Pseudomonas aeruginosa infection alters the macrophage phenotype switching process during wound healing in diabetic mice

Abstract

Macrophages play critical roles in wound healing process. They switch from "classically activated" (M1) phenotype in the early inflammatory phase to "alternatively activated" (M2) phenotype in the later healing phase. However, the dynamic process of macrophage phenotype switching in diabetic wounds burdened with bacteria is unclear. In this report, Pseudomonas aeruginosa, frequently detected in diabetic foot ulcers, was inoculated into cutaneous wounds of db/db diabetic mice to mimic bacterium-infected diabetic wound healing. We observed that P. aeruginosa infection impaired diabetic wound healing and quickly promoted the expression of pro-inflammatory genes (M1 macrophage markers) tumor necrosis factor-α (tnf-α), interleukin-1β (il-1β) and il-6 in wounds. The expression of markers of M2 macrophages, including il-10, arginase-1, and ym1 were also upregulated. In addition, similar gene expression patterns were observed in macrophages isolated directly from wounds. Immunostaining showed that P. aeruginosa infection increased both the ratios of M1 and M2 macrophages in wounds compared with that in control groups, which was further confirmed by in vitro culturing macrophages with P. aeruginosa and skin fibroblast conditioned medium. However, the ratios of the expression levels of pro-inflammatory genes to anti-inflammatory gene il-10 was increased markedly in P. aeruginosa infected wounds and macrophages compared with that in control groups, and P. aeruginosa prolonged the presence of M1 macrophages in the wounds. These data demonstrated that P. aeruginosa in diabetic wounds activates a mixed M1/M2 macrophage phenotype with an excessive activation of M1 phenotype or relatively inadequate activation of M2 phenotype.

Biofilm-Innate Immune Interface: Contribution to Chronic Wound Formation

“…Despite forming large abscesses, their structure had diffused immune cell organization and higher bacterial burdens (148). In mice infected with P. aeruginosa, diabetes was associated with prolonged M1 activation, which impaired healing processes by diminishing re-epithelialization, granulation tissue formation and angiogenesis (158). Alternatively, Nguyen et al found diabetic mice inoculated with S. aureus biofilms had reduced TLR2 and TLR4 mRNA expression and high levels of inflammatory cytokines (IL-1b and TNF-a) (159).…”

Macrophage Related Chronic Inflammation in Non-Healing Wounds

“…Chronic wounds are frequently accompanied by the invasion and infection of bacteria due to their unique microenvironment. Multiple species of bacteria have been isolated from chronic wounds, and several also affect the M1 to M2 polarization of macrophages (128). For example, Pseudomonas aeruginosa (P. aeruginosa) is a frequently detected gram-negative pathogen in diabetic non-biofilm wounds (129,130).…”

Effects of des-acyl ghrelin on insulin sensitivity and macrophage polarization in adipose tissue

“…and growth factors [insulin-like growth factor 1 (IGF1), vascular endothelial growth factor (VEGF), transforming growth factor (TGF), etc.]. [15][16][17][18][19] M1 and M2 ATMs constitute different subsets of macrophages. Insulin resistance and adipose tissue inflammation are related to the number of M1 macrophages and the expression of M1 marker genes, such as Tnfa and Mcp1.…”