Over 1 billion people are estimated to be overweight, thus being at risk for diabetes, cardiovascular disease and cancer. We performed a systems-level genetic dissection of obesity regulation using genome-wide RNAi screening in adult Drosophila. Candidate obesity genes were classified functionally, using muscle-, oenocyte-, fat body- and neuron-specific drivers. Of the several known and novel candidate genes revealed by these investigations, hedgehog signaling scored as the most prominent fat-body-specific obesity pathway. To translate these findings into mammals, we generated adipose-tissue-specific Sufu mutant mice to specifically activate the hedgehog pathway in adipose tissue. Interestingly, these aP2-SufuKo mice displayed near total loss of white, but not brown, adipose tissue compartments (Figure 1). Mechanistically, activation of hedgehog signaling blocked differentiation of white adipocytes incompletely and irreversibly through direct dysregulation of early adipogenic factors. These investigations disclosed a novel role for hedgehog signaling in white/brown adipocyte determination, and link in vivo RNAi-based scanning of the Drosophila genome to regulation of adipocyte cell fate in mammals (Pospisilik et al. Cell, 2010).

Heart disease is the most common cause of morbidity and death in humans. using heart-specific RNAi silencing in Drosophila, we knocked-down 7061 evolutionary conserved genes under conditions of stress. This enabled us to develop a first global road map of pathways that might play conserved roles in the cardiovascular system. One critical pathway we identified was the CCR4-Not complex implicated in transcriptional and post-transcriptional regulatory mechanisms. Silencing of CCR4-Not components in adult Drosophila resulted in myofibrillar disarray and dilated cardiomyopathy. Heterozygous not3 knockout mice showed spontaneous impairment of cardiac contractility and greater susceptibility to heart failure. These heart defects were reversed via inhibition of HDACs, suggesting a mechanistic link to epigenetic chromatin remodeling. In humans, we showed that a common NOT3 SNP correlates with altered cardiac QT intervals, which is a known cause of lethal arrhythmias (Figure 2). Thus, functional genome-wide screens in Drosophila can identify candidates that directly translate into conserved mammalian genes involved in cardiac function (Neely et al. Cell 2010).

Breast cancer is one of the most common cancers in humans and is anticipated to affect one of every eight women in the US and Europe. The Women’s Health Initiative (WHI) and the Million Women study have shown that hormone replacement therapy (HRT) is associated with an increased risk of incident and fatal breast cancer. In particular, synthetic progesterone derivatives (progestins) such as medroxyprogesterone acetate (MPA), used by millions of women as HRT and in contraceptives, markedly increase the risk of developing breast cancer. Receptor activator of NF-κB Ligand (RANKL, also known as ODF, TRANCE, OPGL, TNFSF11) and its receptor RANK (TRANCE-R, TNFRSF11A) are essential for the development and activation of osteoclasts. Our group has also reported that RANKL/RANK controls lymph node organogenesis (Kong et al., nature), central thermoregulation (Hanada et al., nature), and the formation of a lactating mammary gland during pregnancy (Fata et al., Cell). Both RANKL and RANK expression have been observed in primary breast cancers in humans and breast cancer cell lines. We and others have proposed that the RANKL/RANK system may regulate bone metastases of epithelial tumors (Jones et al., nature). Given the facts that the inhibition of RANKL is now approved for potentially millions of patients to prevent bone loss, the genetically defined role of RANKL/RANK in mammary epithelial proliferation in pregnancy, and the regulation of the RANKL/RANK system by sex hormones, we speculated that RANKL/RANK might play a role in the development of primary hormone-driven mammary cancer.

We have now been able to show that in vivo administration of MPA triggers massive induction of RANKL in epithelial cells of the mammary gland. Genetic inactivation of the RANKL receptor RANK in mammary gland epithelial cells (RANK^Δmam ) prevents MPA-induced epithelial proliferation, impairs expansion of the CD49f^hi stem cell-enriched population, and protects these cells to apoptosis induced by damage to DNA. Importantly, RANK deletion in the mammary epithelium markedly reduces the occurrence of, and delays the onset of, MPA-driven mammary cancer (Figure 3). these data show that RANKL/RANK control the incidence and onset of progestin-driven breast cancer (Schramek et al., Nature 2010). our results were directly confirmed in a back-to-back publication by Bill Dougall’s group (Gonzalez-Suarez et al. Nature 2010). Since our results show that the RANKL/RANK system is an important molecular link between progestins and epithelial carcinogenesis, RANKL inhibition should be considered as a novel approach to prevent and/or treat breast cancer.