Our data demonstrated that PVT1 was significantly up-regulated in the PBMCs of the CAD patients. Up- or down-regulated expression of CAD has been reported from different pathological states. It was reported that PVT1 expression is decreased in the dorsal root ganglia of diabetic rats (17). In addition, Wang et al. reported that down-regulated long non-coding RNA PVT1 contributes to human gestational diabetes mellitus and preeclampsia and the PVT1 expression was lower in the gestational diabetes mellitus and preeclampsia placentas than the normal placentas (19). Another study reported that PVT1 was down-regulated in clinical villi samples from spontaneous abortion (20). In contrast to these findings, an increased expression of PVT1 has also been previously reported. The level of PVT1 expression was significantly increased in cancers. A meta-analysis on a total of 23 studies reported that high PVT1 expression levels correlated with poor overall survival, larger tumor size, distant metastasis, and some other risk factors in cancer patients (21). In addition, it is found to be up-regulated in atrial muscle tissues from atrial fibrillation patients (22), and the myocardial tissues of sepsis rats (23). More importantly, a very recent study by Quan et al. reported a similar finding to our findings, in which PVT1 was highly expressed in the serum of CAD patients (24). Furthermore, it was demonstrated that PVT1 directly correlated with Gensini score in CAD patients, suggesting the involvement of PVT1 in the development of atherosclerosis. In this paper, PVT1 was highly expressed in PBMCs of CAD patients compared to healthy controls, and also up-regulated upon LPS-stimulation in both groups.
To study the role of PVT1 in the production of the IL-10 super family cytokines and MMP-9, we assessed the IL-10, IL-22, and MMP-9 production in both basal and LPS treated states. IL-10 is a pleiotropic cytokine with immune-regulatory properties, produced mostly by Tregs and B regulatory cells. Due to its anti-inflammatory properties, IL-10 is believed to have inhibitory effects on the plaque development and atherosclerosis progression (25). In the present study, we also found that as PVT1 increases, the production of IL-10 is reduced from PBMCs of the total population examined. Therefore, PVT1 might be the factor contributing to anti-inflammatory cytokine IL-10 secretion from PBMCs.
To the best of our knowledge, this is the first to show the relationship between PVT1 expression and IL-10 production in NCAD and CAD patients. Zhao et al. reported high expression of PVT1 in the cartilage of osteoarthritis patients and IL-1β-stimulated chondrocytes. Moreover, in support of this finding, it has been reported that a defect cessation of PVT1 inhibition antagonized the production of inflammatory cytokines upon IL-1β stimulation, including prostaglandin E2, IL-6, IL-8 and TNF-α. However, the precise molecular mechanisms of this correlation is not well understood; however, different factors might be involved, such as anti-inflammatory microRNAs, e.g. microRNA (miR)-146a, miR-27b-3.
Several studies have reported the association between miR-14a and CAD; the results of a recent systematic review and meta-analysis supported the existence of a role for miR-146a rs2910164 polymorphism in determining the susceptibility to cardio-cerebrovascular diseases, especially CAD (26). Another study reported that the expression of miR-146a in PBMCs and plasma was significantly higher in CAD patients compared to NCAD patients (27). In addition, it has been suggested that PVT1 is a mediator of miR-146a expression by inducing the methylation of CpG Island in its promoter so that the miR-146a overexpression eliminates the effects of PVT1 knockdown on prostate cancer cells. Liu et al. showed that miR-146a was down-regulated and negatively correlated with the PVT1 level in prostate cancer. PVT1 mediated miR-146a expression by inducing the methylation of CpG Island in its promoter. MiR-146a over-expression eliminated the effects of PVT1 knockdown on prostate cancer cells (28). It should be noted that miR-146a, as a target of PVT1, has been documented as an anti-inflammatory mediator (29), which not only correlates with increased production of anti-inflammatory cytokines TGF-β1 and IL-10 (30), but also distinguishes CAD patients from NCAD patients, as mentioned above. MiR-27b-3p could be another possible mediator to justify the observed correlation between PVT1 and IL-10. Complementary sequences of PVT1 and miR-27b-3p has been predicted. In addition, the effect of PVT1 on miR-27b-3p has been previously evaluated in C28/I2 human chondrocyte cell line, and results showed that overexpression of PVT1 significantly decreased, and interference of PVT1 increased the miR-27b-3p expression (13). Rouas et al. showed that overexpression of miR-27b-3p, down-regulated IL-10 expression upon targeting its 3'-UTR in T-cells; however, to the best of our knowledge, the deregulation of miR-27b-3p in CAD patients has not been reported yet (31).
In this study, we also found a higher level of MMP-9 in the plasma of CAD patients compared to healthy controls. However, in spite of some other studies in other pathologic conditions, e.g. in aortic aneurysm model (12), and lung cancer cell lines (23), no significant correlation was observed between PVT1 expression and plasma or supernatant levels of MMP-9.
So far, there has been relatively little research conducted on the relationship between IL-22 and coronary artery disease. According to the study of Gong et al., the elevated serum IL-22 was associated with the incidence of type 2 diabetes mellitus and CAD. Furthermore, they showed IL-22 was able to protect the endothelial cells against lysophosphatidylcholine high and glucose-induced injury (32). In the present study, our results demonstrated that the serum IL-22 level elevated in response to the LPS-induced inflammation. Therefore, it could be suggested that keeping IL-22 levels high, through inhibiting inflammation, can be another therapeutic therapeutic target for microvascular diseases with chronic low-grade inflammation, such as diabetes and CAD. However, interleukin has been introduced as a double-edged sword (32), and more studies are needed in this area.