Introducing the brain: the microbiome in the brain (Introduction)

by David Turell , Saturday, September 28, 2024, 18:23 (4 hours, 16 minutes ago) @ David Turell

Very new discoveries:

https://www.newscientist.com/article/mg26335104-500-the-brain-has-its-own-microbiome-he...

"...when the late Robert Moir at Harvard Medical School and his colleagues took a closer look at the beta-amyloid plaques that characterise Alzheimer’s. These sticky bundles of protein are toxic to neurons and have long been considered the primary cause of the condition, yet the team’s research revealed they had an unexpected function. “Their role is to entrap and kill pathogens,” says Lathe. “They are defending the brain.” And the discovery that beta-amyloid is found across amphibians, reptiles, birds and mammals suggests that invading pathogens have been a considerable threat to the brain’s health for much of evolution. What’s more, it indicates a clear mechanism through which microbes might influence the development of dementia. “It was a turning point,” says Lathe.

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"Lathe recently attempted to take stock of the brain microbiome in people with and without dementia. Working with colleagues at the University of Edinburgh, he examined genetic material from 79 neural samples held in brain banks in the UK and US. The analysis revealed a remarkable diversity of organisms, with as many as 100,000 species per sample. The community included viruses, bacteria and fungi. The researchers even found the remnants of a plant or alga-like organism, though they admit it could have come from pollen that somehow got into the brain. Intriguingly, this microbiome was a subset of the microbes found in the gut – representing about 20 per cent of the species found there.

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"Other research suggests that the presence of any single pathogen may be less important in causing dementia than the overall composition of the brain microbiome. Jeffrey Lapides and his colleagues at Drexel University College of Medicine in Pennsylvania recently examined post-mortem brain tissue from 32 individuals, half of whom had had Alzheimer’s. Like Lathe’s team, they found a large variety of organisms. But they also learned that particular combinations of microbes were associated with different stages of the disease. A group of bacteria known as Comamonas, for instance, were considerably more prevalent in people without dementia, while Methylobacterium and Cutibacterium acnes (which causes teenage spots) dominated the distribution during the later stages of Alzheimer’s. We can only speculate about the reasons for these changes, but Lapides suggests that interactions between the different species might put additional strain on the brain. “The chemical results of their competition may be toxic,” he says.

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"Other measures could bolster the brain’s defences against a whole range of invaders. For instance, the BCG jab – most commonly used as a vaccine against tuberculosis – seems to ramp up the immune system, reducing the risk of many infections besides TB for up to a year. Quite remarkably, and presumably as a result of this, some studies indicate that the injection can cut the prevalence of dementia by as much as 45 per cent. Excitingly, several other vaccines, including flu jabs and the shingles injection Zostavax, appear to offer similar protection.

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"Interest in the brain’s microbiome is certainly growing. In July this year, the AlzPI held a day-long symposium on the topic, and the Infectious Diseases Society of America now offers funding for Alzheimer’s studies. Understandably, the link with dementia still leads research efforts, but, more broadly, there is still so much about the brain microbiome that remains to be discovered. This even includes the identity of some of our brain’s inhabitants. “We sometimes see RNA sequences that are not present in any of the genome databases,” says Link. He calls this clandestine community the “dark microbiome”. “There are probably lots of viruses and other things out there that we don’t know anything about.”

Comment: another example of bugs wandering into bad places. Which leads into the usual theodicy discussion.