Single-cell transcriptome reveals myocardial heterogeneity in HF
After normalizing and merging the GSE145154 dataset, cells were clustered using Seurat. The results showed that the cells could be bunched into 24 clusters(Supplementary Figure S1). Specifically, based on the annotation information BlueprintEncodeData, we divided the entire cell population into small groups with similar cell states using the R package singleR. These clusters were annotated into 18 cell sorts (Fig. 1A, Figure S1). We further compared the cell type differences in mild lesions with the culprit lesions in DCM and ICM hearts. Surprisingly, epithelial cells and mesangial cells were missing in the mild lesion myocardium (Fig. 1A).
Next, we analyzed the DEG between different cell types and noticed significantly different expression patterns between the populations (Fig. 1B). The cell types for each sample differed immensely from sample to sample (Fig. 1C). Therefore, there was significant cellular heterogeneity in the heart failure samples. Moreover, in the mild (marked as normal) and the culprit lesions in DCM and ICM hearts (marked as HF samples), we counted the proportion of different cell types between different samples. In the HF samples, monocytes and macrophages were significantly decreased, while NK cells and T cells were remarkably increased. (Fig. 1D).
Single-cell Transcriptome Resolves Dysregulation Of Cellular Senescence Genes
A total of 7811 differential genes between cell types were identified from the Sc-RNA sequencing (GSE145154 dataset) (Supplementary Table S1). As the cell senescence DEG, we intersected the cell cluster differential genes with the 279 senescence gene sets obtained from the CellAge database (Supplementary Table S2). 85 differential expression cell senescence genes were obtained for further analysis, including 49 senescence induce genes, 35 senescence inhibit genes, and one with unclear effect (Supplementary Table S3). The top5 cell expression genes of the cell senescence DEGs displayed according to LogFC ranking between normal and HF samples were TXNIP, IGFBP5, IGFBP3, AGT, and CAV1.They are senescence-induced genes highly expressed in heart failure samples compared to the normal controls (Fig. 2A). Further, dug inside the individual cell type, the top5 cell expression genes were TNXIP in B cells, TNXIP in T cells, IGFBP5 in Fibroblasts, TNXIP in NK cells, and IGFBP3 in Fibroblasts.
Subsequently, the activity scores of cells were calculated using AUCell. Based on the AUCell, we specified 398 cells with cell senescence DEG activity (Fig. 2B). These 398 active cells were distributed among Adipocytes, Endothelial cells, Fibroblasts, Monocytes, muscle cells, and Myocytes (Fig. 2C).
Since Monocytes had significant comparative differences between normal and heart failure samples, as we mentioned above, GO analysis and KEGG enrichment analysis were conducted to discover monocyte's differentially expressed genes in normal and HF myocardium (Fig. 2D).
The results showed that the DEGs of monocytes were significantly enriched in lipid and atherosclerosis, lysosome, pertussis, and other disease-related pathways. It was suggested that the gene expression profile of monocytes might play a role in the development of HF.
Bulk Rna-sequencing Analysis Of Hf Gene Expression Characteristics
We analyzed the bulk sequencing data GSE141910 dataset to distinguish the differentially expressed genes between HF and non-HF samples by limma. With a threshold value of adj. p < 0.05, we obtained 2552 DEGs (Supplementary Table S4). To further investigate these DEGs, 29 senescence genes were included. They were ALOX15B, BCL6, CCND1, CDKN1A, CDKN2A, CENPA, CPEB1, DHCR24, EHF, EPHA3, ERRFI1, HJURP, HK3, IRF7, MAP2K6, MAP3K6, MATK, MMP9, MYC, PDZD2, PIK3R5, PIK3C2A, PIM1, SERPINE1, SGK1, TNFSF15, TP63, XAF1, and WWP1. (Fig. 3A, 3C).
Following, PCA was performed based on these 29 differentially expressed senescence genes. HF and non-HF groups were well clustered in the space, suggesting each group had distinctive expression patterns of senescence (Fig. 3B).
GO, and KEGG enrichment analyses were performed to explore the potential biological function of 2552 common DEGs. In the present study, the DEGs were primarily enriched in leukocyte cell-cell adhesion (BP) (Monocytes, Supplementary Figure S2D), collagen-containing extracellular matrix (CC) (Adipocytes, Figure S2A), endoplasmic reticulum lumen (CC)(Fibroblasts, Supplementary Figure S2C), glycosaminoglycan binding(MF)(Adipocytes, Supplementary Figure S2A), Phagosome(KEGG) (Monocytes, Supplementary Figure S2D) and other pathways (Fig. 3D). A similar enrichment was observed in the single cell analysis of senescence-active cells, Monocytes (Supplementary Figure S2D), Adipocytes (Supplementary Figure S2A), and Fibroblasts (Supplementary Figure S2C).
Gene Expression Characteristics Of Common Cell Senescence And Its Regulatory Network
After analyzing the DEGs in the bulk dataset, the DEGs in each active cell type, and the senescence genes, the inclusion relationship was analyzed (Fig. 4A). We identified ten genes as senescence genes present in bulk and on all active cell types. The genes involved were CCND1, CDKN1A, IRF7, MAP3K6, MYC, PIK3C2A, PIM1, SERPINE1, SGK1, and XAF1. Figure 4B illustrates their differential expression between different cell subpopulations. Surprisingly, these ten genes were also differently expressed in the scRNA sequencing (GSE145154 dataset) mentioned above.
Next, transcription factors for common senescence genes were obtained from HumanTFDB and intersected with DEGs from active cells and bulk RNA sequencing. This step aimed to determine which transcription factors were specific to active cell types. By first analyzing their inclusion relationship (Fig. 4C), 372 transcription factors for senescence genes (Supplementary Table S5) were identified. Their expression among different cell subpopulations is shown in Fig. 4D. Our bulk analysis revealed 45 transcription factors to be differentially expressed among the DEGs (Supplementary Table S6, Fig. 4E).
Following, we distinguished active cell types and constructed a PPI network between key transcription factors of active cell types (Fig. 4F-J). The key node factors in the PPI network are highlighted in yellow.
Finally, we tended to construct the ceRNA network of these senescence genes. First, DEmRNAs and DElncRNAs were identified by using bulk data. By searching public databases, we predicted the upstream target miRNAs of these DEmRNAs and DElncRNAs. Based on information on the common senescence genes, their upstream miRNAs, and DElncRNAs, we constructed the ceRNA network (Fig. 4K). The ceRNA network contains 21 miRNAs, 3 DElncRNAs, and 9 common senescence genes.
Potential Drugs Targeting Common Senescence Genes
The DGIdb database gene-drug interactions were used for common senescence genes to identify potential therapeutic drugs. We excluded chemotherapeutic drugs from the DGIdb database (chemotherapeutic drugs are not considered for the treatment of heart failure) and then identified promising interaction relationships between 21 drugs and 4 common senescence genes (CCND1, CDKN1A, MYC, PIM1). No potential target drugs exist for endothelial cells' corresponding common senescence genes. Figure 5 shows potential drugs targeting the senescence genes for different cell types (adipocytes, fibroblasts, monocytes, and muscle cells) on the four common senescence genes. In addition, we included key transcription factors in the analysis (Figure S3).