Mechanism Of LKB1 In Inhibiting Adipogenesis And Differentiation

In recent years,the proportion of obese people in the world is increasing year by year. Obesity is considered to be the greatest public health threats. Obesity links to metabolic diseases such as type 2 diabetes and fatty hepatitis, and circulatory system diseases such as cardiovascular disease. Apart from gene mutation, energy balance disorder, abnormal adipogenesis is also the mainly pathogenesis of obesity. Hypothalamus, as a superior center, participate in the regulation of energy and metabolism homeostasis. AMPK can monitor energy status of cells. When energy is insufficient, AMPK was activited and cause a series of cascade downstream. Hormone such as leptin, insulin and ghrelin regulate the acitvity of AMPK in hypothalamus and periphery and participate in the regulation of energy homeostasis. Liver Kinase B1(LKB1) plays an important role in adipogenesis, but the mechanism underline in unclear. LKB1-STRAD-MO25 heterotrimeric can phosphorylate AMPK and activate it. Our group have found LKB1 was downregulated in hypothalamus and WAT, and this may relate to the accumulation of fat mass in DIO. Here, we mainly study the role and mechanism of LKB1 in hypothalamus and adipose tissue in adipogenesis and differentiation.This study is divided into three parts:1. We establishment diet induced obesity by high fat diet or chow diet in SD rats. 16 weeks later, according to body weight, animals in high fat diet group(HF) were divided into diet induced obesity(DIO) group and diet resistance(DR) group. Animals in control group(CF) were fed with normal diet. Food intake and body weight were monitored, fat mass and lean lean mass were detected by dual energy X-ray, body composition were calculated; expression of LKB1/AMPK, mTOR pathway and MC3 R in hypothalamus and epididymal fat were detected by Western Blot. This part is meaning to study the relationship between the changes of LKB1/AMPK/mTOR cascade and body fat content.2. We constructed recombinant adeno-associated virus(AAV) which overexpress LKB1. We wanted to overxpress LKB1 in the central by intraventricular injection AAV to the rat’s third ventricle. Animals were divided into four group: high dose group(H), middle dose group(M), low dose group(L) and control virus group(V). Body weight and food intake were monitored, fat mass and lean lean mass were detected by dual energy X-ray; expression of LKB1/AMPK and MC3/4R in hypothalamus were detected by Western Blot. This part is meaning to study the relationship between LKB1 in hypothalamus and adipogenesis in peripheral.3. We constructed overexpress and silence LKB1 3T3-L1 monoclonal cell lines. Cells were induced by reagents containing insulin, 3-isobutyl-1-methylxanthine and dexamethasone. Lipid droplets were detected by Oil red O staining; expression of LKB1/AMPK, mTOR pathway, PPARγ and Pref-1 were detected by Western Blot. This part is meaning to study the relationship between LKB1 and differentiation of preadipocytes in vitro. Conclusions:1. The gain of fat mass and body weight of DIO rats was mainly due to increased energy intake. We also detected impaired LKB1/AMPK cascade and increased, and mTOR pathway was activated in the hypothalamus and adipose tissue of DIO. This may be the cause of obesity, despite the mechanism of central and peripheral were distincted. LKB1 may participate in the development of LR in central, and the accumulation of fat mass in peripheral.2. DR rats can maintain normal fat mass and fat composition, along with lower body weight. And this may related to the normal acitivity of mTOR pathway despite LKB1/AMPK is impaired in WAT, and the activation of AMPK and melanocortin system in hypothalamus.3. Overexpress LKB1 in the central reduces body weight. The reduction is mainly due to the reduction of fat mass in trunk. Overexpress LKB1 in hypothalamus activates AMPK and melanocortin system in hypothalamus. So AMPK and melanocortin system may participate in the process of LKB1 inhibiting adipogenesis in the central.4. Overexpress LKB1 in 3T3-L1 cells suppresses the differentiation of preadipocytes, and silence LKB1 promotes differentiation. Combined with previous experiment, we confirem the inhibitory function of LKB1 on differentiation of 3T3-L1 was mediated by AMPK and mTOR.