Comparative analysis of microbial sensing molecules in mucosal tissues with aging

Abstract

Host-bacterial interactions at mucosal surfaces require recognition of the bacteria by host cells enabling targeted responses to maintain tissue homeostasis. It is now well recognized that an array of host-derived pattern recognition receptors (PRRs), both cell-bound and soluble, are critical to innate immune engagement of microbes via microbial-associated molecular patterns (MAMP). This report describes the use of a nonhuman primate model to evaluate changes in the expression of these sensing molecules related to aging in healthy gingival tissues. Macaca mulatta aged 3-24 years were evaluated clinically and gingival tissues obtained, RNA isolated and microarray analysis conducted for gene expression of the sensing pattern recognition receptors (PRRs). The results demonstrated increased expression of various PRRs in healthy aging gingiva including extracellular (CD14, CD209, CLEC4E, TLR4), intracellular (NAIP, IFIH1, DAI) and soluble (PTX4, SAA1) PRRs. Selected PRRs were also correlated with both bleeding on probing (BOP) and pocket depth (PD) in the animals. These findings suggest that aged animals express altered levels of various PRRs that could affect the ability of the tissues to interact effectively with the juxtaposed microbial ecology, presumably contributing to an enhanced risk of periodontitis even in clinically healthy oral mucosal tissues with aging.

Keywords: Aging; Microbial sensing; Nonhuman primates; Oral mucosa; Pattern recognition receptors; Periodontitis.

Figure 1

Correlation of mouth mean bleeding on probing (BOP) and pocket depth (PD) measures related to age of the animals. Each point represents one animal.

Figure 2

Distribution of gene expression of PRRs in healthy aging gingival tissues compared to other age groups. The bars denote the mean levels in healthy aged (n=6), and all other healthy (n-17). Significant differences are denoted by p-values.

Figure 2

Distribution of gene expression of PRRs in healthy aging gingival tissues compared to other age groups. The bars denote the mean levels in healthy aged (n=6), and all other healthy (n-17). Significant differences are denoted by p-values.

Figure 3

Identification of gene expression profiles in healthy gingival tissues comparing aged tissues to all other age groups. Points denote individual genes plotted as fold-difference with aging and p-value.

Figure 4

Correlation of PRR expression in healthy gingival tissues for genes that significantly correlated with age. Each point denotes the values from 1 animal (n=41). Genes CLEC4M (Rhesus Macaque Genome Array; n=23) and PTX4 (Rhesus Gene 1.x ST Exon Array; n=18) are only currently annotated for one of the microarray chips that were used in the experiments.

Figure 5

Correlation of PRR gene expression in healthy gingival tissues related to mouth mean PD or BOP. Each point denotes the values for 1 animal (n=41).

Figure 6

Schematic of network of gene expression correlations among the array of PRRs in healthy gingival tissues. The characteristics of the PRRs are identified by speckled (surface PRRs), slanted lines (intracellular PRRs), and solid (soluble PRRs) ovals. The green lines denote a significantly positive (at least p<0.05) correlation and red line denotes a significant negative correlation in expression of 2 genes. Pink highlights are genes with 5 or more correlations, blue highlights signify genes with 3–4 correlations, and white highlights denote 1–2 correlations.