may have an impact on certain illnesses, including inflammatory bowel disease, colorectal and pancreatic cancer, obesity, diabetes mellitus, autism, and Alzheimer’s disease;
- They constantly interact with gut bacteria and immune cells via various substances (peptides, (sidenote: Short chain fatty acids (SGFA) Short chain fatty acids are a source of energy (fuel) for an individual’s cells. They interact with the immune system and are implicated in communication between the gut and the brain. Silva YP, Bernardi A, Frozza RL. The Role of Short-Chain Fatty Acids From Gut Microbiota in Gut-Brain Communication. Front Endocrinol (Lausanne). 2020;11:25. ) , cytokines, etc.);
- Stable interactions with the bacteria in the microbiota appear to be a marker of good health.
Influence on the bacteria of the gut microbiota
Another finding was that in the depressed teenagers, the presence of certain fungi was associated with that of certain bacteria, suggesting a strong interaction between these two major groups of microorganisms.
Furthermore, these connections between fungal and bacterial populations were markedly different than in the healthy adolescents. We know that strong interactions between bacteria and fungi are the marker of a stable microbial ecosystem.
For example, in the gut microbiota of the depressed teenagers, the fungus Penicillium and the bacterial genus Faecalibacterium were both diminished. The bacterium Faecalibacterium prausnitzii is well known to researchers for its anti-inflammatory properties and potential anxiolytic and antidepressant effect (in animals). Conversely, the fungus Candida, known for its adverse effects on health, was positively associated with Bacteroides and Parasutterella, with this “co-presence” potentially associated with depression.
The gut microbiota
Towards new treatments for depression
This study is the first to explore the links between the mycobiota and depression in teenagers. Although they must still be confirmed, the results open up new prospects for one day modulating the gut mycobiota (with the help of probiotics, prebiotics, antifungal drugs, fecal mycobiota transplants, etc.) to treat depression, an illness that remains poorly managed to this day.
2 Zhang F, Aschenbrenner D, Yoo JY, Zuo T. The gut mycobiome in health, disease, and clinical applications in association with the gut bacterial microbiome assembly. Lancet Microbe. 2022 Dec;3(12):e969-e983.