Ischemic preconditioning is a well-established phenomenon, in which a brief episode(s) of controlled ischemia and reperfusion renders cardioprotection from a subsequent sustained episode of ischemia. An emerging body of evidence demonstrated that neural regulated heart rate modulation confers cardiac preconditioning responses. Understanding the mechanism through model systems of preconditioning would help us identify the genes and proteins when designing future drug targets for the prevention of ischemic cardiac injury. As a promising alternative to electrical pacing to modulate heart rate, optogenetic pacing does not require physical contact, has high spatial and temporal precision, offers more specific excitation, and avoids artifacts from electrical stimulation. Recent developments in the field of optogenetics make it possible for non-invasive and specific optical control of the heart rhythm in animal models, such as in Drosophila melanogaster. Drosophila is a powerful genetic model system that has been used since the early 1900s to characterize genes associated with human diseases, including cardiac diseases. Studies performed in flies can provide insights into conserved mechanisms in cardiac diseases, which can be applied to higher organisms, including humans. Working in collaboration with Drs. Airong Li and Rudolph Tanzi from the Massachusetts General Hospital, we demonstrated non-invasive optogenetic pacing and concurrent optical coherence tomography (OCT) imaging of the Drosophila heart for the first time. Recently, we further demonstrated red-light optogenetic pacing and successful optical control of tachycardia, bradycardia, and restorable cardiac arrest in fly models. Building on the decade-long productive collaboration with Drs. Li and Tanzi and new collaborations with Dr. Abhinav Diwan (cardiologist) and Dr. Jeanne Nerbonne (cardiac electrophysiologist) and Dr. Kenneth Schechtman (biostatistician) at Washington University, we propose to develop a high-throughput integrated OCT imaging and dual-color optogenetic pacing system and establish a novel research platform to study preconditioning and hypoxia responsiveness in the fly heart. We hypothesize that periods of bradypacing will precondition the fly heart to protect against hypoxia, via activation of the autophagy-lysosome pathway.
The specific aims are: 1) Develop and optimize a high-throughput integrated instrument for non-invasive OCT imaging and optogenetic control of fly heart function in vivo; 2) Develop double transgenic fly models and functional assays based on OCT imaging to characterize fly heart physiology in vivo; 3) Define functional and molecular changes in response to hypoxia and optogenetic preconditioning in transgenic fly models. If successful, the high-throughput optical imaging and dual-color optogenetic pacing platform developed in this program combined with powerful double transgenic fly models will enable us to characterize changes of the fly heart function in response to different stress challenges that is not feasible before. This will allow us to perform a series of new experiments, providing insights into conserved molecular mechanisms on hypoxia-induced cardiac changes and preconditioning.
We will develop a novel research platform to noninvasively image and control heart function in fly models. Tachycardia, bradycardia and cardiac arrest will be stimulated using light and the cardioprotective effects of preconditioning will be explored. The new knowledge and novel insights gleaned from these studies will advance our understanding of conserved molecular mechanisms on hypoxia-induced changes in the heart and ischemic preconditioning.
