Multiple sclerosis and the microbiome: Study suggests complex relationship
A new study investigating the relationship between the gut microbiome, genetics, and multiple sclerosis, is suggesting bacteria certainly plays a role in modulating the effects of the disease but whether that role is positive or negative may be fundamentally determined by individual genetics.
"Our gut bacteria are part of a complex ecosystem that holds great potential for the prevention, treatment, and/or diagnosis of chronic diseases,” explains study leader Dimitry Krementsov, from the University of Vermont. “However, many scientists have been going at it with a one-size-fits-all approach, and our research suggests that this is unlikely to work. Instead, a more personalized approach is needed."
There has been a significant amount of study in recent years looking at the ways our gut bacteria can both protect from, and amplify, a number of different autoimmune conditions. In the context of MS, researchers have found those with the disease do certainly display detectable microbiome impairments, or imbalances, generally referred to as dysbiosis.
A recent review article examining decades of gut microbiome/MS research found it is still unclear whether gut bacteria plays a causative role in the onset of the disease. But gut microbiome modulation, either through probiotics or fecal transplants, is presenting as a promising intervention to help manage the disease. The problem, the review notes, is just how profoundly variable MS is from patient to patient.
“Though it is widely accepted that the gut microbiome in patients with MS is characterized by moderate dysbiosis, a clear and consistent multiple sclerosis microbiome phenotype has not been described,” the review states. “Moreover, given that a myriad of microbes have been implicated in MS, it is unlikely that, in the future, a single microbial organism will be isolated and characterized as an environmental trigger towards disease.”
The new research led by Krementsov set out to explore what influence an individual host’s genetics has on the relationship between MS and the gut microbiome. Using an animal model of MS, the research looked at 29 distinct genotypes.
In the animals with the highest susceptibility to MS-like disease, the researchers zoomed in on specific bacterial differences. Ultimately the investigation homed in on one bacterial species, Lactobacillus reuteri, that seemed to exacerbate the disease in one particular animal genotype.
The controversy here is that prior research into this same bacterium has found it may actually reduce the severity of the disease in certain animal models. One study last year even suggested it to be a novel probiotic candidate to treat MS.
The conclusion of this new study is that no single bacterium, or broader microbiome profile, can necessarily be considered good or bad in relation to MS. The researchers suggest context is key, and host genetics is most likely fundamental to whether a species of bacteria generates positive or negative effects in a given individual.
“These results reveal complex interactions between host genetics and gut microbiota modulating susceptibility to CNS (central nervous system) autoimmunity, providing insights into microbiome-directed strategies aimed at lowering the risk for autoimmune disease and underscoring the need to consider host genetics and baseline gut microbiome composition,” the researchers conclude in the new study.
Despite an incredible flurry of microbiome research over the past few years, perhaps the single overriding theme that consistently appears is just how profoundly complex the relationship between gut bacteria and health is. One astonishing study last year attempted to catalog all the genes in the collective human microbiome and the first published paper from the research reported nearly 46 million unique genes.
The conclusion of that study last year mirrors the findings of this new research, suggesting the future of microbiome therapy will most likely not hinge on specific bacterial types, Instead, for these kinds of therapies to work, they will need to be highly personalized.
This new research builds on that idea, offering evidence that there is not necessarily any such thing as objectively “good” or “bad” bacteria, but the relationship between certain bacteria and disease can vary from person to person depending on many factors, including genetics.
The new study was published in the journal PNAS.