ESPE Abstracts

MicroRNAs (miRNAs) are small non-coding RNA molecules and play an important role in the post-transcriptional regulation of gene expression and thereby influence important cellular functions. In adipocytes, miRNAs regulate key processes such as differentiation, inflammation, metabolism, and adipokine secretion. Recently, we found that miR-27a is upregulated under proinflammatory conditions in human adipocytes. Thus, our goal was to better understand the function of miR-27a in adipocytes. The expression of the 3p and 5p strand of miR-27a was measured in Simpson-Golabi-Behmel-Syndrom cells (SGBS), human multipotent adipose-derived stem cells (hMADS) and human primary adipose-derived stromal cells. Gain-of-function and loss-of-function studies were performed by transfection of miRNA mimics and inhibitors. Adipogenesis was analysed by measuring the mRNA and protein expression of adipogenic marker genes as well as triglyceride content. Cellular respiration was studied using the Seahorse XFe96 extracellular flux analyser. Potential target genes of miR-27a-5p were identified by mRNA sequencing and in silico target gene prediction, and their role in human adipogenesis was assessed by siRNA-mediated knockdown. The expression of both, miR-27a-3p and -5p levels decreased during adipogenic differentiation in all model systems. We confirmed that miR-27a-3p is an important negative regulator of adipogenesis by targeting the transcription factor PPARγ. Interestingly, modulation of miR-27a-5p did not alter the adipogenic differentiation capacity but led to an 85% decrease of uncoupling protein 1 (UCP1), the major marker of brown, thermogenic adipocytes. The change in gene expression was paralleled by a significant impairment in cellular respiration after miR-27a-5p transfection. mRNA sequencing followed by gene set enrichment analysis revealed crucial change in gene ontologies like ‘mitochondrial gene expression’, ‘respiratory electron transport chain’, and ‘oxidative phosphorylation’. Subsequent in silico analyses identified several potential miR-27a-5p target genes, among them chemerin (RARRES2). SiRNA-mediated knockdown of chemerin resulted in decreased UCP1 protein expression and significant alterations of cellular respiration. Taken together, we conclude that miR-27a is an important regulator of human adipogenesis and adipocyte function. While miR-27a-3p inhibits the adipogenic program per se by targeting PPARγ, miR-27a-5p acts as a strong inhibitor of UCP1 expression and function. Tackling either the miRNA or its downstream targets might provide a useful strategy to induce browning or UCP1 expression in white adipocytes.