Effects of low intensity pulsed ultrasound stimulation on metabolic lipolysis of adipocytes

Obesity is closely related to several metabolic diseases along with abnormal increase in fat cells. Reducing size and number of fat cells, a procedure known as lipolysis, may be used to prevent obesity as a potential therapy, which also requires fundamental understanding of the mechanisms of lipolysis at molecular level upon different types of stimulations. Here, we used low intensity pulsed ultrasound (LIPUS) stimulation to investigate underlying mechanisms of the activation of lipolysis and autophagy related genes and signaling pathways of adipocytes differentiated from 3T3-L1 cells. LIPUS with the center frequency of 2 MHz was applied for 10 minutes per day for three days. After LIPUS stimulation, quantitative reverse transcription polymerase chain reaction (RT-qPCR) and Western blot were used to determine the regulation of lipolytic factors such as adipose triglyceride lipase (ATGL), hormone-sensitive lipase (HSL), and monoacylglycerol lipase (MGL). At RNA level, all three factors were upregulated while only MGL was upregulated at protein level, which presents slightly different activation pattern of lipolysis compared to widely used chemical stimulation. These results demonstrate that LIPUS stimulation can promote the lipolytic capacity of adipocytes in the differentiated state. The differences between transcriptional genes and metabolites were analyzed by transcript analysis and metabolomic profiling experiments. Cellular RNA-sequencing (RNA-Seq) showed an increase in lipolysis and immune-related genes and autophagy related genes after LIPUS stimulation. This study may provide an important experimental basis for the clinical applications and a fundamental understanding of the mechanisms of lipolysis using LIPUS stimulation.