Qualitative and Quantitative Regulation of the Leptin Gene in vivo

The high prevalence of obesity is a major public health concern worldwide. Conventional strategies have failed to provide solid solutions, greater than 90% of individuals who lost weight by diet and exercise eventually regained the weight (Arner and Spalding, 2010a). As such, biological factors including genetic contributions have become the research focus on pathogenesis of obesity and the target of effective disease control. Central to energy homeostasis is the mechanism by which animals regulate and/or response to fluctuation in energy intake and output. Adipose tissues participate in metabolic regulation by serving as an energy store and by secreting adipokines such as leptin and adiponectin. Leptin functions as the afferent signal to the central nervous system in a negative feedback loop that maintains homeostatic control of adipose tissue mass. Leptin gene expression is highly correlated with cellular lipid content in adipocytes but the transcriptional mechanisms controlling leptin expression in vivo are poorly understood. Leptin-BAC Luciferase transgenic mice combining with other computational and molecular techniques were used to identify transcription regulatory elements including a CCAAT-binding protein Nuclear Factor Y (NF-Y). The function of NF-Y in adipocyte was studied in vitro with 3T3-L1 cells and in vivo with adipocyte-specific knockout of NF-Y. The results showed that NF-Y binding site is essential for transcriptional regulation of leptin and NF-Y is also an adipogenic factor important for adipocyte development in vivo (Chapter 3 and Chapter 4). Finally, since obesity is defined as excess accumulation of adipose tissue, understanding developmental control of adipose tissue size and body adiposity will aid the study on disease progress of obesity. We employed a blastocyst complementation method where wild-type ES-cell is injected into AZIP lipodystrophic blastocyst. The result suggested that while leptin production adipocyte-autonomous, adipose tissue expandability and glucose metabolism is controlled by other factors involving other cell types in adipose tissues and/or other organs (Chapter 5). In sum, the thesis identifies adipocyte specific quantitative and qualitative control of leptin transcription, at the same time presents the complexity of metabolic regulation in vivo