A cardiac Wingless-Snail-Tep2 axis directs normal lipid homeostasis and protects against diet-induced obesity

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Abstract The heart is now recognized as an important organ in the regulation of systemic lipid homeostasis; however, our understanding of the molecular basis remains limited. It was recently shown that Wingless (Wg) signaling in the heart controls systemic lipid homeostasis. However, how cardiac Wg signaling controls this process is unknown. In a genetic screen in Drosophila, we discovered that the Snail family of transcription factors (Sna TFs) act in the heart to regulate systemic lipid metabolism. Our preliminary results also showed that Wg signaling in the heart activates the cardiac expression of Sna TFs. These findings led us to hypothesize that a Wg-Sna TF axis in the heart regulates lipid homeostasis in a systemic manner. This hypothesis will be tested in Aim 1. Building on our previous proteomic analysis of fly hemolymph (blood), we further discovered that a soluble protein thioester-containing protein 2 (Tep2), a secreted protein previously unknown to be involved in lipid metabolism, is up-regulated in the heart by Sna signaling and secreted to the circulation. Our further preliminary data showed that Tep2 mutation alters systemic lipid levels and that both Sna TF and Tep2 control TGF signaling in the fat body, in which TGF is known to be implicated in lipid metabolism. We therefore hypothesize that Tep2 secreted from heart to circulation serves as a functional effector of Wg-Sna axis in regulating systemic lipid homeostasis by modulating TGF pathway in fat body. This hypothesis will be tested in Aim 2. Furthermore, we found that high fat diet (HFD) induces the cardiac expression of Wg and Sna TFs. Based on our preliminary observation that activation of Sna TFs decreases systemic lipid levels, we hypothesize that a cardiac WgSna TF–Tep2 axis protects against HFD-induced obesity. This hypothesis will be tested in Aim 3. Together, this proposal will reveal novel insights into the heart control of normal systemic lipid homeostasis and provide knowledge that may help guide future therapeutics for human obesity and its comorbidities.