Hensley-McBain, T. | bioRxiv Science

bioRxiv2025

APOE genotype and sex drive microbiome divergence after microbiome standardization in APOE-humanized mice

The APOE4 allele is the greatest known genetic factor for sporadic or late onset Alzheimers Disease (LOAD). Gut microbiome (GMB) dysbiosis can lead to poorer outcomes in disease. The intersection of sex, APOE genotype, inflammation, and gut microbiota is incompletely understood. Previous studies in humans and humanized APOE mice have demonstrated APOE-genotype specific differences in the GMB. However, most of these studies were unable to resolve bacteria to the species level. It remains unclear how GMB changes with age and sex in the context of APOE genotype. In this study, humanized male mice with either APOE 2, 3, or 4 genotype were bred with the same two C57BL/6J sisters to standardize microbiomes across lines and monitor divergence based on APOE allele. Stool samples were collected at breeder set up and from the heterozygous (F1) and homozygous (F2) generations at wean and 6 months old. Stool was assessed via shallow shotgun sequencing to enable species and strain level taxonomic resolution. The heterozygous pups microbiome resembled each other at wean across all genotypes. However, the heterozygous pups, and their homozygous offspring continued to diverge, particularly the APOE2 females. In homozygous mice, the GMB demonstrated significance divergence at 6 months of age based on sex and APOE genotype. In comparison to their APOE3 and APOE4 counterparts, APOE2 females and males demonstrated an increased quantity of bacteria associated with anti-inflammatory profiles, including in the Lachnospiraceae family (Lachnospiraceae bacterium UBA3401) and decreased quantities in the Turicibacteraceae family (higher levels are associated with LOAD). ImportanceThe APOE4 allele is implicated as a significant risk factor for many diseases including cardiovascular disease (responsible for more deaths than any other disease) and sporadic or late onset Alzheimers Disease (accounts for an estimated 60% to 80% of all dementia cases). It is known that the gut microbiome (GMB) is affected by different genotypes and disease states. Mouse model studies have environmental and genetic controls allowing a specific gene to be studied. This study aims at discovering key GMB species differences allowing for future therapeutic targets. The GMB of the experimental mice was standardized and genotype and sex-specific divergence was observed with species and even strain level taxonomic resolution. Reported here are the first data demonstrating GMB divergence over time driven by APOE genotype from an inherited source and the first data to identify APOE genotype-specific bacteria species that may serve as therapeutic targets in APOE-driven disease.

microbiology↗

bioRxiv2023

Elevated peripheral and nervous system inflammation is associated with decreased short-chain fatty acid levels in Zika-virus infected macaques

Zika virus (ZIKV) infection of central nervous system (CNS) tissue is associated with CNS inflammation, which contributes to ZIKV pathology. Similarly, ZIKV infection has been associated with increased vaginal and rectal mucosal inflammation. As mucosal dysfunction may contribute to elevated systemic inflammation, ZIKV-induced mucosal alterations could potentiate CNS disruptions, leading to ZIKV pathogenesis. However, the potential link between mucosal dysfunction, CNS inflammation and the underlying mechanisms causing these disruptions in ZIKV infection has not been well described. Here, we assessed plasma and CSF indicators of inflammation, including neopterin, tryptophan, kynurenine and serotonin by liquid chromatography tandem mass spectrometry. We observed significant increases in neopterin formation, tryptophan catabolism and serotonin levels in the plasma and CSF of ZIKV-infected pigtail macaques (PTM), rhesus macaques (RM) and in the plasma of ZIKV-infected humans. We next examined whether ZIKV infection resulted in microbial translocation across mucosal surfaces by evaluating plasma and cerebrospinal fluid (CSF) levels of soluble CD14 (sCD14) and lipopolysaccharide-binding protein (LBP) by enzyme-linked immunosorbent assay (ELISA). Increased sCD14 was observed in the CSF of PTM and rhesus macaque (RM), while increased LBP was observed in pigtail macaque (PTM) plasma. Finally, to examine whether ZIKV-induced microbial dysbiosis could underlie increased microbial translocation and inflammation, we characterized intestinal microbial communities by 16s rRNA gene sequencing and microbial functional changes by quantifying short-chain fatty acid (SCFA) concentrations by gas chromatography mass spectrometry. We observed that although ZIKV infection of PTM did not result in significant taxonomic shifts in microbial communities, there were significant reductions in SCFA levels. Loss of microbial function in ZIKV infection could cause decreased intestinal integrity, thereby contributing to elevated microbial translocation and systemic and CNS inflammation, providing a possible mechanism underlying ZIKV pathogenesis. Further, this may represent a mechanism underlying inflammation and pathogenesis in other diseases. Author SummaryZika virus (ZIKV) can be transmitted to humans via the bite of an infected mosquito or between humans during sexual intercourse, typically resulting in mild symptoms, which has been linked to elevated inflammation in the CNS and the development of more serious conditions, including severe neurological syndromes. Previous studies have observed that ZIKV infection is associated with increased mucosal dysfunction, including elevated inflammation in rectal and vaginal mucosal tissue. However, the mechanism of ZIKV-induced mucosal dysfunction may contribute to systemic and CNS inflammation has not been previously investigated. Here, we used the non-human primate (NHP) model and clinical specimens from ZIKV-infected humans to examine markers of systemic and CNS inflammation and microbial translocation. We observed elevated markers indicative of microbial translocation and inflammation in the CNS of ZIKV-infected macaques and humans. A potential association with mucosal dysfunction in ZIKV infection is shifts in microbial dysbiosis. We also observed that there were no significant overall taxonomic shifts in microbial communities, but a reduction of bacterial-derived short-chain fatty acid (SCFA) levels. Finally, we observed that the decrease in SCFA levels significantly negatively correlated with the elevated peripheral and CNS inflammatory markers, suggesting a link between ZIKV-driven disease pathology and microbial function. Taken together, our study provides new insight into a previously unconsidered mechanism underlying ZIKV pathogenesis.

microbiology↗