Hypothesis

Age-associated gut microbiota secrete proteinaceous molecules that mimic host histones, leading to aberrant chromatin remodeling in immune and epithelial cells, thereby perpetuating inflammaging.

Mechanistic rationale

• Dysbiosis in old age enriches Gram‑negative bacteria that express histone‑like proteins (HLPs) or secrete enzymes (e.g., bacterial lysine acetyltransferases) that modify host histones.
• Increased intestinal permeability allows HLPs to translocate into the bloodstream.
• HLPs are taken up by peripheral immune cells, brain endothelium and microglia, where they compete with endogenous histones for DNA nucleosome binding.
• This competition shifts chromatin toward a hypoacetylated, pro‑inflammatory state, amplifying NF‑κB driven transcription of IL‑6, TNF‑α and NLRP3 components.
• Heightened cytokine output further loosens tight junctions, worsening gut leak and feeding back to expand HLP‑producing microbes.

Testable predictions

1. Serum from aged mice will contain detectable bacterial histone‑like peptides; targeted mass spectrometry will reveal enrichment of specific microbial sequences absent in young animals.
2. Colonizing germ‑free young mice with a defined strain engineered to secrete HLPs will reproduce inflammaging hallmarks (elevated serum IL‑6, LPS, microglial Iba1 activation) without chronological aging.
3. Neutralizing circulating HLPs with monoclonal antibodies or administering a competitive peptide antagonist will reduce systemic cytokines and neuroinflammation even when dysbiosis persists.
4. In elderly humans, high circulating HLP levels will correlate with accelerated epigenetic clocks (e.g., GrimAge) and increased gut permeability markers (zonulin, LPS‑binding protein).

Falsifiability

If any of the above predictions fail—for instance, if aged serum lacks histone‑like peptides, or HLP neutralization does not attenuate inflammaging—the hypothesis would be refuted, indicating that microbial histone mimicry is not a central driver of the aging‑associated immune‑brain circuit.

References (implicit)

Age‑related gut dysbiosis drives systemic inflammation via bacterial LPS translocation, activating NLRP3 and breaching the BBB Immunometabolic failure of T cells driven by TNF‑α is sufficient to cause systemic inflammaging and multimorbidity Gut enteroendocrine cells regulate systemic aging through neuropeptide secretion Microbiome‑targeted interventions restore barrier function, enhance SCFA production and reduce inflammation Age‑related dysbiosis enriches Gram‑negative bacteria, amplifying the LPS‑NLRP3 cascade