The impact of blood pressure variability on neurovascular function

Intravascular pressure drives perfusion, which is critical for optimal neuronal function. High blood pressure (hypertension), however, is a risk factor for cognitive decline. Emerging evidence identifies increased blood pressure variability (IBPV), before the development of hypertension, as a strong predictor for vascular cognitive impairment and dementia. The mechanism whereby IBPV mediates cognitive decline is unknown and is the subject of this novel proposal. The myogenic response of cerebral arterioles protects the brain from blood pressure fluctuations that could cause hyper- or hypoperfusion. Mechanosensory mechanisms are essential in this process, but the impact of chronic blood pressure elevations at the level of the neurovascular unit has not been previously described. For example, mechanosensitive Ca2+-permeable cation channels are expressed on endothelial cells and astrocytes. Our exciting preliminary data demonstrate that increased intravascular pressure significantly increased astrocyte Ca2+ in a a process that is enhanced in hypertension. Astrocyte Ca2+ dysregulation is often observed in neurodegenerative diseases suggesting it may underlie cellular processes that contribute to the loss of homeostatic function and transition into reactive astrocytes. Because aberrant blood pressure fluctuations are an early predictor of hypertension, we will explore the cellular mechanisms by which intermittent increases in arterial pressure contribute to cognitive decline. Specifically, we will test the central hypothesis that chronic IBPV amplifies mechano-driven Ca2+ increases at the NVU, which impairs astrocyte homeostasis, decreases perfusion, and causes cognitive decline. Studies will be conducted in a novel murine model of chronic increased blood pressure variability induced by pulsatile angiotensin II infusion coupled with continuous blood pressure measurement in conscious mice. Aims 1-3 will test the following hypotheses: 1) that IBPV impairs vascular function and causes cerebral hypoperfusion; 2) that increased IBPV enhances myogenic- induced increases in astrocyte Ca2+and shifts astrocytes toward a pro-inflammatory/reactive phenotype; and 3) that IBPV compromises sensory-evoked increases in cerebral blood flow, contributing to neuronal dysfunction. Using in vivo and ex vivo approaches, we will link macroscopic cardiovascular variables to microscopic cellular events at the neurovascular unit and assess how IBPV progressively impairs vascular, glial and neuronal function. A longitudinal approach will determine the relationship between blood pressure fluctuations and aberrant Ca2+ dynamics in astrocytes, endothelial cells and neurons. Pharmacological, molecular, and genetic tools will be used to identify the cellular pathways underlying the loss of function at the neurovascular unit. Findings from this innovative application will establish IBPV as a key driver and predictor of cognitive decline, introduce a novel murine model to investigate the impact of IBPV on brain (and multi-organ) function, and identify cellular and molecular targets of pressure-induced vascular and astrocyte dysfunction leading to compromised cerebral perfusion and ultimately, neuronal dysfunction.