STAT3 and obesity due to melanocortin 4 receptor deficiency: In mice with obesity induced by a high-fat diet, miR-21 has been described to be overexpressed in epididymal fat and associated with an increased number of adipocytes and of signal transducer and activator of transcription 3 (STAT3), a key protein that responds to cytokines and growth factors [37], whereas if knocked-down, reduced weight and adipocyte size were observed [38].