Periodontitis is a common chronic inflammatory disease that causes the periodontal bone destruction and may ultimately result in tooth loss. With the progression of periodontitis, the osteoimmunology microenvironment in periodontitis is damaged and leads to the formation of pathological alveolar bone resorption. CD301b⁺ macrophages are specific to the osteoimmunology microenvironment, and are emerging as vital booster for conducting bone regeneration. However, the key upstream targets of CD301b⁺ macrophages and their potential mechanism in periodontitis remain elusive. In this study, we concentrated on the role of Tim4, a latent upstream regulator of CD301b⁺ macrophages. We first demonstrated that the transcription level of Timd4 (gene name of Tim4) in CD301b⁺ macrophages was significantly upregulated compared to CD301b⁻ macrophages via high-throughput RNA sequencing. Moreover, several Tim4-related functions such as apoptotic cell clearance, phagocytosis and engulfment were positively regulated by CD301b⁺ macrophages. The single-cell RNA sequencing analysis subsequently discovered that Cd301b and Timd4 were specifically co-expressed in macrophages. The following flow cytometric analysis indicated that Tim4 positive expression rates in total macrophages shared highly synchronized dynamic changes with the proportions of CD301b⁺ macrophages as periodontitis progressed. Furthermore, the deficiency of Tim4 in mice decreased CD301b⁺ macrophages and eventually magnified alveolar bone resorption in periodontitis. Additionally, Tim4 controlled the p38 MAPK signaling pathway to ultimately mediate CD301b⁺ macrophages phenotype. In a word, Tim4 might regulate CD301b⁺ macrophages through p38 MAPK signaling pathway in periodontitis, which provided new insights into periodontitis immunoregulation as well as help to develop innovative therapeutic targets and treatment strategies for periodontitis.

牙周炎是一种常见的慢性炎症性疾病，会导致牙周骨破坏，最终可能导致牙齿脱落。随着牙周炎的进展，牙周炎内的骨免疫微环境被破坏，导致病理性牙槽骨吸收的形成。 CD301b ⁺巨噬细胞是骨免疫微环境特有的，并且正在成为骨再生的重要助推器。然而，CD301b ⁺巨噬细胞的关键上游靶点及其在牙周炎中的潜在机制仍不清楚。在这项研究中，我们集中研究了 Tim4（CD301b ⁺巨噬细胞的潜在上游调节因子）的作用。我们首先通过高通量RNA测序证明，与CD301b-巨噬细胞相比^， CD301b ⁺巨噬细胞中Timd4 （Tim4的基因名称）的转录水平显着上调。此外，一些与Tim4相关的功能，如凋亡细胞清除、吞噬作用和吞噬作用，受到CD301b ⁺巨噬细胞的正向调节。随后的单细胞RNA测序分析发现Cd301b和Timd4在巨噬细胞中特异性共表达。以下流式细胞术分析表明，随着牙周炎的进展，总巨噬细胞中Tim4阳性表达率与CD301b ⁺巨噬细胞的比例呈现高度同步的动态变化。此外，小鼠中 Tim4 的缺乏会减少 CD301b ⁺巨噬细胞，并最终放大牙周炎中的牙槽骨吸收。 此外，Tim4 控制 p38 MAPK 信号通路，最终介导 CD301b ⁺巨噬细胞表型。总之，Tim4可能通过p38 MAPK信号通路对牙周炎中的CD301b ⁺巨噬细胞进行调节，这为牙周炎免疫调节提供了新的见解，并有助于开发牙周炎的创新治疗靶点和治疗策略。