Gut microbiota lipopolysaccharide accelerates inflamm-aging in mice

Abstract

Background: The constitutive inflammation that characterizes advanced age is termed inflamm-aging. This process is associated with age-related changes to immune homeostasis and gut microbiota. We investigated the relationship between aging and gut microbiota lipopolysaccharide (LPS)-inducible inflammation.

Results: A taxonomy-based analysis showed that aging resulted in increased prevalence of the phyla Firmicutes and Actinobacteria and a reduced prevalence of Bacteroidetes and Tenericutes, resulting in an increase in the Firmicutes to Bacteroidetes ratio. The levels of plasmatic and fecal lipopolysaccharides were higher in aged mice. Aging induced the expression of p16 and the activation of nuclear factor-kappa B (NF-κB) in the colon of aged mice. Interestingly, the expression level of sterile α-motif domain- and HD domain-containing protein 1 (SAMHD1) in the colon was higher in aged mice than in young mice, while cyclin-dependent kinase-2 and cyclin E levels were lower in aged mice than in young mice. The lipopolysaccharide fraction of fecal lysates (LFL) from young or aged mice increased p16 and SAMHD1 expression and NF-κB activation in peritoneal macrophages from wild-type mice, in a TLR4-dependent manner. However, LFLs did not induce NF-κB activation and SAMHD1 expression in peritoneal macrophages from TLR4-deificent mice, whereas they significantly induced p16 expression. Nevertheless, p16 expression was induced more potently in macrophages from WT mice than in macrophages from TLR4-deficient mice.

Conclusion: Aging increased p16 and SAMHD1 expression, gut microbiota LPS production, and NF-κB activation; thereby, signifying that gut microbiota LPS may accelerate inflamm-aging and SAMHD1 may be an inflamm-aging marker.

Fig. 1

The composition of intestinal microbiota. The relative contributions of dominant (a) phyla and (b) families (individual samples are shown in the left panels and pooled samples are shown in the right panels) and (c) the Firmicutes to Bacteroidetes ratio are shown as identified from pyrosequencing data. d Hierarchical clustering of gut microbial gene expression profiles. The distances between microbial communities from each sample are represented as an Unweighted Pair Group Method with Arithmetic Mean (UPGMA) clustering tree describing the dissimilarity between multiple samples. All values are indicated as the mean ± standard error of the mean (n = 4). *, p < 0.05 in comparison with young mice. YM, young mice; AM, aged mice

Fig. 2

Effects of aging on endotoxin levels in young and aged mice. a Body weight (g) and epididymal fat pad weight (mg/g of body weight) of male C57BL/6 J mice (4 and 18 months old) were measured. b The fecal endotoxin concentration per gram (EU/g of feces) and plasma endotoxin concentration per mL (EU/mL) were measured using the Limulus amebocyte lysate assay. All values are indicated as the mean ± standard error of the mean (n = 8). *, p < 0.05 in comparison with young mice. YM, young mice; AM, aged mice

Fig. 3

Effects of aging on inflammation, p16, cell cycle-regulators, and SAMHD1 levels in the colon of young and aged mice. Western blot analysis was performed on colon lysates from young mice or aged mice. All values are indicated as the mean ± standard error of the mean (n = 8). YM, young mice; AM, aged mice

Fig. 4

Effects of LPS on SAMHD1 expression in peritoneal macrophages. Peritoneal macrophages from mice were incubated with 10, 50, or 100 ng/mL lipopolysaccharides and used for immunoblotting. All values are indicated as the mean ± standard error of the mean (n = 3). YM, young mice; AM, aged mice

Fig. 5

Effects of fecal lysates from young or aged mice on the expression levels of SAMHD1 and the senescence marker p16. Peritoneal macrophages from wild-type mice (top panel) and toll-like receptor 4-deficient mice (bottom panel) were incubated with fecal lysates from young or aged mice maintained on a low-fat or high-fat diet and then used for immunoblotting. All values are indicated as the mean ± standard error of the mean (n = 3). YM, young mice; AM, aged mice