Pulmonary arterial hypertension (PAH) is defined as a devastating disease of the small pulmonary arteries manifesting aberrant vascular proliferation and remodeling [29, 30]. Pulmonary vascular remodeling, along with vasoconstriction and thrombosis in situ, are three primary factors leading to the elveated pulmonary vascular resistance . As a complex pathological process, pulmonary vascular remodeling is characterized by the disrupted HPASMC proliferation and migration, as well as the inhibited apoptosis. Therefore, exploring the molecular and cellular mechanism underlying HPASMC proliferation and apoptosis in PAH would greatly contribute to the understanding of PAH pathology. In the present study, the results demonstrated that the expression of PVT1 was increased in PA tissues and HPASMCs of patients with PAH and its expression was positively correlated with pulmonary artery pressure. In addition, the knockdown and overexpression of PVT1 inhibited and promoted HPASMC proliferation and migration, respectively. Furthermore, bioinformatics analysis and functional studies showed that the effect of PVT1 on HPASMC cellular activities in PAH may be mediated by the miR-140-5p/Fxr1 signaling axis.
The lncRNA PVT1 is 1716 nucleotides in length and is encoded by an oncogene PVT1 . It has been reported that PVT1 exerts essential roles in various types of tumors, including hepatocellular carcinoma , malignant pleural mesothelioma, bladder cancer , and gastric cancer , where PVT1 suppresses apoptosis while promoting cell proliferation and migration, eventually facilitating cancer progression . Since PASMCs and cancer cells share some common cellular properties, such as hypermetabolism, aberrant mitochondrial function, and high proliferative activity [35, 36], PVT1 may also function as a stimulator for PASMC proliferation and migration. In this study, PVT1 was upregulated in both PA tissues and HPASMCs. Functional studies revealed that overexpression of PVT1 significantly elevated viability and proliferation of HPASMCs. The results are consistent with the hypothesis that PVT1 promotes pulmonary vascular remodeling by enhancing proliferation and inhibiting apoptosis, as its roles in several tumor types . However, since the effect of PVT1 displays the MYC copy-number-dependent pattern, the mechanism underlying its effect may vary in each pathological process .
In addition to its role in cellular activities, this study found that the expression of PVT1 was positively correlated with pulmonary artery pressure, indicating PVT1 may be a promising diagnostic biomarker for patients with PAH. Similarly, PVT1 has been identified as an ideal prognostic biomarker in several cancer types [32, 38, 39], in which the upregulation of PVT1 is significantly correlated with poor overall survival, distant metastasis, and poor differentiation grade . Therefore, more studies are needed to further determine the predictive value of PVT1 in PAH.
It has been well-documented that lncRNAs can function as ceRNA to regulate the expression of microRNAs (miRNAs), primarily through sponging and silencing miRNAs [40, 41]. Therefore, to further determine the mechanism underlying the effect of PVT1 on PAH, bioinformatics analysis was performed to screen the putative miRNAs interacting with PVT1. Combining with the mechanic and functional studies, the results revealed that the expression of PVT1 was negatively correlated with the level of miR-140-5p and their physical and functional interactions played important roles in the regulation of PAH progression, suggesting that PVT1 may act as a ceRNA of miR-140-5p in PAH. As a multifunctional factor, miR-140-5p exerts essential roles in various pathological processes, such as osteogenesis , epithelial mesenchymal transition , and autophagy . A comprehensive bioinformatics analysis also demonstrated that miR-140-5p was associated with 23 target genes and seven signaling pathways in multiple biological processes, such as signal transduction and cell proliferation . The expression of miR-140-5p is downregulated in PAH and the suppression of miR-140-5p facilitates proliferation and migration in HPASMCs , which agrees with the observation in the present study. As such, like PVT1, miR-140-5p may also serve as a potential biomarker for PAH.
In this study, the results also demonstrated that Fxr1 was upregulated in both PA tissues and HPASMCs and its effect on vascular remodeling was opposite to those of miR-140-5p. These results together indicated that miR-140-5p may act as a sponge of Fxr1 in PAH, which was confirmed by bioinformatics analysis and luciferase reporter assays. The Fxr1 is an RNA-binding protein and its sequence is highly conservative across many species [47, 48]. Like the roles of RNA-binding proteins, Fxr1 is associated with gene translation, mRNA transport, and mRNA binding through G4 RNA structures or AU-rich elements [48, 49]. On the basis of modulation of cellular activities, Fxr1 participates in the regulation of p21 expression via p53-dependent patterns to regulate cell proliferation in the head and neck squamous cell carcinoma and non-small cell lung cancer cells . Also, Fxr1 functions as an oncogene promoting proliferation, invasion, as well as migration in cancer cells . Together, Fxr1 may be an important regulator of cell proliferation and migration.
In this study, we have demonstrated that the important role of PVT1 in the HPASMCs of PAH. However, some limitations in this study should not be ignored. For example, the animal experiment should be perfomed to validate the effect of PVT1 in vivo. Also, the pathogenesis of PAH is heterogeneous [52, 53] and there are several subtypes of PAH, such as idiopathic PAH (IPAH), heritable PAH (HPAH), and associated PAH (APAH) . Of which, we only included HPASMCs of HPAH in the present study. Thus, more subtype of PAH should be covered in future study.
In conclusion, PVT1 was upregulated in PA tissues and HPASMCs and the expression of PVT1 was positively correlated with pulmonary artery pressure. Also, PVT1 could promote proliferation while inhibiting apoptosis in HPASMCs though the miR-140-5p/Fxr1 signaling axis. Understanding the molecular mechnisms of PVT1 in PAH may provide novel insight into developing therapy for PAH.