Atf4 regulates angiogenic differences between alveolar bone and long bone macrophages by regulating M1 polarization, based on single-cell RNA sequencing, RNA-seq and ATAC-seq analysis.

ABSTRACT

In the repair of maxillofacial bone defects, autogenous craniofacial bone can often provide superior clinical results over long bone grafts. Most current studies have focused on the osteogenic differences between alveolar bone marrow (ABM) and long bone marrow (LBM), however, studies about the angiogenic differences between the two are currently lacking. We downloaded single-cell RNA sequencing (scRNA-seq) of mouse ABM and LBM respectively from the public database, and the data were processed by using Seurat package. CellphoneDB2 results showed that macrophages had the strongest interaction with mesenchymal stem cells (MSCs) and endothelial cells (ECs). ELISA results confirmed that ABM macrophages secreted a higher level of vascular endothelial growth factor A (Vegfa) compared to LBM macrophages, which further promoted angiogenesis of ECs and MSCs. Using SCENIC package, six key transcription factors (TFs) were identified to regulate the difference between ABM and LBM macrophages, and activating transcription factor 4 (Atf4) was confirmed to be more expressed in ABM macrophages by polymerase chain reaction (PCR) and western blot (WB), with predicted target genes including Vegfa. Besides, the result of scRNA-seq implied ABM macrophages more in M1 status than LBM macrophages, which was confirmed by the following experiments. From the results of another assay for transposase accessible chromatin sequencing (ATAC-seq) and RNA-seq about M1 macrophages, Atf4 was also confirmed to regulate the M1 polarization. So, we suspected that Atf4 regulated the different expression of Vegfa between ABM and LBM macrophages by activating M1 polarization. After knocking down Atf4, the expression of M1 polarization markers and Vegfa were downregulated and vasculogenic differences were eliminated, which were subsequently reversed by the addition of LPS/IFN-γ. Our study might provide a new idea to improve the success rate of autologous bone grafting and treatment of oral diseases.