The Effect Of Letm1 On Adipogenesis And The Induction Of Beige-like Adipocytes

Obesity, an increasing global pandemic over the past few decades, is thought to result from the excessive accumulation of triglyceride, which is associated with adipocytes. Controlling adiposity, by attenuating adipogenesis and converting white adipocytes to beige adipocytes, could provide an alternative approach to preventing obesity and related diseases. The transformation of white adipocytes into beige adipocytes has especially been under intense investigation. A complex network regulates adipogenesis, thus the studies of critical molecules participating in adipocyte differentiation should offer novel insights into strategies for preventing obesity.Letml (leucine-zipper-EF hand containing transmembrane protein 1), a mitochondrial inner membrane protein, is ubiquitously expressed. It has been reported that Letm1 regulates mitochondrial biogenesis and ATP production. There are many researches illustrating the importance of mitochondrion in brown adipocytes and beige adipocytes, mainly focusing on the morphological change. However, no study discusses the function of Letml in the browning process. Here, we report the effect of knocking down the Letml in the commonly used in vitro adipocyte differentiation model 3T3-L1 cells. Letml expression was knocked-down in pre-adipocytes 3T3-L1 using a lentivirus bearing LV-Letml-sh. Then, the pre-adipocytes 3T3-L1 were differentiated into mature adipocytes by the IBMX/DEX/insulin adipogenic cocktail. In addition,3T3-L1 cells were induced into beige-like adipocytes by isoproterenol with the addition of rosiglitazone and IBMX.Real-time quantitative PCR (RT-qPCR) was used to measure the expression level of related genes. According to data, the expression of Letml in 3T3-L1 cells was reduced by 90% compared with the control and LV-Scr-sh transduced cells, which means the silencing efficiency is 90%. Compared with control, the decreased expression level of Fabp4 in LV-Letml-sh transduced cells after differentiation indicated that the knock-down 3T3-L1 cells displayed a noticeable reduction in lipid accumulation and differentiation potential, which was also examined by Oil-Red-O staining. This reduction could be rescued by a Ppary agonist, rosiglitazone, or increased insulin concentrations (> 5 μg/ml).When 3T3-L1 cells were induced into beige-like adipocytes, we found that the expression of Ucpl and Pgc-1α in control cells was significantly increased by 73 and 3.2 fold, respectively, while only increased by 12.7 and 1.7 fold in LV-Letm1-sh transduced cells. This suppressed expression of Ucpl and Pgc-1α. in Letml silenced 3T3-L1 adipocytes points to a novel role of Letm1 in the browning process. These results suggest that Letml contributes to the maturation of fat cells and the adipocyte browning process.