There are a score or so of different forms of amyloid that accumulate in the aging body and brain. These are misfolded proteins that precipitate out of tissue fluids to form clumps, and the biochemistry surrounding this process can cause harm in numerous ways. Alzheimer's disease is associated with amyloid-beta, and long years of research in that field illustrate that the mechanisms by which amyloid formation can damage tissue function are potentially very complex. A few other forms of amyloid are directly linked to age-related disease, but many are not, or ambiguity remains regarding how they are harmful. Still, the presence of amyloid is a clear difference between young tissue and old tissue. Any potential rejuvenation toolkit should include a way to safely clear these misfolded protein aggregates, such as via immunotherapies of the sort under development as potential Alzheimer's treatments.
Here is a speculative paper on the role of microbes in amyloid accumulation in the body. While reading note that amyloid levels, at least for amyloid-beta, are very dynamic. The body can clear it, but those clearance processes either diminish with the damage of aging or are slowly overwhelmed by increased generation:
Atypical amyloid generation, folding, aggregation and impaired clearance are characteristic pathological features of human neurodegenerative disorders including Alzheimer's disease (AD). What is generally not appreciated is that a major secretory product of microbes is amyloid, and that the contribution of microbial amyloid to the pathophysiology of the human central nervous system (CNS) is potentially substantial. While earlier findings suggested that these amyloids may serve some immune-evasive strategy, it has recently become evident that humans have a tremendously heavy systemic burden of amyloid which may contribute to the pathology of progressive neurological diseases with an amyloidogenic component.
Diverse microbes of the human microbiome generate functional amyloids. The large amount of microbial-generated GI amyloid implicates high potential systemic exposure to bacterial amyloid, and the bioavailability of amyloid to the CNS increases as humans age. Microbial and CNS amyloids are biologically similar in their structure and immunogenicity and complex mechanistic interrelationships between these amyloids are beginning to emerge.
Microbes or their secretory or degradation products including their amyloids and lipopolysaccharides are powerful inflammatory activators and inducers of cytokines and complement proteins, affecting vascular permeability and generating free-radicals that further support amyloidogenesis. These pathogenic signaling features are also highly characteristic of AD neuropathology. A more detailed understanding of human microbial ecosystems and their amyloids should give insight into amyloid-misfolding and their contribution to inflammatory-signaling in health, aging and disease. It will certainly be interesting to see: (i) if any microbial-generated amyloids co-localize with the amyloid-dense senile plaque deposits of AD; (ii) if GI tract microbiome-derived amyloids become more available systemically as humans age; and (iii) what the evolution and nature of amyloid-related communication between the gastrointestinal tract and the CNS has on the development or propagation of amyloids in pro-inflammatory degenerative disease.