Blocking AGE-RAGE Signaling Improved Functional Disorders of Macrophages in Diabetic Wound

Abstract

Advanced glycosylation end products (AGEs) accumulate in diabetic wounds. Interactions between AGEs and their receptor (RAGE) leads to dermatologic problems in diabetes. Macrophage, which plays important roles in wound healing, highly expresses RAGE. Therefore, we investigated whether RAGE-expressing macrophages might be responsible for impaired wound healing on diabetes. We used anti-RAGE antibody applied topically on diabetic wounds. After confirming that wound healing was improved in anti-RAGE antibody group compared with normal mice, our results showed that macrophages appeared insufficient in the early stage and fading away slowly in the later proliferative phase compared with the control group, which was ameliorated in anti-RAGE antibody-applied wounds. Blocking AGE-RAGE signaling also increased neutrophils phagocytized by macrophages and promoted the phenotypic switch of macrophages from proinflammatory to prohealing activities. In vitro, phagocytosis of THP-1 (M0) and lipopolysaccharide- (LPS-) induced (M1) macrophages was impaired by treatment with AGEs, while IL-4- and IL-13-induced (M2) macrophages was not. Finally, AGEs increased the proinflammatory response of M1 macrophages, while inhibiting the polarization and anti-inflammatory functions of M2 macrophages. In conclusion, inhibition of AGE-RAGE signaling improved functional disorders of macrophages in the early inflammatory phase, which promoted the healing of wounds in diabetic mice.

Macrophage Dysregulation and Impaired Skin Wound Healing in Diabetes

“…In addition, reduced PPAR-γ expression in diabetic wound Mϕ and improved wound healing in diabetic mice with topical wound treatment with PPAR-γ agonist is consistent with the idea that PPAR-γ-mediated macrophage clearance of apoptotic wound neutrophils may play an important role in wound healing ( Khanna et al, 2010 ; Chen et al, 2015 ; Mirza et al, 2015 ). In another report, antibody mediated topical inhibition of receptor for advanced glycation end products (RAGE) signaling showed reduced number of neutrophils in diabetic wounds in association with enhanced phagocytosis by Mϕ and improved wound healing further supporting the notion that increased neutrophil accumulation in diabetic wounds results from reduced phagocytic ability of Mϕ which is closely associated with impaired wound healing in diabetes ( Figure 1C ) ( Wang et al, 2017 ). Together, these reports suggest that decreased efferocytosis by wound Mϕ is critical for impaired wound healing in diabetes.…”

“…Later in the healing process, Mϕ secrete other growth factors such as TGF-β, FGF, and IGF-1 that induce cell proliferation and protein synthesis which are critical for healing ( Hunt et al, 1984 ; Rappolee et al, 1988 ). Finally, Mϕ have been shown to be involved in collagen degradation during tissue remodeling phase of repair ( Madsen et al, 2013 ; Roch et al, 2014 ; Wang et al, 2017 ). A study that depleted Mϕ in LysM-Cre/DTR mice at different stages of wound healing supports the notion that Mϕ change functions throughout the healing process – loss of Mϕ during early stages of healing leads to reduced epithelialization, granulation tissue formation and wound contraction whereas Mϕ depletion during the mid-phase abrogates transition of wound tissues from regeneration to maturation phase ( Lucas et al, 2010 ).…”

“…In summary, both sustained increases in the number of wound Mo/Mϕ and dysregulation of their phenotype, caused both by intrinsic alterations in bone marrow progenitors and by a pro-inflammatory wound microenvironment, lead to impaired wound healing in diabetes ( Mirza et al, 2013 , 2014 ; Nagareddy et al, 2014 ; Singer et al, 2014 ; Gallagher et al, 2015 ; Yan et al, 2018 ). Improved understanding of factors that regulate wound Mo/Mϕ numbers and phenotype have led to new therapeutic interventions attempting to normalize the Mϕ response in mice targeting the NLRP3 inflammasome/IL-1β and RAGE pathways; these findings await translation to humans ( Mirza et al, 2013 ; Wang et al, 2017 ). Another approach for normalizing Mϕ phenotypes in non-healing wounds could be altering epigenetic modifications of genes associated with dysregulated Mϕ phenotype ( Gallagher et al, 2015 ; Yan et al, 2018 ).…”

Annexin A1‐derived peptide Ac2‐26 facilitates wound healing in diabetic mice

“…Besides efferocytosis, macrophages could also change their phenotype to mediate the transition from inflammation to cell proliferation during wound repair 4 . In diabetes, however, hyperglycemia and the relevant advanced glycation end products may cause abnormal M1 macrophage activation and inhibit the development of M2 macrophage 31,32 . A failed conversion from pro‐inflammatory M1 to pro‐repair M2 phenotype, as demonstrated by macrophages in diabetic wounds, results in excessive inflammation and impaired wound healing 4,5,8,9 .…”

Macrophage functions in wound healing

“…Because the collagen removal and turnover are crucial for tissue remodelling during wound healing, this information can potentially be applied for development of novel wound healing strategies. Wang et al () studied macrophage functions in diabetic wound healing. Diabetic wound accumulates high levels of advanced glycosylation end products (AGEs).…”