It seems that the interplay between the brain and gut and the composition of microbial organisms plays a crucial role in the development of neurodegenerative conditions. Despite the growing evidence supporting a connection between the gut-brain axis (MGBA) and Alzheimer's disease, the exact mechanism behind this relationship remains poorly understood. Utilizing the largest study ever of the human gut microbiome, a team of researchers from the United States sought to find a clearer relationship between Alzheimer's disease and the mix of organisms living within the gastrointestinal tract. The analysis not only revealed a genetic link between different genera of gut bacteria and the diagnosis of Alzheimer's disease but also uncovered a connection between the microbes and the genetic risk factor for the neurodegenerative disorder.
The study also emphasizes the interaction between genetic factors and inflammatory gut bacteria in maintaining healthy brain function. Experts explained that early in our development, our bodies are colonized by a diverse array of bacteria, fungi, and viruses that form a temporary truce with the immune system. The microbes obtain a habitat, while we gain a frontline defense against invasive entities in our bodies. However, shifts in our immune system can give certain species an advantage over others. Similarly, changes in microbial composition—perhaps due to alterations in our diet—can profoundly affect how the body performs its functions, for better or worse.
In recent years, researchers have focused on this complex relationship between gut bacteria, the immune system, and neurological performance, in an effort to understand why certain brain regions deteriorate and lead to the symptoms of memory loss and cognitive decline we refer to as Alzheimer's disease. Observational studies have revealed a decrease in gut microbial diversity among individuals diagnosed with this condition, while analyses have shown that gut bacteria can release chemicals that may trigger harmful inflammatory signals in the brain.
Additionally, there is a gene involved in fat transport in the blood, known as apolipoprotein E (APOE). The variant known as E4 appears to represent a genetic risk for Alzheimer's disease. There is good reason to suspect that having at least one copy of APOE E4 may impact our microbial composition. In this context, the team examined detailed records of 119 bacterial genera based on a study that involved thousands of participants, known as the MiBioGen Consortium.
The preliminary research on the bacterial genes that could be associated with Alzheimer’s disease identified around 20 genera suspected of playing a role in the disease’s development. A second search from a more restricted sample produced 10 genera, six of which were less prevalent among diagnosed patients, while the remaining four were more common. Four of these appear to be associated with the APOE allele, which is believed to increase the risk of developing Alzheimer's disease.
For example, Actinobacterium Collinsella is linked to Alzheimer's and the APOE variant, as well as to rheumatoid arthritis, atherosclerosis, and type 2 diabetes. Researchers suspect that Collinsella's ability to enhance the expression of inflammatory signaling hormones may exacerbate—if not trigger—neuro damage.
