Differential lncRNAs and circRNAs in leukocytes
Compared with the control population (healthy individuals, n = 5), 365 and 468 differential lncRNAs (Supplemental Tables S2 and 3), as well as 126 and 139 differential circRNAs (Supplemental Tables S4 and 5), were respectively identified in the leukocytes from two case populations, including the CAG patients with PDHS (n = 5) and CAG patients with PQDS (n = 5) (Fig. 1a). In particular, we performed HCL analyses of expression profiles of differential lncRNAs and circRNAs in leukocytes from the three populations (Fig. 1b, c). The generated HCL heatmaps showed that the expression profiles of differential lncRNAs and circRNAs in the leukocytes of individuals belonging to the same population clustered together well, distinguishable from those of other populations.
The Zheng-specific lncRNAs and circRNAs
The Zheng (syndrome)-specific lncRNAs and circRNAs in this study mean that they were identified to be differentially expressed in the leukocytes of individuals only with the TCM-defined PQDS or PDHS, excluding their common differential lncRNAs and circRNAs. Namely, the PQDC-specific lncRNAs and circRNAs were observed only in the leukocytes of CAG patients with PQDS rather than PDHS. As presented (Fig. 1a), 385 lncRNAs and 121 circRNAs were PQDS-specific in the leukocytes. Also, 282 lncRNAs and 108 circRNAs were found to be PDHS-specific in the leukocytes.
Targets of the PQDS-specific cis-acting lncRNAs and circRNAs
Total 323 and 124 neighboring genes were found to be corresponding to the differential lncRNAs and circRNAs, respectively. Several of them, including 12 (lncRNA target) and 2 (circRNA target) neighboring genes, were also identified to be differentially expressed in the leukocytes from PQDS population (Fig. 2a). To overview the possible interaction relationships of these obtained neighboring genes, a corresponding protein-protein interaction network was generated. The differential neighboring genes were specially indicated in red, including NR4A2 (nuclear receptor subfamily 4 group A member 2), FOS (Fos proto-oncogene, AP-1 transcription factor subunit), HLA-DRB5 (major histocompatibility complex, class II, DR beta 5), OSM (Oncostatin M), EGF (epidermal growth factor), HIP1 (huntingtin interacting protein 1), AATK (apoptosis associated tyrosine kinase), RARRES1 (retinoic acid receptor responder 1), ARSJ (arylsulfatase family member J), LOC100289279, COL13A1 (collagen type XIII alpha 1 chain) and RAB6C (member RAS oncogene family) (Fig. 2b). Especially, another interaction network was carefully created for the observed 12 target genes. The network not only detailed the interactions between cis-acting lncRNAs/circRNAs and their corresponding target genes, including the interactions among target genes (edge width indicates interaction strength of data support), but also presented the expression pattern (shade of blue or red depends on degree of downregulation or upregulation of gene and ncRNA expression) (Fig. 2c). Also, the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway-based enrichment analyses were performed to decode the potential pathways of 12 possible target genes, and a network was generated to present the relationships of the enriched pathways of genes. These enriched pathways are involved in helper T (Th)1, Th2 and Th17 cell differentiation, mitogen-activated protein kinase (MAPK) signaling, phosphatidylinositol 3-kinase (PI3K)-serine/threonine-protein kinase (AKT) signaling, janus kinase (JAK)-signal transducer and activator of transcription (STAT) signaling, colorectal cancer, as well as programmed cell death-ligand 1 (PD-L1) expression and PD-1 checkpoint (Fig. 2d). Furthermore, we particularly analyzed the linear correlation of expression levels between the 12 target genes and their neighboring cis-acting lncRNAs/circRNAs (Supplemental Fig. S2). A dot plot scattergrams were specially drawn to show the strong negative linear correlation pairs of LOC105378347-COL13A1 (Fig. 2e).
Targets of the PDHS-specific cis-acting lncRNAs and circRNA
Total 269 and 115 neighboring genes were corresponding to the differential lncRNAs and circRNAs, respectively. Seven neighboring genes of 12 lncRNAs belonged to the differential genes identified in the leukocytes from the PDHS population, including EGR3 (early growth response 3), NR4A2 (nuclear receptor subfamily 4 group A member 2), LOC102724843, RCAN2 (regulator of calcineurin 2), GPM6A (glycoprotein M6A), KLHL14 (kelch like family member 14) and VAMP7 (vesicle associated membrane protein 7) (Fig. 3a). An interaction network was created to overview the possible relationships among all the neighboring genes of the differential lncRNAs and circRNAs. For the obtained seven neighboring genes, they were considered as the candidate targets of the cis-acting lncRNAs, and were specially denoted in red to facilitate manual check in the resultant network (Fig. 3b). Another network was also carefully drawn to detail the possible regulation relationships between the cis-acting lncRNAs and their corresponding neighboring genes, and the expression patterns were also presented in the generated network (Fig. 3c). The reactome and KEGG pathway-based enrichment analyses of the seven candidate target genes revealed the potential pathways related to SUMOylation, vesicle biogenesis, nuclear receptor transcription, interleukin (IL)-12 signaling and C-type lectin receptor signaling. A network was created to show the relationships of the enriched pathways (Fig. 3d). We also checked the linear correlation of expression levels between the seven candidate targets and their neighboring cis-acting lncRNAs (Supplemental Fig. S3). Notably, two strong linear correlation pairs of cis-acting lncRNAs and targets, LOC107984113-GPM6A and LOC105372055-KLHL14, were found in the leukocytes from the PDHS population (Fig. 3e).
The Zheng-specific ceRNA-gene binary relationship networks
Several classes of ncRNA molecules, including lncRNA and circRNA, could counteract the gene repressive activity of miRNA by sequestering miRNA within a cell. Such lncRNAs and circRNAs were described as miRNA sponges/decoys, target mimics (in plants) or competing endogenous RNA (ceRNA) (in mammals) [15, 17]. As indicated (Supplemental Fig. S1), based on the expression profile data covering the lncRNAs, circRNAs, genes and miRNAs, several original networks were carefully generated to detail the ceRNA (lncRNA/circRNA)-gene relationship pairs in the leukocytes from the PQDS and PDHS populations. The observed relationship pairs in the original networks were further filtered using the above-mentioned Zheng-specific lncRNAs, circRNAs and genes to get the Zheng-specific ceRNA-gene relationship networks. Especially, considering that ceRNA could competitively bind with shared miRNAs through miRNA response elements (MREs), indirectly regulating gene expression in cytoplasm, we also eliminated the ceRNAs predicted to be incapable of locating into cytosol/cytoplasm. Therefore, the resultant ceRNA networks could hold more confident ceRNA-gene relationship pairs to detail the Zheng-specific ceRNA-gene regulation relationships in the leukocytes (Fig. 4a and c).
As shown (Fig. 4a), an integrated binary ceRNA network, was particularly generated to detail the PQDS- and PDHS-specific lncRNA-gene relationship pairs in the leukocytes (Supplemental Tables S6 and 7), including the common lncRNAs and genes implicated in the ceRNA-gene pairs. In the lncRNA-associated ceRNA network, overall, almost each lncRNA could compete with multiple targets and even additional common genes. For instance, each of these PQDS-specific lncRNAs could compete with multiple genes (more than ten), including ENST00000447519 (AP001189.1), XR_001744971.1 (LOC105375433), ENST00000433310 (AF165147.1), XR_926748.2 (LOC105375035), XR_001752213.1 (LOC107984889), XR_001739495.1 (LOC105374768), XR_945327.3 (LOC105369968), NR_120454.1 (LINC02449), NR_109859.1 (LINC01730), ENST00000635072 (LINC01358), ENST00000433669 (LINC00954) and XR_001746085.1 (LOC105375754). Also, each of these PDHS-specific lncRNAs containing NR_027412.1 (LINC00910), ENST00000451362 (AL139130.1), XR_944918.2 (LOC102725258), XR_001746915.1 (LOC105376244) and XR_001739484.1 (LOC105377632), were capable of competing with multiple targets (over four). Notably, six exosome-encapsuled lncRNAs were found and marked in the obtained lncRNA-gene network, including ENST00000416824 (LINC00957), NR_036658.2 (ZFAS1), NR_024061.1 (LOH12CR2), ENST00000566847 (AL353719.1) and two additional novel lncRNAs named TCONS_00038035 and TCONS_00027600 (Fig. 4a). Similarly, another integrated circRNA-associated ceRNA network was drawn to present the PQDS- and PDHS-specific circRNA-gene regulation relationship pairs in the leukocytes (Fig. 4c; Supplemental Tables S8 and 9). Obviously, each of these PQDS-specific circRNAs competed with multiple genes (over six), including circRNA_05342, circRNA_17558 (hsa_circ_0003910), circRNA_20312, circRNA_26206 (hsa_circ_0002483), circRNA_22470, circRNA_01462, circRNA_12753 and circRNA_11374 (hsa_circ_0043114). But most of the PDHS-specific circRNA competed only with one gene, and only the PDHS-specific circRNA_20312 (hsa_circ_0001440) could compete with more than two PDHS-specific genes (Fig. 4c). In addition, two corresponding heatmaps were generated to profile the expression of the observed lncRNA and circRNAs involved in the Zheng-specific ceRNA-gene relationship pairs in the leukocytes. Particularly, two special heatmap were also created to show the possibility that the obtained Zheng-specific ceRNAs could locate in cytoplasm, cytosol, ribosome, nucleus and exosome (Fig. 4b, d). These Zheng-specific ceRNA-gene pairs identified in the different leukocytes suggested their potential roles in regulating the Zheng-specific gene expression profiles, which might contribute to the characteristics and functions of leukocytes in the TCM-defined PQDS and PDHS resulting from CAG.
The Zheng-specific ceRNA-miRNA-gene triple relationship networks
In each ceRNA (lncRNA/circRNA)-gene relationship pair, ceRNA competitively binds with the shared miRNAs by the MREs, thus enabling the indirect regulation of the gene expression. To decode the shared miRNAs, especially the key hub miRNAs implicated in multiple ceRNA-gene pairs in the leukocytes from the PQDS and PDHS populations, several ceRNA-miRNA-gene triple relationship networks were also carefully generated using the above-obtained Zheng-specific ceRNA-gene pairs and their corresponding shared miRNAs (Fig. 5; Supplemental Tables S6 to 9). In these miRNA-centered ceRNA regulatory networks (Fig. 5), all the shared miRNAs involved in the Zheng-specific ceRNA-gene pairs were visually presented, including the Zheng-specific miRNAs as well as the common miRNAs identified in the leukocytes from the PQDS and PDHS populations.
As show (Fig. 5a, b), obviously, most of the PQDS-specific miRNAs were involved in at least three PQDS-specific ceRNA-gene pairs. The PQDS-specific miRNAs corresponding to both lncRNA-gene pairs and lncRNA-gene pairs, were particularly labeled in bold font (the blue font denoted the known miRNAs among them) to facilitate manual check. Such key hub miRNAs implicated in multiple (at least four) PQDS-specific ceRNA-gene pairs, contained hsa-miR-6873-3p, hsa-miR-6509-3p, hsa-miR-136-5p, hsa-miR-1260b, hsa-miR-7110-3p, hsa-miR-4701-5p and several novel miRNAs discovered in this study (Fig. 5a, b). Besides, concern the PDHS-specific hub miRNAs involved in multiple ceRNA-gene pairs, each of the miRNAs of hsa-miR-6855-5p and has-miR-6855-5p could correspond to six PDHS-specific lncRNA-gene pairs, and the hsa-miR-133a-5p was involved in two PDHS-specific lncRNA-gene pairs (Fig. 5c). Also, three novel miRNAs labeled in bold were implicated be not only lncRNA-gene pairs but also circRNA-gene pairs (Fig. 5c, d). These observed Zheng-specific miRNAs in the ceRNA networks, especially the key hub miRNAs linking to multiple Zheng-specific ceRNA-gene relationship pairs, indicated their important roles in the Zheng-specific gene expression regulation, suggesting a class of potential biomarkers in leukocytes for differentiating TCM-defined PQDS and PDHS resulting from CAG.
Interaction networks and functions of Zheng-specific ceRNA-regulated genes
In order to detail the possible interactions between each gene belonging to the Zheng-specific ceRNA-gene pairs, two interaction complex networks were carefully generated, integrated with any type of edge and node attribute data such as gene expression pattern and the number of regulating ceRNAs (Fig. 6). The resultant networks not only show the possible interactions between each Zheng-specific node gene (edge thickness indicates interaction strength of data support) (Supplemental Tables S10 and 11), but also present the expression pattern of each node gene (node shade of blue or red relies on degree of down-regulation or upregulation of gene expression). Node size depends on the number of Zheng-specific ceRNAs (lncRNAs/circRNAs) targeting to the corresponding node gene, and the number is also displayed near the corresponding gene node in format of “lncRNAs number/lncRNAs number”. Moreover, the pathway and GO function enrichment analyses were also performed to reveal the potential functions and pathways of these node genes governed by the Zheng-specific ceRNAs (Supplemental Figs. S4 and 5). Several enriched pathways and function terms were also notably highlighted and annotated in the resultant interaction networks. As presented (Fig. 6a), overall, most of the PQDS-specific node genes could be governed by more than three PQDS-specific ceRNAs. Although many node genes had no observed interactions with each other (no edge between each other), they were also found to be regulated by multiple PQDS-specific ceRNAs. The node genes keeping more complex relationships with each other, were enriched in the pathways involved in MAPK signaling, receptor tyrosine kinases signaling as well as complement and coagulation cascades. Also, the enriched pathways related to adherens junction, focal adhesion, ECM organization, ECM-receptor interaction and cell surface interactions at the vascular wall, were implicated in cell-to-cell adhesion/junction and communication, probably contributing to the characteristics and functions of leukocytes in TCM-defined PQDS resulting from CAG. Notably, the common node genes involved in multiple crosstalks between these enriched pathways, including EGF (epidermal growth factor), COL4A2 (collagen, type IV, alpha 2 chain), COL4A4 (collagen, type IV, alpha 4 chain), PROCR (protein C receptor) and PROS1 (protein S), seemed to undergo a more complex regulation of the PQDS-specific lncRNAs and circRNAs in the leukocytes.
In addition, for the genes belonging to the PDHS-specific ceRNA-gene pairs, another network was carefully created to present the possible interactions between them (Fig. 6b). As shown, except the interaction of ARHGEF4 (rho guanine nucleotide exchange factor 4) and CHN1 (chimerin 1), no additional interaction relationships were observed among these genes governed by the PDHS-specific ceRNAs. ARHGEF4 and CHN1 were enriched in the biological processes such as regulation of cell morphogenesis, Rho GTPase cycle and regulation of small GTPase-mediated signal transduction. Especially, CR2 (complement component receptor 2) and ULBP3 (UL16-binding protein 3) were related to lymphocyte mediated immunity, including complement and coagulation cascades, B-cell receptor signaling and regulation of NK/T-cell mediated cytotoxicity. CEACAM6 (carcinoembryonic antigen related cell adhesion molecule 6) were involved in neutrophil activation and degranulation, cell-matrix/cell adhesion and cell migration. GNAI1 (G protein subunit alpha i1) was associated with regulation of protein localization to cell periphery. VWDE (von Willebrand factor D and EGF domain-containing protein) was associated regulation of canonical Wnt signaling.