MicroRNAs miR-146a1,miR-155_2,and miR-200a1 Are Regulated in Autoimmune Thyroid Diseases

Dear Editor:

Graves' disease (GD) and Hashimoto's thyroiditis (HT) are the most common autoimmune thyroid diseases (AITDs). The exact etiology of the immune response in both is still unknown.

MicroRNAs (miRNAs) constitute a recently discovered family of small RNAs that control gene expression. Accumulating data suggest that miRNAs crucially control innate and adaptive immune responses, and implicate some miRNAs as having an important role in the pathophysiology of immunity and autoimmunity (1). To the best of our knowledge, there are currently no data on the involvement of miRNA in AITDs. We have determined the levels of some key immunoregulatory miRNAs in the thyroid glands of AITD patients and healthy controls.

We investigated the thyroid gland fine-needle aspiration biopsies of patients with HT and GD. There were 28 unrelated Caucasians who were included in this study. The control groups comprised 9 Caucasians without AITDs; there were 9 patients with GD in the GD, and there were 10 patients with HT in the HT group. Ultrasound-guided fine-needle aspiration biopsies were performed using a 20-gauge needle.

Total RNA, including miRNA, was extracted from thyroid tissue samples and reverse transcribed with an miRNeasy Mini Kit (Qiagen GmbH). Semiquantitative TaqMan PCR was performed in an ABI PRISM 7700 Sequence Detector (PE Applied Biosystems) using the miScript SYBR Green PCR Kit (Qiagen GmbH). The specific miScript Primer Assays (Qiagen GmbH) were used for the amplification of 13 miRNAs: miR-34a, miR-143_1, miR-143_1*, miR-146a_1, miR-155*_1, miR-155_2, miR-181a*_1, miR-181a2*, miR-181b1, miR-200a1, miR-200a*2, miR-200a1, and miR-1238. All data were analyzed using the nonparametric Kruskal–Wallis test. Results with p<0.05 were considered statistically significant. Bonferroni-corrected Mann–Whitney U-tests were used as post hoc tests (see Supplementary Data, available online at www.liebertpub.com/thy).

In the thyroid tissue of the GD group, miR-146a1 was significantly decreased in comparison to the control group (mean relative expression 5.17 vs. 8.37, respectively, p=0.019). In the HT group, miR-155_2 was significantly decreased in comparison to the control group (8.30 vs. 11.20, respectively, p=0.001), and miR-200a1 was significantly increased (12.02 vs. 8.01, p=0.016). There were no significant differences between the HT and GD groups (see Supplementary Data) or for the other miRNAs tested.

Our pilot study was undertaken to evaluate the influence of candidate miRNAs in AITDs that have been suspected of being involved in immunoregulation based on previously published observations (1 –4). We found a significant decrease of miR-146a1 in the thyroid tissue of a patient with GD. miR-146a has been reported to be differentially regulated in other autoimmune diseases. Nakasa et al. demonstrated that miR-146a was highly expressed in rheumatoid arthritis (RA) synovial tissue compared to normal synovial tissue (2). This is in contrast to the decrease of miR-146a in our study, and is consistent with the perception that RA is characterized by a predominance of Th1-cytokines, while GD is characterized by the production of Th2-cytokines in thyroid tissue-emigrating mononuclear cells. Furthermore, we report here that miR-200a1 is increased in the thyroid tissue of HT patients, but not in that of patients with GD. This further substantiates the findings by Glinsky, who found in an SNP-guided miRNA map that miR-200, miR-34a, miR-143, and miR-1238 were associated with AITDs in general and GD in particular (4). To date, the potential role of miR-200a1 is not understood and warrants further research.

This is the first report that there is a significant decrease of miR-155_2 in the thyroid tissue of patients with HT. This miRNA was previously shown to possess important functions in the mammalian immune system by Thai et al. (3). The other miRNA candidates tested did not significantly differ between AITDs, even though evidence exists for their involvement in immunoregulation. We assume that the reported miRNA variations in thyroid tissue are caused by infiltrating activated lymphocytes, because—according to additionally performed microscopy of fine-needle aspirations—these cells are dominant.

Although limited by small sample size and some other limitations (e.g., missing matching for age and medication), our preliminary data open up a new field of research concerning miRNAs in thyroid diseases. Further studies in this interesting field are clearly warranted.