Regulation of brown and beige fat by microRNAs.

MicroRNAs (miRNAs) are small non-coding RNA molecules consisting of approximately 20 to 22 nucleotides. They play a very important role in the regulation of gene expression. miRNAs can be found in different species and a variety of organs and tissues including adipose tissue. There are two types of adipose tissue in mammals: White adipose tissue (WAT) is the largest energy storage, whereas brown adipose tissue (BAT) dissipates energy to maintain body temperature. BAT was first identified in hibernating animals and newborns as a defense against cold. Later on, it was also discovered in human adults, suggesting its potential role in energy balance and metabolism. Moreover, "brown-like" adipocytes present in WAT depots, so called beige or brite (brown-in-white) cells, were discovered by several groups. In recent years, miRNAs were found to have important regulatory function during brown fat differentiation, brown fat activation and white fat "browning". In this review, we focus on the regulation of brown and beige fat by miRNAs including the role in their differentiation and function, providing evidence for their therapeutic potential in metabolic diseases.