Wound healing in periodontal disease induces macrophage polarization characterized by different arginine‐metabolizing enzymes

Abstract

Background and objective Macrophages play important roles from the initiation of inflammation to wound healing. Two phenotypes of macrophages, namely pro‐inflammatory type macrophages (M1‐MΦ) and anti‐inflammatory type macrophages (M2‐MΦ), have been reported. Two contrasting metabolic enzymes that use arginine as a substrate, inducible nitric oxide synthase (iNOS), and arginase‐1 (Arg‐1), have been identified as M1‐MΦ and M2‐MΦ markers, respectively. The purpose of this study was to elucidate the temporal dynamics of the macrophage phenotype during the progression and healing phases of experimental periodontitis in mice. Material and methods A total of 63 C57BL/6J mice were divided into the following 3 groups: control (C), periodontitis (P), and healing (H). To induce periodontitis, a silk ligature was placed around the maxillary bilateral second molars of mice in the periodontitis and healing groups. In the healing group, the ligature was removed 3 days after ligation to induce tissue healing. Maxillary tissue was collected on day 0 for the control group, days 1, 3, 5, and 7 for the periodontitis group (P1, P3, P5, and P7), and days 5 and 7 for the healing group (H5 and H7: 3 days with the ligation + 2 days or 4 days following ligature removal). The left side of the maxilla was subjected to bone structure analysis using micro‐computed tomography and gene expression analysis using polymerase chain reaction. On the right side, immunohistochemistry was performed to histopathologically evaluate the localization of macrophages by phenotype in the periodontal tissue. Results In the alveolar bone structure analysis, the linear distance of bone height increased significantly in the P5 and P7 groups, whereas bone volume fraction and bone mineral density decreased over time after ligature placement; in the healing group (H5 and H7), these parameters improved significantly compared with the periodontitis group (P5 and P7). Expression of genes encoding pro‐inflammatory cytokines and iNOS increased in the periodontitis group, and expression of anti‐inflammatory cytokine genes and Arg‐1 increased in the healing group. Furthermore, the iNOS/Arg‐1 expression ratio increased with ligation, whereas the ratio in the healing groups (H5 and H7) significantly decreased compared with the periodontitis groups (P5 and P7). Immunofluorescence staining revealed a significant increase in the number of iNOS‐positive macrophages in the periodontitis group and decrease in the healing group. In contrast, the number of Arg‐1‐positive macrophages decreased in the periodontitis group and increased in the healing group. Conclusion The results of the present study suggest that wound healing in periodontal disease induces macrophage polarization from M1‐MΦ to M2‐MΦ characterized by iNOS and Arg‐1.

Oxidative Stress Inhibits Endotoxin Tolerance and May Affect Periodontitis

“…It also suggests that endotoxin inhibition functions as a protective mechanism to alleviate inflammatory symptoms and promote resolution upon LPS stimulation in the gingiva. This is in agreement with another study on mice in which the gingival tissue was hypo-responsive to ligature stimulation from the third-day postplacement, suggesting establishment of endotoxin tolerance (Miyashita et al 2021).…”

Macrophages contribute to periodontal wound healing mainly in the tissue proliferation stage

“…Although previous studies have shown the basic function of M1 and M2 macrophages in periodontal healing, a more continuous alterations in the proportion, distribution and function of M1 and M2 macrophages are not clear. 13 Notably, although it has been suggested that an increase in the number of M2 macrophages promotes tissue repair and scar formation, 5,6,8 it is reported that exogenous M2 macrophages can delay tissue healing. 9 The timing of cell administration may contribute to this process.…”

Mitigating Lactate-Associated Immunosuppression against Intracellular Bacteria Using Thermoresponsive Nanoparticles for Septic Arthritis Therapy

“…Twelve hours post-treatment, MRSA-infected macrophages in all groups were polarized toward the M1-like polarization (Figure 4b and Figure S12), caused by the high expression of HIF-1α, which upregulates the expression of immune-associated genes (especially iNOS expression). 20,29,44 As depicted in Figure 4b, HIF-1α is highly expressed in all groups, including the uninfected macrophages due to the anaerobic conditions. Interestingly, HIF-1α, purported to be one of the oxygensensitive proteins, 23,44 was still highly expressed after treatment with oxygen-producing nanopartcles (CP NPs and CVP NPs), indicating that the CVP NPs are able to stabilize HIF-1α in the process of producing oxygen.…”

“…M2-polarized macrophages (anti-inflammatory) are incompetent to eliminate infection due to the drastic expression changes of immune-associated proteins . For example, M2-polarized macrophages express excess arginase-1 (Arg-1) to competitively inhibit iNOS by consuming its substrate ( l -arginine) to reduce the production of RNS, which plays a pivotal role in killing intracellular bacteria. , Therefore, in septic arthritis, macrophages cannot maintain M1-like polarization for a long time and are coerced to M2-like polarization, which causes local immunosuppression, further hindering the eradication of intracellular MRSA . Consequently, incomplete clearance of MRSA sequestered inside macrophages not only causes recurrent infections in the initial site of infection but also acts as a “Trojan horse” to spread the bacteria to other tissues or organs through the bloodstream. , Accordingly, eradicating the intracellular bacteria is critical to the clinical success of MRSA-infected diseases.…”