Increased neuronal activity in the central nervous system (CNS) elicits corresponding increases in local cerebral blood flow. This response, termed neurovascular coupling, is lost or attenuated in several CNS disorders, including stroke, Alzheimer's disease (AD), amyotrophic lateral sclerosis (ALS), multiple sclerosis (MS), and traumatic brain injury (TBI). The resulting decrease in blood glucose and oxygen available to actively firing and recovering neurons is likely to exacerbate neuronal damage and contribute to neurological deterioration. Therefore, a key goal of therapeutic management in these conditions includes restoration of blood flow. However, the mechanisms underlying the attenuation of neurovascular coupling in disease are unknown, complicating the development of effective therapeutics for use in the clinic. We have previously demonstrated that astrocytes are necessary intermediates that convey signals from metabolically active neurons to microvascular capillaries but not arterioles. Of relevance to this proposal, astrocytes are also exquisitely sensitive to changes in their environment and become reactive in response to CNS insults. This response encompasses drastic changes in astrocyte morphology and gene expression patterns, but the consequence of these changes on neurovascular coupling remain undefined. We hypothesize that aberrant signals from reactive astrocytes are responsible for the attenuation of neurovascular coupling in injury or disease. Our preliminary data support this hypothesis: after an experimental model of stroke wherein astrocyte reactivity is induced, activity-dependent dilation is significantly attenuated at capillaries, the vascular compartment regulated by astrocytes. Therefore, our goal is to determine the mechanism(s) by which reactive astrocytes might suppress capillary dilation. Specifically, we will test the hypothesis that neurovascular coupling is suppressed selectively at capillaries but not arterioles following stroke (Aim 1), determine whether activity-evoked responses of reactive astrocytes are selectively altered in astrocyte endfeet terminating on capillaries but not on arterioles (Aim 2), and identify the signaling pathways responsible for the suppression of activity-evoked capillary dilation (Aim 3).
The loss of neurovascular coupling that occurs in many nervous system disorders results in a mismatch between the energy needs of active neurons and their nutrient supply; this is a major barrier for recovery of neurological functions. Here, we propose to determine the role of reactive astrocytes in neurovascular dysfunction and elucidate the molecular mechanisms that underlie loss of neurovascular coupling after stroke. These studies will help identify potential new strategies to restore cerebral blood flow after injury or disease.
