THE MOLECULAR CIRCUITS OF THE LIVING BRAIN:
Development, behavior and cognition are at once microscale processes and macroscale interactions between a living organism and its environment. To understand the living brain and its pathologies we must similarly scale from molecular mechanisms to whole brain function, which has proven to be one of the greatest challenges faced in neurobiology. Meeting this challenge demands an approach that can reveal molecular events across the brain, without disrupting the very processes we wish to study. The most powerful technology available for noninvasive whole brain molecular imaging is MRI, with the potential for subsecond and near cellular resolution. It is my overarching goal to realize the potential of MRI to resolve the diverse molecular signaling of development, function, and degeneration across the whole mammalian brain in vivo. To this end, I have established a versatile molecular toolkit for MRI1, including calcium sensors and genetic reporters2–4. Here, I propose hypothesis driven projects that focus the application of my methods on two forms of neurobiological signaling that offer the greatest impact on human health: calcium imaging of neural activity and neuroimmune interactions in regeneration. The work of my lab will establish the field of molecular fMRI, bringing powerful new capabilities to research by bridging functional and mechanistic biology.
PARSING SLEEP CIRCUITS WITH Ca-fMRI:
Neurological conditions from autism to Alzheimer’s Disease have characteristic sleep pathologies marked by aberrant “delta waves,” oscillatory brain activity from 0.5-4Hz5. Typically, periods of increased delta are observed in deep sleep and focused attention, suggesting multiple circuits oscillate in this range for network synchronization and gain modulation between cognitive states. Delta oscillations are a reliable biomarker for many neural pathologies, but the causal relationship between delta and cognition is unknown.Few candidate delta oscillating circuits have been identified and the molecular basis of how delta waves initiate, propagate, or terminate remains unclear. Fundamentally, brain-wide, oscillating circuits, are extremely difficult to parse with current methods of functional imaging, making them critically understudied relative to their therapeutic potential.
We have created a breakthrough molecular sensor for functional imaging of calcium with MRI (Ca-fMRI), capable of resolving oscillations in the delta band. In conjunction with electrophysiology, this novel method offers the unprecedented ability to map delta activity and potentially describe long range oscillatory circuits in animal models. The resulting datasets will be compiled into a whole brain atlas of delta oscillating circuits for comparative analysis with genetic models of disease, providing a critical bridge between described molecular pathologies and their less understood, systems level effects. I suspect the molecular dysregulation of delta oscillating circuits is a root cause of the pathologies of sleep and focal attention prominent in neurodevelopmental and degenerative disorders. Determining the mechanisms that shape and regulate these circuits offers new therapeutic targets for diseases of cognition, sleep, and attention.
PROBING THE NEUROIMMUNE REGENERATIVE SIGNALING AXIS WITH MRI REPORTER GENES:
PROBING THE NEUROIMMUNE REGENERATIVE SIGNALING AXIS WITH MRI REPORTER GENES: Stem cells build and replenish the mammalian brain through developmental tissue patterning6 and through adult neuronal regeneration, both basally7, and in response to injury8. Neuroimmune cells, like microglia, have an established neogenic role in healthy brain development, but the same cells are highly susceptible to external factors, leading to pathologies9. Immune challenges affect development10, while regeneration can be inhibited by inflammation, leading to degenerative disorders11. Neuroimmune signaling remains extremely difficult to study in vivo given the sensitivity of microglia to the invasive methods needed to image the brain12. New technologies for noninvasive functional studies would greatly accelerate research on any major neurodegenerative or inflammatory disease.
I have invented several genetic reporters for MRI and generated a transgenic mouse line that labels cell types responding to the neogenic cytokine Ang11,3. In preliminary studies, I have imaged activated microglia responding to a brain injury model (Fig. 2), an unprecedented functional study of a molecular circuit involved in neuroinflammation and adult neurogenesis. The proposed studies will further define capabilities of genetic imaging with MRI by using this established model to test a hypothesis that adult neogenic neuroimmune interactions recapitulate developmental signaling.The full diversity of cell types and signaling molecules in development and regeneration continues to be described13, however the in vivo signaling dynamics of cytokines are virtually unknown, for lack of in vivo assays of function. Parsing neuroimmune signaling modes offers a new means to determine therapeutic targets for neurodegenerative disorders.
REFERENCES: *Co-first authorship
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