Tissue specific expression of extracellular microRNA in human breast cancers and normal human breast tissue in vivo

Abstract

Extracellular circulating microRNAs (miRNAs) have been suggested to be biomarkers for disease monitoring but data are inconsistent, one reason being that blood miRNA is of heterogeneous origin. Here, we sampled extracellular microRNAs locally in situ using microdialysis. Three different cohorts of women were included; postmenopausal women with ongoing breast cancer investigated within the cancer and in normal adjacent breast tissue, postmenopausal women investigated in their normal healthy breast and subcutaneous fat before and after six weeks of tamoxifen therapy, premenopausal women during the menstrual cycle. Samples were initially screened using TaqMan array cards with subsequently absolute quantification. 124 miRNA were expressed in microdialysates. After absolute quantifications extracellular miRNA-21 was found to be significantly increased in breast cancer. In addition, the levels were significantly higher in pre-menopausal breast tissue compared with postmenopausal. In breast tissue of pre-menopausal women miRNA-21 exhibited a cyclic variation during the menstrual cycle and in postmenopausal women six weeks of tamoxifen treatment decreased miRNA-21 suggesting that this miRNA may be important for breast carcinogenesis. None of these changes were found in plasma or microdialysates from subcutaneous fat. Our data revealed tissue specific changes of extracellular circulating miRNAs that would be otherwise unraveled using blood samples.

Keywords: estrogen; mammary gland; microdialysis; sex steroids; tamoxifen.

Figure 1. Increased extracellular in vivo levels of miRNA-21 in human breast cancers and normal human breast tissue of women during increased sex steroid levels

Microdialysis was used for sampling of extracellular miRNA-21 in vivo in breast cancer and normal adjacent breast tissue in women before surgery, n = 13, in normal human breast tissue in pre-menopausal women, n = 16, and postmenopausal women, n = 12, in normal human breast tissue and abdominal subcutaneous fat of pre-menopausal women during the follicular and luteal phases of one menstrual cycle, n = 8, and in normal human breast tissue and abdominal subcutaneous fat of postmenopausal women before and after six weeks of tamoxifen therapy, n = 12. Bars represent mean±SEM, *p < 0.05, **p < 0.01.

Figure 2. Extracellular in vivo levels of miRNAs in breast cancers and normal breast tissue of women during various hormone exposures

Microdialysis was used for sampling of extracellular miRNAs in vivo in breast cancer and normal adjacent breast tissue in women before surgery, n = 13, in normal human breast tissue in pre-menopausal women, n = 16, and postmenopausal women, n = 12, in normal human breast tissue and abdominal subcutaneous fat of pre-menopausal women during the follicular and luteal phases of one menstrual cycle, n = 8, and in normal human breast tissue and abdominal subcutaneous fat of postmenopausal women before and after six weeks of tamoxifen therapy, n = 12. Bars represent mean±SEM, *p < 0.05, **p < 0.01.

Figure 3. Extracellular in vivo levels of miRNAs in breast cancers and normal breast tissue of women during various hormone exposures

Microdialysis was used for sampling of extracellular miRNAs in vivo in breast cancer and normal adjacent breast tissue in women before surgery, n = 13, in normal human breast tissue in pre-menopausal women, n = 16, and postmenopausal women, n = 12, in normal human breast tissue and abdominal subcutaneous fat of pre-menopausal women during the follicular and luteal phases of one menstrual cycle, n = 8, and in normal human breast tissue and abdominal subcutaneous fat of postmenopausal women before and after six weeks of tamoxifen therapy, n = 12. Bars represent mean±SEM, *p < 0.05, **p < 0.01.