Morphological and pathological studies
The animal model dosing strategy is shown in Table 1. MCT injection induced pulmonary artery remodeling, while C75 (50 μg/kg/week) administration partially inhibited the ratio of vascular medial thickness of total vessel size (Figure 1A). Likewise, compared to the control, mice after MCT treatment showed significantly increased collagen content, and was partially reduced after C75 administration (Figure 1B). In line with the morphological change, we also observed a significant increase of both right ventricular systolic pressure (RVSP) and the ratio of the right ventricular wall weight to the left ventricular wall plus septum (RV/LV+S) following MCT injection. C75 reduced the increase of RVSP due to the MCT effect, but such effect was not significant in RV/LV+S (Figure 1C).
Characteristics of mRNAs and lncRNAs
The raw and clean data were submitted to the GEO repository (series record GSE128358). A total of 9,082 lncRNA transcripts were selected by intersecting coding potential calculator, coding non-coding index, and protein family database. These lncRNAs were classified into antisense lncRNAs (45.75%), bidirectional lncRNAs (1.65%), intergenic lncRNAs (41.75%), intrinsic sence lncRNAs (9.12%), overlapping sence lncRNAs (0.43%), and retained intron lncRNAs (1.3%) (Figure 1D). Compared to mRNAs, lncRNAs exhibited much lower transcript abundance (Figure 2A), higher tissue specificity (Figure 2B), and less conservative (Figure 2C). The lncRNAs identified are over 200 bps, containing more than 2 exomes (Figure 2D). These properties are consistent with lncRNA traits.
Profiles of mRNAs and lncRNAs
Volcano plots were plotted using gglot2 package to demonstrate gene/lncRNA expression based on RPKM among the three groups. Conservation analysis was performed and JS score was calculated. Correlations between mRNA and lncRNA profiles were significantly higher within groups than inter-group correlations (Figure 3A-B), suggesting that the results are highly reliable. Compared to the control group, 285 mRNAs (113 upregulated and 172 downregulated) and 147 lncRNAs (82 upregulated and 65 downregulated) were differentially expressed in the MCT-Vehicle group. Top 10 deregulated mRNAs and lncRNAs are presented in Tables 3-1 and 3-2, respectively. After five weeks of C75 treatment, 514 mRNAs (401 upregulated and 113 downregulated) and 84 lncRNAs (35 upregulated and 49 downregulated) were aberrantly expressed in the MCT-C75 group compared to the MCT-Vehicle group. The top 10 disordered mRNAs and lncRNAs are shown in Tables 4-1 and 4-2, respectively. Heat maps and volcano plots illustrate the expression profiles of mRNAs and lncRNAs after MCT and C75 treatment (Figure 3C-D). Venn diagram showed that only one mRNA, Hsd17b2, was decreased in the MCT-Vehicle group, but returned to normal level after C75 intervention (Figure 4A); not one lncRNA altered among them (Figure 4B). Aberrantly expressed mRNAs (Retnlg, Mmp8, S100a9, Ll1r2, S100a8, Slfn4, Ntrk2, and Ckap2) were selected and validated using RT-PCR assay (Figure 4C). Based on the RT-PCR results, six genes exhibited lower expression, while two genes exhibited higher expression in the MCT-Vehicle group. These effects were partially reversed by C75 treatment. These results of RT-PCR were consistent with the HTS (Figure 4D).
GO and KEGG analyses
Both GO and KEGG analyses were performed to explore the functions of aberrantly expressed mRNAs. Top 10 GO terms are illustrated in Figure 5. GO analysis revealed that up-regulated mRNAs between the MCT-Vehicle and control group were primarily associated with the cell cycle, microtubule-based movement, cell division, and mitotic nuclear division. Down-regulated mRNAs were mainly associated with neutrophil chemotaxis, inflammatory response, and immune response (Figure 5A). Up-regulated mRNAs between the MCT-C75 and MCT-Vehicle were centered on fibrinolysis, hemostasis, and acute-phase response. Down-regulated mRNAs were involved in intracellular transport, cilium morphogenesis, cellular response to DNA damage stimulus, and actin filament polymerization (Figure 5A). KEGG analysis revealed that up-regulated mRNAs were mainly concentrated in the p53 signaling pathway, a PPAR signaling pathway, glycerophospholipid metabolism, pancreatic secretion, and metabolic pathways. Down-regulated mRNAs were involved with malaria, African trypanosomiasis, cytokine-cytokine receptor interaction, osteoclast differentiation, hematopoietic cell lineage, and cell adhesion molecules (Figure 5B). These results suggested that up-regulated mRNAs may directly promote PAH pathogenesis, while down-regulated mRNAs may suppress cell division and may indirectly contribute to PAH pathogenesis. GO and KEGG analysis indicated that the inflammatory response may play crucial roles in the PAH, we used RT-PCR assay to detect the pro-inflammation, anti-inflammation signal and metabolic pathways. Compared to the control group, the mRNA levels of TNF-α, IL-4, IL-5, IL6, IL-13 were increased. And C75 treatment can partially decrease TNF-α, IL-4, IL-5 (Figure 6A-E). PPAR-α mRNA level was increased in the MCT-treated mice, C75 treatment has little effect on the PPAR-α expression (Figure 6F).While PPAR-γ mRNA level was decreased in the MCT-treated mice, C75 treatment can increase the PPAR-γ expression (Figure 6G). We also detected Fas, CPT1, and GLUT mRNA levels, and found that C75 treatment can reverse the Fas increase (Figure 6H), reverse decreased GLUT mRNA (Figure 6I), and can partially reverse the CPT1 decrease induced by MCT (Figure 6J). The RT-PCR results indicated that inflammatory was activated in this PAH model, while C75 treatment can reverse the inflammatory partially.
Functional prediction of mRNAs regulated by aberrantly expressed cis- and trans-acting lncRNAs
GO analysis was performed to examine the function of mRNAs regulated by lncRNAs in cis and trans. Compared to the MCT-Vehicle group, aberrantly expressed lncRNA in C75-treated mice are shown in Figure 7. The mRNAs targeted in cis by aberrantly expressed lncRNAs are involved in multiple biological processes, such as cellular protein catabolic processes, modification-dependent protein catabolic processes, and macromolecule catabolic processes (Figure 7A). Disordered mRNAs targeted in trans by aberrantly expressed lncRNAs are associated with various biological processes, such as regulation of transcription, response to DNA damage stimulus, protein secretion, organelle fission, mitosis, cell cycle, and DNA repair (Figure 7B). Moreover, lncRNA-mRNA network analysis exhibited the possible relationship in trans (Figure 7C). Based on RT-PCR results, lncRNAs Gm41235 and Mirt2 exhibited lower expression in the MCT-Vehicle group compared to the control group. It was observed that the expression of lncRNAs Gm41235, Mirt2, and Gm38850 was partially rescued after C75 treatment (Figure 7D). And these RT-PCR results were consistent with the HTS (Figure 7E).
Co-expression networks
A comprehensive analysis of lncRNAs in lung tissues was carried out to understand the possible impacts of lncRNAs on PAH. A number of lncRNAs were aberrantly expressed after C75 treatment. A co-expression network (protein-coding genes and lncRNAs) was constructed to identify the potential functions and regulatory mechanisms of lncRNAs (Supplementary Figure 1).
Network of lncRNAs and miRNAs
It is known that lncRNAs and mRNAs have similar sequences and can be linked to a common miRNA. When lncRNAs bind to miRNA, upregulated lncRNAs act as competing endogenous RNAs, which prevent miRNAs from binding to untreated mRNA targets, thereby increasing their expression at post-transcriptional levels[24,25]. According to the predicted score of >140, and energy < −20, six lncRNAs and 1623 miRNAs that met these criteria were selected (Supplementary Table 2). Thereafter, 259 lncRNA-miRNA relationship pairs (at least five miRNA binding events), including six lncRNAs and 221miRNA (Supplementary Table 3) were filtered. The constructed lncRNA-miRNA network revealed the relationships between six abnormally expressed lncRNAs and 221 potential target miRNAs (Figure 8).
PASMC cell proliferation and cell cycle following C75 treatment
The PAMSCs cell proliferation ability was significantly increased under hypoxia condition, and its proliferation ability was decreased after incubation with C75 (50 μg/mL, 24 h) (Figure 9A). Fas mRNA expression was increased in hypoxia-induced, and C75 incubation could inhibit hypoxia-induced Fas increase (Figure 9B). Based on the flow cytometry assay, G1 phase duration was marginally reduced in hypoxia compared to that of control, whereas the ratio of S and G2 phase (S+G2) was increased. Incubation with 50 μg/mL of C75 for 24 h was able to restore the S and G2 phase (S+G2) ratio to that of the control group (Figure 9 C-F).
As MMP8 plays a crucial role in the PAH, and is widely expression in PAMSCs, we knochdown MMP8 in order to seek its role in vitro. We found that the MMP8 gene knockdown, it can inhibit hypoxia-induced PAMSCs cell proliferation (Figure 10A). We also found that MMP8 knockdown can inhibit hypoxia-induced inflammation, such as IL-6 and TNF-α expression (Figure 10 B-D).