| Summary: | This thesis examines the role of microRNAs in renal fibrosis. MicroRNAs constitute a large family of approximately 22-nucleotide-long non-coding RNAs, that in animal cells regulate gene expression posttranscriptionally. At the start of the project, microRNAs were emerging as potentially important factors in various physiological and pathological processes however, there was very little known about their expression and function in the kidney, in particular in tubulointerstitial fibrosis. In this thesis, global microRNA expression has been analysed in vitro in proximal tubular epithelial cells, and in vivo in formalin-fixed, paraffin-embedded kidney biopsy samples from patients with diabetic nephropathy. Among microRNAs altered by profibrotic stimuli, the greatest difference has been found in expression ofmiR-192, which is downregulated in severe diabetic nephropathy. Further examination of miR-192 in kidney biopsy samples has revealed that its expression correlates well with renal function and inversely correlates with fibrosis. A possible function of miR-192 has been then studied in vitro in proximal tubular epithelial cells. It has been found that treatment of the cells with the profibrotic cytokine TGF-β1 downregulates miR-192. Moreover, manipulation of miR-192 expression has shown that miR-192 is involved in E-cadherin regulation. The mechanism of that regulation has been investigated, pointing to two transcriptional repressors of E-cadherin, ZEB1 and ZEB2, as direct targets of miR-192. The presented data suggest that, in the kidney, miR-192 may prevent epithelial-to-mesenchymal transition, known to contribute to renal fibrosis. In parallel, global microRNA downregulation in proximal tubular epithelial cells has been attempted. However, knockdown of Dicer or TRBP, proteins involved in microRNA processing, has not been sufficient to induce changes in microRNA expression. The possible explanations have been discussed. Finally, microRNA role in direct regulation of TGF-β1 synthesis has been investigated. In particular, human microRNAs similar to viral hsv-miR-LAT, reported to directly target TGF-β1 mRNA, have been tested.
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