Interleukin-1 receptor-associated kinase-3 is a key inhibitor of inflammation in obesity and metabolic syndrome

Background

Visceral obesity is associated with the rising incidence of type 2 diabetes and metabolic syndrome. Low-grade chronic inflammation and oxidative stress synergize in obesity and obesity-induced disorders.

Objective

We searched a cluster of molecules that support interactions between these stress conditions in monocytes.

Methods

RNA expressions in blood monocytes of two independent cohorts comprising 21 and 102 obese persons and 46 age-matched controls were determined by microarray and independently validated by quantitative RT-PCR analysis. The effect of three-month weight loss after bariatric surgery was determined. The effect of RNA silencing on inflammation and oxidative stress was studied in human monocytic THP-1 cells.

Results

Interleukin-1 receptor-associated kinase-3 (IRAK3), key inhibitor of IRAK/NFκB-mediated chronic inflammation, is downregulated in monocytes of obese persons. Low IRAK3 was associated with high superoxide dismutase-2 (SOD2), a marker of mitochondrial oxidative stress. A comparable expression profile was also detected in visceral adipose tissue of the same obese subjects. Low IRAK3 and high SOD2 was associated with a high prevalence of metabolic syndrome (odds ratio: 9.3; sensitivity: 91%; specificity: 77%). By comparison, the odds ratio of high-sensitivity C-reactive protein, a widely used marker of systemic inflammation, was 4.3 (sensitivity: 69%; specificity: 66%). Weight loss was associated with an increase in IRAK3 and a decrease in SOD2, in association with a lowering of systemic inflammation and a decreasing number of metabolic syndrome components. We identified the increase in reactive oxygen species in combination with obesity-associated low adiponectin and high glucose and interleukin-6 as cause of the decrease in IRAK3 in THP-1 cells in vitro.

Conclusion

IRAK3 is a key inhibitor of inflammation in association with obesity and metabolic syndrome. Our data warrant further evaluation of IRAK3 as a diagnostic and prognostic marker, and as a target for intervention.     

Chikungunya Virus Exploits miR-146a to Regulate NF-κB Pathway in Human Synovial Fibroblasts

Objectives

Chikungunya virus causes chronic infection with manifestations of joint pain. Human synovial fibroblasts get infected with CHIKV and could lead to pro-inflammatory responses. MicroRNAs have potentials to regulate the gene expression of various anti-viral and pro-inflammatory genes. The study aims to investigate the role of miR-146a in modulation of inflammatory responses of human synovial fibroblasts by Chikungunya virus.

Methods

To study the role of miR-146a in CHIKV pathogenesis in human synovial cells and underlying inflammatory manifestations, we performed CHIKV infection in primary human synovial fibroblasts. Western blotting, real-time PCR, luciferase reporter assay, overexpression and knockdown of cellular miR-146a strategies have been employed to validate the role of miR-146a in regulation of pro-inflammatory NF-κB pathway.

Results

CHIKV infection induced the expression of cellular miR-146a, which resulted into down-regulation of TRAF6, IRAK1, IRAK2 and increased replication of CHIKV in human synovial fibroblasts. Exogenous expression of miR-146a in human synovial fibroblasts led to decreased expression of TRAF6, IRAK1, IRAK2 and decreased replication of CHIKV. Inhibition of cellular miR-146a by anti-miR-146a restored the expression levels of TRAF6, IRAK1 and IRAK2. Downregulation of TRAF6, IRAK1 and IRAK2 led to downstream decreased NF-κB activation through negative feedback loop.

Conclusion

This study demonstrated the mechanism of exploitation of cellular miR-146a by CHIKV in modulating the host antiviral immune response in primary human synovial fibroblasts.     

Therapeutic silencing miR-146b-5p improves cardiac remodeling in a porcine model of myocardial infarction by modulating the wound reparative phenotype

Fibrotic remodeling is an adverse consequence of immune response-driven phenotypic modulation of cardiac cells following myocardial infarction(Ml).MicroRNA-146b(miR-146b)is an active regulator of immunomodulation,but its function in the cardiac inflammatory cascade and its clinical implication in fibrotic remodeling following Ml remain largely unknown.Herein,miR-146b-5p was found to be upregulated in the infarcted myocardium of mice and the serum of myocardial ischemia patients.Gain-and loss-of-function experiments demonstrated that miR-146b-5p was a hypoxia-induced regulator that governed the pro-fibrotic phenotype transition of cardiac cells.Overexpression of miR-146b-5p activated fibroblast proliferation,migration,and fibroblast-to-myofibroblast transition,impaired endothelial cell function and stress survival,and disturbed macrophage paracrine signaling.Interestingly,the opposite effects were observed when miR-146b-5p expression was inhibited.Luciferase assays and rescue studies demonstrated that the miR-146b-5p target genes mediating the above phenotypic modulations included interleukin 1 receptor associated kinase 1(IRAKI)and carcinoembryonic antigen related cell adhesion molecule 1(CEACAM1).Local delivery of a miR-146b-5p antagomir significantly reduced fibrosis and cell death,and upregulated capillary and reparative macrophages in the infarcted myocardium to restore cardiac remodeling and function in both mouse and porcine Ml models.Local inhibition of miR-146b-5p may represent a novel therapeutic approach to treat cardiac fibrotic remodeling and dysfunction following Ml.     

MicroRNA-146a and MicroRNA-146b Regulate Human Dendritic Cell Apoptosis and Cytokine Production by Targeting TRAF6 and IRAK1 Proteins

We have previously reported 27 differentially expressed microRNAs (miRNAs) during human monocyte differentiation into immature dendritic cells (imDCs) and mature DCs (mDCs). However, their roles in DC differentiation and function remain largely elusive. Here, we report that microRNA (miR)-146a and miR-146b modulate DC apoptosis and cytokine production. Expression of miR-146a and miR-146b was significantly increased upon monocyte differentiation into imDCs and mDCs. Silencing of miR-146a and/or miR-146b in imDCs and mDCs significantly prevented DC apoptosis, whereas overexpressing miR-146a and/or miR-146b increased DC apoptosis. miR-146a and miR-146b expression in imDCs and mDCs was inversely correlated with TRAF6 and IRAK1 expression. Furthermore, siRNA silencing of TRAF6 and/or IRAK1 in imDCs and mDCs enhanced DC apoptosis. By contrast, lentivirus overexpression of TRAF6 and/or IRAK1 promoted DC survival. Moreover, silencing of miR-146a and miR-146b expression had little effect on DC maturation but enhanced IL-12p70, IL-6, and TNF-α production as well as IFN-γ production by IL-12p70-mediated activation of natural killer cells, whereas miR-146a and miR-146b overexpression in mDCs reduced cytokine production. Silencing of miR-146a and miR-146b in DCs also down-regulated NF-κB inhibitor IκBα and increased Bcl-2 expression. Our results identify a new negative feedback mechanism involving the miR-146a/b-TRAF6/IRAK1-NF-κB axis in promoting DC apoptosis.     

miR-146a Is Critical for Endotoxin-induced Tolerance: IMPLICATION IN INNATE IMMUNITY*

The human toll-like receptor 4 (TLR4) pathway is activated in response to lipopolysaccharide (LPS), and subsequent signal transductions lead to the production of cytokines such as tumor necrosis factor-α (TNF-α) by innate immune cells. Defects in innate immune response may contribute to the overproduction of TNF-α leading to systemic inflammation and diseases. Thus, the innate immune response needs to be tightly regulated by elaborate mechanisms to control its onset and termination. LPS tolerance is a state of hyporesponsiveness to subsequent LPS challenge and is achieved by monocytic cells after prolonged exposure to LPS. In this report, kinetics of endotoxin-responsive microRNAs expression analysis revealed a unique pattern of gradual increase for miR-146a starting 4 h after LPS stimulation in THP-1 cells and continued up to 35-fold over 24 h. Conversely, TNF-α increased up to 4 h and then decreased gradually implicating a negative correlation with miR-146a progression. The characteristic up-regulation of miR-146a toward subsequent LPS challenge in THP-1 cells was studied. Strikingly, microRNA expression analysis during the tolerized state of THP-1 cells showed only miR-146a overexpression suggesting its important role in LPS tolerance. In addition, LPS tolerance was dependent on a LPS-priming dose and associated miR-146a up-regulation. LPS-tolerized cells were observed to regain responsiveness in TNF-α production 22 h after LPS removal correlating with a decrease in miR-146a level. Transfection of miR-146a into THP-1 cells mimicked LPS priming, whereas transfection of miR-146a inhibitor largely abolished LPS tolerance. Thus our studies demonstrated that miR-146a is critical for the in vitro monocytic cell-based endotoxin tolerance.     

Mechanistic role of microRNA-146a in endotoxin-induced differential cross-regulation of TLR signaling

Human TLRs are critical sensors for microbial components leading to the production of proinflammatory cytokines that are controlled by various mechanisms. Monocytes pretreated with LPS exhibit a state of hyporesponsiveness, referred to as cross-tolerance, to both homologous and heterologous ligands, which play a broader role in innate immunity. To date, LPS-induced cross-tolerance has not been examined regarding microRNA expression kinetics. In this study, THP-1 monocytes treated with various inflammatory ligands showed a continuous amplification of microRNA (miR)-146a over 24 h that is inversely correlated to TNF-α production. In contrast, inhibition of miR-146a showed a reciprocal effect. Thus, the characteristic upregulation of miR-146a in LPS-exposed THP-1 monocytes was studied for cross-tolerance. Strikingly, in LPS-tolerized THP-1 monocytes, only miR-146a showed a continuous overexpression, suggesting its crucial role in cross-tolerance. Similarly, peptidoglycan-primed THP-1 cells showed homologous tolerance associated with miR-146a upregulation. Subsequently, interchangeable differential cross-regulation was observed among non-LPS ligands. TLR2 and TLR5 ligands showed both homologous and heterologous tolerance correlated to miR-146a overexpression. More importantly, inflammatory responses to TLR4, TLR2, and TLR5 ligands were reduced due to knockdown of miR-146a targets IL-1R-associated kinase 1 or TNFR-associated factor 6, suggesting the regulatory effect of miR-146a on these TLRs signaling. Transfection of miR-146a into THP-1 cells caused reduction of TNF-α production, mimicking LPS-induced cross-tolerance. Aside from individual ligands, a whole bacterial challenge in LPS-primed THP-1 monocytes was accompanied by less TNF-α production, which is conversely correlated to miR-146a expression. Our studies have thus demonstrated that miR-146a plays a crucial role for in vitro monocytic cell-based endotoxin-induced cross-tolerance.     

Cardiovascular and Cerebrovascular Disease Associated microRNAs Are Dysregulated in Placental Tissues Affected with Gestational Hypertension,Preeclampsia and Intrauterine Growth Restriction

Aims

To demonstrate that pregnancy-related complications are associated with alterations in cardiovascular and cerebrovascular microRNA expression. Gene expression of 32 microRNAs (miR-1-3p, miR-16-5p, miR-17-5p, miR-20a-5p, miR-20b-5p, miR-21-5p, miR-23a-3p, miR-24-3p, miR-26a-5p, miR-29a-3p, miR-33a-5p, miR-92a-3p, miR-100-5p, miR-103a-3p, miR-122-5p, miR-125b-5p, miR-126-3p, miR-130b-3p, miR-133a-3p, miR-143-3p, miR-145-5p, miR-146a-5p, miR-155-5p, miR-181a-5p, miR-195-5p, miR-199a-5p, miR-208a-3p, miR-210-3p, miR-221-3p, miR-342-3p, miR-499a-5p, and miR-574-3p) was assessed in placental tissues, compared between groups (35 gestational hypertension, 80 preeclampsia, 35 intrauterine growth restriction and 20 normal pregnancies) and correlated with the severity of the disease with respect to clinical signs, delivery date, and Doppler ultrasound parameters. Initially, selection and validation of endogenous controls for microRNA expression studies in placental tissues affected by pregnancy-related complications have been carried out.

Results

The expression profile of microRNAs was different between pregnancy-related complications and controls. The up-regulation of miR-499a-5p was a common phenomenon shared between gestational hypertension, preeclampsia, and intrauterine growth restriction. Preeclamptic pregnancies delivering after 34 weeks of gestation and IUGR with abnormal values of flow rate in the umbilical artery demonstrated up-regulation of miR-1-3b. Preeclampsia and IUGR requiring termination of gestation before 34 weeks of gestation were associated with down-regulation of miR-26a-5p, miR-103a-3p and miR-145-5p. On the other hand, some of microRNAs (miR-16-5p, miR-100-5p, miR-122-5p, miR-125b-5p, miR-126-3p, miR-143-3p, miR-195-5p, miR-199a-5p, miR-221-3p, miR-342-3p, and miR-574-3p) were only down-regulated or showed a trend to down-regulation just in intrauterine growth restriction pregnancies requiring the delivery before 34 weeks of gestation.

Conclusion

Epigenetic changes induced by pregnancy-related complications in placental tissue may cause later onset of cardiovascular and cerebrovascular diseases in offspring.     

Evidence in Obese Children: Contribution of Hyperlipidemia,Obesity-Inflammation,and Insulin Sensitivity

Background

Evidence shows a high incidence of insulin resistance, inflammation and dyslipidemia in adult obesity. The aim of this study was to assess the relevance of inflammatory markers, circulating lipids, and insulin sensitivity in overweight/obese children.

Methods

We enrolled 45 male children (aged 6 to 13 years, lean control = 16, obese = 19, overweight = 10) in this study. The plasma total cholesterol, HDL cholesterol, triglyceride, glucose and insulin levels, the circulating levels of inflammatory factors, such as TNF-α, IL-6, and MCP-1, and the high-sensitive CRP level were determined using quantitative colorimetric sandwich ELISA kits.

Results

Compared with the lean control subjects, the obese subjects had obvious insulin resistance, abnormal lipid profiles, and low-grade inflammation. The overweight subjects only exhibited significant insulin resistance and low-grade inflammation. Both TNF-α and leptin levels were higher in the overweight/obese subjects. A concurrent correlation analysis showed that body mass index (BMI) percentile and fasting insulin were positively correlated with insulin resistance, lipid profiles, and inflammatory markers but negatively correlated with adiponectin. A factor analysis identified three domains that explained 74.08% of the total variance among the obese children (factor 1: lipid, 46.05%; factor 2: obesity-inflammation, 15.38%; factor 3: insulin sensitivity domains, 12.65%).

Conclusions

Our findings suggest that lipid, obesity-inflammation, and insulin sensitivity domains predominantly exist among obese children. These factors might be applied to predict the outcomes of cardiovascular diseases in the future.     

MicroRNA-146a Represses Mycobacteria-Induced Inflammatory Response and Facilitates Bacterial Replication via Targeting IRAK-1 and TRAF-6

Background

Apart from triggering host immune responses, macrophages also act as a major reservoir for mycobacteria. For better survival, mycobacteria have evolved various mechanisms to modulate the production of proinflammatory cytokines in macrophages, and manipulation of micro-RNA (miRNA) expression has been considered as an important one.

Methodology/Principal Findings

In this study, we found that miR-146a expression was significantly increased in a time- and dose-dependent manner in mycobacteria-infected macrophages. It could obviously reduce the induction of proinflammatory cytokines TNF-α, IL-1β, IL-6 and chemokine MCP-1 by targeting interleukin-1 receptor-associated kinase-1 (IRAK-1) and TNF receptor-associated factor-6 (TRAF-6), two key elements involved in the TLR/NF-κB signaling pathway cascades. Consistent with the anti-inflammation effect, a higher bacterial burden was seen in miR-146a mimics-treated macrophages.

Conclusion/Significance

Here, we demonstrated that mycobacteria-induced miR-146a could modulate inflammatory response by targeting IRAK1 and TRAF6 and facilitate mycobacteria replication in macrophages.     

Regulatory roles of miR-155 and let-7b on the expression of inflammation-related genes in THP-1 cells: effects of fatty acids

The main aim of this investigation was to study the regulatory roles of let-7b and miR-155-3p on the expression of inflammation-associated genes in monocytes, macrophages, and lipopolysaccharide (LPS)-activated macrophages (AcM). A second goal was to analyze the potential modulatory roles of different fatty acids, including oleic, palmitic, eicosapentaenoic (EPA), and docosahexaenoic (DHA), on the expression of these miRNAs in the three cell types. This hypothesis was tested in human acute monocytic leukemia cells (THP-1), which were differentiated into macrophages with 2-O-tetradecanoylphorbol-13-acetate (TPA) and further activated with LPS for 24 h. Monocytes, macrophages, and AcM were transfected with a negative control, or mimics for miR-155-3p and miR-let-7b-5p. The expression of both miRNAs and some proinflammatory genes was analyzed by qRT-PCR. Interestingly, let-7b mimic reduced the expression of IL6 and TNF in monocytes, and SERPINE1 expression in LPS-activated macrophages. However, IL6, TNF, and SERPINE1 were upregulated in macrophages by let-7b mimic. IL6 expression was higher in the three types of cells after transfecting with miR-155-3p mimic. Similarly, expression of SERPINE1 was increased by miR-155-3p mimic in monocytes and macrophages. However, TLR4 was downregulated by miR-155-3p in monocytes and macrophages. Regarding the effects of the different fatty acids, oleic acid increased the expression of let-7b in macrophages and AcM and also increased the expression of miR-155 in monocytes when compared with DHA but not when compared with non-treated cells. Overall, these results suggest anti- and proinflammatory roles of let-7b and miR-155-3p in THP-1 cells, respectively, although these outcomes are strongly dependent on the cell type. Noteworthy, oleic acid might exert beneficial anti-inflammatory effects in immune cells (i.e., non-activated and LPS-activated macrophages) by upregulating the expression of let-7b.     

MicroRNA-146b-5p promotes atrial fibrosis in atrial fibrillation by repressing TIMP4

Alteration of tissue inhibitors of matrix metalloproteinases (TIMP)/matrix metalloproteinases (MMP) associated with collagen upregulation has an important role in sustained atrial fibrillation (AF). The expression of miR-146b-5p, whose the targeted gene is TIMPs, is upregulated in atrial cardiomyocytes during AF. This study was to determine whether miR-146b-5p could regulate the gene expression of TIMP4 and the contribution of miRNA to atrial fibrosis in AF. Collagen synthesis was observed after miR-146b-5p transfection in human induced pluripotent stem cell-derived atrial cardiomyocytes (hiPSC-aCMs)-fibroblast co-culture cellular model in vitro. Furthermore, a myocardial infarction (MI) mouse model was used to confirm the protective effect of miR-146b-5p downregulation on atrial fibrosis. The expression level of miR-146b-5p was upregulated, while the expression level of TIMP4 was downregulated in the fibrotic atrium of canine with AF. miR-146b-5p transfection in hiPSC-aCMs-fibroblast co-culture cellular model increased collagen synthesis by regulating TIMP4/MMP9 mediated extracellular matrix proteins synthesis. The inhibition of miR-146b-5p expression reduced the phenotypes of cardiac fibrosis in the MI mouse model. Fibrotic marker MMP9, TGFB1 and COL1A1 were significantly downregulated, while TIMP4 was significantly upregulated (at both mRNA and protein levels) by miR-146b-5p inhibition in cardiomyocytes of MI heart. We concluded that collagen fibres were accumulated in extracellular space on miR-146b-5p overexpressed co-culture cellular model. Moreover, the cardiac fibrosis induced by MI was attenuated in antagomiR-146 treated mice by increasing the expression of TIMP4, which indicated that the inhibition of miR-146b-5p might become an effective therapeutic approach for preventing atrial fibrosis.     

Interactions of adiponectin and lipopolysaccharide from Porphyromonas gingivalis on human oral epithelial cells

Background

Periodontitis is an inflammatory disease caused by pathogenic microorganisms, such as Porphyromonas gingivalis, and characterized by the destruction of the periodontium. Obese individuals have an increased risk for periodontitis and show decreased serum levels of adiponectin. This in-vitro study was established to examine whether adiponectin modulates critical effects of lipopolysaccharide (LPS) from P. gingivalis on oral epithelial cells (OECs).

Methodology/Principal Findings

The presence of adiponectin and its receptors in human gingival tissue samples and OECs was analyzed by immunohistochemistry and PCR. Furthermore, OECs were treated with LPS and/or adiponectin for up to 72 h, and the gene expression and protein synthesis of pro- and anti-inflammatory mediators, matrix metalloproteinases (MMPs) and growth factors were analyzed by real-time PCR and ELISA. Additionally, cell proliferation, differentiation and in-vitro wound healing were studied. The nuclear translocation of NFκB was investigated by immunofluorescence. Gingival tissue sections showed a strong synthesis of adiponectin and its receptors in the epithelial layer. In cell cultures, LPS induced a significant up-regulation of interleukin (IL) 1β, IL6, IL8, MMP1 and MMP3. Adiponectin abrogated significantly the stimulatory effects of LPS on these molecules. Similarly, adiponectin inhibited significantly the LPS-induced decrease in cell viability and increase in cell proliferation and differentiation. Adiponectin led to a time-dependent induction of the anti-inflammatory mediators IL10 and heme oxygenase 1, and blocked the LPS-stimulated NFκB nuclear translocation.

Conclusions/Significance

Adiponectin may counteract critical actions of P. gingivalis on oral epithelial cells. Low levels of adiponectin, as observed in obese individuals, may increase the risk for periodontal inflammation and destruction.     

Inhibition of PTEN Gene Expression by Oncogenic miR-23b-3p in Renal Cancer

Background

miR-23b is located on chromosome number 9 and plays different roles in different organs especially with regards to cancer development. However, the functional significance of miR-23b-3p in renal cell carcinoma (RCC) has not been reported.

Methods and Results

We measured miR-23b-3p levels in 29 pairs of renal cell carcinoma and their normal matched tissues using real-time PCR. The expression level of miR-23b-3p was correlated with the 5 year survival rate of renal cancer patients. In 15 cases (52%), miR-23b-3p expression was found to be high. All patients with moderate to low miR-23b-3p expression survived 5 years, while those with high miR-23b-3p expression, only 50% survived. After knocking down miRNA-23b-3p expression in RCC cell lines, there was an induction of apoptosis and reduced invasive capabilities. MiR-23b-3p was shown to directly target PTEN gene through 3′UTR reporter assays. Inhibition of miR-23b-3p induces PTEN gene expression with a concomitant reduction in PI3-kinase, total Akt and IL-32. Immunohistochemistry showed the lack of PTEN protein expression in cancerous regions of tissue samples where the expression of miR-23b-3p was high. We studied the in vitro effects of the dietary chemo preventive agent genistein on miR-23b-3p expression and found that it inhibited expression of miR-23b-3p in RCC cell lines.

Conclusions

The current study shows that miR-23b-3p is an oncogenic miRNA and inhibits PTEN tumor suppressor gene in RCC. Therefore, inhibition of miR-23b-3p may be a useful therapeutic target for the treatment of renal cell carcinoma.     

miR-130b-3p/301b-3p negatively regulated Rb1cc1 expression on myogenic differentiation of chicken primary myoblasts

Objectives

To explore the roles of miR-130b-3p and miR-301b-3p which may regulate Rb1-inducible coiled-coil 1 (Rb1cc1) expression during myogenic differentiation of chicken primary myoblasts.

Results

After 4 days of myogenic differentiation, myotubes appeared and after 6 days the cells fused to each other and expression of MyHC could be detected by immunofluorescence staining. TargetScan and RNAhybrid 2.2 showed miR-130b-3p and miR-301b-3p were well complementary with the target site of Rb1cc1 3′-untranslated region (3′-UTR). Using the dual-luciferase assay, we found miR-130b-3p and miR-301b-3p could inhibit Rb1cc1 expression by binding to its 3′-UTR. Real-time PCR showed Rb1cc1 mRNA expression level was almost reciprocal to that of miR-130b-3p or miR-301b-3p during myogenic differentiation. Furthermore, over-expression of miR-130b-3p or miR-301b-3p down-regulated the expression levels of Rb1cc1, myoblast determination protein, myogenin and myosin heavy chain.

Conclusions

miR-130b-3p or miR-301b-3p negatively regulate Rb1cc1 expression to affect myogenic differentiation.

     

Family of microRNA-146 Regulates RARβ in Papillary Thyroid Carcinoma

Retinoic acid is a promising tool in adjuvant cancer therapies, including refractory thyroid cancer, and its biological role is mediated by the retinoic acid receptor beta (RARβ). However, expression of RARβ is lowered in papillary thyroid carcinoma (PTC), contributing to promotion of tumor growth and inefficiency of retinoic acid and radioactive iodine treatment. The causes of aberrant RARB expression are largely unknown. We hypothesized that the culpable mechanisms include the action of microRNAs from the miR-146 family, previously identified as significantly upregulated in PTC tumors. To test this hypothesis, we assessed the expression of RARB as well as miR-146a-5p and miR-146b-5p in 48 PTC tumor/normal tissue pairs by Taqman assay to reveal that the expression of RARB was 3.28-fold decreased, and miR-146b-5p was 28.9-fold increased in PTC tumors. Direct interaction between miRs and RARB was determined in the luciferase assay and further confirmed in cell lines, where overexpression of miR-146a-5p and miR-146b-5p caused a 31% and 33% decrease in endogenous RARB mRNA levels. Inhibition of miR-146a and miR-146b resulted in 62.5% and 45.4% increase of RARB, respectively, and a concomitant decrease in proliferation rates of thyroid cancer cell lines, analyzed in xCELLigence system.We showed that two microRNAs of the miR-146 family directly regulate RARB. Inhibition of miRs resulted in restoration of RARB expression and decreased rates of proliferation of thyroid cancer cells. By restoring RARB levels, microRNA inhibitors may become part of an adjuvant therapy in thyroid cancer patients.