Integrating TPM and PAM to examine the metabolic underpinning of neurovascular repair after stroke

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PROJECT SUMMARY Each year, over 800,000 people in the United States suffer from a stroke. Although the vast majority survive the acute event, over half of survivors suffer moderate to severe impairment in motor, sensory, or cognitive function. As a consequence, stroke remains the leading cause of long-term disability, costing over $34 billion annually in direct medical costs and indirect costs (lost productivity) in the United States. In the face of this enormous disease burden, there are few therapies to improve stroke recovery. The brain has some intrinsic capacity for repair, but our understanding of the underlying mechanisms remains very limited. Recent studies suggest that a successful recovery from stroke injury requires neurovascular remodeling to reorganize the damaged brain network. Indeed, circuit repair and the resultant remapping is essential for stroke recovery. Moreover, cerebrovascular remodeling and changes in cerebral oxygen metabolism are observed in animals and patients after stroke and are associated with improved outcomes. Tight coordination of neural repair and cerebrovascular remodeling is likely required to meet energy requirements of brain repair. However, the spatiotemporal coordination of neurovascular repair and the attendant changes in oxygen metabolism after stroke remain incompletely understood. We seek to answer these important questions by developing a new dual-modal intravital imaging technique that integrates 2-photon fluorescence microscopy (TPM) and multi-parametric photoacoustic microscopy (PAM) for high-resolution, time- lapse and comprehensive imaging of neurovascular repair and metabolic changes after stroke. To this end, we have developed a prototype TPM-PAM system and a new cranial window with dual transparency (i.e., light and ultrasound), long lifetime, and compatibility for awake-brain imaging. Building on the strong scientific basis, this proposed project will focus on the development of a high-sensitivity TPM-PAM system for longitudinal imaging of the spatiotemporal interplay of post-stroke neural repair and cerebrovascular remodeling, as well as dynamic imaging of the coupling between neuronal activity, blood flow, and blood oxygen supply, at single-neuron single- capillary level in the awake mouse brain. The proposed research has three specific aims: (1) develop an optically transparent and acoustically sensitive microresonator for integration of TPM and PAM with high sensitivity, (2) develop and validate the microresonator-based TPM-PAM for neurovascular imaging in GCaMP mice, and (3) determine the spatiotemporal relationship between functional vascular repair and neuronal circuit repair after stroke. Advancing our understanding of stroke repair through the development and application of TPM-PAM may reveal promising new therapeutic targets to enhance functional recovery.