We carried out RNA-seq approach to investigate the whole-transcriptome profiles for left ventricle (LV) tissues from patients suffering from HF due to DCM (n = 162) and HCM (n = 28) as previously described [15]. The transcriptome profiles of the SOX genes were extracted for comparisons. Among 20 SOX genes, eight were expressed in at least one of the three groups (cut-off > 1 TPM) (Table 1). The expressed SOX genes shared between the NF, DCM, and HCM groups are SOX4, SOX9, SOX7, SOX12, SOX17, and SOX18. Interestingly, these expressed SOX genes fall into three subgroups of SOX TF. They are SOXC, SOXE, and SOXF. All the SOXF group genes, including SOX7, SOX17, and SOX18, were present in NF, DCM, and HCM. Two of three SOXC genes, SOX4 and SOX12, were expressed in NF and HF. One SOXE gene, SOX9, was detected in all three groups. Two genes were only found to be expressed in failing human LVs but not in normal ones. They are SOX8, which belongs to the E group and SOX15, a G group SOX gene. Some of these expressed SOX genes displayed differential expression between the non-failing and failing groups (fold changes ≥ 1.5). These included SOX4 (SOXC), SOX8 and SOX9 (SOXE) and SOX15 (SOXG). SOX4 RNA level was upregulated by 1.6- and 2.1-fold in DCM and HCM, respectively, in comparison to NF, whereas the SOX8 RNA level was significantly increased in DCM by 2.6-fold and in HCM by 2.8-fold in comparison to the NF LVs (Fig. 1A & D and Table 1). To a lesser extent, SOX9, another E group gene, was found to be increased by more than 1.5-fold in HCM but not in DCM (fold change 1.14; Fig. 1G and Table 1). Additionally, SOX15, a solo member of SOXG, was increased by 1.9-fold in both DCM and HCM compared to NF (Fig. 1J and Table 1). In contrast, other members of the SOX genes found to be expressed in the heart (SOX12, SOX7, SOX17, and SOX18) showed no significant differences between the NF and HF groups (Table 1).
Table 1
List of all SOX genes RNA level in human left ventricle. RNA level is present as Transcripts Per Kilobase Million (TPM)
Group | SOX | NF | DCM | HCM | Fold change [DCM/NF] | Fold change [HCM/NF] |
A | Sry | 0.009062 ± 0.003347 | 0.00295 ± 0.004618 | 0.00295 ± 0.002950 | n.d | n.d |
B1 | SOX1 | 0.001116 ± 0.0004903 | 0.003521 ± 0.001127 | 0.005152 ± 0.001921 | n.d | n.d |
| SOX2 | 0.3361 ± 0.02409 | 0.2474 ± 0.01995 | 0.2612 ± 0.05040 | n.d | n.d |
| SOX3 | 0.006036 ± 0.001629 | 0.006856 ± 0.001455 | 0.01279 ± 0.006416 | n.d | n.d |
B2 | SOX14 | n/a | n/a | n/a | n.d | n.d |
| SOX21 | 0.003249 ± 8.050e-005 | 0.003263 ± 8.066e-005 | 0.00599 ± 0.003815 | n.d | n.d |
C | SOX4 | 3.107 ± 0.1512 | 5.08 ± 0.3159* | 6.398 ± 0.7877* | 1.63 | 2.06 |
| SOX11 | 0.5313 ± 0.03375 | 0.6286 ± 0.03241 | 0.749 ± 0.09887 | n.d | n.d |
| SOX12 | 2.975 ± 0.1706 | 3.497 ± 0.1457 | 3.634 ± 0.3834 | 1.17 | 1.22 |
D | SOX5 | 0.01179 ± 0.0005469 | 0.01251 ± 0.001629 | 0.01149 ± 0.002472 | n.d | n.d |
| SOX6 | 0.04034 ± 0.001615 | 0.05744 ± 0.002764 | 0.06774 ± 0.007039 | n.d | n.d |
| SOX13 | 0.6468 ± 0.02202 | 0.6974 ± 0.02828 | 0.7598 ± 0.06953 | 1.07 | 1.17 |
E | SOX8 | 0.646 ± 0.04810 | 1.675 ± 0.1026* | 1.815 ± 0.2003* | 2.59 | 2.81 |
| SOX9 | 9.367 ± 0.4458 | 10.73 ± 0.5473 | 15.03 ± 1.449* | 1.14 | 1.60 |
| SOX10 | 0.2814 ± 0.01847 | 0.2616 ± 0.01441 | 0.2935 ± 0.03643 | 0.93 | 1.04 |
F | SOX7 | 4.469 ± 0.1750 | 5.183 ± 0.2518 | 6.208 ± 0.4956 | 1.16 | 1.39 |
| SOX17 | 8.93 ± 0.6237 | 10.77 ± 0.6649 | 10.72 ± 1.445 | 1.21 | 1.20 |
| SOX18 | 12.33 ± 1.105 | 13.13 ± 1.211 | 14.93 ± 3.284 | 1.06 | 1.21 |
G | SOX15 | 0.8379 ± 0.05817 | 1.584 ± 0.07436* | 1.576 ± 0.1280* | 1.89 | 1.88 |
H | SOX30 | 0.006429 ± 0.0008755 | 0.007274 ± 0.0008103 | 0.007515 ± 0.001856 | n.d | n.d |
* p < 0.01 ANOVA; n/a: Not available; n.d: Not determined. |
We validated the protein levels of the differentially expressed SOX genes found within the three groups using Western blot. The SOX4 protein level was significantly elevated by 2.27-fold and 3.67-fold in DCM and HCM, respectively (Fig. 1B-C). The SOX8 protein in the NF group was barely detected, which was consistent with its RNA level (TPM < 1), whereas the SOX8 protein level increased 2.83-fold in DCM and increased (rather robustly) 6.78-fold in HCM (Fig. 1E-F). However, the SOX9 and SOX15 protein levels were not significantly different among the three groups (Fig. 1H-I & K-L).
The gene network analysis of genes expressed in HCM or DCM using co-expressed gene network analysis showed several genes associated with SOX4 in the left ventricle of hearts. These genes included collagen-related genes, COL6A1 and COL6A2, a putative calcium-binding protein, reticulocalbin-3 (RCN3), an enzyme involved in cell migration proliferation and the epithelial-to-mesenchymal transition, dihydropyrimidinase-related protein 3 (DPYSL3) [19], a secreted sulfated glycoprotein, C-type lectin domain containing 11A (CLEC11A), an actin-binding protein, retinoic acid-induced protein 14 (RAI14), and an ETS transcription factor ELK3 (ELK3) (Fig. 2A). However, we did not observe any significant genes linked to SOX8. Among the SOX4-associated genes, CLEC11A, COL6A2, DPYSL3, and RCN3 were upregulated significantly at least 1.5-fold in both DCM and HCM, whereas COL6A1 and ELK3 were only found to have increased considerably in DCM or HCM (Fig. 2B).
We subsequently analyzed chromatin state data and integrated them with the GWAS signals for both SOX4 and SOX8 loci from public data resources. We included all the GWAS signals and variants associated with the HF phenotype from the cardiovascular disease knowledge portal (CVDKP) [17, 18] and compared them with the Roadmap epigenomics data [16]. Roadmap epigenomics revealed several active enhancers along with transcriptional activity at both gene loci in fetal heart, left and right ventricular, and atrial tissues (Fig. 3). Several genomic variants with a p-value of < 0.05 were found within ± 20 kilobases (kb) of the SOX4 and SOX8 loci and overlapped with active cis-regulatory element signatures in the fetal heart and left and right ventricular tissues. At the SOX4 loci, one variant, rs192898967, located upstream 5.8 kb, overlapped with the DNase hypersensitivity signal, H3K27ac, the H3K4me1 enhancer signatures, and the H3K4me3 promoter mark, indicating the variant is associated with cis-regulatory elements, which may interact with a trans-acting element to regulate the transcription of SOX4. Additionally, variants 2–4 and 5–9 were located at 3’ UTR and downstream of the gene, respectively (Fig. 3A). The frequency of the variants 5–9 was more common than others. At the SOX8 loci, a board variety of cis-regulatory elements was present. However, its neighbor gene, LMF1 (Lipase Maturation Factor 1), is only 10 kb away from the transcription start site of SOX8. Therefore, both genes may share the same cis-regulatory elements. Nevertheless, we observed two variants, rs12448761 and rs552159903, which were located 7 kb and 12 kb upstream of SOX8 that also belonged to the intron of LMF1. These regions overlapped with the active enhancer marks as well as the DNase hypersensitivity peaks, suggesting they may be involved in controlling the expression of both genes (Fig. 3B). There are eight additional variants found in the SOX8 coding regions, at 3’ UTR, and in the downstream regions. Even though these eight variants are not linked with active cis-regulatory elements, their occurrence was more frequent than that of the other two variants located upstream of SOX8; therefore, they may be more likely to contribute to the effect.