Elsevier

Journal of Endodontics

Volume 39, Issue 11, November 2013, Pages 1390-1394
Journal of Endodontics

Basic Research
Absent in Melanoma 2 (AIM2) in Rat Dental Pulp Mediates the Inflammatory Response during Pulpitis

https://doi.org/10.1016/j.joen.2013.07.003Get rights and content

Abstract

Introduction

In recent years, the inflammasome has been determined to play an important role in inflammatory diseases. However, the role of the inflammasome in pulpitis remains unclear. Absent in melanoma 2 (AIM2) is a type of inflammasome that recognizes cytosolic double stranded DNA and forms a caspase-1–activating inflammasome with apoptosis-associated speck-like protein containing a caspase activating recruiting domain. In this study, we determined whether AIM2 was expressed in pulp cells and defined the role of AIM2 in the initiation of inflammation within the dental pulp.

Methods

In the in vivo study, the right maxillary molars from male adult Sprague-Dawley rats (250–350 g) were exposed to the pulp. In the in vitro study, the pulp cells isolated from the mandibular incisors of the Sprague-Dawley rats (2 weeks) were conventionally cultured. Immunofluorescence staining was used to determine the expression and distribution of AIM2 in the rat dental pulp tissues and cells in the presence or absence of inflammatory stimulation. Western blotting and real-time polymerase chain reaction were performed to determine whether there was a correlation between AIM2 expression levels and inflammation both in vivo and in vitro.

Results

In healthy dental pulp tissues and cells, AIM2 was only detected in the odontoblast layer. Stimulation significantly increased AIM2 expression in both the dental pulp tissues and cultured cells. The mRNA and protein levels of AIM2 were significantly up-regulated in response to inflammatory stimulation in a dose-dependent manner. Moreover, we also found that AIM2 expression correlated with interleukin-1 levels. These results reveal a direct relationship between the AIM2 inflammasome and pulpitis.

Conclusions

Our study demonstrates that AIM2 is expressed in dental pulp tissues and mediates the inflammatory response during pulpitis. Therapeutic interventions aimed at reducing AIM2 expression may be beneficial in the treatment of pulpitis.

Section snippets

Rat Pulpitis Model

Adult male Sprague-Dawley rats, each weighing 250–350 g, were anesthetized intraperitoneally with chloral hydrate (10%, 1 mL/250 g).The mouths of the rats were opened with metal tweezers, and the right maxillary first and second molars were drilled with a high-speed handpiece and 1/4 round bar 12, 13, 14. The rats were divided into 4 groups (3-day, 5-day, 7-day, and 10-day), with each group consisting of 3 animals.

Primary Dental Pulp Cell Culture

We prepared cells from the mandibular central incisors of 2-week Sprague-Dawley

Expression of AIM2 in Rat Dental Pulp Tissues and Cells

The dental pulp tissues and stimulated dental pulp cells both expressed AIM2 (Fig. 1E and H). AIM2 was expressed in the cytoplasm of odontoblasts but not in fibroblasts from healthy pulp tissues (Fig. 1A–C). In contrast, AIM2 was strongly expressed in the inflammatory cells and fibroblasts from the inflamed dental pulp (Fig. 1D–F). The immunofluorescence staining of the dental pulp cells demonstrated the same results as those described above (Fig. 1G and H). We also performed RT-PCR and Western

Discussion

On activation, AIM2 assembles into inflammasomes, which regulate the secretion and bioactivity of cytokines belonging to the IL-1 family (IL-1β, IL-18), but the exact mechanism leading to the activation of the AIM2 inflammasome remains unclear 3, 4. AIM2 is mainly expressed in cells of the host defense system, including spleen cells, macrophages, dendritic cells, B and T lymphocytes, skin keratinocytes, peripheral blood cells, and gingival epithelial cells (19). These observations, along with a

Acknowledgments

The authors deny any conflicts of interest related to this study.

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Yafei Wang and Shafei Zhai contributed equally to this work.

Supported by grant 81170946 from the National Natural Science Foundation of China.

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