Long non-coding RNA placenta‑specific protein 2 regulates micorRNA-19a/tumor necrosis factor α to participate in polycystic ovary syndrome.

Polycystic ovary syndrome (PCOS) is a type of hormonal disorder that affects about 5-20% of females at their reproductive age worldwide. MicorRNA-19a (miR-19a) is a well-characterized miRNA in cancer biology and its function is mainly mediated by targeting tumor necrosis factor α (TNF-α), which plays critical roles in PCOS. Our preliminary analysis predicted the potential interaction between miR-19a and long non-coding RNA (lncRNA) placenta‑specific protein 2 (PLAC2). Therefore, this study aimed to explore the role of PLAC2 in PCOS. Ovarian tissues were collected from 62 PCOS patients and 62 healthy females. Granulosa-like tumor cells (KGN) was prepared, and transient transfections was conducted. Dual-luciferase activity assay was used to investigate the interaction between PLAC2 and miR-19a. qPCR assays were performed for the expression analysis of miR-19a/TNF-α. In addition, Western blot analysis and cell apoptosis assay were conducted. The results showed that PLAC2 was upregulated in PCOS. PLAC2 and miR-19a showed a direct interaction, while overexpression of PLAC2 and miR-19a did not affect the expression of each other in KGN cells. Instead, overexpression of PLAC2 led to upregulated TNF-α, which is a target of miR-19a. Cell apoptosis analysis showed that PLAC2 and TNF-α promoted the apoptosis of KGN cells. Overexpression of miR-19a played an opposite role. In addition, the overexpression of PLAC2 reduced the effects of overexpression of miR-19a. Therefore, PLAC2 may regulate miR-19a/TNF-α to participate in PCOS.

Introduction

PCOS is a type of hormonal disorder that affects about 5–20% of females at their reproductive age worldwide [1]. The production of male hormones was increased in PCOS patients, which results in hormone imbalance [2]. As a consequence, menstrual periods are affected and getting pregnant is harder compared with healthy females [3]. At present, there is no cure for PCOS [4]. Treatment approaches for PCOS mainly include weight loss, exercise, and birth control pills [5]. However, treatment outcomes are generally not satisfying. It has been well established that PCOS is closely correlated with various genetic and environmental factors, such as the lack of physical exercise, obesity, and family history of PCOS [6]. However, the molecular pathogenesis remains elusive.

The development of PCOS is accompanied with alteration in a considerable number of molecular factors [7,8], which can be used to facilitate the development of therapies, such as targeted therapy, which can be applied to suppress PCOS by regulating gene expression [7,8]. The development of PCOS requires the involvement of non-coding RNAs (ncRNAs), such as microRNAs (miRNAs) and long (>200 nt) ncRNAs (lncRNAs) [9,10]. Therefore, certain critical ncRNAs may serve as novel targets for the development of anti-PCOS therapy. However, the functions of most miRNAs in PCOS remain unclear. MiR-19a is well-characterized miRNA in cancer biology and it functions mainly by regulating tumor necrosis factor α (TNF-α) [11], which plays critical roles in PCOS [12,13]. In our preliminary RNA interaction prediction analysis, we found that miR-19a may interact with placenta‑specific protein 2 (PLAC2), which is a recently identified lncRNA in cancer biology [14-16].

PLAC2 is downregulated in hepatocellular carcinoma and glioma, and overexpression of PLAC2 inhibits cancer progression [14,15]. In contrast, PLAC2 is highly upregulated in oral squamous cell carcinoma and interacts with the Wnt/β‑catenin pathway to suppress cancer development [16]. Therefore, PLAC2 may interact with miR-19a to regulate TNF-α, thereby participating in PCOS. This study was therefore carried out to investigate the interactions among miR-19a, PLAC2 and TNF-α in PCOS.

Methods

PCOS patients and controls

Study subjects of this study included 62 PCOS patients (21–34 years old, mean age 27.6 ± 3.6 years old) and 62 healthy females (21–34 years old, mean age 27.5 ± 3.7 years old). All the participants were enrolled at the First Affiliated Hospital of Xi’an Jiaotong University between July 2017 and October 2019 after the ethics approval was obtained from the Ethics Committee of this hospital. Patients’ inclusion criteria: 1) newly diagnosed PCOS; 2) patients were willing to participate. Patients’ exclusion criteria: 1) patients complicated with other clinical disorders; 2) patients with blood relationship. The 62 healthy controls were randomly selected from more than 30,000 healthy people who received systemic physiological examination at the aforementioned hospital during the same time period. No therapy was initiated before this study. All participants signed the informed consent. Clinical characteristics of patients and controls were presented in Table 1.

Table 1.

Clinical characteristics of patients and controls

Parameters	Controls	PCOS
Age	27.6 ± 3.6	27.5 ± 3.7
BMI	23.56 ± 3.14	24.34 ± 4.63
Basal antral follicle count	14.01 ± 3.19	28.21 ± 6.99*
Basal E2 (pg/ml)	41.33 ± 14.23	57.23 ± 18.23*
Basal testosterone (nmol/ml)	0.91 ± 0.41	1.82 ± 0.31*
Basal FSH (mlU/ml)	6.99 ± 2.11	5.54 ± 1.92*
Basal LH (mlU/ml)	4.82 ± 2.13	8.62 ± 5.37*

*, p < 0.05.

Ovary biopsy

All 62 PCOS patients were subjected to ovary biopsy to collect ovarian tissues from the affected sites. The 62 healthy females were diagnosed with suspected ovary diseases. Ovary biopsy was also performed on these 62 healthy females to confirm the ovary diseases, while suspected ovarian disorders were excluded after biopsy. All ovarian tissues were stored in a liquid nitrogen before use.

Granulosa-like tumor cells (KGN) and transient transfections

KGN cells were prepared and cultivated using the methods described by Nishi et al. [17]. Medium was composed of 45% F12 medium, 45% DME medium and 10% FBS (Sigma-Aldrich). Expression vectors of PLAC2 and TNF-α (pcDNA3.1) and mimic of miR-19a and NC miRNA were prepared. KGN cells harvested at 48 h post-transfection were transfected with expression vector (10 nM) and/or miRNA (40 nM). Cells collected at 48 h post-transfection were used for the subsequent experiments.

Dual luciferase activity assay

Luciferase vector of PLAC2 (pGL3) was prepared and KGN cells were co-transfected with PLAC2 luciferase vector + miR-19a mimic (miR-19a group) or PLAC2 luciferase vector + NC miRNA (NC group). At 48 h post-transfection, luciferase activity was measured and compared between two groups.

Preparation of RNA samples and qPCR assays

KGN cells and ovarian tissues were subjected to RNA isolation and genomic DNA removal using the Direct-zol RNA Kit (ZYMO RESEARCH). RNA samples were subjected to reverse transcriptions (RTs) to prepare cDNA samples using Tetro Reverse Transcriptase (Bioline). THUNDERBIRD™ SYBR® qPCR Mix (Cosmo Bio Co., Ltd.) was used to carry out all qPCRs to measure the expression levels of PLAC2 and TNF-α mRNA as well as miR-19a with GAPDH or U6 as the internal control. All experiments were performed in three replicates and 2−ΔΔCt method was used to normalize gene expression levels.

Western blot analysis

KGN cells were subjected to protein isolation, followed by BCA assay (Sigma-Aldrich) to measure protein concentrations. Protein samples were incubated in boiling water for 10 min to achieve protein denaturation. Denatured protein samples were separated using 8% SDS-PAGE gel, followed by gel transfer. Blocking was then performed, and membranes were first incubated with TNF-α (ab9635, Abcam) and GAPDH (ab9485, Abcam) rabbit primary antibodies at 4°C for 12 h. After that, membranes were further incubated with anti-rabbit IgG-HRP secondary antibody (ab6721, Abcam) at room temperature for 2 h. Signals were produced using ECL reagent (Sigma-Aldrich). Signals were normalized using Image J v.146 software.

Cell apoptosis assay

KGN cells were first digested with 0.25% trypsin, followed by washing with cold PBS. After that, KGN cells were incubated with propidium iodide (PI) and Annexin V-FITC for 4 h in dark. After that, apoptotic cells were separated using flow cytometry.

Statistical analysis

Unpaired t test was used to compare two groups. Three or more groups were compared by ANOVA Tukey’s. Correlations were analyzed by Pearson’s correlation coefficient. P < 0.05 was statistically significant.

Results

The expression of PLAC2 and miR-19a were altered in ovarian tissues from PCOS patients

Differential expression indicates potential function. Therefore, the expression of PLAC2 and miR-19a in ovarian tissues from both PCOS patients (n = 62) and the healthy controls (control group, n = 62) were determined by RT-qPCR. Compared with the control group, the expression levels of PLAC2 were significantly higher in PCOS group (Figure 1(a), p < 0.0001). In contrast, miR-19a was significantly downregulated in PCOS group (Figure 1(b), p < 0.0001). Therefore, PLAC2 may participate in PCOS. Correlations between PLAC2 and miR-19a across control and PCOS samples were analyzed by Pearson’s correlation coefficient. It showed that PLAC2 and miR-19a were not closely correlated across the control (Figure 1(c)) and PCOS (Figure 1(d)) samples.

Figure 1.

The expression of PLAC2 and miR-19a were altered in ovarian tissues from PCOS patients.

Relationship between PLAC2 and miR-19a

IntaRNA2.0 prediction showed that PLAC2 and miR-19a could form multiple-base pairing (Figure 2(a)), indicating the possible interaction between then. Dual luciferase assay was performed to evaluate their direct interaction. Significantly higher luciferase activity was observed in miR-19a group, indicating the direct interaction between PLAC2 and miR-19a (Figure 2(b), p < 0.05). To further confirm the relationship between PLAC2 and miR-19a, KGN cells were overexpressed with PLAC2 or miR-19a (Figure 2(c), p < 0.05). It showed that PLAC2 and miR-19a did not regulate the expression of each other (Figure 2(d)). Therefore, PLAC2 and miR-19a could interact with each other but not regulate the expression of each other.

Figure 2.

The relationship between PLAC2 and miR-19a.

Overexpression of PLAC2 upregulated TNF-α through miR-19a

To explore whether PLAC2 could sponge miR-19a, the role of PLAC2 and miR-19a in regulating the expression of TNF-α, which can be targeted by miR-19a, was evaluated by RT-qPCR (Figure 3(a)) and Western blot analysis (Figure 3(b)). Compared with C group, overexpression of miR-19a led to downregulated expression of TNF-α. In contrast, overexpression of PLAC2 resulted in increased expression levels of TNF-α and reduced the effects of miR-19a (p < 0.05). Therefore, PLAC2 may sponge miR-19a to upregulate TNF-α.

Figure 3.

Overexpression of PLAC2 upregulated TNF-α through miR-19a.

Overexpression of PLAC2 promoted the apoptosis of KGN cells through the miR-19a/ TNF-α axis

Cell apoptosis promotes PCOS. Therefore, the effects of overexpression of PLAC2, miR-19a, and TNF-α ion on the apoptosis of KGN cells were analyzed by cell apoptosis assay. Compared with C group, overexpression of PLAC2 and TNF-α promoted the apoptosis of KGN cells. However, overexpression of miR-19a played an opposite role. In addition, overexpression of PLAC2 reduced the effects of overexpression of miR-19a (Figure 4, p < 0.05).

Figure 4.

Overexpression of PLAC2 promoted the apoptosis of KGN cells through the miR-19a/ TNF-α axis.

Discussion

In this study, we investigated the involvement of PLAC2, miR-19a, and TNF-α in PCOS. We found that PLAC2 was upregulated in PCOS, and it may increase the expression levels of TNF-α by sponging miR-19a, thereby promoting cell apoptosis.

The function of PLAC2 has been investigated in cancer biology [14-16]. PLAC2 is downregulated in hepatocellular carcinoma and glioma to induce cancer cell apoptosis and suppress cancer cell apoptosis by interacting with p53 and STAT1, respectively [14,15]. In contrast, PLAC2 is upregulated in oral squamous cell carcinoma and interacts with the Wnt/β‑catenin pathway to promote cancer cell invasion and proliferation [16]. Based on our knowledge, the involvement of PLAC2 in other human diseases remains unclear. In this study we reported the upregulation of PLAC2 in ovarian tissues of PCOS patients. Increased cell apoptosis is frequently observed in PCOS patients [18]. In our study we showed that overexpression of PLAC2 resulted in the increased apoptotic rate of KGN cells. Therefore, overexpression of PLAC2 may participate in PCOS by promoting cell apoptosis.

TNF-α promotes PCOS by mediating inflammatory responses [12], and the inhibition of TNF-α is considerable as a promising target for the treatment of PCOS [13]. It has been reported that TNF-α can be targeted by miR-19a [11]. Therefore, miR-19a may also participate in PCOS. In this study we showed that miR-19a can also target TNF-α in KGN cells to suppress cell apoptosis.

Remarkably, our study showed that PLAC2 and miR-19a could interact with each other, while overexpression experiments showed that PLAC2, miR-19a and TNF-α did not regulate the expression of each other. In contrast, overexpression of PLAC2 reduced the inhibitory effects of overexpression of miR-19a on the expression of TNF-α and KGN cell apoptosis. It has been well established that lncRNAs may sponge miRNAs to attenuate their roles in both pathological and physiological processes without affecting their expression and accumulation. Therefore, PLAC2 may sponge miR-19a in KGN cells to suppress its function in regulating the expression of TNF-α and the apoptosis of KGN cells.

Although the molecular mechanisms of PCOS have been revealed by researchers, and the participation of RNAs has also been studied [19,20]. More studies are still needed to further elucidate the mechanisms and develop novel therapeutic approaches.

Conclusion

PLAC2 is upregulated in PCOS. In addition, PLAC2 may sponge miR-19a to upregulate TNF-α, thereby promoting cell apoptosis.