Necessity of AMPK Activation for Caloric Restriction-Induced Cardioprotection

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Project Summary Excessive calorie intake poses an increased risk for cardiovascular disease. By contrast, caloric restriction (CR) can enhance cardiovascular health. Indeed, CR not only reduces several risk factors for heart disease, but also directly affects cardiac growth and function. These observations demonstrate a preventive and therapeutic potential of CR for heart disease. Recent research has focused on developing drugs that mimic CR's health-promoting effects without reducing food intake. However, the mechanisms of cardioprotection by CR remain speculative, making it hard to design mimetics for harnessing the full benefits of CR. Therefore, our long-term goal is to identity the underlying mechanisms responsible for CR-induced cardioprotection. AMP- activated protein kinase (AMPK) is an energy sensor that regulates multiple metabolic pathways to maintain cellular energy homeostasis. AMPK has been implicated in CR-induced longevity in lower organisms and in CR-conferred resistance to cardiac injury in rodents. However, the specific role of AMPK in CR-induced cardioprotection has never been definitively confirmed. It is also unclear whether and how AMPK engages its downstream effectors to exert the cardioprotective effects in response to CR. We showed that CR dramatically improved cardiac function and attenuated pressure overload-induced pathological cardiac remodeling. The cardioprotective effect of CR was accompanied by the activation of AMPK and the corresponding alteration of its potential downstream effectors. These results not only demonstrate the ability of CR to protect the heart in the setting of pressure overload, but also lead us to hypothesize that the activation of AMPK signaling pathway is essential for CR to maintain cardiac homeostasis at baseline and to antagonize pathological cardiac remodeling in response to pressure overload. This hypothesis will be tested in two specific aims. Using AMPK deficient mice including knockout and dominant negative transgenic mice, Aim1 will examine whether AMPK activation is required for CR to provide cardioprotection under both baseline and pressure overload conditions. Using both animal and cardiomyocyte culture models, Aim 2 will explore the mechanisms by which AMPK mediates the cardioprotective effects of CR. We will examine whether AMPK functions upstream of the mammalian target of rapamycin and autophagy to enhance mitochondrial quality control and promote myocardial survival. We have constructed a novel reporter that will allow direct quantification of the mitochondria that are being degraded through the mitophagic process in cultured cardiomyocytes. Successful completion of the proposed study will provide novel insights into the signaling mechanisms that mediate the cardioprotective effects of CR and facilitate the targeted design of effective mimetics to harness the power of CR for preventive and therapeutic intervention of heart disease.