Macrophage populations show an M1‐to‐M2 transition in an experimental model of coronal pulp tissue engineering with mesenchymal stem cells

Abstract

Aim To assess M1/M2 macrophage phenotypes in a coronal pulp regeneration model in rats, under the hypothesis that there are dynamic M1/M2 phenotype changes during the different stages of the pulp regeneration. Methodology The maxillary first molars of Wistar rats were pulpotomized, and biodegradable hydrogel‐made scaffolds carrying rat bone marrow mesenchymal stem cells were implanted in the pulp chamber. After 3, 7 and 14 days, samples were processed for (i) histological analysis and double immunoperoxidase staining for CD68 (a general macrophage marker) and one of either CCR7 (an M1 marker), CD163 (an M2 marker) or CD206 (an M2 marker); (ii) real‐time PCR for AIF1 (an M1 marker), CD163, CD206, IL‐10 and TNF‐α mRNA expression; and (iii) Western blotting for the detection of CD68, CCR7 and CD206 proteins. Results Histological analysis of the implanted region revealed sparse cellular distribution at 3 days, pulp‐like tissue with a thin dentine bridge‐like structure at 7 days, and dentine bridge‐like mineralized tissue formation and resorption of most scaffolds at 14 days. CCR7+ macrophages had the highest density at 3 days, and then significantly decreased until 14 days (P < 0.05). In contrast, M2 marker (CD163 or CD206) expressing macrophages had the lowest density at 3 days and significantly increased until 14 days (P < 0.05). AIF1 and TNF‐α mRNA levels, and CD68 and CCR7 protein levels were highest at 3 days. CD163 and CD206 mRNA levels, and CD206 protein levels increased with time and showed the highest at 14 days. IL‐10 mRNA was highest at 3 days, decreased at 7 days and increased at 14 days. Conclusions Macrophages in the regenerating pulp tissue underwent a distinct transition from M1‐dominant to M2‐dominant, suggesting that the M1‐to‐M2 transition of macrophages plays an important role in creating a favourable microenvironment necessary for pulp tissue regeneration.

Role of the CXCR4-SDF1-HMGB1 pathway in the directional migration of cells and regeneration of affected organs

“…In response to injury and subsequent healing, macrophages are capable of polarization towards a spectrum of phenotypes. Based on the environmental cues and molecular mediators, these cells will differentiate into either pro-inflammatory type I macrophage (M1) or anti-inflammatory type II macrophage (M2) phenotypes[ 25 - 27 ].…”

M2 Macrophages Enhance the Cementoblastic Differentiation of Periodontal Ligament Stem Cells via the Akt and JNK Pathways

“…It has become increasingly clear that different polarization states of Mφs exert different influences, most likely via paracrine action, on their cocultured cells in vitro (for example, see ) and their surrounding neighbors in vivo (for examples, see ). Although both the M1 and M2 phenotypes are involved in and necessary for many if not all wound healing cascades, a high ratio of wound healing Mφs normally leads to a favorable tissue regenerative outcome, which includes regeneration of the periodontium (for examples, see ). Therefore, modulating proper Mφ polarization to provide a delicate balance of cytokines and mediators is a critical target for tissue regeneration (for examples, see ).…”

MicroRNA-enriched small extracellular vesicles possess odonto-immunomodulatory properties for modulating the immune response of macrophages and promoting odontogenesis

“…Paula-Silva et al [4] found that TNF-α released from M1 macrophages promotes the odontogenic differentiation of dental pulp cells. However, macrophages undergo M1-to-M2 phenotypical switch in pulp tissue engineering, indicating that such macrophage transition is essential for building a suitable microenvironment for pulp tissue repair [9,10]. M2 macrophages can release odontogenic factors, such as BMP2, TGFβ1, and TGFβ3, to actively participate in odontogenesis [11][12][13].…”

“…M1 macrophages exert proinflammatory functions through helper T (Th) type 1 (Th1)-associated immune reactions [7], whereas M2 macrophages enhance Th2-related reactions, downregulating inflammation [8]. Besides regulating immune reactions, macrophages affect the odontogenic differentiation of stem cells as well as dental pulp repair [9,10]. Macrophages can release regulatory factors such as BMP2, TGFβ1, and TGFβ3 [11][12][13], to actively participate in odontogenic differentiation of DPSCs [12].…”

“…Macrophages can release regulatory factors such as BMP2, TGFβ1, and TGFβ3 [11][12][13], to actively participate in odontogenic differentiation of DPSCs [12]. During pulp tissue bioengineering, macrophages in the repaired pulp tissue phenotypically switch from M1 to M2, creating an optimal microenvironment for pulp tissue repair [9,10].…”