2.1 Analysis of differentially expressed genes for ferroptosis
Four hundred eighty-four ferroptosis-related genes were gathered and compiled from the "FerrDb" database. By combining the genes from the training set with those associated with ferroptosis, 127 ferroptosis-related differentially expressed genes were discovered, comprising 44 up-regulated genes and 83 down-regulated genes (Table 2). In order to identify the genes that differ between normal control and heart failure groups, differentially expressed genes were analyzed using R software and shown in a heat map (Figure 2). Samples were categorized, with normal control shown in blue and heart failure in red.
Table 1 Gene expression datasets used in this study
GEO accession
|
Platform
|
Year
|
Tissue
|
GSE5406
|
GPL96
|
2006
|
Left ventricular myocardium
|
GSE57338
|
GPL11532
|
2015
|
Heart left ventricle
|
GSE1145
|
GPL570
|
2004
|
Left Ventricle Biopsy
|
Table 2: Genes with differential expression
Gene
|
Control Mean
|
Treat Mean
|
pvalue
|
Type
|
PTGS2
|
3.735865938
|
3.860145361
|
0.027794258
|
Up
|
CS
|
10.626706
|
10.8006121
|
0.009957624
|
Up
|
EMC2
|
6.018840313
|
6.297643418
|
0.006439808
|
Up
|
ACSF2
|
5.820696063
|
6.022310149
|
0.000822308
|
Up
|
VDAC2
|
10.84736325
|
10.94575248
|
0.011049296
|
Up
|
NCOA4
|
9.868979313
|
10.08575503
|
0.006030582
|
Up
|
GABARAPL2
|
10.23240013
|
10.38750678
|
0.005536831
|
Up
|
PEBP1
|
9.85000675
|
10.08034807
|
0.003226382
|
Up
|
TGFBR1
|
5.507920188
|
5.590214753
|
0.03465182
|
Up
|
PEX12
|
4.819798313
|
4.993629665
|
0.002389567
|
Up
|
PEX3
|
4.748285
|
4.834721593
|
0.033924416
|
Up
|
SNCA
|
6.131134813
|
6.245663582
|
0.015494996
|
Up
|
SIRT3
|
7.307551063
|
7.4604355
|
0.023683465
|
Up
|
DLD
|
8.949755688
|
9.262399665
|
0.006607947
|
Up
|
PRKCA
|
5.906490188
|
6.002175459
|
0.002910267
|
Up
|
MICU1
|
7.571580875
|
7.733151072
|
0.000973354
|
Up
|
GSTZ1
|
6.554007813
|
6.752168397
|
0.001058303
|
Up
|
GJA1
|
8.94431375
|
9.629693392
|
7.94199E-06
|
Up
|
CIRBP
|
8.771418
|
9.06842033
|
0.000980565
|
Up
|
TRIM26
|
7.033414563
|
7.158416273
|
0.030978671
|
Up
|
FADS2
|
6.65823725
|
6.886957588
|
0.003782746
|
Up
|
EGR1
|
6.621337
|
6.912063237
|
0.032858933
|
Up
|
ADAM23
|
6.832706875
|
7.043762639
|
0.044239696
|
Up
|
MEG3
|
5.198592
|
5.325323912
|
0.012501913
|
Up
|
ENPP2
|
5.468563563
|
5.91218001
|
4.23552E-05
|
Up
|
ISCU
|
10.05952925
|
10.50558616
|
3.26565E-06
|
Up
|
CHMP5
|
6.620764375
|
6.861778526
|
0.001503779
|
Up
|
SLC16A1
|
6.5797635
|
6.848754711
|
0.008110024
|
Up
|
FZD7
|
5.624075813
|
6.231583784
|
1.91977E-05
|
Up
|
BRD3
|
7.4041135
|
7.649242608
|
0.001514856
|
Up
|
DECR1
|
9.244252
|
9.42292384
|
0.049936576
|
Up
|
PPP1R13L
|
7.823658563
|
8.036244665
|
0.00518761
|
Up
|
KDM3B
|
7.103550625
|
7.375644907
|
0.000263162
|
Up
|
PARP2
|
6.776521938
|
6.891308371
|
0.024488476
|
Up
|
PARP8
|
5.61751475
|
5.755076129
|
0.005726621
|
Up
|
PARP12
|
5.567965313
|
5.800322794
|
0.004390677
|
Up
|
BEX1
|
7.038020438
|
7.475995608
|
0.004822257
|
Up
|
TMSB4X
|
9.387276813
|
9.679762887
|
0.019317533
|
Up
|
KDM4A
|
6.97379375
|
7.080841325
|
0.012962154
|
Up
|
MPC1
|
9.885591688
|
10.14856652
|
0.003937913
|
Up
|
SIRT2
|
8.470080063
|
8.642663129
|
0.016623215
|
Up
|
MEF2C
|
6.712090188
|
6.91678732
|
0.008913374
|
Up
|
GSTM1
|
7.96118175
|
8.145704778
|
0.022518902
|
Up
|
RARRES2
|
5.613869313
|
5.910758706
|
0.010605693
|
Up
|
CHAC1
|
6.923034125
|
6.703196861
|
0.015133924
|
Down
|
HSPB1
|
11.85432056
|
11.39584508
|
0.004979217
|
Down
|
IREB2
|
3.612065813
|
3.501706
|
0.001074216
|
Down
|
G6PD
|
5.994550938
|
5.778824691
|
0.002339222
|
Down
|
PGD
|
7.340181625
|
6.970997706
|
0.000248243
|
Down
|
ACSL4
|
4.040328813
|
3.826882335
|
0.005432759
|
Down
|
LPCAT3
|
6.703436438
|
6.427789201
|
0.000809707
|
Down
|
NRAS
|
4.562735188
|
4.33994067
|
0.003077033
|
Down
|
SLC38A1
|
9.277158438
|
8.696509665
|
0.000995861
|
Down
|
SLC1A5
|
7.70871725
|
7.485839686
|
0.000803468
|
Down
|
ALOX5
|
5.241757688
|
5.140545964
|
0.009196584
|
Down
|
KEAP1
|
7.092501875
|
6.979204371
|
0.016721237
|
Down
|
ATG5
|
5.699945438
|
5.556223665
|
0.00040348
|
Down
|
PHKG2
|
6.805893563
|
6.672770665
|
0.003436858
|
Down
|
BECN1
|
7.743867
|
7.644581258
|
0.0458427
|
Down
|
SNX4
|
5.212448625
|
5.060937933
|
0.014955971
|
Down
|
SAT1
|
8.153058125
|
7.741631258
|
0.00210145
|
Down
|
MAPK1
|
7.0139955
|
6.75637768
|
0.001741221
|
Down
|
BID
|
5.789904688
|
5.573732144
|
0.000104356
|
Down
|
MAPK9
|
6.280735188
|
6.162290768
|
0.019210838
|
Down
|
MAPK14
|
6.173374
|
6.000712686
|
0.000809713
|
Down
|
PRKAA1
|
3.803406625
|
3.732561639
|
0.03114367
|
Down
|
ELAVL1
|
7.681876563
|
7.542367634
|
0.005153338
|
Down
|
EPAS1
|
8.7215115
|
8.527743062
|
0.011623874
|
Down
|
LPIN1
|
6.623586375
|
6.304288974
|
2.98129E-06
|
Down
|
TLR4
|
6.02606875
|
5.908545655
|
0.03950418
|
Down
|
ATF3
|
7.352771813
|
6.55603134
|
0.001296489
|
Down
|
MTDH
|
6.615996938
|
6.400821211
|
0.004048925
|
Down
|
POR
|
6.599822188
|
5.963002763
|
4.41598E-06
|
Down
|
ELOVL5
|
6.211679188
|
6.081705103
|
0.020225149
|
Down
|
PTEN
|
5.339030625
|
5.147868964
|
0.001983921
|
Down
|
TBK1
|
6.814853438
|
6.694369613
|
0.032683783
|
Down
|
IL6
|
5.22229475
|
4.920458366
|
0.030978616
|
Down
|
ATF4
|
9.910998188
|
9.320672938
|
1.18315E-06
|
Down
|
AQP3
|
6.6776735
|
6.184862644
|
3.68554E-05
|
Down
|
DCAF7
|
6.093050813
|
5.984369696
|
0.017315676
|
Down
|
MTCH1
|
10.42536638
|
10.12269746
|
6.04256E-05
|
Down
|
SLC39A14
|
9.363982063
|
8.920519273
|
2.09227E-05
|
Down
|
SLC25A28
|
7.386891188
|
7.200388412
|
0.002012683
|
Down
|
IFNA2
|
3.729314125
|
3.672419835
|
0.045146938
|
Down
|
PPARG
|
5.804893313
|
5.588686546
|
0.001003542
|
Down
|
QSOX1
|
8.118508313
|
7.770224696
|
2.83554E-05
|
Down
|
PIEZO1
|
6.497534375
|
6.294135531
|
0.014434041
|
Down
|
LIFR
|
3.974079125
|
3.859653294
|
0.019431835
|
Down
|
TIMP1
|
9.41335775
|
8.681354572
|
7.64864E-05
|
Down
|
CCDC6
|
4.801594188
|
4.594966144
|
0.023816177
|
Down
|
KMT2D
|
5.285662313
|
5.20385134
|
0.012884611
|
Down
|
AKR1C1
|
7.371374813
|
7.044923402
|
0.000944175
|
Down
|
AKR1C3
|
6.38689925
|
6.006244072
|
0.00919672
|
Down
|
NQO1
|
6.672161063
|
6.46768768
|
0.000803461
|
Down
|
SLC3A2
|
7.7229475
|
7.568800325
|
0.040540365
|
Down
|
MT1G
|
7.578630188
|
7.472363113
|
0.04846139
|
Down
|
SCD
|
7.07732775
|
6.557209325
|
0.040123468
|
Down
|
STAT3
|
9.485480063
|
8.79114951
|
6.70632E-07
|
Down
|
MTOR
|
5.905657625
|
5.843011948
|
0.025037898
|
Down
|
CDKN1A
|
9.301168875
|
8.543084103
|
3.04352E-06
|
Down
|
CBS
|
5.068929063
|
4.811010165
|
0.000440978
|
Down
|
BRD4
|
7.221245875
|
6.711181031
|
5.37517E-07
|
Down
|
PRDX6
|
9.670188938
|
9.269505299
|
0.000191083
|
Down
|
NF2
|
4.913303125
|
4.831663325
|
0.027341993
|
Down
|
ARNTL
|
5.864491938
|
5.61160816
|
0.000158411
|
Down
|
PLIN2
|
6.737046188
|
6.193575979
|
8.54368E-07
|
Down
|
ZFP36
|
8.994726063
|
8.675310959
|
0.03081177
|
Down
|
DAZAP1
|
6.689931563
|
6.291527067
|
5.5276E-06
|
Down
|
PIR
|
4.27115825
|
4.073019974
|
0.013762003
|
Down
|
FTL
|
11.07947188
|
10.76440668
|
0.012726159
|
Down
|
NT5DC2
|
6.920454938
|
6.532587041
|
0.001955557
|
Down
|
NCOA3
|
6.549206875
|
6.335434268
|
0.000489516
|
Down
|
ARF6
|
7.24059575
|
7.117578974
|
0.048706259
|
Down
|
AHCY
|
7.259544688
|
6.907764701
|
4.11952E-05
|
Down
|
SIAH2
|
6.72897925
|
6.554368912
|
0.00225734
|
Down
|
RELA
|
7.400368375
|
7.21615001
|
0.011207269
|
Down
|
PRDX1
|
9.817919
|
9.43888382
|
3.48088E-06
|
Down
|
MTF1
|
6.687935688
|
6.574762799
|
0.003013464
|
Down
|
COPZ1
|
7.69138125
|
7.587267887
|
0.012056201
|
Down
|
PARP6
|
7.715632438
|
7.59077383
|
0.013118598
|
Down
|
TXN
|
5.762842938
|
5.551780191
|
0.01409466
|
Down
|
CREB3
|
7.607109625
|
7.412534979
|
0.000254528
|
Down
|
MLST8
|
6.920732688
|
6.801852108
|
0.015495163
|
Down
|
VCP
|
8.008710813
|
7.785856964
|
0.001058196
|
Down
|
TRIB2
|
7.411926625
|
7.251504299
|
0.022519732
|
Down
|
PDK4
|
8.824693
|
7.619592098
|
0.009370584
|
Down
|
MAPKAP1
|
7.547510063
|
7.260061284
|
8.52003E-06
|
Down
|
2.2 Correlation analysis of differentially expressed genes
R software was used to analyze differential genes, and correlations were obtained by correlation analysis of differential genes (Figure 3). The asterisk in the square of the graph denotes a significant correlation between the corresponding two genes, with the red asterisk grid denoting a positive regulatory relationship between genes and the blue asterisk grid denoting a negative regulatory relationship between two genes. The graph's colors, red for a positive correlation and blue for a negative correlation.
2.3 Enrichment analysis of differentially expressed genes
R software was used to analyze the enrichment analysis of differentially expressed genes (Figure 4), and P values less than 0.05 were used to filter the results. Hepatitis B, mastocytosis, Kaposi's sarcoma-associated herpesvirus infection, human cytomegalovirus infection, lipid and arteriosclerosis, AGE-RAGE signaling pathway in diabetic complications, FoxO signaling pathway, autophagy-animal, NOD-like receptor signaling pathway, and human T-cell leukemia virus one infection made up the top 10 enriched pathways in the KEGG analysis based on P value. The primary areas of cellular response to chemical stress, response to nutritional levels, response to oxidative stress, response to oxidative stress, response to external stimuli, etc., were enriched in GO-BP analysis through the GO medium. TORC2 complex, secretory granule lumen, TOR complex, cytoplasmic vesicle lumen, etc., are all considerably enriched in CC analysis. NAD+ ADP-ribosyltransferase activity, DNA-binding transcription factor binding, RNA polymerase II-specific DNA-binding transcription factor binding, NAD+-protein ADP-ribosyltransferase activity, and antioxidant activity were all enriched in GO-MF. According to the enrichment analysis's findings, heart failure may be significantly influenced by the activation of oxidative stress, ferroptosis, etc.
2.4 Screening for Ferroptosis-related signature genes in heart failure by machine learning
The R software "glmnet" package was used to perform LASSO regression analysis to clarify the diagnostic value of differentially expressed genes linked to ferroptosis (Figure 5A,5B). The number of genes corresponding to the point with the least cross-validation was discovered to be the number of signature genes found. Furthermore, the discovery of 17 genes using the LASSO regression method: BECN1, LPIN1, ATF4, AQP3, SLC39A14, QSOX1, STAT3, ENPP2, CBS, BRD4, PRDX6, DAZAP1, AHCY, PRDX1, CREB3, TMSB4X, and MAPKAP1.
The accuracy graph (Figure 5C), where the horizontal coordinate indicates the number of genes and the vertical coordinate represents the cross-validation accuracy, can be created by applying the SVM-RFE method to screen for disease signature genes. The point corresponding to the lowest cross-validation error, i.e., the number of genes to be looked up, needs to be located on the graph of cross-validation error (Figure 5D), where the horizontal coordinate represents the number of genes, and the vertical coordinate represents the error of cross-validation. So far, 18 distinct genes have been identified, including SLC25A28, SLC39A14, MLST8, TMSB4X, KEAP1, CHAC1, EMC2, MEG3, PTGS2, QSOX1, MTDH, BECN1, KDM4A, SCD, AKR1C3, DAZAP1, MTOR, and ACSF2.
2.5 Venn diagram
The intersection of the genes discovered by the R software "VennDiagram" package was analyzed using the LASSO regression and SVM algorithms. As a result, five genes related to ferroptosis were identified for the diagnosis of heart failure (Figure 6), namely BECN1, SLC39A14, QSOX1, DAZAP1, and TMSB4X.
2.6 Construction of the diagnostic model
For each signature gene, a ROC curve can be generated using the R package (glmnet,pROC); the area under the curve ranges from 0.5 to 1, and the larger the area under the curve, the higher the accuracy of the gene as a disease diagnostic gene. As seen in the figure (Figure 7A), the DAZAP1 curve has the largest area under the curve, with an AUC value of 0.842, indicating higher accuracy in predicting the disease. The ROC curves of the distinctive genes were effectively generated (Figure 7B), and the AUC was evaluated, yielding an AUC value of 0.952 (95% CI: 0.894-0.993). The five differentially expressed genes of ferroptosis were successfully constructed as gene diagnostic models. The five differentially expressed genes for ferroptosis demonstrated good diagnostic value in differentiating between standard control and heart failure patients, demonstrating the diagnostic model's good diagnostic performance (Figure 7C). The box plot revealed significant differences in the levels of five genes between the standard control and heart failure groups. These five genes were dubbed heart failure diagnostic genes as a result.
The R software's "RMS" package created a nomogram (Figure 8). According to the nomogram, each gene's relative expression level is assigned a score. The total score, the sum of each score, can be used to identify heart failure and forecast its occurrence.
2.7 GSEA enrichment analysis
The expression of the signaling pathway in the signature gene can be seen by using the R software "GSEA" package to assess the up- and down-regulated signaling pathways for each diagnostic gene. If the peak of the curve is on the upper left side, this indicates that the signaling pathway is highly expressed in the signature gene. If it is on the lower right side, this indicates that the signaling route is lowly expressed in the diagnostic gene (Figure 9). Systemic lupus erythematosus, neuroactive ligand-receptor interaction, leishmania infection, cytokine receptor interaction, and cell adhesion molecules cams were expressed less frequently in the diagnostic gene BECN1. Systemic lupus erythematosus, ecm receptor interaction, cytokine receptor interaction, complement, and coagulation cascades were substantially elevated among the diagnostic genes QSOX1. However, Parkinson's disease and oxidative phosphorylation were expressed at low levels.
2.8 Immunocell infiltration analysis
The gene expression data for cell infiltration analysis was analyzed using the CIBERSORT method with 1000 simulations; the more simulations, the higher the accuracy gained; the findings were then filtered with P <0.05 to maintain the immune cell infiltration results. The results demonstrate that T cells CD4 naive differed between the two groups and if P< 0.05, this suggests a difference between the normal control group and the heart failure group. Twenty-two different infiltrating immune cells were seen (Figure 10A). Using the R software "corrplot" package, the correlation between the characteristic genes and immune cells was examined. A heat map of the correlation was produced (Figure 10B), with red denoting genes that are positively correlated and white denoting genes that are negatively correlated. It is clear that the genes for Macrophages M2 and TMSB4X are positively correlated.
2.9 Validation of diagnostic models using external datasets
To further validate the diagnostic model, the diagnostic performance of the characterized genes was further evaluated in the test set by assessing the expression differences in the normal control and heart failure groups. In the test set (GSE57388) (Figure 11A), the diagnostic genes BECN1, DAZAP1, SLC39A14, and QSOX1 were low expressed in the samples (P < 0.05), and TMSB4X was highly expressed in the samples (P < 0.05), indicating differences between the normal control and heart failure groups. In the test set (GSE1145) (Figure 11B), DAZAP1, SLC39A14, and QSOX1 were lowly expressed in the samples (P < 0.05), and TMSB4X were highly expressed in the samples (P < 0.05), however, the diagnostic gene BECN1 was lowly expressed in the samples (P > 0.05), with no significant differences.