REMOTE BURN INJURY IN AGED MICE INDUCES COLONIC LYMPHOID AGGREGATE EXPANSION AND DYSBIOSIS OF THE FECAL MICROBIOME WHICH CORRELATES WITH NEUROINFLAMMATION.

ABSTRACT: The Earth's population is aging, and by 2050, one of six people will be 65 years or older. Therefore, proper treatment of injuries that disproportionately impact people of advanced age will be more important. Clinical studies reveal people 65 years or older account for 16.5% of all burn injuries and experience higher morbidity, including neurocognitive decline, and mortality that we and others believe are mediated, in part, by heightened intestinal permeability. Herein, we used our clinically relevant model of scald burn injury in young and aged mice to determine whether age and burn injury cooperate to induce heightened colonic damage, alterations to the fecal microbiome, and whether resultant changes in the microbiome correlate with neuroinflammation. We found that aged, burn-injured mice have an increase in colonic lymphoid aggregates, inflammation, and proinflammatory chemokine expression when compared with young groups and sham-injured aged mice. We then performed fecal microbiota sequencing and found a striking reduction in gut protective bacterial taxa, including Akkermansia , in the aged burn group compared with all other groups. This reduction correlated with an increase in serum fluorescein isothiocyanate-Dextran administered by gavage, indicating heightened intestinal permeability. Furthermore, loss of Akkermansia was highly correlated with increased messenger RNA expression of neuroinflammatory markers in the brain, including chemokine ligand 2, TNF-α, CXC motif ligand 1, and S100 calcium-binding protein A8. Finally, we discovered that postburn alterations in the microbiome correlated with measures of strength in all treatment groups, and those that performed better on the rotarod and hanging wire tests had higher abundance of Akkermansia than those that performed worse. Taken together, these findings indicate that loss of protective bacteria after burn injury in aged mice contributes to alterations in the colon, gut leakiness, neuroinflammation, and strength. Therefore, supplementation of protective bacteria, such as Akkermansia , after burn injury in aged patients may have therapeutic benefit.

Changes in gut microbiome correlate with intestinal barrier dysfunction and inflammation following a 3-day ethanol exposure in aged mice.

Alcohol use among older adults is on the rise. This increase is clinically relevant as older adults are at risk for increased morbidity and mortality from many alcohol-related chronic diseases compared to younger patients. However, little is known regarding the synergistic effects of alcohol and age. There are intriguing data suggesting that aging may lead to impaired intestinal barrier integrity and dysbiosis of the intestinal microbiome, which could increase susceptibility to alcohol's negative effects. To study the effects of alcohol in age we exposed aged and young mice to 3 days of moderate ethanol and evaluated changes in gut parameters. We found that these levels of drinking do not have obvious effects in young mice but cause significant alcohol-induced gut barrier dysfunction and expression of the pro-inflammatory cytokine TNFα in aged mice. Ethanol-induced downregulation of expression of the gut-protective antimicrobial peptides Defa-rs1, Reg3b, and Reg3g was observed in aged, but not young mice. Analysis of the fecal microbiome revealed age-associated shifts in microbial taxa, which correlated with intestinal and hepatic inflammatory gene expression. Taken together, these data demonstrate that age drives microbiome dysbiosis, while ethanol exposure in aged mice induces changes in the expression of antimicrobial genes important for separating these potentially damaging microbes from the intestinal lumen. These changes highlight potential mechanistic targets for prevention of the age-related exacerbation of effects of ethanol on the gut.

Age-Related Intestinal Dysbiosis and Enrichment of Gut-specific Bacteria in the Lung Are Associated With Increased Susceptibility to Streptococcus pneumoniae Infection in Mice.

The portion of the global population that is over the age of 65 is growing rapidly and this presents a number of clinical complications, as the aged population is at higher risk for various diseases, including infection. For example, advanced age is a risk factor for heightened morbidity and mortality following infection with Streptococcus pneumoniae. This increased vulnerability is due, at least in part, to age-related dysregulation of the immune response, a phenomenon termed immunosenescence. However, our understanding of the mechanisms influencing the immunosenescent state and its effects on the innate immune response to pneumonia remain incomplete. Recently, a role for the gut microbiome in age-specific alterations in immunity has been described. Here, we utilized a murine model of intranasal Streptococcus pneumoniae infection to investigate the effects of age on both the innate immune response and the intestinal microbial populations after infection. In aged mice, compared to their younger counterparts, infection with Streptococcus pneumoniae led to increased mortality, impaired lung function and inadequate bacterial control. This poor response to infection was associated with increased influx of neutrophils into the lungs of aged mice 24 h after infection. The exacerbated pulmonary immune response was not associated with increased pro-inflammatory cytokines in the lung compared to young mice but instead heightened expression of immune cell recruiting chemokines by lung neutrophils. Bacterial 16S-rRNA gene sequencing of the fecal microbiome of aged and young-infected mice revealed expansion of Enterobacteriaceae in the feces of aged, but not young mice, after infection. We also saw elevated levels of gut-derived bacteria in the lung of aged-infected mice, including the potentially pathogenic symbiote Escherichia coli. Taken together, these results reveal that, when compared to young mice, Streptococcus pneumoniae infection in age leads to increased lung neutrophilia along with potentially pathogenic alterations in commensal bacteria and highlight potential mechanistic targets contributing to the increased morbidity and mortality observed in infections in age.