Mef2c調控基因之鑑定及漿狀樹突細胞的發育和功能的研究

Abstract

樹突狀細胞（DCs），包括漿細胞樣樹突狀細胞（pDCs）和經典樹突狀細胞（cDCs），在橋接先天免疫和適應性免疫中發揮著至關重要的作用。雖然cDCs根據發育過程中的表面標記和轉錄因子分為cDC1和cDC2，但pDCs仍然是異質的。多種轉錄因子對pDCs的發育和命運至關重要，但這些調節因子的詳細網絡仍然不明。此前，我們已經確定Mef2c是pDC發育的關鍵轉錄因子。Mef2c在小鼠中的缺失導致骨髓（BM）、脾臟（SP）和淋巴結（LN）中pDC數量和頻率的減少。此外，Mef2c缺失的BM在體外也顯示出pDC發育受損，這表明pDC發育的缺陷是由BM前體細胞中Mef2c的喪失引起的。與pDC發育相關的關鍵轉錄因子如Tcf4、Spib和Runx2在缺乏Mef2c的情況下表現減少。此外，與對照組相比，Mef2c缺失的pDCs在穩態下的pDC特異性標誌物如Siglec-H、BST2和B220的表面表達也減少，這表明Mef2c可能是pDC特異性基因的上游調節因子。由於Siglec-H已知是pDC功能的負調節因子，我們推測Mef2c也可能在調節中起作用。事實上，使用CpG或R848刺激BM衍生的DCs顯示pDCs和cDC2s中CD40、MHC II和PD-L1的表達增加，而cDC1s則沒有。此外，未刺激或TLR刺激誘導的促炎細胞因子如IL-6、TNF-a和IL-12p40以及I型干擾素（IFN-I）的表達在缺乏Mef2c的情況下也增加，這表明Mef2c負向調節pDCs和可能cDC2s的功能。總之，我們將Mef2c定義為pDC發育的新型正向調節因子和pDC功能的負向調節因子。

Dendritic cells (DCs), including plasmacytoid DC (pDCs) and classical DC (cDCs), play a crucial role in bridging innate adaptive immunity. While cDCs are classified into cDC1 and cDC2 based on surface markers and transcription factors during development, pDC remains heterogeneous. Various transcription factors are critical for the development and fate of pDCs, but the detailed network of these regulators remains elusive. We have previously identified Mef2c as a critical transcription factor (TF) for pDC development. Mef2c deletion in mice resulted in reduced number and frequency of pDC population in the bone marrow (BM), spleen (SP), and lymph nodes (LN). Moreover, Mef2cKO BM also showed impaired pDC development in vitro, suggesting that the defect of pDC development was intrinsic to the loss of Mef2c in BM progenitors. Interestingly, TFs critical for pDC development, such as Tcf4, Spib, and Runx2, were found to be decreased in the absence of Mef2c. Moreover, the surface expression of pDC-specific markers, such as Siglec-H, BST2, and B220, was also reduced in Mef2KO pDCs compared to the control at a steady state, suggesting that Mef2c might be upstream of pDC-specific genes. Since Siglec-H is known to be a negative regulator of pDC function, we reasoned that Mef2c might also play a regulatory role. Indeed, stimulation of BM-derived DCs with CpG or R848 showed a higher expression of CD40, MHC II, and PD-L1 in pDCs and cDC2s but not cDC1s. Additionally, basal and TLR-stimulation-induced expression of proinflammatory cytokines, such as IL-6, TNF, and IL-12p40, and type I IFN (IFN-I) was also increased in the absence of Mef2c, suggesting that Mef2c negatively regulates pDCs’ and maybe cDC2’s functions. In sum, we define the dual roles of Mef2c as a novel positive regulator for pDC development and a negative regulator for pDC functions.