Si-Ni-San reverses dietary fat absorption defects in a murine model of depression

Depression is often associated with fatigue/energy loss. However, we lack a detailed understanding of the factors explaining this association. In this study, we uncovered that depressed mice have a defect in fat absorption, resulting in weight loss and reduced circulating lipid levels. Si-Ni-San (SNS), a basic formula of traditional Chinese medicine (TCM) for the treatment of depression, was found to not only alleviate depression-like behaviors, but also reverse the weight loss and dietary fat absorption of depressed mice. We found that SNS improved body weight and circulating lipid levels of depressed mice by up-regulating proteins [such as FFA uptake protein (CD36), TAG synthesis proteins (GPAT3, MOGAT2, DGAT1 and DGAT2) and chylomicron packaging proteins (MTP and APOB)] in the fat absorption pathway. Furthermore, cell-based results conducted with LPS-stimulated mouse MODE-K and human Caco-2 cells support that SNS, as well as Sinensetin (SIN) and Nobiletin (NOB), the two active components of the formula, have a role in regulating lipid absorption. Mechanistic studies revealed that SNS reverses body weight and fat absorption defects of depressed mice in part through the NR1D1/BMAL1/DGAT2 axis. These findings advance our understanding of the crosstalk between depression and energy loss, highlight the importance of gut function in disease management, and provide a basis for the application of SNS in the clinical treatment of depression and related disorders.