Research Progress of MicroRNAs and Related Factors in the Pathogenesis of Lichen

Yuan-Yuan Li, Jun Wang∗, Cui-Ping Zhang, Pei Yang, Ying-Ying Wang

Department of Dermatology, Affiliated Hospital of Qingdao University, Qingdao, Shandong 266003, China.

Abstract More evidences show that microRNAs play an important role in the pathogenesis of inflammation and autoimmune diseases including Lichen planus,and are an attractive therapeutic target.MicroRNA family plays an important role in the regulation of gene expression,which involves cell proliferation,apoptosis,growth,differentiation and metabolism,vascularization,immune response and other biological processes.The changes of expression profile and expression level are closely related to the occurrence and development of many diseases,such as tumor,inflammatory disease and autoimmune disease relevant. However, there are few reports on microRNA in the pathogenesis of LP. This review summarizes the research advance of microRNAs(microRNAs-137,microRNAs-125b,microRNAs-138,microRNAs-27b, microRNAs -203) and their downstream proteins in LP.

Keywords: lichen planus, pathogenesis, microRNAs

Introduction

Lichen planus (LP) is an immune-mediated inflammatory disease that affects the skin and mucous membranes. Its etiology is unclear and its characteristic pathological changes include hyperkeratosis, an inflammatory infiltration zone in the upper dermis,and liquefaction degeneration of basal cells. A growing body of evidence suggests that microRNAs (miRNAs) play an important role in the pathogenesis of inflammatory and autoimmune diseases and are an attractive therapeutic target.Recent advances in the knowledge of microRNAs in LP are reviewed in the following sections.

MiRNA-27b and its related factors with LP

Previous studies of autoimmune diseases have shown that miRNA-27 is keratin-specific miRNA. The expression level of miRNA-27 in oral LP(OLP)tissues was found to be significantly downregulated,more so with aggravation of the disease.Aghbari et al.1detected CD8 and miRNA-27b expression in tissues of 20 patients with OLP and 20 patients without OLP(controls),and found that miRNA-27b expression was downregulated in OLP tissues,however, the difference was not statistically significant.In addition,miRNA-27b was found to be highly sensitive as an OLP biomarker (up to 100%). miRNA-27b is thus considered to have potential as a biomarker of OLP disease.Other studies have confirmed that miRNA-27b-3p regulates keratinocyte apoptosis through the cyclin D/Bcl-2 signaling pathway, suggesting that miRNA-27b-3p is involved in the pathogenesis of OLP.2

Zhang et al.3indicated that downregulation of miRNA-27b in OLP epithelial keratinocytes may be part of the specific inflammatory response of activated cytotoxic T cells, which may trigger apoptosis of epithelial cells.

Polo-like kinase 2

The Polo-like kinase (PLK) family comprises highly conserved serine/threonine protein kinases. Its members in mammals include PLK1,PLK2,PLK3,and PLK4,which are generally believed to be involved in regulation of the cell cycle.PLK2 has the highest expression in the G1 phase and may be involved in controlling the entry of cell into the S phase.

Chen et al.4found that the expression of miRNA-27b in OLP tissues was significantly downregulated compared with the normal control group. Bioinformatics has predicted that PLK2 might be a potential target for miRNA-27b, while luciferase reporter assay results have shown that miRNA-27b directly inhibits the untranslated region of PLK2 and PLK3.Functional analysis has shown that miRNA-27b downregulation leads to the growth of human keratinocytes and that PLK2 overexpression promotes keratinocyte proliferation.Therefore,a decrease in miRNA-27b may induce cell proliferation by increasing the level of PLK2 in human keratinocytes.

Matrix metalloproteinase

Recent studies have shown that matrix metalloproteinase(MMP)-2 increases to varying degrees in proliferative diseases such as LP and psoriasis.5Imbalance of MMP-2 and its regulatory factors leads to weakened degradation of MMP-2, and increased MMP-2 damages epithelial connective tissue, inducing basal membrane damage and leading to chronic development of LP.6-7In addition, one study confirmed the increased expression of hypoxiainducible factor 1a(HIF-1a),vascular endothelial growth factor,and MMP-9 in keratinocytes of patients with OLP under hypoxic conditions.8Some studies have immunohistochemically confirmed that MMP-9 is overexpressed in LP, which may be related to the incidence of LP.9Overall, it is generally believed that MMP-9 plays an important role in LP by destroying the basement membrane, regulating T-cell migration, and promoting the apoptosis of keratinocytes.

Notably, Li et al.10found that miRNA-27b attenuates the migration of retinal pigment epithelial cells(ARPE-19 cell line) by downregulating MMP-2 and MMP-9. Both MMP-2 and MMP-9 are gelatin enzymes(gelatinases)that are able to degrade components of the cell skeleton (type IV collagen,layer adhesion protein),and this degradation is considered the main causative factor in collapse of the basement membrane.MMP-2 and MMP-9 are considered the most relevant MMPs in the pathogenesis of LP.Therefore,the authors speculated that miRNA-27b might be involved in the pathogenesis of LP.

MiRNA-138 and its related factors with LP

Cyclin D1

Wang et al.11found that an increased level of miRNA-138 inhibited the proliferation,G1/S transition,migration,and invasion of bile duct carcinoma cells, and reduced the expression of MMP-2 and MMP-9 in bile duct carcinoma cells. As already mentioned, MMP-2 and MMP-9 are considered the most relevant MMPs in the pathogenesis of LP. Ghallab et al.12collected oral biopsy specimens from 60 patients with OLP and found that miRNA-138 gene expression in the samples obtained from patients with OLP was significantly insufficient, with overexpression of the cyclin D1 gene (CCND1) and protein levels, and the expressions of the two were negatively correlated.Downregulation of miRNA-138 is believed to increase the gene and protein expression of its potential target CCND1 in OLP-affected mucosa, which may play a key role in the pathogenesis of the disease.

HIF-1a

HIF-1a is primarily influenced by the hypoxic environment, where the hypoxic signal binds to the c-terminal–specific oxygen degradation region of HIF-1a to regulate the transcription response.Normally,HIF-1a is degraded after translation. In the presence of inflammation or hypoxia,HIF-1a is overexpressed in cells and accumulates within nuclei to become a transcriptional dimer. Yeh et al.13found that miRNA-138 inhibits the invasion and metastasis of ovarian cancer in mice by targeting HIF-1a.A study on malignant melanoma revealed that the upregulation of miRNA-138 significantly inhibits glycolysis and reverses the overproliferation of HIF-1a.14In other words,the inhibition of miRNA-138 on glycolysis may be exerted by direct inhibition of HIF-1a. Zhou et al.15suggested that miRNA-138 inhibits the proliferation of hypoxia-induced endothelial progenitor cells, possibly by inhibiting the HIF-1a–mediated signaling pathway.

Recent studies have shown that HIF-1a is highly expressed in LP.16In addition, HIF-1a was found to regulate MMP-2 under hypoxic conditions.Yasuda et al.17found that the mRNA of MMP-2 was significantly increased under hypoxic conditions by using cobalt chloride to simulate hypoxia and reduce the oxygen partial pressure on fat cells,suggesting that HIF-1a and MMP-2 may have a certain correlation under hypoxic conditions.Other studies have shown that MMP-2 expression is increased in an anoxicenvironment andMMP-2 waspreviously mentioned as a factor closely related to the pathogenesis LP.18-19

MiRNA-137 and its related factors with LP

CD8

Aghbari et al.20compared the expressions of miRNA-27b and miRNA-137 in tissues and saliva of patients with versus without OLP by reverse-transcription quantitative PCR and found that the expressions of both of these miRNAs were lower in the tissues and saliva of patients than controls. Changes in the expression of the miRNA-27b and miRNA-137 genes were suggested to be biomarkers of disease activity and malevolent tendencies.In another study, the authors compared 20 patients with OLP versus 20 healthy controls.21The results showed that the expression of CD8 in OLP patients was higher than that in the control group (P<0.01), the expression of mirna-137 was lower than that in the control group(P<0.001),and the tissue expression of mir-137 and CD8 was negatively correlated. These findings indicate the therapeutic potential of miRNA-137 in patients with OLP.

Cyclooxygenase-2

Cyclooxygenase (COX), also known as prostaglandin endoperoxide synthase,plays a crucial role in the synthesis of prostaglandin(PG),and prostaglandin E2(PGE2)plays a role in immune regulation. COX-2 is inductively expressed in most tissues, and becomes important in the development of inflammation after stimulation,so COX-2 is an important target in the treatment of inflammation.

El-Rifaie et al.22detected COX-2 mRNA and PGE2 protein in 31 patients with skin LP and 30 healthy controls. The COX-2 mRNA and PGE2 secretion were significantly higher in LP than those of controls indicating that COX-2 and its product PGE2 have immunomodulating effects and play a certain role in the pathogenesis of LP.Singh et al.23showed a significant correlation between COX-2 protein expression and the mast cell count; the number of mast cells nearly doubled as the intensity of COX-2 increased from mild to moderate or severe. The authors reported that the interactions among COX-2,mast cells,and the basilar membrane form a vicious circle associated with the nature of chronic diseases and that COX-2 inhibitors can reduce the inflammatory process before an OLP-related immune disorder develops.

Zhang et al.24verified that COX-2 is a potential target gene of miRNA-137 through a Dual-Luciferase®Reporter Assay(Promega Corporation,Madison,WI).The authors also confirmed that miRNA-137 negatively regulates the expression of COX-2 and the production of PGE2 in retinoblastoma cells, and confirmed that miRNA-137 inhibits the proliferation and invasion of retinoblastoma cells by targeting COX-2/PGE2. Thus, the authors speculated that miRNA-137 may play a role in LP by regulating COX-2 and PGE2.

MiRNA-125b and its related factors with LP

Wang et al.6confirmed that miRNA-125b in a lipopolysaccharide-induced OLP model targets MMP-2 expression through the PI3K/Akt/mTOR pathway, inhibits keratinocyte proliferation, and promotes keratinocytes apoptosis,indicating that miRNA-125b is a potential target for OLP therapy. In a study of psoriasis inhibition of endogenous miRNA-125b promoted keratinocyte proliferation and delayed differentiation.25

ETS-1

E26 transformation-specific sequence-1(ETS-1)is a protooncogene in the family of ETS transcriptional regulators that regulates the expression of genes related to extracellular matrix reconstruction. Studies have confirmed that ETS-1 protein upregulates the expression of MMP-9 and MMP-13 mRNA in the human ovarian cancer cell line SKOV-3 by regulating vascular endothelial growth factor and MMP-9.26ETS-1 can upregulate MMP-9 and MMP-13, thus promoting tumor cell invasion. Another study showed that MMP-9 expression reached 90%in 56.2%of breast cancer tissues with positive expression of ETS-1,confirming that ETS-1 can upregulate the expression of MMP-9.27ETS-1 expression is low in normal mucosa but high in OLP-affected tissue,which is related to the clinical classification; expression increases as the severity of inflammation increases and the disease course becomes more prolonged.28Studies have confirmed that MMP-9,tissue inhibitor-1 of matrix metalloproteinase (TIMP-1),and ETS-1 are overexpressed in LP and that the expression levels of the three are positively correlated,which may be related to the incidence of LP.9Zhang et al.29found that the ETS-1 gene was a new direct target of miRNA-125b and that the two genes were negatively correlated.Therefore, miRNA-125b and its target gene ETS-1 might be involved in the pathogenesis of LP.

Bcl-2

Zhao et al.30confirmed that miRNA-125b has the ability to significantly inhibit the transcription of antiapoptotic protein Bcl-2, suggesting that Bcl-2 is a target gene of miRNA-125b. Inhibition of the gene expression of Bcl-2 can significantly inhibit the proliferation and promote apoptosis of hepatocellular carcinoma cells. Previous studies confirmed that the expression rate of Bcl-2 was significantly higher in patients with LP than those without.31Whether regulation of miRNA-125b on Bcl-2 plays a role in the pathogenesis of LP needs further study.

MiRNA-635, miRNA-578, and their related factors with LP

Interleukin (IL)-17

Wang et al.32found that the IL-9 and MMP-9 mRNA levels inOLPlesionswere positively correlated,whiletheIL-9 and MMP-9 mRNA levels in epithelial part(EP)and LP lesions of patients with invasive OLP were significantly increased.After coculture of CD4+ T-helper(Th)cells and keratinocytes,Th9 and Th17 cells were significantly increased,and the levels of MMP-9,IL-9,and IL-17 were also increased.Treatment with recombinant human IL-17 in vitro significantly increased MMP-9 mRNA and protein levels,while IL-9 and IL-17 had no synergistic effect. However,further results showed that theadditionof recombinantIL-9 to cultured CD4+T cells resulted in significant increases in Th17 cells,IL-17,and MMP-9.These findings indicate that Th9 cells/IL-9 can induce an increase in the MMP-9 level andaggravate the severityof OLP,which may occur directly through an increase in the Th17 cell level or indirectly through the synergistic effect with Th17 cells.

One research has also shown that the expression of IL-17 are higher in LP lesions.33Solimani et al.34firstly confirmed that the use of Th17/Tc17 cells as therapeutic targets significantly improved the clinical manifestations of patients with LP and that Th17 cells are likely to be at the core of the pathogenesis of the disease. Thus, targeting Th17/Tc17 cells in the treatment of intractable LP may open a new way to treatment. Shen et al.35showed that miRNA-635 and miRNA-578 were the target miRNAs of IL-17a in human embryonic kidney 293 cells through the Dual-Luciferase®Reporter gene detection system (Promega Corporation), which was consistent with our bioinformatics software analysis and prediction by them in that study. Their study showed that low expression levels of miRNA-635 and miRNA-578 were related to high expression of IL-17a, suggesting that IL-17a and its targeted miRNA are involved in the pathogenesis of OLP.

MiRNA-562, miRNA-203, and their related factors with LP

IL-22

Di Stasio et al.36found through low-density chip analysis that the levels of mir-21 mir-125b and mir-203 in OLP were increased,while the expression levels of mir-27b were decreased.However, Danielsson et al.37found thatthe expression of mir-21 and mir-203 in OLP increased,while the expression of mir-125 decreased. El-rifaie et al.38found that the mRNA expressions of mir-203 and mir-125b in LP were both significantly reduced,suggesting that mir-125b and mir-203 may be involved in the pathogenesis of cutaneous LP. Studies have proven that IL-22 expression was increased in the skin lesions of patients with LP,33,39which is consistent with the results reported by Chen et al.40In addition, Chen et al.40found that the expression rate of IL-22 in OLP was significantly higher than that in skin LP. Shen et al.41also found that the expression of IL-22 was significantly increased in OLP.Moreover,analysis of human embryonic kidney 293 cells using the Dual-Luciferase®Reporter gene detection system showed that miRNA-562 and miRNA-203 were the target miRNAs of IL-22,which was consistent with the analysis and prediction of bioinformatics software. Interestingly,the expression of miRNA-562 in the OLP group was significantly lower than that in the normal control group,while the expression of miRNA-203 in OLP was significantly increased. This study was the first to show that the abnormal expression levels of miRNA-562 and miRNA-203 were correlated with the high expression of IL-22, indicating that IL-22 and its targeted miRNA may be involved in the pathogenesis of OLP.

Conclusions

The current review summaries the advance of miRNAs in the pathogenesis of LP. However, there are also some limitations in the research:how to select specific miRNAs related to LP disease, how to determine the specific mechanism of miRNA in the pathogenesis of LP, the establishment of related research cell model, the selection of disease treatment targets,etc.,need to be further clarified by large-scale in-depth study of different clinical types based on patients.

The regulation of miRNAs in immune diseases is not limited to immune cells. Several effector cells, such as keratinocytes, are also regulated by miRNAs. Therefore,the correlation between miRNAs and LP is a promising field of research. More in-depth studies on the role of miRNAs in the pathogenesis of LP are necessary.