A team of researchers from institutions in China and the U.S reports a link between human Gut microbiome disturbances and major depressive disorder.
The gut microbiota interacts with the host via neuroimmune, neuroendocrine, and neural pathways. These pathways are components of the brain-gut-microbiota axis and preclinical evidence suggests that the microbiota can recruit this bidirectional communication system to modulate brain development, function, and behavior.
Gut bacterial microbiome has gained great attention. It has been hypothesized to play a critical role in the onset of various neuropsychiatric disorders such as Parkinson’s disease, autism, and bipolar disorder.
What is Major Depressive Disorder (MDD)?
Depression is a mood disorder that causes persistent feelings of sadness and loss of interest. MDD is clinical depression, it affects how you think, feel, and behave, which leads to a variety of emotional and physical problems.
The gut microbiome, a vital and direct environmental contributor to central nervous system development, consists of a vast bacterial and viral community that can significantly influence host health and disease.
It is believed that depression is simply from having too much or too little of certain brain chemicals. In this new effort of research, the researchers suggest they have found evidence that links MDD symptoms with the gut microbiome.
Fecal Transplantation Experiment
Using fecal transplantation experiments, one study has further shown that transplanting the “MDD microbiota” into germ-free mice or microbiota-depleted rats can induce depression-like behaviors in recipient animals, which clarifies a causal role of gut microbiome in MDD onset
The research involved 311 Fecal samples from 156 people with MDD and 155 people that did not have the disorder.
Each sample underwent genetic analysis (whole-genome shotgun metagenomic and untargeted metabolomic methods) to identify microbes and other material found in samples. Metagenomic analysis, gas chromatography-mass spectrometry (GC-MS)–based fecal metabolomics analysis was also performed.
What was found: 3 bacteriophages, 47 bacterial species, and 50 fecal metabolites showing notable differences in abundance between MDD patients and healthy controls. Patients with MDD were mainly characterized by increased abundance of the genus Bacteroides and decreased abundance of the genera Blautia and Eubacterium. These multilevel omics alterations generated a characteristic MDD coexpression network.
A gene co-expression network (GCN) is an undirected graph, where each node corresponds to a gene, and a pair of nodes is connected with an edge if there is a significant co-expression relationship between them.
The team also noted that higher levels of Bacteroides in the microbiome might help to explain why so many MDD patients have heightened levels of cytokines and associated inflammation compared to the general populace.
Currently, we diagnose MDD in patients throughout the interview process, is it possible in the future we can test the presence of certain elements in the gut microbe as a part of screening efforts to confirm the disorder.